| 渡邉 隆行（わたなべ たかゆき） | データ更新日：2024.04.24 |
教授 ／
工学研究院
化学工学部門
生産システム工学
| 1. | Yiran Wang, Xiaoyu Zhang, Byeong-il Min, Manabu Tanaka, Takayuki Watanabe, Formation Mechanism of Amorphous Li4GeO4 Nanoparticles Synthesized by Induction Thermal Plasma for All-Solid-Sate Battery, The Journal of Physical Chemistry C, 10.1021/acs.jpcc.3c02465, 137, 10, 9964-9972, 2023.05, 誘導加熱プラズマはアモルファスナノ粒子の高度な合成法として注目されている。Li4GeO4ナノ粒子は、Li/Geモル比と急冷ガス流量を変えて誘導加熱プラズマにより合成した。生成物の形態と化学組成を理解するために、透過型電子顕微鏡、X線回折、ラマン分光を行った。実験結果と熱力学的解析に基づき、生成メカニズムを調べた。調製したナノ粒子のトポロジカル秩序は、O-Ge-OおよびGe-O-Geの角度分布に基づいて、それぞれ短距離および中間距離で議論した。高いGe含有量と急冷速度の条件下では、Li4GeO4のアモルファス度が向上し、高温相のγ-Li4GeO4の割合が得られた。アモルファスLi4GeO4度は、10L/minの急冷ガス注入で約65%を達成した。しかしながら、過剰なGe含有量と急冷速度は副生成物であるLi2GeO3の生成にもつながる。以上の結果から、適切なLi/Geモル比とクエンチ速度を用いれば、誘導加熱プラズマによりアモルファスLi4GeO4ナノ粒子を効率よく合成できることがわかった。. |
| 2. | Yiran Wang, Xiaoyu Zhang, Byeong-il Min, Manabu Tanaka, Takayuki Watanabe, Synthesis of Amorphous Li3BO3 Nanoparticles as Solid Electrolyte for All-Solid-State Battery by Induction Thermal Plasma, Journal of Solid State Chemistry, 10.1016/j.jssc.2022.123775, 318, 123775, 2023.02, 誘導加熱プラズマはアモルファスナノ粒子の高度な合成法として注目されている。Li4GeO4ナノ粒子は、Li/Geモル比と急冷ガス流量を変えて誘導加熱プラズマにより合成した。生成物の形態と化学組成を理解するために、透過型電子顕微鏡、X線回折、ラマン分光を行った。実験結果と熱力学的解析に基づき、生成メカニズムを調べた。調製したナノ粒子のトポロジカル秩序は、O-Ge-OおよびGe-O-Geの角度分布に基づいて、それぞれ短距離および中間距離で議論した。高いGe含有量と急冷速度の条件下では、Li4GeO4のアモルファス度が向上し、高温相のγ-Li4GeO4の割合が得られた。アモルファスLi4GeO4度は、10L/minの急冷ガス注入で約65%を達成した。しかしながら、過剰なGe含有量と急冷速度は副生成物であるLi2GeO3の生成にもつながる。以上の結果から、適切なLi/Geモル比とクエンチ速度を用いれば、誘導加熱プラズマによりアモルファスLi4GeO4ナノ粒子を効率よく合成できることがわかった。. |
| 3. | Soon-Ho Kim, Manabu Tanaka, Myeong-Hoom Lee, Takayuki Watanabe, Enhanced Decomposition of Caffeine by Water Plasma Combined with Mist Generator, Chemosphere, 10.1016/j.chemosphere.2022.136056, 307, 3, 136056, 2022.11, カフェイン廃水の分解にミスト発生装置と組み合わせた水プラズマを導入した。ミスト状の水分子を直接プラズマ形成ガスとして使用し、追加ガスを使用しなかった。カフェインの分解に及ぼすアーク電流の影響を詳細に解明した。アーク電流に応じて投入電力を0.8kWから1.1kWに増加させると、全有機炭素とカフェインの除去効率は増加し、9.5Aでそれぞれ91.1%と99.8%に達した。H2、CO、CO2、N2が主な排水ガス種であり、そのうちH2の発生量はすべての条件で40%以上であった。このプロセスで同定された11種類の中間生成物から、詳細な分解経路を推定し，電子衝撃と ヒドロキシルラジカルがカフェインの分解において主要な役割を果たすことがわかった。. |
| 4. | Kazumasa Oshima, Hiromichi Kondo, Eriko Konishi, Tsuyoshi Yamamoto, Yoshifumi Tsuge, Takayuki Watanabe, Masahiro Kishida, As(III) Removal through Catalytic Oxidation and Fe(III) Precipitation, Royal Society of Chemistry Advances, https://doi.org/10.1039/d2ra02537j, 12, 16843-16846, 2022.06. |
| 5. | Soon-Ho Kim, Manabu Tanaka, Myeong-Hoom Lee, Takayuki Watanabe, Decomposition of N, N-Diethyl-m-Toluamide by Water Plasma with Mist Generation, Journal of Environmental Chemical Engineering, 10.1016/j.jece.2022.107817, 10, 3, 107817, 2022.06. |
| 6. | Chengyuan Duan, Manabu Tanaka, Takayuki Watanabe, Treatment of Pyridine in Industrial Liquid Waste by Atmospheric DC Arc Plasma, Journal of Hazardous Materials, 10.1016/j.jhazmat.2022.128381, 430, 15, 128381, 2022.05, ピリジンは毒性が強い塩基性複素環化合物で、工業プロセスから排出される廃液中に広く見出されている。新規ミスト型水熱プラズマトーチを用いて、高濃度ピリジンの処理方法を開発した。分解率およびTOC除去率はすべての条件で94%以上、最大エネルギー効率は約23g/kWhに達した。5,500〜7,500Kの高温では、ピリジン中の95%以上の炭素が有価ガス生成物に変換され、液体副生物としてギ酸および酢酸が少量観測された。これらの実験結果に基づき、高温領域と下流領域における詳細な分解機構をそれぞれ考察した。水プラズマは、生分解性のない産業廃液の処理に大きな可能性を示している。. |
| 7. | Eri Kumai, Fuyumi Shimono, Manabu Tanaka, Takayuki Watanabe, Yuji Fujita, Takeshi Hoshino, Satoshi Hosoda, Hiroshi Kanamori, Large-Scale synthesis of Functional Tungsten oxide with Controlled Oxygen-Deficiency by a Continuous Screw Reactor, Journal of Industrial and Engineering Chemistry, 10.1016/j.jiec.2021.11.051, 107, 25, 239-248, 2022.06. |
| 8. | Xiaoyu Zhang, Kentaro Yamano, Ririko Hayashida, Manabu Tanaka, Takayuki Watanabe, Effect of Methane Injection Method on Preparation of Silicon Nanoparticles with Carbon Coating in Induction Thermal Plasma, Journal of Chemical Engineering of Japan, 10.1252/jcej.21we068, 55, 1, 22-28, 2022.06. |
| 9. | 松井和希, 田中学, 渡辺隆行, ロングDCアークにおける難分解性SF6の分解機構, 化学工学論文集, https://doi.org/10.1252/kakoronbunshu.47.211, 47, 6, 211-216, 2022.06. |
| 10. | Da Zhang, Kai Ye, Tao Qu, Yaochun Yao, Wenhui Ma, Bing Yang, Yongnian Dai, Feng Liang, Takayuki Watanabe, Controlled Regulation of The Transformation of Carbon Nanomaterials under H2 Mixture Atmosphere by Arc Plasma, Chemical Engineering Science, https://doi.org/10.1016/j.ces.2021.116695, 241, 116685, 2021.09. |
| 11. | Chengyuan Duan, Manabu Tanaka, Takayuki Watanabe, N,N-dimethylformamide Decomposition by DC Water Plasma at Atmospheric Pressure, Journal of Chemical Engineering of Japan, https://doi.org/10.1252/jcej.21we019, 54, 9, 486-492, 2021.09. |
| 12. | Xiaoyu Zhang, Yiran Wang, Byeongil Min, Eri Kumai, Manabu Tanaka, Takayuki Watanabe, A controllable and Byproduct-free Synthesis of Carbon-Coated Silicon Nanoparticles by Induction Thermal Plasma for Lithium Ion Battery, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2021.06.003, 32, 8, 2828-2838, 2021.08, 炭素で被覆されたシリコンナノ粒子は、次世代のリチウムイオン電池の負極材料として有望視されているが、費用対効果に優れ、環境に優しい調製法の開発は未だ困難であり、実用化の妨げとなっている。本研究では、アモルファス水素化炭素コーティングを施したシリコンナノ粒子の調製のために、制御可能で副生成物のない合成法を開発した。プラズマ特性は、プラズマシースガスを構成する接線方向ガス流量と半径方向ガス流量の比を調整することにより調整可能である。従来の問題であったSiCの生成は、接線方向ガス流量を大きくすることで消失し、電池用シリコン負極の容量が向上することが予測される。これらの成果は，プラズマ合成プロセスを深く理解し、優れた性能を持つ電池を設計するために重要である。. |
| 13. | Xiaoyu Zhang, Byeongil Min, Yiran Wang, Ririko Hayashida, Manabu Tanaka, Takayuki Watanabe, Preparation of Carbon-Coated Silicon Nanoparticles with Different Hydrocarbon Gases by Induction Thermal Plasma for Lithium Ion Battery, The Journal of Physical Chemistry C, https://doi.org/10.1021/acs.jpcc.1c03209, 25, 28, 15551-15559, 2021.07, シリコンは非常に高い充電容量を持つため、グラファイトに代わるリチウムイオン電池の負極材として有望視されている。しかし、充電時の体積膨張が大きく、安定性に大きな問題がある。この問題を解決し、シリコン負極の実用化を促進するために、保護膜でコーティングされたシリコンナノ粒子は信頼性が高い。本研究では、高周波熱プラズマを応用して、アモルファス水素化炭素コーティングを施したシリコンナノ粒子を合成し、追加の炭素源の影響を調べた。副生成物の生成を制限するために、炭化水素の新規かつ簡便な注入方法を導入した。カーボンコーティングの厚さは、炭化水素ガス流量が多いほど2〜8 nmの範囲となり、シリコン粒子の平均直径は約70 nmと一定であった。sp2比やH含有量などのカーボンコーティングの特性は調整可能であり、カーボンソースの熱分解メカニズムが重要な要因であると考えられている。また、豊富な炭素と水素ラジカルを放出したグラフェンフレークも得ることができる。材料の特性評価から、アセチレンは炭素コーティングを調製するためのより良い候補物質とみなされている。以上の結果は、次世代リチウムイオン電池の設計に重要な意味を持つと考えられる。. |
| 14. | Soon-Ho Kim, Manabu Tanaka, Takayuki Watanabe, Myeong-Hoom Lee, Arc behavior and Temperature Distribution in Water Thermal Plasma with Mist Generation, Journal of Chemical Engineering of Japan, https://doi.org/10.1252/jcej.21we020, 54, 6, 277-282, 2021.06. |
| 15. | Eri Kumai, Manabu Tanaka, Takayuki Watanabe, Takeshi Hoshino, Satoshi Hosoda, Hiroshi Kanamori, A Continuous Hydrogen Reduction Process for the Production of Water on the Moon, International Journal of Microgravity Science and Application, 10.15011/jasma.38.380203, 38, 2, 380203, 2021.04, [URL]. |
| 16. | Junya Matsuno, Akira Tsuchiyama, Takayuki Watanabe, Manabu Tanaka, Aki Takigawa, Satomi Enju, Chiyou Koike, Hiroki Chihara, and Akira Miyake, Condensation of Glass with Multimetal Nanoparticles: Implications to a Formation Process of GEMS Grains, The Astrophysical Journal, 10.3847/1538-4357/abe5a0, 911, 1, 47, 2021.04, [URL], 惑星間塵粒子には、太陽系を構成する元素のひとつと考えられている金属・硫化物内包ガラス（GEMS）粒子が含まれている。GEMS粒子が凝縮過程で形成されることを調べるために、Si-Mg-Fe-Al-Ca-Ni-O系とMg-Si-Fe-Ca-Al-Na-O系で誘導加熱プラズマ炉を用いた凝縮実験を行った。すべての実験において、直径100nmの非晶質ケイ酸塩粒子が凝縮した。鉄は、酸化的実験の多くで微細なマグネタイト粒を、中間の酸化還元条件下では10 nmの金属粒を、還元的実験の多くでは30～100 nmのFeケイ化物粒を形成した。中間の酸化還元条件下では、いくつかの非晶質ケイ酸塩粒子は、FeSを除いてGEMS粒子に非常によく似たテクスチャを持つ複数のFe包有物を示し、GEMSが高温ガスの凝縮によって形成される可能性を示した。. |
| 17. | Xiaoyu Zhang, Zishen Liu, Manabu Tanaka, and Takayuki Watanabe, Formation Mechanism of Amorphous Silicon Nanoparticles with Additional Counter-Flow Quenching Gas by Induction Thermal Plasma, Chemical Engineering Science, 10.1016/j.ces.2020.116217, 230, 116217, 2020.12, [URL], The fabrication process of amorphous silicon nanoparticles by induction thermal plasma was studied by experiments and numerical simulation. Additional quenching gas was introduced as counter-flow to plasma flame tail for an effective synthesis of amorphous phase, and the flow rate was determined to range from 0 to 70 L/min to understand the effect on the prepared products. Amorphous silicon nanoparticles were confirmed by electronic diffraction analysis with random shapes and serious agglomerate, while the crystal particles have a totally different morphology which are spherical and freestanding. The ratio of amorphous silicon increased with quenching gas flow rate, and the reliability was verified by comparison between XRD and Raman results. The quenching rate increased from 3.2x104 to 8.9x105 K/s with quenching gas flow rate and was insufficient for the formation of amorphous silicon. The enhanced fabrication of small nanoparticles (˂ 5 nm) with quenching gas injection was demonstrated as the reason of increased amorphous silicon ratio, which suggested the formation of amorphous silicon by thermal plasma is controllable.. |
| 18. | Naoki Sakura, Masaki Yoshida, Manabu Tanaka, and Takayuki Watanabe, Investigation of Electrode Erosion Mechanism in Ar-N2 DC Arc based on Visualization of Electrode Phenomena, Japanese Journal of Applied Physics, 10.35848/1347-4065/abbd7d, 59, 11, 116011, 2020.10, [URL], Investigation of Electrode Erosion Mechanism in Ar-N2 DC Arc based on Visualization of Electrode Phenomena. |
| 19. | Da Zhang, Kai Ye, Tao Qu, Yaochun Yao, Wenhui Ma, Bing Yang, Yongnian Dai, Feng Liang, Takayuki Watanabe, Controlled Regulation of The Transformation of Carbon Nanomaterials under H2 Mixture Atmosphere by Arc Plasma, Chemical Engineering Science, 10.1016/j.ces.2021.116695, 241, 116685, 2020.09, [URL]. |
| 20. | Hirotaka Sone, Shuhei Yoshida, Takuya Kageyama, Manabu Tanaka, Takayuki Watanabe, Li-Ni-Mn Oxide Nanoparticle Synthesis by Induction Thermal Plasmas for Lithium Ion Battery Electrode, Journal of The Ceramic Society of Japan, 10.2109/jcersj2.20087, 128, 9, 635-640, 2020.09, [URL]. |
| 21. | Takafumi Okuma, Hiroki Maruyama, Tomoyuki Imatsuji, Taro Hashizume, Manabu Tanaka, Hisao Nagai, Takeshi Koiwasaki, Takayuki Watanabe, Investigation of Arc Behavior and Temperature Distribution Corresponding to Electrode and Phase Configurations in a Multiphase AC Arc, Journal of Chemical Engineering of Japan, 10.1252/jcej.20we001, 53, 9, 509-515, 2020.09, [URL]. |
| 22. | Xiaoyu Zhang, Ririko Hayashida, Manabu Tanaka, Takayuki Watanabe, Synthesis of Carbon Coated Silicon Nanoparticles by Induction Thermal Plasma for Lithium Ion battery, Powder Technology, 10.1016/j.carbon.2018.10.062, 371, 26-31, 2020.06, [URL]. |
| 23. | Manabu Tanaka, Yuki Saito, Hiroki Maruyama, Takayuki Watanabe, High-Speed Visualization of Metal Oxide Precursor in Multiphase AC Arc during Nanoparticle Formation, Japanese Journal of Applied Physics, 10.35848/1347-4065/ab7e15, 59, SH, SHHC08, 2020.04, [URL], The purpose of the present work is to elucidate the formation mechanism of metal oxide nanoparticles in a multiphase AC arc, which is one of the most attractive thermal plasma sources. Lanthanum oxide nanoparticles were focused on, on the basis of spectroscopic diagnostics and thermodynamic considerations. The dynamic behavior of lanthanum vapor and lanthanum monoxide in a multiphase AC arc was visualized by a high-speed camera through band-pass filter optics. Furthermore, the two-dimensional temperature field of the multiphase AC arc was successfully estimated by the same camera system based on the relative intensity method, which included the emissions from the lanthanum atom and lanthanum ion. The obtained temperature profile and intensity profile of lanthanum and lanthanum monoxide suggest that the oxidation from lanthanum to lanthanum monoxide occurred following thermodynamic equilibrium. Understanding these fundamental phenomena in the thermal plasma nanofabrication process enables one to expand the capability of thermal plasma for innovative material processing.. |
| 24. | Hirotaka Sone, Shuhei Yoshida, Takuya Kageyama, Manabu Tanaka, Takayuki Watanabe, Li-Ni-oxide Nanoparticle Synthesis by Induction Thermal Plasmas for Lithium Ion Battery Electrode, Journal of Chemical Engineering of Japan, 10.1252/jcej.19we124, 53, 2, 78-83, 2020.02. |
| 25. | Hirotaka Sone, Shuhei Yoshida, Manabu Tanaka, and Takayuki Watanabe, Thermal Plasma Synthesis and Electrochemical Properties of High-Voltage LiNi0.5Mn1.5O4 Nanoparticles, Materials Research Express, 10.1088/2053-1591/ab5f2e, 7, 015015, 2019.12, [URL], 熱プラズマを高温反応場として活用する材料プロセスが注目されている．高周波熱プラズマによるナノ粒子の材料合成は，無電極放電のため電極からの汚染を防ぐことが可能である．また，合成中の雰囲気制御の選択，異なる元素化合物の合成および高純度材料の製造など，多くの利点を有している． リチウムイオン二次電池は高エネルギー密度の向上が望まれている．高エネルギー密度の向上の研究として正極・負極材料の元素選定，結晶構造の選定および粒子径の改良が多数報告されている．しかしながら，その多くは液相法や固相法による合成例である．一般的に液相法および固相法は，組成の制御が容易であるという利点を持っているが，不純物の混入が避けられず，電池容量の変動および高純度のナノ粒子合成に課題がある．そこで本研究では，数ミリ秒の短時間合成および純度の高いナノ粒子の合成プロセスである高周波熱プラズマを用い，リチウムイオン二次電池の正極・負極材料ナノ粒子の合成を行い，その特性および生成機構について解明することを目的とした．. |
| 26. | Manabu Tanaka, Yuki Saito, Yushi Nawata, Takayuki Watanabe, High-Speed Visualization of Metal Oxide Precursor in Thermal Plasma Flow during Nanoparticle Formation, Journal of Fluids Science and Engineering, 10.1299/jfst.2019jfst0024, 14, 3, JSFT0024, 2019.12. |
| 27. | Naoki Sakura, Masaki Yoshida, Manabu Tanaka, Takayuki Watanabe, Investigation of erosion mechanism of tungsten-based cathode in Ar-N2 DC arc, Journal of Physics D: Applied Physics, 10.1088/1361-6463/ab3139, 52, 40, 404002, 2019.07, [URL], Direct current arc has been used in a wide industrial field. Reducing in cathode erosion is an important issue for process cost reduction, however the erosion mechanism under molecular gas as plasma supporting gas has not been clarified yet. The purpose of this research is to elucidate the erosion mechanism of tungsten based cathodes in atmospheric pressure Ar-N2 DC arc. The metal vapor generated from the cathode surface was successfully visualized by a high speed camera system with a pair of band pass filters. Combing the visualization with the cahtode temperature measurements provides the tungsten vapor evaporation mechanism; tungsten vapor was generated not from the high temperature part of the cathode tip but from the peripheral part. The arc temperature measurement confirmed that ionization of tungsten atoms in the high-temperature region of the arc caused to this characteristic distribution of tungsten vapor. These findings advance the understanding of such electrode phenomena leading to increased use time of the electrode, and as a result the industrial use of N2 arcs is expected to expand.. |
| 28. | Aki Takigawa, Tae-Hee Kim, Yohei Igami, Tatsuki Umemoto, Akira Tsuchiyama, Chiyoe Koike, Junya Matsuno, Takayuki Watanabe, Formation of Transition Alumina Dust around Asymptotic Giant Branch Stars: Condensation Experiments using Induction Thermal Plasma Systems, The Astrophysical Journal Letters, 10.3847/2041-8213/ab1f80, 878, L8, 2019.06. |
| 29. | Da Zhang, Kai Ye, Yaochun Yao, Feng Liang, Tao Qu, Wenhui Ma, Bin Yang, Yongnian Dai, Takayuki Watanabe, Controllable Synthesis of Carbon Nanomaterials by Direct Current Arc Discharge from The Inner Wall of The Chamber, Carbon, 10.1016/j.carbon.2018.10.062, 142, 278-284, 2019.02. |
| 30. | Takafumi Okuma, Hiroki Maruyama, Taro Hashizume, Manabu Tanaka, Takayuki Watanabe, Hisao Nagai, Takeshi Koiwasaki, and Hiroshi Nasu, Effects of The Driving Frequency on Temperature in a Multiphase AC Arc, IEEE Transactions on Plasma Science, 10.1109/TPS.2018.2832286, 47, 1, 32-38, 2019.01. |
| 31. | Manabu Tanaka, Hirohiko Soeda, Takayuki Watanabe, and Koji Ohtsuki, Plasma Jet Characteristics in Long DC Arc with Ring-Shaped Anode, Journal of Fluid Science and Technology, 10.1299/jfst.2018jfst0027, 13, 4, 2018.11. |
| 32. | Takafumi Okuma, Tomoyuki Imatsuji, Taro Hashizume, Manabu Tanaka, Takayuki Watanabe, Hisao Nagai, Takeshi Koiwasaki, and Hiroshi Nasu, Effects of Working Pressure on Temperature Characteristics in Multiphase Ac Arc, Journal of Fluid Science and Technology, https://doi.org/10.1299/jfst.2018jfst0024, 13, 4, JFST0024, 2018.11. |
| 33. | Fengmei Su, Xuechao Qiu, Manabu Tanaka, Tao Qu, Yaochun Yao, Wenhui Ma, in Yang, Yongnian Dai, Katsuro Hayashi, Takayuki Watanabe, Preparation of Nickel Nanoparticles by Arc Discharge Method and Their Catalytic Application in Hybrid Na-Air Battery, Nanomaterials, https://doi.org/10.3390/nano8090684, 8, 684, 2018.09. |
| 34. | Manabu Tanaka, Tomoyuki Imatsuji, Taro Hashizume, Takayuki Watanabe, Hisao Nagai, Takeshi Koiwasaki, and Takafumi Okuma, Investigation of Temperature Characteristics of Multiphase AC Arc by High-Speed Visualization, Journal of Fluid Science and Technology, https://doi.org/10.1299/jfst.2017jfst0024, 12, 3, JFST0024, 2017.12. |
| 35. | Yutaro Ozeki, Tsuyoshi Matsuo, Manabu Tanaka, Takayuki Watanabe, Characteristics of Water Thermal Plasma for Biomass Utilization System, Journal of Fluid Science and Technology, https://doi.org/10.1299/jfst.2017jfst0022, 12, 3, JFST0022, 2017.12. |
| 36. | Manabu Tanaka, Taro Hashizume, Koki Saga, Tsugio Matsuura, and Takayuki Watanabe, Diode-Rectified Multiphase AC Arc for Improvement of Electrode Erosion Characteristics, Journal of Physics, D: Applied Physics, https://doi.org/10.1088/1361-6463/aa8cac, 50, 46, 465604, 2017.10. |
| 37. | Feng Liang, Manabu Tanaka, Sooseok Choi, Takayuki Watanabe, Formation of Different Arc-Anode Attachment Modes and their Effect on Temperature Fluctuation for Carbon Nanomaterial Production in DC Arc Discharge, Carbon, 10.1016/j.carbon.2017.02.084, 117, 100-111, 2017.06, [URL], A direct current (DC) has been applied to prepare many carbon nanomaterials, including fullerene, graphene, and carbon nanohorns (CNHs) from inner wall of chamber. However, the growth mechanism of these carbon nanomaterials is not clear. Amorphous spherical carbon nanoparticles (SCNs), the typical ‘dahlia-like’ CNHs, and graphene with the layer numbers of 2e5 were synthesized controllably from the inner wall of the chamber by DC arc discharge method using argon, nitrogen, and hydrogen as buffer gas. Simultaneously, the effect of buffer gas pressure on the morphology of carbon nanomaterials was investigated systematically. Furthermore, the formation mechanism of these carbon nanomaterials by DC arc discharge was also investigated. Given that argon atom was difficult to bond with the carbon cluster, the random bond between carbon clusters contributed to combine into amorphous SCNs; the CeN bond was the key factor in the formation of CNHs, and hydrogen contributes to form graphene sheets by terminating carbon dangling bonds. With increasing the pressure of buffer gas, intense quenching resulted in formation of carbon nanomaterials with high purity. The study on the growth mechanism of carbon nanomaterials in the inner wall of chamber promotes the preparation of carbon nanomaterials controllable by arc discharge method.. |
| 38. | Taro Hashizume, Manabu Tanaka, and Takayuki Watanabe, Effect of Arc Current on Droplet Ejection from Tungsten-Based Electrode in Multiphase AC Arc, Japanese Journal of Applied Physics, http://doi.org/10.7567/JJAP.56.056101, 56, 5, 056101, 2017.05. |
| 39. | Takayuki Watanabe, Taro Hashizume, Tomoyuki Imatsuji, Manabu Tanaka, High-Speed Visualization of Thermal Plasma Characteristics, SPIE Proceedings, http://doi.org/10.1117/12.2269401, 10328, 1032812, 2017.02. |
| 40. | 松尾剛, 田中 学, 渡邉 隆行, 水プラズマの変動現象の解析, 電気学会論文誌B, http://dx.doi.org/10.1541/ieejpes.136.749, 136, 9, 749-754, 2016.09, A water plasma was generated by DC arc discharge with a hafnium cathode and a cupper anode. Arc fluctuation in water plasma was examined by arc image observation synchronized with voltage measurement. The main parameters that cause arc fluctuation was a feed rate of solution. The dynamic behavior of the arc as a restrike mode has faster fluctuation than the decomposition process in the water plasma. Axial and radial extent of the arc is increased with increasing in the feed rate. Therefore, effective energy of the arc is decreased with increasing in the feed rate. Decomposition rate of the treated material can be improved by controlling the arc fluctuation in the anode nozzle.. |
| 41. | Manabu Tanaka, Taro Hashizume, Tomoyuki Imatsuji, Yushi Nawata, Takayuki Watanabe, Investigation of Erosion Mechanism of Tungsten-Based Electrode in Multi-Phase AC Arc by High-Speed Visualization of Electrode Phenomena, Japanese Journal of Applied Physics, http://doi.org/10.7567/JJAP.55.07LC01, 55, 7S2, 07LC01, 2016.06. |
| 42. | Manabu Tanaka, Takuya Kageyama, Hirotaka Sone, Shuhei Yoshida, Daisuke Okamoto, Takayuki Watanabe, Synthesis of Lithium Metal Oxide Nanoparticles by Induction Thermal Plasmas, Nanomaterials, http://dx.doi.org/10.3390/nano6040060, 6, 4, 60, 2016.04, Lithium metal oxide nanoparticles were synthesized by induction thermal plasma. Four different systems-Li-Mn, Li-Cr, Li-Co, and Li-Ni-were compared to understand formation mechanism of Li-Me oxide nanoparticles in thermal plasma process. Analyses of X-ray diffractometry and electron microscopy showed that Li-Me oxide nanoparticles were successfully synthesized in Li-Mn, Li-Cr, and Li-Co systems. Spinel structured LiMn2O4 with truncated octahedral shape was formed. Layer structured LiCrO2 or LiCoO2 nanoparticles with polyhedral shapes were also synthesized in Li-Cr or Li-Co systems. By contrast, Li-Ni oxide nanoparticles were not synthesized in the Li-Ni system. Nucleation temperatures of each metal in the considered system were evaluated. The relationship between the nucleation temperature and melting and boiling points suggests that the melting points of metal oxides have a strong influence on the formation of lithium metal oxide nanoparticles. A lower melting temperature leads to a longer reaction time, resulting in a higher fraction of the lithium metal oxide nanoparticles in the prepared nanoparticles.. |
| 43. | Masaya Shigeta, Takayuki Watanabe, Effect of Pressure Difference on Metal-Silicide Nanopowder Formation in Thermal Plasma Synthesis, Nanomaterials, http://dx.doi.org/10.3390/nano6030043, 6, 3, 43, 2016.03, A computational investigation using a unique model and a solution algorithm was conducted, changing only the saturation pressure of one material artificially during nanopowder formation in thermal plasma fabrication, to highlight the effects of the saturation pressure difference between a metal and silicon. The model can not only express any profile of particle size-composition distribution for a metal-silicide nanopowder even with widely ranging sizes from sub-nanometers to a few hundred nanometers, but it can also simulate the entire growth process involving binary homogeneous nucleation, binary heterogeneous co-condensation, and coagulation among nanoparticles with different compositions. Greater differences in saturation pressures cause a greater time lag for co-condensation of two material vapors during the collective growth of the metal-silicide nanopowder. The greater time lag for co-condensation results in a wider range of composition of the mature nanopowder.. |
| 44. | Feng Liang, Manabu Tanaka, Sooseok Choi, Takayuki Watanabe, Investigation of the relationship between arc-anode attachment mode and anode temperature for nickel nanoparticle production by a DC arc discharge, Journal of Physics D: Applied Physics, 10.1088/0022-3727/49/12/125201, 49, 12, 2016.02, [URL], Multiple and constricted arc-anode attachment modes were observed in helium arc discharge to prepare nickel nanoparticles. The electron overheating instability resulted in the formation of multiple attachment modes. The effects of hydrogen concentration and shield gas flow rate on the characteristics of nickel nanoparticles were investigated. The evaporation rate of anode material contributed to forming different arc-anode attachments. The surface temperature of the electrode was measured during the arc discharge by two-color pyrometry combined with a high-speed camera which employs appropriate band-pass filters. The relationship between the arc-anode attachment mode and the temperature behavior of the anode surface was investigated by using two synchronized high-speed cameras. The waveform of anode jet area variation with time follows that of the highest temperature variation of anode surface with time. The fluctuation of the highest anode temperature increased when the arc anode attachment changed from multiple into constricted mode. The highest temperature fluctuation and stability of the arc contributed to nanoparticle size distribution. Nickel nanoparticles with large productivity and narrow size distribution were obtained when shield gas was employed by controlling the residence time of nanoparticle growth. The formation mechanism of different arc-anode attachment modes was explained.. |
| 45. | Masaya Shigeta, Takayuki Watanabe, Effect of precursor fraction on silicide nanopowder growth under thermal plasma conditions A computational study, Powder Technology, 10.1016/j.powtec.2015.11.005, 288, 191-201, 2016.01, [URL], Computational study is carried out to clarify the growth mechanisms and the effects of the silicon fraction in precursor on the fabricated nanopowders for metal-silicon binary systems (Co-Si, Mo-Si, and Ti-Si systems) under a thermal plasma condition, using a model that can simulate the collective and simultaneous combined processes of binary homogeneous nucleation, binary heterogeneous co-condensation, and coagulation among nanoparticles with different compositions as well as solidification temperature depression. Those three systems that have different ratios of the materials' saturation pressures show different growth behaviors and mature states of the nanopowders. Furthermore, parametric studies indicate that the majority of the fabricated nanoparticles have the silicon content identical to the initial precursor's silicon fraction. Because the solidification temperature depends on the silicon content in the material, the yield and size of the nanopowder are also affected indirectly by the precursor's silicon fraction.. |
| 46. | Hirotaka Sone, Takuya Kageyama, Manabu Tanaka, Daisuke Okamoto, Takayuki Watanabe, Induction thermal plasma synthesis of lithium oxide composite nanoparticles with a spinel structure, Japanese Journal of Applied Physics, 10.7567/JJAP.55.07LE04, 55, 7S2, 2016.01, [URL], Li-Mn composite oxide nanoparticles are synthesized using an induction thermal plasma, and the formation mechanism is investigated on the basis of the homogenous nucleation rate and thermodynamic considerations. Under a high O2 partial pressure, MnO crystals nucleate and Li oxide condenses on MnO nuclei at a relatively high rate, forming LiMn2O4 in a single phase. On the other hand, under a low partial pressure of O2, LiMnO2 is obtained owing to the low condensation rate of Li oxide. This study presents the successful selective synthesis of LiMn2O4 nanoparticles by controlling the partial pressure of O2.. |
| 47. | Manabu Tanaka, Taro Hashizume, Tomoyuki Imatsuji, Yushi Nawata, Takayuki Watanabe, Investigation of erosion mechanism of tungsten-based electrode in multiphase AC arc by high-speed visualization of electrode phenomena, Japanese Journal of Applied Physics, 10.7567/JJAP.55.07LC01, 55, 7S2, 2016.01, [URL], Electrode phenomena in a multiphase AC arc were successfully visualized using a high-speed observation system with a bandpass filter system to understand the erosion mechanisms of tungsten-based electrodes due to the droplet ejection and electrode evaporation. The obtained results indicated that both droplet ejection and electrode evaporation contributed to the electrode erosion in the multiphase AC arc. The erosion by droplet ejection mainly occurred during the cathodic period, while electrode evaporation mainly occurred during the anodic period. The rates of erosion by droplet ejection and evaporation were estimated to be 6 and 3 g/min, respectively, when the arc current was 100 A. The results of an evaluation of the possible forces acting on the electrode tip suggested that the electromagnetic force was the dominant force in the cathodic period, resulting in droplet ejection.. |
| 48. | Masaya Shigeta, Takayuki Watanabe, Effect of Precursor Fraction on Silicide Nanopowder Growth under A ThermalPlasma Condition: A Computational Study, Powder Technology, http://dx.doi.org/10.1016/j.powtec.2015.11.005, 288, 191-201, 2015.11. |
| 49. | Taro Hashizume, Tanaka Manabu, Takayuki Watanabe, Investigation of Droplet Ejection Mechanism from Electrode in Multi-Phase AC Arc, Quarterly Journal of the Japan Welding Society, 33, 2, 44s-48s, 2015.05. |
| 50. | Feng Liang, Tanaka Manabu, Sooseok Choi, Takayuki Watanabe, Measurement of Anode Surface Temperature in Carbon Nanomaterial Production by Arc Discharge Method, Material Research Bulletin, http://dx.doi.org/10.1016/j.materresbull.2014.08.029, 60, 158-165, 2014.12. |
| 51. | M. Rafiqul Alam, Feroza Begum, Quazi Delwar Hossain, M. Mofazzal Hossain, T. Watanabe, Comparative performance study of short and long induction plasma torches A numerical approach, 9th International Forum on Strategic Technology, 10.1109/IFOST.2014.6991177, 511-515, 2014.12, [URL], In developing the ITP (induction thermal plasma) source for the thermal modification of micro-particles, it is crucial to comprehensively explore the effects of plasma torch dimensions, effects of plasma discharge conditions and particle parameters. Considering the plasma-particle interactions and particle loading impacts, a interactive flow model for argon-oxygen mixed-gas plasma is developed to investigate the performances of short (ST:138 mm) and long (LT:190 mm) induction plasma torches. Solving the model numerically using control volume algorithm, we predicted the plasma isotherm, injected particle's temperature history, trajectory, velocity and diameter at any location along its flight path for both the torches. In this model, the plasma is in local thermal equilibrium (LTE) i.e the temperatures of electron and heavy particle (ion or neutral particle) are the same. From the plasma isotherms of argon-oxygen, it is observed that higher plasma temperature (around 8000K at the torch exit) is obtained in short torch, compared with that of in long torch (around 5000 K at the torch exit). It has also been noticed that more particle diameter shrinkage is occurred in short torch than that of long torch.. |
| 52. | Yaping Liu, Manabu Tanaka, Sooseok Choi, Takayuki Watanabe, Investigation of In-Flight Glass Melting by Controlling the High-Temperature Region of Multiphase AC Arc Plasma, International Journal of Applied Glass Science, 10.1111/ijag.12081, 5, 4, 443-451, 2014.12, [URL], A large volume discharge produced by a stable 12-phase alternating current (AC) arc plasma is preferable to melt the granulated glass materials for time and energy saving. The discharge behavior and the high-temperature region of the plasma system can be controlled by the electrode configurations. In this study, the spatial characteristics of the arc discharge were examined by image analysis with a high-speed camera. The melting characteristics of alkali-free glass particles were investigated by microscope and X-ray diffractometry. This is the first time to investigate the relationship between spatial characteristics of plasma and glass particle property. Results show the arc existence area is strongly related to the electrode configuration. Distributions of in-flight powders and the spatial characteristics of arc are important factors when using multiphase AC arc for in-flight melting. This study provides information of efficient particle treatment according to the electrode configuration.. |
| 53. | Chenning Zhang, Tetsuo Uchikoshi, Ji Guang Li, Takayuki Watanabe, Takamasa Ishigaki, Photocatalytic activities of europium (III) and niobium (V) co-doped TiO2 nanopowders synthesized in Ar/O2 radio-frequency thermal plasmas, Journal of Alloys and Compounds, 10.1016/j.jallcom.2014.03.191, 606, 37-43, 2014.09, [URL], Europium (III) and niobium (V) co-doped TiO2 nanopowders were synthesized in Ar/O2 radio-frequency thermal plasmas by pyrolyzing aqueous precursors that contained various concentrations of Eu 3+/(Eu3+ + Nb5+ + Ti4+) = 0-0.5 at.% and Nb5+/(Eu3+ + Nb5+ + Ti4+) = 0-1.0 at.%. Phase identification was performed by X-ray diffraction (XRD), particle morphology was observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), and UV-vis absorption spectra were determined by UV-vis spectroscopy. The photocatalytic activities under UV and visible light irradiations were both evaluated by bleaching 20 μM of a methyl orange aqueous solution. All the resulting powders had a phase composition of anatase (30-66 nm crystalline size) (major phase: ∼80% mass proportion) and rutile (56-94 nm crystalline size) polymorphs, with a relatively wide particle size distribution from several nanometers (faceted crystallites) to ∼100 nm (spherical particles). The photocatalytic activities dominated by oxygen defects in the TiO2 host lattice for the powders prepared with identical doping concentrations of Eu3+ and Nb5+ were both superior under UV and visible light irradiations over those obtained with different doping amounts. More interestingly, the co-doped powder exhibited an improved photocatalytic performance under 600-700 nm visible light illumination than the Eu3+-doped TiO2 and P25 commercial powders.. |
| 54. | Feng Liang, Tanaka Manabu, Sooseok Choi, Takayuki Watanabe, Effect of Arc Behaviour on the Temperature Fluctuation of Carbon Electrode in DC Arc Discharge, Journal of Physics: Conference Series, http://dx.doi.org/10.1088/1742-6596/518/1/012027, 518, 012027, 2014.06. |
| 55. | Yingying Cheng, Tanaka Manabu, Takayuki Watanabe, SunYong Choi, MyoungSun Shin, KyuHang Lee, Synthesis of Ni2B Nanoparticles by RF Thermal Plasma for Fuel Cell Catalyst, Journal of Physics: Conference Series, http://dx.doi.org/10.1088/1742-6596/518/1/012026, 518, 012026, 2014.06. |
| 56. | Tanaka Manabu, Jun Noda, Takayuki Watanabe, Junya Matsuno, Akira Thuchiyama, Formation Mechanism of Metal Embedded Amorphous Silicate Nanoparticles by Induction Thermal Plasmas, Journal of Physics: Conference Series, http://dx.doi.org/10.1088/1742-6596/518/1/012025, 518, 012025, 2014.06. |
| 57. | Takayuki Watanabe, Makoto Sekine, Takanori Ichiki, Masaharu Shiratani, Akimitsu Hatta, Preface, Journal of Physics: Conference Series, 10.1088/1742-6596/518/1/011001, 518, 1, 2014.06, [URL]. |
| 58. | Takayuki Watanabe, Yaping Liu, Tanaka Manabu, Investigation of Electrode Phenomena In An Innovative Thermal Plasma for Glass Melting, Plasma Chemistry and Plasma Processing, 10.1007/s11090-014-9530-8, 34, 3, 443-456, 2014.04, [URL], A multi-phase alternating current (AC) arc has been applied to glass melting technology. The large volume discharge produced by a stable multi-phase AC arc is preferable to melt the granulated glass materials. The discharge behavior and the hightemperature region of the plasma can be controlled by the electrode configurations. In this study, the spatial characteristics of the arc discharge were examined by image analysis of high-speed camera. Results show arc existence area is related with electrode configuration. This study provides the useful information of efficient particle treatment in the preferred electrode configuration. However, the electrode erosion is one of the most considerable issues to be solved. The combination of high-speed video camera and band-pass filters was introduced to measure the electrode temperature to investigate the erosion mechanism of the multi-phase AC arc. The dynamic behavior of the electrode vapors in the arc was investigated by using the same high-speed camera system. Results show the tungsten electrode mainly evaporates at the anodic period during AC cycle.. |
| 59. | Feng Liang, Tanaka Manabu, Sooseok Choi, Takayuki Watanabe, Investigation of Carbon Nanomaterials Growth on Anode Surface by Arc Discharge Method, Journal of Chemical Engineering of Japan, 10.1252/jcej.13we174, 47, 3, 296-300, 2014.03. |
| 60. | Sooseok Choi, Yingying Cheng, Lorico DS. Lapitan Jr., Takayuki Watanabe, Synthesis of Cobalt Boride Nanoparticles using RF Thermal Plasma, Advanced Powder Technology, 25, 365-371, 2014.03. |
| 61. | Ikuo Taniguchi, Daichi Ioh, Shigenori Fujikawa, Takayuki Watanabe, Yosuke Matsukuma, Masaki Minemoto, An alternative carbon dioxide capture by electrochemical method, Chemistry Letters, 10.1246/cl.140508, 43, 10, 1601-1603, 2014.01, [URL], CO2capture with liquid amine scrubbing has received current acceptance; however, the energy intensive heating process in CO2recovery requires alternate effective CO2separation methods. Condensation of CO2-trapping solutions by electrodialysis and successive CO2recovery under reduced pressure would decrease the required energy in the CO2capture drastically. Energy calculations and basic experiments reveal that the required energy can be reduced to less than 2.0 GJ (t-CO2)-1, which is about a half of the energy required for aqueous monoethanolamine.. |
| 62. | Sooseok Choi, Lorico D S Lapitan, Yingying Cheng, Takayuki Watanabe, Synthesis of cobalt boride nanoparticles using RF thermal plasma, Advanced Powder Technology, 10.1016/j.apt.2013.06.002, 25, 1, 365-371, 2014.01, [URL], Nanosize cobalt boride particles were synthesized from the vapor phase using a 30 kW-4 MHz radio frequency (RF) thermal plasma. Cobalt and boron powder mixtures used as precursors in different composition and feed rate were evaporated immediately in the high temperature plasma and cobalt boride nanoparticles were produced through the quenching process. The X-ray diffractometry (XRD) patterns of cobalt boride nanoparticles prepared from the feed powder ratio of 1:2 and 1:3 for Co:B showed peaks that are associated with the Co2B and CoB crystal phases of cobalt boride. The XRD analysis revealed that increasing the powder feed rate results in a higher mass fraction and a larger crystalline diameter of cobalt boride nanoparticles. The images obtained by field emission scanning electron microscopy (FE-SEM) revealed that cobalt boride nanoparticles have a spherical morphology. The crystallite size of the particles estimated with XRD was found to be 18-22 nm.. |
| 63. | Yaochun Yao, Takayuki Watanabe, In-Flight Melting Bahavior of Grannulated Alkali-Free Raw Material in Induction Thermal Plasmas, Plasma Chemistry and Plasma Processing, 10.1007/s11090-013-9490-4, 33, 6, 1111-1119, 2013.12, [URL], A new in-flight glass melting technology with induction thermal plasmas was developed to reduce the energy consumption and the emissions of greenhouse gases for glass production. The effects of carrier gas on the in-flight melting behavior of granulated alkali-free raw material were investigated by various modern analyses. Results show that the particles have smooth spherical surface and compact structure after heat treatment. As the carrier gas flow rate increases, the vitrification degree decreases and the average diameter increases. Higher vitrification results in more shrinkage of particle. The carbonates in raw material decompose completely during in-flight melting. The highest volatilization of B2O3 is attributed to more heat transferred from plasmas to particles at the lowest carrier gas flow rate.. |
| 64. | Yaping Liu, Manabu Tanaka, Tomoki Ikeba, Sooseok Choi, Takayuki Watanabe, Fluctuation measurement of multi-phase AC arc and in-flight particle temperature, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.13we098, 46, 10, 672-676, 2013.10, [URL], A stable 12-phase alternating current (AC) arc has been successfully applied to melt granulated glass materials. The discharge behavior and the high temperature region of the plasma system can be controlled by the electrode configurations. In this study, the temporal characteristics of the arc discharge were examined by image analysis with a high-speed camera. The instabilities of particle surface temperature were investigated by a high-speed camera equipped with a band-pass filter system. This is the first time that particle temperature measurement of millisecond order has been performed by high-speed camera. Results show the amplitude of the variation in the in-flight particle temperature depends on the amplitude of the arc fluctuation. The periodicity of arc fluctuation is strongly related with transition of discharge pattern.. |
| 65. | Yingying Cheng, Sooseok Choi, Takayuki Watanabe, Effect of nucleation temperature and heat transfer on synthesis of Ti and Fe boride nanoparticles in RF thermal plasmas, Powder Technology, 10.1016/j.powtec.2013.05.028, 246, 210-217, 2013.09. |
| 66. | Manabu Tanaka, Yaping Liu, Sooseok Choi, Takayuki Watanabe, High-Speed Visualization of Electrode Erosion in Multi-Phase Alternating Current Arc, Journal of Fluid Science and Technology, 8, 2, 160-171, 2013.09. |
| 67. | TianMing Li, Takayuki Watanabe, Kaoru Ochi, Koji Ohtsuki, Liquid waste decomposition by long DC arc under atmospheric pressure, Chemical Engineering Journal, 10.1016/j.cej.2013.07.003, 231, 152-162, 2013.09. |
| 68. | Yaochun Yao, Takayuki Watanabe, In-flight melting behavior of granulated alkali-free raw material in induction thermal plasmas, Plasma Chemistry and Plasma Processing, 10.1007/s11090-013-9490-4, 33, 6, 1111-1119, 2013.09, [URL], A new in-flight glass melting technology with induction thermal plasmas was developed to reduce the energy consumption and the emissions of greenhouse gases for glass production. The effects of carrier gas on the in-flight melting behavior of granulated alkali-free raw material were investigated by various modern analyses. Results show that the particles have smooth spherical surface and compact structure after heat treatment. As the carrier gas flow rate increases, the vitrification degree decreases and the average diameter increases. Higher vitrification results in more shrinkage of particle. The carbonates in raw material decompose completely during in-flight melting. The highest volatilization of B2O3 is attributed to more heat transferred from plasmas to particles at the lowest carrier gas flow rate.. |
| 69. | Sooseok Choi, Jiro Matsuo, Yingying Cheng, Takayuki Watanabe, Preparation of boron-rich aluminum boride nanoparticles by RF thermal plasma, Journal of Nanoparticle Research, 10.1007/s11051-013-1820-1, 15, 8, 1820, 2013.08. |
| 70. | Sooseok Choi, Jiro Matsuo, Takayuki Watanabe, Synthesis of AlB12 and YB66 Nanoparticles by RF Induction Thermal Plasmas, Journal of Physics: Conference Series, http://dx.doi.org/10.1088/1742-6596/441/1/012030, 411, 012030, 2013.06. |
| 71. | Yingying Cheng, Sooseok Choi, Takayuki Watanabe, Synthesis of Niobium Boride Nanoparticle by RF Thermal Plasma, Journal of Physics: Conference Series, http://dx.doi.org/10.1088/1742-6596/441/1/012031, 411, 012031, 2013.06. |
| 72. | Manabu Tanaka, Yaping Liu, Sooseok Choi, Takayuki Watanabe, Investigation of Electrode Erosion Mechanism of Multi-Phase AC Arc by High-Speed Video Camera, Journal of Physics: Conference Series, http://dx.doi.org/10.1088/1742-6596/441/1/012015, 411, 012015, 2013.06. |
| 73. | Manabu Tanaka, Takayuki Watanabe, Mechanism of Enhanced Vapourization from Molten Metal Surface by Ar-H2 Arc Plasma, Japanese Journal of Applied Physics, 52, 7, 076201, 2013.06. |
| 74. | Narengerile, Takayuki Watanabe, Decomposition of Glycerine by DC Water Plasmas at Atmospheric Pressure, Plasma Science and Technology, http://dx.doi.org/10.1088/1009-0630/15/4/09, 15, 4, 357-361, 2013.04. |
| 75. | Takayuki Watanabe, Narengerile, Decomposition of glycerine by water plasmas at atmospheric pressure, Plasma Science and Technology, 10.1088/1009-0630/15/4/09, 15, 4, 357-361, 2013.04, [URL], High concentration of aqueous glycerine was decomposed using a direct current (DC) plasma torch at atmospheric pressure. The torch can generate the plasma with water as the plasma-supporting gas in the absence of any additional gas supply system and cooling devices. The results indicated that 5 mol% glycerine was completely decomposed by water plasmas at arc powers of 0.55∼1.05 kW. The major products in the effluent gas were H2 (68.9%∼71.1%), CO2 (18.9%∼23.0%), and CO (0.2%∼0.6%). However, trace levels of formic acid (HCOOH) and formaldehyde (HCHO) were observed in the liquid effluent. The results indicated that the water plasma waste treatment process is capable of being an alternative green technology for organic waste decomposition.. |
| 76. | Sooseok Choi, Tian Ming Li, Takayuki Watanabe, Takashi Nakayama, Koji Otsuki, Numerical analysis of temperature distribution in the long DC arc thermal plasma for waste treatment, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.12we201, 46, 3, 201-208, 2013.03, [URL], Numerical analysis has been conducted to characterize thermal plasma generated by a novel long direct current (DC) arc discharge system for waste treatment. Effects of arc current, gas flow rate, confinement tube diameter, and electrode gap distance on the temperature distribution of thermal plasma were investigated. From the numerical results, the design variables were expected to control over waste treatment processes effectively in the long DC arc thermal plasma. A broad high temperature distribution with low power consumption was predicted in the case of large diameter of the plasma confinement tube, because the less intrusion of cold gas into the arc column leads to the expanding of current density profile in the radial direction. In the downstream region, the fraction of low temperature area to cross sectional area that hinders the decomposition of wastes was decreased with increasing the electrode gap distance.. |
| 77. | Takayuki Watanabe, Manabu Tanaka, Tasuku Shimizu, Feng Liang, Metal nanoparticle production by anode jet of argon-hydrogen DC arc, 2012 International Conference on Manufacturing Engineering and Technology for Manufacturing Growth, 10.4028/www.scientific.net/AMR.628.11, 11-14, 2013.02, [URL], The purpose of this paper is to prepare nickel particles by arc plasma method with hydrogen addition. The effect of anode jet formation on the nanoparticle production was investigated by high-speed camera observations. The high-speed camera system with appropriate band-pass filters successfully provides the observation of anode jet image without cathode jet image. The areas of the anode jet and the cathode jet were separately estimated from the high-speed images. From these observations, the periodical fluctuation of the anode jet was confirmed. Higher hydrogen concentration leads to larger anode jet area, resulting from the enhanced evaporation of the anode material.. |
| 78. | M. Tanaka, T. Ikeba, Y. Liu, S. Choi, T. Watanabe, Investigation of electrode erosion mechanism of multi-phase AC arc by high-speed video camera, Journal of Physics: Conference Series, 10.1088/1742-6596/441/1/012015, 441, 1, 2013.01, [URL], A multi-phase AC arc has been applied to the glass melting technology. However, the electrode erosion is one of the most considerable issues to be solved. In order to investigate the erosion mechanism of the multi-phase AC arc, the combination of the high-speed video camera and the band-pass filters was introduced to measure the electrode temperature. Results indicated the tip temperature of the electrode surface in the 12-phase arc was lower than that in the 2-phase arc, while erosion rate in 12-phase arc was higher than that in the 2-phase arc. Furthermore, the dynamic behaviour of the vapours in the arc was investigated by using the same high-speed camera system. The tungsten electrode mainly evaporates at the anodic period during AC cycle. The oxygen concentration in the arc increases with larger number of the phases, resulting in the higher erosion rate in the 12-phase arc.. |
| 79. | H. Kanamori, T. Watanabe, S. Aoki, Power requirements for the construction and operation of a lunar oxygen plant, Journal of Aerospace Engineering, 10.1061/(ASCE)AS.1943-5525.0000180, 26, 1, 160-168, 2013.01, [URL], Construction work and machines required to build lunar facilities including an oxygen plant were specified, and power requirements for the construction and operation of these facilities were estimated based on a proposed evolutional scenario. Individual components of lunar facilities such as habitat/laboratory modules, corridor modules, and connection/evacuation modules were designed, and specifications of lunar construction machines were determined. A realistic oxygen plant was also designed by referring to the experimental and analytical results of hydrogen reduction of ilmenite processes. The energy required for soil work is estimated to exceed the energy for a construction facility, and the covering of facilities with regolith is expected to be the most energy-consuming work. Estimated power demands for construction in the evolutional Phases 1, 2, and 3 were 75, 75, and 155 kW, whereas those for operation of the oxygen plant were 2.3, 31, and 761 kW, respectively.. |
| 80. | Takayuki Watanabe, Toshio Kaneko, Makoto Sekine, Yasunori Tanaka, Preface, Journal of Physics: Conference Series, 10.1088/1742-6596/441/1/011001, 441, 1, 2013.01, [URL]. |
| 81. | Feng Liang, Tasuku Shimizu, Manabu Tanaka, Sooseok Choi, Takayuki Watanabe, Preparation of polyhedral graphite particles by arc discharge under atmospheric pressure, Japanese journal of applied physics, 10.7567/JJAP.52.01AK01, 52, 1 PART2, 2013.01, [URL], Polyhedral graphite particles (PGPs) were synthesized by arc discharge method under atmospheric pressure in the relatively short electrode gap distance of 1 mm, while graphene flakes and turbostratic graphite were found by increasing the electrode gap distance. The selective synthesis of nano-sized carbon allotropes was controlled by the contribution of carbon ions and carbon radicals with the change of the electrode gap distance. The formation mechanism of PGPs and other carbon allotropes were proposed according to the experimental results. The low concentration of carbon ions to carbon radicals contributes to the formation of PGPs. In contrast, relatively high concentration of carbon ions to carbon radicals contributes to the formation of graphene flakes and turbostratic graphite.. |
| 82. | M. Mofazzal Hossain, M. Rafiqul Alam, Takayuki Watanabe, Thermal treatment of Al2O3, MgO, and CeO2 granulated powders by induction thermal plasma A numerical approach, Japanese journal of applied physics, 10.7567/JJAP.52.01AL01, 52, 1 PART2, 2013.01, [URL], A plasma-particle interactive flow model has been developed for the investigation of plasma temperature, velocity, particle temperature, diameter, and flight path during in-fight thermal treatment of granulated powders-Al 2O3, MgO, and CeO2 in induction thermal plasma, taking into account of plasma particle interaction and particle loading effects. In this model, the conservative equations are solved to investigate the influence of feedrate and particle diameter on the melting behavior of granulated powders and to predict particle trajectories, temperature histories etc. In this paper attention is given to the effects of carrier gas flow-rate, powder feed-rate and secondary gas (oxygen) flow-rate on the particles' final diameter and trajectory for Al2O3, MgO, and CeO 2 powders. Results show that the particles diameter after thermal treatment is strongly dependent on the powder feed-rate, oxygen gas flow-rate and carrier gas flow-rate. Among the three types of powders, particle diameter decrement is significant in case of MgO and less significant in case of Al 2O3; and the effect of oxygen flow-rate on the particle diameter decrement is significant in case of MgO. Particles trajectories are wider for smaller particles than that of larger particles. Particle temperature is lowest for MgO and highest for Al2O3 particles.. |
| 83. | Manabu Tanaka, Yaping Liu, Sooseok Choi, Takayuki Watanabe, High-speed visualization of electrode erosion in multi-phase alternating current arc, Journal of Fluid Science and Technology, 8, 160-171, 2013. |
| 84. | Tianming Li, Sooseok Choi, Takayuki Watanabe, Discharge characteristics of DC arc water plasma for environmental applications, Plasma Science and Technology, 10.1088/1009-0630/14/12/11, 14, 12, 1097-1101, 2012.12, [URL], A water plasma was generated by DC arc discharge with a hafnium embedded rodtype cathode and a nozzle-type anode. The discharge characteristics were examined by changing the operation parameter of the arc current. The dynamic behavior of the arc discharge led to significant fluctuations in the arc voltage and its frequency. Analyses of the high speed image and the arc voltage waveform showed that the arc discharge was in the restrike mode and its frequency varied within several tens of kilohertz according to the operating conditions. The larger thermal plasma volume was generated by the higher flow from the forming steam with a higher restrike frequency in the higher arc current conditions. In addition, the characteristics of the water plasma jet were investigated by means of optical emission spectroscopy to identify the abundant radicals required in an efficient waste treatment process.. |
| 85. | Tianming Li, Sooseok Choi, Takayuki Watanabe, Takashi Nakayama, Toshio Tanaka, Discharge and optical characteristics of long arc plasma of direct current discharge, Thin Solid Films, 10.1016/j.tsf.2012.07.061, 523, 72-75, 2012.11, [URL], Arc discharge with argon and nitrogen was generated across the long electrode gap distance of 400 mm to produce a stable thermal plasma and large volume with low power under atmospheric pressure. In the case of nitrogen as plasma forming gas, an increase of the gas flow rate increases the arc voltage, thus the center temperature of the arc column reached higher. For the argon arc, the arc voltage decreases with increasing gas flow rates. Due to the arc constriction in both cases of nitrogen and argon, the center temperature of the arc column increases under the constant current. The result of emission intensity distribution across nitrogen arc column reveals that the arc column diameter increases with increasing gas flow rate because of the increase of the input power. On the other hand, in the argon arc, the diameter decreases by strong thermal pinch in large flow rate of argon. The measured excitation temperature is uniform along with axial direction of the arc column which is an important feature for waste materials processing due to the long direct current arc plasma that provides long residence time for injected materials.. |
| 86. | Manabu Tanaka, Yaping Liu, Yosuke Tsuruoka, Takayuki Watanabe, Experimental investigation of in-flight melting by hybrid heating of multi-phase alternating current arc with oxygen burner for alkali-free glass raw materials, Thin Solid Films, 10.1016/j.tsf.2012.07.064, 523, 67-71, 2012.11, [URL], An innovative in-flight glass melting technology was developed for a purpose of energy saving and environmental protection. Granulated glass raw materials with small diameter were treated by hybrid heating of multi-phase AC arc combined with an oxygen burner. A multi-phase AC arc and hybrid plasma were compared to study the in-flight melting efficiency of the granulated raw materials. The effects of the input energy and the primary size of SiO 2 in the glass raw materials on the characteristics of the in-flight melted particles were investigated. The reaction rate inside the individual in-flight particles was enhanced with decreasing the primary size of SiO 2 particles, resulting in the more effective in-flight melting by the hybrid plasma.. |
| 87. | Feng Liang, Tasuku Shimizu, Manabu Tanaka, Sooseok Choi, Takayuki Watanabe, Selective preparation of polyhedral graphite particles and multi-wall carbon nanotubes by a transferred arc under atmospheric pressure, Diamond and Related Materials, 10.1016/j.diamond.2012.09.004, 30, 70-76, 2012.11, [URL], High-purity polyhedral graphite particles (PGPs) and multi-wall carbon nanotubes (MWNTs) were selectively synthesized by a transferred arc discharge method under atmospheric pressure. PGPs and MWNTs were characterized by the field emission scanning electron microscope (FE-SEM), transition electron microscopy (TEM), and Raman spectroscopy. The products were successfully controlled by varying the arc current and the anode diameter. PGPs were the main products in the case of a relatively high arc current of 100 A or a large anode diameter of 30 mm, while MWNTs were the main products when the arc current was reduced to 80 A or the anode diameter was decreased to 15 and 10 mm. The ratio of carbon ions to carbon radicals near the cathode tip was employed to explain the mechanisms of PGP and MWNT formation. Relatively high ratio of carbon ions to carbon radicals contributed to the formation of PGPs. In contrast, relatively low ratio of carbon ions to carbon radicals led to the formation of MWNTs.. |
| 88. | T. Shirafuji, Y. Setsuhara, M. Shiratani, T. Kaneko, T. Watanabe, N. Ohtake, The 24th Symposium on Plasma Science for Materials (SPSM-24), Thin Solid Films, 10.1016/j.tsf.2012.10.002, 523, 2012.11, [URL]. |
| 89. | S. Inoue, T. Watanabe, T. Yano, O. Sakamoto, K. Satoh, S. Kawachi, T. Iseda, Future of glass melting through the in-flight melting technique, Processing, Properties, and Applications of Glass and Optical Materials: Ceramic Transactions, http://dx.doi.org/10.1002/9781118472590.ch3, 231, 37-44, 2012.09, The principle of the in-flight glass melting technique is reviewed and the future of the industrial glass melting is discussed based on the achievements of the on-going project on the development of the in-flight glass melting technology. In the in-flight melting, a granular batch is charged directly into a burner flame. The heat transfer from heating source to a glass batch is enhanced very much and the glass melting energy can be saved by more than 50% of the current glass tank furnaces. The innovative glass melting technique will trigger the revolution in glass production to push the glass industry into a new era. The technique can also reduce the melting furnace sizes, which will contribute to the reduction of furnace construction cost. The standard soda-lime-silica glass composition can be melted using only an oxy-gas firing burner. The oxy-gas burner can be combined with an are plasma torch to compose the hybrid heating in the new technique. The hybrid heating source can generate higher temperature than the burner heating and is applicable to the melting of high liquidus temperature glass forming systems. The feature will enable the production of the new functional glasses which are difficult to be fabricated by the currently popular Siemens type melting furnaces.. |
| 90. | Yaping Liu, Manabu Tanaka, Sooseok Choi, Takayuki Watanabe, In-flight Particle Measurement of Alkali-Free Glass Raw Materials in 12-Phase AC Arc Plasma, Journal of Thermal Spray Technology, 21, 863-872, 2012.09. |
| 91. | Yaping Liu, Manabu Tanaka, Sooseok Choi, Takayuki Watanabe, In-flight particle measurement of alkali-free glass raw materials in 12-phase AC Arc plasma, Journal of Thermal Spray Technology, 10.1007/s11666-012-9758-x, 21, 5, 863-872, 2012.09, [URL], In-flight particle measurements of the surface temperature and velocity are important for understanding of melting behavior of glass particles during in-flight melting by multi-phase AC arc plasma. However, the use of optical pyrometry for particle surface temperature has inevitable uncertainties due to non-thermal emissions signals from the plasma plume. This work presents spectroscopic measurements of the non-thermal signals which were found to be caused mainly by the plasma emissions scattered by the particles and the radiation emitted by vapor. After that, the accuracy of thermal radiation measurement was estimated and surface temperature of in-flight glass particle was corrected.. |
| 92. | Sooseok Choi, Takayuki Watanabe, Decomposition of 1-decanol emulsion by water thermal plasma jet, IEEE Transactions on Plasma Science, 10.1109/TPS.2012.2206059, 40, 11 PART1, 2831-2836, 2012.07, [URL], Water-insoluble organic compound of 1-decanol was decomposed by a water plasma system operated at atmospheric pressure. It was dispersed in water by a surfactant generating an oil-in-water emulsion, and then, the emulsion was used as the feeding liquid and plasma-forming gas of the water plasma jet. The input power supplied to the dc water plasma system was less than 1 kW. High decomposition rate over 99.9999% was achieved with the conversion of 1-decanol emulsion intoH2, CO,CO2, CH4, condensed liquid, and solid-state carbon. The gas conversion rate of carbon in 1-decanol and the removal rate of total organic carbon concentration were increased by increasing the arc current due to enhanced O radicals in the high temperature of the water plasma jet. Different from the decomposition of water-soluble 1-butanol, noticeable changes in the decomposition rate and pH level were not founded in the treatment of 1-decanol emulsion according to carbon concentration in the feeding liquid. The main organic substance in the treated liquid of 1-decanol emulsion was methanediol which was produced by the hydration of formaldehyde.. |
| 93. | S. Choi, K. S. Choi, D. W. Park, T. Watanabe, Numerical investigation on counter flow injection of waste gas into thermal plasma jet, International Journal of Plasma Environmental Science and Technology, 6, 1, 68-73, 2012.07, Numerical analysis on thermal plasma processing for waste gas treatment was carried out considering counter flow injection of the waste gas into the thermal plasma jet. Different plasma flames were generated according to plasma gas flow rate, arc current and nozzle diameter. Thermal plasma jet from a small torch exit which has higher axial velocity than that from a large torch exit penetrates deep into the reaction tube in spite of relatively low input power and plasma gas flow rate. The major parameter influencing on the thermal flow field inside the reactor is the reaction tube diameter at top position, and thermal plasma introducing into the reaction tube comes hard by decreasing its size. At the same top diameter, the reaction tube with expansion type has an effect to increase the high temperature area in radial direction.. |
| 94. | Feng Liang, Yaochun Yao, Yongnian Dai, Bin Yang, Wenhui Ma, Takayuki Watanabe, Preparation of porous structure LiFePO 4/C composite by template method for lithium-ion batteries, Solid State Ionics, 10.1016/j.ssi.2012.02.043, 214, 31-36, 2012.04, [URL], Cationic surfactant cetyltrimethylammonium bromide (CTAB) was used as template to prepare porous structure LiFePO 4/C composite by the template method. The porous structure LiFePO 4/C composites were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transition electron microscopy (TEM), high voltage electron microscopy (HVEM), and nitrogen adsorption-desorption test. The structures and electrochemical performances of the samples calcined at different calcination times at 700 °C were studied. The results indicate that the porous structure LiFePO 4/C composite prepared at 700 °C for 24 h exhibited the best electrochemical performance, the discharge capacity is up to 152.1 mAh g - 1 at 0.1 C rate. Compared with nano-sized LiFePO 4/C composite without template, porous structure LiFePO 4/C could dramatically improve the rate capability because of its higher specific surface area and more channels for fast lithium ion diffusion.. |
| 95. | Sooseok Choi, Sang Hee Hong, Hyun Seok Lee, Takayuki Watanabe, A comparative study of air and nitrogen thermal plasmas for PFCs decomposition, Chemical Engineering Journal, 10.1016/j.cej.2012.01.077, 185-186, 193-200, 2012.03, [URL], Air and nitrogen thermal plasmas were generated from a plasma torch with hollow electrodes to abate CF 4 which is a serious non-degradable greenhouse gas exhausted from the semiconductor manufacturing process. Numerical analysis and experimental demonstration have been carried out to compare effects of plasma forming gas on the decomposition process at the same electric input power of 60kW and waste gas flow rate of 200L/min. Higher temperature and longer residence time were expected in nitrogen thermal plasma than air thermal plasma, because relatively low flow rate of nitrogen plasma gas is required at fixed input power compared with air plasma gas. Although small quantity of NF 3 was produced in nitrogen thermal plasma process with hydrogen reactant gas, high destruction and removal efficiency of 99.6% was achievable along with suppression of unwanted NOx generation.. |
| 96. | Yaochun Yao, Takayuki Watanabe, Kazuyuki Yatsuda, Characterization of 12-phase AC arc discharge and glass in-flight melting behavior, 2nd International Conference on Information Science, Automation and Material System, 10.4028/www.scientific.net/AMR.485.185, 185-188, 2012.03, [URL], Thermal plasma of 12-phase AC arc was successfully developed and applied in the field of glass in-flight melting, and the arc discharge behavior was characterized by image analysis. The effects of sheath gas flow rate on arc discharge and melting behavior of granulated glass raw material were investigated. Results show that different sheath gas flow rates lead to various arc discharge and high-temperature region. The fluctuation of luminance area ratio and coefficient of variation reflects the change of arc discharge behavior. As the sheath gas flow rate increases, the ratio of luminance area decreases and the center temperature of arc increases. The vitrification degree of glass raw material is mostly dependent on the center temperature of arc, higher center temperature and more vitrification degree.. |
| 97. | Yaochun Yao, Takayuki Watanabe, Kazuyuki Yatsuda, Discharge behavior characterization of 12-phase AC arc and its application, 3rd international Conference on Manufacturing Science and Engineering, 10.4028/www.scientific.net/AMR.479-481.615, 615-618, 2012.03, [URL], A stable 12-phase AC arc was successfully developed and applied in the field of glass in-flight melting, and the arc discharge behavior was characterized by image analysis. The effects of sheath gas flow rate on arc discharge and melting behavior of granulated glass raw material were investigated. Results show that different sheath gas flow rates lead to various arc discharge and high-temperature region. The fluctuation of luminance area ratio and coefficient of variation reflects the change of arc discharge behavior. As the sheath gas flow rate increases, the ratio of luminance area decreases and the center temperature of arc increases. The vitrification degree of glass raw material is mostly dependent on the center temperature of arc, higher center temperature and more vitrification degree.. |
| 98. | Narengerile, T. Watanabe, Acetone decomposition by water plasmas at atmospheric pressure, Chemical Engineering Science, 10.1016/j.ces.2011.10.045, 69, 1, 296-303, 2012.02, [URL], Decomposition of aqueous acetone was performed using a direct current (DC) plasma torch at atmospheric pressure. The torch can generate the plasma with water as the plasma-supporting gas in the absence of any additional gas supply system and cooling devices. The results indicated that 5mol% acetone was drastically decomposed by water plasmas with energy efficiencies of 1.7×10 -7molJ -1. The major products in the effluent gas were H 2 (60-70%), CO 2 (5-16%), CO (6-16%), and CH 4 (0.2-0.9%). However, trace levels of formic acid (HCOOH) and formaldehyde (HCHO) were observed in the liquid effluent. Based on the experimental results and information from the literature, the following decomposition mechanism was proposed for acetone in water plasmas: first, electron dissociation in arc region generates acetyl (CH 3CO) and methyl (CH 3) radicals; then, chemical oxidation or reduction in plasma flow region forms CO and CH x(x:1-3) radicals there. Finally, the generated intermediate species undergo complex reactions to form stable compounds such as CO in downstream region. However, if little oxygen is present, those intermediate species easily recombine with each other or are oxidized by OH to form unwanted by-products, such as HCOOH and HCHO.. |
| 99. | Yingying Cheng, Masaya Shigeta, Sooseok Choi, Takayuki Watanabe, Formation mechanism of titanium boride nanoparticles by RF induction thermal plasma, Chemical Engineering Journal, 10.1016/j.cej.2011.12.040, 183, 483-491, 2012.02, [URL], The formation mechanism of titanium boride functional nanoparticles by the radio frequency induction thermal plasma was investigated by experiment and numerical analysis. The mixed powders of titanium and boron were injected into the plasma and evaporated immediately, and then nanoparticles were produced through the quenching process. The nanoparticle products were characterized by phase composition and crystalline diameter. TiB 2 was easily synthesized with a low powder feed rate in the boron-rich condition, because the molar ratio of evaporated and nucleated boron in plasma was enhanced. The prepared titanium boride nanoparticles had the average crystalline diameter ranging from 10 to 30nm, and it was reduced with decreasing the powder feed rate and titanium content in the raw material due to abundant number of boron nuclei. This paper demonstrates the feasibility of the control of titanium boride nanoparticles' crystalline mean diameter and phase composition with different raw material condition in the RF induction thermal plasma synthesis.. |
| 100. | Takayuki Watanabe, Narengerile, Hiroshi Nishioka, Role of CH, CH 3, and OH radicals in organic compound decomposition by water plasmas, Plasma Chemistry and Plasma Processing, 10.1007/s11090-011-9329-9, 32, 1, 123-140, 2012.02, [URL], Decomposition of acetone, methanol, ethanol, and glycerine by water plasmas at atmospheric pressure has been investigated using a direct current discharge. At torch powers of 910-1,050 W and organic compound concentrations of 1-10 mol%, the decomposition rate of methanol and glycerine was over 99%, while those of acetone and ethanol was 95.4-99%. The concentrations of H 2 obtained were 60-80% in the effluent gas for any compounds by pyrolysis. Based on the experimental results, the decomposition mechanism of organic compounds in water plasmas was proposed and the roles of intermediate species such as CH, CH 3, and OH have been investigated; CH radical generated from organic compounds decomposition was easily oxidized to form CO; incomplete oxidation of CH 3 leads to C 2H 2 generation as well as soot formation; and negligible amount of soot observed from glycerine decomposition even at high concentration indicated that oxidation of CH×( ×:1-3) was enhanced by OH radical.. |
| 101. | Sooseok Choi, Dong Wha Park, Takayuki Watanabe, Thermal plasma decomposition of fluorinated greenhouse gases, Nuclear Engineering and Technology, 10.5516/NET.77.2012.003, 44, 1, 21-32, 2012.02, [URL], Fluorinated compounds mainly used in the semiconductor industry are potent greenhouse gases. Recently, thermal plasma gas scrubbers have been gradually replacing conventional burn-wet type gas scrubbers which are based on the combustion of fossil fuels because high conversion efficiency and control of byproduct generation are achievable in chemically reactive high temperature thermal plasma. Chemical equilibrium composition at high temperature and numerical analysis on a complex thermal flow in the thermal plasma decomposition system are used to predict the process of thermal decomposition of fluorinated gas. In order to increase economic feasibility of the thermal plasma decomposition process, increase of thermal efficiency of the plasma torch and enhancement of gas mixing between the thermal plasma jet and waste ga s are discussed. In addition, noble thermal plasma systems to be applied in the thermal plasma gas treatment are introduced in the present paper.. |
| 102. | Yaochun Yao, Takayuki Watanabe, Kazuyuki Yatsuda, Application and characterization of 12-phase AC arc for glass in-flight melting, International Conference on Manufacturing Science and Materials Engineering, 10.4028/www.scientific.net/AMR.443-444.637, 637-642, 2012.01, [URL], A stable 12-phase AC arc was successfully generated and applied in the field of glass in-flight melting, the arc behavior was characterized by image analysis. The effects of electrode configuration and sheath gas flow rate on arc and melting behavior of granulated glass raw material were investigated. Results show that different electrode configurations leads to various arc discharge and high-temperature region. The luminance area with high-temperature region and its fluctuation reflect the change of arc discharge behavior. The vitrification degree of glass raw material is mostly dependent on the center temperature of arc. As the sheath gas flow rate increases, the ratio of luminance area decreases and the center temperature of arc increases.. |
| 103. | Sooseok Choi, Takayuki Watanabe, Decomposition of water-insoluble organic waste by water plasma at atmospheric pressure, Journal of Physics: Conference Series, 10.1088/1742-6596/406/1/012003, 406, 1, 2012.01, [URL], The water plasma was generated in atmospheric pressure with the emulsion state of 1-decanol which is a source of soil and ground water pollution. In order to investigate effects of operating conditions on the decomposition of 1-decanol, generated gas and liquid from the water plasma treatment were analysed in different arc current and 1-decanol concentration. The 1-decanol was completely decomposed generating hydrogen, carbon monoxide, carbon dioxide, methane, treated liquid and solid carbon in all experimental conditions. The feeding rate of 1- decanol emulsion was increased with increasing the arc current in virtue of enhanced input power. The generation rate of gas and the ratio of carbon dioxide to carbon monoxide were increased in the high arc current, while the generation rate of solid carbon was decreased due to enhanced oxygen radicals in the high input power. Generation rates of gas and solid carbon were increased at the same time with increasing the concentration of 1-decanol, because carbon radicals were increased without enhancement of oxygen radicals in a constant power level. In addition, the ratio of carbon dioxide to carbon monoxide was increased along with the concentration of 1-decanol due to enhanced carbon radicals in the water plasma flame.. |
| 104. | M. Tanaka, T. Ikeba, Y. Liu, T. Matsuura, T. Watanabe, Electrode temperature measurements of multi-phase AC arc by high-speed video camera, Journal of Physics: Conference Series, 10.1088/1742-6596/406/1/012008, 406, 1, 2012.01, [URL], The multi-phase AC arc plasma has been applied in the glass melting technology as a promising heat source. The electrode erosion of the multi-phase arc is one of the most important issues to be solved. In the present work, the theory of the two-colour pyrometry by using the high-speed video camera with band-pass filters was applied to the electrode temperature measurements. First, the spectroscopic measurements of the electrode region in the multi-phase arc were conducted to select the appropriate wavelengths of band-pass filters. Then, the electrode temperatures of 2-phase, 6-phase, and 12-phase arcs were measured. The electrode tip temperature and the molten area were evaluated from the obtained 2-dimensional temperature distributions. Results indicated that the increase of the number of the phases leads to the lower tip temperature and the larger molten area. Observation of the multiple arcs further revealed the particular characteristics of the multi-phase arc, such as the periodical arc motion has important role on the electrode molten state.. |
| 105. | Y. Liu, M. Tanaka, T. Ikeba, S. Choi, T. Watanabe, In-flight particle measurement of glass raw materials in hybrid heating of twelve-phase AC arc with oxygen burner, Journal of Physics: Conference Series, 10.1088/1742-6596/406/1/012022, 406, 1, 2012.01, [URL], The high temperature provided by a 12-phase AC arc plasma is beneficial to finish vitrification reaction in milliseconds. Another heating method called "hybrid plasma" combines multi-phase AC arc and oxygen burner are expected to improve glass quality and increase productivity with minimum energy consumption. In this study, recent works on the development of in-flight particle measurement in hybrid plasma system are presented. Two-colour pyrometry offers considerable advantages for measuring particle temperatures in flight. A high-speed camera equipped with a band-pass filter system was applied to measure the in-flight temperatures of glass particles. The intensity recorded by the camera was calibrated using a tungsten halogen lamp. This technique also allows evaluating the fluctuation of the average particle temperature within millisecond in plasma region.. |
| 106. | Rei Niimi, Toshihiko Kadono, Akira Tsuchiyama, Kyoko Okudaira, Sunao Hasegawa, Makoto Tabata, Takayuki Watanabe, Masahito Yagishita, Nagisa MacHii, Akiko M. Nakamura, Kentaro Uesugi, Akihisa Takeuchi, Tsukasa Nakano, Size and density estimation from impact track morphology in silica Aerogel Application to dust from comet 81p/wild 2, Astrophysical Journal, 10.1088/0004-637X/744/1/18, 744, 1, 2012.01, [URL], A large number of cometary dust particles were captured with low-density silica aerogel during the NASA Stardust mission. The dust particles penetrated into the aerogel and formed various track shapes. To estimate the properties of the dust particles, such as density and size, based on the morphology of the tracks, we carried out systematic experiments testing impacts into low-density aerogel at 6kms-1 using projectiles of various sizes and densities. We found that the maximum track diameter and the ratio of the track length to the maximum track diameter in aerogel are good indicators of projectile size and density, respectively. Based on these results, we estimated the size and density of individual dust particles from comet 81P/Wild 2. The average density of the "fluffy" dust particles and the bulk density of all dust particles were obtained as 0.35 ± 0.07 and 0.49 ± 0.18gcm -3, respectively. These statistical data provided the content of monolithic and coarse grains in the Stardust particles, ∼ 30wt%. Combining this result with some mid-infrared observational data, we found that the content of crystalline silicates is ∼ 50wt% or more of non-volatile material.. |
| 107. | Manabu Tanaka, Yosuke Tsuruoka, Yaping Liu, T. Matsuura, Takayuki Watanabe, Investigation of multiphase ac arc behavior by high-speed video observation, IEEE Transactions on Plasma Science, 10.1109/TPS.2011.2149545, 39, 11 PART 1, 2904-2905, 2011.11, [URL], A stable multiphase ac arc was generated by transformers at a commercial electric system. The arc discharge behavior is investigated by high-speed video camera observation synchronized with voltage waveform analysis. The multiphase ac arc-generating system enables one to obtain wide high-temperature region, which is expected to be suitable for powder heat treatment such as in-flight glass production.. |
| 108. | Chenning Zhang, Tetsuo Uchikoshi, Ji Guang Li, Takayuki Watanabe, Takamasa Ishigaki, Influence of niobium doping on phase composition and defect-mediated photoluminescence properties of Eu3+-doped TiO2 nanopowders synthesized in Ar/O2 thermal plasma, Journal of Alloys and Compounds, 10.1016/j.jallcom.2011.06.089, 509, 36, 8944-8951, 2011.09, [URL], Nb5+:Eu3+-codoped TiO2 nanopowders for chemical composition adjustment have been synthesized via Ar/O2 radio-frequency thermal plasma. X-ray diffraction (XRD) results reveal that all the resultant powders exhibited mixture polymorphs of anatase (mean size: ∼45 nm) as the major phase and rutile (mean size: ∼71 nm). Rutile formation was promoted by the Eu3+ doping but suppressed by the Nb5+ addition. Combined observation using FE-SEM and TEM indicates that all the plasma-synthesized powders had a majority of facet-shaped particles (several nanometers) and a small proportion of nearly spherical crystals (∼150 nm). For the defect-mediated photoluminescence (PL) emission through the energy transfer from the TiO2 host to the Eu3+ activator, the PL intensity originating from the 5D0 → 7F2 electronic transition weakened but that from the 5D0 → 7F1 electronic transition strengthened with increasing Nb5+ content. This may be a result of the decrease in the oxygen vacancy defects in the TiO2 host lattice, as revealed by the joint means of UV-vis absorption spectra and excitation and emission spectra.. |
| 109. | Chenning Zhang, Masashi Ikeda, Masaaki Isobe, Tetsuo Uchikoshi, Ji Guang Li, Takayuki Watanabe, Takamasa Ishigaki, Phase composition and magnetic properties of niobiumiron codoped TiO 2 nanoparticles synthesized in Ar/O2 radio-frequency thermal plasma, Journal of Solid State Chemistry, 10.1016/j.jssc.2011.07.025, 184, 9, 2525-2532, 2011.09, [URL], Nanoparticles of Nb5Fe3 codoped TiO2 with various Nb5 concentrations (Nb/(TiFeNb)=010.0 at%) and Fe3 (Fe/(TiFeNb)=02.0 at%) were synthesized using Ar/O2 thermal plasma. Dopant content, chemical valence, phase identification, morphology and magnetic properties were determined using several characterization techniques, including inductively coupled plasma-optical emission spectrometer, X-ray photoelectron spectroscopy, X-ray diffraction, UVvis diffuse reflectance spectrometer, field-emission scanning electron microscopy, transmission electron microscopy and SQUID commercial instrument. The XRD revealed that all the plasma-synthesized powders were exclusively composed of anatase as major phase and rutile. The rutile weight fraction was increased by the substitution of Fe3 for Ti4 whereas it was reduced by the Nb5 doping. The plasma-synthesized Nb5Fe3 codoped TiO 2 powders had intrinsic magnetic properties of strongly paramagnetic and feebly ferromagnetic at room temperature. The ferromagnetic properties gradually deteriorated as the Fe3 concentration was decreased, suggesting that the ferromagnetism was predominated by the phase composition as a carrier-mediated exchange.. |
| 110. | Manabu Tanaka, Yosuke Tsuruoka, Yaping Liu, Tsugio Matsuura, Takayuki Watanabe, Stability analysis of multi-phase AC arc discharge for in-flight glass melting, Current Applied Physics, 10.1016/j.cap.2011.05.037, 11, 5 SUPPL., S35-S39, 2011.09, [URL], A stable multi-phase AC arc was generated to by transformers at a commercial electric system. The arc discharge behavior and the stability were investigated by the high-speed video camera observation synchronized with the voltage waveform analysis. The effect of the number of phase and the flaming gas addition into the arc region on the arc behavior and the arc stability were studied. Results showed that the re-ignition occurred between adjacent electrodes periodically. Two kinds of the stability analysis methods were introduced. The estimated fluctuation degree showed that an increase of the number of the phase leads to the stable multi-phase AC arc. The deviation of the arc voltage from the average arc voltage was estimated to evaluate the uniformity of the multi-phase AC arc. Although an addition of the oxygen flame into the arc region leads to lower uniformity, the modification of the electrode position can improve the uniformity of the multi-phase AC arc.. |
| 111. | Norio Kobayashi, Takamasa Ishigaki, Takayuki Watanabe, Ji Guang Li, Synthesis of pure, crystalline (Ba,Sr)TiO3 nanosized powders in radio frequency induction thermal plasma, International Journal of Applied Ceramic Technology, 10.1111/j.1744-7402.2010.02546.x, 8, 5, 1125-1135, 2011.09, [URL], Barium strontium titanate ((Ba,Sr)TiO3) nanosized powders were synthesized via spray pyrolysis of a liquid precursor mist in Ar-O2 radio frequency induction thermal plasma. To adjust the cation stoichiometry of the complex oxide, liquid precursors were prepared by mixing titanium butoxide (Ti(OBu)4) stabilized with diethanolamine and aqueous solutions of barium nitrate (Ba(NO3)2) and strontium nitrate (Sr(NO3)2) stabilized with citric acid. The molar ratios of titanium, barium, and strontium ions (Ba/(Ba+Sr) and (Ba+Sr)/Ti ratios) in the liquid precursor were varied. Pure, high-crystalline (Ba,Sr)TiO3 (Ba/(Ba+Sr)=0.0-1.0) powders of ∼45 nm in size were synthesized in this one-step process.. |
| 112. | Yaping Liu, Yosuke Tsuruoka, Manabu Tanaka, Toshio Ichihashi, Tetsuji Yano, Takayuki Watanabe, In-flight melting behavior of different glass raw materials by hybrid heating of twelve-phase ac arc with oxygen burner, Thin Solid Films, 10.1016/j.tsf.2010.11.056, 519, 20, 7005-7008, 2011.08, [URL], An innovative in-flight glass melting technology was developed for a purpose of energy saving and environmental protection. Granulated glass raw materials with small diameter were treated by hybrid heating of twelve-phase ac arc combined with an oxygen burner. X-ray diffraction analysis showed that all carbonates in raw materials were decomposed and > 94% SiO2 (quartz) was reacted into a noncrystalline state. The high vitrification degree achieved within several milliseconds reveals that the new in-flight melting technology of hybrid plasma treating can reduce energy consumption and shorten the glass production cycle.. |
| 113. | M. Tanaka, Y. Tsuruoka, Y. Liu, T. Watanabe, Investigation of in-flight melting behaviour of granulated glass raw material by multi-phase ac arc plasma and hybrid plasma, 3rd International Congress on Ceramics, ICC3 IOP Conference Series: Materials Science and Engineering, 10.1088/1757-899X/18/11/112010, 18, SYMPOSIUM 8, 2011.08, [URL], An innovative in-flight glass melting technology was developed for a purpose of energy saving and environmental protection. Granulated glass raw materials with small diameter were treated by twelve-phase AC arc and that combined with an oxygen burner. The particle measurement was carried out to investigate the in-flight melting behavior of glass raw materials during the in-flight melting by twelve-phase AC arc. Obtained results show the mean particle velocity was about 9 m s-1 and mean temperature was about 2600 K. The high vitrification degree achieved within several milliseconds reveals that the new in-flight melting technology of hybrid plasma treating can reduce energy consumption and shorten the glass production cycle.. |
| 114. | Narengerile, Hiroshi Nishioka, Takayuki Watanabe, Mechanisms of decomposition of organic compounds by water plasmas at atmospheric pressure, Japanese journal of applied physics, 10.1143/JJAP.50.08JF13, 50, 8 PART 2, 2011.08, [URL], The decomposition of acetone, methanol, and ethanol by water plasmas at atmospheric pressure has been investigated using a direct current (DC) discharge. At torch powers of 910-1050W and organic compound concentrations of 1-10 mol%, the decomposition rate of methanol was over 99.99%, while those of acetone and/or ethanol was 96-99%. The concentrations of H2 obtained were 65-71% in the effluent gas and the removal efficiencies of 90-95% for total organic carbon (TOC) were achieved in liquid effluent for any compounds by pyrolysis. Over 50 wt% carbon in acetone or ethanol fed as the plasma supporting gas was transformed into soot, while the soot formation was negligible during methanol decomposition. On the basis of the experimental results, the mechanisms of decomposition of organic compounds in water plasmas were proposed and the mechanism of soot formation was clarified for the first time.. |
| 115. | C. N. Zhang, M. Ikeda, T. Uchikoshi, J. G. Li, Takayuki Watanabe, T. Ishigaki, Photocatalytic performance of iron (III) and niobium (V)-codoped TiO 2 nanopowders synthesized by a radio frequency thermal plasma process, Thin Solid Films, 10.1016/j.tsf.2010.11.050, 519, 20, 6940-6943, 2011.08, [URL], Iron (III) and niobium (V)-codoped TiO2 nanopowders have been synthesized by Ar/O2 RF thermal plasma. Phase composition, morphology, and photocatalytic performance of the plasma-generated powders have been investigated by the combined means of XRD, FE-SEM/TEM, and UV-vis absorption spectroscopy. Rutile formation in the plasma-produced phase composition of anatase and rutile was promoted by Fe3+ addition but was inhibited by Nb5+ doping. The resultant powders consisted of a majority of fine crystallites (several nanometers) and a small portion of coarse particles (~ 100 nm). In comparison with TiO2 singly doped with 0.1 at.% of Fe3+, photocatalytic reactivity of codoped TiO2 was improved at 2.0 at.% of Nb5+ but was depressed at 6.0 at.% under the UV irradiation, indicating that UV-induced photocatalytic capability was dominated by Nb5+ doping concentration. In contrast to the case of 1.0 at.% of Fe3+ single addition, the codoped sample obtained the decreased photocatalytic performance with increasing Nb5+ content under the visible light irradiation, due to the low visible light absorption resulting from a broadened band gap.. |
| 116. | Yingying Cheng, Takayuki Watanabe, Synthesis of titanium boride nanoparticles by induction thermal plasmas, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.10we328, 44, 8, 583-589, 2011.08, [URL], An experimental study has been conducted for TiB and TiB 2 nanoparticle fabrication by radio frequency induction plasmas. TiB and TiB 2 nanoparticles were selected as the model for the investigation. In the thermal plasma, the mixed powders of titanium with boron were evaporated immediately and nanoparticles were produced through the cooling process. The parameters of powder feed rate and boron content in the feed powders played an important role in the formation of boride nanoparticles. The nanoparticles were characterized based on phase composition in the product and crystalline diameter. The nanoparticles of TiB and TiB 2 nanoparticles had an average crystalline diameter from 10 to 45 nm. The diameter of TiB was smaller than that of TiB 2. The mass fraction of TiB had the range from 0 to 99.58%. These results suggest that boride nanoparticles can be produced by induction thermal plasma and also that the crystalline diameter and composition were controllable.. |
| 117. | H. Y. Chae, Chin Wook Chung, J. W. Chung, M. P. Hong, J. H. Joo, H. J. Kim, D. H. Kim, E. Kusano, L. Overzet, Yi Kang Pu, Y. Setsuhara, J. J. Shi, K. Terashima, Takayuki Watanabe, The 10th Asia-Pacific conference on Plasma Science and Technology (APCPST 2010) The 153rd symposium on Plasma Science for Materials (SPSM 2010), Thin Solid Films, 10.1016/j.tsf.2011.06.001, 519, 20, 6637-6638, 2011.08, [URL]. |
| 118. | Narengerile, Min Hao Yuan, Takayuki Watanabe, Decomposition mechanism of phenol in water plasmas by DC discharge at atmospheric pressure, Chemical Engineering Journal, 10.1016/j.cej.2011.01.072, 168, 3, 985-993, 2011.04, [URL], The decomposition mechanism of high concentration of phenol solution in water plasmas at atmospheric pressure was investigated at different arc currents. The results showed that the removal efficiencies of phenol, total organic carbon, and chemical oxygen demand were increased with the increase in arc current. The concentration of phenol was reduced from 52.8gL-1 down to 1.0×10-5gL-1 at an arc current of 8A with the energy yield of 8.12gkWh-1. Major gaseous compounds were H2, CO2, CO, and CH4. However, at a low arc current, trace levels of benzene (C6H6), and cyclopentadiene (C5H6) were detected in effluent gas, and formic acid (HCOOH) and formaldehyde (HCHO) were observed in liquid effluent. By the analysis of reaction intermediates and a calculation of carbon balance, the main reaction pathways were proposed as follows: firstly, electron dissociation in arc region to generate phenoxy (C6H5O) radical; second, chemical oxidation or reduction in plasma flame region to form C6H5O and C6H6. After phenol decomposition, the generated intermediate species would undergo complex reactions to form stable compounds in plasma flame region. The most favorable mechanism is the formation of CO, which is conducted by the ring open step of C6H5O and C6H6 by thermal decomposition or the attachment of active radicals such as O, H, and OH with respect to CO generation. In downstream region, the generated intermediate species were easily recombined with H or oxidized by OH to form unwanted products, such as HCOOH, HCHO, and H2O2.. |
| 119. | Chenning Zhang, Masashi Ikeda, Tetsuo Uchikoshi, Ji Guang Li, Takayuki Watanabe, Takamasa Ishigaki, High-concentration niobium (V) doping into TiO2 nanoparticles synthesized by thermal plasma processing, Journal of Materials Research, 10.1557/jmr.2011.16, 26, 5, 658-671, 2011.03, [URL], High-concentration niobium (V)-doped titanium dioxide (TiO2) nanoparticles of the nonequilibrium chemical composition have been synthesized via Ar/O2 radio-frequency thermal plasma oxidation of mist precursor solutions with various Nb5+ concentrations (Nb/(Ti + Nb) = 0-25.0 at.%). The solubility as high as ∼25.0 at.% has not been achieved before by wet-chemical techniques. The preferable anatase formation was attained in the plasma-synthesized powders and was enhanced by the niobium doping. All the powders were heated at high temperatures (600-800 °C) to investigate their phase transformation, band gap variation, inter-particulate binding behavior, and photocatalytic stability. The transformation from anatase to rutile was effectively inhibited by increasing the Nb5+ content. The Nb 5+ doping prevented the band gap of TiO2 from narrowing after the heating. At high temperatures, Nb5+ doping could not only preserve particle size but also prevent inter-particulate binding. High concentration (25.0 at.%) Nb5+ doping retained the photocatalytic performance almost invariably irrespective of being thermally treated.. |
| 120. | Takayuki Watanabe, Masaya Shigeta, Nanoparticle synthesis by thermal plasmas, Nanomaterials Properties, Preparation and Processes, 115-176, 2011.01, Thermal plasmas, source of very high enthalpy, high chemical reactivity offer rapid evaporation rate, steep temperature gradients, wide area and high deposition/growth rate, and an attractive and chemically nonspecific route for the synthesis of fine powders down to the nanometer size range. Among various types of thermal plasma reactors, radio frequency induction thermal plasma (ITP) reactors offer several advantages such as high purity due to absence of electrode, large volume of plasma for processing, low plasma velocity, simple power supply unit and wide pressure range. ITP reactors, which basically convert the electrical energy into heat energy, have been widely used as a clean heat source for synthesis of nanoparticles. The high-temperature of ITP leads to short evaporation time which translates into relatively small torch with high throughput. Powder synthesis needs sharp temperature gradient for rapid condensation in the reaction chamber. ITP offers the distinct advantage of providing essentially one-step processes, avoiding the multitude of steps required in the creation of particles with conventional methods. The feasibility of producing nanoparticles of various intermetallic compounds, alloys, oxides, and nitrides by vapor-phase synthesis in reactive thermal plasma systems will be demonstrated in this chapter. To investigate the complicated phenomena in the synthesis processes of nanoparticles by ITP, theoretical and numerical studies are powerful approaches. The precursory powders of the raw material are injected into the plasma and vaporized due to the heat transfer from the plasma. The vapor is transported downstream with the plasma flow. Since the saturation pressure drastically decreases with the rapid temperature drop at the tail of the plasma, the vapor falls into a supersaturated state. As a result, nuclei are generated by homogeneous nucleation, and the supersaturated vapor easily condenses on the nuclei by heterogeneous condensation. This process is the fundamental formation mechanism of nanoparticles by ITP. Simultaneously nanoparticles collide and coagulate among themselves. Coagulation also plays an important role for the nanoparticle growth. The mathematical models are introduced to simulate the phenomena. The fields in the plasma are expressed on the basis of the electromagnetic fluid dynamics. The trajectory and temperature history of the precursory powders are examined by Lagrangian approach taking into account the rarefied gas effects. The nanoparticle formation can be modeled by the aerosol dynamics, basically with Eulerian approach, taking into account not only nucleation, condensation, and coagulation but also convection, diffusion, and thermophoresis. Through the computation with these models, the particle size distributions or compositions of the produced nanoparticles are obtained and the formation mechanisms are clarified.. |
| 121. | Narengerile, Hironori Saito, Takayuki Watanabe, Decomposition mechanism of fluorinated compounds in water plasmas generated under atmospheric pressure, Plasma Chemistry and Plasma Processing, 10.1007/s11090-010-9259-y, 30, 6, 813-829, 2010.12, [URL], Decomposition mechanism of HFC-134a, HFC-32, and CF 4 in water plasmas at atmospheric pressure has been investigated. The decomposition efficiency of 99.9% can be obtained up to 3.17 mol kWh -1 of the ratio of hydrofluorocarbon (HFC) feed rate to the arc power and 1.89 mol kWh -1 of the ratio of perfluorocarbon (PFC) feed rate to the arc power. The species such as H 2, CO, CO 2, CH 4, and CF 4 were detected from the effluent gas of both PFC and HFC decomposition. However, CH 2F 2 and CHF 3 were observed only in the case of HFC decomposition. The HFC and PFC decomposition generate CH 2F, CHF x (x:1-2), and CF y (y:1-3) radicals, then those radicals were subsequently oxidized by oxygen, leading to CO and CO 2 generation in the excess oxygen condition. However, when there is insufficient oxygen available, those radicals were easily recombined with fluorine to form by-product such as CH 2F 2, CHF 3, and CF 4.. |
| 122. | Takayuki Watanabe, Water Plasmas for Environmental Application, Industrial Plasma Technology Applications from Environmental to Energy Technologies, 10.1002/9783527629749.ch6, 65-77, 2010.10, [URL]. |
| 123. | Masaya Shigeta, Takayuki Watanabe, Growth model of binary alloy nanopowders for thermal plasma synthesis, Journal of Applied Physics, 10.1063/1.3464228, 108, 4, 2010.08, [URL], A new model is developed for numerical analysis of the entire growth process of binary alloy nanopowders in thermal plasma synthesis. The model can express any nanopowder profile in the particle size-composition distribution (PSCD). Moreover, its numerical solution algorithm is arithmetic and straightforward so that the model is easy to use. By virtue of these features, the model effectively simulates the collective and simultaneous combined process of binary homogeneous nucleation, binary heterogeneous cocondensation, and coagulation among nanoparticles. The effect of the freezing point depression due to nanoscale particle diameters is also considered in the model. In this study, the metal-silicon systems are particularly chosen as representative binary systems involving cocondensation processes. In consequence, the numerical calculation with the present model reveals the growth mechanisms of the Mo-Si and Ti-Si nanopowders by exhibiting their PSCD evolutions. The difference of the materials' saturation pressures strongly affects the growth behaviors and mature states of the binary alloy nanopowder.. |
| 124. | Shojiro Komatsu, Kazuaki Kobayashi, Yuhei Sato, Daisuke Hirano, Takuya Nakamura, Takahiro Nagata, Toyohiro Chikyo, Takayuki Watanabe, Takeo Takizawa, Katsumitsu Nakamura, Takuya Hashimoto, Photoinduced phase transformations in boron nitride New polytypic forms of SP3-bonded (6H- and 30H-) BN, Journal of Physical Chemistry C, 10.1021/jp1028728, 114, 31, 13176-13186, 2010.08, [URL], New sp3-bonded polytypic forms of boron nitride (BN), namely, 6H-BN and 30H-BN, were prepared by plasma-assisted chemical vapor deposition (CVD) with an excimer laser at 193 nm being irradiated on the growing film surface. Only the 6H-BN was formed by postdeposition laser irradiation (PDL) of sp2-bonded BN precursor films prepared by plain plasma-assisted CVD. The PDL demonstrated direct photoinduced phase transformation from sp 2-bonded BN into denser sp3-bonded BN here. Typical lattice constants a and c for 6H-BN determined by X-ray diffraction were 2.501 Å and 12.45 Å, respectively, while those for 30H-BN were 2.538 Å and 62.61 Å, respectively. The polytypic structures were analyzed in terms of "hexagonality" H and "close-packing" index D, and the "metastability" E estimated by the first principles calculations. Linear relationships were found among the H, D, and E for the polytypes of BN, AlN, and SiC, whose behavior proved to depend on the degree of ionicity in their iono-covalent bonds. The growth mechanism was discussed with regard to the "bond-strength initiative rule", according to which the local thermodynamics at very early stage of growth should favor the formation of the strongest bond available (e.g., sp2-hybridized bonds in BN). Our conclusion that the ultraviolet laser irradiation induced the structural relaxation of the sp2-bonded "metastable" phase into more stable sp3-bonded phases at relatively lower temperatures (850 °C in our case) and below atmospheric pressure appears to be consistent with the recent pressure-temperature phase diagram of BN.. |
| 125. | Min Hao Yuan, Narengerile, Takayuki Watanabe, Ching Yuan Chang, DC water plasma at atmospheric pressure for the treatment of aqueous phenol, Environmental Science and Technology, 10.1021/es9038598, 44, 12, 4710-4715, 2010.06, [URL], This study investigated the decomposition of aqueous phenol by direct current (DC) water plasma. The operation of DC water plasma was carried out in the absence of inert gases or air injected and cooling-controlled and pressure-controlled devices. The results indicated that 1 mol.% (52.8 g L -1) phenol was drastically decomposed by DC water plasma touch with energy efficiencies of 1.9 - 108-2.2 - 108 mol J -1. Also, the value of chemical oxygen demand (COD) was reduced from 100-000 mg L-1 down to 320 mg L-1 over a short retention time. The maximum decomposition rate of the COD was 258 mg COD min-1 for the arc power of 0.91 kW. In the effluent analysis, H2 (63-68%), CO (3.6-6.3%), CO2 (25.3-28.1%) were major products in the exhaust gas and CH4, C2H2, HCOOH and C 6H6 in trace level. Further, HCOOH and HCHO were observed in the liquid effluents. Within the current paper, the results indicated that the DC water plasma torch is capable of an alternative green technology for phenol wastewater containing high COD.. |
| 126. | Takayuki Watanabe, Kazuyuki Yatsuda, Yaochun Yao, Tetsuji Yano, Tsugio Matuura, Innovative in-flight glass-melting technology using thermal plasmas, Pure and Applied Chemistry, 10.1351/PAC-CON-09-09-19, 82, 6, 1337-1351, 2010.06, [URL], A stable 12-phase AC arc was generated by transformers at a commercial electric power system, and the arc behavior was characterized by image analysis. For the unique advantages, the multiphase AC arc was developed to apply to in-flight glass melting for the purpose of energy-saving and emission reduction. The effects of electrode configuration and sheath gas flow rate on the arc and melting behavior of granulated glass raw material were investigated. Results show that the discharge behavior and the high-temperature region can be controlled by the electrode configuration. The luminance area of the high-temperature region and its fluctuation reflect the discharge behavior. The vitrification degree of glass raw material is mostly dependent on the center temperature of arc. As sheath gas flow rate increases, the ratio of luminance area decreases and the center temperature of arc increases.. |
| 127. | C. N. Zhang, J. G. Li, Y. H. Leng, T. Uchikoshi, Takayuki Watanabe, T. Ishigaki, (Eu3+-Nb5+)-codoped TiO2 nanopowders synthesized via Ar/O2 radio frequency thermal plasma oxidation processing Phase composition and photoluminescence properties through energy transfer, Thin Solid Films, 10.1016/j.tsf.2009.11.036, 518, 13, 3531-3534, 2010.04, [URL], (Eu3+-Nb5+)-codoped TiO2 nanopowders have been prepared by Ar/O2 radio frequency (RF) thermal plasma oxidizing liquid precursor mists, with various addition contents of dopants (molar ratio of Eu3+:Nb5+ = 1:1). Characterizations have been performed by the combined studies of XRD, TEM, Raman spectra, UV-vis spectroscopy, and excitation and PL spectra. The plasma-generated nanopowders mainly consist of anatase and rutile polymorphs. Doping Nb5+ cannot have appreciable influence on Eu3+ solubility (0.5 at.%) in the TiO2 host lattice, but can significantly inhibit the increase of rutile weight fraction for TiO2. 617 nm PL intensity at 350 nm indirect excitation through energy transfer is considerably weaker than that at 467 nm direct excitation, indicating that a defect state level in the TiO2 host lattice might be lowered below the excited state of Eu3+ by doping Nb5+, which is conceivable from a relatively large amount of oxygen deficiencies yielded in the TiO2 host lattice.. |
| 128. | K. Terashima, T. Watanabe, T. Ichiki, Y. Inoue, Preface, Thin Solid Films, 10.1016/j.tsf.2009.11.027, 518, 13, 2010.04, [URL]. |
| 129. | Takayuki Watanabe, Masaya Shigeta, Nanoparticle synthesis by thermal plasmas, Nanoparticles Properties, Classification, Characterization, and Fabrication, 149-212, 2010.02, Thermal plasmas, source of very high enthalpy, high chemical reactivity offer rapid evaporation rate, steep temperature gradients, wide area and high deposition/growth rate, and an attractive and chemically nonspecific route for the synthesis of fine powders down to the nanometer size range. Among various types of thermal plasma reactors, radio frequency induction thermal plasma (ITP) reactors offer several advantages such as high purity due to absence of electrode, large volume of plasma for processing, low plasma velocity, simple power supply unit and wide pressure range. ITP reactors, which basically convert the electrical energy into heat energy, have been widely used as a clean heat source for synthesis of nanoparticles. The high-temperature of ITP leads to short evaporation time which translates into relatively small torch with high throughput. Powder synthesis needs sharp temperature gradient for rapid condensation in the reaction chamber. ITP offers the distinct advantage of providing essentially one-step processes, avoiding the multitude of steps required in the creation of particles with conventional methods. The feasibility of producing nanoparticles of various intermetallic compounds, alloys, oxides, and nitrides by vapor-phase synthesis in reactive thermal plasma systems will be demonstrated in this chapter. To investigate the complicated phenomena in the synthesis processes of nanoparticles by ITP, theoretical and numerical studies are powerful approaches. The precursory powders of the raw materials are injected into the plasma and vaporized due to the heat transfer from the plasma. The vapor is transported downstream with the plasma flow. Since the saturation pressure drastically decreases with the rapid temperature drop at the tail of the plasma, the vapor becomes supersaturated. As a result, nuclei are generated by homogeneous nucleation, and the supersaturated vapor easily condenses on the nuclei by heterogeneous condensation. This process is the fundamental formation mechanism of nanoparticles by ITP. Simultaneously nanoparticles collide and coagulate among themselves. Coagulation also plays an important role for the nanoparticle growth. The mathematical models are introduced to simulate the processes. The fields in the plasma are expressed on the basis of the electromagnetic fluid dynamics. The trajectory and temperature history of the precursory powders are examined by Lagrangian approach taking into account the rarefied gas effects. The nanoparticle formation can be modeled by the aerosol dynamics, basically with Eulerian approach, taking into account not only nucleation, condensation, and coagulation but also convection, diffusion, and thermophoresis. Through the computation with these models, the particle size distributions or compositions of the produced nanoparticles are obtained and the formation mechanisms are clarified.. |
| 130. | Hiroshi Nishioka, Hironori Saito, Takayuki Watanabe, Decomposition mechanism of organic compounds by DC water plasmas at atmospheric pressure, Thin Solid Films, 10.1016/j.tsf.2009.07.160, 518, 3, 924-928, 2009.12, [URL], The purpose of this paper is to investigate the decomposition mechanism of organic compounds by water plasmas. The plasma torch can generate 100%-steam by DC discharge without a commercially available steam generator. Methanol or ethanol used as a model substance of water-soluble organic compounds was mixed with water for plasma supporting gas. The main gases after the decomposition were H2, CO, and CO2. The 50 wt.% of carbon was transformed into solid carbon in 5 mol%-ethanol decomposition, while the solid-carbon formation from 5 mol%-methanol was negligible. Larger amount of solid-carbon formation from ethanol decomposition indicates the different mechanism between methanol and ethanol decomposition.. |
| 131. | Narengerile, Hironori Saito, Takayuki Watanabe, Decomposition of tetrafluoromethane by water plasma generated under atmospheric pressure, Thin Solid Films, 10.1016/j.tsf.2009.07.164, 518, 3, 929-935, 2009.12, [URL], Tetrafluoromethane (CF4) decomposition by water plasma generated under atmospheric pressure was investigated by means of thermodynamic analyses and experiments. Thermodynamic equilibrium calculations were performed between 300 and 6000 K at atmospheric pressure. Experimental results indicated that CF4 was completely decomposed by water plasma, and recovery of fluorine can be achieved more than 99%. Influence of factors such as arc current and additive flow rate of O2 on CF4 decomposition was determined. Furthermore, the decomposition mechanism of CF4 was investigated from chemical kinetics consideration. CFx (x: 1-4) was thermally decomposed above 4000 K, oxidized in the temperature range of 4000-2400 K, and removed by H radical at temperatures below 2400 K.. |
| 132. | Takayuki Watanabe, Tatsuru Shirafuji, Yikang Pu, Editorial, Thin Solid Films, 10.1016/j.tsf.2009.07.155, 518, 3, 2009.12, [URL]. |
| 133. | Yaochun Yao, K. Yatsuda, T. Watanabe, T. Yano, Effect of injection position on in-flight melting behavior of granular alkali-free glass raw material in 12-phase AC Arc plasma, Plasma Science and Technology, 10.1088/1009-0630/11/6/12, 11, 6, 699-703, 2009.12, [URL], An innovative in-flight glass melting technology with a multi-phase AC arc plasma was developed to save energy and reduce emissions for the glass industry. The effect of the injection position on the in-flight melting behavior of granulated powders was investigated. Results show that the injection position has a strong effect on the melting behavior of alkali-free glass raw material. With the increase in injection distance, the vitrification, decomposition, and particle shrinkage of initial powders are improved. Longer injection distance causes much energy to transfer to particles due to a longer residence time of powder in the high temperature zone. The high vitrification and decomposition degrees indicate that the new in-flight melting technology with 12-phase AC arc can substantially reduce the melting and refining time for glass production.. |
| 134. | Masaya Shigeta, Takayuki Watanabe, Two-directional nodal model for co-condensation growth of multicomponent nanoparticles in thermal plasma processing, Journal of Thermal Spray Technology, 10.1007/s11666-009-9316-3, 18, 5-6, 1022-1037, 2009.12, [URL], A more precise but easy-to-use model is developed and proposed to clarify nanoparticle growth with two-component co-condensation in thermal plasma processing. Computations performed for the molybdenum-silicon and titanium-silicon systems demonstrate that the model quantitatively estimates both the particle size distribution and the composition distribution of the silicide nanoparticles produced through co-condensation as well as nucleation and coagulation. The model also successfully obtains information that cannot be acquired by any other models. As a consequence, the detailed growth mechanisms of the silicide nanoparticles are eventually revealed. The present model is thus an "adaptable" and useful tool for analyzing nanoparticle growth processes, including co-condensation, with sufficient accuracy.. |
| 135. | Shojiro Komatsu, Yuhei Sato, Daisuke Hirano, Takuya Nakamura, Kazunori Koga, Atsushi Yamamoto, Takahiro Nagata, Toyohiro Chikyo, Takayuki Watanabe, Takeo Takizawa, Katsumitsu Nakamura, Takuya Hashimoto, Masaharu Shiratani, P-type sp3-bonded BN/n-type Si heterodiode solar cell fabricated by laser-plasma synchronous CVD method, Journal of Physics D: Applied Physics, 10.1088/0022-3727/42/22/225107, 42, 22, 2009.11, [URL], A heterojunction of p-type sp3-bonded boron nitride (BN) and n-type Si fabricated by laser-plasma synchronous chemical vapour deposition (CVD) showed excellent rectifying properties and proved to work as a solar cell with photovoltaic conversion efficiency of 1.76%. The BN film was deposited on an n-type Si (1 0 0) substrate by plasma CVD from B2H6 + NH3 + Ar while doping of Si into the BN film was induced by the simultaneous irradiation of an intense excimer laser with a pulse power of 490 mJ cm-2, at a wavelength of 193 nm and at a repetition rate of 20 Hz. The source of dopant Si was supposed to be the Si substrate ablated at the initial stage of the film growth. The laser enhanced the doping (and/or diffusion) of Si into BN as well as the growth of sp3-bonded BN simultaneously in this method. P-type conduction of BN films was determined by the hot (thermoelectric) probe method. The BN/Si heterodiode with an essentially transparent p-type BN as a front layer is supposed to efficiently absorb light reaching the active region so as to potentially result in high efficiency.. |
| 136. | Yaochun Yao, Kazuyuki Yatsuda, Takayuki Watanabe, Tsugio Matsuura, Tetsuji Yano, Characteristics of multi-phase alternating current arc for glass in-flight melting, Plasma Chemistry and Plasma Processing, 10.1007/s11090-009-9182-2, 29, 5, 333-346, 2009.10, [URL], An innovative in-flight melting technology with multi-phase AC arc was developed for glass industry. The enthalpy probe and high speed video camera were used to characterize the temperature, velocity, and discharge behavior of multi-phase AC arc. The effects of input power and sheath gas flow rate on arc and melting behavior were investigated. Results show that the temperature and velocity on arc center are increased with input power or sheath gas flow increase. The fluctuation of luminance area ratio and coefficient of variation reflects the change of arc discharge behavior. High temperature of plasma enhances the melting of granulated raw particles during in-flight heating treatment. The shrinkage of particle and the volatilization degree of Na 2 O increase under a larger flow rate of sheath gas. The characterized arc behavior agrees with the melting behavior of glass raw materials, which can provide valuable guidelines for the process control of glass melting.. |
| 137. | M. Mofazzal Hossain, Yaochun Yao, Takayuki Watanabe, Fuji Funabiki, Tetsuji Yano, In-flight thermal treatment of soda-lime-silica glass powders for glass production by argon-oxygen induction thermal plasmas, Chemical Engineering Journal, 10.1016/j.cej.2009.03.013, 150, 2-3, 561-568, 2009.08, [URL], In order to investigate the plasma-particle energy exchange dynamics and optimize the plasma discharge and particle parameters during in-flight thermal treatment of soda-lime-silica glass powders, a plasma-particle interaction model was developed. This model solved the conservation equations to predict the plasma temperature and flow fields, and then calculated the injected individual particle trajectories and temperature histories, and the particle source terms to take into account the plasma-particle interaction. It was noticed that particle injection significantly reduced the plasma temperature around the centerline of the torch and hence decreased the heat transfer to particles at higher carrier gas flow-rate and powder feed-rate. As a result the size and composition of quenched particles were affected significantly by the above factors. The simulated results were consistent with those of experiment, which provided valuable guidelines in optimizing the plasma discharge and particle parameters for the efficient thermal treatment of soda-lime-silica glass particles.. |
| 138. | M. Mofazzal Hossain, Yaochun Yao, Takayuki Watanabe, A numerical study of plasma-particle heat transfer dynamics in induction thermal plasmas for glassification, IEEJ Transactions on Electrical and Electronic Engineering, 10.1002/tee.20436, 4, 4, 504-509, 2009.07, [URL], Dependence of energy exchange between plasma and soda-lime-silica glass particles on the particle size, powder feedrate and nozzle insertion length during in-flight thermal treatment for glassification by induction thermal plasmas has been studied. For the numerical investigation into the plasma-particle energy exchange dynamics during melting and vaporization of particles, a thermofluid plasma-particle interaction model has been developed taking into account the strong plasma-particle interactions and particle loading effects. It is found that heat transfer to the particles depends strongly on the particles' size, powder feed-rate, nozzle insertion length, and plasma discharge parameters. Thus, for the efficient thermal treatment of particles, the above parameters should be optimized.. |
| 139. | Yao Yaochun, M. Hossain, Takayuki Watanabe, Numerical and experimental investigation on the in-flight melting behaviour of granulated powders in induction thermal plasmas, Plasma Science and Technology, 10.1088/1009-0630/11/1/15, 11, 1, 71-77, 2009.05, [URL], An innovative in-flight glass melting technology with thermal plasmas was developed for the purpose of energy conservation and environment protection. In this study, modelling and experiments of argon-oxygen induction thermal plasmas were conducted to investigate the melting behaviour of granulated soda-lime glass powders injected into the plasma. A two-dimensional local thermodynamic equilibrium (LTE) model was performed to simulate the heat and momentum transfer between plasma and particle. Results showed that the particle temperature was strongly affected by the flow rate of carrier gas and the particle size of raw material. A higher flow rate of carrier gas led to lower particle temperature and less energy transferred to particles which resulted in lower vitrification. The incomplete melting of large particles was attributed to the lower central temperature of the particle caused by a larger heat capacity. The numerical analysis explained well the experimental results, which can provide valuable practical guidelines for the process control in the melting process for the glass industry.. |
| 140. | Masaya Shigeta, Takayuki Watanabe, Model integration for metal nanoparticle synthesis by an rf thermal plasma flow with counterflow cooling, Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B, 10.1299/kikaib.75.758_2019, 75, 758, 2019-2028, 2009.01, [URL], Comprehensive modeling is attempted to simulate metal nanoparticle synthesis by an RF thermal plasma flow. On the basis of electromagnetic hydrodynamics, plasma heat transfer, and aerosol dynamics, the significant processes are modeled and integrated. The numerical results show good agreements with the experimental ones, which supports the validity of the present model. The model is applied to the efficient nanoparticle production system with counterflow cooling. The result shows that the RF thermal plasma flow has a high temperature zone over 9 000 K and a recirculating zone due to the Lorentz force. Nanoparticles are first formed at the interface between the plasma flow and the counterflow. Subsequently, the nanoparticles increase their sizes by coagulation among them with the decrease of their number and by heterogeneous condensation with vapor consumption. Because of the saturation pressure difference, a larger number of the platinum nanoparticles are produced and they provide a smaller volume mean diameter than the titanium nanoparticles.. |
| 141. | Fuji Funabiki, Tetsuji Yano, Yaochun Yao, Takayuki Watanabe, In-flight-melted soda-lime-silica glass by RF induction thermal plasma, Journal of the American Ceramic Society, 10.1111/j.1551-2916.2008.02768.x, 91, 12, 3908-3914, 2008.12, [URL], Granulated raw materials with a particle size of 20-80 μm were prepared from a slurry of Na2CO3, CaCO3, and SiO 2 (quartz) by the spray-dry method, and injected with carrier gas into a radio-frequency induction thermal plasma. Spherical particles 5-60 μm in size were obtained and analyzed. Thermo-gravimetric analysis and X-ray diffraction analysis showed that during the short flight of the order of milliseconds, all carbonates were decomposed and >95% quartz was reacted into a noncrystalline state. Glass transition was clearly observed by differential thermal analysis. Increase of the carrier gas from 3 to 6 L/min led to a decrease in the volatilization ratio of Na2O from 46% to 18% with a slight decrease of the reaction ratio of quartz in trade balance. Electron probe microanalysis showed that the volatilization could be attributed to an excess heating of small particles |
| 142. | M. Mofazzal Hossain, Y. Yao, M. Rafiqul Alam, M. Maksud Alam, T. Watanabe, Modeling and numerical analysis of thermal treatment of granulated porous particles by induction plasma, 5th International Conference on Electrical and Computer Engineering, 10.1109/ICECE.2008.4769325, 827-832, 2008.12, [URL], In this paper it is aimed to describe the modeling and numerical analysis of thermal treatment of granulated porous particles by induction plasma. To investigate the heat exchange dynamics between plasma and particles during the flight of granulated porous particles through the hot plasma, a plasma-particle interactive flow model has been developed. This model solves the conservation equations to predict the temperature and flow fields of plasma, under local thermal equilibrium (LTE) conditions, and then computes the injected particles trajectories, temperature and size histories, and the particle source terms to incorporate the particle loading effects. It is found that the size and dose of injected particles greatly affect the particle trajectory and temperature, and hence the heat transfer to particles at higher powder feed-rate.. |
| 143. | Katsuya Sueyoshi, Takayuki Watanabe, Yoshio Nakano, Hiroshi Kanamori, Shigeru Aoki, Akira Miyahara, Kai Matsui, Reaction mechanism of various types of lunar soil simulants by hydrogen reduction, Proceedings of the 11th Aerospace Division International Conference on Engineering, Science, Construction, and Operations in Challenging Environments Earth and Space Conference, 2008.12, Several processes to produce water and oxygen from lunar regolith have been proposed. Among these processes, hydrogen reduction process of lunar regolith has several advantages. Therefore, we have investigated the water-production mechanism by H2 reduction for three types of lunar soil simulants. The maximum of water-production was obtained for all lunar soil simulants at 1323 K. Mössbauer spectra of FJS-1 revealed that the produced water was generated from ilmenite, Fe3+ phase(s), and magnetic materials such as hematite or magnetite. The cross-section observation of scanning electron microscope and BET method presented that the surface area was decreased at higher temperature owing to melting of some components in the cracks, and the surface area was increased as the progress of hydrogen reduction. The kinetic consideration using thermogravimetry indicated that hydrogen reduction for lunar soil was controlled by chemical reaction.. |
| 144. | Yaochun Yao, Kazuyuki Yatsuda, Takayuki Watanabe, Fuji Funabiki, Tetsuji Yano, Investigation on in-flight melting behavior of granulated alkali-free glass raw material under different conditions with 12-phase AC arc, Chemical Engineering Journal, 10.1016/j.cej.2008.06.039, 144, 2, 317-323, 2008.10, [URL], An innovative in-flight melting technology with 12-phase alternating current (AC) arc has been developed to investigate the melting behavior of granulated alkali-free glass raw material. Results show that the melted particles have spherical shape with smooth surface and compact structure. Lower vitrification and decomposition degrees of raw material as well as lower volatilization of B2O3 are attributed to less heat transferred per particle under larger flow rate of carrier gas and higher feed rate. The high vitrification and decomposition degrees indicate that the new in-flight glass melting with 12-phase AC arc will be a promising technology for glass production.. |
| 145. | M. Mofazzal Hossain, Yaochun Yao, Takayuki Watanabe, A numerical analysis of plasma-particle heat exchange during in-flight treatment of granulated powders by argon-oxygen induction thermal plasmas, Thin Solid Films, 10.1016/j.tsf.2007.11.038, 516, 19, 6634-6639, 2008.08, [URL], A plasma-particle interaction flow model has been developed to investigate the effects of plasma and particle parameters on the energy transfer to particles, and thermal treatment of soda-lime-silica glass powders. In this paper attention will be given to the effects of individual particle diameter, size distribution, and average diameter, which govern the plasma-particle energy transfer to a large extent. To investigate the size distributions, computations have been carried out for two size distributions: flat and Maxwellian. Computations have also been performed for Maxwellian size distribution with three different average diameter (51, 58 and 84 μm) powders. It is found that the energy transfer to particles is higher with flat diameter distribution than that of with Maxwellian distribution; however individual particle temperature becomes lower with flat distribution. On the other hand, smaller average diameter of powders leads much heat transfer to powders, but individual particle temperature becomes lower. Both the effects come from the intense cooling of plasma due to the large heat transfer to large number of particles with flat distribution as well as small average diameter powders.. |
| 146. | Yaochun Yao, M. Mofazzal Hossain, Takayuki Watanabe, Tomoyuki Tsujimura, Fuji Funabiki, Tetsuji Yano, Effects of feed rate and particle size on the in-flight melting behavior of granulated powders in induction thermal plasmas, Thin Solid Films, 10.1016/j.tsf.2007.11.084, 516, 19, 6622-6627, 2008.08, [URL], The innovative in-flight glass melting technology with induction thermal plasmas has been performed to investigate the influence of feed rate and particle size on the melting behavior of granulated powders for glass production. Results show that the properties of quenched glass powders are strongly dependent on the feed rate and particle size, especially for the alkali-free glass powders. Higher feed rate and larger particle size lead to lower vitrification degree and decomposition rate of raw material. The average diameter of quenched powders increases with an increase in feed rate and particle size of raw material. The high vitrification degree and decomposition rate obtained in short time shorten the melting and fining time of glass considerably.. |
| 147. | Manabu Tanaka, Takayuki Watanabe, Vaporization mechanism from Sn-Ag mixture by Ar-H2 Arc for nanoparticle preparation, Thin Solid Films, 10.1016/j.tsf.2007.11.096, 516, 19, 6645-6649, 2008.08, [URL], The purpose of this paper was to describe the synthesis of Sn-Ag nanoparticles by an arc plasma method. Sn-Ag nanoparticles have been successfully prepared by DC arc plasma with hydrogen addition. The prepared nanoparticles were characterized by X-Ray diffraction, transmission electron microscopy and inductively coupled plasma-atomic emission spectrometry. The obtained results indicated that the nanoparticles have high-purity and spherical shape. The average diameter of the nanoaprticles with 100%-Ar arc was 19.8 nm and that with 50%-H2 arc was 56.5 nm. Another purpose of this work is to investigate the vaporization behavior from molten Sn-Ag mixture with Ar and Ar-H2 arc. We confirmed the vaporization enhancement of Sn from Sn-Ag mixture by hydrogen in arc plasma.. |
| 148. | Y. Yao, M. M. Hossain, T. Watanabe, T. Matsuura, F. Funabiki, T. Yano, A multi-phase AC arc discharge and its application in in-flight thermal treatment of raw glass powders, Chemical Engineering Journal, 10.1016/j.cej.2007.11.016, 139, 2, 390-397, 2008.06, [URL], The in-flight melting technology with multi-phase alternating current (AC) arc was developed for the purpose of saving energy and shortening production cycle for glass industry. The 6-phase arc and 12-phase arc were used to investigate the in-flight melting behavior of soda-lime and alkali-free glass powders. Results showed that the vitrification degree of raw materials and the shrinkage of particle diameter increased with the increase of input power. The higher melting temperature and viscosity were responsible for the lower vitrification degree of alkali-free glass powders. Compared with 6-phase arc, 12-phase arc improved the vitrification degree of raw material for the longer residence time and higher plasma temperature under the same transformer current. The high vitrification degree achieved in short time indicated that the new in-flight melting technology with multi-phase ac arc would be a promising method for energy conservation in glass industry.. |
| 149. | Yaochun Yao, M. M. Hossain, T. Watanabe, F. Funabiki, T. Yano, Application of in-flight melting technology by RF induction thermal plasmas to glass production, Plasma Science and Technology, 10.1088/1009-0630/10/3/15, 10, 3, 344-347, 2008.06, [URL], An innovative in-flight glass melting technology with induced thermal plasmas was developed for the purpose of energy conservation and environmental protection. Two-dimensional modeling was used to simulate the thermofluid fields in the plasma torch. The in-flight melting behavior of glass raw material was investigated by various analysis methods. Results showed that the plasma temperature was up to 10000 K with a maximum velocity over 30 m/s, which made it possible to melt the granulated glass raw material within milliseconds. The carbonates in the raw material decomposed completely and the compounds in the raw material attainted 100% vitrification during the in-flight time from the nozzle exit to substrate. The particle melting process is similar to the unreacted-core shrinking model.. |
| 150. | Manabu Tanaka, Takayuki Watanabe, Growth mechanism of Sn-Ag nanoparticles prepared by Ar-H2 arc, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.55.446, 55, 6, 446-451, 2008.06, [URL], The purpose of this paper was to investigate the growth mechanism of the Sn-Ag nanoparticles prepared by Ar -H2 arc. The effects of the H 2 concentration in the arc, initial composition of raw materials, and gas flow rate of circulation gas on particle diameter was investigated. Numerical analysis was conducted for the growth process with nucleation and co-condensation. Tin vapor was consumed by nucleation and condensation, followed by the condensation of silver vapor. Tin and silver were well synthesized in a liquid state in the co-condensation process since the particles grow at higher temperature than the melting point of Sn-Ag alloy.. |
| 151. | Takayuki Watanabe, Ryoichi Sataka, Kenji Yamamoto, Effect of bias application on c-BN synthesis by induction thermal plasmas under atmospheric pressure, Thin Solid Films, 10.1016/j.tsf.2007.10.018, 516, 13, 4462-4467, 2008.05, [URL], Synthesis of c-BN was enhanced with DC bias application on the substrate in atmospheric pressure induction plasmas in this study. Previous c-BN synthesis has been performed under reduced pressure using explosive and hazardous gases. For industrial application such as coating on cutting tools, improvement of c-BN synthesis method has been strongly required. Therefore, the purpose of this paper is to investigate the mechanism of enhanced c-BN synthesis with bias application using safe starting material, h-BN and boron powder, under atmospheric pressure. The bias application leads to the optimum B/N ratio as well as the reduction of oxygen impurity in the deposits, resulting in the successful c-BN synthesis under atmospheric pressure. Important process for c-BN formation is attributed to the formation of high density of activated species such as N+, and the quenching process on the substrate. We conclude that bias application is important to increase activated species.. |
| 152. | N. Kobayashi, Y. Kawakami, K. Kamada, J. G. Li, R. Ye, Takayuki Watanabe, T. Ishigaki, Spherical submicron-size copper powders coagulated from a vapor phase in RF induction thermal plasma, Thin Solid Films, 10.1016/j.tsf.2007.10.064, 516, 13, 4402-4406, 2008.05, [URL], Spherical submicron-sized powder of copper was synthesized through condensation from a vapor phase with a significantly high degree of supersaturation in thermal plasma. The degree of supersaturation was increased by the relatively high feed rate of raw copper powder. A high concentration of metal vapor was attained by using copper powder in Ar-H2 plasma, and relatively large particles of up to 0.1 μm in diameter were prepared. The powder feed rate, reactor pressure and gas flow rate of hydrogen were varied to examine their effects on the evaporation of the raw powder. Particle size and its distribution in the powder sample were evaluated by image analysis. The total amount of evaporated raw powder depended on the powder feed rate, the reactor pressure and hydrogen flow rate. The copper vapor concentration increased in proportion to the total amount of evaporation. Particle growth subsequently took place through heterogeneous condensation to form submicron-sized particles.. |
| 153. | Masaya Shigeta, Takayuki Watanabe, Two-dimensional analysis of nanoparticle formation in induction thermal plasmas with counterflow cooling, Thin Solid Films, 10.1016/j.tsf.2007.10.022, 516, 13, 4415-4422, 2008.05, [URL], Two-dimensional numerical analysis is conducted to investigate the spatially complicated formation of nanoparticles in an induction thermal plasma (ITP) with counterflow cooling. The effects of convection, diffusion, and thermophoresis as well as nucleation, condensation, and coagulation are taken into account. It is clarified that counterflow cooling leads to effective conversion of vapor into nanoparticles. Furthermore, the growth mechanisms of the nanoparticle formation for six kinds of materials (B, Cr, Fe, Mo, Pt, and Si) are also studied. As the result, their dominant processes are revealed.. |
| 154. | Takayuki Watanabe, Taira Tsuru, Water plasma generation under atmospheric pressure for HFC destruction, Thin Solid Films, 10.1016/j.tsf.2007.10.062, 516, 13, 4391-4396, 2008.05, [URL], The purpose of this paper is to investigate the decomposition process of hydrofluoroethylene (HFC-134a) by water plasmas. The water plasma was generated by DC arc discharge with a cathode of hafnium embedded into a copper rod and a nozzle-type copper anode. The advantage of the water plasma torch is the generation of 100%-water plasma by DC discharge. The distinctive steam generation leads to the portable light-weight plasma generation system that does not require the gas supply unit, as well as the high energy efficiency owing to the nonnecessity of the additional water-cooling. HFC-134a was injected into the water plasma jet to decompose it in the reaction tube. Neutralization vessel was combined to the reaction tube to absorb F2 and HF generated from the HFC-134a decomposition. The decomposition was performed with changing the feed rate of HFC-134a up to 185 mmol/min. The decomposition efficiency of 99.9% can be obtained up to 0.43 mmol/kJ of the ratio of HFC-134a feed rate to the arc power, hence the maximum feed rate was estimated to be 160 g/h at 1 kW of the arc power.. |
| 155. | Yaochun Yao, Takayuki Watanabe, Tetsuji Yano, Toru Iseda, Osamu Sakamoto, Masanori Iwamoto, Satoru Inoue, An innovative energy-saving in-flight melting technology and its application to glass production, Science and Technology of Advanced Materials, 10.1088/1468-6996/9/2/025013, 9, 2, 2008.04, [URL], The conventional method used for glass melting is air-fuel firing, which is inefficient, energy-intensive and time-consuming. In this study, an innovative in-flight melting technology was developed and applied to glass production for the purposes of energy conservation and environmental protection. Three types of heating sources, radio-frequency (RF) plasma, a 12-phase alternating current (ac) arc and an oxygen burner, were used to investigate the in-flight melting behavior of granulated powders. Results show that the melted particles are spherical with a smooth surface and compact structure. The diameter of the melted particles is about 50% of that of the original powders. The decomposition and vitrification degrees of the prepared powders decrease in the order of powders prepared by RF plasma, the 12-phase ac arc and the oxygen burner. The largest heat transfer is from RF plasma to particles, which results in the highest particle temperature (1810°C) and the greatest vitrification degree of the raw material. The high decomposition and vitrification degrees, which are achieved in milliseconds, shorten the melting and fining times of the glass considerably. Our results indicate that the proposed in-flight melting technology is a promising method for use in the glass industry.. |
| 156. | Masaya Shigeta, Takayuki Watanabe, Numerical investigation of cooling effect on platinum nanoparticle formation in inductively coupled thermal plasmas, Journal of Applied Physics, 10.1063/1.2903918, 103, 7, 2008.04, [URL], A mathematical model is developed to simulate the comprehensive systems of platinum nanoparticle synthesis using an argon inductively coupled thermal plasma flow with forced cooling portions. Numerical investigation using the model is conducted to clarify and discuss the effects of several cooling methods on the formation mechanisms of nanoparticles in distinctive thermofluid fields with strong two dimensionality. The computational results show that cooling by a radial gas injection, and a counterflow, engenders the remarkable promotion of nanoparticles.. |
| 157. | Norio Kobayashi, Rubin Ye, Takayuki Watanabe, Takamasa Ishigaki, Improvement of UV luminescence properties of gallium nitride powder by hydrogen radical irradiation, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.55.211, 55, 3, 211-215, 2008.03, [URL], Hydrogen plasma irradiation technique was applied to improve UV luminescence properties of commercial GaN powder which contained the dissolved oxygen in GaN lattice and a small amount of Ga2O3. RF induction thermal plasma of pulse-modulated mode was used to generate a high concentration of hydrogen radical species. The treatment of a green compact of GaN powder in the tail flame of Ar-H2 PM-ICP gave rise to the increase of photo luminescent intensity at 380 nm. The strongest intensity was obtained when a GaN specimen was set in the plasma tail flame region, where the numerical analysis predicted the increase of hydrogen radical concentration and the decrease of heat flux. When the treatment time increased, partial decomposition of GaN took place in due to excess heat energy. A short time Ar-H2 plasma irradiation gave the appropriate heating and the optimal emission efficiency. Raman scattering spectroscopy showed the impurity Ga 2O3 in plasma-irradiated specimens.. |
| 158. | Manabu Tanaka, Teisuke Hiyama, Takayuki Watanabe, Control of Size and Composition of Sn Based Nanoparticles Prepared by Ar-H2 Arc, Transactions on Materials Research Society of Japan, 33, 3, 687-690, 2008. |
| 159. | M. M. Hossain, Y. Yao, T. Watanabe, A numerical study of plasma-particle energy exchange dynamics in induction thermal plasmas for classification, Materials Science and Technology Conference and Exhibition, 1667-1676, 2007.12, Dependence of energy exchange between plasma and soda-lime-silica glass particles on the particle size, powder feed-rate and nozzle insertion length during in-flight thermal treatment for glassification by induction thermal plasmas has been studied. For the numerical investigation into the plasma-particle energy exchange dynamics during melting and vaporization of particles, a thermofluid plasma-particle interaction model has been developed taking into account the strong plasma-particle interactions and particle loading effects. It is found that heat transfer to the particles depends strongly on the particles size, powder feed-rate, nozzle insertion length, and plasma discharge parameters. Thus, for the efficient thermal treatment of particles, the above parameters should be optimized.. |
| 160. | Yaochun Yao, Yongnian Dai, Bin Yang, Wenhui Ma, Takayuki Watanabe, Synthesis and characterization of LiCo x Mn2-x O 4 cathode materials, Journal Wuhan University of Technology, Materials Science Edition, 10.1007/s11595-005-2307-4, 22, 2, 307-310, 2007.06, [URL], LiCo x Mn2-x O4 cathode materials for lithium ion batteries were synthesized by mechanical activation-solid state reaction at 750°C for 24 h in air atmosphere, and their crystal structure, morphology, element composition and electrochemical performance were characterized with XRD, SEM, ICP-AES and charge-discharge test. The experimental results show that all samples have a single spinel structure, well formed crystal shape and uniformly particle size distribution. The lattice parameters of LiCo x Mn2-x O4 decrease and the average oxidation states of manganese ions increase with an increase in Co content. Compared with pure LiMn2O4, the LiCo x Mn 2-x O4 (x=0.03-0.12) samples show a lower special capacity, but their cycling life are improved. The capacity loss of LiCo 0.09Mn1.91O4 and LiCo0.12Mn 1.88O4 is only 1.85% and 0.95%, respectively, after the 20th cycle. The improvement of the cycle performance is attributed to the substitution of Co at the Mn sites in the spinel structure, which suppresses the Jahn-Teller distortion and improves the structural stability.. |
| 161. | M. Shigeta, T. Watanabe, Growth mechanism of silicon-based functional nanoparticles fabricated by inductively coupled thermal plasmas, Journal of Physics D: Applied Physics, 10.1088/0022-3727/40/8/S20, 40, 8, 2407-2419, 2007.04, [URL], An experimental and computational study is conducted for the Si-based functional nanoparticle fabrication in an inductively coupled thermal plasma reactor. In the computational study, the improved multi-component co-condensation model with nodal discretization is proposed to clarify the nanoparticle growth mechanism in the consideration of coagulation and thermophoresis as well as simultaneous co-condensation. The nanoparticle growth by nucleation and co-condensation completes approximately in 12.6 ms for the Mo-Si system and in 5.0 ms for the Ti-Si system. Mo nanoparticles grow in advance, and then Si vapour condenses on the Mo nanoparticles in the Mo-Si system, while vapours of Si and Ti simultaneously co-condense following Si nucleation in the Ti-Si system. A smaller number of larger nanoparticles are created with an increase in the powder feed rate. When the silicon content in the feed powders is 66.7%, nanoparticles of MSi2 (M ≤ Mo, Ti) are fabricated as the main product. Nanoparticles of Ti5Si3 are mainly synthesized in the case of the silicon content 33.0%. In the experiment, the nanoparticles are successfully fabricated and examined by x-ray diffractometry and transmission electron microscopy. The experimental and computational results show good agreement in the size distribution and the composition.. |
| 162. | Tsugio Matsuura, Keiji Taniguchi, Takayuki Watanabe, A new type of arc plasma reactor with 12-phase alternating current discharge for synthesis of carbon nanotubes, Thin Solid Films, 10.1016/j.tsf.2006.02.086, 515, 9, 4240-4246, 2007.03, [URL], A new type of arc plasma reactor with 12-phase alternating current (AC) discharge for synthesis of carbon nanotubes (CNTs) is proposed. A couple of six discharge electrodes by which have mutually electrical connection between them to enlarge the high-temperature regions in the reactor are arranged to three-dimensional locations. A new method of CNTs fabrication by this reactor, which accomplishes to enlarge the suitable growth region in high purity and at high yield, was developed.. |
| 163. | Masayuki Araya, Toshifumi Yuji, Takayuki Watanabe, Junzou Kashihara, Yoshitake Sumida, Application to cleaning of waste plastic surfaces using atmospheric non-thermal plasma jets, Thin Solid Films, 10.1016/j.tsf.2006.02.066, 515, 9, 4301-4307, 2007.03, [URL], The removal of paint on the surface of waste plastics is difficult by the conventional process; in this research, a new cleaning mechanism using atmospheric plasmas was examined through optical emission spectroscopy, electron spectroscopy for chemical analysis, and scanning electron microscopy. Results indicate that an increase of pulse frequency enables for a short processing time for the removal of the paint film, signifying that the production of radicals in plasma, especially oxygen radicals, can be controlled by pulse frequency. Plasma jets were generated under the experimental conditions of an input power of 250 W to 400 W, a pulse frequency of 2 kHz to 12 kHz, and a plasma gas flow rate of 30 L/min. Examination of the intensity ratio of the reactive species, as measured by emission spectroscopy, showed that the O/N value increased with an increase in pulse frequency. Results of analysis with electron spectroscopy for chemical analysis show that nitrogen atoms and molybdenum in only the paint film decreased through plasma processing.. |
| 164. | Takayuki Watanabe, Nobuhiko Atsuchi, Masaya Shigeta, Modeling of non-equilibrium argon-hydrogen induction plasmas under atmospheric pressure, Thin Solid Films, 10.1016/j.tsf.2006.02.100, 515, 9, 4209-4216, 2007.03, [URL], Modeling of induction thermal plasmas has been performed to investigate chemically non-equilibrium effect for dissociation and ionization. Computations were carried out for argon-hydrogen plasmas under atmospheric pressure. The thermofluid and concentration fields were obtained by solving of two-dimensional modeling. This formulation was presented using higher-order approximation of the Chapman-Enskog method for the estimation of transport properties. A deviation from the equilibrium model indicates that argon-hydrogen induction plasmas should be treated as non-equilibrium for dissociation and ionization near the torch wall.. |
| 165. | Masaya Shigeta, Takayuki Watanabe, Multi-component co-condensation model of Ti-based boride/silicide nanoparticle growth in induction thermal plasmas, Thin Solid Films, 10.1016/j.tsf.2006.02.042, 515, 9, 4217-4227, 2007.03, [URL], Numerical analysis is conducted for the titanium-based boride and silicide nanoparticle synthesis using an induction thermal plasma including the material evaporation process and the nanoparticle growth process with nucleation and co-condensation. Both systems present the nano-scaled particle size distributions. Ti-B system shows the smaller particle diameter, sharper distribution, larger particle number density, and wider range of the composition than Ti-Si system. Ti-Si system provides a narrower range of the silicon content due to the simultaneous co-condensation of titanium and silicon. Finally the correlation between the particle size and the nonmetal content of the synthesized nanoparticles is presented on a chart.. |
| 166. | Norio Kobayashi, Yuji Kawakami, Keiji Kamada, Ji Guang Li, Takayuki Watanabe, Takamasa Ishigaki, Spherical submicron-size copper and copper-tungsten powders prepared in RF induction thermal plasma, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.54.39, 54, 1, 39-43, 2007.01, [URL], Spherical submicron copper particles were synthesized through evaporation and subsequent condensation of copper powders in Ar-H2 thermal plasma. Copper powders of ∼40μm in size injected into the plasma, evaporated instantly and fine particles were formed through homogeneous nucleation and subsequent heterogeneous condensation. Particle size and the distribution in the synthesized powders were changed depending on the powder feed rate. Formation of submicron size spherical powders attributed to a significantly high degree of supersaturation in a vapor phase. Particle sizes of the as-produced powders range from submicron to several tens of micrometers. A simple sedimentation treatment was successfully applied to separate the as-formed powders with alcohol solvent to give uniform spherical submicron-size particles with monomodal size distributions. Cu-W composite powders were synthesized through the Ar-H2 plasma treatment of Cu-WO3 composite powders. The starting temperature of shrinkage was made significantly higher than pure Cu powders by mixing with several wt% of W.. |
| 167. | Masaya Shigeta, Nobuhiko Atsuchi, Takayuki Watanabe, Numerical investigation of a local oxygen injection effect on argon induction plasmas using a chemically non-equilibrium model, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.39.1255, 39, 12, 1255-1264, 2006.12, [URL], Effective generation of chemical reactive species in thermal plasmas has been required in the field of material processing and waste treatment. The effect of oxygen injection into argon induction plasmas was investigated by numerical analysis without chemical equilibrium assumptions. Reaction kinetics rates of the dissociation and recombination of oxygen as well as the ionization were taken into account. The transport properties were estimated using higher-order approximation of the Chapman-Enskog method for required accuracy. Oxygen dissociation and heat flux to a torch wall can be controlled by oxygen injection location. Therefore, suitable oxygen injection needs to be chosen according to the application requirement. The present modeling would give more precise information and provide the guidance for the rational design of new material processing with effective reactive gas injection into plasmas.. |
| 168. | Takayuki Watanabe, Masaya Shigeta, Nobuhiko Atsuchi, Two-temperature chemically-non-equilibrium modeling of argon induction plasmas with diatomic gas, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2006.05.039, 49, 25-26, 4867-4876, 2006.12, [URL], A non-equilibrium modeling of argon-oxygen and argon-hydrogen induction thermal plasmas was performed without thermal and chemical equilibrium assumptions. Reaction rates of dissociation and recombination of diatomic gas and ionization were taken into account with two-temperature modeling. A substantial deviation from LTE exists near the torch wall in argon-oxygen induction plasmas under atmospheric pressure, while small deviation in argon-hydrogen plasmas results from the large collision frequency between electrons and hydrogen atoms.. |
| 169. | Yaochun Yao, Yongnian Dai, Bin Yang, Wenhui Ma, Takayuki Watanabe, Surface modification and characterization of F-Co doped spinel LiMn2O4, Rare Metals, 10.1016/S1001-0521(07)60040-0, 25, 6 SUPPL. 1, 33-38, 2006.10, [URL], Spinel LiCo0.09Mn1.91O3.92F0.08 as cathode material was modified with LiCoO2 by the sol-gel method, and the crystal structure, morphology and electrochemical performance were characterized with XRD, SEM, EDS, AAS and charge-discharge test in this paper. The results show that a good clad coated on parent material can be synthesized by the sol-gel method, and the materials with modification have perfect spinel structure. LiCo0.09Mn1.91O3.92F0.08 materials coated by LiCoO2 improve the stability of crystal structure and decrease the dissolution of Mn into electrolyte. With the LiCoO2 content increasing, the specific capacity and cycle performance of samples are improved. The capacity loss is also suppressed distinctly even at 55°C.. |
| 170. | Atsushi Nezu, Kouichi Moro, Takayuki Watanabe, Thermal plasma treatment of waste ion exchange resins by CO2 injection, Thin Solid Films, 10.1016/j.tsf.2005.08.033, 506-507, 432-435, 2006.05, [URL], The amount of waste ion exchange resin generated from nuclear power plants is increasing; therefore, the effective method to reduce the volume of the waste resins is required. The purpose of this paper is to reduce the weight and volume of the resin and to stabilize the radionuclide such as cobalt by reactive thermal plasmas with carbon dioxide injection, and to investigate the reaction mechanism of the resins doped with cobalt. The resins were treated by thermal plasmas under atmospheric pressure. The weight was reduced to 70% after 40 min of treatment without reactive gas injection. At 12 L/min of carbon dioxide injection, the weight reduction was enhanced to 96%. Thermal plasma treatment provides the effective and rapid reduction in weight and volume of the resins. Moreover, the treatment has good advantages for the stabilization of the doped metal.. |
| 171. | Yukio Watanabe, Tanemasa Asano, Hong Young Chang, Hiroshi Fujiyama, Roger McWillimas, Takayuki Watanabe, Thin Solid Films Preface, Thin Solid Films, 10.1016/j.tsf.2005.08.012, 506-507, 2006.05, [URL]. |
| 172. | Takayuki Watanabe, Takahiro Notoya, Takamasa Ishigaki, Hiroyuki Kuwano, Hideki Tanaka, Yusuke Moriyoshi, Growth mechanism for carbon nanotubes in a plasma evaporation process, Thin Solid Films, 10.1016/j.tsf.2005.08.289, 506-507, 263-267, 2006.05, [URL], Carbon nanotubes (CNTs) were synthesized through raw-material evaporation and condensation in RF thermal plasmas to investigate co-condensation process of the vapor mixture of carbon and metals. Addition of 10 wt.%-Ni was the most effective for the CNT synthesis, while Co, Fe, Mo, LaB6 had poor activity. These metal combinations presented synergy effect for the CNT formation. The combinations of Ni-Co, Ni-Fe, and Ni-LaB6 provided more effective activity in the CNT synthesis. Furthermore, the CNT growth mechanism from the vapor mixture of carbon and metals was discussed. Heterogeneous condensation model and carbon-metal molten model were selected as the CNT growth model.. |
| 173. | Nobuhiko Atsuchi, Masaya Shigeta, Takayuki Watanabe, Modeling of non-equilibrium argon-oxygen induction plasmas under atmospheric pressure, International Journal of Heat and Mass Transfer, 10.1016/j.ijheatmasstransfer.2005.07.052, 49, 5-6, 1073-1082, 2006.03, [URL], Modeling of induction thermal plasmas has been performed to investigate chemically non-equilibrium effect for dissociation and ionization. Computations were carried out for argon-oxygen plasmas under atmospheric pressure. The thermofluid and concentration fields were obtained by solving two-dimensional modeling. This formulation was presented using higher-order approximation of the Chapman-Enskog method for the estimation of transport properties. A deviation from the equilibrium model indicates that argon-oxygen induction plasmas should be treated as non-equilibrium for dissociation and ionization. The present modeling would give the guidance for the rational design of new material processing using thermal plasmas.. |
| 174. | Masaya Shigeta, Takayuki Watanabe, Numerical analysis for preparation of silicon-based intermetallic nano-particles in induction thermal plasma flow systems, JSME International Journal, Series B: Fluids and Thermal Engineering, 10.1299/jsmeb.48.425, 48, 3, 425-431, 2006.02, [URL], Numerical analysis is conducted for silicon-based intermetallic nano-particle preparation in induction thermal plasma flow systems. In the nucleation region, the temperature decreases drastically (104 - 105 K/s), which results in a great promotion of nano-particle nucleation. In Mo-Si system, nuclei of molybdenum are produced and grow in the upstream region and then silicon vapor condenses on the molybdenum particles. The composition shows wide range since condensations of molybdenum and silicon occur at the different positions. On the other hand in Ti-Si system, it shows narrow range since condensations of titanium and silicon occur simultaneously. The difference of the formation mechanisms leads to the preparation of disilicides as well as the sub-products which are estimated from the phase diagrams. The particle size distributions and the compositions obtained from the present model show good agreements with the experimental results.. |
| 175. | Hossain M. Mofazzal, Okumiya Hideaki, Watanabe Takayuki, Nucleation and growth of cobalt and iron silicide nanoparticles in rf induction thermal plasma reactor, Proceedings of 4th International Conference on Electrical and Computer Engineering, 10.1109/ICECE.2006.355648, 370-373, 2006.01, [URL], The nucleation and growth mechanism of cobalt (Co) and iron (Fe) silicide nanoparticles from metals themselves in an induction thermal plasma reactor at atmospheric pressure has been described. The parameters which affected the metal composition of silicides, particle size distributions and morphology of silicide nanoparticles have also been discussed. It was found that synthesized Co silicides have large particle size distribution than that of Fe silicides, and Co silicides formation strongly depended on quenching position but Fe silicides did not.. |
| 176. | Masaya Shigeta, Takayuki Watanabe, Numerical analysis for co-condensation processes in silicide nanoparticle synthesis using induction thermal plasmas at atmospheric pressure conditions, Journal of Materials Research, 10.1557/JMR.2005.0351, 20, 10, 2801-2811, 2005.10, [URL], Numerical analysis is conducted to clarify the formation mechanisms of silicide nanoparticles synthesized in an induction thermal plasma maintained at atmospheric pressure. The induction thermal plasma is analyzed by an electromagnetic fluid dynamics approach, in addition to a multi-component co-condensation model, proposed for the silicide nanoparticle synthesis. In the Cr-Si and Co-Si systems, silicon vapor is consumed by homogeneous nucleation and heterogeneous condensation processes; subsequently, metal vapor condenses heterogeneously onto liquid silicon particles. The Mo-Si system shows the opposite tendency. In the Ti-Si system, vapors of silicon and titanium condense simultaneously on the silicon nuclei. Each system produces nanoparticle diameters of around 10 nm, and the required disilicides, with the stoichiometric composition, are obtained. Only the Ti-Si system has a narrow range of silicon content. The numerical analysis results agree with the experimental findings. Finally, the correlation chart, predicting the saturation vapor pressure ratios and the resulting silicon contents, is presented for estimation of nanoparticle compositions produced in the co-condensation processes.. |
| 177. | A. Takeuchi, S. Kato, Takayuki Watanabe, Effect of MgO concentration in solid reactants on decomposition treatment of Halon 1301, Chemical Engineering Communications, 10.1080/00986440490472751, 191, 12, 1671-1685, 2004.12, [URL], Halon 1301 (bromotrifluoromethane) is known as both an ozone-depleting and global-warming substance. In this study, a drying treatment was developed for halon 1301 decomposition. Burnt lime, burnt dolomite, and burnt brucite were used as reactants. Halon 1301 is decomposed to gases containing halogen, and these gases react with the reactants simultaneously. The effects of the treatment temperatures, the treatment times, and the reactant compositions on the effective treatment process were investigated. Bromine in halon was almost completely recovered with the reactants. However, the recovery of fluorine was low. Burnt dolomite and burnt brucite were better reactants than burnt lime. The presence of MgO in the reactants plays an important role in this process.. |
| 178. | Takayuki Watanabe, Keiji Fujiwara, Nucleation and growth of oxide nanoparticles prepared by induction thermal plasmas, Chemical Engineering Communications, 10.1080/00986440490464264, 191, 10, 1343-1361, 2004.10, [URL], The reactive evaporation method of injected metal powders was investigated for preparing oxide nanoparticles. The method has advantages such as evaporation is enhancement of the injected powder owing to exothermic reaction heat of the metal powder oxidation in induction thermal plasmas. Tangential gas flow injection to the plasma tail flame controls the diameter and the yield of the oxide nanoparticles. The purpose of this research is to investigate the effect of the injection gas flow on the preparation mechanism of oxide nanoparticles in thermal plasmas by experimental work and numerical analysis. An increase in the flow rate of the injection gas leads to an increase in the diameter as well as the yield of the prepared nanoparticles. Numerical analysis for nucleation and growth provides the preparation mechanism of the oxide nanoparticles; however, a more sophisticated model should be developed.. |
| 179. | Takayuki Watanabe, Hideaki Okumiya, Formation mechanism of suicide nanoparticles by induction thermal plasmas, Science and Technology of Advanced Materials, 10.1016/j.stam.2004.03.015, 5, 5-6, 639-646, 2004.09, [URL], The condensation mechanism of metal mixture in thermal plasmas was investigated experimentally and numerically to prepare nanoparticles of silicon base intermetallic compounds. Silicon powder premixed with metal powder (Mo, Ti, Co, Fe, Cr, or Mn) was introduced into the plasma. The nanoparticles were prepared on condition that metal vapor was quickly quenched by the water-cooled copper coil. The nucleation rate expression was used for the estimation of critical saturation ratio. The nucleation temperature of the metal almost corresponds to the melting temperature, while silicon has wide liquid range between the nucleation and melting temperature, resulting in better preparation of silicide. For Mo-Si system, nucleation position of Mo is different from that of Si. Therefore, quenching position has strong effect on the particle composition of molybdenum silicide nanoparticles.. |
| 180. | Takayuki Watanabe, Noriaki Sugimoto, Numerical analysis of oxygen induction thermal plasmas with chemically non-equilibrium assumption for dissociation and ionization, 16th Symposium on Plasma Science for Materials (SPSM-16) Thin Solid Films, 10.1016/j.tsf.2003.12.022, 457, 1, 201-208, 2004.06, [URL], Modeling of induction thermal plasmas has been performed to investigate a chemically non-equilibrium effect for dissociation and ionization. Computations were carried out for oxygen plasmas under atmospheric pressure. The thermofluid and concentration fields were obtained by solving of two-dimensional modeling. This formulation was presented using higher-order approximation of the Chapman-Enskog method for the estimation of transport properties. A deviation from the equilibrium model indicates that oxygen induction plasmas should be treated as non-equilibrium for dissociation and ionization. The present modeling would give the guidance for the rational design of new material processing using thermal plasmas.. |
| 181. | Masaya Shigeta, Takayuki Watanabe, Hideya Nishiyama, Numerical investigation for nano-particle synthesis in an RF inductively coupled plasma, 16th Symposium on Plasma Science for Materials (SPSM-16) Thin Solid Films, 10.1016/j.tsf.2003.12.020, 457, 1, 192-200, 2004.06, [URL], Since plasma is regarded as one of the multifunctional fluids which has high energy density, chemical reactivity, controllability by an external electromagnetic field and variable transport properties such as electrical conductivity, it is considerably effective for the synthesis of nano-particles. Since a radio frequency inductively coupled plasma (RF-ICP) has several advantages, the synthesis of ultrafine powders of metals and ceramics with high purity can be easily achieved by the steep temperature gradients at the tail. In the present study, it is clarified how the number density, diameter and specific surface of the produced nano metal-particles of Al, Ti, Au and Pt are influenced by the operating conditions such as the quenching gas flow rate and the powder feed rate of the RF-ICP reactor by numerical investigation. For all the metals, the increase in the quenching gas flow rate results in the increase in the particle number density, the decrease in the mean diameter and the increase in the specific surface. The increase in the powder feed rate causes the increase in the mean diameter but the decrease in the specific surface. The results of four metals are markedly different from each other due to their own material properties of saturation pressure and surface tension.. |
| 182. | T. Ishigaki, H. Fujioka, K. Terashima, T. Watanabe, Thin Solid Films Preface, 16th Symposium on Plasma Science for Materials (SPSM-16) Thin Solid Films, 10.1016/j.tsf.2003.12.001, 457, 1, 2004.06, [URL]. |
| 183. | Maria Natalia Roxas Dimaano, Takayuki Watanabe, The transient behavior analysis of the capric acid and lauric acid mixture in a vertical tube, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.36.1421, 36, 12, 1421-1431, 2003.12, [URL], The thermal performance of the capric acid and lauric acid mixture (C-L acid), in the respective composition of 65% and 35% by mole was investigated for its cooling capacity. A vertical cylindrical storage capsule was employed for the study. A supplementary simplified numerical model for the behavior analysis of the C-L acid employing the experimental design was made. The mathematical model was numerically solved using a finite difference method. The radial temperature distribution, the melting time and solidification time results performed from the charge and discharge experiments are verified to evaluate the reliability of the assumptions made on the numerical model. A two-dimensional heat transfer is represented by a one-dimensional model accounted by the effective thermal conductivity that considers both the natural convection and two-dimensional effects. The numerically estimated radial temperature distribution during melting and solidification are within the experimentally obtained ranges.. |
| 184. | Takayuki Watanabe, Atsushi Nezu, Yoshiyuki Abe, Yoshiro Ishii, Kenji Adachi, Formation mechanism of electrically conductive nanoparticles by induction thermal plasmas, Proccedings of the Joint International Plasma Symposium Thin Solid Films, 10.1016/S0040-6090(03)00369-9, 435, 1-2, 27-32, 2003.07, [URL], The purpose of this paper is to prepare electrically conductive nanoparticles such as borides, mixture of nitrides and borides by induction thermal plasmas. Another purpose is to correlate the prepared particle composition with thermodynamic parameters. For B-N-M (M=Ti, Cr, V) system that has low Gibbs free energy of nitridation and boridation, boride and nitride nanoparticles were prepared. While B-N-M (M=Co, Fe, Mo) system that has high Gibbs free energy of nitridation, boride nanoparticles were mainly prepared. For B-N-M (M=Ta, Nb) system that has much higher nucleation temperature of metal than that of boron, nanoparticles of nitride with small fraction of boride were prepared, because these systems have different nucleation mechanism. The composition of prepared nanoparticles depends on the Gibbs free energy as well as the nucleation temperature.. |
| 185. | Atsushi Nezu, Tatsuhiko Morishima, Takayuki Watanabe, Thermal plasma treatment of waste ion-exchange resins doped with metals, Proccedings of the Joint International Plasma Symposium Thin Solid Films, 10.1016/S0040-6090(03)00364-X, 435, 1-2, 335-339, 2003.07, [URL], The amount of the waste ion-exchange resins are increasing, therefore, the effective method to reduce the volume of the waste resins, is required. The purpose of this paper is to reduce the weight and volume of the resins by reactive thermal plasmas, and to investigate the reaction mechanism of the resins doped with Co and Cs. In this experiment, cation exchange resins doped with Co and Cs were used as sample resins. The resins were treated by thermal plasmas under atmospheric pressure. The weight was reduced to approximately 51% after 60 min treatment without oxygen injection. At 18 1/min of oxygen flow rate, the weight was reduced to approximately 91%. Small difference in the weight reduction was found among the undoped resins and Co and Cs doped resins. Thermal plasma treatment provides the effective and rapid reduction in weight and the volume of resins. The treatment has good advantages for the stabilization of the doped metals.. |
| 186. | Takayuki Watanabe, Shigehiro Shimbara, Halogenated hydrocarbon decomposition by steam thermal plasmas, High Temperature Material Processes, 10.1615/HighTempMatProc.v7.i4.30, 7, 4, 455-474, 2003.01, [URL], Applications for the destruction of hazardous and waste materials such as halogenated hydrocarbons by reactive thermal plasmas are reviewed. For halogenated hydrocarbon decomposition, key technologies are the stable generation of DC steam plasmas and the off-gas treatment after the decomposition of halogenated hydrocarbon. Therefore, DC 100%-steam plasma characteristics were investigated for the application of halogenated hydrocarbon decomposition. The described steam plasma system is a portable light-weight plasma generation system that does not require any gas supply. The system has high energy-efficiency since cooling water is not needed. In addition, a dry process was developed for halogenated hydrocarbon decomposition and simultaneously adsorbing fluorine and bromine with solid alkaline reactants.. |
| 187. | M. N. Roxas-Dimaano, T. Watanabe, The capric and lauric acid mixture with chemical additives as latent heat storage materials for cooling application, Energy, 10.1016/S0360-5442(02)00024-5, 27, 9, 869-888, 2002.09, [URL], The mixture of capric acid and lauric acid (C-L acid), with the respective mole composition of 65% and 35%, is a potential phase change material (PCM). Its melting point of 18.0°C, however, is considered high for cooling application of thermal energy storage. The thermophysical and heat transfer characteristics of the C-L acid with some organic additives are investigated. Compatibility of C-L acid combinations with additives in different proportions and their melting characteristics are analyzed using the differential scanning calorimeter (DSC). Among the chemical additives, methyl salicylate, eugenol, and cineole presented the relevant melting characteristics. The individual heat transfer behavior and thermal storage performance of 0.1 mole fraction of these additives in the C-L acid mixture are evaluated. The radial and axial temperature distribution during charging and discharging at different concentratations of selected PCM combinations are experimentally determined employing a vertical cylindrical shell and tube heat exchanger. The methyl salicylate in theC-L acid provided the most effective additive in the C-L acid. It demonstrated the least melting band width aimed at lowering the melting point of the C-L acid with the highest heat of fusion value with relatively comparable rate of heat transfer. Furthermore, the thermal performance based on the total amount of transferred energy and their rates, established the PCM's latent heat storage capability.. |
| 188. | Maria Natalia R. Dimaano, Takayuki Watanabe, Performance investigation of the capric and lauric acid mixture as latent heat energy storage for a cooling system, Solar Energy, 10.1016/S0038-092X(01)00101-3, 72, 3, 205-215, 2002.03, [URL], The thermal performance of the capric acid and lauric acid mixture (C-L acid) in the respective composition of 65% and 35% by mole was investigated for its cooling capacity. Pentadecane was used for comparison. A vertical cylindrical storage capsule was employed for the study. The temperature distribution of the C-L acid during charging and discharging inside a vertical tube was experimentally determined in both radial and axial directions. A melting point of 18-19.5°C was observed. This value corroborates with the DSC-obtained values for the C-L acid. The calculated stored energy based on the radial temperature distribution during charge and discharge processes indicates that the C-L acid is a potential latent heat storage material.. |
| 189. | Maria Natalia R. Dimaano, Takayuki Watanabe, The capric-lauric acid and pentadecane combination as phase change material for cooling applications, Applied Thermal Engineering, 10.1016/S1359-4311(01)00095-3, 22, 4, 365-377, 2002.03, [URL], The mixture of 65 mol% capric acid and 35 mol% lauric acid (C-L acid) is a potential latent heat storage material. However, its melting temperature of 18.0 °C is quite high for low-temperature thermal energy storage. Addition of pentadecane, with a melting point of 9.9 °C, is proposed. The thermal characteristics of the combination of the C-L acid with pentadecane (CL:P) in different volume ratio are investigated employing the DSC analysis. The actual thermal performance of each CL:P combination is further determined from their radial and axial temperature distribution employing a fabricated thermal storage capsule. The 90:10 CL:P combination manifests an improvement in the melting characteristic of the C-L acid.. |
| 190. | Akihiro Takeuchi, Shinichi Kato, Takayuki Watanabe, Yoshimasa Akatsuka, Effect of solid reactant conditions on adsorption of halon decomposition gases, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.35.234, 35, 3, 234-240, 2002.03, [URL], Carbon halides, especially halons (bromofluorocarbons), are compounds known to deplete the ozone layer and contribute to global warming. Appropriate treatments to decompose halon waste is important to protect the environment. A dry process to decompose halon has been developed. Solid alkaline carbonate and hydrate obtained from dolomite were prepared for the reactants to decompose halon and to react with the fluorine and bromine produced by the halon decomposition. Twelve kinds of reactants were obtained by changing the burning temperature and burning time. The amount of the decomposed halon and the conversion were correlated with the pore distributions in the reactants. The distributions of F and Br differed depending on the preparation of the reactants. The difference would be attributed to the reactivity and the diffusion rate of the gases produced by the decomposing halon.. |
| 191. | Takayuki Watanabe, Tadayuki Sato, Atsushi Nezu, Electrode phenomena investigation of wire arc spraying for preparation of Ti-Al intermetallic compounds, Proceedinggs of the 14th Symposium on Plasma Science for Marteri (SPSM-14) Thin Solid Films, 10.1016/S0040-6090(02)00019-6, 407, 1-2, 98-103, 2002.03, [URL], Electric arc spraying with dual wires is an economical coating process. The electrode fluctuation of titanium and aluminum wires was investigated to prepare intermetallic compound coatings. The combination of Ti-cathode and Al-anode leads to arc instability owing to unbalanced melting rates at electrode tips. Therefore, higher m.p. material can be used as the anode, while lower m.p. material can be used as the cathode for obtaining of better droplet dispersion from the corresponding wires, resulting in better preparation of compound coatings. Wire arc spraying provides a new attractive process for preparation of intermetallic compounds or alloys. The compounds are mainly prepared during the droplet deformation process on the substrate.. |
| 192. | Yusuke Moriyoshi, Yoshiki Shimizu, Takayuki Watanabe, B-C-N nanotubes prepared by a plasma evaporation method, Thin Solid Films, 10.1016/S0040-6090(01)00936-1, 390, 1-2, 26-30, 2001.06, [URL], B-C-N nanotubes prepared by a flush evaporation method using a d.c. arc plasma were mainly characterized by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The nanotubes obtained were divided into three types, such as carbon-, boron nitride-, or carbon nanotubes surrounded with boron nitride nanotubes. These types of nanotubes were obtained at temperatures higher than approximately 3000 K; however, these were not formed at temperatures lower than approximately 3000 K. On the other hand, nanocapsules were formed at all the temperature regions, but the nanocapsules obtained were smaller at lower temperatures. The addition of nickel produced a bundle of single walled carbon nanotubes and boron nitride nanocapsules surrounding nickel particles. Based on the experimental data obtained, the formation mechanisms of both nanotubes and nanocapsules were discussed.. |
| 193. | Takayuki Watanabe, Hajime Itoh, Yoshiro Ishii, Preparation of ultrafine particles of silicon base intermetallic compound by arc plasma method, Thin Solid Films, 10.1016/S0040-6090(01)00923-3, 390, 1-2, 44-50, 2001.06, [URL], The purpose of this paper was to prepare ultrafine particles of Si-based intermetallic compounds, TiSi2, MoSi2 and VSi2, by an arc plasma method with hydrogen addition. The properties of the prepared particles were affected by the vapor pressure ratio (Ti/Si, V/Si: 10-1; Mo/Si: 10-3) of the constituent metals. The vaporization and condensation rates of the constituent metals should be controlled to prepare intermetallic compound particles in the case of large different vapor pressures. The vaporization rate can be controlled by H2 concentration in the arc; for example, an increase in H2 concentration leads to an increase in Ti fraction in the prepared particles in a Si-Ti system. The preparation of ultrafine particles of TiSi2 was most successful from the 60-wt.% Ti raw material with the 50%-H2 arc. MoSi2 particles were prepared from the 85-wt.% Mo raw material with the 50%-H2 arc. A single phase of VSi2 particles was prepared successfully from the 60-wt.% V raw material with the 50%-H2 arc. Another purpose was to investigate the mechanism of vaporization enhancement of particular metals from a metal mixture by hydrogen in arc plasmas. The vaporization enhancement was mainly attributed to the formation of intermediate products such as hydride and/or activity modification by hydrogen in molten metals.. |
| 194. | Mina Sakano, Motofumi Tanaka, Takayuki Watanabe, Application of radio-frequency thermal plasmas to treatment of fly ash, 12th Symposium on Plasma Science for Materials Thin Solid Films, 10.1016/S0040-6090(00)01641-2, 386, 2, 189-194, 2001.05, [URL], RF thermal plasma systems for treatment of fly ash have been proposed in order to recover the useful metals and materials from fly ash discharged from a melting furnace. The fundamental investigations for recovering the detoxified and useful materials from fly ash by means of RF thermal plasma process were performed. In terms of the numerical analysis and the experimental results, it is verified that fly ash is decomposed by RF thermal plasmas and heavy metal species separate from fly ash by means of the effects of temperature control and hydrogen.. |
| 195. | Yoshihisa Abe, Toshiyuki Kikuchi, Hideo Nakanishi, Takayuki Watanabe, Numerical Analysis of the Heat Transfer Mechanism in an Arc Furnace for Silica Grass Crucible Production, Kagaku Kogaku Ronbunshu, 10.1252/kakoronbunshu.27.535, 27, 5, 535-539, 2001.01, [URL], High quality, large-scale silica glass crucibles are strongly required for large-diameter silicon crystal production using the Czochralski process. Silica glass crucibles are usually produced from silica powder, which is fused at high temperature in an arc. In this study, we made a numerical analysis model taking account of the high temperature plasma jet induced by the arc between carbon electrodes, and measured the temperature variation of the fusing silica powder in a crucible-production process to verify the propriety of the analytical model. The calculated results were found to show good agreement with the actual temperature measurements. The arc furnace was found to have two different heating conditions that depend on the crucible positions. One is put under the control of high-temperature jet generated by the arc. The other is put under the control of radiation heat transfer near the electrodes. Our developed calculation model is expected to be of use in clasifying the optimum conditions for the fusing mechanism in the arc furnace. Key words: computer simulation, plasmas jet, arc furnace, heat and mass transfer, silica glass crucible.. |
| 196. | Yusuke Moriyoshi, Yoshiki Shimizu, Takayuki Watanabe, Preparation and characterization of B-C-N nanotubes by a rapid quenching method, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.47.627, 47, 6, 627-635, 2000.06, [URL], B-C-N nanotubes prepared by a plasma evaporation method were characterized by a transmission-electron microscopy (TEM) and an electron-energy-loss spectroscopy (EELS). The nanotubes obtained were divided into three types of carbon-, boron nitride-, and combined nanotubes of boron nitride with carbon. However, BCxN nanotubes of homogeneous phase could not be obtained. This indicated that a stable phase in the experimental condition was in the mixtures of carbon and boron nitride rather than in a homogeneous phase of BCxN compounds. Also the effect of temperatures on the formation of nanotubes was studied. Resultantly it was shown that nanotubes were formed at higher temperatures than 3000 K and, on the other hand, nanocapsules were formed at lower temperatures than 3000 K. Based on the microstructural data obtained, the formation mechanisms of both nanotubes and nanocapsules were described.. |
| 197. | Sachio Ogiwara, Kunihisa Eguchi, Hiroshi Kanamori, Hideto Yoshida, Takayuki Watanabe, Study on a hydrogen-reduced reactor design for lunar water production, Proceedings of Space 2002, 10.1061/40479(204)96, 798-804, 2000.01, [URL], Our research group has been conducting a basic work on experimental missions for lunar resource utilization since 1996. The objective of the research work is to provide a conceptual design of the In-situ Space Resource Utilization (ISRU) experiment system for unmanned water production on the Moon, and to define essential technological breakthroughs. As part of the research program, an experimental study on the hydrogen reduction of lunar soil has been performed to design a chemical reactor for water production.. |
| 198. | Takayuki Watanabe, Tadayuki Sato, Atsushi Nezu, Electrode phenomena investigation of wire arc spraying for preparation of Ti-Al intermetallic compounds, IEEE International Conference on Plasma Science, 2000.01, A new preparation method of Ti-Al intermetallic compounds by wire arc spraying is developed. Titanium wire used as the anode and aluminum wire is used as the cathode was sprayed. The intermetallic compounds were prepared during the droplet deformation on the substrate as well as during the droplet flight. Enhancement of the intermetallic compound preparation results from higher substrate temperature.. |
| 199. | Yusuke Moriyoshi, Yoshiki Shimizu, Takayuki Watanabe, The preparation and characterization of boron-carbon-nitrogen nanotubes by a dc arc plasma, Proceedings of the Second International Conference on Processing Materials for Properties, 387-392, 2000.06, B-C-N nanotubes prepared by a flush evaporation method using a dc arc plasma were mainly characterized by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The nanotubes obtained were divided into three types such as carbon-, boron nitride-, and carbon or carbon nanotubes surrounded with boron nitride nanotubes. These types of nanotubes were obtained at higher temperatures than about 3000 K, however, these were not formed at lower temperatures than about 3000K. On the other hand, nanocapsules were formed at all the experimental temperatures and nanocapsules with a homogeneous phase were obtained at lower temperatures than about 3000 K. The effect of additives on the formation of B-C-N nanotubes was not clear. Based on these experimental data depending on temperatures and corresponding microstructures, the formation mechanisms of both nanotubes and nanocapsules were briefly discussed.. |
| 200. | K. Eguchi, S. Ogiwara, M. Oguchi, H. Kanamori, T. Yoshida, Y. Nakamura, T. Watanabe, A design concept of water production experiment mission for lunar resource utilization, Solar System Research, 33, 5, 376-381, 1999.12, Future missions for the Moon and the Mars exploration are advancing to a more active phase, and meanwhile in-situ resource utilization (ISRU) technologies will be much more important for their engineering purposes. Our research group in Japan has been conducting a feasibility study on experimental missions for lunar resource utilization since 1996. The objective of the research work is to conceptually design the unmanned ISRU experiment system for water production on the Moon, and to define the design requirements, essential technology breakthroughs, and a technical scenario for the mission development. This paper describes outline and recent status of our study.. |
| 201. | Takayuki Watanabe, Haruo Kawasaki, Atsushi Kanzawa, Effects of depolymerization rate on system performance of paraldehyde chemical heat pump, Sekiyu Gakkaishi (Journal of the Japan Petroleum Institute), 42, 1, 35-36, 1999.12, The paraldehyde chemical heat pump system combines the effects of a chemical reaction and a vapor-compression. The paraldehyde chemical heat pump is used as a cooling system. This study is on the effects of the paraldehyde depolymerization rate on the cooling rate, the coefficient of performance (COP), and the required amount of catalyst in the endothermic reactor. An increase in the amount of paraldehyde reacted in the endothermic reactor results in improvement in the COP and the cooling rate, but leads to an increase in the required amount of catalyst weight. The required amount of catalyst is 0.4 kg, having the effectiveness factor of 0.6, for the heat pump system with COP of 6 and cooling rate of 3.8-4.0 kW, for a flow rate of 4.0 g s-1 in the cycle.. |
| 202. | Takayuki Watanabe, Makoto Soyama, Atsushi Kanzawa, Akihiro Takeuchi, Mamoru Koike, Reduction and separation of silica-alumina mixture with argon-hydrogen thermal plasmas, Proceedings of the 1998 11th Symposium on Plasma Science for Materials (SPSM-11) / 4th Asia-Pacific Conference on Plasma Science and Technology (APCPST-4) Thin Solid Films, 10.1016/S0040-6090(99)00071-1, 345, 1, 161-166, 1999.05, [URL], Thermal plasma reduction of a SiO2-Al2O3 mixture for metal production was investigated. The understanding of the reaction mechanism would be applied to metal recovery from coal ash. Thermal equilibrium and free energy of formation of the reaction systems were estimated to predict the evaporated species and to evaluate the predominant reactions. Atomic hydrogen plays an important role in the reduction of the SiO2-Al2O3 mixture. Argon and argon-hydrogen plasma jets were used for the treatment of the SiO2-Al2O3 mixture with various compositions. The argon plasma produces gaseous silicon and SiO from the SiO2-Al2O3 mixture, though the recovered amount was very little, while Al2O3 has not been reduced. The argon-hydrogen plasma produces mainly gaseous silicon with some additions of gaseous SiO and aluminum. Both of the argon and the argon-hydrogen plasmas produce the silicon component collected as the fumes having the purity of 98-99% from the SiO2-Al2O3 mixture.. |
| 203. | Haruo Kawasaki, Takayuki Watanabe, Atsushi Kanzawa, Proposal of a chemical heat pump with paraldehyde depolymerization for cooling system, Applied Thermal Engineering, 19, 2, 133-143, 1999.02, A chemical heat pump system with paraldehyde/acetaldehyde (Pa/A) is proposed for a cooling system. This chemical heat pump is similar to the vapor-compression heat pump. The coefficient of performance (COP) was estimated from equilibrium data. The coefficient of performance (COP) was estimated from equilibrium data. The pressure and the concentration at the reaction equilibrium state were measured for estimation of the performance of the CHP. The COP of the Pa/A system is same as the COP of a vapor-compression heat pump with CFCs.. |
| 204. | Akihiro Takeuchi, Takayuki Watanabe, Selective reaction of Fe-Co-Ni alloys with Ar-Cl2 plasmas, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.63.1_28, 63, 1, 28-33, 1999.01, [URL], Peculiar reactions are known to occur using the features of arc plasmas, high temperature and high chemical activity, according to circumstances that are very effective. However few chemical reactions of arc plasmas have been unknown. Researches in the field of arc plasma reactions have been used hydrogen plasma gas to reduce metal oxides and to add heat to samples excessively, but there are very few thermodynamic data on hydrides which cause the plasma reactions. We have investigated the arc plasma reactions with chlorine because it reacts with metal to form chlorides which have high vapor pressure to be separated peculiarly and there are many available thermodynamic data on chlorides to study the reaction mechanism theoretically, and succeeded in separating iron component from Fe-Co-Ni alloys.. |
| 205. | Takayuki Watanabe, Haruo Kawasaki, Side-reactions in Chemical Heat Pump System with Paraldehyde Depolymerization, kagaku kogaku ronbunshu, 10.1252/kakoronbunshu.25.672, 25, 4, 672-675, 1999.01, [URL], The paraldehyde chemical heat pump generates cold thermal energy with depolymerization of paraldehyde (2,4,6-trimethyl-trioxane). This study investigates the by-products in the heat pump system. Crotonaldehyde (2-butenal) and the polymer of crotonaldehyde are main by-products. The proposed heat pump system has the solution cycle for the by-product. The cooling rate and the coefficient of performance of the proposed system decreases with a decrease in the amount of cyclic solution.. |
| 206. | Takayuki Watanabe, Munemitsu Usui, Effect of atomizing gas on oxidation of droplets in wire arc spraying, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.63.1_98, 63, 1, 98-102, 1999, [URL], Wire arc spraying is one of the most economical thermal plasma coating processes. The disadvantage of wire arc spraying is larger porosity and larger oxide content of the coatings. The purpose of this study is to reduce the oxidation of droplets, and to investigate the effect of atomizing gas on the droplet formation. Lower oxidation at the electrodes results in the stability of the arcing process, and in a decrease in production of AlO in gas phase. The stable arcing process resulting from the lower oxidation leads to the improvement of the coatings. Argon used as the atomizing gas leads to the smallest diameter of the droplets. This is due to the highest temperature of the atomizing gas. Oxidation during the droplet flight is stronger than that at the droplet formation from the electrodes. Argon or nitrogen used as the atomizing gas cannot decrease the oxide content of the droplets.. |
| 207. | Mina Sakano, Takayuki Watanabe, Motofumi Tanaka, Numerical and experimental comparison of induction thermal plasma characteristics between 0.5 MHz and 4 MHz, Journal of Chemical Engineering of Japan, 10.1252/jcej.32.619, 32, 5, 619-625, 1999, [URL], Generation of larger and more stable RF plasmas at atmospheric pressure is important in order for their more widespread adoption in industrial applications. The applied frequency is strongly related to the size of the plasma torch, and also to the distributions of temperature, velocity and species concentration. In this work, the results of the investigation of the characteristics in argon-hydrogen plasmas generated at frequencies of 0.5 MHz and 4 MHz are presented by comparing the two-dimensional modeling approach and the observations of the plasma generated in a 80-mm diameter plasma tube. The fields of flow, temperature and concentration of RF thermal plasmas have been calculated by solving the two-dimensional continuity, momentum, energy, and species conservation equations using a SIMPLEC algorithm. The electromagnetic (EM) fields have been analyzed by solving Maxwell's equations on the basis of the two-dimensional modeling approach. An Ar-H2 atmospheric pressure plasma is successfully operated at 0.5 MHz frequency and up to 75 kW RF power condition. The observations of the plasma region are performed by an air-cooled CCD camera system. Lower induction frequency generates a longer and narrower plasma region. The penetration depth of the time-varying magnetic field into plasmas, namely skin depth, increases with a decrease in frequency. At lower induction frequency, the high temperature region in the plasma exists more inside than at higher induction frequency. Numerical and experimental results show good agreement qualitatively and indicate that lower induction frequency generates a longer and narrower plasma region. The choice of induction frequency is important in determining the optimum torch diameter for the generation of larger RF plasmas.. |
| 208. | Vichan Tangkengsirisin, Atsushi Kanzawa, Takayuki Watanabe, A solar-powered adsorption cooling system using a silica gel-water mixture, Energy, 10.1016/S0360-5442(98)00002-4, 23, 5, 347-353, 1998.05, [URL], Solar-powered adsorption cooling is an attractive solar energy application. Metallic solar collectors with fins have been used to increase the thermal conductivity in solar collectors. This approach has a negative effect due to solar energy loss by reflection and heat loss resulting from the sensible heat of the metal. For these reasons, a direct-radiation absorption collector is proposed here. The effects of the wavelength of the absorbed light, types of silica gel used and additives to improve the absorptivity have been investigated. We have verified that blue silica gel has a better absorptivity in the near-infrared region than white silica gel. The addition of activated carbon to the silica gel improves the desorption rate and regeneration temperature of the packed bed.. |
| 209. | T. Watanabe, X. Wang, E. Pfender, J. Heberlein, Correlations between electrode phenomena and coating properties in wire arc spraying, Thin Solid Films, 10.1016/S0040-6090(98)00409-X, 316, 1-2, 169-173, 1998.03, [URL], Electric arc spraying with dual wires is an economical coating process finding diverse applications. Electrode phenomena, such as oxidation and turbulence have strong effects on the droplet formation, therefore on the coating properties. Low turbulence intensity of an atomizing gas flow can be related to higher frequency and smaller amplitude of the arc voltage fluctuations. Nitrogen reduces oxidation and turbulence at the electrode region. A converging-diverging nozzle provides higher gas velocity with less turbulence. These operations lead to coatings with lower oxidation and lower porosity.. |
| 210. | Haruo Kawasaki, Atsushi Kanzawa, Takayuki Watanabe, Characteristics of Chemical Heat Pump through Kinetic Analysis of Paraldehyde Depolymerization, Journal of Chemical Engineering of Japan, 10.1252/jcej.31.374, 31, 3, 374-380, 1998.01, [URL], The paraldehyde/acetaldehyde (Pa/A) chemical heat pump is used as a cooling system. The present study investigates depolymerization of paraldehyde for a chemical heat pump cycle. The depolymerization rate of paraldehyde was measured in a range from 286 K to 303 K on an acid resin catalyst (Amberlyst 15E). The rate determining step of the depolymerization is the paraldehyde ring-opening step on the cataly t. The depolymerization rate equation on the solid catalyst is described by the Langmuir-Hinshelwood kinetic model. The cooling rate of the Pa/A system at 286 K is estimated from the reaction rate equation. The cooling rate is 10 kW per unit catalyst-weight and higher than other CHPs. The coefficient of performance of the Pa/A system is 6.3.. |
| 211. | Takayuki Watanabe, Haruo Kawasaki, Haruo Kawasaki, Effects of Acid Strength of Solid Catalyst on Cooling Rate of a Chemical Heat Pump with Paraldehyde Depolymerization, kagaku kogaku ronbunshu, 10.1252/kakoronbunshu.24.874, 24, 6, 874-880, 1998.01, [URL], The paraldehyde chemical heat pump is combined with a chemical reaction and a vapor-compression heat pump. The paraldehyde chemical heat pump generates cold thermal energy with depolymerization of paraldehyde (2, 4, 6-trimethyl-trioxane). The cooling rate of the paraldehyde chemical heat pump depends on the catalyst activity of the paraldehyde depolymerization. This study investigates the effect of the acid strength of the solid catalyst on the paraldehyde depolymerization rate, the cooling rate, and the coefficient of performance of the heat pump. The acid strength distribution of Amberlyst 15 E was measured for estimation of the catalyst activity of the paraldehyde depolymerization. The depolymerization rate was measured with Amberlyst 15 E of modified acid strength distribution. The high activity range of the acid strength is — 7.1 |
| 212. | Takayuki Watanabe, Hidehiko Inoue, Atsushi Kanzawa, Sterilization mechanism of escherichia coli by a silent discharge, Kagaku Kogaku Ronbunshu, 24, 1, 142, 1998, A silent discharge has been used for sterilization of Escherichia coli. Silent discharge has advantages such as simple apparatus less energy input and no temperature rise. Silent discharge with air or oxygen is most effective for the sterilization. Nitrogen discharge also has significant effect however argon discharge has no significant effect. Sterilization results from injury caused by the discharge current and from ozone or nitrogen oxide produced by the discharge.. |
| 213. | Takayuki Watanabe, Naoya Akiyama, Atsushi Kanzawa, Proposal of a chemical heat pump with hydrolysis of acetal for cold thermal energy generation, kagaku kogaku ronbunshu, 22, 6, 1421-1422, 1996.12, A chemical heat pump with hydrolysis of acetal is a new heat-driven heat pump system for generation of cold thermal energy. Acetal hydrolysis consists of four elemental reactions. The most feasible rate-controlling step is in the hemiacetal production process. A reaction rate equation has been proposed from the above reaction mechanism. The generation rate of cold thermal energy evaluated from the reaction rate equation is high enough for the heat pump system. Improvement of the separation process is required for practical use of the heat pump system. The reaction system of acetal hydrolysis can be used for chemical heat transport.. |
| 214. | Takayuki Watanabe, Atsushi Kanzawa, Takamasa Ishigaki, Yusuke Moriyoshi, Thermal plasma treatment of titanium carbide powders Part I. Numerical analysis of powder behavior in argon-hydrogen and argon-nitrogen radio frequency plasmas, Journal of Materials Research, 10.1557/JMR.1996.0327, 11, 10, 2598-2610, 1996.01, [URL], Modeling of TiC powder behavior in Ar-H2 and Ar-N2 RF thermal plasmas has been performed as well as the numerical analysis of the plasma fields to investigate the plasma/powders interaction. The heat transfer rate from the plasma to the powders decreases with increasing the powder feed rate and with decreasing the plasma pressure, because of the significant local cooling owing to the presence of the injected powders. These results agree fairly well with the experimental results of our following paper. The modeling herein gives guidance for the rational design of new material processing using thermal plasmas.. |
| 215. | Takamasa Ishigaki, Yusuke Moriyoshi, Takayuki Watanabe, Atsushi Kanzawa, Thermal plasma treatment of titanium carbide powders Part II. In-flight formation of carbon-site vacancies and subsequent nitridation in titanium carbide powders during induction plasma treatment, Journal of Materials Research, 10.1557/JMR.1996.0356, 11, 11, 2811-2824, 1996.01, [URL], The in-flight modification of titanium carbide powders was carried out in radio-frequency (rf) inductively coupled plasmas. The powders were partially melted and evaporated, and then subjected to modifications in morphology, size, and chemical composition. Both the Ar-H2 and Ar-N2 plasma treatments induced the formation of carbon-site vacancies in titanium carbide. The mixing of NH3 to Ar-H2 plasma at the plasma tail, and the Ar-N2 plasma treatment resulted in the partial substitution of carbon by nitrogen. The variation in physical and chemical modification was discussed compared with the predictions by the thermochemical analysis, and the numerically obtained heat transfer of our preceding paper.. |
| 216. | Yuji Kiguchi, Hidetoshi Sekiguchi, Takayuki Watanabe, Atsushi Kanzawa, Heat transfer with tert-butanol dehydration reaction, Kagaku Kogaku Ronbunshu, 22, 2, 402-403, 1996, The heat transfer in an endothermic tert-butanol dehydration reaction was investigated under the condition that the temperature difference between the heat source and the heating medium was extremely small. The conversion per unit volume of catalyst is dependent on the residence time of heating medium, both in a fluidized catalyst bed and in a fixed catalyst bed. The heat flow has a maximum with the mass flow rate of heating medium. The heat flow by this reaction per unit mass flow rate of heating medium is related to the conversion.. |
| 217. | Takayuki Watanabe, Atsushi Kanzawa, Second law optimization of a latent heat storage system with PCMS having different melting points, Heat Recovery Systems and CHP, 10.1016/0890-4332(95)90044-6, 15, 7, 641-653, 1995.10, [URL], The exergy efficiency, as well as the charging and discharging rates, in a latent heat storage system can be improved by use of the PCMs having different melting points. The melting point distribution of the PCMs has substantial effects on the exergy efficiency. The optimum melting point distribution of the PCMs has been estimated from numerical simulations and also from simple equations. The fast charging or discharging rate leads to high exergy efficiency.. |
| 218. | Yuji Kiguchi, Takayuki Watanabe, Atsushi Kanzawa, Heat transfer characteristics in tert-butanol dehydration reaction used for heat transport, kagaku kogaku ronbunshu, 10.1252/kakoronbunshu.21.746, 21, 4, 746-752, 1995.01, [URL], The reaction system of tert-butanol/isobutene/water was considered for use in chemical heat transport. In this study, the heat transfer characteristics in an endothermic tert-butanol dehydration reaction which occurred in the heat supply side of this reaction system was investigated. The heat flow was obtained by measuring the reactant composition change and temperature change in the catalyst bed. The heat flow consists of reaction heat, the latent heat of isobutene, and sensible heat in this reaction system. Numerical calculations based on a two-dimensional model were carried out and the results showed good agreement with experimental ones. It was noticed that the heat flow with chemical reaction was much higher than without reaction. These results indicated that the dehydration reaction promoted the heat transfer rate, because of the increase in temperature difference between the heating medium and the wall by making use of chemical reaction for heat transport. The apparent local heat transfer coefficient with chemical reaction was higher than without reaction. The possibility of a high efficiency heat transport which used this reaction system was suggested.. |
| 219. | Y. Kiguchi, Takayuki Watanabe, A. Kanzawa, Heat-transfer characteristics in tert-butanol dehydration reaction used for heat transport, Heat Transfer - Japanese Research, 24, 3, 288-302, 1995, The heat-transfer characteristics in an endothermic tert-butanol dehydration reaction which occurred in the heat-supply side of this reaction system was investigated. The heat flow was obtained by measuring the reactant composition change and temperature change in the catalyst bed. The heat flow consists of reaction heat, and latent heat of isobutene, and sensible heat in this reaction system. Numerical calculations based on a two-dimensional model were carried out and the results showed good agreement with experiment. The heat flow with chemical reaction was much higher than without reaction. These results indicated that the dehydration reaction promoted the heat-transfer rate, because of the increase in temperature difference between the heating medium and the wall by making use of chemical reaction for a heat transport. The apparent local heat-transfer coefficient with chemical reaction was higher than without reaction.. |
| 220. | Takayuki Watanabe, Hisashi Kikuchi, Atsushi Kanzawa, Enhancement of charging and discharging rates in a latent heat storage system by use of PCM with different melting temperatures, Heat Recovery Systems and CHP, 10.1016/0890-4332(93)90025-Q, 13, 1, 57-66, 1993.01, [URL], A latent heat storage module with rapid charging and discharging rates has been developed. The heat storage module consisted of horizontal cylindrical capsules filled with three types of PCM with different melting temperatures. A numerical model has been developed to predict the transient behavior of the heat storage module. Both the experimental and numerical results showed some improvements in charging and discharging rates by use of a "three-type" PCM.. |
| 221. | Takayuki Watanabe, I. Kuribayashi, T. Honda, A. Kanzawa, Deformation and solidification of a droplet on a cold substrate, Chemical Engineering Science, 10.1016/0009-2509(92)87006-C, 47, 12, 3059-3065, 1992.01, [URL], The numerical simulation of a droplet deformation and solidification on a cold substrate was performed with SMAC algorithm. The substrate temperature histories and the degree of deformation were measured by use of a droplet of n-eicosane and n-cetane. The numerical results showed good agreement with the measured ones. The solidification of a droplet on a substrate occurs immediately after the deformation. A simple model to estimate the deformation and the solidification time was also proposed. Both the normalized deformation and solidification time are proportional to the 0.2 power of the Reynolds number. The solidification time is two orders of magnitude higher than the deformation time.. |
| 222. | Takayuki Watanabe, Naoto Tonoike, Takuya Honda, Atsushi Kanzawa, Flow, temperature and concentration fields in reactive plasmas in an inductively coupled rf discharge —Characteristics in argon-oxygen and argon-nitrogen thermal plasmas—, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.24.25, 24, 1, 25-32, 1991.01, [URL], Numerical simulations of RF argon-oxygen and argon-nitrogen thermal plasmas under atmospheric pressure were performed. Two-dimensional continuity, momentum, energy and species equations were solved simultaneously with the electromagnetic equations by using the SIMPLER algorithm. Dissociation and recombination rates of oxygen or nitrogen in the plasmas were taken into account in the numerical model. Distributions of the plasma enthalpy and concentration were measured with a water-cooled probe. The numerical results were in good agreement with the experimental ones. The argon-oxygen plasma has a strong recirculating eddy. 02 is dissociated completely downstream from the eddy except near the tube wall. In the argon-nitrogen plasma, the mass fraction of N2 is significant even in the high-temperature region.. |
| 223. | Hisashi Kikuchi, Takayuki Watanabe, Takuya Honda, Atsushi Kanzawa, Effect of Phase Change Material(PCM) m.p. Distribution on Latent Heat Storage, kagaku kogaku ronbunshu, 10.1252/kakoronbunshu.16.982, 16, 5, 982-989, 1990.01, [URL], Charge and discharge heat transfer rates were investigated by using a latent heat storage reservoir with sloped distribution of m.p. The heat storage reservoir consisted of 45 vertical cylindrical capsules. The heat transfer fluid was air and paraffin wax within the capsules was the phase change material (PCM). Melting and solidification time of the PCM were measured for three kinds of m.p. distributions. The charge and discharge heat transfer rates were estimated from the melting and solidification time respectively. Numerical results agreed with the experimental results. For the PCM with constant m.p. the charge and discharge heat transfer rates decreased downstream from the air inlet of the reservoir. The charge and discharge heat transfer rates increased by sloping m.p. distribution. The analytical investigation showed that m.p. distribution with too large or too small slope was not suitable.. |
| 224. | Takayuki Watanabe, Kazuhiko Yanase, Takuya Honda, Atushi Kanzawa, The flow, temperature and concentration fields in a radio-frequency argon-helium plasma, JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 10.1252/jcej.23.389, 23, 4, 389-395, 1990.01, [URL], The numerical simulation of an RF argon-helium thermal plasma under atmospheric pressure was performed. The two-dimensional continuity, momentum, energy and species equations along with the electromagnetic equations were solved simultaneously with the SIMPLER algorithm. The physical properties of the argon-helium mixed plasma were taken into account. The plasma velocity, temperature and concentration were measured with a water-cooled probe. The numerical results were in good agreement with the experimental ones. The results demonstrate the existence of an inward radial flow induced by the electromagnetic pumping effect. The recirculating eddy formed by the inward radial flow becomes stronger in an argon-helium plasma than that in an argon plasma. A uniform distribution of helium concentration is obtained upstream from the discharge region.. |
| 225. | T. Watanabe, T. Honda, A. Kanzawa, Concentration of a plasma energy flow by a blowing gas, International chemical engineering, 29, 4, 663-670, 1989.10, Experiments were carried out on the concentration of the energy flow density of a thermal argon plasma and the concentration of the heat flux from a plasma jet to a flat plate by an injected gas blowing radially inwards through a slit around the nozzle outlet. The Q-value, which is analogous to the sharpness of the resonance curve of an electrical circuit, and which is defined as the ratio of the maximum energy flow to its half width, was used to evaluate the degree of concentration achieved. Both Q values attained maxima with a radially blowing gas at about the same rate of flow.. |
| 226. | Takayuki Watanabe, Takuya Honda, Atsushi Kanzawa, Concentration of a Plasma Energy Flow by a Blowing Gas, kagaku kogaku ronbunshu, 10.1252/kakoronbunshu.14.1, 14, 1, 1-7, 1988.01, [URL], Control of energy flow density is required when a plasma flow is used for material treatment. For this purpose, hydrodynamic, magnetic or mechanical control may be used. The object of this study is to suppress the outward radial flow of the plasma flow. Sharpness of heat flux distribution to a flat plate is required in plasma cutting. Therefore, the following two experiments were carried out. One was to sharpen the enthalpy flow distribution of a thermal argon plasma jet, and the other was to sharpen the heat flux distribution to the plate. These energy flow densities of the plasma flow were raised by an inward radial blowing gas. This radial blowing gas was injected through a circumferential slit around the jet nozzle exit. Q-value, defined as the ratio of maximum energy flow to the half-value width, is adopted as an evaluation of sharpness. Not only the Q-value of enthalpy flow of the plasma but also that of heat transfer to the plate reached maximum with the radial blowing gas flow rate.. |
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