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Takayuki Watanabe Last modified date:2021.06.04

Professor / Product System Engineering
Department of Chemical Engineering
Faculty of Engineering

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Thermal plasmas have attracted extensive attention due to their unique advantages, and it is expected to be utilized for a number of industrial applications such as plasma spraying, film deposition, decomposition of harmful materials, recovery of useful materials from wastes, and synthesis of high-quality and high-performance nanoparticles. The advantages of thermal plasmas including high enthalpy to enhance reaction kinetics, high chemical reactivity, and oxidation or reduction atmospheres in accordance with required chemical reactions are beneficial for innovative processing. .
Academic Degree
Dr. of Engieering
Country of degree conferring institution (Overseas)
Field of Specialization
Plasma Chemistry, Plasma Processing
Total Priod of education and research career in the foreign country
Outline Activities
Thermofluid and Heat Transfer Phenomena in Thermal Plasma System
Environmental Processing using Plasma Chemistry
Nanomaterial Synthesis using Thermal Plasmas
Green Process using Atmospheric Plasmas
Next Generation Energy System Development
Lunar Resources Utilization
Research Interests
  • Thermofluid and Heat Transfer Phenomena in Thermal Plasma System
    Environmental Processing using Plasma Chemistry
    Nanomaterial Synthesis using Thermal Plasmas
    Green Process using Atmospheric Plasmas
    Next Generation Energy System Development
    Lunar Resources Utilization
    keyword : Thermal plasma, Atmospheric Plasma, Nanoparticle Synthesis, Waste Treatment, Plasma Chemistry, Plasma Processing
Academic Activities
1. 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, Interplanetary dust particles contain glass with embedded metals and sulfides (GEMS) grains (i.e., amorphous silicate grains with diameters of a few hundred nanometer containing Fe nanoinclusions and Fe sulfide particles), which are considered to be among the building blocks of the solar system.
For exploring that GEMS grains formed during the condensation process, condensation experiments were carried out in Si–Mg–Fe–Al–Ca–Ni–O and Mg–Si–Fe–Ca–Al–Na–O systems using an induction thermal plasma furnace. In all experimental runs, spherical grains (mostly composed of amorphous silicate) and with diameter <100 nm were condensed. The analysis of the amorphous silicates, which were classified as Mg rich or Si rich, indicated that the condensates formed via melting. Fe led to the formation of fine magnetite grains in most of the oxidative experiments, to 10-nm metal grains (i.e., kamacite and taenite) under intermediate redox conditions, and to 30- to 100-nm Fe silicide grains (i.e., gupeiite, xifengite, and fersilicite) in most of the reductive experiments. Under intermediate redox conditions, some amorphous silicate particles showed multiple Fe inclusions with textures very similar to those of GEMS grains except for FeS, indicating that GEMS could form by condensation of high-temperature gases.
Considering the nucleation and growth of solids from high-temperature gas during cooling, we infer that GEMS grains formed either in the local environment of our protoplanetary disk (and be related to chondrule formations) or around evolved stars related to II-P SNe and AGB type stars..
2. 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, 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..
3. 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, 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.
4. 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, 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..
5. 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, 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..
6. 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, 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..
7. 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, 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..
8. 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, 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..
1. Hydrogen reduction of lunar soil simulants by a fixed bed reactor has drawbacks of a decrease in the reaction rate due to temperature distribution and uneven filling of the sample. One of the processes to solve these problems is the fluidized bed. Hydrogen reduction experiments have been conducted on lunar soil simulants of 100 g by a fluidized bed reactor. Although the fluidized bed gives uniform temperature distribution and high efficiency in the reaction, gravity and the powder characteristics have a significant effect on the fluidization. In addition, continuous operation is difficult for the fluidized bed reaction system.
In this study, a continuous reactor has been built for hydrogen reduction of lunar soil simulants. The continuous screw reactor can handle a wide variety of samples for continuous operation. The reaction efficiency is high due to the large contact area of the sample as it passes through the reactor while rotating.
The developed system will be used for hydrogen reduction of metal oxides with the aim of industrial application. Production of oxygen-deficient metal oxides are expected to be used as highly functional materials in various fields., [URL].
2. Takayuki Watanabe, Manabu Tanaka, Hiiro Murakami, Soon-Ho Kim, and Myeong-Hoon Lee, Water Thermal Plasma Characteristics with Mist Generation for Waste Treatment, 4th Asia Pacific Conference on Plasma Physics, 2020.10, [URL], 基調講演:An innovative water plasma torch with mist generation was developed for stable water plasma under atmospheric pressure. The purpose of this study is to investigate the arc fluctuation phenomena in the water plasma torch with mist generation. High-speed camera observation synchronized with arc voltage measurement was performed to understand the arc fluctuation. Results revealed that the arc fluctuation in the developed torch can be classified as perfect restrike mode. Effect of arc current on the discharge characteristics was examined. Another work aims to treat bisphenol A (BPA) by the water plasma reactor, and the experiment results showed that the decomposition rate of BPA could be over 99.2% at 9.5 A and the monocyclic aromatics were suggested as main by-product. Moreover, the operation condition has been proved with effect for the decomposition rate of BPA and by-product generation..
3. Takayuki Watanabe, Thermal Plasma Characterization and Process Control Diagnostics for Innovative Material Processing, The 11th Asia-Pacific International Symposium in the Basics and Applications of Plasma Technology, 2019.12, [URL], 基調講演:Thermal plasmas are expected to be utilized for a number of innovative industrial applications such as decomposition of harmful materials, recovery of useful materials from wastes, and synthesis of high-quality and high-performance nanoparticles. The advantages of thermal plasmas including high enthalpy to enhance reaction kinetics, high chemical reactivity, and oxidation or reduction atmospheres in accordance with required chemical reactions are beneficial for innovative processing.
The experimental and modeling efforts on thermal plasma characteristics has been devoted to industrial application. However, thermal plasma characteristics remain to be explored in spite of these efforts. The electrode phenomena are one of the most considerable issues, because it determines the processing performance in thermal plasmas. The objective of the study is to investigate the physical and chemical phenomena in thermal plasma processing for innovative material processing..
4. Hiroki Munekata, Manabu Tanaka, Takayuki Watanabe, Discharge Characteristics of Water Plasma with Mist Generation, 24th International Symposium on Plasma Chemistry, 2019.06, [URL], 本研究では水プラズマを用いて,従来のプロセスでは処理できない難分解物質を処理する方法を開発している。水プラズマ中には電子のみならずイオンや原子などの重い粒子も高温度であり,かつ各種のラジカルを豊富に有しており,処理対象物質を短時間で高温にすることができる。プラズマ中のラジカルによる新規の廃棄物処理として,ゴミから水素を製造するプロセス開発を行っている。.
5. Development of novel thermal plasma systems is introduced in this paper. Fundamental researches such as electrode phenomena and arc fluctuation are essential for revealing thermal plasma characteristics. These efforts lead to innovative industrial applications of material processing and waste treatment using thermal plasmas..
6. Thermal plasmas have attracted extensive attention due to their unique advantages, and it is expected to be utilized for a number of industrial applications. The advantages of thermal plasmas including high enthalpy to enhance reaction kinetics, high chemical reactivity, and oxidation or reduction atmospheres in accordance with required chemical reactions are beneficial for innovative processing. Water plasma waste treatment is one of green technology for the utilization of organic wastes. Since a large amount of H, O, and OH radicals are generated in the water plasma, decomposition and syngas production are accelerated in the treatment of water-soluble organic compounds..
7. Takayuki Watanabe, Shuhei Yoshida, Tadashi Nonaka, Takahiro Sone, and Manabu Tanaka, Oxide Nanoparticle Synthesis by Thermal Plasmas for Lithium Ion Battery Electrode, The 4th Annual Symposium of Nonferrous Metallurgy of China, 2017.11, 招待講演:リチウムイオン電池の負極材料としては,グラファイトの10倍以上の理論容量を有していることからシリコンが期待されているが,シリコンの使用に関連する課題として充放電時の体積変化の問題がある。この課題を解決するアプローチとして,熱プラズマによるアモルファスシリコンやカーボン被覆シリコンナノ粒子の合成が期待されている。一方,正極材料は高エネルギー密度,良好なサイクル特性,安全性,低コストなどが要求課題となっており,正極材料をナノ粒子化することで比表面積が増大することから反応速度の向上が見込まれ,この分野でも熱プラズマによる正極材料ナノ粒子の合成が期待されている。本論文ではではリチウムイオン電池の現状と将来展望をはじめとし,熱プラズマによるナノ粒子合成の特徴を議論し,今後のリチウムイオン電池の材料開発における熱プラズマの役割を議論した。.
8. Takayuki Watanabe, Yutaro Ozeki, and Manabu Tanaka, Thermal Plasma Characterizations for Environmental Application, The 11th Asian-European International Conference on Plasma Surface Engineering, 2017.09, 招待講演:水プラズマは水を原料としてプラズマを発生させる手法である.豊富なH,O,OHラジカルによる高活性およびプラズマの持つ高エンタルピーという特長から,物質の大量処理を見込んだ廃棄物処理技術への応用が検討されている..
9. Takayuki Watanabe, Water Thermal Plasmas for Environmental Application, The 10th Asian-European International Conference on Plasma Surface Engineering, 2015.09, 招待講演:水プラズマは水を原料としてプラズマを発生させる手法である.豊富なH,O,OHラジカルによる高活性およびプラズマの持つ高エンタルピーという特長から,物質の大量処理を見込んだ廃棄物処理技術への応用が検討されている..
10. Takayuki Watanabe, Multi-Phase AC Arc for Innovative Glass Melting, 13th European Plasma Conference, 2014.06, 基調講演:プラズマプロセッシングの開発には電極におけるアークの物理現象の解明が重要である。新しいプラズマプロセッシングのために開発した新規の多相交流アークに関する講演を行った。このプラズマは直径が100 mm以上のアークを発生することができ,エネルギー効率が高いことが利点である。.
11. Takayuki Watanabe, Innovative Thermal Plasma Processing from Fundamental Research, 21st International Symposium on Plasma Chemistry, 2013.08, [URL], 基調講演:プラズマプロセッシングの開発には電極におけるアークの物理現象,新規のプラズマ発生方法,プラズマの流体解析等の基礎研究が必須である。これらの基礎研究に基づく新しいプラズマプロセッシングの開発に関する基調講演を行った。新規のガラス溶融技術として注目されているインフライト溶融技術は,造粒したガラス原料を熱プラズマ中で瞬時に溶解する方法である。このインフライト溶融は,シーメンス炉の複雑な原料溶解過程を一本の熱プラズマで置き換えてしまう方式であり,この技術が成功すれば大半のガラス製造プロセスに適用することが可能となり,溶融炉の大幅な小型化と消費エネルギーの大幅な削減ができる。.
Membership in Academic Society
  • International Plasma Chemistry Society
  • The Japan Society of Applied Physics
  • The Society of Chemical Engineers, Japan
  • The Japan Society of Mechanical Engineers
  • The Japan Society of Plasma Science and Nuclear Fusion Research
  • The Society of Inorganic Materials, Japan
  • Smart Processing Society for Material, Environment & Energy
  • Development of innovative plasma processing and establishment of plasma analysis
  • Waste Treatment by Plasmas under Atmospheric Pressure
  • Modeling of plasma flows
Educational Activities
Fundamental Physicsfor Freshman, Fundamental Fluid Dynamics and Chemical Engineering Fluid Dynamics in Undergraduate school. Environmental Fluid Transport Phenomena and Advanced Chemical Engineering Fluid Dynamics in Graduate school.