Language：English   Publishing type：Research paper (scientific journal)  

Polymeric materials are widely used in hydrogen energy system such as FCEV and hydrogen refueling stations under high-pressure condition. The permeation property (coefficients of permeation, diffusion and solubility) of polymers under high-pressure hydrogen condition should be discussed as parameters to develop those devices. Also the property should be determined to understand influence of the compression by the pressure on polymer materials. A device which can measure gas permeation property of polymer materials accurately in equilibrium state under high-pressure environment is developed, and the reliability of the measurements is ensured. High-pressure hydrogen gas permeability characteristics up to 100 MPa are measured for high-density polyethylene. An advantage of the method is discussed comparing with the non-equilibrium state method, focusing on the hydrostatic pressure effect. Deterioration of hydrogen permeability is observed along with the decrease of diffusion coefficient, which is supposedly affected by hydrostatic compression effect with the increase of environment pressure.

DOI： 10.1016/j.ijhydene.2020.07.215

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After 90 MPa hydrogen exposure, the time resolved infrared spectroscopy and the hydrogen content measure- ment for bisphenol A polycarbonate (PC) during hydrogen desorption process were conducted. The foreign peak at 4125 cm−1 in the infrared spectra of high-pressure hydrogen exposed PC was observed. Judging from the proportion of the absorbance of the peak to hydrogen content and the molar concentration of the penetrated hydrogen in PC, the peak was assigned to the H-H stretching of penetrated hydrogen molecule in PC. The hydrogen molecule is considered to be isolated by the PC molecular chain.

DOI： 10.1016/j.cplett.2019.137053

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A quantitative evaluation of the bulk damage level after high-pressure hydrogen exposure for the hydrogen compatible polymeric materials are developed. The bulk damage level of the internal damage induced by high-density polyethylene (HDPE) after 90 MPa hydrogen exposure repetition were evaluated. Based on the light scattering by the internal damage, we established a quantitative damage index in terms of the light transmittance as brightness (B) of transmitted light digital image of the HDPE disk specimen; the relative extinction ratio of transmitted light intensity (β_r) as the brightness change ratio. β_r was obtained for each pixel of the image for whole specimen. According to the results of the specimen, β_r around the central region of specimen was higher than that of the edge region. Averaged β_r around the center of specimen (β_r¯) logarithmically increased with the increase in exposure number (N_ex). Judging from the results, the internal damage tends to generate at the center of specimen, and the internal damage amount increased with increase in N_ex.

DOI： 10.1016/j.ijhydene.2019.07.035

Language：Japanese   Publishing type：Research paper (scientific journal)  

要 旨
カーボンナノチューブ(CNT)はナノサイズの直径で長さが μm 以上と非常に高いアスペクト比の繊維状 炭素材料であることから，他の材料との複合材料において 少ない添加で高い電気伝導性，熱伝導性や強度特性を発現 することができる.本研究では，CNT/ゴム複合材料の高 圧水素特性を評価し，CNT，その中でも単層カーボンナノ チューブ (SWCNT) をゴム中に均一に分散させることで，高 圧水素に曝露後の水素侵入量が低く，かつ，体積変化も小 さくすることができることを明らかとした.また，CNT の 分散度と高圧水素特性の関係から，水素侵入量は組成が支 配的で，体積変化は分散構造が支配的であることが示唆さ れた.本報のカーボンナノチューブ/ゴム複合材料は，その 高圧水素特性から高圧水素環境下での変化が小さく，高圧 水素環境下における高耐久シール材として期待される.

DOI： 10.1295/koron.2019-0008

Language：Japanese   Publishing type：Research paper (scientific journal)  

Relation between high-pressure hydrogen resistance and morphology on blends of nylon 6-66 and ethylene vinyl alcohol copolymer with 1,2-diol side chains

DOI： 10.2472/jsms.68.34

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A series of unfilled acrylonitrile butadiene rubber (NBR) composites, which consists of several types of NBR with acrylonitrile (AN) monomer unit ratio (Х AN ) and sulfur or dicumyl peroxide (DPO) as a vulcanizer, were exposed to 90 MPa hydrogen gas to measure the saturated hydrogen content: C.H(0) and the volume change ratio when the sample volume is the maximum: VMAX/V0. The aim of this paper is to reveal the dominant characteristics for C.H(0) and VMAX/V0 of unfilled NBR composites. Mechanical properties, ХAN, the mo- lecular weight of the number average molecular weight between the effective crosslinks (Mef), the molecular weight between the chemical crosslink (MC) and the fractional free volume (FFV) were employed to examine the relationship between the characteristics and C.H(0) and VMAX/V0 of the NBR composites. Judging from the results of the comparisons of C.H(0) and VMAX/V0 with ХAN, Mef, MC and FFV, it is revealed that C.H(0) and VMAX/V0 were dominantly correlate with FFV and MC, respectively.

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The role of dimethallyl carbonate (DMAC), which has a multiple functional group, as an additive in electrolyte have been studied for improving thermal stability of lithium ion batteries (LIB). During the initial charging of the negative electrode with an electrolyte that contains the DMAC additive, film formation occurs near 1 V vs. Li/Li+. Furthermore, increases in the amount of DMAC additive are accompanied by increases in the height of the dq/dV peaks and film formation progresses. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) results show that increasing the amount of DMAC additive promotes the formation of aliphatic hydrocarbons of C5 or more in the Solid-Electrolyte-Interfase (SEI) and polymerization proceeds. The temperature programmed desorption mass spectrometry (TPD-MS) results show that the DMAC additive raises the peak temperature for CO2 generation to 100◦C or higher. The DMAC additive suppresses self discharge of LIB and suppresses the increase in direct current resistance (DCR) after storage at 50◦C.

DOI： 10.1149/2.0331805jes

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Unlike for other gases, the volume change of the rubber materials due to the sorption of hydrogen is very low and hence difficult to measure. Conversely, the volume change occurring during decompression is significantly more than that occurring during sorption equilibrium. The aim of the present experiment is to measure the significantly different volume changes due to hydrogen content during the two stages of a high-pressure exposure cycle at room temperature simultaneously. Spherical samples of unfilled NBR were tracked by two high and low-resolution devices, with a good connection of measurements series in both conditions. The effect of thermal expansion (Joule-Thomson effect) and the compressibility contributions were removed to measure the term due to hydrogen sorption precisely.

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Properties of polymer solid electrolytes composed of poly(ethylene carbonate) [PEC], lithium bis(trifluoromethane sulfonimide) [LiTFSI, LiN(CF3SO2)2] and propylene carbonate [PC] as plasticizer have been analyzed using Raman spectroscopy and ac impedance spectroscopy. Including 14 wt% of PC in the PEC based polymer electrolyte with LiTFSI concentration of 0.2 mol per polymer repeat unit, made it possible to increase the ionic conductivity (σ) by one order of magnitude to a practical-use level of 1.3 mS cm−1 at 20°C. The correlation between σ and temperature fits well the Williams-Landel-Ferry equation, so it is considered that ionic conductivity depends on thermal activation of the polymer chains. From the correlation between σ and temperature, it is concluded that PC (with greater mobility than the polymer chains) partly solvates with lithium ions, and σ is improved by lowering its activation energy.

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The redox reaction of tetravalent Mn4 + ions has attracted much interest since it is considered that this reaction is closely related to the generation of high capacity in layered cathodes with excess lithium.
We considered that to investigate materials, which include tetravalent Mn4 + ions and have a different crystal structure from Li2MnO3, is valuable for understanding the reaction mechanism. The result will reveal whether Mn4 + ion in the Li2MnO3 structure is essential or only existence of Mn4 + ion is sufficient for appearance of the high capacity. In this work, we investigated Li-rich Li1 + xMn2 − xO4 (x = 0.20, 0.25, 0.30, 0.33) stoichiometric spinels. For a Li content of x = 0.33, a capacity of 50 mAh g− 1 was observed in 5-V region. It is possible that the Li-rich spinel includes a small amount of Li 2MnO 3 impurity, which exhibits the 5-V plateau. No significant changes in lattice constants are observed from x = 0.25 to 0.33, which indicates generation of Li 2MnO 3. We estimated the amount as 9.2 wt.% for x = 0.33 by standard addition analysis, and true Li concentration of the spinel component as 0.23. However, the observed 5-V capacity cannot be attributed to only the impurity phase of Li 2MnO 3, because the specific capacity must exceed 540 mAh g − 1 to explain it. It is considered that the observed 5-V capacity is caused by two components of the Li-rich spinel and the other phase like a composite material of Li 2MnO 3/Li-rich spinel. The 5-V capacity for the pure spinel component estimated by extrapolating the 5-V capacity vs. impurity-concentration plot is 7.9 mAh g − 1.

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Fuel cell systems, such as those used in electric vehicles require lightweight hydrogen fuel storage. Polymer composites are candidate materials for storage vessels requiring high fracture resistance for high pressure cycling, as well as high thermal conductivity. Here, we investigate 4,4′-diglycidyloxybiphenyl (DGOBP) epoxy for such applications, and clarified the relationship between the hydrogen penetration properties and the ordered structure of the epoxy. We controlled the ordered structure of the DGOBP polymer by adjusting the curing temperature of a 4,4′-diaminodiphenyl methane (DDM) curing system. We obtained a series of cured DGOBP with DDM samples with crystallinity values of 19%, 27%, 32%, and 36%, corresponding to curing temperatures of 130, 120, 110, and 100 °C, respectively. The thermal conductivities of these samples were 0.26–0.31 Wm−1 K−1. Cured DGOBP showed hydrogen contents of 403–1271 ppm (25–75% smaller than that of conventional epoxies). Liquid crystalline epoxy polymers can be a candidate material for hydrogen storage systems requiring well-controlled hydrogen penetration properties.

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The deterioration of rubber composites filled with different types of fillers was analyzed to determine the influence of cyclic high-pressure hydrogen exposure. The mechanical properties of acrylonitrile butadiene rubber (NBR) unfilled and filled with carbon black or silica were evaluated. The storage modulus of the silica-filled NBR decreased in the rubbery state as the number of exposures increased, while those of the unfilled and carbon black-filled NBR did not change. Changes in the chemical structure such as hydrogenation or chain scission were not detected in the solid state NMR spectra of the exposed composites. However, deterioration of the filler–gel structure formed at the interface of the filler and polymer was observed in the silica-filled NBR. Fracture of this filler–gel structure occurred due to fatigue in the silica-filled NBR resulting from a reduction of the elastic storage modulus caused by cyclic high-pressure hydrogen exposure.

Language：English   Publishing type：Research paper (scientific journal)  

Properties of polymer electrolytes composed of poly(ethylene carbonate) [PEC] and lithium bis(trifluoromethane sulfonimide) [LiTFSI, LiN(CF3SO2)2] have been analyzed using Raman spectroscopy, dynamic mechanical analysis (DMA) measurements, and ac impedance spectroscopy. The lithium ion transference number of a PEC based polymer electrolyte is 0.4, which is 4 times higher than that of a poly(ethylene oxide)[PEO] based polymer electrolyte. The glass transition temperature of a PEC based polymer electrolyte decreases with the increase of LiTFSI concentration above 0.2 molar ratio of LiTFSI to repeat unit of the carbonate in PEC. Raman spectra show that the abundance ratio of undissociated LiTFSI increases at LiTFSI concentration above 0.2 molar ratio. Moreover, ionic conductivity of a PEC based polymer electrolyte increases with the increase of LiTFSI concentration above 0.2 molar ratio. The highest ionic conductivity is 0.47 mS cm− 1 at 20 °C.

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The layered complex cathode has attracted much interest recently due to its high capacity, which exceeds 250 mAhg−1. On the other hand, it also shows large voltage hysteresis which causes energy loss when applied as a practical battery material. It has been reported that the hysteresis is an intrinsic bulk property, and the phenomenological model due to the migration of transition metal has been also proposed. Then, it is considered that to study the hysteresis for various compositions of transition metal is valuable to clarify the phenomenon. In this work, the layered complex cathode of 0.5Li2MnO3-0.5LiNi1/3Co1/3Mn1/3O2 was investigated. The results are discussed in comparison with the previous reports for 0.5Li2MnO3-0.5LiMn0.5Ni0.5O2. Investigating dQ/dV profilesrevealed that redox peaks at around 3.75 V showed small dependency on composition of transition metal, while it seemed that a reduction peak at 3.26 V was independent on the composition. Precise measurement of open circuit potential vs. capacity characteristics demonstrated that the energy dissipation during a cycle was abut 26 kJmol−1.

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This paper presents the effects of hydrogen pressure, ambient temperature and pressure cycle pattern on fracture behavior of O-rings moulded from a peroxide-crosslinked EPDM rubber with white reinforcing filler under cyclic exposure to high-pressure hydrogen gas. By using a developed durability tester which enables the O-rings to expose cyclically high-pressure hydrogen gas, pressure cycle tests were performed at hydrogen pressures ranging from 10 to 70 MPa and ambient temperatures ranging from 30 to 100 °C under two pressure cycle patterns (test frequencies). The cyclic hydrogen exposure caused cracks in the O-rings, and their crack damage became more serious with an increase in the hydrogen pressure and the ambient temperature. The serious crack damage under high temperature is believed to be due to degradation of mechanical properties with increasing ambient temperature. At a hydrogen pressure of 10 MPa, cracks (blisters) caused by bubbles formed from supersaturated hydrogen molecules after decompression were observed. At a hydrogen pressure of 35 MPa or more, a large volume increase of the O-rings was observed by swelling; then, its volume increase induced extrusion fracture of the O-rings in addition to blister fracture. The crack damage also became more serious with a decrease in test frequency. The effect of the test frequency on the crack damage of the O-rings is presumed to be attributed to time-dependent crack growth behavior of the EPDM rubber.

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The influence of high-pressure hydrogen on the chemical structure of organic materials is essential for designing suitable materials for the safe and efficient use of hydrogen. In this paper, we clarify the cause and mechanism of “explosive failure by decompression” (XDF) in rubber used under high-pressure hydrogen circumstances, and the chemical structure of acrylonitrile butadiene rubber (NBR), which is commonly used for O-rings, was analyzed after exposure to hydrogen at 100 MPa. Solid-state nuclear magnetic resonance (NMR) and liquid-phase NMR for 1H and 13C, as well as infrared and Raman spectroscopy, were employed for the evaluation. The results show no evidence of structural changes in NBR such as hydrogenation of the olefinic bonds in butadiene or of the cyano groups in acrylonitrile.

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To identify components with different spin–spin relaxation times, T2, in the solid-echo pulse proton nuclear magnetic resonance (1H-NMR) spectra of crude acrylonitrile (AN)–butadiene rubbers (NBRs) with five different AN contents, we tried to understand the inhomogeneity in the crude NBRs in terms of their microstructures and molecular mobilities. The results of small-angle X-ray scattering, differential scanning calorimetry and dynamic mechanical analysis showed that crude NBRs have a single-phase and homogeneous morphology on the nanoscale. The microstructure of the crude NBRs shows alternately copolymerized AN–butadiene (BU) and BU block sequences, as indicated by 1H-NMR spectra. The T2 of the crude NBRs revealed three components with different molecular mobilities, even in homogeneous samples. The content of the highest-mobility component with T2l is negligible. Judging from the AN content dependence of the 1H ratio of these components, the low-mobility component with T2s and high-mobility component with T2m were assigned to the alternately copolymerized AN–BU sequences and BU block sequences, respectively.

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This study presents the effects of the type of polymer and gas on blister fracture in terms of visualizing O-ring behavior under high-pressure gas. To visualize blisters (internal cracks) by optical microscopy, transparent EPDM and VMQ O-rings were molded, and a special viewable high-pressure vessel with a glass viewport was developed. The O-ring specimens were exposed to high-pressure hydrogen, helium, and nitrogen gases at 10 MPa under room temperature, 25°C, after which these gases were rapidly decompressed for 0.3 seconds. The blister fracture occurred in EPDM but not in VMQ even though the two materials had the same Young's modulus. It is presumed by AFM observation that the difference in microstructure at sub-micrometer level between EPDM and VMQ influenced their blister initiation. The blister damage of the transparent EPDM O-ring in nitrogen gas was the most serious, while that in the helium gas was the slightest. The reason why the blister damage of the O-ring in the helium gas was the slightest is considered to be because solute helium gas diffused out from the O-ring after decompression faster than the other gases.

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Rubber O-rings exposed to high-pressure hydrogen gas swell, and the volume increase induced by swelling influences tensile properties of the O-rings. Samples of nonfilled (NF), carbon black-filled (CB), and silica-filled (SC) sulfur-vulcanized acrylonitrile-butadiene rubber were exposed to hydrogen at 30 °C and pressures of up to 100 MPa, and the effect of hydrogen exposure on the volume increase, hydrogen content, and tensile properties was investigated. The residual hydrogen content, measured 35 minutes after decompression, increased with increasing hydrogen pressure in the range 0.7-100 MPa for all three samples. In contrast, the volumes of NF, CB, and SC barely changed at pressures below 10 MPa, whereas they increased at pressures above 10 MPa. This nonlinear volume increase is probably related to the free volume of the rubber structure. The volume increase of the CB and SC samples was smaller than that of the NF samples, possibly because of the superior tensile properties of CB and SC. As the volumes of the NF, CB, and SC samples increased, their tensile elastic moduli decreased as a result of a decrease in crosslink density and elongation by volume increase. Although the true fracture stress of NF was barely dependent on the volume of the specimen, those of CB and SC clearly decreased as the volume increased. The decrease in the true fracture stress of CB and SC was related to the volume increase by swelling, showing that the boundary structure between the filler and the rubber matrix was changed by the volume increase.

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Hydrogen molecules dissolved in rubber due to high-pressure hydrogen gas exposure have been analyzed using 1H nuclear magnetic resonance (NMR) with solution and solid-state probes. To analyze the characteristics of dissolved hydrogen in rubber materials and to compare them with gaseous phase hydrogen, we measured the NMR spectra of gaseous phase hydrogen and evaluated the chemical shifts and pressure dependency. Measurement using a sealed tube and liquid phase probes enabled the simultaneous analysis of dissolved hydrogen in rubber and gaseous phase hydrogen eliminated from the rubber. Two peaks at 4.3 and 4.8 p.p.m. were observed in the 1H MAS NMR of the rubber samples after high-pressure hydrogen exposure. Using information from the chemical shift of the free hydrogen gas and the time dependency of hydrogen quantification in the rubber, both of these peaks were confirmed to be attributable to dissolved hydrogen. Their differences in relaxation time confirmed that their mobilities were different. In conclusion, the hydrogen dissolved in acrylonitrile butadiene rubber exists in two different forms with different mobilities. The ratio of those two hydrogens differs and is affected by the exposure pressure and elimination process time.

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to establish a hydrogen energy system, the reliability of sealing rubber for high-pressure hydrogen has been required. The rubber O-ring for hydrogen energy system is used with pressurized-decompress cycle of high-pressure hydrogen. It causes internal cracks referred as blister fracture. Degradation of seal performance originated from blister fracture is one of the important issues to improve the reliability. This study focused on the blister initiation behavior and the effect of materials, gas species and decompression rate on blister fracture in terms of visualizing O-ring behavior under high-pressure gas. For the visualizing evaluation, a transparent ethylene-propylene rubber (EPDM) and vinyl-methyl silicone rubber (VMQ) O-rings were molded, and a special viewable high-pressure vessel with a glass viewport was developed. The O-ring specimens were exposed to high-pressure hydrogen, helium, and nitrogen at 10 MPa until gas solubility content in O-ring was saturated; afterwards, these gases were decompressed with some rate. It was obviously visualized that the blister fracture did not occur in VMQ O-ring but occurred in EPDM. The blister fracture of the EPDM O-ring in nitrogen was the most serious in the tested gases. These blister behaviors are considered to be related to gas diffusivity of hydrogen, helium and nitrogen.

Language：English   Publishing type：Research paper (scientific journal)  

Rubber materials, which are used for hydrogen gas seal, can dissolve hydrogen during exposure in high-pressure hydrogen gas. Dissolved hydrogen molecules were detected by solid state 1H NMR of the unfilled vulcanized acrylonitrile butadiene rubber. Two signals were observed at 4.5 ppm and 4.8 ppm, which were assignable to dissolved hydrogen, in the 1H NMR spectrum of NBR after being exposed 100 MPa hydrogen gas for 24 h at room temperature. These signals were shifted from that of gaseous hydrogen molecules. Assignment of the signals was confirmed by quantitative estimation of dissolved hydrogen and peak area of the signals.

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Eight carbon black (CB)-filled ethylene–propylene–diene–methylene linkage (EPDM) rubbers were manufactured by varying the content and type of CB. Then, the relationship among crack damage caused by high-pressure hydrogen decompression, the hydrogen permeation properties, and the mechanical properties of the rubbers was investigated. The hydrogen gas permeability of the rubbers decreased with an increase in the CB content and depended little on primary particle size. In contrast, the hydrogen gas diffusivity and solubility depended on both the CB content and primary particle size, that is, the hydrogen gas diffusivity decreased with an increase in the CB content and a decrease in the primary particle size, and the hydrogen gas solubility increased with an increase in the CB content and a decrease in the primary particle size. As for the mechanical properties, the CB-filled rubbers were more strongly reinforced by an increase in the CB content and a decrease in the primary particle size. The crack damage by high-pressure hydrogen decompression became larger as the ratio of the hydrogen gas solubility to estimated internal pressure at crack initiation relating to the mechanical properties became larger. As a smaller CB particle increases the hydrogen gas solubility of EPDM rubbers, while at the same time it reinforces the rubbers, the crack damage in the CB-filled rubbers was not influenced by the primary particle size.

Language：English   Publishing type：Research paper (scientific journal)  

In order to enable hydrogen society in the near future, it is necessary to clarify the influence of hydrogen on the mechanical, physical and chemical properties of the materials used for hydrogen energy systems. In the case of rubbers, there is a particular danger of mechanical damage resulting from internal fracture, which occurs when high-pressure hydrogen gas is suddenly decompressed. Although our previous studies focused on fracture and deformation caused by high-pressure hydrogen decompression, the fracture and deformation of rubber materials under pressurization have not been studied. From this viewpoint, static crack growth tests of an unfilled sulfur-crosslinked ethylene-propylene-diene monomer (EPDM) rubber were conducted in hydrogen gas at 10 MPa and room temperature (around 25°C) by using a high-pressure hydrogen vessel with glass viewing ports. Deformation of the rubber during pressurization was hardly seen at ≤ 10 MPa, although hydrostatic pressure was applied and hydrogen gas penetrated into the rubber. The static crack growth rate for hydrogen gas at 10 MPa was consistent with that in air (0.1 MPa). A lot of facets with about 100 µm in size caused by the initiation and successive coalescence of secondary cracks ahead of the main crack were observed on the fracture surface of the specimens tested in air and hydrogen gas at 10 MPa, and these fracture surfaces showed a similar aspect. From these results, it was clarified that a hydrogen environment at ≤ 10 MPa did not influence the static crack growth characteristic of the rubber.

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The rubber O-rings used in high-pressure hydrogen environment sometimes suffer from the decrease in durability due to decompression failure. A high-pressure durability tester, which enables rubber O-rings to expose repeatedly high-pressure hydrogen gas at arbitrary test conditions, was employed, and then sensitive factors for the durability of the O-rings were evaluated by using a L18 orthogonal array. Of lower-limit pressure, upper-limit pressure, material, temperature, O-ring filling ratio, holding time at lower limit, holding time at upper limit, and decompression time, it was clarified that the material, temperature, O-ring filling ratio, and decompression time were sensitive factors.

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In order to clarify the influence of high pressure hydrogen gas on mechanical damage in a rubber O-ring, the fracture analysis of the O-ring used for a sealing material of a pressure hydrogen vessel was conducted. The O-ring was exposed twenty cycles to hydrogen gas at 100 MPa. All the cracks observed in this study emanated from the interior, which can be classified into two types, type 1 and type 2, from the viewpoint of the location of crack initiation and the direction of crack growth. The type-1 cracks started from the center of the O-ring, while the type-2 cracks started from the sites near the surface of the O-ring. It is implied that tensile stress by compression influenced crack initiation and growth of the type-1 cracks. The mechanical damage by the type-1 cracks was more serious than that by the type-2 cracks. Stress analysis was conducted by the nonlinear FEM; then fatigue crack initiation of the O-ring was evaluated in terms of the maximum principal strain criterion, which has been widely employed for the evaluation of fatigue strength of rubber materials. The strain generated by compression was considerably smaller than fatigue fracture strain although the increase in the strain due to swelling was considered. It is considered that the type-1 cracks initiated and grew due to strain concentration caused by bubbles which were formed from supersaturated hydrogen molecules after decompression in addition to the strain due to compression and swelling.

Language：Japanese   Publishing type：Research paper (scientific journal)  

When a rubber O-ring was used as a sealing material of a pressure vessel for high-pressure hydrogen gas such as 70MPa, which is the hydrogen pressure for fuel cell electric systems, the O-ring was extruded from the pressure vessel due to an increase in volume by gas absorption, and consequently cracks initiated in the previous study. Therefore, it is important to clarify the influence of hydrogen pressure on the increase in volume and mechanical properties in order to design the rubber O-ring for high-pressure hydrogen gas. From this viewpoint, unfilled and carbon black-filled sulfur-vulcanized NBR composites were exposed to hydrogen gas at a maximum pressure of 100MPa ; then, the influence of hydrogen exposure on volume increase and tensile properties of the composites was investigated. The residual hydrogen content which was measured 35 min after decompression increased with an increase in the hydrogen pressures ranging from 0.7 to 100MPa for the unfilled composite (NF) and the filled composite (CB). In contrast, the volume of NF and CB was hardly changed less than 10MPa, and the increase in volume by gas absorption was observed more than 10MPa. The elastic modulus of NF and CB decreased with an increase in volume, and this tendency can be successfully explained in term of the decrease in the crosslink density and elongation by volume increase. Although the tensile strength of NF hardly depended on the volume of specimen, the tensile strength of CB clearly decreased with an increase in volume. This is considered to be because a boundary structure between carbon black and rubber matrix was changed by hydrogen exposure.

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An acoustic emission (AE) method was used to detect internal fracture of sealing rubber material by high pressure hydrogen decompression. According to preliminary results, AE signals were hardly detected during the tensile test in air, but many signals were detected during the static crack growth test in air. AE measurement of hydrogen exposed specimens was also conducted. With the increase in number and size of internal cracks generated due to high pressure hydrogen decompression, the AE event count and amplitude also increased. In addition, AE signals were generated from the specimen exposed to hydrogen gas at 0.7 MPa, although no cracks were initiated. It is inferred that these AE signals were generated due to bubbles, which are mechanically reversible cavities formed by dissolved hydrogen molecules after decompression.

Language：Japanese   Publishing type：Research paper (scientific journal)  

When a cylindrical specimen (φ29.0mm × 12.5mm) made from sealing rubbers was exposed in high-pressure hydrogen gas, it was clarified that cracks initiated in the specimen after decompression in previous studies. However, it was not clear whether crack damage obtained from the cylindrical specimen was the same as that obtained from an O-ring specimen used for practical sealing or not, because the shapes and dimensions of these specimens were different. From this viewpoint, seven cylindrical specimens (φ13.0mm × 2.0, 4.0, 6.0, 8.0, 10.0, 12.0 mm, and φ29.0mm × 12.5mm) made from an unfilled peroxide-crosslinked EPDM composite were exposed to high-pressure hydrogen gas at a maximum pressure of 10MPa ; then, the influence of the shape of specimen on crack initiation and growth behavior was investigated. Micrometer-sized defects, facets, and notch-like regions were observed at fracture origins of internal cracks by SEM observation. It was inferred that micrometer-sized bubbles were formed at these sites by the coalescence of submicrometer-sized bubbles, and internal cracks initiated due to stress concentration of the micrometer-sized bubbles. Measurement of AE (acoustic emission) was also conducted to confirm the existence of the sub-micrometer-sized bubbles. The crack damage became more serious with an increase in the thickness of specimen as well as an increase in hydrogen pressure. Although the critical hydrogen pressures at crack initiation of the specimens with thicknesses from 2.0 to 6.0mm decreased with an increase in the thickness of specimen, those of the specimens with thicknesses from 6.0 to 12.0mm were the same. The influence of the shape of specimen on the crack damage and the critical hydrogen pressure was successfully explained in terms of retained hydrogen content and fracture mechanics.

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The relationship between internal fracture due to high-pressure hydrogen decompression and microstructure of ethylene–propylene–diene–methylene linkage (EPDM) rubber was investigated by atomic force microscopy (AFM). Nanoscale line-like structures were observed in an unexposed specimen, and their number and length increased with hydrogen exposure. This result implies that the structure of the unfilled EPDM rubber is inhomogeneous at a nanoscale level, and nanoscale fracture caused by the bubbles that are formed from dissolved hydrogen molecules after decompression occurs even though no cracks are observed by optical microscopy. Since this nanoscale fracture occurred at a threshold tearing energy lower than that obtained from static crack growth tests of macroscopic cracks (Ts,th), it is supposed that nanoscale structures that fractured at a lower threshold tearing energy (Tnano,th) than Ts,th existed in the rubber matrix, and these low-strength structures were the origin of the nanoscale fracture. From these results, it is inferred that the fracture of the EPDM rubber by high-pressure hydrogen decompression consists of two fracture processes that differ in terms of size scale, i.e., bubble formation at a submicrometer level and crack initiation at a micrometer level. The hydrogen pressures at bubble formation and crack initiation were also estimated by assuming two threshold tearing energies, Tnano,th for the bubble formation and Ts,th for the crack initiation, in terms of fracture mechanics. As a result, the experimental hydrogen pressures were successfully estimated.

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to evaluate the influence of environmental condition on durability and permeation properties of sealing rubber materials under high pressure hydrogen gas, a durability tester which enables the sealing rubber to expose repeatedly high pressure hydrogen gas at arbitrary test conditions (maximum pressure is 90 MPa and the range of ambient temperature is from –60 to 100 °C) was developed. In this study, durability and hydrogen permeation properties of peroxide- vulcanized EPDM composite filled with white reinforcing filler were evaluated under hydrogen gas at a maximum pressure of 70 MPa and the range of ambient temperature from 0 to 100 °C. The dependence of the ambient temperature on permeability, diffusivity, and solubility was not influenced by the hydrogen pressure and the shape of specimen. Moreover, although we can regard that hydrogen content was approximately proportional to the hydrogen pressure at ≤10 MPa, this relationship became non-linear when a hydrogen pressure became higher. As for durability, blister damage became more serious with an increase in the hydrogen pressure and ambient temperature. Furthermore, damage by extrusion was also observed at ≥35 MPa due to large gas absorption.

Language：English   Publishing type：Research paper (scientific journal)  

The precise and detailed chemical shift of gas-phase hydrogen molecules was successfully determined by 1H nuclear magnetic resonance (NMR), avoiding the intervention of neighboring molecules such as in hydrogen occluding materials (free hydrogen). The measurement was conducted with double walled NMR sample tube taking into consideration the change of hydrogen pressure. The inner tube was filled with standard substance (DHO in D2O at 4.8 ppm). The chemical shift of free hydrogen molecules was determined to be 7.40 ± 0.01 ppm at 0.18 MPa, 25 °C, which is different from previously reported chemical shifts of hydrogen gas with intervention of neighboring molecules.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fracture Analysis of Rubber Sealing Meterial for High Pressure Hydrogen Vessel

Language：Japanese   Publishing type：Research paper (scientific journal)  

Structural Analysis of Vulcanized NBR Using Swollen State, Solution State and Solid State 1H, 13C NMR Spectroscopy

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fracture Analysis of Rubber Sealing Meterial for High Pressure Hydrogen Vessel

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Estimation of Hydrogen Pressure at Blister Initiation of EPDM Composite Exposed to High Pressure Hydrogen Gas

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Event date： 2009.12

Presentation type：Oral presentation (general)  

Venue：東京理科大学森戸記念館   Country：Japan  

Estimation of Critical Hydrogen Pressure at Crack Initiation of Silica-filled EPDM Composite Exposed to High Pressure Hydrogen

Event date： 2009.12

Presentation type：Oral presentation (general)  

Venue：東京理科大学森戸記念館   Country：Japan  

Hydrogen Permeation Properties and Blister Fracture of EPDM for Sealing of Hydrogen Gas in 70MPa Hydrogen Gas

Event date： 2009.10

Presentation type：Oral presentation (general)  

Venue：愛媛大学工学部   Country：Japan  

Event date： 2009.10

Presentation type：Oral presentation (general)  

Venue：名古屋国際会議場   Country：Japan  

Event date： 2009.10

Presentation type：Oral presentation (general)  

Venue：名古屋国際会議場   Country：Japan  

Event date： 2009.10 - 2009.11

Venue：九州大学馬出病院キャンパス医学部百年講堂（福岡市）   Country：Japan  

Event date： 2009.9

Presentation type：Oral presentation (general)  

Venue：大阪市立大学   Country：Japan  

Event date： 2009.9

Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2009.9

Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2009.5

Presentation type：Oral presentation (general)  

Venue：パシフィコ横浜   Country：Japan  

Event date： 2009.5

Presentation type：Oral presentation (general)  

Venue：ホテルアウィーナ大阪   Country：Japan  

Event date： 2009.5

Presentation type：Oral presentation (general)  

Venue：ホテルアウィーナ大阪   Country：Japan  

Event date： 2009.5

Presentation type：Oral presentation (general)  

Venue：ホテルアウィーナ大阪   Country：Japan  

Event date： 2008.12

Presentation type：Oral presentation (general)  

Venue：名古屋国際会議場   Country：Japan  

Event date： 2008.12

Presentation type：Oral presentation (general)  

Venue：名古屋国際会議場   Country：Japan  

Event date： 2008.9

Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2008.8

Presentation type：Oral presentation (general)  

Venue：岩手大学   Country：Japan  

Blister Fracture of Rubbers Exposed to High Pressure Hydrogen Gas and the Influence of Fillers on Tensile and Hydrogen Penetration Properties

Event date： 2008.8

Presentation type：Oral presentation (general)  

Country：Japan  

Blister Fracture of Rubbers Exposed to High Pressure Hydrogen Gas and the Influence of Fillers on Tensile and Hydrogen Penetration Properties

Event date： 2008.5

Presentation type：Oral presentation (general)  

Venue：パシフィコ横浜   Country：Japan  

Event date： 2008.5

Presentation type：Oral presentation (general)  

Venue：鹿児島大学工学部   Country：Japan  

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Seminar, workshop