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Takayuki Ichikawa, Teruto Kanadani, Keitaro Horikawa, Koji Murakami
2013 Volume 77 Issue 12 Pages
551
Published: 2013
Released on J-STAGE: December 01, 2013
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Hiroki Miyaoka, Takayuki Ichikawa, Yoshitsugu Kojima
2013 Volume 77 Issue 12 Pages
552-558
Published: 2013
Released on J-STAGE: December 01, 2013
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Hydrogen is chemically absorbed into graphite by mechanical ball-milling process under H
2, and its hydrogen capacity reaches to about 3.6 mass%. Noteworthy, when iron (Fe) mingles with graphite from steel balls during the milling process, the hydrogen capacity is drastically enhanced. In this work, the hydrogen absorption and desorption properties of the hydrogenated graphite with and without Fe were investigated. The hydrogen capacity of graphite including Fe was about 6 mass% (H/C), suggesting that the excess hydrogen of 2.4 mass% would originate in the Fe related phase. It is clarified by spectroscopic studies that the mingled iron formed a non-stoichiometric iron-carbon (Fe-C) phase as hydrogen absorption site. Assuming that the Fe/C ratio is 1, its hydrogen capacity is estimated to be H/(Fe-C-H)>10 mass%, which is a larger value than that of the conventional hydrogen storage materials. The hydrogen absorbed in the C-Fe phase is released at 450℃ with the transformation of the C-Fe phase to well-ordered carbides such as Fe
3C. Therefore, if the C-Fe phase could be synthesized independently, it should be recognized as a promising hydrogen storage material.
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Keitaro Horikawa, Yasuhito Fujii, Hidetoshi Kobayashi, Kenji Kobayashi
2013 Volume 77 Issue 12 Pages
559-564
Published: 2013
Released on J-STAGE: December 01, 2013
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Hydrogen microprint technique (HMT) is known as one of the hydrogen visualizing methods using the redox reaction between hydrogen atom and AgBr. In the previous studies about HMT, plural specimens were needed to know the hydrogen emission behavior during deformation according to the number of testing condition. In this study, an original testing jig was made in order to perform the repetition in HMT by holding the deformation state using one specimen. By using this testing jig, we could verify the hydrogen emission behavior in the same microstructure of pure iron during deformation.
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Takahito Watakabe, Goroh Itoh, Yuji Hatano
2013 Volume 77 Issue 12 Pages
565-570
Published: 2013
Released on J-STAGE: December 01, 2013
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Behavior of hydrogen that invades pure aluminum, 6061 and 7075 aluminum alloys from two environments, water and hydrogen gas, has been investigated by means of tritium autoradiography, TARG, a technique to visualize the hydrogen atoms in a specimen by using tritium, radioisotope of hydrogen, as a tracer. Sheet specimens of aluminum of 99.99% purity rolled and then annealed, and T6-tempered 6061 and 7075 alloys were subjected to tritium charging in tritiated water and tritium gas, and then to TARG. The TARG was made in the following way. Photographic emulsion was covered on the polished specimen surface, exposed in liquid nitrogen for 14 d, developed, fixed, rinsed and finally observed with an SEM equipped with an EDXS device. In pure aluminum, hydrogen invasion was not detected, while hydrogen was observed in the constituent particles in the two alloys; hydrogen invades 6061 aluminum alloy through Al-Fe-Si phase and 7075 aluminum alloy through Al
7Cu
2Fe phase. This feature was commonly observed irrespective of the environment, i.e., tritiated water or tritium gas. The number of silver particles detected was larger in 7075 than in 6061.
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Shigehito Isobe, Miki Dohkoshi, Yongming Wang, Naoyuki Hashimoto, Some ...
2013 Volume 77 Issue 12 Pages
571-574
Published: 2013
Released on J-STAGE: December 01, 2013
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In order to clarify the reaction mechanism of the hydrogenation process in the Li
2NH system, we have observed the partially hydrogenated samples by transmission electron microscopy (TEM). From the TEM images of partially hydrogenated samples, it was shown that the LiNH
2 phase was located between Li
2NH phase, which was almost at the center of the particle, and LiH particles with the size of 100 nm. This result indicated that LiH was generated and grew up at the outside of the complex particle of Li
2NH and LiNH
2 with Li moving from the center to the surface of the particle.
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Norihito Nagata, Teruto Kanadani, Hayato Hiraoka, Minoru Fukuhara, Kou ...
2013 Volume 77 Issue 12 Pages
575-579
Published: 2013
Released on J-STAGE: December 01, 2013
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In this study, the effect of electroless Ni-P plating on the mechanical properties of an Al-1.2%Si alloy was investigated. As results, the following points were clarified. (1) Fatigue strength of the specimen subjected to zincate treatment only after furnace cooling treatment was almost the same as the furnace cooling only. (2) Fatigue strength of the specimen subjected to Ni-P plating after furnace cooling treatment, was reduced overall, except for high-stress region, rather than one of non-processing materials. (3) Fatigue strength of the specimen subjected to Ni-P plating after aging treatment showed a clear increase in comparison with one of non-processing materials. (4) Tensile strength of the specimen subjected to Ni-P plating after aging treatment or furnace cooling treatment was improved by about 10% in comparison with one of non-processing materials. (5) Breaking elongation of the specimen subjected to Ni-P plating after aging treatment showed no significant changes in comparison with one of non-processing materials. On the other hand, breaking elongation of the specimen subjected to Ni-P plating after furnace cooling treatment reduced by half in comparison with one of non-processing materials. Especially, it seems that poor fatigue strength and ductility of plating materials are mainly caused due to interaction between surface precipitates and hydrogen gas.
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Kiyotaka Goshome, Hiroki Miyaoka, Tomoyuki Ichikawa, Takayuki Ichikawa ...
2013 Volume 77 Issue 12 Pages
580-584
Published: 2013
Released on J-STAGE: December 01, 2013
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Lithium nitride can be formed in the reaction of lithium metal with nitrogen gas under moderate condition and has attracted attention as a hydrogen storage system; Li
3N+2H
2 → 2LiH+LiNH
2. Li
3N is hydrogenated below 300℃ under 0.5 MPa of H
2, and then LiNH
2 is formed as product. Furthermore, the reaction between
MNH
2 and H
2;
MNH
2+H
2 →
MH+NH
3, can proceed below 250℃ under 0.5 MPa H
2 flow condition to form
MH and NH
3. In this study, we proposed and investigated synthesis method of ammonia run under more moderate conditions than those of current Haber-Bosch process by using combination of above two reactions. As the result, it was experimentally clarified that the ammonia synthesis can be operated in realistic reaction rate below 300℃ by producing non-equilibrium reaction field under 1.0 MPa H
2 flow condition.
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Yoshihisa Matsumoto, Hiroshi Yukawa, Tomonori Nambu
2013 Volume 77 Issue 12 Pages
585-592
Published: 2013
Released on J-STAGE: December 01, 2013
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For the group 5 metals, even in an ambient hydrogen atmosphere (pressure), a large amount of hydrogen dissolves into them and severe hydrogen embrittlement occurs. This means that there is a large barrier to the practical application of these metals as a hydrogen permeation membrane for hydrogen separation and purification. In this study, we have found that a ductile-to-brittle transition occurs for the niobium (Nb) or vanadium (V) metals as a function of the “hydrogen concentration”, by using a special setup of the
in-situ small punch (SP) testing apparatus equipped with a gas-flow system. This paper deals with a definition for the discovered phenomenon that group 5 metals have hydrogen concentration which changes from ductile-to-brittle fracture (DBTC: Ductile-to-Brittle Transition hydrogen Concentration). The grain size and the alloying effects of tungsten (W) and molybdenum (Mo) on the DBTC of Nb or V have also been clarified. Using this advanced approach, the importance of the DBTC analyses is described on the design of group 5 metal based hydrogen permeation membranes.
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Masaharu Hatano, Akihiko Takahashi, Hideki Fujii, Shinichi Omiya
2013 Volume 77 Issue 12 Pages
593-598
Published: 2013
Released on J-STAGE: December 01, 2013
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High pressure gaseous hydrogen is regarded as one of the effective means of energy transportation and storage. To confirm the compatibility of newly developed austenitic stainless steels with reduced amount of nickel and molybdenum for hydrogen energy systems, tensile properties were evaluated in high pressure gaseous hydrogen and helium up to 90 MPa and in air at room temperature. Elongation of new austenitic stainless steels “STH1” increased with increasing the hydrogen and helium pressure up to 90 MPa than in air. The deformation microstructure of STH1 after tensile test in gaseous hydrogen and helium was closely observed by transmission electron microscope. The effect of twinning induced plasticity on high pressure gaseous hydrogen and helium is discussed.
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Koji Murakami, Makoto Hino, Norihito Nagata, Teruto Kanadani
2013 Volume 77 Issue 12 Pages
599-603
Published: 2013
Released on J-STAGE: December 01, 2013
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Effect of alloying elements and generation of hydrogen gas during zincate treatment and electroless nickel-phosphorus plating were studied by using electron microscopy. Hydrogen gas was vigorously evolved during the zincate treatment for binary Al-2 at%Mg and Al-2 at%Si alloys, and the zincated surfaces were nonuniformly covered with excess coarse zinc particles, due to continuing oxidation of the substrate and reduction of proton and zincate ions. On the other hand, the surfaces of ternary Al-2 at%Zn-0.2 at%Mg and Al-2 at%Zn-4.5 at%Mg alloys were immediately covered with thin and uniform film of zinc.
Magnesium in aluminum alloys and the excess precipitation of zinc were found to lower adhesion of electroless nickel-phosphorus plated films. When the zincated Al-2Mg and Al-2Si alloys were immersed in the plating solution, dissolution of the excess zinc generated hydrogen gas, and the plated films poorly adhered to the substrates. Despite the thin and uniform zincate film, the plated film on Al-2Zn-4.5Mg alloy was easily peeled due to the voids formed between the plated film and the substrate. Magnesium in the alloy may suppress precipitation of nickel, and accelerate generation of hydrogen gas at the beginning of the plating.
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Shigeyuki Takagi, Tamio Ikeshoji, Toyoto Sato, Katsutoshi Aoki, Shin-i ...
2013 Volume 77 Issue 12 Pages
604-608
Published: 2013
Released on J-STAGE: December 01, 2013
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The crystal and electronic structures, and thermodynamic stability of hypothetical complex hydride Li
4FeH
6 were examined using first-principles calculations. We found that the hydride occurs in a K
4CdCl
6-type structure with space group
R-3
c (No. 167), which is the same as that reported for Na
4RuH
6. The calculated enthalpy change of the reaction, 4LiH+Fe+H
2→Li
4FeH
6, is −54 kJ/mol H
2. Given that Fe does not form any stable binary compounds with both Li and H, Li
4FeH
6 could be the most stable phase among the compounds consisting of Li, Fe and H. Using a calculated entropy change of −115 J/mol H
2•K, the equilibrium pressure under 773 K is estimated to be 24 MPa. The electronic structure illustrates that four Li atoms donate a total of four electrons per formula unit to the FeH
6 octahedron, forming an ionic configuration of Li
+4[FeH
6]
4−. The complex hydride reported here has the higher hydrogen gravimetric density, a value of 6.7 mass%, than other Fe-based complex hydrides ever reported, and thus would be of interest in terms of hydrogen storage.
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Tessui Nakagawa, Takayuki Ichikawa, Hiroki Miyaoka, Masami Tsubota, Yo ...
2013 Volume 77 Issue 12 Pages
609-614
Published: 2013
Released on J-STAGE: December 01, 2013
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The milling effect during hydrogenation under various conditions for a CaH
2-CaB
6 mixture was investigated. Two different starting materials, 1) dehydrogenated Ca(BH
4)
2 and 2) the mixture of commercial CaH
2 and CaB
6, were used. TG-MS profiles indicated that the hydrogenation kinetics of dehydrogenated Ca(BH
4)
2 was better than the commercial CaH
2-CaB
6 especially at high temperature. XRD and IR profiles revealed that Ca(BH
4)
2 and/or its intermediate state were produced after milling. These results indicate that milling technique accelerates hydrogenation of CaH
2-CaB
6 even at room temperature, and the initial crystalline size of CaB
6 is important to improve the kinetics of the first hydrogenation step.
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Kenichi Takai, Shoko Hirota, Hiroshi Suzuki, Yuusuke Seko, Hiroyuki Mo ...
2013 Volume 77 Issue 12 Pages
615-621
Published: 2013
Released on J-STAGE: December 01, 2013
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States of hydrogen present in cold-rolled pure iron specimens charged by hydrogen gas and cathodic electrolysis have been compared using thermal desorption analysis to obtain the fundamental properties for evaluating the hydrogen embrittlement susceptibility of hydrogen gas pipeline steels. Hydrogen was charged into the cold-rolled pure iron specimens in gaseous hydrogen at pressures of 4, 7, and 10 MPa at temperatures of 30, 60, 90, 120℃, and in an aqueous solution of NaOH with pH of 13, to which 5 g•L
−1 of NH
4SCN was added, at current densities in the range of 0 to 50 A•m
−2 and at temperatures of 30, 60 and 90℃. For charging at 30℃ under various hydrorgen pressures, hydrogen peak temperatures are approximately 60℃ and the peak profiles are identical. In contrast, when the charging temperature is increased to 90℃ under various hydrorgen pressures, hydrogen desorption newly occurred above approximately 100℃. The hydrogen peak at 60℃ corresponds to hydrogen trapped at dislocations and vacancies, whereas the hydrogen desorption above approximately 100℃ corresponds to hydrogen trapped at vacancy clusters formed during hydrogen charging at higher temperatures. In addition, equilibrium hydrogen content in solid solution and at trapping sites decreases with increasing charging temperature, since enthalpy of hydrogen solution is −27.3 kJ•mol
−1. These results indicate that higher-temperature charging causes the states of hydrogen present in cold-rolled pure iron to change due to the formation of vacancy clusters and reduces the equilibrium hydrogen content including that in solid solution and at trapping sites.
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Eiji Akiyama, Saburo Matsuoka
2013 Volume 77 Issue 12 Pages
622-626
Published: 2013
Released on J-STAGE: December 01, 2013
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The relation between hydrogen distribution and metallographic microstructure was investigated by means of Ag decoration technique for a SUS304 austenitic stainless steel, and martensitic and spheroidized SCM440 steels precharged with hydrogen. Preferential distribution of Ag particles was seen on the slip lines of the deformed and hydrogen-charged SUS304 stainless steel, suggesting that the slip lines act as hydrogen trap sites. The martensitic SCM440 steel showed almost no selective Ag deposition, indicative of apparently homogeneous distribution of hydrogen. This is probably because the distribution of dislocations with relatively high concentration and the fine structure including lath boundaries etc. acting as hydrogen traps is homogeneous. The spheroidized SCM440 steel showed almost no Ag deposition on the coarse cementite particles and the Ag particle distribution on the other areas did not show clear selectivity. This result suggests that the hydrogen does not diffuse through the cementite particles. The smallest Ag particle size observed by means of atomic force microscope was in the order of 10 nm. Though the minimum size of the Ag particle does not necessarily indicate the resolution of the hydrogen visualization, Ag decoration technique is useful to observe the hydrogen distribution.
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Hai-Wen Li, Daiju Matsumura, Yasuo Nishihata, Etsuo Akiba, Shin-ichi O ...
2013 Volume 77 Issue 12 Pages
627-630
Published: 2013
Released on J-STAGE: December 01, 2013
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The dehydrogenation property of Mg(BH
4)
2 as a function of the added TiCl
3 content was systematically investigated from viewpoints of kinetics and thermodynamics. The dehydrogenation temperature decreased when the TiCl
3 content
x was increased from 0.02 to 0.20 mol, and the initial dehydrogenation temperature notably decreased to approximately 350 K at
x=0.20. The main improvement effects of TiCl
3 on the dehydrogenation properties of Mg(BH
4)
2 changed from kinetic to thermodynamic aspects with the increasing addition content. That is, Mg(BH
4)
2 tended to react with TiCl
3 to produce thermodynamically unstable Ti
xMg
(1−3x/2)(BH
4)
2 (
x=0~0.67). With relatively high addition content (
x≥0.10), thermodynamic destabilization of Mg(BH
4)
2 becomed more dominant. However, with relatively low addition content (
x<0.10), TiB
2 formed from the dehydrogenation of Ti
xMg
(1−3x/2)(BH
4)
2 mainly showed kinetic improvement effect.
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Kazuya Shibata, Koji Tanaka, Kosuke Kurumatani, Ryota Kondo, Hiroyuki ...
2013 Volume 77 Issue 12 Pages
631-635
Published: 2013
Released on J-STAGE: December 01, 2013
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We proposed that there are two kinds of competitive processes in the hydrogenation of Mg/Cu super-laminate composites; the one in which alloying (formation of MgCu
2 from Mg and Cu) occurs in advance and Mg
2Cu is hydrogenated to form MgH
2 and MgCu
2, and the other in which Mg is hydrogenated and then MgH
2 and Cu react to form MgCu
2 together with H
2 gas, according to a hypothesis that the reaction of MgH
2+2Cu→MgCu
2+H
2 occurs. In order to confirm that the hypothesis is true, we investigated the conditions such as H
2 pressure and temperature at which the above-mentioned reaction proceeds. Well-mixed MgH
2 and Cu powder was compacted to form pellet at 1.73 GPa and then heated at various hydrogen pressures and temperatures. Experimental results at 673 K indicated that the above-mentioned reaction occurs at pressures higher than 6.5 MPa, approximately the lower limit for the hydrogenation of Mg
2Cu, whereas both Mg
2Cu and MgCu
2 are formed at 3.3 MPa.
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Toru Kimura, Hiroki Miyaoka, Takayuki Ichikawa, Yoshitsugu Kojima
2013 Volume 77 Issue 12 Pages
636-640
Published: 2013
Released on J-STAGE: December 01, 2013
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Hydrogen absorption of magnesium (Mg) catalyzed by 1 mol% niobium oxide (Nb
2O
5) was demonstrated under the low temperature condition even at −50℃. The kinetic and thermodynamic properties were examined for MgH
2 with and without Nb
2O
5. By considering the remarkable absorption features at such low-temperature, the essential hydrogen absorption properties were investigated under accurate isothermal conditions. As a result, the activation energy of hydrogen absorption for the catalyzed Mg was evaluated to be 38 kJ•mol
−1, which was significantly smaller than that of MgH
2 without the catalyst. The kinetic improvement was also found on the hydrogen desorption process. On the other hand, thermodynamic properties were not changed by the catalyst. Therefore, the Nb
2O
5 addition mainly affects the reaction rates between Mg and hydrogen and shows the excellent catalytic effects.
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