The Residual Stress Control of the Fastening Bolt for Bridges　　　　　　　　　　　　　　　
Takanori Ebata; Hitoshi Yokota; Testuya Suzuki
Asian Conference on Engineering and Natural Sciences, 2017年01月

Structural change of NdNi3 during hydrogen absorption-desorption cycle
Kenji Iwase; Kazuhiro Mori; Suguru Tashiro; Hitoshi Yokota; Tetsuya Suzuki, The structural change of NdNi3 during the hydrogen absorption-desorption cycle and the P-C isotherm have been investigated. The maximum hydrogen capacity achieved in the first absorption process is 1.05 H/M. After the first desorption, 0.75 H/M of hydrogen capacity remains in the alloy. The trigonal crystal structure of the original alloy (R-3m) transforms to monoclinic (C2/m) in the first absorption. The crystal structure of the hydride phase remains monoclinic during the first desorption. The metal sublattice expands anisotropically during phase transformation from the alloy to the monoclinic hydride (NdNi3H4.0); a, b, and c axes expand by 8%, 7%, and 44%, respectively. The volumes of the unit cell, and the Nd2Ni4 and NdNi5 cells expand by more than 60%. Phase transformation of NdNi3H is irreversible during the first absorption-desorption cycle. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 2016年02月, ［査読有り］

Effect of Mg substitution on hydrogen absorption-desorption behavior and crystal structure of Gd2-xMgxNi7
Kenji Iwase; Naoyoshi Terashita; Kazuhiro Mori; Suguru Tashiro; Hitoshi Yokota; Tetsuya Suzuki, The hydrogen absorption-desorption behavior and the crystal structure of Gd2-xMgxNi7 were investigated by pressure composition (PC) isotherm measurements and X-ray diffraction (XRD). Gd1.5Mg0.5Ni7 consists of two phases: 75% Gd2Co7-type structure and 25% PuNi3-type structure. Mg atoms substitute at the Gd site of the MgZn2-type cell in both Gd2Co7-type and PuNi3-type phases. In the hydrogen-free alloy after the PC isotherm measurement, the volumes of the (Gd/Mg)Ni-2 and GdNi5 cells of the Gd2Co7-type phase do not change appreciably, while those of the PuNi3-type phase experience shrinkage and expansion, respectively. A plateau region of Gcl(1.5)Mg(1.5)Ni(7) is observed between 0.06 H/M and 0.82 H/M. The reversible hydrogen content in the absorption desorption cycle is approximately 1.0 H/M. The enthalpy of hydride formation is evaluated as -24 kJ/mol H-2 from the Van't Hoff plot. The absorption desorption behavior is excellent even at low temperatures below 243 K. The hydrogen storage property of Gd1.5Mg1.5Ni7 is markedly improved by Mg substitution. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 2016年01月, ［査読有り］

Effects of Mg substitution on crystal structure and hydrogenation properties of Pr1-xMgxNi3
Kenji Iwase; Naoyoshi Terashita; Kazuhiro Mori; Suguru Tashiro; Hitoshi Yokota; Tetsuya Suzuki, The effects of substitution of Pr by Mg in PrNi3 with a PuNi3-type structure were investigated using pressure composition (P-C) isotherm measurements and X-ray diffraction. The unit cell of Pr0.68Mg0 Ni-32(3.04) contracted anisotropically in comparison to that of PrNi3. The maximum hydrogen capacity of PrNi3 reached 1.25 H/M in the first absorption. A plateau region was observed between 0.82 H/M and 1.04 H/M in the first absorption cycle. However, 0.85 H/M of hydrogen remained in the sample after the first full desorption. Pr0.68Mg0.32Ni3.04 showed reversible hydrogenation properties. The maximum hydrogen capacity was 1.22 H/M. The plateau region of Pr0.68Mg0.32Ni3.04 was between 0.08 H/M and 0.87 H/M, which was wider than that of PrNi3. Pr0.68Mg0.32Ni3.04 retained the PuNi3-type structure after hydrogenation, whereas the crystal structure of PrNi3 changed from that of PuNi3-type to an unknown structure. The structural change in PrNi3 during hydrogenation was evidently different from that in Pr0.68Mg0.32Ni3.04. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 2014年08月, ［査読有り］

Crystal structure and cyclic hydrogenation property of Pr 4MgNi19
Kenji Iwase; Naoyoshi Terashita; Kazuhiro Mori; Hitoshi Yokota; Tetsuya Suzuki, The hydrogen absorption-desorption property and the crystal structure of Pr4MgNi19 was investigated by pressure-composition isotherm measurement and X-ray diffraction (XRD). Pr4MgNi 19 consisted of two phases: 52.9% Ce5Co19-type structure (3R) and 47.0% Gd2Co7-type structure (3R). Sm5Co19-type structure (2H) and Ce2Ni 7-type structure (2H) were not observed in the XRD profile. The Mg atoms substituted at the Pr sites in a MgZn2-type cell. The maximum hydrogen capacity reached 1.14 H/M (1.6 mass%) at 2 MPa. The hysteresis factor, Hf = ln(Pabs/Pdes), was 1.50. The cyclic hydrogenation property of Pr4MgNi19 was investigated up to 1000 absorption-desorption cycles. After 250, 500, 750, and 1000 cycles, the retention rates of hydrogen were reduced to 94%, 92%, 91%, and 90%, respectively. These properties were superior to those of Pr2MgNi 9 and Pr3MgNi14. © 2013 American Chemical Society.
Inorganic Chemistry, 2013年12月16日, ［査読有り］

Development of aluminum-alloy coating on type 316SS for nuclear systems using liquid lead–bismuth
Yuji Kurata; Hitoshi Yokota; Tetsuya Suzuki, An Al-alloy coating method using Al, Ti and Fe powders and the laser beam heating has been developed for nuclear systems using liquid lead-bismuth eutectic (LBE). Main defects formed in the coating process were surface defects and cracks. It was effective to decrease a laser beam scanning rate to 20 mm/min to avoid surface defects. It was necessary to adjust the Al concentration in the coating layer to be lower than 12 wt.% in order to avoid significant cracking. A static corrosion test was conducted in liquid LBE at the controlled oxygen concentrations of 10(-6)-10(-3) wt.% at 550 degrees C for 3000 h. The Al-alloy coating layer on 316SS prevented severe corrosion attack such as Ni dissolution, partial loss of grains and LBE penetration which were observed in 316SS without AI-alloy coating. Liquid LBE penetrated into the surface defects formed in the Al-alloy coating layers produced using a laser beam with the scanning rate of 60 mm/min. The AI-alloy coating layer, which was formed without surface defects and cracks under the optimum condition of the scanning rate of 20 mm/min, exhibited good corrosion resistance in liquid LBE. (C) 2012 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Journal of Nuclear Materials, 2012年, ［査読有り］

Applicability of Al-Powder-Alloy Coating to Corrosion Barriers of 316SS in Liquid Lead-Bismuth Eutectic
Yuji Kurata; Hidetomo Sato; Hitoshi Yokota and Tetsuya Suzuki, A new Al-alloy coating method using Al, Ti and Fe powders has been applied to 316SS in order to develop corrosion resistant coating in liquid lead-bismuth eutectic: (LBE). The 316SS plates with coating layers of different Al concentrations were exposed to liquid LBE with controlled oxygen concentrations of 10(-6) to 10(-4) mass% at 823 K for 3600 ks. While surface oxidation and grain boundary corrosion accompanied by liquid LBE penetration are observed in 316SS without Al-alloy coating, the Al-alloy coating is effective to protect such severe corrosion attacks in liquid LBE. Although the coating layer containing 2.8 mass% Al does not always keep sufficient corrosion resistance, good corrosion resistance is obtained through the Al-oxide film formed in liquid LBE in the coating layer where the average Al concentration is 4.2 mass%. Cracks are formed in the coating layer containing 17.8 mass% Al during the coating process. The Al-powder-alloy coating applied to 316SS is promising as a corrosion resistant coating method in liquid LBE environment. [doi:10.2320/matertrans.M2010337], JAPAN INST METALS
Mater. Trans., 2011年05月, ［査読有り］

溶融塩ホウ化処理によるTiAlの耐酸化性改善　　　　　　　　　　　　　　　
横田仁志; 鈴木徹也
鉄と鋼, 2005年

Oxidation resistance of boronized MoSi2
Hitoshi Yokota; Tatsumi Kudoh; Tetsuya Suzuki, Intermetallic compound MoSi2 is expected to be one of the light heat-resisting materials. However, MoSi2 suffers from accelerated oxidation at low temperatures called as 'pest oxidation'. In this study MoSi2 was boronized to improve its low temperature oxidation by molten salt process. Molybdenum boride was formed on the surface of MoSi, and no pest disintegration was observed after cyclic oxidation test. (C) 2003 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE SA
Surface and Coatings Technology, 2003年

Oxidation resistance of boronized MoSi2　　　　　　　　　　　　　　　
Hitoshi Yokota; Tatsumi Kudoh; Tetsuya Suzuki
Frontiers of Surface Engineering 2001, 2001年

DEVELOPMENT OF ALUMINUM POWDER ALLOY COATING FOR INNOVATIVE NUCLEAR SYSTEMS WITH LEAD-BISMUTH
Yuji Kurata; Hidetomo Sato; Hitoshi Yokota; Tetsuya Suzuki
OECD/NEA International Workshop on Structural Materials for Innovative Nuclear Systems, 2010年08月31日