Yuji Hatano, Kuniaki Watanabe

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 933-8555, Japan

Abstract

    Hydrogenation of MgNi₂ by hydrogen plasma was examined at elevated temperatures. Powder of MgNi₂ was compacted into a disk and heated in vacuum at 773 K. MgNi₂ was transformed into MgNi₂ by evaporation of Mg. This specimen was hydrogenated by rf-discharged hydrogen plasma (10-30 Pa) at 673 and 773 K. At 673 K, hydrogen was not absorbed. At 773 K, however, the specimen was hydrogenated up to [H]/[M]=0.14 within 25 ks. New peaks appeared in the X-ray diffraction pattern at 2q=34.0, 42.0, 48.9, and 86.6゜. The peaks at 42.0, 48.9, and 86.6゜ were assigned to Ni hydride, which can be formed in hydrogen gas atmosphere at high pressure (10 ⁸ Pa). Hydrides of Mg and MiNi, however, were not observed.

Keywords: magnesium(Mg); nickel(Ni); intermetallic compound; hydrogen; hydride; plasma; atom

Kan Ashida^a, Yuji Hatano^a, Wataru Nishida^a, Kuniaki Watanabe^a,
Asami Amano^b, Kenji Matsuda^b, Susumu Ikeno^b

^a Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama-shi, Toyama 930-8555 ^b Department of Material Systems Engineering and Life Science, Faculty of Engineering, Toyama University, Gofuku 3190, Toyama-shi, Toyama 930-8555

Abstract

    Effect of Pd coating on recovery of hydrogen isotopes from inert gas atmosphere was investigated for intermetallic compounds ZrNi. Powder of ZrNi was coated with Pd by electroless plating. Subsequent annealing at 1073 K led to the formation of ZrPd at the powder surface. The durability in deuterium recovery from Ar gas was examined for the bare and the Pd-coated powders at temperatures from 373 to 573 K as well as the kinetics of deuterium absorption and desorption. The absorption and desorption of deuterium obeyed the first and the second order kinetics, respectively. The ZrPd layer on ZrNi did not alter the absorption and the desorption kinetics, The deuteium recovery by the bare powder was degraded with time owing to oxidation of powder surfaces by impurities contained in the Ar gas. The durability in deuterium recovery was markedly improved by Pd coating, and no significant degradation was observed for the Pd-coated specimen at 573 K. This difference in the durability was ascribed to the difference in the oxidation behavior between ZrNi and ZrPd. It was concluded that Pd coating significantly improves the applicability of ZrNi to tritium recovery in blanket systems.

M. Matsuyama^a, T. Tanabe^b, N. Noda^c, V. Philipps^d, K.H. Finken^d, K. Watanabe^a

^a Hydrogen Isotope Research Center, Toyama university, Gofuku 3190, Toyama 930-8555, Japan

^b Center for Integrated Research in Science and Engineering, Nagoya University, Nagoya 464-8603, Japan

^c National Institute for Fusion Science, Oroshi-cho, Toki 509-5292, Japan

^d Institute of Plasma Physics, Julich Research Center, Julich 52428, Germany

Abstract

    Applicability of a newly developed b-ray induced X-ray spectrometry (BIXS) has been examined to measure nondestructively tritium retained on/in the graphite samples. Examination was carried out by using the graphite plates irradiated with tritium ions and an ALT-Ⅱ limiter tile exposed to D-plasmas in TEXTOR. For the former samples, a sharp intense peak and a broad weak peak appeared clearly in the spectra; the former peak was attributed to the characteristic X-rays from argon used as a working gas, and the latter peak was assigned to the bremsstrahlung X-rays from sub-surface layers of graphite. On the other hand, for the latter sample, a rather weak characteristic X-ray peak was observed along with a diminutive bremsstrahlung X-ray peak. Although the intensities of those x-rays differed from spot to spot, the tritium levels retained on the limiter tile were determined to be 58-132 Bq/cm². It was concluded, therefore, that valuable information on the amount and the distribution of tritium retained on/in the wall materials can be nondestructively obtained by using the BIXS.

Keywords: Surface tritium measurement; b-ray induced X-ray spectrometry (BIXS); Tritium retention; Graphite materials

K. Ashida^a, K. Fujino^b, T. Okabe^b, M. Matsuyama^a, K. Watanabe^a

^a Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

^b Department of Physics, Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    The solid-state reaction between hydrogen-containing carbon and tungsten was studied by means of infrared, Raman, X-ray photoelectron (XPS) and thermal desorption (TDS) spectroscopies. Infrared and Raman spectroscopies revealed that as-prepared hydrogen-containing films were composed of carbon atoms with sp₂ and sp₃ hybridized orbitals, where hydrogen was bound to carbon as-CH₃ and >CH₂. Vacuum heating of the carbon films deposited on tungsten caused thermal desorption peaks of hydrogen at about 723 and 1173 K in TDS. The former was accompanied by other desorption of CO, CO₂ and hydrocarbons, whereas the latter was evolved with only a minor amount of CO. It was observed by XPS that the W4f peak began to appear at about 773 K, with an increasing surface composition corresponding to tungsten carbide at 1273 K. These observations indicate that a solid-state reaction between the carbon film and tungsten took place extensively above 973K to yield an intermetallic compound of W₂C at 1273 K.

Keywords: Tungsten; Carbon; Co-deposition; Solid-state reaction; Heat load; Hydrogen

Shotaro Morozumi^{a, c}, Hiroshi Saikawa^b, Kuniaki Watanabe^c

^a Magnesium Research Center, Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino-shi, Chiba 275-0016

^b Department of Metallurgical Engineering, Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino-shi, Chiba 275-0016

^b Hydrogen Isotope Research Center, Toyama University

^* The term "demagnesization" used here means the depletion of magnesium from the specimen by sublimation

Abstract

    Cut pieces of cast Mg₂Ni ingot were heated in a vacuum of about 10^-2 Pa for 1.8-14.4 Ks at 773, 823 and 873 K, and then examined using X-ray diffraction, optical microscopy and electron probe X-ray microanalyzer with EDX. The vacuum heating resulted in the demagnesization of Mg₂Ni phase by sublimation of magnesium from the surface, forming porous layer of MgNi₂. Thickness of the layer increased with increasing temperature and/or heating time. Approximate estimation, using these kinetic data, showed that apparent activation energy of the growth of the layer was 210 kJ/mol. Based on the estimation, the whole Mg₂Ni specimen with 0.7x10^-3m thickness was found to change into the porous MgNi₂ after vacuum-heating for 14.4 ks at 923 K.

Keywords: Mg₂Ni; MgNi₂; demagnesization; magnesium; pore

Takayuki Abe, Sachio Inoue, Daobin Mu, Yuji Hatano, Kuniaki Watanabe

Hydrogen Isotope Research Center, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

Abstract

    The effect of surface modification of amorphous MgNi by carbon or Ni was examined by conventional charge/discharge cycle tests and by a newly developed micro-paste electrode method. The charge/discharge tests showed that the surface modification by Ni had no effect on the capacity degradation of amorphous MgNi. The carbon modification, however, clearly improved the degradation; the discharge capacity after 6 cycles was still ca. 220 mA/g, which was about two-times larger than that for the unmodified sample. In the cyclic voltammogram (CV) obtained for the carbon-modified samples using the micro-paste electrode technique, the potential at rising of the cathodic current shifted to the anodic direction and the anodic peak was shaper and larger in comparison with that for the unmodified sample. Moreover, the CV observed for a carbon-modified sample immersed in 6N KOH solution, which can be regarded as a degraded sample, revealed that the deposited carbon suppressed the reduction in the electron transfer rate due to Mg(OH)₂ formation.

Keywords: rechargeable hydrogen batteries; micro-paste electrode technique; amorphous MgNi; Mg(OH)₂