発表論文 2003年

[2003_01]

Hydrogen-induced disproportionation of Zr2M (M=Fe, Co, Ni) and reproportionation

Masanori Hara, Ryo Hayakawa, Yoshinobu Kaneko, Kuniaki Watanabe

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

Abstract

    Hydrogen induced disproportionation for Zr2Fe, Zr2Co and Zr2Ni were studied by means of volumetric measurements of hydrogen absorption and desorption, and X-ray diffraction analyses of the product phases. These alloys formed respective hydrides of Zr2MH5 (M=Fe, Co and Ni) type at room temperature only under conditions of very slow hydrogen absorption, otherwise the alloys disproportionated. Heating Zr2MH5 to 1073K gave Zr2Ni and Zr2Co through decomposition, disproportionation and reproportionation. On the other hand, heating Zr2FeH5 to 1073K yielded ZrFe2 and Zr3Fe. At the elevated temperature of 773K, each alloy disproportionated very fast, within several tens of seconds, to ZrH2 and Zr-deficient alloys such as ZrCo, ZrNi and ZrFe for Zr2Co, Zr2Ni and Zr2Fe, respectively. ZrCo and ZrNi further disproportionated to ZrCo2 and Zr7Ni10 at this temperature, but the rates were very slow. These observations showed that the stability to hydrogen induced disproportionation is in the order of Zr2Ni > Zr2Co > Zr2Fe. This order is also valid for the ease of reproportionation, although the behavior of Zr2Fe was completely different from the others.

Keywords: Hydrogen absorbing materials; Zr-based alloy; Disproportionation; Reproportionation

[2003_02]

Non-destructive tritium measurements of Mk IIA divertor tile by BIXS

M. Matsuyama a, N. Bekris b, M. Glugla b, N. Noda c, V. Phillipps d, K. Watanabe a

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

b Tritium Laboratory, Forschungszentrum Karlsruhe, D-76021Karlsruhe, Germany

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

d Institute for Plasma Physics, Forschungszentrum Julich, Association EURATOM, Trilaternal Euregio Cluster (TEC), 52425 Julich, Germany

Abstract

    b-ray -induced X-ray spectrometry was applied to determine the amounts and depth profiles of tritium captured by graphite tiles used in the PTE1 campaign and by carbon fiber composite tiles in the DTE1 campaign of JET. Although, the X-ray spectra observed for both carbon tiles consisted of characteristic and bremsstrahlung X-rays, the intensities and shapes of the X-ray spectra were quite different between these tiles. The analyses of the X-ray spectra showed that the amount of tritium retained in the latter tile was on average 15,500 times greater than that in the former tile, and the tritium depth profile extended to 60 mm for the latter tile compared to 5 mm for the former tile. In addition, characteristic X-rays corresponding to Cl, Cr, Fe, Ni and Mo appeared in the latter tile, where Ni showed the highest concentration, indicating that considerable erosion and deposition of caccum vessel materials took place in the DTE1 campaign.

Keywords: Amount and depth profile of tritium; Metallic impurities; Non-destructive measurement; b-ray -induced X-ray spectrometry; JET divertor tiles

[2003_03 ]

Electrochemical studies of the effect of surface modification of amorphous MgNi electrodes by carbon or Ni

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 six cycles was still 〜220m A/g, which was about twice that of the unmodified sample. In cyclic voltammograms (CVs) obtained for the carbon-modified samples using the micro-paste electrode technique, the potential at the rising of the cathodic current shifted to the anodic direction and the anodic peak was sharper and larger than those for the unmodified sample. In addition, the CVs observed for carbon-modified samples immersed in 6N KOH solution, which can be regarded as degraded samples, revealed that the deposited carbon suppressed the reduction in the electron transfer rate due to Mg(OH)2 formation. Potential step measurements for the carbon-modified samples, on the other hand, showed that carbon modification on MgNi did not affect the diffusion process of hydrogen.

Keywords: Ni-MH batteries; Micro-paste electrode technique; Amorphous MgNi; Mg(OH)2

[2003_04]

Gas-driven hydrogen permeation in the surface-limited regime

A. Pisarev a, V. Shestakov b, R. Hayakawa a, Y. Hatano a, K. Watanabe a

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

b The State University of Kazakhstan, Almaty 480100, Kazakhstan

Abstract

    Gas-driven permeation of hydrogen through metal membranes in the surface-limited regime (SLR) is analyzed. An analytical solution for the concentration and permeation flux as a function of time is given for permeation through the asymmetric membrane having different conditions on the inlet and outlet sides. The features of the steady state and transient permeation are discussed. Comparison of calculations with an experiment on deuterium permeation through vanadium, which is available from literature, is performed. It has been demonstrated that the parameters, extracted from the measurements of the permeation rate in SLR are very uncertain. Even the calculations with opposite asymmetries can be equally well adjusted to the experiment. Non-zero initial conditions in SLR experiments are additional source of uncertainty. Measurements of the accumulation in a closed volume instead of the permeation rate can seriously mislead in the interpretation of the experiment. Complementary experiments on permeation in two opposite directions and measurements of permeation decay could increase the reliability of the data obtained.

[2003_05]

Hydrogen absorption by Pd-coated ZrNi prepared by using Barrel-Sputtering System

M. Hara a, Y. Hatano a, T. Abe a, K. Watanabe a, T. Naitoh b, S. Ikeno b, Y. Honda c

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

b Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930-8555, Japan

c Youtec Company, Nishihirai 986-1, Nagareyama, Chiba 270-156, Japan

Abstract

    To improve the durability of hydrogen storage materials against surface poisoning by impurity gases, effectiveness of Pd-coating layer prepared by using a Barrel-Sputtering System was examined for ZrNi powder. The effectiveness of Pd-coating was evaluated by activation temperature, at which Pd/ZrNi poisoned by air could be activated to absorb hydrogen. Characterization of Pd-coated ZrNi (denoted as Pd/ZrNi) by scanning electron microscopy, electron probe microanalysis and X-ray diffraction showed that a uniform Pd-coating layer was formed with the barrel-sputtering system. It was found that the poisoned Pd/ZrNi sample could be activated even at 423 K to absorb hydrogen at room temperature. This exhibits remarkable contrast to bare ZrNi, which could be only activated appreciably above 1073 K. It is concluded that the Pd-coating by barrel sputtering is quite effective to avoid the effect of surface poisoning of powdery hydrogen storage materials. However, the activation at excessively high temperature resulted in the loss of high activity to absorb hydrogen. It was concluded that this phenomenon was associated with reactions between Pd and ZrNi to form PdZr and other byproducts.

[2003_06]

Relation between recombination rate constant of deuterium at niobium surface and Oxygen Concentration in Bulk

R. Hayakawaa, A. Busnyukb, Y. Hatanoa, A. Livshitsb, K. Watanabea

aHydrogen Isotope Research Center, Toyama University, Toyama 930-8555, Japan

bBonch-Bruyevich University, 61 Moika, St. Petersburg 191186, Russia

Abstract

    A systematic study was carried out on the relation between the surface recombination rate constant of deuterium at a Nb surface and the oxygen concentration in bulk. Oxygen was introduced into a Nb specimen up to concentrations from 0.12 to 4.3 at.%. Then, deuterium was introduced into the specimens, and the surface recombination rate constant was measured by thermal desorption in a temperature range from 623 to 913K. The surface recombination rate constant of deuterium decreased with increasing oxygen concentration in the solid solution phase. This reduction in the recombination rate constant was attributed to the increase of oxygen coverage at the surface with the bulk concentration. Irrespective of the bulk oxygen concentration, no significant increase was observed in the height of the potential barrier against desorption processes.

[2003_07]

Flibe-D2 permeation experiment and analysis

S. Fukadaa, R.A. Anderlb, R.J. Pawelkob, G.R. Smolikb, S.T. Schuetzb, J.E. O'Brienb, H. Nishimurac, Y. Hatanod, T. Teraic, D.A. Pettib, D.-K. Szec, S. Tanakac

aKyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan

bIdaho National Engineering and Environment Laboratory (INEEL), Idaho Falls, ID 83415, USA

cUniversity of California, Center for Energy Research, San Diego, CA 92093-0417, USA

dToyama University, Gofuku, Toyama 930-8555, Japan

Abstract

    Experiment of D2 permeation through Ni facing with purified Flibe is being carried out under the Japan-US joint research project (JUPITER-II). The experiment is proceeding in the following phases; (i) fabrication and assembly of a dual-probe permeation apparatus, (ii) a single-probe Ni/D2 permeation experiment without Flibe, (iii) a dual-probe Ni/D2 permeation experiment without Flibe, (iv) Flibe chemical purification by HF/H2 gas bubbling, (v) physical purification by Flibe transport through a porous Ni filter, (vi) Ni/Flibe/D2 permeation experiment, and (vii) Ni/Flibe/HT permeation experiment. The present paper describes results of the single and dual Ni/D2 permeation experiments in detail.