Yuji Hatano, Yoshiyasu Nanjo, Ryo Hayakawa, Kuniaki Watanabe

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

Abstract

    Hydrogen permeation through vanadium was examined under helium ion irradiation. The upstream surface of a vanadium membrane was exposed to hydrogen gas at 673K and 640 Pa, and the downstream surface was irradiated with 5 keV helium ions. No significant variation in the permeation rate was observed in the initial stage of irradiation. The permeation rate, however, started to decrease at a helium ion dose of 10²¹m^-2 with further irradiation. In this region, the permeation rate dropped immediately by intermission of irradiation and shot up by resumption. These results were successfully explained with a model that helium bubbles act as trapping sites of hydrogen and detrapping is enhanced under irradiation.

Masanori Hara^a, Ryo Hayakawa^b, Kuniaki Watanabe^a

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

^b Graduate Student, Toyama University

Abstract

    The kinetics of hydrogen-induced disproportionation of Zr₂Co was studied by the conventional constant volume method in a temperature range of 773 to 873 K. It was found that Zr₂Co disproportionated as 2Zr₂Co + 3H₂→ 3ZrH₂ + ZrCo₂ through a two-step mechanism as 1) Zr₂Co + H₂→ ZrH₂ + ZrCo and 2) 2ZrCo + H₂→ ZrH₂ + ZrCo₂. The first step was very fast and completed within only 100s at 773K. The rate, however, decreased with increases in temperature. The apparent rate constant for the first step disproportionation was determined to be κ=2.0×10^-2 exp [15.0×10³ (J/mol)/RT], where the kinetics could be explained by nucleation and one-dimensional growth model. The kinetics of the second step disproportionation could be explained by nucleation and three-dimensional growth model.

Keywords: disproportionation; hydrogen; kinetics; hydrogen absorbing alloy; zirconium-based alloy; Zr₂Co; ZrCo

Masao Matsuyama, Satoshi Ueda, Kuniaki Watanabe

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

Abstract

    A newly developed technique, beta-ray induced X-ray spectrometry (BIXS), was applied to in situ and real-time measurements of depth profiles of tritium in palladium and zirconium. Two distinct spectra were detected by BIXS, one due to the characteristics X-rays giving rise to a sharp intense peak; and the other due to the bremsstrahlung X-rays leading to a broad weak peak. The intensities of these peaks for palladium decreased with time at room temperature, while they were almost constant for the Zr-sample at room temperature. Heating the Zr-sample, however, caused similar changes in the spectra as those for palladium at room temperature. It was found that these phenomena are due to the diffusion of tritium into the bulk regions, causing a reduction of the tritium concentration in the sub-surface layers of the samples. All of the observed beta-ray induced X-ray spectra could be reproduced well by computer simulation by assuming respective depth profiles of tritium in the samples.

It was confirmed that BIXS in quite useful to analyze the dynamic transport behavior of tritium in materials.

Keywords: Tritium interaction; β-Ray; X-Ray spectrometry; Depth profiles; In situ measurement

Masanori Hara^a, Toshio Okabe^b, Katsunori Mori^c, Kuniaki Watanabe^a

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

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

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

Abstract

    The kinetics and mechanism of the hydrogen-induced disproportionation of ZrCo was studied experimentally. In general, the time dependence of the disproportionation has a sigmoidal shape. The disproportionation rate increased with increasing initial hydrogen pressure and showed a 3/2-power dependence on the pressure. As for the temperature dependence, the rate increased with temperature only up to 815 K and then decreased at higher temperatures. Namely, a volcano-type pattern was observed in the Arrhenius plot of the rate constant. In addition, a fairly large isotope effect was observed for the rate of disproportionation between hydrogen and deuterium. These results were explained well by a nucleation and nuclei growth model, in which hydrogen solubility in the ZrCo phase was assumed to play an important role.

Keywords: ZrCo; Kinetics; Mechanism; Hydrogen-induced disproportionation