Kuniaki Watanabe, Kan Ashida, Masaru Sonobe

Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    The diffusion constants of hydrogen in metals scatter considerably in the Arrhenius plot diagram even for a given metal. We found regularity in the scattering of the diffusion constants of hydrogen in some metals: namely, there is a linear relationship between the pre-exponential factors and activation energies for C, Al, α-Fe, Cu and Pd. This is similar to the phenomenon known as the compensation effect in heterogeneous catalysis.
    Three different interpretation are proposed: they are based on the assumption of energetically heterogeneous sites, energetically homogeneous sites on which there exists a linear relationship between entropies and heats of adsorption, or the presence of two distinct diffusion paths. Three of them could give the relation, log(D₀) = αE_d + β. In contrast to the above, no clear correlation was observed for V, Nb, Zr, and Ta which belong to the IVB or VB groups in the periodic table.

Katsunori Mori^a, Yosikazu Isikawa^a, Kiyoo Sato^b, Kan Ashida^c, Kuniaki Watanabe^c

^a College of Liberal Arts, Toyama University, 3190 Gofuku, Toyama 930, Japan

^b Facully of Science, Toyama University, 3190 Gofuku, Toyama 930, Japan

^c Tritium Research Center, Toyama University, 3190 Gofuku, Toyama 930, Japan

Abstract

    Superconducting transition temperatures, T_Cs, and structural phase transition temperatures, T_Ms, of V₂ZrH_x, V₂ZrD_x and V₂ZrT_x have been measured in the composition range from x = 0 to 0.11, respectively. Protium(H),deuterium(D) or tritium(T) absorption is found to increase T_C up to x = 0.04 and it suggests the correlation with the structural phase transition. Above x = 0.04, T_Cs decrease with increasing composition, x, but inverse isotope effects have been observed apparently.

Masaru Sonobe^a, Sizuo Tada^a, Susumu Ikeno^b, Kan Ashida^c, Kuniaki Watanabe^c

^a Department of Metallurgical Engineering, Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930, Japan

^b Center for Cooperative Research, Toyama University, Gofuku 3190, Toyama 930, Japan

^c Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    As a step to understand factors affecting tritium inventory in Al alloys at low temperatures, diffusion of deuterium in Al at a low temperature region was measured using the ion-implantation techniques and secondary ion mass spectroscopy. The diffusion constants were evaluated as 1×10^-20 and 1×10^-18 m²/s at 20 and 70℃, respectively. Those values are considerably smaller than those by Ishikawa et al. in a similar temperature region. The compensation effect being taken into account, the difference in those diffusion constants as well as those reported so far were analyzed by assuming the presence of two parallel and/or series diffusion channels. The analysis could interpret the scattering of diffusion constants and compensation effect, suggesting that the observed diffusion constants of hydrogen are not necessarily unique to a given material, but depend on sample preparations and temperatures in which measurements are performed.

S. Usami^a, Y. Asai^a, M. Matsuyama^b, K. Watanabe^b

^a Department of Industrial Chemistry, Faculty of Engineering, Toyama University, Gofuku 3190, Toyama 930, Japan

^b Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    A part of tritium loaded in thermonuclear fusion reactors will be released to the environment. It is oxidized to form tritiated water, which is considerably more hazardous than elemental tritium (T₂ and/or HT). Investigations on the oxidation carried so far are radiochemical (including effects of X- and γ-rays), catalytic, and biochemical oxidation processes. We examined the effect of UV irradiation and found that the UV irradiation remarkably enhanced the oxidation rate of elemental tritium, suggesting that this effect plays an important role for the formation of tritiated water from elemental tritium in the atmosphere.