Diffusion of Hydrogen at High Temperatures in the Group V Transition Metals and Alloying Effect on the Diffusion(Metallurgy)
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Diffusion coefficients of hydrogen in the Group V transition metals, i.e. vanadium, niobium and tantalum, and those in vanadium alloys containing chromium, iron, niobium and titanium were measured in the temperature range of 500〜1100℃ by the absorption method. The following results were obtained : (1) Diffusion data at high temperatures in the Group V transition metals in the present experiment coincided well with data obtained at low temperatures by different methods, e.g. electrical resistivity, etc., but not with data at moderate temperatures measured by the same absorption method. (2) Below some critical temperature of the metals (540 to 700℃), the values of diffusion coefficient deviated downward from the linearity of Arrhenius plots. This deviation might be attributed to the effect of surface layers, probably oxide films, of the specimens, which would depress the absorption process of hydrogen in the metals. (3) The diffusion coefficient of hydrogen in vanadium was decreased by alloying chromium, iron or niobium, but increased by addition of 40at.% titanium. (4) Variations of the vibrational frequency term, D_0, and the activation energy, ΔHD, with the alloy concentration were almost parallel to that of the electric specific heat coefficient so far reported. Therefore, it was concluded that the screening of proton by electrons seemed to play an important role in the diffusion process, as with the case of the solubility of hydrogen in the metals.
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