Diffusion of Hydrogen in Vanadium-Based BCC Alloys
A resistiometric technique for measurement of large diffusion coefficients of hydrogen in metals is described. Diffusion is along the length of a foil (7.0 cm × 0.15 cm × 100 μm) which has been loaded electrolytically to a hydrogen concentration of approximately 0.5 atomic per cent. Initially the hydrogen is held at a uniform concentration in essentially half the length of the foil by the effect of a DC electrotransport current of 2500 A/cm2 in the other half. After this current is removed, the diffusion of H into the empty half is monitored by its effect on the resistivity of the foil. The sensitivity to hydrogen concentration is better than ± l0ppm. Recovery of equilibrium resistivity at essentially one point in the foil measures recovery of equilibrium hydrogen concentration because of the linear dependence of resistivity upon concentration. Good fits to the diffusion equation are obtained though 99 percent of full recovery. Values of diffusion coefficients of 1H and 2H have been measured in the vanadium-based BCC alloy system, V-Ti and V-Cr up to about ten percent Ti and Cr. Before adding hydrogen, the V-Ti foils are purified and annealed at 1800°K in a pure argon atmosphere using electrotransport to remove O, N, and C impurities. V-Cr foils are annealed in a similar way but cannot be similarly purified because of high Cr vapor pressure at the temperature needed for electrotransport. The addition of Ti or Cr to V causes an increase in the activation energy of diffusion for both hydrogen isotopes.