Diffusion and Absorption of Hydrogen in Liquid-Quenched and Annealed Ni₈₁P₁₉ Alloy

Transport and absorption of hydrogen were studied in the Ni₈₁P₁₉ alloy in the as-quenched amorphous state and after annealing for 1 h at temperatures up to 873°K. The diffusivity and the amount of diffusible and trapped hydrogen were determined from electrochemical permeation measurements performed at 298°K. After annealing below the crystallization temperature (T_c ≃ 560°K), the hydrogen diffusivity and absorption rose by up to about twice, whereas at higher temperatures (formation of the Ni and Ni₃P phases) they drastically decreased, with a drop in diffusivity being almost three orders of magnitude. Below T_c, the ratio of trapped hydrogen to total absorbed hydrogen almost did not change with the annealing temperature, being about 0.75. The rise in the hydrogen diffusivity and absorption below T_c may result from local ordering of atoms; it demonstrates that the behavior of hydrogen may be a sensitive measure of structural relaxation in the amorphous alloy.