The dependence of H permeability upon H pressure and sample thickness was investigated systematically. The H permeability in Ni was determined at 473 to 973K, H pressures ranging from 340 to 8.67 x 104Pa, and sample thicknesses of 0.20 to 0.80mm. The data were fitted by:

P (cm2/s Pa½) = 5.94 x 10-5 exp[-51.5(kJ/mol)/RT]

It was confirmed that bulk diffusion was the rate-limiting step in H permeation through Ni, and that the solution of H in Ni depended upon Sievert's law. The H permeability of Hastelloy-X at 673 to 873K was described by:

P (cm2/s Pa½) = 5.62 x 10-5 exp[-58.2(kJ/mol)/RT]

for a sample without heat-treatment. By

P (cm2/s Pa½) = 3.14 x 10-4 exp[-75.3(kJ/mol)/RT]

for a sample heated (1023K, 30h) before measurement, and by

P (cm2/s Pa½) = 3.27 x 10-4 exp[-71.6(kJ/mol)/RT]

for a sample heated longer (1023K, 100h) before measurement. The activation energy for H permeation in Hastelloy-X was thus increased by heat treatment, and this was qualitatively attributed to the effect of precipitates.

Hydrogen Permeation through Nickel and Hastelloy X. T.Namba, S.Kokubo, M.Yamawaki, M.Kanno: Journal of the Japan Institute of Metals, 1978, 42[4], 374-80