CONCENTRATION-DEPENDENCE OF HYDROGEN DIFFUSIVITY IN AMORPHOUS FE40NI38MO4B18 ALLOY

Hydrogen permeation in amorphous Fe40Ni38Mo4B18 alloy was studied using an electrochemical technique in the temperature range 303-348 K. Hydrogen diffusivities were calculated by several methods. They increased as the charging current density increased. The surface, concentration, and trapping effects on hydrogen diffusion were carefully examined. It was suggested that the surface impedance was not existent and diffusivity was affected by the "intrinsic" concentration and trapping effects. When diffusivities were correlated with hydrogen concentration, the effective activation energy decreased from 36.8 to 34.8 kJ/mol as the surface hydrogen concentration increased from 1000 to 6000 mol H/m3. Under the same charging current density, hydrogen concentration in the alloy decreased as temperature increased. Therefore, lower effective activation energies would be obtained if diffusivities were correlated with the charging current density. The concentration dependence of hydrogen diffusivity was rationalized on the basis of the structural features of amorphous alloys.