HYDROGEN DIFFUSIVITY IN NOBLE METALS AT LOW TEMPERATURES (ELECTROCHEMICAL)
ISHIKAWA, TOMAZ TOSHIMI
Doctor of Philosophy
An electrochemical technique has been used to measure the diffusivity of hydrogen in high purity noble metals (Ag, Au, Cu, Pd and Pt) in the well-annealed state at low temperatures (283-323K). The data obtained have been considered in conjunction with those for as-quenched and aged Au samples in order to draw conclusions concerning the interactions between dissolved H atoms and lattice vacancies. It has been concluded, at least, in Pd, Cu and Au, that the H-vacancy interaction energy is too low to render diffusion anomalies observable at high temperatures. This is in accord with theoretical calculations based on the effective medium technique. The resulting diffusivities for quenched and aged Au are consistent with a simple statistical model in which a fraction of the H atoms saturate traps formed by quenching in vacancies, but the mobility is primarily determined by the excess of nontrapped H atoms diffusing through "normal" sites in FCC metals.
Engineering; Materials science