Isotope Effect in Hydrogen Diffusion in Copper

Abstract

Hydrogen isotopes, H and D, were dissolved in excess in copper by means of the liquid hydrogen quenching technique and their diffusion process at temperatures between 220 K and 350 K was studied by the electrical resistivity measurement. In this temperature range, an abnormal mass effect in diffusion was observed. The activation energies of diffusion of the isotopes were; E_H=34.3 kJ/mol and E_D=36.1 kJ/mol for hydrogen and deuterium, respectively. The relation, E_H⁄E_D<1, is not expected from the classical diffusion theory, and the ratio of diffusion constant, D_H⁄D_D, increased with decreasing temperature, exceeding the classical value, \sqrt2, in the lowest temperature region in the present experiment. The observed behaviour is explained by a tunneling diffusion mechanism as in the case of hydrogen diffusion in nickel.