The Electrochemical Determination of Diffusivity and Solubility of Hydrogen in Copper

The diffusivity and solubility of hydrogen in both annealed and as-cold-rolled copper were determined at room temperature by means of the electrochemical permeation method under the galvanostatic charging condition. Results obtained were as follows:(1) The observed build-up transient of hydrogen permeation through Cu foil specimens coincided with the theoretical transient which is the boundary condition of constant hydrogen concentration directly beneath the cathodic surface. Furthermore, the specimen thickness dependence of the steady state permeation current density was examined and consequently, the diffusion of hydrogen through the Cu foil in the permeation process was the rate determining step.(2) The diffusivity in the annealed Cu did not depend on the cathodic current densities in the range of ic=2.5 to 250 A·m−2, i.e., the hydrogen concentration in the cathodic surface, but in the case of as-cold-rolled Cu, it was slightly low, when the hydrogen was introduced at low ic values. While the solubility of hydrogen beneath the cathodic surface for each specimen increased with an increase of ic value, the difference of solubility between the annealed Cu specimen and the as-cold-rolled one was not remarkable at 315±1 K.(3) The temperature dependences of the diffusivity (D) and solubility (C) of hydrogen in the annealed Cu determined at the temperature range of 292 to 339 K under ic=10 A·m−2 can be described as follows:(This article is not displayable. Please see full text pdf.) \ oindentOn the other hand, compared with annealed Cu, the as-cold-rolled Cu had a lower diffusivity and slightly higher activation energy for diffusion, and the hydrogen absorption occurred by the exothermic reaction.