Chronoamperometric Determination of Solid State Diffusion Coefficients in Copper-Gold Alloys Using a Molten Salt Electrolyte

Abstract

The intermetallic diffusion coefficient in Cu-Au alloy between 400 °C and 550 °C is measured by chronoamperometry using a Cu-Au electrode in a molten LiCl-KCl electrolyte containing small amounts of Cu+ ions. The current response to a defined constant potential step is controlled by the rate of diffusion in the alloy electrode. The mathematical treatment developed by introducing the Boltzman transformation shows that the current density is a linear function of the reciprocal square root of time whatever the dependence of D versus concentration is. The method is applied to cathodic as well as anodic potential pulses which correspond to surface alloying or dissolution i.e. diffusion “in” or “out” the sample. The shift of the interface due to the copper deposition or dissolution is considered according to the Oldham and Raleigh’s method. By studying the electrochemical response at very short times the diffusion can be examined in the first atomic layers of the electrode interface. © 1983, Walter de Gruyter. All rights reserved.