Use of electrochemical methods to determine chemical-diffusion coefficients in alloys: application to ‘LiAI’

Abstract

The use of electrochemical techniques to measure chemical-diffusion coefficients in solid alloys is reviewed. The theoretical basis and experimental aspects of four different approaches are discussed in detail: the potentiostatic, galvanostatic, potentiometric, and steady- state ac methods. As an example, all four of these techniques have been employed to determine the chemical-diffusion coefficient in the vario- stoichiometric intermetallic phase ‘LiAl’ as a function of composition. It is shown that experiments are relatively simple and rapid, and that the results obtained by the different methods are in good agreement. On the lithium-deficit side of the ideal stoichiometry in this phase, the chemical-diffusion coefficient increases rapidly with decreasing lithium concentration, reaching 10^-4 cm²s^-1 at 415°C near the aluminium-rich phase boundary. On the other hand, the chemical-diffusion coefficient is essentially independent of composition on the lithium-rich side of LiAI, having a mean value of 2. 4 × 10^-6 cm²s^-1