Electrochemical cells were used to generate and detect a sinusoidally oscillating wave of Ag chemical potential which propagated through a sectional sample of the pure sulfide, and a composite. The chemical diffusion coefficients of Ag in the pure and composite sections were determined by fitting mathematical relationships to the experimentally determined amplitude attenuation and phase shift of a wave. These relationships were deduced by solving Fick’s second law under suitable conditions. It was found that the presence of Al2O3 particles in the composite significantly altered its diffusional properties. This was attributed to the adsorption-desorption of Ag ions at the Ag2S/Al2O3 interfaces. The determination of the frequency dependence permitted the evaluation of the chemical diffusion coefficient of Ag in the pure and composite materials. At 168C, the diffusivities of the pure and composite materials were shown to peak at chemical potentials of about -3.3 and 2.4RT, respectively, with peak diffusivities of 0.53 and 0.10cm2/s, respectively. At 200C, the diffusivity of the pure sulfide increased to a value of 0.44cm2/s, without exhibiting a peak at up to about -4.7RT. The diffusivity of the composite peaked at -3.9RT, with a value of 0.19cm2/s. The shifting and generation of peaks, and the decreased chemical diffusivities which were due to the presence of particles in the composite material, were attributed mainly to changes in the thermodynamic factor ratio. This was assumed to imply that the component diffusion coefficient in the sulfide was independent of the existence of Ag2S/Al2O3 interfaces.

S.Ding, W.T.Petuskey: Journal of the Electrochemical Society, 1995, 142[7], 2306-16