Interfacial effects on Ag:S nonstoichiometry in silver sulfide/alumina composites

The relative stoichiometry of Ag₂S containing dispersions of 0.2 μm Al₂O₃ particles was measured as a function of the chemical potential of silver between 158 and 220°C using solid state coulometric titration. For composites consisting of 3.5 m² of interface area per 1 cm³ of Al₂O₃Ag₂S composite, the effective homogeneity range in comparison to the pure material was as much as 120 times greater for the low temperature phase (α-Ag₂S) and 50% greater for the high temperature phase (β-Ag₂S). The process was described as that of silver absorption at solid-solid interfaces. Absorption isotherms and partial molar quantities for the interface were determined at 158 and 200°C.