Kinetics and mechanism of solid state reactions of silver tungstate with mercuric bromide and mercuric chloride

Abstract

The kinetics and mechanism of the Ag 2WO 4HgBr 2 and Ag 2WO 4HgCl 2 reactions have been studied in the solid state. The kinetics have been carried out by a visual technique. Both the reactions follow the parabolic rate law X 2 = Kt, where X is the thickness of product layer at time t and K is the parabolic rate constant. The kinetics have been studied at several temperatures, for different lengths of air-gap between the two reactants and for different particle sizes of the reactants. It has been demonstrated that diffusion in both the reactions is predominantly controlled by the vapour phase, but diffusion by surface migration is also significant. In order to understand the mechanism of the reactions, X-ray powder diffraction, chemical analysis, conductivity and thermal studies have been carried out. Silver tungstate reacts with mercuric bromide and mercuric chloride in the molar ratio 1:1 to give AgBr, HgWO 4 and AgCl, HgWO 4, respectively, as the end products.