KINETICS AND MECHANISM OF SOLID-STATE REACTIONS OF SILVER TUNGSTATE WITH MERCURIC BROMIDE AND MERCURIC-CHLORIDE

1The kinetics and mechanism of the Ag2WO4-HgBr2 and Ag2WO4-HgCl2 react ions have been studied in the solid state. The kinetics have been carr ied out by a visual technique. Both the reactions follow the parabolic rate law X(2) = Kt, where Xis 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 h as been demonstrated that diffusion in both the reactions is predomina ntly controlled by the vapour phase, but diffusion by surface migratio n is also significant. In order to understand the mechanism of the rea ctions, X-ray powder diffraction, chemical analysis, conductivity and thermal studies have been carried out. Silver tungstate reacts with me rcuric bromide and mercuric chloride in the molar ratio 1:1 to give Ag Br, HgWO4 and AgCl, HgWO4, respectively, as the end products.