Kinetics of reaction of ZrCl4--HfCl4 vapor mixtures with solid sodium chloride spheres

Reaction of ZrCl4--HfCl4 vapor mixture with solid sodium chloride forms solid solution of the hexachloro compounds. The kinetics of this competitive reaction have been studied over a range of temperature and total pressures. It is postulated that the rate determining step pertains to outward migration of sodium and chlorine ions through the product layer with concurrent diffusion of the vacancies in the opposite direction. Based on this model, a kinetic equation has been derived which is identical to the Carter--Valensi equation for the overall weight fraction gained as a function of time provided the composition of the solid solution product layer remains invariant with the progress of the reaction. The experimental weight gain data are in good agreement with the model