Theoretical calculation of vapor transport of solid in the ZnS: HCl system

Abstract

A theory has been previously developed which allows calculation of the rate of diffusion-limited vapor transport of solids in a multicomponent multireaction system which is driven by a small temperature gradient. This theory is applied to the case of ZnS(e) being transported by reaction with HCl-4;. All the required parameters, i.e., gaseous diffusion coefficients, thermodynamic data, etc., are either known or independently estimated. The calculated results are found to be in quantitative agreement with the experimental results within the estimated uncertainties in the thermodynamic and diffusion coefficient data over a wide range of initial HC1 pressures. Below an initial HC1 pressure of 1 atm, it is seen that the experimental rate of transport drops sharply in comparison to the theoretical prediction. This has previously been attributed to kinetic limitations. It is shown that the assumption of a single binary diffusion coefficient, applying to all pairs of component species, may lead to results in approximate agreement with the more "exact" theoretically predicted results.