The transport properties of transition metal sulfides were considered in terms of chemical diffusion and self-diffusion coefficients. It was shown that, in the case of highly non-stoichiometric sulfides such as Co1-xS, the chemical diffusion coefficient could be easily deduced from thermogravimetric measurements of the re-equilibration kinetics. If the non-stoichiometry and resultant defect concentration was small, as in the case of Mn1-xS, the re-equilibration kinetics were difficult or impossible to monitor thermogravimetrically, but the electrical conductivity method could be used. If the non-stoichiometry of a given metal sulfide was known as a function of temperature and S activity, chemical diffusion data could be used to calculate the parabolic rate constants of metal sulfidation. By using this procedure, it was shown that sulfide scales on Co and Mn grew via the outward volume diffusion of cations. The chemical diffusion coefficient could also be used to calculate the self-diffusion coefficient of cations (or anions) if non-stoichiometry data for a given sulfide were available. It was shown that the self-diffusion coefficients of Mn in Mn1-xS, which were obtained in this manner, were in full agreement with experimentally determined values.

S.Mrowec, K.Hashimoto: Journal of Materials Science, 1995, 30[19], 4801-16