Transport properties of transition metal sulphides have been discussed
in terms of chemical- and self-diffusion coefficients. It has been sh
own that in the case of highly non-stoichiometric sulphides (Co1-yS) t
he chemical diffusion coefficient may easily be obtained from thermogr
avimetric measurements of re-equilibration kinetics. If the non-stoich
iometry and thereby defect concentration is low (Mn1-yS), the re-equil
ibration kinetics is difficult or impossible to follow thermogravimetr
ically, and the electrical conductivity method can be applied, If the
non-stoichiometry of a given metal sulphide is known as a function of
temperature and sulphur activity, chemical diffusion data may successf
ully be utilized for calculation of parabolic rate constants of metal
sulphidation and to obtain better insight into the growth mechanism of
the sulphide scale. Using this procedure it has been shown that the s
ulphide sea les on cobalt and manganese grow by the outward volume dif
fusion of cations. The chemical diffusion coefficient may also be used
in the calculation of the self-diffusion coefficient of cations (or a
nions) if the non-stoichiometry data of a given sulphide are available
. It has been shown that the self-diffusion coefficients of manganese
in Mn1-yS obtained in such a way are in full agreement with those dete
rmined experimentally.