TRANSPORT-PROPERTIES OF NONSTOICHIOMETRIC MANGANOUS SULFIDE

The chemical diffusion coefficient in non-stoichiometric manganous sul phide, Mn1-yS, has been measured as a function of temperature (1073-13 73 K) and sulphur activity (10(-2)-10(3) Pa) using electrical conducti vity reequilibration method. It has been shown that the mobility of do ubly ionized cation vacancies, constituting the predominant point defe cts in Mn1-yS, is independent of their concentration and characterized by the following empirical relationship: D-v = 1.3.10(-2)exp (76.4+/- 0.5 kJ mol(-1)/RT). Using these data and those of non-stoichiometry th e self-diffusion coefficient of cations in metal deficient manganous s ulphide has been calculated: D-Mn = 6.5.10-4p(s2)(1/6)exp (-119.0+/-0. 7 kJ mol(-1)/RT). This relationship is in agreement with that calculat ed from manganese sulphidation kinetics. It may be then concluded, tha t the growth process of alpha-MnS scale on manganese at high temperatu res (> 1000 K) is governed by the volume diffusion of cations.