Microthermogravimetry in studying the defect and transport phenomena in transition metal sulfides

The chemical diffusion coefficient and point defect concentration in metal-deficit sulfides (Co9−yS8, Ni1−yS and Mn1−yS) has been studied as a function of temperature and sulfur activity using reequilibration and two-stage kinetic methods. Measurements have been carried out in a novel microthermogravimetric apparatus, enabling the mass changes of the sulfidized samples to be determined as a function of time with the accuracy of the order of 10−6 g. The diffusivity and defect concentration in investigated sulfides have been studied at high temperatures (873–1273 K) in pure sulfur vapours (10−1–104 Pa) and H2–H2S gas mixture with p(S2) ranging from 10−5 up to 1 Pa. The results described in the present paper show clearly that the microthermogravimetry may successfully be utilized in studying the defect and transport properties of nonstoichiometric metal sulfides.