CHEMICAL DIFFUSION AND POINT-DEFECT PROPERTIES OF IRON SULFIDE (FE1-DELTA-S) AT TEMPERATURES 600-DEGREES-1000-DEGREES-C

Measurements of the sulfidation scaling kinetics of iron under transient and steady-state conditions and relaxation kinetics of different changes in the nonstoichiometry of FeS plates were carried out under sulfur pressures 10-11-10-3 atm in the temperature range 600°-1000°C. The scales and plates exhibited a preferred texture in the “a” crystallographic direction. The chemical diffusion coefficient is independent of the degree of nonstoichiometry at a given temperature and its temperature dependence is given by The sulfur pressure and temperature dependence of the nonstoichiometry of iron sulfide is interpreted by a point defect model involving a large repulsive interaction between iron vacancies. The resulting correlation yields an expression for evaluating the iron self-diffusion coefficient from the chemical diffusion coefficient. The predicted values for the iron self-diffusion coefficient, the sulfur pressure, and temperautre dependence are in good agreement with results for the iron tracer-diffusion coefficient in the “a” crystallographic direction of monocrystal iron sulfide. © 1979, The Electrochemical Society, Inc. All rights reserved.