The Oxidation of Fe-Mn Alloys in Carbon Dioxide-Carbon Monoxide Atmospheres at 1000°C

Abstract

<p> The oxidation kinetics of iron-manganese alloys with manganese contents up to 60 w/o exposed to carbon dioxide-carbon monoxide atmospheres at 1000°C have been determined as a function of gas composition by a gravimetric technique. The experimental conditions were chosen in order that the product of the reaction between metal and oxidizing atmosphere would be a single-phase oxide scale.</p> <p> The main objective of this study was to determine the oxidation characteristics of iron-manganese alloys. It has been found that the rate of oxidation of alloys up to 12% manganese at the early stages is limited by interfacial reaction control and later by diffusion processes in the oxide scale. Oxidation rates of alloys containing more than 27% manganese are entirely controlled by diffusion in the oxide scales. The experiments show that the linear oxidation rate is independent of alloy composition. On the other hand, the rate of parabolic oxidation becomes lower with increasing manganese content in the alloy.</p> <p> The results from gravimetric measurements and chemical analyses have been interpreted by a model for the diffusion of iron and manganese through the wustite scale. The phenomenological equations from this theoretical approach have enabled calculations of self-diffusion coefficients for iron and manganese and the concentration of defects in the FeO-MnO solid solution as a function of MnO content. The calculated defect concentrations are compared with theoretical models assuming different types of defect structures.</p>