Cementite Formation from Magnetite under High Pressure Conditions

Abstract

Measurements have been made of the rate of Fe3C formation from Fe3O4 powder and Fe3O4 single crystals at 773 K and 1 023 K under the high pressure of 0.5 and 1.0 MPa by using thermo-gravimetric method. Along with the kinetic study of Fe3C formation, high resolution TEM observation around the interface between Fe3O4 matrix and the formed Fe3C have been carried out to confirm the thermodynamically possible direct Fe3C formation from Fe3O4 without the formation of intermediate metallic Fe. Analysis of the rate results suggests that the reaction mechanism of Fe3C formation was possibly described by the sequential reactions of the conversion of Fe3O4 to Fe3C via intermediate metallic Fe although the metallic Fe existence was not confirmed by TEM observation. This inconsistency was explained by considering the relative reaction rates of Fe3C formation from Fe and Fe formation from Fe3O4. It was also found that not only the carbon activity of more than unity but also the low oxygen potential enough for metallic Fe existence might be required for the Fe3C formation.