Oxidation kinetics of typical high FeO ferrous spinels

Abstract

In this study, the isothermal oxidation kinetics of magnetite (OM), high-Mg magnetite (MM), titanomagnetite (TM), and chromite (CM) were investigated by applying thermogravimetry (TG) analysis at temperatures ranging from 1073 K to 1223 K. The results show that different high-FeO spinels possess distinct oxidizability. The oxidation process of OM in the temperature range from 1073 K to 1223 K is faster than others, followed by MM and TM. While CM exhibits the poorest oxidizability, and generally undergoes complex phase transitions. In the initial stage of oxidation, high FeO spinels have a higher oxidation rate due to the surface oxidation of spinel particles. However, the oxidation rate gradually declines in the later stages of oxidation due to increased internal diffusion resistance. The results of oxidation kinetics indicate that the initial oxidation stage of four spinels can be described as random nucleation and subsequent growth mechanism. The average apparent activation energies of the initial oxidation stage of OM, MM, TM, and CM are 25.09 kJ/mol, 32.39 kJ/mol, 58.10 kJ/mol, and 82.42 kJ/mol, respectively.