Oxidation behavior of FeV₂O₄ and FeCr₂O₄ particles in the air: non-isothermal kinetic and reaction mechanism

The oxidation behavior of ferrovanadium spinel (FeV₂O₄) and ferrochrome spinel (FeCr₂O₄) at high temperature is crucial for the application of energy materials with spinel structure, as well as the cleaner utilization of high-chromium vanadium slag. In this study, the non-isothermal oxidation behavior of FeV₂O₄ and FeCr₂O₄ synthesized through high-temperature solid-state reaction, were investigated by thermogravimetry and X-ray diffraction at heating rates of 5, 10, and 15K/min respectively. The apparent activation energy was determined using the Kissinger-Akahira-Sunose (KAS) method, while the Malek method was employed to ascertain the mechanism function. Additionally, in-situ X-ray Diffraction (XRD) analysis was conducted to deduce the phase transformation of the oxidation mechanism for FeV₂O₄ and FeCr₂O₄. The results demonstrate a gradual increase in overall apparent activation energies for both FeV₂O₄ and FeCr₂O₄ during oxidation. The oxidation process can be divided into four stages based on the reduction conversion rate of each compound. The oxidation mechanisms of FeV₂O₄ and FeCr₂O₄ are complex with distinct mechanism functions. Specially, chemical reaction controls the entire oxidation process for FeV₂O₄ whereas FeCr₂O₄ it transitions from a three-dimensional diffusion model to a chemical reaction model. In-situ XRD results reveal numerous intermediate products during the oxidation process of both compounds; ultimately resulting in formation of final products such as FeVO₄ and V₂O₅ for FeV₂O₄, as well as Fe₂O₃ and Cr₂O₃ for FeCr₂O₄.