Mechanism of Carbothermic Reduction of Fe₃O₄ Irradiated by Microwave with 2.45 GHz

Abstract

The reaction mechanism of the carbothermic reduction of Fe₃O₄ powder heated by radiating multi-mode microwave with 2.45 GHz and 2.8 kW was clarified by means of gas analysis and changing the contact state of mixed powder. The reaction process was classified in three stages. In the stage I, the powder was heated by the magnetic loss of Fe₃O₄ and the induction current loss of graphite (Gr) and reached peak temperature of 1000°C to 1200°C in 30 s to 40 s after irradiation, and then dropped rapidly at 600°C to 700°C. Fe₃O₄ was reduced to FeO. In the stage II, the powder was heated by the induction current loss of FeO and Gr, and the entropy production was maximum after about 100 s. In the stage III, molten pig iron was produced with light emission. The reaction rate was always larger for the Boudouard reaction than the reduction of Fe₃O₄ or FeO. This indicates that the Boudouard reaction is preferentially promoted by microwave near the contact points between Gr particles. The dominant reactions were determined to be Fe₃O₄+CO→3FeO+CO₂, FeO+CO→Fe+CO₂ and the Boudouard reaction from the smaller negative value of the Gibbs energy change of reactions. In the stage I and III, the pre-exponential factor of reaction rate increased with time. In the stage II, the apparent activation energy of reduction rate of iron oxide heated by microwave was lower than conventional heating.