Crystallization Kinetics of 2CaO·Fe₂O₃ and CaO·Fe₂O₃ in the CaO–Fe₂O₃ System

Abstract

In this study, the non-isothermal crystallization kinetics of 2CaO·Fe₂O₃ and CaO·Fe₂O₃ were investigated by DSC measurement. Crystallization of CaO–Fe₂O₃ system includes three reactions and can be explained using Fe₂O₃–CaO phase diagram. The mechanisms of 2CaO·Fe₂O₃ and CaO·Fe₂O₃ crystallization were analyzed using Avrami and Mo models. Results of the Avrami model analysis indicated that growth of 2CaO·Fe₂O₃ and CaO·Fe₂O₃ include two stages, which are controlled first by a fibril-like mechanism followed by a spherulitic-type mechanism. The Mo model analysis yielded results similar to those of the Avrami model and further concluded that Avrami exponent/Ozawa exponent is constant despite the changes in cooling rate. Calculations using Kissinger method revealed that the activation energy of 2CaO·Fe₂O₃ and CaO·Fe₂O₃ crystallization were −464.16 kJ·mol⁻¹ and −172.61 kJ·mol⁻¹, respectively. Moreover, 2CaO·Fe₂O₃ crystallization occurs in a difficult manner but proceeds at a faster rate than CaO·Fe₂O₃ crystallization. Increasing the cooling rate promotes CaO·Fe₂O₃ crystallization but inhibits 2CaO·Fe₂O₃ crystallization, which is beneficial during sintering.