Reaction sequence and formation kinetics of perovskite by calcium ferrite–titania reaction

Abstract

Controlling the generation of perovskite (CaO·TiO2, CT) during sintering with vanadium–titanium magnetite (VTM) is the key to improve the strength and yield of VTM sinters. This study determined whether adding pre–formed calcium ferrite (CaO·Fe2O3, CF) effectively prevents the formation of CT during sintering with VTM. The formation behavior of CT in the CF–T system was investigated using X–ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Phase composition analysis by XRD indicates that CT is formed significant quantities in the CF–T system when the temperature is higher than the melting temperature of CF. DSC analysis shows that the CF–T samples undergo two reaction stages in continuous heating. Namely, CF first melts and forms its liquid phase, then TiO2 substitutes Fe2O3 in liquid CF to produce CT. SEM images confirm that CT could be generated at regions with a high concentration of CF. Non–isothermal DSC measurements on the formation kinetics of CT indicate that its activation energy reaches 252.00 kJ/mol and that the model function is f(α)=(1–α)2, revealing a second–order reaction based on Malek analysis. The kinetics equation of CT formation can be expressed by ln(dαdt)=2ln(1−α)−216805+70382αRT+16.71+10.33α. Quantitative calculation on enthalpy change by DSC curves shows that raising heating rates enhance the consolidation ability of CF–T samples as the melting of CF increases and the formation of CT decreases.