Evolution of MnO–SiO₂–Al₂O₃–MgO inclusions during heat treatment at 1100 °C

Abstract

To investigate the evolutionary behavior of the MnO–SiO₂–Al₂O₃–MgO inclusions during heat treatment, water quenched samples were isothermally held at 1100 °C for 120 min in Ar and air atmosphere, and the obtaining samples were analyzed by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer. It showed that 3MnO·Al₂O₃·3SiO₂ and MnO·SiO₂ were detected in the 5 wt.% MgO system after isothermal holding in Ar atmosphere, while MgO·Al₂O₃, MnO·SiO₂ and Mn₇O₈·SiO₄ were detected in air atmosphere. The evolutionary behavior of the 10, 15 and 20 wt.% MgO systems after isothermal holding in different atmosphere were consistent. Oxygen affected the solid phase transformation of the low MgO content systems. The calculation results of FactSage 8.1 showed that MgO·Al₂O₃ was formed in the 5 wt.% MgO system with air atmosphere. The solid phase transformation was accompanied by grain coarsening during the isothermal holding process. The differences in the solid phase transformation in different atmosphere of the 5 wt.% MgO system indicated that it was a gas-phase transport grain coarsening mechanism. The enrichment of Al element in the liquid phase region at the grain edges, the homogeneous distribution of Mg element and the disappearance of the liquid phase within the crystal revealed that other MgO content systems were liquid–solid transport grain coarsening mechanism.