Microstructure and phase evolution of Indian magnesite‐derived MgAl2O4 as a function of stoichiometry and ZrO2 doping

Abstract

AbstractTo aid development of cost‐effective sintered spinel as a refractory raw material, this paper presents an extensive analysis of microstructure and complex phase evolution of Al‐rich, Mg‐rich, and stoichiometric spinel aggregates derived from Indian magnesite and calcined alumina. Pore morphology in Al‐rich spinel was transformed upon sintering at 1650°C and corundum laths embedded in porous Al‐rich spinel matrix was formed. Stoichiometric spinel sintered at 1600°C consisted of mostly direct bonded angular equiaxed spinel grains which incorporated the impurities in solid solution. Mg‐rich spinel was composed of spinel grains with reduced angularity along with intergranular amorphous phase, small round monticellite grains, and periclase. EDS line scan revealed impurity‐free joins existed between direct bonded spinel grains. Mg‐rich spinel containing 0.65 wt% ZrO2 formed cubic ZrO2‐CaO‐MgO solid solution located along spinel boundaries, which reduced both intergranular amorphous phase and monticellite. This increased SiO2 and MgO content in spinel solid solution triggering exsolution of metastable cubic forsterite manifested as split spinel peaks in XRD pattern. A 14.7% reduction in slag penetration was exhibited upon doping Mg‐rich spinel with 0.21% ZrO2. Stoichiometric and Mg‐rich spinels attained 0.35% and 0.54% apparent porosity at 1600°C, which is better than most commercial sintered refractory spinels.