To 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% ZrO 2 formed cubic ZrO 2 -CaO-MgO solid solution located along spinel boundaries, which reduced both intergranular amorphous phase and monticellite. This increased SiO 2 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% ZrO 2 . 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. K E Y W O R D S

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