A comparative study on the effect of different additives on the formation and densification of magnesium aluminate spinel

Commercially available fused magnesia and sintered alumina sources were used to form reaction sintered spinel by solid oxide reaction route in a single firing. The effect of the addition of four different additives, namely MgCl2, LiF, AlCl3, and MnO2, at 2 wt% level was studied. Mixed oxide compositions were compacted under a uniaxial pressure of 150 MPa and then sintered between 1200 and 1600 °C. The dilatometric study and phase analysis was done to observe the spinel formation reaction. Densification study of the sintered product was done to understand the effect of additives. Cold Crushing strength and thermal shock resistance of 1600° sintered pellets were studied. Microstructural study using field emission scattered electron microscopy (FESEM) was also done to understand the grain development on sintering in the compositions and the effect of different additives on sintering. LiF and MgCl2 were found to strongly enhance the spinel formation reaction. Bulk density values were found to be lower for the additive containing batches at 1200 °C due to enhanced spinel formation but higher at 1600 °C due to greater sintering. Strength values were strongly enhanced by LiF and MnO2 due to the development of dense, compact microstructure. Also, additives containing compositions showed much higher strength retainment even after 6 cycles of thermal shock.