Effect of in situ generated nascent magnesia and alumina from nitrate precursor on reaction sintered magnesium aluminate spinel

Abstract

Synthesis of dense magnesium aluminate spinel using a single stage solid oxide reaction is difficult owing to volume expansion associated with spinel formation. In the present work, reaction sintered magnesium aluminate spinel was prepared using commercial grade oxide in a single stage solid oxide reaction reactants. The effect of incorporation of nascent MgO and Al2O3 from nitrate precursor additives was studied. Aluminium nitrate nonahydrate and magnesium hexahydrate were used up to 2wt.% as a source of nascent Al2O3 and MgO respectively. Sintering of the mixed oxide compositions was done in the temperature range 1200–1600°C after compaction under a uniaxial pressure of 150MPa. The dilatometry study was used as a tool to observe the spinel formation reaction. Sintered products were characterised by densification study, flexural strength, thermal shock resistance measurement, phase analysis and microstructural development. The presence of excess MgO and Al2O3 enhanced the spinel formation reaction and densification of spinel at a higher temperature. The template mechanism of spinel formation was observed in the microstructures. The addition of excess alumina and magnesia was found to increase strength values. Also, much higher strength retainment even after 6–8cycles of thermal shock was observed in additive contained batches.