Thermal shock study of α-alumina doped with 0.2% MgO

Thermal shock behaviour of α-alumina doped with 0.2% MgO is studied. A uniformly mixed powder of α-alumina, magnesia and 2% PVA solution is dried, granulated and uniaxially pressed into circular discs of 30 mm diameter and 3 mm thick. The discs are sintered at a maximum temperature in the range of 1500-1650 deg. C for 3 h. The thermal shock test is carried out by heating the sample with an oxy-hydrogen flame and by monitoring the crack formation by acoustic emission technique. In general, the samples possess high thermal shock resistance close to their melting temperature. The spinels formed due to MgO doping possess low fusion temperature which hinders the crack growth. The same has been confirmed from scanning electron microscope (SEM) studies. The samples sintered at lower temperature possess higher thermal shock resistance than those sintered at higher temperature. This is attributed to the higher porosity. The abnormal grain growth (AGG) associated with high sintering temperature might have contributed to lowering of thermal shock resistance. To summarize, MgO-doped alumina samples possess high thermal shock resistance by avoiding the catastrophic failure due to the formation of low fusion spinels