Effect of additives on densification of tabular alumina: A case of single additive doping and co-doping

Abstract

The effect of doping and co-doping of oxide additives on sintering properties and microstructural features of tabular alumina is investigated. To examine the effects of single doping, 2 wt % of each of CaO, Fe2O3, SiO2 and TiO2 were added to tabular alumina fines and the samples were sintered at 1550 °C, 1600 °C and 1650 °C. Single oxide doped batches showed improved density except the samples doped with CaO. The phase analysis and microstructural results of CaO doped samples revealed the formation of calcium hexa-aluminate phases which resulted in poor density. The abnormality in grain-growth on addition of TiO2 was found to have a deteriorating effect on the strength of samples at 1650 °C despite of maximum densification. To observe the effects of co-doping of oxides, 1 wt % of each of CaO, Fe2O3, SiO2 and TiO2 were added to tabular alumina in unique combinations under same sintering conditions. Co-doping of oxides was found to be effective in property development of samples at higher sintering temperatures. The characteristics of secondary phases so formed influenced the properties of tabular alumina through liquid phase sintering, abnormal grain growth or decreasing the bulk density of samples. The strength value increases with temperature, more prominently for samples with liquid phase formation, but decreases for samples with abnormal grain growth and hexagonal shaped secondary phase formation.