Structural and mechanical characterisation of MgO-, CaO- and BaO-doped aluminosilicate ceramics

The influence of oxides of divalent cations on the microstructure and on the physical properties of sintered aluminosilicates was studied. The results revealed that doping the aluminosilicates with 5 vol.% of BaO or CaO lead to high densities and good mechanical properties due to the formation of more abundant liquid phases, within which crystalline phases developed, in contrast to those found for MgO. Higher amounts of BaO led to porosity increase, devitrification and deterioration of mechanical properties. Comparing with the non-doped aluminosilicates, the pore volume fraction decreased for all doped ceramics but their final properties were seen to depend on the oxide additive. Moreover, ceramics performance under thermal fatigue was in agreement with the structural and mechanical analysis.