Fabrication and Characterization of Hydroxyapatite/Mullite and Tricalcium Phosphate/Al2O3 Composites Containing 30 wt% of Bioactive Components

Mullite-matrix and Al2O3-matrix composites were fabricated with 30 wt% hydroxyapatite (HA) and tricalcium phosphate (TCP), respectively, as additives to give bioactivity. A diphasic gel process was employed to lower the densification temperature of the mullite matrix to 1320 degrees C. A polymer complexation process was used to synthesize a TCP powder that was fully densified at 1250 degrees C, for application to the matrix. For the HA/mullite composite, HA decomposed during sintering by reactions with the matrix components of Al2O3 and SiO2, resulting in a mixture of Al2O3, TCP, and other minor phases with a low densification of less than 88% of the theoretical density (TD). In contrast, the TCP/Al2O3 composite was highly densified by sintering at 1350 degrees C to 96% TD with no reaction between the components. Different from the TCP monolith, the TCP/Al2O3 composite also showed a fine microstructure and intergranular fracture, both of which characteristics are advantageous for strength and fracture toughness.