Fabrication and characterisation of a calcium phosphate/zirconia composite

The aim of this study is to fabricate high strength calcium phosphate/ yttrium artially stabilised zirconia (Y-PSZ) composites using a simple powder pressing technique. Various compositions of hydroxyapatite and zirconia powder, ranging from 10 to 90 wt% Y-PSZ, were prepared using a wet mixing process. Ten compacts (13.5mm×3mm) were made for each composition, pressed and fired in air at sintering temperatures from 1100 to 1450 o C for up to 12 hours. The bulk density, true porosity, linear shrinkage and biaxial flexural strength (BFS) were measured using standard methods. Microstructural changes were examined using XRD, DTA and SEM. The true porosity reduced and linear shrinkage increased with increasing sintering temperature and amounts of zirconia, whereas the firing time had little effect. The highest mean value achieved for the BFS was 269±20 Mpa for a composition of 70% Y-PSZ, fired at 1450 o C for 6 hours, however with the hydroxyapatite (Hap) decomposed to α-TCP. XRD and DTA data show an interaction between the zirconia and the Hap at temperature lower than changes normally encountered for pure Hap. We conclude that sintering temperature and composition affect densification behaviour of calcium phosphate/Y-PSZ composites. The BFS increases with a reduction of porosity and increases with both sintering temperature and additions of zirconia. It was noted that there is considerable scope for improvement in the BFS values by reducing the porosity of these composites. Further work is needed to elucidate the microstructural changes.