Synthesis and sintering of hydroxyapatite–zirconia composites

Hydroxyapatite (HA) has been synthesised in presence of 10–30 wt.% of m-ZrO2 by solid state reaction between tricalcium phosphate (TCP) and Ca(OH)2 at 1000 °C for 8 h. The m-ZrO2 was partly converted into t-ZrO2 by partial consumption of CaO which in turn resulted in a mixture of β-TCP and HA. On sintering these HA–β-TCP–ZrO2 composite powders at 1100–1400 °C for 2 h, the HA is further decomposed into β-TCP and CaO. The CaO so produced reacts further with m-ZrO2/t-ZrO2 generating a mixture of t-ZrO2 and CaZrO3 in different proportions. These various phases formed interfere with the sinterability of the composites due to their differential shrinkages leading to a overall reduced density as compared to that of pure HA. The composites show a T-onset of decomposition at around 1150 °C and a 40% HA yield was obtained at the highest sintering temperature of 1400 °C. The products were subjected to XRD for phase analysis and the microstructural features were studied by SEM.