Synthesis and Sintering of Hydroxyapatite in Presence of Oxide Additives

Hydroxyapatite (HAP) has been synthesised in the presence of Al2O3 and ZrO2 additives by solid state reaction between tricalcium phosphate (TCP) and Ca(OH)2 at 1000°C/8 h. The doping by Al2O3 and ZrO2 resulted in the formation of CaAl2O4 and t-ZrO2 as the secondary phases by partial consumption of CaO which in turn leads to the appearance of (beta)-TCP along with HAP. The amount of HAP in the product is further reduced due to decomposition into (beta)-TCP and CaO when these powder products are pelletised and sintered at 1300°C for 2 h. While in Al2O3 doped samples, CaO after reaction with Al2O3 and/or CaAl2O3 results in the formation of CaAl2O4 and/or CaAl4O7, in ZrO2 doped samples t-ZrO2 and CaZrO3 are formed by solid-solution of CaO into ZrO2. The products will have lower density as compared to pure HAP without additives owing to the differential shrinkage between the various phases present in the product.