Water-based synthesis and characterization of sol-gel hydroxyapatite ceramics

Sol-gel technology for hydroxyapatite (HAp) synthesis has been developed more than a decade ago. The existing sol-gel HAp synthetic methods which used alkoxide-based precursors require solvent-based diluting media, a moisture-controlled atmosphere, prolonged synthesis time generally greater than 24 hours, and a heat treatment at temperature >500°C over a time period of several hours. Those factors limit practical applications of HAp, in particular as coatings. Therefore, in this work, HAp ceramics were synthesized using a novel water-based sol-gel route with triethyl phosphite and calcium nitrate as phosphorous and calcium precursors, respectively. The use of water as the only diluting medium and the alkoxide-metal salt combination as the precursors have never been reported in the literature. It was also expected that the novel sol-gel process developed in this work can be a feasible materials technology for biomedical applications, particularly coatings.; Processing design in terms of time and temperature for both hydrolysis and ageing steps of the sol-gel synthesis was thoroughly investigated and successfully optimized for phase-pure HAp formation. This also allows further consolidation of a phase evolution map, which can instructively be used as a guidance for the synthesis of the sol-gel HAp at relatively low temperature. It is found that the novel sol-gel process currently developed for HAp provides advantages, included environmentally-friendly, cost-effective, and user-friendly over existing technologies. The process has been granted US patent number 6426114 B1, 2003 and US patent #2002155144 and is now under use in the biomedical industry.