Study on phase transformation and controllable synthesis of calcium phosphate using a sol–gel approach

It is always difficult to achieve pure hydroxyapatite (HA) and tricalcium phosphate (TCP) at high temperatures by using non-alkoxide-based sol?Cgel techniques and other related techniques, which have limited their application. In this paper, our study brought to light that the reason for that was a non-uniform mixing of the reactants at molecular-level, which led to different Ca/P ratios and hence to the occurrence of three high temperature stable phases of HA, TCP and CaO at high temperatures. A series of experiments were designed to demonstrate this proposed hypothesis. Our study firstly revealed that by introducing ethylene glycol into the sol?Cgel system, the uniform mixing of the reactants at molecular-level could be obtained and then pure HA and TCP phases were achieved at high temperatures.