Sintering of calcium phosphate hydroxyapatite Ca10(PO4)6(OH)2 I. Calcination and particle growth

The influence of the temperature and the partial pressure of water vapour on the kinetic of surface reduction of hydroxyapatite during calcination treatment was studied. The water vapour catalysed the growth of HAP grains. A theoretical model was proposed and compared with the experimental data. It allowed the identification of the mechanisms of surface reduction and the determination of the kinetic laws. At low temperature (T<850 °C), grain coalescence occurs without densification. The superficial diffusion is the predominant mechanism and it is controlled by the adsorption–desorption of water vapour on the surface of the HAP grains. At higher temperature, the densification mechanisms are effective.