Effect of Super Saturation Level on the size and morphology of Hydroxyapatite precipitate

Hydroxyapatite (HA) is synthesized through acid-base reaction by adding an aqueous solution of orthophosphoric acid to an aqueous solution of calcium hydroxide maintained at 40, 80 and 100°C. X-ray diffraction of the precipitate particles revealed HA as the predominant phase in all the temperatures and that the morphology of the particles changed from needle-shaped at 40°C to spheroid at 100°C. The changes in the morphology with temperature were analyzed taking into account the driving force for the HA precipitation and the super saturation level of Ca²⁺and PO4^3-ions with respect to HA. It appears that the effect of temperature on morphology is less pronounced compared to that of super saturation level. The analysis also indicated that the super saturation level of the reactants, especially the concentration of Ca²⁺ions, played a predominant role on the precipitate morphology for this classical acid-base reaction.