Morphology variation of cadmium hydroxyapatite synthesized by high temperature mixing method under hydrothermal conditions

Cadmium hydroxyapatite (Cd HAp) pure crystals were synthesized by high temperature mixing method under hydrothermal conditions using the solutions of Cd(NO3)2·4H2O and (NH4)2HPO4. The influences of pH values and reaction time on the structure and morphology of Cd HAp crystals were investigated. The results indicate that the pH value has a great influence on the morphology which varies from bulk-like to fiber with the increase of the pH value. The intermediate phase of Cd5H2(PO4)4·4H2O is formed in the weak alkali reaction medium of (NH4)2HPO4 at pH 9, and it take long time to be dissolved and changed into pure phase of bulk-like Cd HAp crystal. In the strong alkali reaction medium of (NH4)2HPO4 solution at pH 11, the intermediate phase of Cd2P2O7·5H2O is formed, and then dissolved, and rapidly changed to pure phase of Cd HAp fiber. Cd3(OH)5NO3 crystals are formed in the nitrate solution before mixing at 200 °C, its influences on crystallinity, morphology and size of Cd HAp crystals were also discussed.