Wet synthesis and characterization of modified hydroxyapatite powders

Hydroxyapatite powders with reproducibly different Ca/P ratios and powders with varying amounts of co-precipitated magnesium, sodium and potassium were synthesized by a wet method. Solids composition, particle size and morphology, crystalline structure, sintering behaviour and microstructure were investigated in order to understand the effect of composition in the properties of the powders. Under the present conditions of synthesis, it was concluded that magnesium, sodium and potassium will enter the hydroxyapatite lattice in vestigial amounts. Magnesium gives rise to a co-precipitated amorphous phase which crystallizes as beta-whitlockite on calcining. A relationship was found between the Ca/P ratio in hydroxyapatite and its sinterability. The sintering process of pure and alkali-containing hydroxyapatites is completed at 1300 degrees C and leads to dense ceramics in the case of pure and sodium-containing hydroxyapatites but not in potassium-containing material.