Precipitate Formation in the Strontium-Phosphate System

Study of the precipitation process in the aqueous Sr(OH)(2)-H(3)PO(4) system, in order to elucidate the phase transformations and the nature of the final solid phases, shows that over much of the range of compositions studied the initial precipitate is poorly crystalline; the x-ray pattern resembles that of strontium hydroxyapatite but has a strontium: phosphorus molar ratio close to 1.3. Within 1 hour the initial precipitate changes to a stable crystalline phase (or phases), with corresponding change, either up or down, in the strontium: phosphorus ratio. At high ratios of Sr(OH)(2) to H(2)PO(4) the initial precipitate is Sr(3)(PO(4))(2)-4H(2)O, which then converts to a phase having the x-ray diffraction pattern of strontium hydroxyapatite, but having a strontium: phosphorus ratio that depends somewhat on the initial ratio of Sr(OH)(2) to H(3)PO(4) used in the precipitation.