Homogeneous octacalcium phosphate precipitation: Effect of temperature and pH

Octacalcium phosphate (OCP) was prepared by homogenous precipitation at 40 to 60degreesC in the pH range 6.0 to 7.5 and depending on conditions either no precipitate was formed or a variety of morphologies of OCP were produced. At a given temperature, in low pH conditions no precipitate was formed, at higher pHs large OCP particles were precipitated which were spherical in shape with long plate-like (LP) crystals radiating from a central nucleus. At higher pH, within a very narrow pH range, the spherical particles were covered by short-plate (SP) like crystals. As the pH was raised further, aggregated spheres (AS) of poorly crystalline OCP were precipitated. The spherical crystals had a mean particle size range from 20 to 1000 mum. FTIR spectra of AS were more similar to that of hydroxyapatite than OCP. As the size of the precipitated particles increased, the spectral similarity with OCP also increased.