The different phases in the precipitation of dicalcium phosphate dihydrate

The precipitation of dicalcium phosphate dihydrate, brushite, by mixing a calcium hydroxide suspension and an orthophosphoric acid solution in equimolar quantities, has been investigated in a batch system at 25degreesC. The concentration of calcium hydroxide and orthophosphoric acid, before mixing, ranged from 50 to 300 mmol dm(-3). The phase first precipitated is Ca5OH(PO4)(3), hydroxyapatite. The precipitation process of brushite is divided into five stages and is similar for all initial experimental conditions. The extension of each stage varies with the initial reagents' concentrations. These stages are discussed individually as a function of pH and reagents' concentrations. The precipitate was analysed by scanning electron microscopy and X-ray diffraction. The solubility of brushite was determined at 25degreesC, 30degreesC and 35degreesC, and in the pH range 4.5-8. (C) 2003 Elsevier Science B.V. All rights reserved.