The morphology of hydroxyapatite crystals grown in aqueous solution at 37°C

The crystallization of hydroxyapatite is of importance, since it is considered to be a model compound for tooth and bone formation. In this study, interference by precursot phases has been avoided by studying the kinetics of crystallization at sustained low supersaturations using a highly reproducible constant composition method over a pH range 5.0–8.5. The resultant appreciable extent of crystallization, of two to four times the amount of inoculating crystals, has enabled striking changes in the morphology of the grown crystals to be followed as a function of the extent of growth, pH of the supersaturated solution and the presence of the chloride ion. In general, HAP was found to grow in the form of needle-like crystals whose length increased linearly with the extent of precipitation. The presence of chloride in the crystallizing medium favored the formation of platy HAP crystals, irrespective of pH, at large extents of growth.