THE GROWTH OF NONSTOICHIOMETRIC APATITE FROM AQUEOUS-SOLUTION AT 37-DEGREES-C .1. METHODOLOGY AND GROWTH AT PH 7.4

The apatites found in vivo are invariably nonstoichiometric. It has been shown that such phases may also be formed by spontaneous precipitation at lower temperatures and pH. When carbonate is excluded, the stoichiometry of thse phases can be closely approximated by the formula Ca10-uHu(PO4)6(OH)2-u, in which 0 ≤ u ≤ 2. A modification of the constant solution composition method has been used to assess the stoichiometry of phases growth at 37°C in solutions, undersaturated with respect to octacalcium phosphate, of ionic strength 0.100 mole liter-1 (potassium nitrate), pH 7.40, and with total molar concentrations TCa and TP of 4.0 × 10-4 and 2.4 × 10-4 mole liter-1, respectively. The titrants used to replenish these solutions during crystallization experiments contained calcium and phosphate concentrations calculated for precipitated phases having nonstoichiometric coefficients, u, between 0.00 and 1.60. When the titrant stoichiometry did not match that of the precipitating phase, systematic variations in the analyzed solution concentrations of calcium and phosphate were used to determine the composition of the grown phase. In verification experiments with corrected titrant concentrations, the constancy of the analyzed calcium and phosphate concentrations indicated that the solid phase stoichiometry was consistent with a value, u = 0.57. The use of different apatite seed under the same experimental conditions has confirmed this precipitate stoichiometry. © 1990.