STUDY OF CALCIUM DEFICIENT CARBONATE APATITES .1. SYNTHESIS AND STUDY OF CALCIUM PHOSPHATE-CALCIUM CARBONATE COPRECIPITATES

Study of calcium deficient carbonate apatites. I - Synthesis and study of calcium phosphate-calcium carbonate coprecipitates. - The study of products obtained by coprecipitating calcium phosphate and calcium carbonate, in a water-ethanol medium, at 37-degrees-C, enable us to distinguish two composition ranges depending on the atomic ratio R(c) = CO3/(CO3 + PO4) of the dried samples. - When R(c) is less than or equal to 0.15 (Ca/P ratio between 1.33 and 1.67), the coprecipitates are constitued by poorly crystalline apatites, in which carbonate ions in B site substitute for HPO42- ions. - When R(c) is greater than 0.15, the coprecipitates are composed of one or two phases depending on the R(c) value. In the first case (0.15 < R(c) < 0.5), the coprecipitates may be considered as an amorphous solid solution of calcium carbonate into calcium phosphate. In the second case (0.5 < R(c) less-than-or-equal-to 1), they are made of a mixture of amorphous phase and calcite (for R(c) < 0.80) otherwise of a mixture of calcite and vaterite.