Processing of AB-type carbonated hydroxyapatite Ca10-x(PO4)(6-x)(CO3)(x)(OH)(2-x-2y)(CO3)(y) ceramics with controlled composition

This work is devoted to the preparation of carbonated calcium phosphate apatites. The aim was to produce dense ceramics containing various and precisely controlled amounts of carbonate ions partially substituting either for phosphate (B-type apatites) or for hydroxide ions (A-type apatites). Powders were synthesized by a wet chemical process in aqueous media. Heating carbonated powders above 600 degrees C in air or neutral atmosphere led to their thermal decomposition. A CO2 gas partial pressure of 50 kPa in the atmosphere stabilized the carbonated apatites up to temperatures allowing their sintering. But, CO2 gas induced a carbonation of hydroxide sites (A-site) that was detrimental to the sintering. A low partial pressure of water vapour in the atmosphere proved to be efficient to control A-site carbonation and indirectly favoured the sintering. Dense ceramics made of single phased apatite Ca10-x(PO4)(6-x)(CO3)(x)(OH)(2-x-2y)(CO3)(y), with 0 <= x <= 1.1 and 0 <= y <= 0.2 could be produced. The value of x (B-type carbonates) was controlled by the synthesis process and the value of y (A-type carbonates) by the sintering atmosphere