Synthesis of dahllite through a cement setting reaction

Dahllite is a synthetic carbonated hydroxyapatite with a carbonate ion content similar to bone mineral. The first objective of this study was to investigate the stoichiometric conditions under which dahllite formation occurs in a powder mixture of alpha-Ca3(PO4)2, Ca(H2PO4)2 and CaCO3. The second objective was to identify how these conditions apply to commercially available cement, Skeletal Repair System (SRS), and other alpha-Ca3(PO4)2-based cements currently under investigation. The stoichiometric coefficients were found to be a function of both the percentage of carbonate ions incorporated into the hydroxyapatite structure, and the amount of CO2 released during the reaction. As a consequence, a stability field has been obtained where different initial proportions of the reactants in the powder mixture should give the same reaction product if sufficient CO2 is released into the solution. However, increasing amounts of CaCO3 in the initial mixture have been shown to affect the solution pH in such a way that only partial reaction of the reactants takes place. SRS and other alpha-Ca3(PO4)2-based cements have been located inside the stability field and a comparison between their reported setting and hardening properties has been performed.