Effect of mixing ratio and pH on the reaction between Ca4(PO4)2O and CaHPO4

The reaction of Ca(PO4)2O (TTCP) and CaHPO4 (DCPA) in an aqueous solution has been shown to be responsible for the hardening of a calcium phosphate cement. This reaction was investigated by monitoring pH changes and composition of solid phases. In the first set of experiments (no attempt to control pH), 2.5 g each of mixtures of TTCP/DCPA, molar ratio from 0.25 to 2, was placed in 12.5 mL of 0.15 mol/L KCl solution, at initial pH about 7, and the pH was allowed to drift for 24 h. Results show that at any time up to 24 h, the pHs were higher for slurries with higher TTCP/DCPA molar ratios. For the slurries with TTCP/DCPA molar ratio of >/= 0.83, the 24 h pHs of the slurries were 9 to 11, whereas for those with TTCP/DCPA of