Calcium phosphate powders synthesized from calcium chloride and potassium hydrophosphate

Porous ceramics based on Ca3(PO4)2 (TCP) was obtained by sintering of a mixture of hydroxyapatite (HAp) and brushite (CaHPO4·2H2O) powders. The main interaction of HAp + CPP (Ca2P2O7) → TCP type in the composite sample HAp/brushite takes place at temperatures higher than 700 °C and leads to rather uniform porous microstructure. We have suggested that CPP-like phases (and especially K2CaP2O7) undergo partial decomposition accompanied by evaporation of P2O5. The role of KCl—the by-product of solution synthesis of HAp and brushite powder precursors, consists in (i) it replace in part Ca in CPP phase making last one more reactive, (ii) it switches sintering of the ceramics in liquid-phase regime, (iii) at higher temperature it evaporates and, thus, contributes to formation of pores in the ceramics.