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.