Phase equilibria in the tricalcium phosphate-mixed calcium sodium (potassium) phosphate systems

Phase equilibria in the quasi-binary sections Ca-3(PO4)(2)-CaMPO4 (M = Na, K) are distinguished by high-temperature isomorphism of glaserite-like phases alpha'-Ca-3(PO4)(2) and alpha-CaMPO4. The main differences of the Ca-3(PO4)(2)-CaKPO4 system from the Ca-3(PO4)(2)-CaNaPO4 system are a shift of invariant equilibria toward higher temperatures, deceleration of phase transformations, and the emergence of polymorphism of an intermediate phase of an ordered solid solution based on alpha-CaKPO4. The low-temperature modification of this phase of a composition near Ca8K2(PO4)(6) has the apatite structure with unoccupied hexagonal channels.