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

Phase equilibria in the quasi-binary sections Ca3(PO4)2-CaMPO4 (M = Na, K) are distinguished by high-temperature isomorphism of glaserite-like phases α’-Ca3(PO4)2 and α-CaMPO4. The main differences of the Ca3(PO4)2-CaKPO4 system from the Ca3(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 α-CaKPO4. The low-temperature modification of this phase of a composition near Ca8K2(PO4)6 has the apatite structure with unoccupied hexagonal channels.