Phase equilibria in CaNaPO4-CaKPO4 system and their influence on formation of bioceramics based on mixed Ca-K-Na phosphates.

An investigation of the two-component phase diagram of the CaNaPO 4 - CaKPO 4 system performed using various analysis techniques is reported. The continuous solid solution series of α-CaMPO 4 existing above 700 °C undergoes eutectoid decomposition during cooling to β-CaMPO 4 -based solid solutions enriched with Na and K, and to an intermediate nonstoichiometric compound with an ideal composition of CaK 0.6 Na 0.4 PO 4. All three compounds exhibit significant volumetric effects associated with first-order phase transitions, with positive volume changes under cooling for the intermediate compound. Increased K content in ceramics based on CaK y Na 1- y PO 4 compositions enhances the strength properties of those ceramics, including their fracture toughness, which is associated with increased density. Increased K content also has a smaller effect of inducing phase transformations accompanied by strong volume changes. [ABSTRACT FROM AUTHOR]