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

• Published in: Journal of the European Ceramic Society Vol. 39; no. 16; pp. 5410 - 5422
• Main Authors: Orlov, N.K., Evdokimov, P.V., Milkin, P.A., Garshev, A.V., Putlayev, V.I., Grebenev, V.V., Günster, J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2019
• Subjects: Bioceramics; Mixed Ca-K-Na phosphates; Na and K rhenanites; Phase diagram; Phase transformations; Bioceramics; Na and K rhenanites; Mixed Ca-K-Na phosphates; Phase transformations; Phase diagram
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2019.07.044

An investigation of the two-component phase diagram of the CaNaPO4- CaKPO4system performed using various analysis techniques is reported. The continuous solid solution series of α-CaMPO4 existing above 700 °C undergoes eutectoid decomposition during cooling to β-CaMPO4-based solid solutions enriched with Na and K, and to an intermediate nonstoichiometric compound with an ideal composition of CaK0.6Na0.4PO4. 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 CaKyNa1-yPO4 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.