Phase equilibria study and thermodynamic assessment of CaO–MgO–P2O5 system.

The phase diagram of the CaO–MgO–P 2 O 5 system was established by both experimental investigation and thermodynamic assessment. The presence of the contentious binary compound Ca 4 P 6 O 19 in the CaO–P 2 O 5 system was confirmed. The phase relationships in the CaO–MgO–P 2 O 5 system at temperature 1150 °C and 1200 °C were studied via high-temperature quenching experiments in conjunction with X-ray diffraction (XRD) and electron probe micro-analyzer (EPMA) techniques. The CaO–MgO–P 2 O 5 system was critically evaluated and optimized by means of the CALPHAD (CALculation of PHAse Diagrams) methodology. The ionic two-sublattice model (Ca+2, Mg+2) P (O−2,PO 3 −1,PO 4 −3,PO 7/2 −2,PO 5/2) Q is used to describe the liquid phase in the CaO–MgO–P 2 O 5 system due to the ionic nature of oxide melts and the presence of ions with different charges. A set of self-consistent thermodynamic parameters were obtained, showing good agreement between the experimental data and the calculated results. This study holds significant implications for guiding the manufacturing processes of phosphate ceramics. [ABSTRACT FROM AUTHOR]