Phase Equilibria in the Ternary System MgO-Na2O-P2O5. The Partial System Mg2P2O7-Mg6Na8(P2O7)5-NaPO3-Mg(PO)2

The partial system Mg2P2O7-Mg6Na8(P2O7)5-NaPO3-Mg(PO3)2 in the ternary system MgO-Na2O-P2O5, have been investigated and its phase diagram has been proposed. Investigation was carried out by the differential thermal analysis (heating and cooling), X-ray diffraction methods, and microscopy in reflected light. In the composition range under investigation, five ternary phosphates: Mg6Na8(P2O7)5, Mg2Na3P5O16, MgNa(PO3)3, MgNa2(PO3)4 and MgNa4(PO3)6 appear. Two of them,Mg6Na8(P2O7)5 and MgNa4(PO3)6, congruently melt at 808 and 915°C, respectively, the remaining three melt incongruently. Phosphate Mg2Na3P5O16 melts incongruently at 675°C during heating and decomposes in a few stages. Peritectic melting point of MgNa(PO3)3 phosphate is 942°C, and that of MgNa4(PO3)6 is 785°C. For the composition range of Mg2P2O7-Mg6Na8(P2O7)5- NaPO3-Mg(PO3)2, it has been found that six quasi-binary sections, four ternary peritectics (tP 1 = 660°C, tP 2 =876°C, t P 3 = 578°C, tP 4 = 555°C) and three ternary eutectics (tE 1 = 560°C, tE 2 = 845°C, tE 3 = 540°C) occur.