Investigation of phase equilibria in the system Nd2O3–Na2O–P2O5. The partial system NdPO4–Na4P2O7–NaPO3

The NdPO4–Na4P2O7–NaPO3 system being part of the Nd2O3–Na2O–P2O5 oxide system was investigated by thermoanalytical methods, X-ray powder diffraction and microscopy in reflected light. On the basis of the obtained results its phase diagram is proposed. The investigated partial system is bounded by three subsystems (i) NdPO4–NaPO3, (ii) Na4P2O7–NaPO3 and (iii) NdPO4–Na4P2O7. In the system NdPO4–NaPO3 an intermediate compound – NaNdP2O7 occurs, melting incongruently at 790 °C. In the subsystem Na4P2O7–NaPO3 a triphosphate – Na5P3O10 occurs, melting incongruently at 620 °C. In the subsystem NdPO4–Na4P2O7 an eutectic appears at 944 °C. Two isopleths, NaNdP2O7–Na4P2O7 and NaNdP2O7–Na5P3O10, which are quasi-binary only in the subsolidus region, have been discovered. Three invariant points: two ternary peritectics P1 (tP1 = 672 °C) and P2 (tP2 = 618 °C) and ternary eutectic E (tE = 545 °C) have been found in the NdPO4–Na4P2O7–NaPO3 system.

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