Phase equilibria in the oxide system Nd 2O 3–K 2O–P 2O 5

Abstract

A phase equilibria diagram of the partial system NdPO 4–K 3PO 4–KPO 3 has been developed as part of the research aimed at determining the phase equilibrium relationships in the oxide system Nd 2O 3–K 2O–P 2O 5. The investigations were conducted using thermoanalytical techniques, X-ray powder diffraction analysis and reflected-light microscopy. Three isopleths existing between: K 3Nd(PO 4) 2–K 4P 2O 7, NdPO 4–K 5P 3O 10 and NdPO 4–K 4P 2O 7 have been identified in the partial NdPO 4–K 3PO 4–KPO 3 system. Previously unknown potassium-neodymium phosphate “K 4Nd 2P 4O 15” has been discovered in the latter isopleth section. This phosphate exists in the solid phase up to a temperature of 890 °C at which it decomposes into the parent phosphates NdPO 4 and K 4P 2O 7. Four invariant points: two quasi-ternary eutectics, E 1 (1057 °C) and E 2 (580 °C) and two quasi-ternary peritectics, P 1 (1078 °C) and P 2 (610 °C), occur in the NdPO 4–K 3PO 4–KPO 3 region.