Phase equilibria in the oxide system Nd_2O_3—K_2O—P_2O_5

摘要

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 ℃ 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℃) and E_2 (580℃) and two quasi-ternary peritectics, P_1 (1078℃) and P_2 (610℃), occur in the NdPO_4-K_3PO_4—KPO_3 region.