Investigation of phase equilibria in the system Nd_2O_3-Na_2O-P_2O_5 --The partial system NdPO_4-Na_4P_2O_7-NaPO_3

摘要

The NdPO_4-Na_4P_2O_7-NaPO_3 system being part of the Nd_2O_3-Na_2O-P_2O_5 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) NdPO_4-NaPO_3, (ii) Na_4P_2O_7-NaPO_3 and (iii) NdPO_4-Na_4P_2O_7. In the system NdPO_4- NaPO_3 an intermediate compound - NaNdP_2O_7 occurs, melting incongruently at 790 deg C. In the subsystem Na_4P_2O_7-NaPO_3 a triphosphate - Na_5P_3O_(10) occurs, melting incongruently at 620 deg C. In the subsystem NdPO_4-Na_4P_2O_7 an eutectic appears at 944 deg C. Two isopleths, NaNdP_2O_7-Na_4P_2O_7 and NaNdP_2O_7-Na_5P_3O_(10), which are quasi-binary only in the subsolidus region, have been discovered. Three invariant points: two ternary peritectics P_1 (t_(P1) = 672 deg C) and P_2 (t_(P2) = 618 deg C) and ternary eutectic E (t_E = 545 deg C) have been found in the NdPO_4- Na_4P_2O_7-NaPO_3 system.