Phase diagram of the system Al2O3-Nd2O3 at high temperatures.

MIZUNO Masao, YAMADA Toyoaki, NOGUCHI Tetsuo

doi:10.2109/jcersj1950.85.978_90

The liquidus temperature of the Al₂O₃-Nd₂O₃ system was measured from the cooling curve of specimens by the specular reflection method with a heliostat type solar furnace. Quenched specimens from the melt were examined by X-ray diffraction technique, petrographic microscopy and chemical analysis. The single phase of NdAlO₃ with the perovskite structure was obtained by heating at 1300 and 1600°C in an electric resistance furnace, and also by cooling the specimen fused in the solar furnace. The reversible phase transition of NdAlO₃ between the rhombohedral and cubic forms was also confirmed at about 1100°C by the high temperature X-ray diffractometry. The lattice parameters of the rhombohedral phase were a₀=5.351Å, α=60°10' at 1075°C, and that of the cubic phase was a₀=3.792Å at 1150°C. The variation of unit cell volume ΔV was therefore only 0.42 percent. The refractive indices of NdAlO₃ were obtained as γ=2.040±0.002, α=2.030±0.002. The presence of Nd₂O₃⋅11Al₂O₃ (β-Al₂O₃ type) was also observed. However, in a fused specimen of Nd₂O₃⋅11Al₂O₃ composition, Nd₂O₃⋅11Al₂O₃ was not formed as a single phase but always coexisted with NdAlO₃. The lattice parameters of the Nd₂O₃⋅11Al₂O₃ phase were a₀=5.55Å, c₀=22.03Å, c/a=3.97. A tentative phase diagram for the Al₂O₃-Nd₂O₃ system at high a temperature was presented. The phase diagram shows two eutectics points at 1720°C with 23 mole percent Nd₂O₃, and at 1850°C with 80 mole percent Nd₂O₃ composition. The cooling curves of Nd₂O₃ showed exothermic peaks related to solid state phase transformations below the solidification point.

Phase diagram of the system Al2O3-Nd2O3 at high temperatures.

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