Phase Diagram of the System Al₂O₃-Yb₂O₃ at High Temperatures

Abstract

In the phase diagram studies on the Al₂O₃-Yb₂O₃ system, the liquidus and eutectic temperatures were measured from the cooling curves of specimens by the specular reflection method with a heliostat-type solar furnace. Quenched specimens from the melt were examined by X-ray diffractometry and chemical analysis.
Garnet-type compound, 3Yb₂O₃⋅5Al₂O₃, was obtained as a single cubic phase by heating an α-Al₂O₃-Yb₂O₃ mixture of corresponding stoichiometry at 1600°C in an electric resistance furnace and also by crystallization from the melt in the solar furnace.
When the specimens of the 2Yb₂O₃⋅Al₂O₃ composition were quenched from 1700°C and from the melt, both specimens appeared to be the single phase with monoclinic structure.
The freezing points of 3Yb₂O₃⋅5Al₂O₃ and 2Yb₂O₃⋅Al₂O₃ were measured as 2000±20°C and 2002±20°C, respectively.
The lattice parameter of the garnet compound was a₀=11.951Å, and the parameters of the monoclinic phase were a₀=7.278Å, b₀=10.310Å, c₀=11.040Å and β=108.30°.
All of the above compounds appeared to be stable phase, because they showed no phase transition in repeated heating and cooling cycles.
The phase diagram shows three eutectic points at 1845°C, 1875°C, and 1890°C with 18, 52.5, and 82mol% of Yb₂O₃ composition, respectively.
Each of cooling curves of Al₂O₃, 3Yb₂O₃⋅3Al₂O₃ and 2Yb₂O₃⋅Al₂O₃ showed a single exothermic peak which was assigned to solidification point, while Yb₂O₃ showed two exothermic peaks, corresponding to a solid state phase transformation as well as solidification point.
A high temperature phase diagram for Al₂O₃-Yb₂O₃ system was presented.