β-Al₂O₃ Formation in the System NaF-Al₂O₃

Abstract

Formation of β-Al₂O₃ was investigated in the composition range of 73.9-92.6 weight percent (w/0) Al₂O₃ by the use of thermal and X-ray analyses.
Specimens fired at 1000°C for 3h in flowing N₂ gas showed (1) mixed phases of β-Al₂O₃, NaF and Na₃AlF₆ at low Al₂O₃ region, (2) single phase of β-Al₂O₃ at 86.7w/0 Al₂O₃, and (3) mixed phases of β-Al₂O₃ and α-Al₂O₃ at high Al₂O₃ region.
An exothermic peak point starting at 730-780°C in DTA curve ascended from 780 to 840°C and the weight loss due to the AlF₃ sublimation descended with the increase of Al₂O₃ content. The exothermic peak temperature was made clear to correspond to the reaction of β-Al₂O₃ formation by X-ray diffraction.