Structure of β″-Al₂O₃ in Synthetic Magnesium Aluminate Spinel

A sintered spinel material was synthesized with commercial alumina and calcined magnesia. When the Al₂O₃ content was higher than 72% (mass fraction), a small amount of tabular euhedral crystals could be formed between the crystals of spinel. The morphology and composition of the crystals were characterized by field emission scanning electron microscope (FESEM), energy dispersive spectrometer and X-ray diffractometer. The results show that the tabular euhedral crystals have the same lattice constants of Mg–β″- Al₂O₃ in Na₂O–MgO–Al₂O₃ system with the chemical composition range of 3.1% (in mass, the same below)–4.1% of Na₂O, 11.6%–14.4% of MgO and 81.7%–85.3% of Al₂O₃. The nano-grains of Na metal were deposited on the crystal surface of β″- Al₂O₃during the bombardment by electron-beam of FESEM.