Effect of hydrated aluminium fluoride on phase transformation and morphology evolution of alumina

Abstract

In order to verify the formation of gaseous phase fluoride and its influence on the morphological evolution and the growth mechanism of α-Al₂O₃, the α-phase transformation temperature and morphology of α-Al₂O₃ powders from the calcination of commercial γ-Al₂O₃ and Al(OH)₃ precursor with the addition of AlF₃·3H₂O additive have been studied through the incorporation of mixed placement experiments, layered placement experiments and separated placement experiments. The formation of gaseous phase fluoride has been experimentally confirmed by means of layered placement experiments and separated placement experiments, especially by the enhancement of the α-phase transformation occurred outside the small crucible in separated placement experiments. AlF₃·3H₂O additive significantly enhances shape anisotropy of α-Al₂O₃ precursor and lowers the total α-transformation temperature (900 °C for Al(OH)₃ precursor and 1100 °C for γ-Al₂O₃ precursor ), even though the commercial precursor and AlF₃·3H₂O additive has been completely isolated by small crucible with cover.