Tuning Al2O3 crystallinity under supercritical fluid conditions: Effect on sintering

Supercritical fluids have been used to prepare alumina powders. This versatile technique allows the tuning of the crystallinity of the obtained powders by a simple modification of the fluid's nature. Amorphous or boehmite alumina could be successfully synthesised using either CO2/Ethanol or H2O/Ethanol, respectively. The two powders present very different sintering paths, which have been correlated to the grain morphology and crystalline state of the powders. We have established that the alumina elaborated in CO2/ethanol exhibited a significant decrease of the γ-Al2O3 → α-Al2O3 transition temperature resulting in a lower densification temperature.