Preparation of nanometer-sized α-alumina powders by calcining an emulsion of boehmite and oleic acid

Abstract

This study proposes a method to form ultrafine α-Al2O3 powders. Oleic acid is mixed with Al(OH)3 gel. The gel is the precursor of the Al2O3. After it is mixed and aged, the mixture is calcined in a depleted oxygen atmosphere between 25° and 1100°C. Oleic acid evaporates and decomposes into carbon during the thermal process. Residual carbon prevents the growth of agglomerates during the formation of α-Al2O3. The phase transformation in this process is as follows: emulsion → γ-Al2O3 → δ-Al2O3 → θ-Al2O3 → α-Al2O3. This process has no clear θ phase. Aging the mixed sample lowers the formation temperature of α-Al2O3 from 1100° to 1000°C. The average crystallite diameter is 60 nm, measured using Scherrer's equation, which is consistent with TEM observations.