Preparation of Nanometer‐Sized α‐Alumina Powders by Calcining an Emulsion of Boehmite and Oleic Acid

This study proposes a method to form ultrafine α‐Al 2 O 3 powders. Oleic acid is mixed with Al(OH) 3 gel. The gel is the precursor of the Al 2 O 3 . 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‐Al 2 O 3 . The phase transformation in this process is as follows: emulsion →γ‐Al 2 O 3 →δ‐Al 2 O 3 →θ‐Al 2 O 3 →α‐Al 2 O 3 . This process has no clear θ phase. Aging the mixed sample lowers the formation temperature of α‐Al 2 O 3 from 1100° to 1000°C. The average crystallite diameter is 60 nm, measured using Scherrer's equation, which is consistent with TEM observations.