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.