Effect of Fe2O3 as a Dopant in the Transformation of α-Al2O3 from Activated Gibbsite on the Nanocrystalline α-Al2O3 Preparation

The effect of iron oxide in the transformation of alpha-Al2O3 from activated gibbsite was studied with the addition of 4 weight % Fe2O3 of the alumina. Nanocrystalline alpha-Al2O3 was prepared using gibbsite (Al(OH)(3)), sulfuric acid, iron (II) sulphate, and sugar through chemical and physical routes. In the process, Al(OH)(3) reacted with sulfuric acid to form boehmite, whereas 4 weight % FeSO4 and sugar were added as dopants and as a masking agent, respectively. The mixture was heated at 200 degrees C and then was calcined at different temperatures ranging from 500 degrees C to 1000 degrees C for 5 h in an air atmosphere. The addition of 4 weight % Fe2O3 lowered the transformation temperature of alpha-Al2O3 at 500 degrees C-900 degrees C. XRD analysis identified alpha-Al2O3 crystal planes of (102), (104), (113), and (106) at 500 degrees C, having crystallite sizes from 4 to 6 nm. The transformation to alpha-Al2O3 completely occurred at 900 degrees C. As a comparison, alpha-Al2O3 was also prepared from activated gibbsite with sulfuric acid and pure gibbsite. The calcination was conducted at 1000 degrees C for the last two compositions. However, activated gibbsite produced several transition aluminas such as gamma-Al2O3, kappa-Al2O3 and alpha-Al2O3 at 1000 degrees C; whereas pure gibbsite transformed to kappa-Al2O3 and alpha-Al2O3 at the same temperature. Nevertheless, the goal of this study is to prepare iron oxide doped alpha-Al2O3 as a starting material for structural applications.