Economical synthesis of nanocrystalline alumina using an environmentally low-cost binder

Sol-gel, a commonly used technique, involves the formation of an amorphous gel from a precursor solution. In this research nanocrystalline alumina powders have been synthesized through a new sol-gel simplified method. The route involved using an environmentally low-cost binder and aluminum nitrate in an aqueous medium. The added metal ions were dispersed in the gelled binder matrix. The gelled mass was dried and characterized by simultaneous thermogravimetric and differential thermal analysis (TG-DTA) and calcined at 350, 400, 530, 650, and 900 °C for 2 h. The samples were evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The used binder can be applied to form a perfect matrix for the entrapment of metal ions that during heat treatment, gives rise to ultrafine amorphous or crystalline alumina particles. In this study, the transition phases of alumina with particle sizes of 15-25 nm as well as aluminum oxide hydrate phase were produced by the heat treatment of the gelled mass at temperature 650 °C. By increasing the calcinations temperature to 900 °C, alumina transition phases were changed and aluminum oxide hydrate eliminated. The particle sizes at this temperature were obtained in the range 15-30 nm. The particle size and crystallite size of products measured from XRD and TEM were in good agreement.