Effect of Flash Calcined Powders on the Properties of Spherical Alumina Granules

Three types of flash calcined powders with different specific surfaces and phases were selected to make alumina granules. The granulation was performed in a pan granulator as the spherical form. The hydrothermal and calcination conditions were applied to the granules. Physical, chemical and microstructural studies were applied to the hydrated and calcined granules. This study focussed on the thermal historical effects of the initial powders derived from bauxite on the granules. The least physical changes and the highest specific surface area were obtained for the granules prepared with flash calcined powder at 650°C. The hydrated granules can have boehmite, gamma and bayerite phases with rod, porous and plate morphologies, respectively. The presence of rod boehmite phase increases the strength of hydrated granules and plays an important role in the final strength. In the calcination stage, the phases transformed into the transition alumina and gamma phases with the growth of nanometer-sized crystals.