Combustion Synthesis of Powders in the Mullite-Alumina System

摘要

Stoichiometric compositions of aluminium nitrate nonahydrate, Al(NO_3)_3·9H_2O (oxidiser), and urea, CO(NH_2)_2 (fuel), were calculated using the reducing valences of the components and based on batches 5 g of composite powder. The silica component was introduced as an aqueous silica sol containing 50 wt% solids. The reactants were hand-mixed in a wide-mouth vitreous silica basin (300 cm~3) and heated up to about 300℃ on a hot plate inside a fume-cupboard, under ventilation. With the rise in temperature, melting occurs and a clear liquid was produced, which boiled and thickened. Then, the reaction vessel was transferred directly to a muffle furnace pre-heated at 500℃, where ignition took place. The product of combustion was a voluminous and foamy mullite-alumina powder that was calcined at various temperatures and characterised by Thermal Analysis, X-ray Diffraction, and Scanning Electron Microscopy.