Evaluation of Flame-Sprayed Alumina Powders Produced Using Different Ethanol/Water Ratios in the Starting Solutions

Alumina powders were synthesized using a cost-effective process that used a Bunsen-Meker flame as the source of energy for the chemical reactions. With the aim of evaluating the influence of solvents on the morphology of powders, three starting solutions with different ethanol/water volume ratios were prepared. Ethanol/water ratios of 50:50; 20:80, and 1:100 were studied. X-ray diffraction analyses showed amorphous powders in the as-synthesized condition. After calcination at 1150 degrees C, the powders became crystalline, and a major crystalline phase, -alumina, was identified in all the powders. Using scanning electron microscopy, the typical morphology of the flame-sprayed powders, composed of aggregated spherical and unshaped particles, was observed. The specific surface area of the as-synthesized powder was greater than that of the calcined powder, with a maximum value of 36.75m2/g, which corresponded to the powder obtained with the starting solution prepared only with water. Thermogravimetric analyses showed that the powder produced from a precursor solution composed only of water also had the highest loss (34.72%). Transmission electronic microscopy was used to observe the nanostructures of alumina powders. A maximum crystallite size of 24.6nm, corresponding to the starting solution prepared only with water, was obtained.