Abstract
Nanostructured aluminum oxides (Al2O3) have received considerable attention in recent years in several areas. In particular, α-Al2O3 is a stable phase that stands out for its thermal and chemical stability in various applications. Among the α-Al2O3 synthesis techniques, the microwave combustion process has received considerable importance because it is a fast, easy to process and low cost method that allows obtaining ceramic powders with good structural characteristics. Despite its simplicity in terms of processing, several parameters can influence the final properties of the ceramic powder. The aim of this study was to evaluate the influence of the fuel/oxidizer ratio (Rco) and the microwave power (Pmic) on the amount of α-Al2O3 formed, the crystallite size and crystallinity of the obtained powders. Three different values of Rco (1:1, 2.5:1 and 5:1) and Pmic (450, 675 and 900 W) were used to carry out the combustion reactions. The materials obtained were calcined at 900 °C for 2 h to verify the influence of parameters on the formation of α-Al2O3. To better evaluate the influence of synthesis parameters, a 2² factorial design with four central points was used. The techniques of X-ray diffraction and scanning electron microscopy were used to investigate the crystal structure and morphology of the powders, respectively. The results showed that crystallite sizes of 10 to 13 nm were obtained using poor fuel mixture (Rco of 1:1), regardless the microwave power used. The influence of synthesis parameters was also observed in the morphology, where aluminum carbonate species were observed after combustion reaction when the experiment was conducted using rich fuel mixture.
Keywords:
α-Al2O3; combustion; microwave; factorial design
