Obtenção de alumina por síntese de combustão para preparação de membranas assimétricas.

Abstract

The aim of this work was to synthesize alumina by combustion reaction, using microwave, muffle oven and spiral resistance as external heating source. It was evaluate the influence of heating system in the structural and morphological characteristics of the alumina powders to be applied in the preparation of asymmetric membranes. The work was done in two steps. The first consisted in preparation of the alumina samples and their characterization by XRD, textural analysis, particle size distribution and SEM. The second step consisted in the preparation of asymmetric membranes, their characterization by SEM and water flux measurements. To prepare alumina, stoichiometric composition was predefined according to the propellants and explosives theory and valence of the oxidizers (alumina nitrate) and reducers (urea) reagents. During the synthesis it was measured the combustion flame time and temperature of the reactions made in the muffle oven and spiral resistance. The results showed the preparation of α- alumina as unique phase, with crystallite size between 57- 64 nm and surface area between 8 – 41 m2/g. The morphology of the powder was constituted by presintered particles, making hard agglomerates and/or aggregates. In the second step, it was prepared a slip with the alumina samples and made a deposition of a layer by dip coating in pre-prepared ceramic tubes. The membranes were sintered at 1200oC and 1400oC for a period of 30 minutes. To the membranes sintered at 1200oC and prepared with alumina synthesized in microwave and spiral resistance it were observed two different regions indicating an heterogeneity in the deposited layer, with thickness of 9.9 and 27.85μm, respectively. However the samples sintered in muffle oven presented an homogeneous layer with thickness of 35.25μm. To the samples sintered at 1400oC, the deposited layer presented a great irregularity and high porosity. This allowed the partial penetration of the alumina grains in the pores of the support, reducing in this way, the thickness of the layer. The values of the water flux indicated that the membranes are reproducible, free of defects and cracks.