EFEITO DA MOAGEM DE ALTA ENERGIA NA SÍNTESE DE MULITA

Abstract

Among the ceramic materials, one can highlight the mullite, whose characteristics are of great industrial interest. This material consists of silica and alumina has high mechanical strength, high refractory and chemical inertness, and low coefficients of expansion and thermal conductivity, which makes this material synthesis from Al2O3 e SiO2 mixtures or from material showing Al2O3 - SiO2 even more technology important in traditional and advanced ceramic fields. Nevertheless the synthesis of mullite is hampered by the reaction kinetics is very slow, taking long time and large amount of energy during sintering. It takes temperatures above 1500°C to form mullite oxides via. Techniques that facilitate this process has been developed, but they have disadvantages such as high cost of reagents. This work had as objective produce mullite using the high energy milling. It was used as starting materials aluminum hydroxide, aluminum oxide, quartzite and kaolin. It was prepared two mixtures of oxides, which are: aluminum hydroxide with quartzite and quartzite with aluminum oxide. These two mixed oxides plus kaolin were subjected to high energy milling for different times and then the milled and unmilled powders were sintered at different temperatures. The characterization was made by ray-X diffraction and by scanning electronic microscopy and thermal analysis. The results showed that the mechanical activation of powders allowed the formation of mullite phase in a lower temperature and formation of anisotropic mullite grains.