Avaliação da influência de diferentes tratamentos térmicos sobre as transformações de fases de argilas-bentonita e bentonita/caulinita.

Abstract

Clays are essential components of the traditional ceramic materials and promote the development of mullite crystals during firing, which confers mechanical strength to the final product. An important innovation in recent decades in the ceramic industry is the use of fast firing, which can induce changes during thermal processing of the materials and their composition. To implement changes in firing parameters is crucial prior knowledge of phase transformations of clays and traditional ceramic materials, being necessary in some situations the formulation of new compositions. The aim of this study was analyze the influence of different heat treatments on the microstructure and phase changes of smectite and smectite/kaolinite clays, emphasizing the presence of mullite. It was used in this work two samples of natural bentonite and one imported. The effect of some parameters used on the delamination of clays such as: hydration, freezing, milling and centrifugation were investigated, varying the amount of dispersant and stirring time. The clays were heat treated between 800 and 1250°C with heating rate between 5 and 30°C/min and kept at the maximum temperature for 10 and 60 min. The phase evaluation in the powders before and after heating was investigated by X-ray diffraction and the surface morphology was investigated by a scanning electron microscope. The best results of the delamination process were observed for samples that showed no sodium oxide. From the diffraction X-ray observed that the heating rate influence on the reactions during heating, the structure of the clay was kept to 8 0 0 X for faster rates and the peaks of mullite and cordierite were detected to lower temperatures when the heating rate was slower. Regarding the physical and mechanical properties, it was observed that the sample with higher alumina/silica ratio showed the best results.