GONÇALVES, W. P.; http://lattes.cnpq.br/3056392424689139; GONÇALVES, Wherllyson Patrício.
Résumé:
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.
