Influence of the Heating Rate on the Phase and Microstructural Transformations of Smectite Clays

Clays are very important raw materials in the manufacturing of traditional ceramic products. The present study was intended to study the phase transformations of smectites submitted to thermal treatment in conventional stove, applying slow and fast cycles. We used three clays, two national and one imported, which were beneficiated and characterized by mineralogical analysis. Later, they were submitted to a thermal treatment at 1100, 1200 and 1250°C, with heating rate of 5 and 30°C/min, remaining under the maximum temperature for 60 minutes. We observed the presence of mullite peaks starting at 1100°C for all samples. It was verified that the sample with the highest alumina/silica ratio presented more intense mullite peaks, and the sample with the high MgO content, besides the mullite phase, also formed cordierite.