Ceramic behaviour of clays in Central Chile

This study is focussed on the behaviour of clays from some deposits in Metropolitan, Bernardo O'Higgins and the Maule Regions could help to support important ceramic industry. Some deposits of clays with industrial application have been studied. The chemical and mineralogical composition of clays was determined by X-ray fluorescence (XRD) and X-ray diffraction (XRD). Also, the plasticity index (PI) and drying shrinkage was measured for each sample. The chemical and mineralogical compositions of samples differ considerably. Test samples have been prepared by pressing and firing in the range of 800-1150 °C. Linear contraction (LC), water absorption capacity (WAC) and thermodilatometric analysis (TDA) were done in order to characterize clays after firing. A considerable decrease in the WAC is observed between 1050 and 1100 °C. At 1150 °C the porosity of the tile bodies decreases significantly and the tile bodies became earthenware. All studied clays seem to be easily adaptable for dry pressing ceramic process. In particular, kaolinite-rich samples show the best behaviour. Some clays are suitable for the production of fast firing vitreous pieces. Clay samples (3, 4 and 5) from VII Region present the highest refractory behaviour. Clays from the Metropolitan Region could have uses in structural ceramics, stoneware and tiles. The examined clays from Region VI could be used as raw material in ceramic tiles, while the samples from Region VII could be used for the manufacture of floor and wall tiles, in addition to structural ceramics and semi-refractory bricks.