Study of the behavior of three Tunisian clays suitable for the manufacture of ceramics

The behavior of three clays collected from different locations in Tunisia has been studied through their chemical and mineralogical composition, plasticity, specific surface area, cation exchange capacity, via dilatometry and infrared spectroscopy. The mineralogical composition is an indication of the presence of kaolinite, illite and smectite associated with quartz, calcite and hematite. The study of the chemical composition showed that the main oxides in the ClayTeb sample are SiO2 and Al2O3, which were also found in the ClayHorb and ClayMed samples along with Fe2O3, CaO and K2O. The mineralogical metamorphoses during the firing process were recorded via the X-ray diffraction of the raw clays and subsequent firing at 300, 600, 800, 1000 and 1200°C for 3 hours. Kaolinite transformed to metakaolinite was not observed at 600°C. Illite underwent total deshydroxylation at 1000°C. This latter temperature characterizes the main evolution of all samples and the start of the crystallization of mullite, which is dependent on the presence of impurities (Fe2O3) and K2O (lent fondant). For the ClayMed clays, which have the maximum content of illite, only the spinel phase was defined at 1200°C. The samples were dry pressed and fired at temperatures of 950, 1050, and 1100°C and the characteristics of the ceramic were determined by firing shrinkage, water absorption, loss on ignition and flexural strength.