Composition, firing behavior and ceramic properties of the Sejnène clays (Northwest Tunisia)

• The mineralogical, chemical and geotechnical characterization of the Tunisian clays
• The firing behavior of the Tunisian clays
• The ceramic application of the Tunisian clays

This study focuses on the results of various analyses and ceramic aptitude tests carried out on two representative clay samples of the Oligo-Miocene from Sejnène, in Northwest Tunisia. The original clays were characterized by chemical analysis, powder X-ray diffraction (XRD), TGA measurements, infrared spectroscopy, Bigot curves and evaluation of the plasticity. The mineralogical study proved that these clays are mainly composed of kaolinite and illite, with a small amount of interstratified I/S. The chemical analysis indicated that the clays of ClaySej1 are more siliceous than those of ClaySej2, which have higher levels of elemental fluxes (Fe2O3, Na2O, K2O and CaO). 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 h with a heating rate of 10 °C/min. The main transformations were observed at 1000 °C with the appearance of new crystalline phases especially in the ClaySej2 sample. The samples were hand-pressed in a rectangular mold and sintered at 950, 1050 and 1100 °C with a heating rate of 10 °C/min. The variations in flexural strength, linear shrinkage, water absorption and color were also determined and showed sensitivity to the chemical and mineralogical compositions.