Mineralogy and sintering mechanisms of a clay raw material

International audienceThe suitability for traditional ceramics of a clay raw material from Kasrine (Tunisia) was discussed in view of its mineralogy and its sintering behaviour. The mineralogical composition has been estimated by combining the results of complementary techniques (X-ray diffraction (XRD), thermal analysis (DTA-TG) and ICP spectrometry). This evaluation shows that the raw material mainly consists of calcite (29 weight %), quartz (25 weight %), phlogopite (17 weight %), kaolinite (12 weight %), illite (8 weight %) and poorly crystallized goethite (4 weight %). Concerning the sintering mechanisms, the results of linear shrinkages and apparent density evolution, X-ray diffraction analysis and ultrasonic echography lead to conclude that the product of decarbonatation of calcite (650-680°C) begins to react immediately after their formation with clayed derived materials to give mainly anorthite ((Ca,Na)(Al,Si)2Si2O8) and augite (Al0.2Ca0.9Fe0.1MgO6Si1.8). This transformation should be responsible of the Young's modulus increase observed between 830 and 1100°C. The formation of a viscous liquid occurs only above 1100°C. It favors microstructure change: weak densification and pore coalescence