Mineralogy and firing behaviour of a clay raw material form Wislatiya (Tunisia) (original) (raw)

Abstract

The mineralogical composition of a clay raw material picked up from a large clay deposit, located at Wislatiya (Tunisia) has been estimated by combining the results of different techniques (X-ray diffraction (XRD), thermal analysis (DTA-TG) and ICP spectrometry). This evaluation shows that the raw material mainly consists of quartz (30 mass %), illite (25 mass %), montmorillonite (13 mass %), kaolinite (8 mass %), carbonates (calcite and dolomite 10 mass %) and poorly crystallised goethite (7 mass %). The firing behaviour has been investigated using dilatometry and ultrasonic echography. A comparison between shrinkage and Young's modulus evolutions with temperature shows that the fast densification phenomenon which occurs between about 850 and 1075°C is linked to a structural reorganisation and that the fast shrinkage observed above 1075°C is controlled by a viscous flow-type. In addition, it was established that the low alumina content of the raw material and the extensive presence of large amounts of quartz and carbonates favour the formation of anorthite ((Ca,Na) (A1,Si) 2 Si 2 Og), which is present in the fired material immediately after decarbonatation and is still stable at 1150°C.

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