Preparation, qualities and defects of ceramic materials from Tunisian clay minerals

Resumo

Mineralogy, chemistry, and plasticity of the raw clay materials from different Tunisian regions were studied. These clays, exploitable at eight quarries, are the only mineral resources for the ceramic industry in Tunisia. Powder X-ray diffraction revealed that illite and kaolinite are the major mineral phases. However, other clay minerals, such as illite/smectite mixed-layer, and chlorite are also present. The associated minerals detected in powdered materials are: quartz, calcite, feldspar and, dolomite. These raw materials are marly clays with 6–14% CaO, represented mostly by calcite; they show the greatest relative amount of Na₂O+ K₂O (~3.5%) and iron–oxide (~6%). The plasticity index and the liquid limit of the crude samples do not exceed 22 and 42%, respectively. This indicates that these clays belong to illitic clays, classified in the low to moderate plastic domains. The mineralogical, chemical, physical and technical results of the studied clays encourage the use of these materials for traditional ceramic. In addition, this paper shows that the ceramic defects observed in the pieces manufactured from these Tunisian clays are lamination, cracks, and lower mechanical and bending strength. Some solutions are offered to avoid these ceramic defects.