Identification and Ceramic Application of Some Tunisian Clays

Abstract

Mineralogy, chemistry, and plasticity of the raw clay materials, outcropping in different Tunisian domains were studied. These clays constitute the only mineral resource of the ceramic industries in Tunisia, and are exploitable at eight quarries. Powder X-ray diffraction analysis 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 essentially by calcite; they show the greatest relative amount of Na2O K2O (~3.5%) and iron-oxide (~6%). The plasticity index and liquid limit of crude samples do not exceed 22% and 42%, respectively. This indicates that these clays belong to the zone of illitic clays, classified in the low to moderate plastic domain. The analysis will be used to find appropriate applications 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 assured to avoid these ceramic defects.