Iron role on mechanical properties of ceramics with clays from Ivory Coast

Three clays from Gounioubé deposits were used for the manufacture of floor tiles. The strength distributions by the Weibull statistical model are interpreted in relation to clay chemical and mineralogical compositions and particularly to the iron role by Mössbauer spectroscopy. With clays without additions, results of mechanical strength of sintered materials show that clays alone are not really suitable for the manufacture of ceramics. But clay calcite mixes (10 wt% of CaCO₃) favor a significant increase of mechanical resistance, which are similar to used standards. This behavior is due to the formation of a three-dimensional network of anorthite crystals within the silico-aluminate materials. Beside the anorthite role, the iron oxide content of the clays influences the mechanical strength. With Gounioubé clays, it is shown that the increase of iron content in clays causes a decrease of the ceramic strength. This behavior is related to the clay compositions, which contain iron in the form of goethite. During the thermal transformations, part of the iron is involved in both the structural transformations and the densification phenomenon of the silico-aluminate phase. But the most part of iron readily transforms into hematite crystallites, which are embedded within the silico-aluminate. They accentuate the heterogeneous nature of the material and favor the decrease of the mechanical strength.