Prevention of black core formation in ceramic bodies

Ceramics Industry is the major consumer of industrial raw materials including various types of clay minerals. The existence of impurities in ceramic raw materials is a challenging issue to produce high quality ceramics. Coloring impurities such as Fe and Ti cause discoloration within the ceramic bodies and they have to be kept below certain limits. Organic carbon present in clay rocks leads to another aesthetic problem within fired ceramic bodies referred to as “black core”. During biscuit firing process organic carbon in the body composition slowly burns out. Burning requires oxygen and that oxygen is robbed out of Fe₂O₃, which is another impurity, reducing it to FeO. During the ongoing burning process FeO then melts, interacts penetrates within the surrounding matrix creating the so-called black core structures. Black core formation is undesirable both aesthetically and in terms of mechanical durability. In this investigation experimental studies have been conducted to reduce the black core formation in the ceramic bodies where organic carbon rich clay sources are used in the recipe. Test results have proven that black core formation could be greatly reduced to negligible levels by the chemical treatment of the clay raw material containing organic carbon as the impurity.