The excess Silica in the body materials acts as a strong flux. Clays which contain excess quantity of Silica easily sinters. Since the ceramic materials are not melted in the course of manufacturing, the Aluminum Silicates produced in them arise due to the result of reactions in the solid state. In slagged fire clay bricks, rounded grains of mullite are sometimes observed. They are formed when the brick has undergone frequent temperature fluctuations. Mullite first formed partly dissolves, grows again, and on frequent repetition of this process the rounded shape is produced.
Mullite formation can be activated with additions of one percent ZnO, Li2O, MgO, Fe2O3, MnO and Ce2O3 whereas Na2O, K2O, TiO2 and SnO2 has got very least effect in the catalyst activation for mullite formation. Li2O and MgO are active at both high and low temperature whereas ZnO is active only at high temperature. The mixtures of catalysts containing four to five components are the most effective combination in Mullite formation.
To be contd…..
