Dynamic Mineralogical and Structural Transformations in the Process of Siliceous Opal Clays Firing.

With the help of a wide range of studies, it has been found that siliceous clay can be an alternative source of raw materials for the production of various types of building ceramics. Their wide distribution only contributes to their involvement in industrial production. Siliceous clays have a specific mineral composition and were previously considered only as an additive to increase the plasticity of the main raw material. The chemical composition, pre-firing and firing properties of siliceous clays of Malchevskiy deposit were studied in detail. The content of silica is 67-70%, alumina - 13-15%, and alkaline earth oxides - 1-3%. The main minerals are opal silica and mineral beidellite. These thermograph data confirm the presence of montmorillonite, zeolites, micas and hydrated micas, opaline silica and quartz. It is established that siliceous clays belong to the groups of medium-dispersed and highly plastic raw materials. Despite the increased molding moisture content and greater shrinkage, they are moderately sensitive to drying and it is possible to get the molding material with a high bridging capacity. At the firing temperature of 1000-1020 ° C, the brick has no defects, the strength quality is M200-250, and the frost resistance is F75. The data of X-ray patterns of siliceous clays burnt at temperatures of 900, 950, 1000, 1050, 1100 ° C are presented. Significant phase transformations become noticeable at a temperature of 1000 ° C – a dynamic process of transition of amorphous opal silica to cristobalite begins. At 1050 ° C glass phase formation begins. The obtained results suggest that the main phases of the fired material on the basis of siliceous clays are quartz and cristobalite with a low degree of structural perfection, and the dynamic formation of the microstructure occurs in the range of 1000-1100 ° C. Thus, siliceous clay can be considered as the main and additional material for the production of various building ceramic products. [ABSTRACT FROM AUTHOR]