Phase and Mineralogical Transformations of Opal Clays in the Production of Ceramic Bricks

Abstract

Due to a wide range of studies, it has been established that siliceous clays can be an alternative source of raw materials for the production of various types of structural ceramics. Their wide occurrence contributes to their usage in industrial production. Siliceous clays have a specific mineralogical composition and were previously considered only as an additive to increase the plasticity of the main raw material. The chemical composition, properties of green and fired siliceous clays of the Malchevsky deposit has been studied in detail. They consist of 67-70% silica, 13-15% alumina, and 1-3% alkaline earth oxides. The main minerals are opal silica and beidellite. These thermographs confirm the presence of montmorillonite, zeolites, mica and hydromica, opal 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 and great shrinkage, they are moderately sensitive to drying and allow you to get molding masses with high binding property. At the firing temperature of 1000-1020 ° C, the brick is free from defects, the strength grade is M200-250, and the frost resistance is F75. There are X-ray data of siliceous clays burned at temperatures of 900, 950, 1000, 1050, 1100° C. Significant phase transformations become noticeable at a temperature of 1000° C, when the process of transition of amorphous opal silica to cristobalite begins. At 1050° C, the formation of a glass phase begins. The results obtained suggest that the main phases of the fired material based on siliceous clays are quartz and cristobalite with a low degree of structural perfection and the formation of the microstructure occurs in the interval 1000-1100° C. So, siliceous clays can be considered as the main and additional material for the production of various types of structural ceramics.