Characterization of the rocks of the Estrada Nova Formation as ceramic raw material in the State of São Paulo, Brazil

Abstract

The present article presents the geological and technological characteristics of the clayey rocks of the Estrada Nova Formation in the southwest region of the State of São Paulo, as part of the search for new raw materials for the ceramic tile industry. Several lithofacies of shale and siltstones of the Estrada Nova Formation, when submitted to heating at 950 °C showed characteristics adequate for the production of porous coatings and to structural ceramics. However, some samples of the massive and laminated lithofacies submitted to heating under laboratory and industrial conditions at temperatures of 1120 and 1040 °C presented results satisfactory for the production of ceramic coatings by the dry process, or incorporation in the mass composition for the production of porcelain tiles. The massive and laminated basal lithofacies presented more homogeneous particle size distributions than the intercalated and sandy upper lithofacies, which showed two populations of particle sizes. The homogeneity of particle distribution in the samples of the massive lithofacies favored the dry milling process, facilitating the densification stages of the product. A greater presence of CaCO3 was observed in the Teresina Member in relation to the Serra Alta Member, which was responsible for increased numbers of defects and decreased mechanical resistance. In samples of the laminated silty shale lithofacies of the Serra Alta Member, high values for Loss on Ignition allied to low CaCO3 content indicated high organic matter content, which resulted in the swelling of the proof bodies due to internal release of gases. This, however, suggess their possible use as expansive clays.