Technological properties of ceramic produced from steatite (soapstone) residues–kaolinite clay ceramic composites

Abstract Ceramic bodies (7.0 cm × 2.0 cm × 1.0 cm) of kaolinite clay and soapstone residuals collected from workshops in Ouro Preto and Mariana, Minas Gerais, Brazil, containing from 2.5 to 97.5 wt% steatite (soapstone) were prepared and firing at 500, 1000 and 1200 °C, for 2 h, in air. The linear shrinkage, compressive strength, water absorption and mass loss by heating were determined on the samples after heat treatment. The fired samples at 1000 and 1200 °C, with steatite percentages of 85, 90 and 95%, presented the best results for technological applications in ceramic industry. For these samples, the values of the compressive strength were higher than 10 MPa and those of water absorption varied between 8 and 22%, which means that the values of these properties are superior and inferior, respectively, to the reference values established by Brazilian Standards. The linear shrinkage was lower than 6%, which is the maximum value established by the Polo Cerâmico de Santa Gertrudes, in Sao Paulo State. These samples were chemically, mineralogically, and morphologically analyzed using ICP/OES, X-ray diffraction, Mossbauer spectroscopy, SEM and BET. Talc and kaolinite were the dominant minerals, followed by quartz, chlorite, magnetite and magnesite. When firing at 1200 °C, the talc changes to enstatite and the appearance of mullite, periclase, hematite, clinoenstatite and protoenstatite occurs. The partial fusion of the talc promoted an increase in the liquid phase diminishing porosity and, consequently, water absorption. This process and the combination with mullite and periclase, increased the strength, reaching the values of 78 MPa, which is much greater than the minimum value of 10 MPa defined by the Brazilian Standard 15270-1 (ABNT 2005) for application on structural ceramic blocks.