Pyroplasticity on porcelain tiles of the albite-potassium feldspar-kaolin system: A mixture design analysis

Abstract

In the ceramic tile industry, the technology of fast-single firing, with cycles of less than 60 min, has revolutionized the manufacturing process in the last decades. Furthermore, the market has demanded for larger and thinner porcelain tiles produced in rectangular shapes and in faster thermal cycles. For that, strong mineralizers and non-plastic raw materials with smaller particle sizes are needed, resulting in a more frequent occurrence of the pyroplastic deformation during manufacturing. Pyroplastic deformation is the bending of the ceramic tiles during firing when a great amount of liquid phase is formed making the tile sensitive to deformation by its own weight. Therefore, this work aimed at determining the effect of the composition and amount of raw materials on the pyroplastic deformation of porcelain tiles. Albite, potassium feldspar and kaolin were used as a model composition. 10 compositions were made according to a simplex-centroid mixture design, where the vertices were 100% of the raw materials. The chemical, mineralogical and particle size distribution of the raw materials were determined by the XRF, XRD and laser diffraction techniques. After mixing and granulation (with 6% water), the compositions were pressed at 45 MPa and their apparent density and thermal behavior (by dilatometry) were determined. The compacts were dried and fired at 1200 °C for 1 h. The water absorption, apparent density, shrinkage, tensile strength (diametral compression) and pyroplasticity of the fired samples were determined. As a result, the pyroplastic deformation is caused by the presence of albite and potassic feldspar in the porcelain tile compositions. The higher pyroplastic deformations occurred for the samples presenting the lower water absorption and higher tensile strength, i.e., the compositions that formed porcelain tiles (water absorption < 0.5%).