Effect of nanosilica and nanoboehmite in the pyroplastic deformation of a porcelain tile paste

Porcelain tiles are low-porosity ceramic coatings, formed by a mixture of clay minerals, quartz, and feldspars, and fired at temperatures close to 1200°C with formation of a liquid phase that can result in unwanted pyroplastic deformations. In addition, the rectangular formats, large dimensions, reduced thicknesses, and fast thermal cycles worsen the deformations. Therefore, in this study, silica and boehmite-based nanoparticles were used to reduce the incidence of pyroplastic deformation in porcelain tile. Ten compositions were studied using mixture design, where the raw materials, nano-silica and nano-boehmite were the factors, independent variables. The response, dependent variable, was the pyroplastic deformation. The chemical composition of the raw materials and the size and specific surface area of the nanoparticles were determined. The mixture design results were evaluated by ANOVA and response surfaces, showing the effect of nanoparticles on the pyroplastic deformation of porcelain tiles. The composition with the lowest pyroplasticity index compared to the standard was selected, simulating an industrial process. In sequence, the pyroplasticity index was determined and evaluated by Tukey's test. The phase composition was analyzed by XRD after firing and was quantified by the Rietveld method. In addition, rational analysis was performed to estimate the glassy phase and finally the activation energy. There was 23.8% reduction in pyroplastic deformation of the porcelain tiles at 1210°C when 5% nano-boehmite was added to the paste. The chemical composition of the glassy phase was a key role for the pyroplastic of the samples. The activation energy prior to the maximum densification of the samples increased by 43.8%, therefore forming a higher energy barrier against the deleterious effects of pyroplastic deformation.