Investigation of nano-SiO2 and nano-Al2O3 additions in glaze formulation for Brazilian polished glazed porcelain stoneware tile

The ceramic-glaze for polished glazed porcelain stoneware tile is directly linked in determining the quality of the final product, as its characteristics significantly influence surface properties after polishing, including stain resistance, abrasion resistance, and chemical resistance. In this study, the effect of incorporating nanomaterials of alumina and silica into a glaze formulation for polished glazed porcelain stoneware tile was evaluated, with the goal of enhancing stain resistance by reducing surface porosity. Initially, the nanomaterials and the standard glaze formulation (STD) were characterized to assess the individual behavior of each material. Later, ten glaze formulations were developed-in a simplex centroid system-each subjected to postpolishing analysis, with the primary selection criterion being improved stain resistance. Optical microscopy analysis of surface porosity revealed that the addition of nanosilica (nano-SiO2) reduced glaze surface porosity by up to 67%, thereby significantly improving the stain resistance of the final product. Conversely, the addition of nanoalumina (nano-Al2O3) increased surface porosity, negatively affecting stain resistance. The reduction in porosity observed with nano-SiO2 is attributed to enhanced particle packing and an increase in relative density within the glaze matrix. Finally, formulations with the lowest surface porosity were selected for further testing for comparison to STD. These tests included X-ray diffraction, differential scanning calorimetry, thermogravimetric and differential analysis, dilatometry, and scanning electron microscopy. Thermal expansion and hemispherical temperature tests allowed the theoretical viscosity to be calculated using the Vogel-Fulcher-Tammann equation, revealing that formulations containing nano-SiO2 exhibited lower temperatures for dilatometric softening, Littleton softening, and flow point. SEM analysis confirmed a reduction in porosity and a decrease in pore diameter in the nano-SiO2 formulations.