Pyroplastic deformation analysis of Brazilian porcelain tile formulations using mixture design

Pyroplastic deformation is still an important defect caused during firing in the manufacture of porcelain tiles when there is no control over the raw materials used in the formulation of ceramic tiles. The present study used mixing design as a tool in the development of pastes formulations for Brazilian porcelain tile manufacturing in order to reduce their pyroplastic deformation. Ceramic industry in Brazil has typical and complex way to set up porcelain tile formulations, using regularly more than a dozen raw materials. Therefore, the originality in this work was understanding the formulation by means of a pseudocomponent-based approach (multiminerals triaxial diagram) and defining parameters that minimize that problem. Eleven different raw materials, supplied by Brazilian ceramic manufacturer, were used and characterized according to their physical–chemical properties. Later, raw materials were divided into three chemical categories and through a simplex-centroid mixture design, defining the maximum limit of feldspar in 70%, 10 formulations in the experimental region were defined. All formulations were analyzed for particle size distribution, bulk density (postpressing and postburning), mechanical strength (postpressing and postfiring), thermal shrinkage, water absorption, and pyroplastic deformation. Thus, formulations that presented the most admissible behavior in the manufacture of porcelain tiles were selected, and tests were carried out for chemical, mineralogical, thermal (differential scanning calorimeter [DSC]/thermogravimetric [TG]), thermal expansion, porosity analysis, and optical fleximeter (pyroplasticity). All results were analyzed using response surfaces with data obtained by analysis of variance (ANOVA). Mixture design method proved to be a valuable tool to observe the behavior of raw materials and to optimization of Brazilian porcelain tile formulations.