Microstructural evoluation of fast firing soft porcelain

Abstract

The present work deals with the study of the microstructural evolution of fast firing soft porcelains. Soft porcelains are those sintered at low temperatures (bellow 1350°C), and the thermal treatment used was similar to that of industrial products, with 10 minutes of sintering time. As raw materials kaolin, sodium feldspar, potash feldspar and talc, all except the former used as melting oxides in order to form eutectics at low temperatures. The compositions were formulated according the mixture design technique, four factors at three levels, with coordinate transformation by independent variables. The minerals were characterized to determine its chemical and mineral compositions and particle size distribution. Nine compositions were formulated, and the analyses were carried out for the thermal behavior (differential scanning calorimetry, DSC) and evolution of the crystalline phases with temperature (X ray diffraction, XRD). The results were interpreted by analysis of variance (ANOVA) and presented as response surfaces. There was glass formation due the effect of both feldspars (orthoclase and albite). Talc has influenced the porcelain densification. The main crystalline phases obtained were cordierite and cristobalite, due the presence of talc, and mullite and quartz, due the initial content of kaolin.