Phase and microstructural evolution in quartz-free porcelain tile compositions

Abstract

In the present investigation, three quartz-free porcelain compositions were prepared where quartz was fully substituted by fly ash (VPF 1) and feldspar was partly substituted by blast furnace slag (VPF 2) and basic oxygen furnace slag (VPF 3). A quartz-containing porcelain (VPQ) was also considered to compare the results with quartz-free porcelain bodies. Phase transformation and mass loss of the prepared batches were measured up to 1150 °C by simultaneous thermogravimetric and differential thermal analysis (TG-DTA). Endothermic peaks in the range of 519.27–539.01 °C were mainly due to dehydroxylation of kaolin. Exothermic peaks in the range of 814.01–1060.55 °C were attributed to mullite crystallization. No major difference was found in TG-DTA data of quartz-containing sample. Fabricated green samples were heated in the temperature range of 1100–1280 °C based on the softening point (PCE values) of the experimental bodies. Physico-mechanical properties, phase, and microstructure of the heated samples were evaluated by standard techniques. Early vitrification was observed in the case of VPF 1 and VPF 3. Quartz-containing body (VPQ) was vitrified at 1280 °C. X-ray diffraction (XRD), field emission scanning electron microscopic (FESEM), and energy dispersive X-ray analysis (EDAX) studies confirmed the presence of quartz (SiO2) and mullite (3Al2O3·2SiO2) in VPF 1 while quartz, mullite, and anorthite (CaO·Al2O3·2SiO2) were observed in VPF 2 and VPF 3. Alumina-enriched slag used in this study was contributed towards anorthite crystal formation. In quartz-containing body, major phases were found to be quartz and mullite.