Effects of ZnO and Al2O3 on optical properties of sanitary ware glazes without ZrSiO4

In this study, to replace zirconia-based white glaze, 3 wt% TiO2 was added to CaO-Al2O3-SiO2-ZnO with a translucent glaze, and ZnO and Al2O3 were added to suppress the yellowing of TiO2. According to the type and amount of additives, the crystal phases (X-ray diffraction, XRD) and microstructures (scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS)) of the glazes were analyzed, and the whiteness, gloss, reflectance, and absorption coefficient were measured. XRD and SEM analyses revealed the presence of plate-like (SiO2) and needle-like (Al1.488Ca0.491Na0.499Si2.506O8) crystal phases that affected the whiteness of the glaze. The gloss of the specimen was significantly reduced (to <40) with the addition of Al2O3. Color analysis results revealed a yellow index (b*) ranging from 2.8% to 4.9% and whiteness ranging from 89% to 93% for all the specimens, which were similar to the values for the zirconia-based white glaze. Reflectance analysis in the visible range (300-800 nm) using Ultraviolet-visible-near-infrared spectrophotometer (UV-ViS-NIR) indicated a decrease in reflectance in the wavelength range of 400-500 nm and an increase in reflectance in the wavelength range of 500-700 nm.