Phase Separation Behavior and Coloring of Coating Glasses for Sanitary Ware

We investigated the phase separation behavior of multi-component oxide glasses for coating layer of sanitary wares, and the holding time dependence of the microstructure and the coloring nature of phase separated glasses. Two kinds of multi-component silicate glasses (CaO-SiO₂-Al₂O₃-MgO-ZnO-K₂O-Na₂O system) were employed, which had different CaO/SiO₂ ratio. Glass A has higher CaO/SiO₂ ratio, and glass B has lower CaO/SiO₂. Quenched glasses that were pre-melted at 1550 °C for 90 min in advance, were isothermally held at 800∼1100 °C for 0.5∼2 h by the hot-thermocouple. The microstructure of phase-separated glass was observed by using FE-SEM on the polished section. It was found that the glass A and B heat-treated at given temperatures indicated a spinodal and a binodal type phase separation, respectively. Moreover, the glass A was found to have the larger microstructure of phase separation, which caused whitish color. In contrast, the glass B revealed the finer binodal phase separation that resulted in a bluish phase separated glass.