BS in Materials Engineering
Materials Engineering Department
Katherine C. Chen
This study looked at the effects of colorant oxides and firing rate on the nucleation and growth of crystals in zinc-based crystalline glazes. One weight percent of iron and copper oxide powders were mixed separately with a zinc-based crystalline glaze. The uncolored glaze along with both colored glazes were applied to test tiles and fired. Two different firing schedules were used with different ramp up firing rates of 165°C/hr (slow) and 205°C/hr (fast). X-ray diffraction (XRD) analysis found both zinc oxide and silica oxide in the raw glaze, which are the main components in the formation of zinc silicate. XRD analysis of the fired glaze found zinc silicate, the main component of the crystals. XRD analysis was unable to pick up traces of either the copper or iron oxide. X-ray florescence was used to check for oxide concentration in the glaze. 0.59% Cu was found in the copper oxide glaze while 0.92% Fe was found in the iron oxide glaze. The number of nuclei were counted using the assistance of computer software. The size of the crystals was calculated using the intercept method to get a grain size value for the crystals. The addition of copper oxide and iron oxide decreased the number of nuclei by an average of 60.2% and 84.0% respectively. It also reduced the grain size number of the crystals by 35.5% for the copper and 38.5% for the iron. The change from the slower firing rate to the faster firing rate decreased the number of crystals in the uncolored glaze by 43.8% and decreased the average number of crystals in the copper oxide and iron oxide glazes by 76.1% and 61.0% respectively. The crystal sizes were also reduced by 22.8% for the copper, 27.0% for the iron and 18.8% for the uncolored glaze on average. The results of this study showed that the addition of colorant oxides or increasing the ramp up rate produced less crystals which were larger in size.