Study of the correlation between the composition, structure and crystallization in frits designed for single fast-firing glazes with variable BaO content.

The paper presents the results of investigation on the development of frits for single fast-firing glazes with variable BaO content based on the SiO2–Al2O3–CaO–MgO–ZnO–(BaO) system, fired at a maximum temperature of 1220 °C. The study of the correlation between the composition, structure and crystallization of frits and glazes was carried out using various methods for materials characterization, including differential scanning calorimetry (DSC), dilatometry (DIL), hot-stage microscopy (HSM), X-ray diffraction and scanning and transmission electron microscopy. DSC and X-ray diffraction showed a high tendency to crystallize the tested frits. DSC curves showed that all glazes crystallized during heating in a narrow-temperature range ≈ 938–955 °C, and the introduction of BaO shifted the maximum of exothermic peaks toward higher temperatures. X-ray analysis revealed the presence of diopside and anorthite as the main crystalline phases. The introduction of 5 mass% BaO to the frit composition promoted the crystallization of the additional crystalline phase of barium feldspar (BaAl2Si2O8). In addition, in this composition a strong exothermic effect on the DSC curve at the cooling stage was observed. The analysis of data obtained from thermal studies also showed that the addition of BaO to the chemical composition of the frits resulted in a decrease in the glass transition temperature (Tg) and in reduction in viscosity calculated on the basis of the Vogel–Fulcher–Tammann equation (HSM, DIL). [ABSTRACT FROM AUTHOR]