The influence of ZrO2 addition on the thermal properties of glass–ceramic materials from SiO2–Al2O3–Na2O–K2O–CaO system

In this paper, the glass–ceramic materials from SiO2–Al2O3–Na2O–K2O–CaO system were examined. The zirconium oxide was added to this composition in three different amounts (1.5; 3; 6 mass%). In addition, the sample without zirconium oxide as the reference sample was prepared. To determine the effect of zirconium oxide on the thermal parameters, the characteristic temperatures, by using hot stage microscopy (HSM-Misura) and mechanical dilatometry (DL-Netsch), were measured. Based on these results, the viscosity curves were calculated (by the equation of Vogel–Fulcher–Tammann). Furthermore, for the description of the phenomena which occur during the heating–cooling cycle differential scanning calorimetry (DSC) was used. These data were linked with the results from X-ray diffraction and scanning electron microscopy with microanalyzer (EDS). Two crystalline phases in zirconium glazes were identified: zirconium oxide and zirconium silicate. The presence of crystalline phases (zirconium oxide, zirconium silicate) caused a nonlinear increase in the characteristic temperatures obtained by HSM. On DSC curves, the effect probably associated with crystallisation of zirconium silicate was registered. The addition of zirconium oxide to the tested glazes results in an increase in high-temperature viscosity, and the increasing ratio is proportional to the amount of zirconium oxide. The change in the value of this parameter is proportional to the amount of introduced zirconium oxide.