Comparative study of zinc addition effect on thermal properties of silicate and phosphate glasses

The aim of the study was an analysis of two groups of glasses from the SiO2-P2O5-K2O-CaO-MgO system with various content of network formers in the form of P2O5 and SiO2, modified by the addition of ZnO. Their effect on glass-forming ability, glass transition effect, crystallization process and the kind of crystallizing phases was examined using DSC and XRD methods. It was observed that in both matrixes, the addition of ZnO decreases the glass transition temperature (T (g)). The lower T (g) values observed in the phosphate matrix glasses and the accompanying higher values of the changes in molar heat capacity (Delta c (p)) in contrast to the silicate matrix glasses may be considered an indicator of the degree of the reconstruction of their amorphous structure, which facilitates the process of their crystallization. It was found that the crystallizing products of the silicate matrix glasses were silicates and phosphates whose structure contained zinc. In the phosphate matrix glasses, it was observed that zinc inhibited the crystallization of silicate phases.