Thermal properties of MnO2 and SiO2 containing phosphate glasses

Thermal properties of glasses from the P2O5–SiO2–K2O–MgO–CaO system modified by MnO2 addition was studied by DSC, XRD and FTIR methods. It has been found that the replacement of MgO and CaO modifiers by MnO2 in the structural network of phosphate glasses results in decrease in the glass transition temperature (Tg) and thermal stability parameter (ΔT). The identified crystallization products proved to be diversified, including different type of polyphosphates and silicates. It was determined that the type of the crystallizing phosphate phases is consistent with the classification of phosphate glasses, based on the O/P ratio. During the crystallization in higher temperature ranges and with the content of MnO2 over 25 mol%, a change of crystallization products was noted, including the transition of the diopside type silicate (CaMgSi2O6) into the akermanite type silicate (Ca2MgSi2O7). Simultaneously, the nature of transitions taking place during heating of the analyzed glasses was explained on the basis of crystallochemical factors (strengths of bonds) and chemical affinity of the glass components (ΔG of formation).