Thermal (DSC) characterization of xPbO–(1−x)P2O5 glass system

The lead phosphate (LP), xPbO–(1−x)P2O5 glasses, divided into three compositional regions, x=0.3–0.5 (region I), x=0.55–0.6 (region II), and x=0.66–0.75 (region III) were prepared by single-step melt-quenching process with the melt-temperature increasing from 550 to 750 °C. The DSC studies on the glasses in the compositional region, which are hygroscopic, revealed two endotherm peaks. The first and weak endotherm around 130 °C has been attributed to a thermal event in which dehydration of glasses takes place. The second and stronger endotherm has been attributed to the glass transition (Tg) phenomenon. The onset of the glass transition temperature was found to increase from about 212 °C for the glass sample with x=0.3 to about 345 °C for the glass with x=0.6 in the compositional region II where both crystalline and glass phase co-exist. The observed splitting in the endotherms of glasses in the region II co-relates well with the mixed phase. The gradual and linear increase in the average Tg value is consistent with the increase in the melt-temperatures of the glasses and correlates well with increase in the mol% of the modifier PbO in the glasses.