Phase equilibria of Na2O-PbO-SiO2 system between 900 and 1100 °C

Imam Santoso, Pekka Taskinen

In ceramic and glass industries, Na2O-PbO-SiO2 system is important since the materials proposes advance properties for many applications in optic, electronic and nuclear technologies. In the metallurgical process, when lead is removed from metal phase by using soda silicate slag, the information of the Na2O-PbO-SiO2 slag properties is crucial. The ability to accurately measure the melting point of the system can determine the optimum condition to produce the targeted slag or glass. However, a literature review indicates that there are limited data in the liquidus temperature of this system. Moreover, the technique to measure the liquidus adopted by previous investigation can contribute to uncertainties of the result due to, for example, the evaporation of the components in the mixture during experiment. In fact, PbO and Na2O are volatile subtances at high temperature. In the present study, equilibration of the samples at high temperature, quenching the equilibrated samples in an iced cold water and followed by chemical analysis using an electron probe micro analyzer (EPMA) were employed to measure the phase boundaries between liquid and solid primary phase. By using this technique the limitations of the experiment come from conventional method can be resolved. The loss of mixture component during equilibration process will not affect the final equilibrium composition. The samples were carefully examined for wide range of composition starting from binary Na2O-SiO2 to PbO-SiO2 side. Phase properties and liquidus of Na2O-PbO-SiO2 system at silica saturation between 900 and 1100 °C in equilibrium with air have been determined. The data have been compared with previous investigation. In industrial practice, the by using the data obtained from present study, the key operating parameter i.e. temperature during the smelting process effected by variations of slag composition can be predicted. The data also can be utilized for assessing the phase diagram and for improving the expression of thermodynamic data base of the Na2O-PbO-SiO2 system.