抄録
The activity of Na2O in the Na2O-SiO2 system was measured at 1 100°C, 1 200°C and 1 300°C for compositions ranging from 33% to 60% of Na2O. Na2O-SiO2 melts were equilibrated with molten leadsodium alloy to maintain the sodium chemical potential in a graphite crucible under one atmosphere of carbon monoxide. The activity of Na2O was found to vary from 1×10-7 at 40% Na2O to 5×10-5 at 60% Na2O at 1 200°C. The results agree well with those measured by the electrochemical method.
Since the activity coefficient of sodium in lead-sodium alloy at elevated temperatures which was necessary for the calculation of the Na2O activity was not available in the literature, it was also measured by equilibrating Na2O· SiO2 and Na2O·2SiO2 melts, thermodynamic properties of which are known, with carbon-saturated iron and lead-sodium alloy. The activity coefficients of sodium in lead-sodium alloy were found as 0.315 at 1 200°C and 0.582 at 1 300°C.
The activity of SiO2 in the Na2O-SiO2 system was calculated from the activity of Na2O, using the GIBBS-DUHEM relationship.
