化学平衡法による Na_2O-SiO_2 系融体中の Na_2O の活量の測定

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The activity of Na_2O in the Na_2O-SiO_2 system was measured at 1100℃, 1200℃ and 1300℃ for compositions ranging from 33% to 60% of Na_2O. Na_2O-SiO_2 melts were equilibrated with molten lead-sodium alloy to maintain the sodium chemical potential in a graphite crucible under one atmosphere of carbon monoxide. The activity of Na_2O was found to vary from 1×10^<-7> at 40% Na_2O to 5×10^<-5> at 60% Na_2O at 1200℃. 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 Na_2O activity was not available in the literature, it was also measured by equilibrating Na_2O・SiO_2 and Na_2O・2SiO_2 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 1200℃ and 0.582 at 1300℃. The activity of SiO_2 in the Na_2O-SiO_2 system was calculated from the activity of Na_2O, using the GIBBS-DUHEM relationship.
1985-05-01