The activity of sodium oxide in molten float glass by EMF measurements

The Na2O activity in the molten float glass composed of 13.2 m/o Na2O, 70.2 m/o SiO2, 10.0 m/o CaO, 5.9 m/o MgO, etc. was determined in the temperature range from 1260 to 1380 K by means of galvanic cells using Na–β″-alumina as solid electrolyte. The Na2O activity, aNa2O, accompanying the reaction Na2O (dissolved in Na2O–WO3 melt)=Na2O (dissolved in molten glass) was found to be given by log aNa2O=−5.88−6.32×103 T−1 as a function of temperature, and the relative partial molar enthalpy of Na2O was calculated to be ΔHNa2O=−121.0 kJ/mol.