Incorporation of sulphur in silicate glasses produced by reactions between melts and sulphur‐bearing sources at high temperatures was studied by X‐ray absorption near edge structure (XANES) spectroscopy at the sulphur K edge. Three types of syntheses were performed using sodium trisilicate, soda lime silicate, and float glass as starting materials: (i) controlled bubbling of glass melts with SO2 or SO2/O2 gas mixtures at ambient pressure, (ii) melting of glass powder containing various salts (Na2SO4, Na2SO3, Na2S) in excess to the expected solubility in the melt and (iii) fusion of glass powder in gold capsules at 1000°C and 100 MPa with an added amount of salts below the expected sulphur solubility. In some of the latter experiments water was introduced to vary the oxygen fugacity in the system. Sulphur concentrations in the glasses were determined by combustion and subsequent IR spectroscopy; water concentration in the glasses was measured by IR microspectroscopy. Bulk composition and homogeneity of glasses were checked by electron microprobe analyses. XANES spectra obtained at room temperature give evidence for incorporation of sulfate (S6+) and/or sulfide (monosulfide [S2−] and/or polysulfide [Sx2−]) in all glasses, depending on starting materials and run conditions. Clear evidence for sulfite (S4+) was not found in any of the spectra, implying that this sulphur species in glass products at room temperature is at or below the detection limit. We suggest that tetravalent sulphur (as SO2 or Na2SO3) disproportionates into sulfate and sulfide when being dissolved in simple silicate melts or during cooling of the glass melt.

Universal simulation models based on (a) validated mass transfer relations and (b) thermodynamic modeling procedures for glass melts are developed to predict the evaporation rates of volatile species from a large range of glass melt compositions. Depending on the glass composition, temperature of the surface of the melt, local composition of the atmosphere, exposure time of a melt layer to the combustion atmosphere, and local gas velocities above the glass melt surface, the evaporation rates of volatile species can be estimated. Laboratory‐scale transpiration evaporation experiments have been used to study evaporation kinetics, to derive mass transfer relations, as well as to validate the sodium evaporation modeling results for sodium‐silicate melts as well as for soda‐lime‐silicate melts. In these investigations, the molten sodium‐silicate and soda‐lime‐silicate melts are exposed to atmospheres of flowing gases with controlled composition and gas flow rates. In a humid atmosphere for example, sodium mainly evaporates as NaOH. From the measured NaOH evaporation rates and the mass transfer relations, the NaOH vapor pressures in equilibrium with the molten glass at prevalent temperature and furnace atmosphere composition were derived. The NaOH vapor pressures are assumed to be in equilibrium with the glass melt composition at the surface of the melt. During the evaporation test, the Na2O surface composition will change due to depletion. This leads to equilibrium vapor pressures decreasing with time, reflecting the changing chemical activity at the glass melt surface. The results of evaporation tests for sodium‐disilicate and soda‐lime‐silicate glass melts are shown. Chemical activities derived from these measurements are compared with the results of thermodynamic modeling, using a method based on a glass melt from ideal mixtures of associate (stoichiometric) species of structural compounds with known thermodynamic properties.

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