Effects of redox State and atmosphere on the surface tension of ironcontaining soda-lime-silica melts

Abstract

The density and surface tension of 15Na2O 11CaO 74SiO2 glass melts (composition in mol%) containing additions of 0.5 and 1.0 mol% Fe2O3 were measured using the sessile and pendant drop techniques at various temperatures between 1200 and 1400°C. Melts of each composition were prepared under oxidizing and reducing conditions in order to study the effect of iron redox state on the surface tension. Surface tension measurements were carried out in reducing (96 %Ar/4 %Η2), inert (Ar) and oxidizing (dry air) atmospheres. The density of the melts increased with increasing iron content and decreasing melt temperature. The surface tension of the iron containing melts was found to be influenced by the atmosphere and its effect on iron coordination. It was determined that melts with high concentrations of Fe3+ are most susceptible to changes in the atmosphere, since Fe3+ can have either tetrahedral or octahedral coordination. A minimum in melt surface tension was detected between 1300 and 1350°C for the iron containing melts.