Physico-chemical investigation of the behavior of sodium in the float glass process Part 1. Distribution of sodium and tin between the glass melt and the bath of molten tin

Abstract

The chemical equilibrium between a soda-lime-silica melt typifying float glass melts and molten tin is considered for the conditions prevailing in the float glass process. Α consideration of the thermodynamic stability of the relevant oxides of the glass melt reveals that CaO, MgO, AI2O3, and SiO2 are not involved in the heterogeneous reactions occurring in the molten glass/liquid tin system, whereas sodium may be transferred from the glass melt to the metal phase, and tin may be oxidized and dissolved as SnO and SnO2 in the glass melt. Thermochemical information pertaining to the reaction of sodium and tin in the molten glass/liquid tin system has been compiled from the literature. From this data basis, the equilibrium distribution of sodium and tin between the glass melt and the liquid tin is calculated. The results are presented in the form of equilibrium diagrams. Additionally, it is shown that the exchange reactions Na2O(glass melt) + Sn(metal bath) = SnO(glass melt) + 2 Na(metal bath) and 2 Na2O(glass melt) + Sn(metal bath) = SnO2(glass melt) + 4 Na(metal bath) may be considered as electrochemical processes occurring simultaneously and statistically disordered with respect to time and reaction site at the molten glass/liquid tin interface. Certain indications suggest that the rate of these reactions is controlled essentially by the transport of the reaction partners.