Gas release and foam formation during melting and fining of glass

A method for the prediction of gas evolution from a glass melt during fining processes has been described. This procedure is based on the assumption of thermodynamic equilibrium conditions between the species in the glass melt and co-existing gas phases. The method has been applied to estimate (a) the onset temperature of fining and (b) the evolution of different gases from glass melts. Both are strongly dependent on water concentration in the melt, the temperature, and the content of fining agent (sulfates). Expressions for foam bubble lifetimes have been presented, and a combination of these equations with gas evolution rates has been used in a foam formation model. This model calculates the number of bubble layers on top of glass melts during secondary foaming (foam formation during fining). A key parameter for foam stability and the foam layer thickness is the mobility of the surfaces of the lamellae of the bubbles in the foam layers. The water content in the melt, sulfate concentration levels, heating rates, furnace atmospheres, and bubble sizes govern the glass melt foaming behavior.