Redox and foaming behavior of E-glass melts

The effect of the redox state of sulphate fined E-glass batches on the foaming behavior of the melt has been studied by experiments and by thermochemical modelling calculations. The objective of the study is to identify batch-related measures for foam control. It is found that the redox state and SO3 content of the initial melt phase at 1250 degreesC are the key parameters for controlling secondary foam. Oxidized E-glass melts, with relatively high (>0.1 Wt%) SO3-contents in the initial melt phase, are especially prone to excessive foaming. To reduce foam, while maintaining a sufficiently oxidised glass melt with adequate fining efficiency, the amount of sulphate added to the batch can be decreased by replacing a large part of the sulphate by an alternative oxidising agent. From a series of preliminary foaming experiments with alternative oxidants, sodium-perborate appears to have the strongest effect on the decrease of foam.