Foaming of Glass Melts

Influence of Fining Agents on Glass Melting: A Review, Part 2

“…Also an uncontrolled sulphur input into acidic glass, where the sulphate solubility is low, leads to foaming problems [34]. The addition of alumina, accompanied by a decrease of the sulphate solubility in molten glass has the same effect, mirrored in a decrease of the foaming onset temperature and in higher foams [27,36,37]. However, the addition of higher soda levels decreases foaming as it acts as a surface-active compound and increases the sulphate solubility in the melt.…”

“…The addition of fine cullets may also influence foaming as their melting leads to the creation of a very viscous melt covering the unreacted batch [27]. Bubbles of a primary foam contain mainly CO 2 (CO in reduced melts), in much lesser amounts also O 2 , SO 2 and H 2 O vapour [28,34].…”

“…This results either in an increase of the dwell time for the glass melt in the furnace or the glass quality and productivity worsens [28,[31][32][33]. It is also important to mention that foaming is connected to higher crown temperatures, which may result in the higher NO x emissions and also the faster refractories corrosion and the furnace wear [27,28].…”

“…However, the addition of higher soda levels decreases foaming as it acts as a surface-active compound and increases the sulphate solubility in the melt. Every change in the redox state of melt changes the sulphate content in the melt owing to sulphate reduction reactions and thus it may cause a sudden release of gases [27].…”

“…Without surface tension gradients, lamellas are not stable, and the lifespan of the foam becomes shorter. It is shortened also by the growing temperatures in a furnace [26,27]. Bubbles present at the bottom of foam layer are usually spherical, while those on the surface are polyhedral [28].…”