Sodium sulfate is widely used as a fining agent in high-tonnage glass technology. Since the conditions for redox glassmaking and Fe 2+ « Fe 3+ equilibrium displacement are formed under the influence of sulfate, the glassmaking process and glass quality largely depend on the quality and particulars of sulfate interaction with a reducing agent. The reactions and stages of sulfate action in the batch and molten glass are examined.Sodium sulfate Na 2 SO 4 is widely used in batch for making sheet, container, electrotechnical and other types of glass, predominately high-tonnage glass [1]. Its role in glassmaking is multifaceted:Ø source of Na 2 O and SO 3 in the glass; Ø promoting the formation of low-melting eutectic at the silicate-formation stage;Ø fining agent, precipitating during decomposition at high temperatures a gas phase in the form of large bubbles, which entrain via Stoke's law small bubbles ("seeds");Ø oxidizer via oxygen release in the decomposition reaction Na 2 SO 4 ® Na 2 O + SO 2 + 1 2 O 2 ;Ø surface-active component decreasing the surface tension at the gas-phase -molten-glass interface, which promotes dissolution of gaseous inclusions and their breakdown from the surface layer of the molten glass.Sodium sulfate can be used as the main source of Na 2 O (sulfate batches) or a minor additive in soda batch.At present for high-tonnage glass (sheet, container and others) Na 2 SO 4 is used as a minor additive in amounts 1 -5% 3 of the total content of alkali components of the batch.Currently, the sulfate/soda ratio is 1 : 20, down from 1 : 6 used previously. This is dictated by the need to decrease the amount of SO 2 in the kiln gases and by the complexity of melting batches containing sulfate.For batch with > 2% Na 2 SO 4 a reducing agent is added or the glass is made in a reducing medium, since under these conditions sodium nitrate reacts with the batch components and intermediate products are formed.There are ample works devoted to the physical-chemical processes occurring in molten glass with sodium sulfate being used and the interaction of sodium sulfate with a reducing agent during glassmaking. However, the results obtained for different glass compositions do not have a clear interpretation.The first works on sulfate use in glassmaking belong to É. Laksman (1784, Irkutsk). He also proposed adding carbon to sulfate. O. Schott performed more detailed studies in 1871. Subsequent results are presented in a monograph by H. Jebsen-Marwedel and R. Brückner [2].Glass compositions and glassmaking conditions have changed since then. Research in this field is ongoing, since actual batch and glass compositions as well as the glassmaking conditions and redox potential (ORP) of molten glass determine the behavior of sulfate and the sulfate/carbon ratio, which affect the glassmaking process and the quality, spectral characteristics, and uniformity of glass, which in turn affects the mechanical, thermal and chemical properties of the product [3 -6].The requirements for uniformity and the spectral characteristics of...
Mixtures in the system Na 2 SO 4 + C + SiO 2 after heat-treatment at different temperatures are investigated. A characteristic feature of the interaction at 900°C is flotation of quartz grains together with the formation of a dense silica-containing surface layer. Separation of the mixture with flotation of incompletely fused material is characteristic for commercial technology with reducer deficiency. The reactivity of sulfates and carbons is observed to depend explicitly on their dispersity. A combination of coarse sulfate and finely dispersed carbon is best.
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