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Soda-lime-silica (SLS) glass is the most widely used of all commercial types of glass. This type of glass is mainly used for manufacturing windowpanes, household glassware and glass containers (e.g. bottles, jars) for foodstuffs and beverages. These types of end-products differ in their application, and production method (e.g., blowing and pressing for containers and glassware, float process for windows) as well as in their chemical composition. Nevertheless, they are all produced by melting mixed raw materials ( batch) in a glass furnace at maximum temperatures ranging between 1500–1600 °C. The batch consists mainly of silica sand, sodium carbonate (soda), lime, dolomite and variable amounts of glass cullet. Small quantities of alumina-bearing raw materials, fining agents (e.g., sodium sulfate), coloring and reducing/oxidizing agents are also added to the batch. For the production of SLS glass, sulfur containing raw materials (e.g. sulfates and sulfides) play an important role in determining the final product’s quality. These compounds are involved in the final part of the fusion process, known as the fining process. In this process, the decomposition of raw materials generates a large amount of gas. The evolution of those gases from the glass melt is enhanced by the presence of the sulfur compound (Kloužek et al. 2007). Moreover, sulfur compounds act as oxidizing (sulfates) or reducing (sulfides) agents, playing a decisive role in the coloring mechanism of the final glass. Sulfates also enhance the kinetics of the sand’s dissolution by wetting the sand grains at relatively low temperatures thereby, accelerating the melting process (Albayrak and Sengel 2008; Muller-Simon and Gitzhofer 2008; Daneo et al. 2006, 2009). In Table 1⇓, typical composition ranges for SLS containers glasses produced in Italy are reported in wt% of oxides (data from Stazione Sperimentale del Vetro, SSV). The total sulfur concentration in … |
