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1655080 
Journal Article 
Impact of furnace atmosphere and organic contamination of recycled cullet on redox state and fining of glass melts 
Beerkens, RGC; Zaman, L; Laimbock, P; Kobayashi, S 
1999 
72 
5 
127-144 
WOS:000081288500001 
The onset temperature of fining and the quantity of fining gases is not only determined by the amount of fining agents in soda-lime-silica batches, but also by the level of organic contaminants in the cullet or normal batch and the water vapor pressure in the furnace atmosphere. These conditions will also determine the redox state of the glass and residual sulfate or sulfide concentrations in the glass. Organic contaminants will form char during heating of the batch. This char partly reacts with CO2 coming from the decomposition of the soda, limestone or dolomite forming carbon monoxide. Stable types of char or cokes or cullet-rich batches with only small amounts of carbonates will result in some carbon residues after the CO2 evolution. This carbon partly reduces sulfates and ferric iron in the fresh melts. This results in sulfide and ferrous iron formation in these glass melts. At increasing temperatures in the melt, the sulfides and sulfates react together forming sulfur-containing gases between 1000 to 1250 degrees C. The sulfate retention decreases, finally the glass even may contain sulfur only in the sulfide form under very reduced conditions. In batches without reducing agents, sulfates in the melt start to decompose at temperatures exceeding 1400 degrees C. Small amounts of carbon and water vapor reduce the fining onset temperature.



Water vapor from the furnace atmosphere predominantly infiltrates the batch blanket during melting and foaming. The water will enhance the bubble and seed growth during fining. Water in the melt will influence the redox state of the final glass. Only in batches containing coarse raw materials or cullet, reducing or oxidizing gases from the furnace atmosphere infiltrate the batch blanket and these gases will respectively reduce and oxidize components like iron oxides, sulfate/sulfide or chromium oxides in the batch blanket interior.