Sulphur chemistry and sulphate fining and foaming of glass melts

ISSN： 0017-1050

Source： Glass Technology - European Journal of Glass Science and Technology Part A, Vol.48, Iss.1, 2007-02, pp. : 41-52

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Abstract

Sulphate partly reacts during batch melting, dependent on the presence of reducing agents in the glass forming batch. These reactions cause early sulphur losses from the batch or primary melts, thus it reduces the sulphate content available for fining of the fresh melt. The fining mechanism of sulphate containing glass melts is described and a simulation model is derived to calculate gas evolution from thermodynamic properties of gases and fining agents in glass melts at equilibrium conditions. Modelling results have been validated by experimental data, comparing modelled gas evolution with experimentally observed bubble size changes during fining. The model and experiments are consistent for the determined fining gas evolution, and sulphate retention after fining. The influences of sulphate content and water infiltration in the glass melt on fining temperatures and gas evolution have been modelled for float glass type melts. The fining gas evolution depends significantly on the sulphur content of the freshly prepared melt just after batch fusion is completed. Also, the water content is decisive for the fining onset temperature and fining gas formation. An increase of the water content from 300 mg/kg float glass (typical for air fired furnaces) up to more than 450 mg/kg, typical for oxygen-fired furnaces, can lead to an increased gas release of a factor 1·5 to even 3 at fining temperatures. This may even lead to increased float glass melt foaming at surface temperatures above 1450°C.