Gas release phenomena in soda-lime-silica glass

Heterogeneous bubble nucleation during the production of commercial glasses is one of the negative factors affecting their technology and technical properties. In order to eliminate these bubbles, we conducted extensive research of bubble nucleation in soda-lime-silica glass melts at increasing temperatures and variable redox states of glass. Evolved gas analysis (EGA) coupled with gas chromatography and mass spectrometry were used to identify and evaluate crucial chemical reactions during the melting. The reactions were indicated also by the bubble compositions estimated from bubble contraction during the temperature drop. The fining action of sulfates in the reducing conditions was observed at temperatures between 1200 and 1300 degrees C using high temperature monitoring. This was confirmed by the relatively high average values of the bubble growth rates. In addition, extensive nucleation of bubbles took place at relatively low temperatures. The temperature region of nucleation was determined by monitoring bubble nucleation on the Pt wire immersed in the melt at increasing temperatures. The nucleation of the bubbles in variously reduced glasses has been observed at temperatures even lower than 1300 degrees C which further decreased with the increasing C/SO42- ratio. Next, we tried to clarify whether the process of bubble nucleation at a low redox state of glass was caused by supersaturation of the glass melt by either physically dissolved or chemically bound gases. We suppose that the nucleation of bubbles SO2 around 1300 degrees C can be attributed to the reaction between the sulfate remaining in melts and sulfides which have been formed by reduction reactions.