Water release behaviour of soda-lime-silica glass melts

Glass with the composition (in mol%) 16 Na2O . 10CaO . 74SiO(2) and a water content of 0.12 to 0.005 mol/l has been investigated by IR spectroscopy. It has been found that at a water content of <0.01 mol/l the ratio of the extinctions of the absorption bands at 3550 and 2800 cm(-1) is not constant. Through the vacuum hot extraction method it could be shown that the release of bonded water from glass melt does not occur continuously, and is not determined by the kinetics of formation of molecular water. At concentrations >0.01 mol/l the largest part of bonded water is released at temperatures < 1000 degrees C. Small amounts of water can be detected at temperatures > 1250 degrees C as well. This high-temperature release of strongly bonded water is caused by changes in the structure of glass melt or by the simultaneous release of other volatile species.