V.A. Kreisberg, V.P. Rakcheev, I.H. Smith
Glass Technology (2002) (in print)
ABSRACT. Processes of degassing and water release from float glasses of different melting methods and various water contents were investigated by mass spectrometry and IR spectroscopy. The primary impurity released from glass grains in temperature range from 450 upto 1050 K is water. At higher temperature, up to a temperature of 1650 K other gases (SO2, O2, CO2) are mainly evolved. The quantitative relation of SO2 and O2 are consistent with equations of decomposition of SO3 and sulfates taking into account the oxidation of carbon-containing substances by O2 with the formation of CO and CO2. The main desorption of water takes place in two temperature ranges. Dehydration and dehydroxylation of the surface and near-surface regions of the glass cause the first low-temperature thermodesorption peak at 550 K. The position of second thermodesorption peak of water at 850 and 950 K depends on the particle size of glass grains. Water desorption in this temperature range proceeds through the mechanism of diffusion. Good agreement between water content values obtained by mass spectrometry and IR spectroscopy was achieved for the glass melted electrically. A somewhat greater difference in water content was observed for the glass obtained in gas air fired furnace. Diffusion processes in manycomponent glasses were considered in accordance with the mechanism of ion porosity. The coefficients of water diffusion in industrial float glasses were determined from the isothermal parts of kinetic curves of water desorption at temperatures from 750 up to 1050 K at the first time. Water diffusion coefficient values are dictated by the glass composition and do not depend on float glass melting conditions. The full degassing of a glass proceeds under condition of certain optimal relation between temperature, diffusion coefficient value and particle size of the glass sample.