Chemical characteristics of float glass surfaces

Abstract

The regions near the top and bottom surfaces of float glass are chemically different from the bulk glass composition. In addition to the presence of tin oxide at the bottom surface and to a lesser extent at the top surface, differences are found in SiO 2, Na 2O, CaO, SO 3 and Fe 2O 3. The concentrations of Na 2O, CaO and SO 3 are lower at the top surface than in the bulk glass, while SiO 2 is higher. In the case of tin at the bottom surface and iron at both top and bottom surfaces, the components exist in complex concentration gradients. In addition, there are variations in oxidation state for tin, iron and sulfur. Tin appears to exist in both stannous and stannic states near the bottom surface. So far it has been found that iron at the top surface and sulfur at the bottom are largely in reduced states. Some consequences of these effects have been observed in physical and chemical behavior of the surface.