The Morphology And Diffusion Mechanism Of Sulfur In Float Glass Process

Sulfate is often added to the soda-lime float glass manufacturing process as finingagent. However, it does not decompose entirely. The sulfate of float glass is reducedto sulfide in the tin bath, which results in tin loss and defects generation. In order tosolve the problem and understand the redox reactions between a glass and itssurroundings in the float process, it is necessary to reveal the oxidation state of sulfurand the diffusion mechanism of sulfur in glass manufacture process. The oxidationstate of sulfur of both sides of the soda-lime-silicate glass is determined by X-rayabsorption near edge structure （XANES） spectra. The sulfur and other ion depthprofiles are measured by secondary ion mass spectrometry （SIMS）.The results show that the sulfur is mainly in the form of S6+and no S4+, furthermore,the S^2-starts to appear at650℃and the content of S^2-at750℃is higher than that ofthe glass treated at other temperatures, because the S^2-volatilizes to the atmosphereeasily at higher temperature. Two peaks of XANES spectrum are associated withsulfide, the broader one at about2476.3eV and the sharper one with an accurateposition at2473.7eV.By means of experiments and theoretical analysis, it is firstly found that there areSn-S bonding（the shoulder peak between2468.8eV and2473.1eV） and Si-Sbonding（a sharper peak at2473.7eV） in soda-lime float glass. Furthermore, there areFe-S bonding（Ni-S bonding） while some Fe（Ni） presents in glass and the position ofabsorption peak at2469.5eV（2469.8eV）. Following the increase of the content ofFe（Ni）, the Si-S bonding is replaced with Fe-S bonding（Ni-S bonding）.Through the theoretical hypothesis of sulfur diffusion, this paper proposes fourmathematical models and verifies that the Erf fitting model is the most reasonable forthe S6+and S^2-depth profiles. The coefficient of diffusion of the tin side is bigger thanthat of the air side of glass.Based on the cation depth profiles, this paper divides the reduced layer of the airside into three layers: the silica-rich layer, the alkaline earth-rich layer and thealkaline-rich layer. Meanwhile, the reduced layer of the tin side can be divided intothe tin-rich layer, the alkaline earth-rich layer and the alkaline-rich layer. Furthermore,the depth of reduced layer coincides with the S^2-depth profiles.Besides, it is found that the augite crystal is formed in bearing-iron soda-lime-silicate glass which is heat-treated in air and reduced atmosphere, however,the morphology of the crystal is different, so it is possible to deduce the origin of theaugite crystal. The needle-like crystal comes from the tin bath whereas thedendrite-like crystal is from the furnace. Adding some content iron to tin can reducethe stannizing, however, it will reduce the transparency and may generate criss-crosslike defect in the tin side surface, which isrelated to the Fe2O3crystal.