Oxidation state of sulfur, iron and tin at the surface of float glasses

Sulfur is an important element of glasses, not because of its amount, always very low (less than 0.4 % in weight of SO₃), but because of its role since it actively participates to the refinement process and, combined to other elements, it can be responsible for the coloration of the glass. Iron is also of a major importance in most of the glasses. In the case of the float glass, the two faces, because of the fabrication process, are different in terms of composition (presence of Sn for one face) and also in terms of oxidation state of these minority elements (Fe, Sn, S). There should be a subttle interplay between the concentrations and the oxidation states of these different minority elements, and anyway these variations occur over a thickness of the order of few micrometers below the surface.

Using the high intensity and the focusing properties (3 × 3 μm²) of the x-ray beam from the Lucia beamline, we have therefore studied the speciation of iron and sulfur near the face of a float glass in relation with the behavior of tin. This has been obtained by combining elemental x-ray fluorescence cartography and x-ray micro-absorption at the different K-edges.