Investigating sulfur valence depth profile on float glass surfaces using electron probe microanalysis and stepwise etching

•Novel method for detailed sulfur valence depth profiling on glass surfaces.•Combined optimized EPMA with stepwise etching for sulfur valence analysis.•Sulfur valence lower near surfaces, higher internally in float glass. This study introduces a novel method that significantly improves the understanding of sulfur behavior during the float process, which is a key factor for achieving high-quality glass surfaces. We established and demonstrated a novel approach that combines an optimized electron probe micro-analyzer with a stepwise etching technique for obtaining detailed depth profiling of sulfur concentrations as well as the average valence of sulfur on the surfaces of a float glass sample. The average valence of sulfur from each side of the float glass mirrored each other, exhibiting lower values near the surfaces and higher values internally. A reduced layer extending up to approximately 5 μm on both sides was also present. On the atmosphere side, the reduced layer transitioned abruptly to the oxidized layer. In contrast, the tin side featured an intermediate redox layer, where the sulfur valence gradually increased. We proposed two mechanisms for the formation of this intermediate layer: an inward sulfide diffusion, and an oxidation–reduction reaction involving Sn2+ penetrated from the tin bath.