Sulphur in oxide glasses and slags probed by X-Ray Absorption and X-Ray Emission Spectroscopies

Paul A. Bingham* , Andrew J. Connelly, Russell J. Hand and Neil C. Hyatt

It has for some time been broadly accepted that sulphur exists in oxide glasses either as sulphate (S6+) or sulphide (S2-) species depending primarily upon oxygen partial pressure, pO2, during melting. In addition, over a relatively narrow range of pO2, it has been suggested that a combination of S6+ and S2- may coexist. Moreover, some recent research has suggested the presence, under certain melting conditions, of a range of intermediate sulphur species including S4+, S+, S-, and S-S. In some cases these species are hypothetical and have not been spectroscopically observed. When these intermediate species have been observed it has hitherto been in glasses that have different compositions and preparation conditions from commercial silicate glasses; for example natural glasses, glasses produced under high pressure or laboratory conditions and radioactive waste glasses. It is therefore still unproven whether intermediate sulphur species exist in measurable quantities below the glass transition temperature in commercial silicate glasses, and the range of preparation conditions that aid their formation and retention is unknown.
A combination of sulphur K-edge X-ray absorption near edge structure (XANES) and sulphur Ka X-ray emission spectroscopy (XES) have been used to determine the speciation of sulphur in a range of commercial soda-lime-silica glasses and silicate slags. Several sulphur-bearing mineral standards with known sulphur valences and structural environments have been analysed and the results have been used to determine the speciation of sulphur in the glasses and slags. Our results demonstrate that sulphur occurs in the samples studied here primarily as sulphate (S6+), and / or sulphide (S2-) species as expected, however small quantities of intermediate sulphur valences are confirmed to exist in some glasses. Here we link this behaviour with glass melting / preparation conditions, and we suggest that the presently-accepted view of sulphur valence in oxide glasses requires slight modification .

*presenting author

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