Structural investigation of platinum solubility in silicate glasses

Abstract

The coordination environment of 20-200 ppm Pt in yellowish glasses from the CaO-Al2O3-SiO2 (CAS) ternary was studied using X-ray absorption fine structure spectroscopy at the Pt-L(III) edge. Analysis of the Pt-L(III) edge region suggests that Pt in these glasses is mainly tetravalent and sixfold-coordinated by O (with a mean Pt-O distance of 2.08 ± 0.02 Å). No evidence for Pt2+ or Pt6+ was found in any of the glasses studied, suggesting that one can not derive valence information easily from solubility data. No second-neighbor contribution was observed around Pt4+O6 polyhedra. However, bond-valence modeling suggest that these polyhedra are likely to bond mostly to ([VI])Ca2+, which should promote high positional disorder of second-neighbor cations around Pt. This particular bonding arrangement may explain the relatively high solubility of Pt in these relatively depolymerized melts, as CaPtO3-type units.