Structural investigation of platinum solubility in silicate glasses

The coordination environment of 20-200 ppm Pt in yellowish glasses from the CaO-Al 2 O 3 -SiO 2 (CAS) ternary was studied using X-ray absorption fine structure spectroscopy at the Pt-L m 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 A). No evidence for Pt 2+ or Pt 6+ 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 Pt 4+ O 6 polyhedra. How­ever, bond-valence modeling suggest that these polyhedra are likely to bond mostly to [VI] Ca 2+ , 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 CaPtO 3 -type units.