Effect of oxygen fugacity on the coordination and oxidation state of iron in alkali bearing silicate melts

摘要: Abstract In this study the effect of oxygen fugacity (fO2) on oxidation state and coordination Fe was investigated in different alkali trisilicate glasses (Rb2Si3O7 = RFS, K2Si3O7 = KFS; Na2Si3O7 = NFS; Li2Si3O7 = LFS) doped with ~ 5 wt.% Fe2O3 main focus K- Na-bearing compositions. Most experiments were conducted at ambient pressure a gas mixing furnace 1250 °C controlled redox conditions (log fO2/bar: − 0.68 to − 16.18). The quenched analyzed using several methods. Analyses by colorimetric wet chemistry method revealed continuous increase Fe2 +/Fetotal towards more reducing without reaching 100% Fe2 + even extremely (range Fe2 +/Fetotal: from 0.08 air 0.93 H2 atmosphere). X-ray absorption near edge structure (XANES) spectroscopy shows an decreasing ionic radius coexisting alkali, while average number seems be independent iron aside largest studied Rb, which support lower coordinated (tetrahedral) oxidizing conditions. ratios inferred XANES, intensity ratio based calibration Wilke et al. (2004), are systematically higher 10% compared results study, may due external determination (Mossbauer spectroscopy) used their calibration. A new curve centroid positions is proposed for silicate glasses. optical spectroscopy, position Fe2 +-related peak shifts wavenumbers increasing incorporated abundance ferrous iron. Absorption coefficients eFe(II) eFe(III) calculated absorbance band ~ 9000 ~ 26,000 cm− 1, respectively. decrease detected alkalis (eFe(II)KFS = 31.8 ± 2.6 L·mol− 1·cm− 1, eFe(II)NFS = 30.7 ± 2.3 L·mol− 1·cm− 1 eFe(II)LFS = 23.6 ± 1.7 L·mol− 1·cm− 1). Finally, recent models, predict fO2 knowledge ratio. All models overestimate melts very probably unanticipated stabilization Fe3 + adjacent Fe2 +.