Abstract
Cr K-edge X-ray absorption near-edge structure (XANES) spectra were recorded for silicate glasses of various compositions in the system CaO + MgO + Al2O3 + SiO2 ± TiO2, quenched from melts equilibrated as a function of oxygen fugacity (fO₂) at 1400 °C. The spectra vary systematically with fO2 (logfO₂ ∼ 0 to -16) indicating changes in the Cr oxidation state. The intensity of a shoulder on the absorption edge (attributed to the 1s → 4s transition) was quantified using the corresponding peak in the XANES derivative spectrum and used to determine Cr2+/ΣCr. The resulting Cr2+/ΣCr values are in agreement with the theoretical dependence on logfO₂ suggesting that the 1s → 4s feature is diagnostic of Cr2+ in a silicate glass and σ(Cr2+/ΣCr) = ± 0.015. The Cr2+/ΣCr ratio for a given logfO₂ changes with the glass composition which may reflect the ability of the melt to accommodate the Jahn-Teller distorted coordination geometry which stabilizes Cr2+. Cr2+/ΣCr varies between ∼ 0.3 and 0.8 over the logfO₂ range bounded by the Ni/NiO and Fe/FeO fO₂ buffers, suggesting that Cr2+ may be important in natural melts even though this oxidation state has never been identified in a terrestrial material. The development of a methodology for determining Cr2+/ΣCr from XANES spectra of quenched glasses is an essential precursor to in situ experiments on Fe-bearing silicate melts at high temperature
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
