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The oxidation state of europium in silicate melts as a function of oxygen fugacity, composition and temperature

DOI: 10.1016/j.chemgeo.2015.07.002 DOI Help

Authors: A.d. Burnham (Department of Earth Science and Engineering, Imperial College London, South Kensington) , Andrew Berry (Imperial College London) , Helen Halse (Imperial College London) , Paul Schofield (Natural History Museum) , Giannantonio Cibin (Diamond Light Source) , Fred Mosselmans (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemical Geology , VOL 411 , PAGES 248 - 259

State: Published (Approved)
Published: July 2015
Diamond Proposal Number(s): 7452 , 5576 , 3771 , 6300

Abstract: Europium LIII-edge X-ray absorption near edge structure (XANES) spectra were recorded for a series of synthetic glasses and melts equilibrated over a range of oxygen fugacities (fO2s, from -14 to +6 logarithmic units relative to the quartz-fayalite-magnetite, QFM, buffer) and temperatures (1250 – 1500 °C). Eu3+/ΣEu (where ΣEu = Eu2+ + Eu3+) values were determined from the spectra with a precision of ±0.015. Eu3+/ΣEu varies systematically with fO2 from 0 to 1 over the range studied, increases with decreasing melt polymerisation and temperature, and can be described by the empirical equation: Eu3+/ΣEu = 1/[1+10^(-0.25*logfO2 - 6410/T - 14.2Λ - 10.1)], where Λ is the optical basicity of the melt and T is the temperature in K. Eu3+/ΣEu in glasses and melts equilibrated at the same conditions are in excellent agreement for Fe-free systems. For Fe-bearing compositions the reaction Eu2+ + Fe3+= Eu3+ + Fe2+ occurs during quenching to a glass and the high temperature value of Eu3+/ΣEu is not preserved on cooling; in situ measurements are essential for determining Eu3+/ΣEu in natural melts.

Journal Keywords: Xanes Redox Rare Earth Element Silicate Glass In Situ Eu/Eu* Morb

Subject Areas: Earth Science, Chemistry

Instruments: B18-Core EXAFS , I18-Microfocus Spectroscopy

Other Facilities: ESRF