Structural environment of iron and accurate determination of Fe3+/ΣFe ratios in andesitic glasses by XANES and Mössbauer spectroscopy

Abstract

11Andesitic glasses equilibrated at 1350 °C over a range of oxygen fugacities 12 (log fO 2 from -8.63 to -0.68) were examined with Fe K-edge X-ray absorption 13 near-edge structure (XANES) and Mössbauer spectra. XANES spectral features 14 were then calibrated as a function of Mössbauer-derived Fe 3+ /∑Fe ratios. 15Additionally, both methods help characterize the local structure of iron ions in 16 andesitic glasses. Fe 3+ /∑Fe ratios were determined from Mössbauer spectra 17 collected at room temperature but corrected with recoilless fractions obtained 18 from previously reported Mössbauer data collected on one of the glasses from 19 47-293 K. An empirical model was derived for the correlation between the pre-20 edge centroid energy and Fe 3+ /∑Fe ratio for andesitic glasses. This trend is 21 intermediate between those previously determined for rhyolitic and basaltic 22 glasses, but the distinction from basaltic compositions may be owing chiefly to 23

Nitrogen and carbon fractionation during core–mantle differentiation at shallow depth

“…Experimental durations were 6 hours for 1400ºC experiments following previous work (Stanley et al 2014;Armstrong et al 2015), and 4 hours for 1600ºC experiments. Experiments were quenched at rates of ~125°C/s for BaCO 3 and 175 °C/s for CaF 2 cells, respectively (Zhang et al, 2016), by cutting power to the furnace. Recovered capsules were mounted in ethyl-2-cyanoacrylate ("superglue") and polished for electron microprobe analysis (EPMA).…”

“…and the resulting f O2 calculated from equations (3) and (4) was compared to the IW buffer determined following Zhang et al (2016).…”

Local structural variation with oxygen fugacity in Fe2SiO4+ fayalitic iron silicate melts

“…It has been shown that the centroid of the pre-edge feature in Fe K-edge XANES spectra can be used as a quantitative measure of oxidation state (Berry et al, 2003;Cottrell and Kelley, 2011;Cottrell et al, 2009;Knipping et al, 2015;Wilke et al, 2007;Wilke et al, 2005;Zhang et al, 2016). Such quantification typically relies upon calibration to a series of glasses of varying and known (by other means) Fe 3+ /ΣFe, but otherwise fixed composition, and has been shown to depend somewhat on the bulk composition.…”

The fate of iron during the alkali‐activation of synthetic (CaO‐)FeOx‐SiO2 slags: An Fe K‐edge XANES study

“…Additional information on these issues can be expected particularly from X‐ray absorption spectroscopy (XAS) at the Fe K ‐edge. This method has been extensively applied to many different crystalline and amorphous materials and has been proven to be extremely valuable . X‐ray absorption near‐edge structure (XANES) at the Fe K ‐edge, in particular the pre‐edge feature, contains information about the oxidation state and the coordination number of iron in amorphous materials such as glass, while relying on the comparison with model compounds.…”

“…X‐ray absorption near‐edge structure (XANES) at the Fe K ‐edge, in particular the pre‐edge feature, contains information about the oxidation state and the coordination number of iron in amorphous materials such as glass, while relying on the comparison with model compounds. Measurements of many different crystalline model compounds as well as calibration against Mössbauer data and wet chemical analyses have led to the establishment of reliable relationships between oxidation state/coordination number of Fe and position/intensity of the pre‐edge feature in the X‐ray absorption spectrum at the Fe K ‐edge, making these relationships a very useful tool for the interpretation of XANES spectra and the characterization of materials. In this study, three synthetic slags in the CaO–FeO x –SiO 2 system were synthesized, and various IPs were produced by mixing the ground slags with different alkali silicate solutions.…”