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Iron oxidation state variations in zoned micro-crystals measured using micro-XANES

Paper ID Volume ID Publish Year Pages File Format Full-Text
54113 46997 2014 8 PDF Available
Title
Iron oxidation state variations in zoned micro-crystals measured using micro-XANES
Abstract

•We showed that micro-XANES is a powerful tool to investigate the Fe-redox state variation across micro-crystals.•We exploited the X-ray microprobe available at the ESRF ID22 beamline to reach a spot size of 1.7 μm × 5.3 μm.•For garnet (cubic space group) the Fe3+ content was quantified in a space-resolved way, after a careful calibration.•For omphacite (monoclinic space group) a significant dichroism effect was observed in the XANES features.•These zoned micro-crystals are ideal systems to develop analytical procedures, relevant for many other research fields.

The determination of the oxidation state of transition metals at high spatial resolution is a crucial issue for many fields of science, including solid state physics, earth sciences, biology, bio-chemistry and catalysis. Among the other available analytical methods, micro-XANES allows to probe in situ the oxidation state with high lateral resolution, enabling an unprecedented level of description in heterogeneous samples. In geological samples the determination of the Fe3+/ΣFe ratio is of particular interest since it can be used as an indicator of the oxygen fugacity (fO2) at which a mineral formed. With this respect, we performed a micro-XANES experiment aiming to investigate the Fe-redox state variation across single-crystals of both garnet and omphacite exploiting the X-ray microprobe available at the ESRF ID22 beamline to reach a spot size of 1.7 μm × 5.3 μm. For garnet, the absolute Fe3+ content was determined in a space-resolved way. In the case of omphacite, the analysis of the XANES data is not straightforward owing to the presence of a significant dichroism effect and to the random orientation of the different grains in the mineral assemblage. The investigated samples are highly complex materials which represent a challenge for the micro-XANES technique. These zoned micro-crystals are therefore ideal systems to develop analytical procedures which can be subsequently generalized to other relevant fields of science such as the Fe speciation in a single cell or a single grain for life science and catalysis applications, respectively.

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Keywords
Fe oxidation state; Micro-XANES; X-ray micro-beam; In situ characterization; Zoned micro-crystals, Polarization-dependent XANES
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Iron oxidation state variations in zoned micro-crystals measured using micro-XANES
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 229, 15 June 2014, Pages 72–79
Authors
, , , , , , ,
Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us