Abstract
Combining micro-X-ray absorption spectroscopy (μXAS) and micro-X-ray fluorescence spectroscopy (μXRF) is a promising approach for the investigation of complex multi-phase systems. In this work, we have employed this approach to investigate natural sphalerite, the most common form of Zinc Sulfide. Spatially resolved elemental distribution maps of common 3d metal atoms (Zn, Cu, Ni, Co, and Fe) are superimposed with chemical speciation and structural parameter maps in order to understand the sphaleriteore-formation process and metamorphosis. Chemical speciation and structural parameters have been obtained by analyzing the μXAS spectra collected in several representative points of the sample, after μXRF mapping. In the present case, this X-ray based approach has permitted to determine the spatial distribution of the Zn species in sphalerite. The presence of two main zincite and smithsonite inclusions has been established, with the latter located close to copper impurity center. Since copper is known to remarkably reduce the corrosion resistance of zinc, resulting in the formation of carbonate as the corrosion product, this implies a possible role of Cu in the growth of the carbonate inclusions. The results obtained highlight the efficiency of this method in univocally identifying the spatial distribution of phases in complex systems, thanks to the simultaneous access to complementary information.
Highlights
Combining micro-X-ray absorption spectroscopy and micro-X-ray fluorescence spectroscopy is a promising approach for the investigation of complex multi-phase systems
We have unveiled the spatial distribution of Zn-phases by simultaneous linear combination fit (LCF) of the X-ray Absorption Near Edge Structure (XANES) spectra and first shells modeling of Extended X-ray Absorption Fine Structure (EXAFS) data
The measurements of standards have been realized in transmission mode by counting incident and out-going photon fluxes with respect to the sample using gas-filled ionization chambers. μXAS spectra and μXRF elemental maps have been recorded by selecting the Kα fluorescence lines of Zn, Cu, Ni, Co, and Fe in the X-ray fluorescence spectroscopy (XRF) spectrum of the 5 elements Silicon Drift detector
Summary
Combining micro-X-ray absorption spectroscopy (μXAS) and micro-X-ray fluorescence spectroscopy (μXRF) is a promising approach for the investigation of complex multi-phase systems. The understanding of micron-scale processes and mechanisms in complex heterogeneous systems has naturally gathered a considerable effort in developing high resolution analytical probes to extract compositional, electronic, and structural information In this regard, synchrotron-based X-ray absorption spectroscopy (XAS) and X-ray fluorescence spectroscopy (XRF) have become two of the most promising techniques for spatially-resolved studies, thanks to the advent of 3rd generation brilliant sources and the improved focusing capability of modern x-ray optics, which permits beam sizes down to less than 100 μm. The determination of the local structural properties and the spatial distribution of coexisting species in the mineral are essential to shed light on the ore-formation process and metamorphosis We address this issue, combining μ-XRF elemental mapping and μ-XAS at the Zn K-edge. The superimposition of the μ-XRF, the LCF and the EXAFS parameter maps permits the determination of the correlation between first neighbor distances, structural disorder and chemical composition
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