Microbeam X-ray Absorption Research Articles

Performance of micro-beam X-ray absorption spectroscopy at beamline 7.2W of Synchrotron Light Research Institute

The existing BL7.2W beamline at SLRI, initially developed for Macromolecular Crystallography, was upgraded with a Si-drift X-ray detector, sample micro-stage, and polycapillary X-ray lens to provide possibilities for experiments using X-ray fluorescence (XRF) imaging and micro-beam X-ray absorption spectroscopy (μXAS) techniques. The micro X-ray beam was characterized. The beam diameter of approximately 25 μm was determined from the knife-edge scan method. The measured photon flux was 3.8 × 109, 1.8 × 109, and 6.4 × 108 photons/s for 8.0, 10.0, and 12.0 keV X-rays, respectively. Imaging XRF and μXAS measurements were successfully performed on a welding joint of oxygen-free high thermal conductivity copper and AISI304 stainless steel. This opens opportunities for SLRI users to utilize this new measurement setup for elemental and chemical characterizations of small areas on various samples.

Analysis of the Covalence Distributions of the Cross-section of Steam Oxidation Film on the Steel by Micro-beam X-ray Absorption Fine Structure

Analysis of the Covalence Distributions of the Cross-section of Steam Oxidation Film on the Steel by Micro-beam X-ray Absorption Fine Structure

Phase-Contact Engineering in Mono- and Bimetallic Cu-Ni Co-catalysts for Hydrogen Photocatalytic Materials.

Understanding how a photocatalyst modulates its oxidation state, size, and structure during a photocatalytic reaction under operando conditions is strongly limited by the mismatch between (catalyst) volume sampled by light and, to date, the physicochemical techniques and probes employed to study them. A synchrotron micro-beam X-ray absorption spectroscopy study together with the computational simulation and analysis (at the X-ray cell) of the light-matter interaction occurring in powdered TiO2 -based monometallic Cu, Ni and bimetallic CuNi catalysts for hydrogen production from renewables was carried out. The combined information unveils an unexpected key catalytic role involving the phase contact between the reduced and oxidized non-noble metal phases in all catalysts and, additionally, reveals the source of the synergistic Cu-Ni interaction in the bimetallic material. The experimental method is applicable to operando studies of a wide variety of photocatalytic materials.

Visualization of the Phase Propagation within Carbon-Free Li4Ti5O12 Battery Electrodes

The electrochemical reactions occurring in batteries involve the transport of ions and electrons among the electrodes, the electrolyte, and the current collector. In Li-ion battery electrodes, this dual functionality is attained with porous composite electrode structures that contain electronically conductive additives. Recently, the ability to extensively cycle composite electrodes of Li4Ti5O12 without any conductive additives generated questions about how these structures operate, the answers to which could be used to design architectures with other materials that reduce the amount of additives that do not directly store energy. Here, the changes occurring in carbon-free Li4Ti5O12 electrodes during lithiation were studied by a combination of ex situ and operando optical microscopy and microbeam X-ray absorption spectroscopy (μ-XAS). The measurements provide visualizations of the percolation of lithiated domains through the thick (∼40-μm) structure after a depth of discharge of only 1%, followed by a sec...

Elucidating the Driving Force of Relaxation of Reaction Distribution in LiCoO2 and LiFePO4 Electrodes Using X-ray Absorption Spectroscopy

The reaction distribution in the composite electrodes used in lithium-ion batteries greatly affects battery performances, including rate capability and safety. In this study, the generation of the reaction distribution and its relaxation in cross sections of LiCoO2 and LiFePO4 composite electrodes were analyzed using microbeam X-ray absorption spectroscopy. The reaction distribution immediately after delithiation could be observed clearly with different oxidation states of the transition metal (i.e., different concentrations of lithium ions). The distribution in the Li1–xCoO2 electrodes disappeared, whereas that in the Li1–xFePO4 electrodes remained unchanged even after 15 h of relaxation. After comparing the potential profile of both types of electrodes, it is suggested that the potential difference between the more delithiated area and the less delithiated area in the composite electrode is the primary driving force for the relaxation.

Mapping the anode surface-electrolyte interphase: investigating a life limiting process of lithium primary batteries.

Cathode solubility in batteries can lead to decreased and unpredictable long-term battery behavior due to transition metal deposition on the negative electrode such that it no longer supports high current. Analysis of negative electrodes from cells containing vanadium oxide or phosphorus oxide based cathode systems retrieved after long-term testing was conducted. This report demonstrates the use of synchrotron based X-ray microfluorescence (XRμF) to map negative battery electrodes in conjunction with microbeam X-ray absorption spectroscopy (μXAS) to determine the oxidation states of the metal centers resident in the solid electrolyte interphase (SEI) and at the electrode surface. Based on the empirical findings, a conceptual model for the location of metal ions in the SEI and their role in impacting lithium ion mobility at the electrode surfaces is proposed.

Microbeam x-ray absorption spectroscopy study of chromium in large-grain uranium dioxide fuel

Synchrotron-based microprobe x-ray absorption spectroscopy (XAS) has been used to study the local atomic structure of chromium in chromia-doped uranium dioxide (UO2) grains. The specimens investigated were a commercial grade chromia-doped UO2 fresh fuel pellet, and materials from a spent fuel pellet of the same batch, irradiated with an average burnup of ~40 MW d kg-1. Uranium L3-edge and chromium K-edge XAS have been measured, and the structural environments of central uranium and chromium atoms have been elucidated. The Fourier transform of uranium L3-edge extended x-ray absorption fine structure shows two well-defined peaks of U–O and U–U bonds at average distances of 2.36 and 3.83 Å. Their coordination numbers are determined as 8 and 11, respectively. The chromium Fourier transform extended x-ray absorption fine structure of the pristine UO2 matrix shows similar structural features with the corresponding spectrum of the irradiated spent fuel, indicative of analogous chromium environments in the two samples studied. From the chromium XAS experimental data, detectable next neighbor atoms are oxygen and uranium of the cation-substituted UO2 lattice, and two distinct subshells of chromium and oxygen neighbors, possibly because of undissolved chromia particles present in the doped fuels. Curve-fitting analyses using theoretical amplitude and phase-shift functions of the closest Cr–O shell and calculations with ab initio computer code FEFF and atomic clusters generated from the chromium-dissolved UO2 structure have been carried out. There is a prominent reduction in the length of the adjacent Cr–O bond of about 0.3 Å in chromia-doped UO2 compared with the ideal U–O bond length in standard UO2 that would be expected because of the change in effective Coulomb interactions resulting from replacing U4+ with Cr3+ and their ionic size differences. The contraction of shortest Cr–U bond is ~0.1 Å relative to the U–U bond length in bulk UO2. The difference in the local chromium environment between fresh and irradiated UO2 is discussed based on the comparison of quantitative structural information obtained from the two chromia-doped fuel samples analyzed.

Microbeam X-ray Absorption Near-Edge Spectroscopy study of the oxidation of Fe and Nb in zirconium alloy oxide layers

Alloy optimization of zirconium based alloys used for nuclear fuel cladding is key to increasing corrosion resistance and reducing hydrogen pickup. The mechanism by which alloying elements influence these processes is investigated by focusing on the chemical state evolution of two alloying elements, Fe and Nb, when incorporated into the growing oxide layers of various production zirconium alloys – Zircaloy-4, ZIRLO® and Zr–2.5Nb – as well as a model alloy – Zr–0.4Fe–0.2Cr. X-ray Absorption Near-Edge Spectroscopy (XANES) measurements to determine the evolution of their oxidation states is performed using micro-beam synchrotron radiation on cross sectional oxide samples. A thin (∼12μm) cross-sectional sample of Zircaloy-4 oxide was also designed and fabricated to differentiate the signal coming from the Fe in solid solution from the signal coming from the Fe in precipitates. The XANES spectra were fitted using a combination of standards, to determine the evolution of the oxidized fractions of Fe and Nb in the oxide as function of distance from the oxide/metal interface. The results show that the oxidation of Fe and Nb in the oxide layer is delayed relative to that of Zr. Both the second phase precipitates and solid solution Fe atoms were initially incorporated in metallic form into the oxide layer, although it appears that Fe in solid solution oxidizes first. It is shown that after a given distance from the metal/oxide interface (which is alloy dependent), the alloying elements start to oxidize. Qualitative TEM examinations of precipitates embedded in zirconium oxide layers correlate well with the quantitative XANES results. These results allow a discussion of a qualitative oxidation model of Fe and Nb in Zr alloys.

Investigation of the microstructural effect of Ni–yttria stabilized zirconia anode for solid-oxide fuel cell using micro-beam X-ray absorption spectroscopy analysis

The microstructural effect of the solid-oxide fuel cell (SOFC) anode on fuel cell performance has been investigated using X-ray absorption spectroscopy (XAS). Anodes were examined after the fuel cell had operated at 600–700 °C using H2 fuel. The microstructure of micro tubular anodes consisting of conventional Ni–yittria stabilized zirconia (YSZ) has been controlled by altering the co-sintering temperature with the zirconia electrolyte. Impedance analysis has clearly shown that the overpotentials for the gas transport and the electrochemical reactions improve for the anode prepared at lower co-sintering temperatures. Using data from the X-ray absorption near edge structure (XANES) energy region, the metallic Ni fraction as a function of distance from the electrolyte has also been measured for those samples. XANES observation has shown the oxidation status of Ni in the anode is quite sensitive to position relative to the anode/electrolyte interface. These results may be an indication of the positions of the reaction sites for oxide ions and the fuel: assuming the oxidation state of nickel (Ni–O) designates the active triple phase boundary.

Structural properties of rutile TiO2 nanoparticles accumulated in a model of gastrointestinal epithelium elucidated by micro-beam x-ray absorption fine structure spectroscopy

Micro-beam x-ray absorption fine structure spectroscopy was used to investigate rutile TiO2 nanoparticles internalized into gastrointestinal cells during their crossing of a gut model barrier. Nanoparticles diluted in culture medium tend to accumulate in cells after 48 h exposure; however, no spectral differences arise between particles in cellular and in acellular environments, as corroborated by quantitative analysis. This finding establishes that no modification of the lattice properties of the nanoparticles occurs upon interaction with the barrier. These measurements demonstrate the possibility of interrogating nanoparticles in situ within cells, suggesting a way to investigate their fate when incorporated in biological hosts.

Arsenic fractionation in mine spoils 10 years after aided phytostabilization

Aided phytostabilization using a combination of compost, zerovalent iron grit and coal fly ash (CZA) amendments and revegetation effectively promoted the biological recovery of mining spoils generated at a gold mine in Portugal. Selective dissolution of spoil samples in combination with solid phase characterization using microbeam X-ray absorption near edge structure (μXANES) spectroscopy and microbeam X-ray fluorescence (μXRF) mapping were used to assess As associations in spoils ten years after CZA treatment. The results show that As preferentially associates with poorly crystalline Fe-oxyhydroxides as opposed to crystalline Fe-(oxyhydr)oxide phases. The crystalline Fe(III)-phases dominated in the treated spoil and exceeded those of the untreated spoil three-fold, but only 2.6–6.8% of total As was associated with this fraction. Correlation maps of As:Fe reveal that As in the CZA-treated spoils is primarily contained in surface coatings as precipitates and sorbates. Arsenic binding with poorly crystalline Fe-oxyhydroxides did not inhibit As uptake by plants.

Arsenic speciation in fluid inclusions using micro-beam X-ray absorption spectroscopy

Synchrotron radiation X-ray fluorescence (SR-XRF) was used to characterize As speciation within natural fluid inclusions from three deposits with different hydrogeochemical and geological settings. The studied samples represent different compositions of Au-bearing fluids: typical orogenic Au deposit (low-salinity, ~6 mol% CO2 ± CH4; Brusson, Western Italian Alps); brines from a Proterozoic (Fe)- Cu-Au deposit (Starra, Queensland, Australia); and an As-rich magmatic fluid with a bulk composition similar to that typical of orogenic gold (Muiane pegmatite, Mozambique). Arsenic K-edge X-ray absorption spectra (XAS) were obtained from fluid inclusions at temperatures ranging from 25 to 200°C, and compared with spectra of aqueous As(III) and As(V) solutions and minerals. X-ray absorption near edge structure (XANES) data show that initially the fluid inclusions from all three regions contain some As in reduced form [As(III) at Brusson and Muiane; As-sulfide or possibly As(0) at Starra]. However, this reduced As is readily oxidized under the beam to As(V). Therefore, extended X-ray absorption fine structure (EXAFS) spectra for the As(III) aqueous complex could be collected only on the sample from the Muiane pegmatite containing large fluid inclusions with high As concentrations (>>1000 ppm). Analysis of these EXAFS data shows that As(OH)3(aq) (coordination number of 3.0 ± 0.2 atoms, bond length of 1.76 ± 0.01 Å) is the dominant arsenic aqueous species in the Muiane fluid inclusions at 100 °C, in accordance with predictions based on studies conducted using autoclaves. The As(V) complex resulting from photooxidation in the Muiane inclusions was characterized at 200 °C; the As-O bond distance (1.711 ± 0.025 Å) corresponds to that found in the arsenate group in minerals, and to that measured for the (HAsO4)2- complex at room temperature (1.700 ± 0.023 Å).

Earthworms as agents for arsenic transport and transformation in roxarsone-impacted soil mesocosms: A µXANES and modeling study

Earthworms influence soil mixing during their feeding and burrowing activities by causing physical displacement and chemical transformations, potentially impacting the distribution and speciation of soil contaminants. This study investigates the effects of burrowing earthworms on arsenic speciation and mobility in soil mesocosms treated with roxarsone, an increasing anthropogenic source of arsenic used in the poultry industry as a feed supplement. Experiments were designed to test the hypothesis that earthworms and burrows provide means for biotransformation and redistribution of arsenic. Arsenic distribution was determined following earthworm bioturbation in artificial soil columns that were initially constructed with a contaminated layer of designated thickness and depth. The resulting depth profiles were used to indicate bioturbation rates by fitting them to a simple one-dimensional advection/diffusion model with a biodiffusivity that decreases with depth. Synchrotron X-ray methods reveal additional small-scale displacement of arsenic near the burrow and in the bulk soil. Microbeam X-ray Absorption Near Edge Structure spectra were collected to determine arsenic speciation. Arsenic initially introduced as roxarsone tended to be in a methylated form after 30 days. Within the earthworm tissue, arsenic–glutathione complexes were formed. Results are viewed in the context of poultry litter used as agricultural fertilizer. A decrease in tillage arising from soil conservation efforts allows earthworm populations to increase and burrows to become more permanent. This study suggests that (1) burrows serve as macropores allowing rapid transport of arsenic to greater depths during infiltration events; (2) bioturbation rates appear to be depth-dependent; and (3) earthworm soil mixing produces potentially mobile forms of arsenic that may become bioaccessible as arsenic is transported through the subsurface.

Metal speciation in fluid inclusions using microbeam X-ray absorption spectroscopy

Metal speciation in fluid inclusions using microbeam X-ray absorption spectroscopy

Comparison of sediment pollution in the rivers of the Hungarian Upper Tisza Region using non-destructive analytical techniques

The rivers in the Hungarian Upper Tisza Region are frequently polluted mainly due to mining activities in the catchment area. At the beginning of 2000, two major mining accidents occurred in the Romanian part of the catchment area due to the failure of a tailings dam releasing huge amounts of cyanide and heavy metals to the rivers. Surface sediment as well as water samples were collected at six sites in the years 2000–2003, from the northeast-Hungarian section of the Tisza, Szamos and Túr rivers. The sediment pollution of the rivers was compared based on measurements of bulk material and selected single particles, in order to relate the observed compositions and chemical states of metals to the possible sources and weathering of pollution. Non-destructive X-ray analytical methods were applied in order to obtain different kinds of information from the same samples or particles. In order to identify the pollution sources, their magnitude and fate, complementary analyses were carried out. Heterogeneous particulate samples were analyzed from a large geographical territory and a 4-year time period. Individual particles were analyzed only from the “hot” samples that showed elevated concentrations of heavy metals. Particles that were classified as anthropogenic were finally analyzed to identify trace concentrations and chemical states of heavy metals. Although the Tisza river was affected by water pollution due to the two major mining accidents at the beginning of 2000, the concentration of heavy metals in sediments decreased to the mineral background level 1 year after the pollution event. In the tributaries Szamos and Túr, however, no significant decrease of the heavy metal concentrations was observed in the recent years, indicating a continuous pollution. Among the water suspended particles collected from river Túr, fibers of unknown origin were observed by electron microscopy; these particles were aluminosilicates enriched in Zn and Mn. Cd was also concentrated in this particle type. Zn in the sulfide form was observed by microbeam X-ray absorption near-edge structure analysis only in the samples collected from river Tisza in 2000, while this metal was connected to carbonates and silicates in the other samples. The dissolved Zn content of the river water and the chemical state of Zn in the fibers collected from river Túr indicate that the heavy metal pollution arrived to the Hungarian section originally mostly in the dissolved phase. The accidental heavy metal pollution of River Tisza, however, was in the form of microscopic metal sulfide particles.

MICROBEAM XANES AND X-RAY FLUORESCENCE ANALYSIS OF CADMIUM IN KIDNEY

Microbeam X-ray fluorescence spectra and Cd K edge X-ray absorption spectra of rat kidney were measured. Though the Cd concentration in the kidney specimen was 7 ppm, we could detect Cd using microbeam X-ray fluorescence and microbeam X-ray absorption measurements within one hour using SPring-8 BL-39XU beam line.