Operando X-ray absorption spectroscopy investigations have been carried out to follow changes in the atomic and electronic local structures of all three transition metals for the ...Li1.20Mn0.54Co0.13Ni0.13O2 layered oxide during the first and second charges and discharges of lithium batteries. The experiments were performed using a Quick-XAS monochromator on the SAMBA beamline at Synchrotron SOLEIL to record the three K-edges by edge-jumping between two energy ranges (Mn, Co and Co, Ni) every 3 min during the cycling of the battery. The results obtained especially at the Mn K-edge fully support the participation of oxygen in the reversible charge–discharge reaction of this Li- and Mn-rich layered material as a redox center and not only with oxygen loss, as was proposed previously.
ROCK is a new beamline at SOLEIL dedicated to Quick-EXAFS measurements. The optical layout has been optimized to get full advantage of the monochromators, which were designed at SOLEIL and ...successfully used at SAMBA from 2009 to 2014. ROCK has started user operations since March 2015. It is mainly employed to monitor fast kinetic processes in materials used in catalysis and energy sciences. A review of the ROCK performances and capabilities is presented. The high automation achieved for fast change of monochromators, optimization of mirrors for harmonic rejection and detectors allows the simultaneous operando characterization of different chemical elements present in a material during the same reaction.
Results and performances of the QEXAFS double monochromator of the SAMBA beamline (Synchrotron SOLEIL) are presented. The device is capable of speeds of up to 40 Hz, while giving the user the ...possibility to choose the amplitude of the scan from 0.1° to 4° in a few seconds. The device is composed of two independent units and it is possible to perform scans alternating between two different crystals, literally jumping from low (4 keV) to high (37 keV) energies.
The local structure of Ni2+ ions during crystallization of an oxyfluoride aluminosilicate glass was examined by high-temperature in situ spectroscopic experiments coupled with in situ X-ray ...diffraction to characterize the different crystallization steps. We show that Ni2+ ions in the glass are located in the silicate glass network. After heat treatment Ni2+ ions do not partition into the fluorine crystallites as observed for rare-earth metals. Instead, we observed the crystallization of a NiAl2O4 crystalline phase, a largely inverse spinel. The in situ spectroscopic results (XRD, UV-Vis-NIR and Ni K-edge XANES) give new insights on the nickel partitioning between the supercooled liquid and the new crystals and show that the inversion degree of NiAl2O4 spinel during its crystallization depends not only on the temperature but also on the annealing timescale. We also show that the addition of fluorine into aluminosilicate systems favors the formation of spinel crystals at lower temperature than usually observed, thereby playing a role to promote nucleation.
This paper reports on the X‐ray absorption analysis of samples of mineral dust emitted from or transported to Western Africa. We found that iron oxides account, by mass, for 38% to 72% of the total ...elemental iron. They are composed of minerals in the Fe(III) oxidation state: goethite (FeO·OH) and hematite (Fe2O3). The apparent fraction of iron oxide attributed to goethite is higher than hematite regardless of the source region from which the dust originated. The goethite percent content of iron oxides is in the range 52–78% (by mass), the highest values being measured for dust originating in the Sahel. The limited number of samples analyzed and the sample‐to‐sample variability prevent us from concluding firmly on the regional variability of the goethite‐to‐hematite ratio. Based on the experimental data on mineralogical composition and on concurrent measurements of the number size distribution, the optical properties of mineral dust have been calculated in a Mie approximation for homogeneous spherical particles. At 550 nm, the single‐scattering albedo ω0 ranges between 0.89 and 0.93, the asymmetry factor g ranges between 0.76 and 0.8 and the mass extinction efficiency kext varies between 0.5 and 1.1 m2 g−1; these values are all in the range of those from independent direct measurements. Neglecting the partitioning between hematite and goethite and the assimilation of iron oxides by hematite, as it is often done with models, lowers the single‐scattering albedo and increases the asymmetry factor in the UV‐visible spectral region below 550 nm. The mass extinction efficiency is insensitive to the nature of the iron oxides but rather responds to variations in the number size distribution. The mineralogy of iron oxides should therefore be taken into account when assessing the effect of mineral dust on climate and atmospheric chemistry, in particular via interactions involving photolysis.
Key Points
Goethite exceeds hematite in African mineral dustCalculation of optical properties in dust models have to be revised
Three glasses in the Li2O–Al2O3–SiO2 (LAS), MgO–Al2O3–SiO2 (MAS) and ZnO–Al2O3–SiO2 (ZAS) systems were investigated to obtain spinel-based transparent glass-ceramics doped with TiO2 to induce ...internal nucleation and with NiO to provide optically active ion. The sequence of phase transformations of initial glasses during heat-treatments was studied by in situ X-ray absorption spectroscopy, X-ray diffraction and room temperature optical spectroscopy.
For all glasses, there is a change of Ni2+ coordination with the increase of the heat-treatment temperature. The 5Ni2+ sites in the parent glass disappear and new distorted 6Ni2+ sites are formed within aluminotitanate and (Ni, or Ni,Mg, or Ni,Zn) aluminate amorphous regions. The local environment around Ni2+ then evolves from distorted octahedra to regular octahedra due to the nickel-doped spinel crystallization. In LAS glass-ceramics only, Ni2+ incorporates at elevated temperature octahedral and tetrahedral sites in crystals of β-quartz solid solution, whose content increases with time and temperature of heat treatment accompanied by a continuous decomposition or dissolution of spinel. In MAS and ZAS glass-ceramics, Ni-doped spinel exist in the whole temperature range of applied heat-treatments.
•Spinel glass-ceramics investigated in various aluminosilicate systems•In situ X-ray absorption spectroscopy, X-ray diffraction and room temperature optical spectroscopy•In MAS and ZAS glass-ceramics Ni-doped spinel exists in the whole temperature range of applied heat-treatments.•Gahnite-based ZAS glass-ceramics attractive for transparent and luminescent properties
Recently, using an animal model of Charcot-Marie-Tooth human disorder, we showed that ascorbic acid (AA) represses
PMP22 gene expression by acting on intracellular cAMP concentrations. In this work, ...we present kinetics data on the inhibitory effect of AA upon adenylate cyclase activity. The data show that this molecule acts as a competitive inhibitor of the enzyme, a finding that opens new pharmacological avenues.
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