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The use of high-pressure synthesis conditions to produce I-bearing aluminoborosilicate represents a promising issue for the immobilization of 129I radioisotope. Furthermore, iodine appears to be more solubilized in glasses under its iodate (I5+) form rather than its iodide (I−) form. Currently, the local atomic environment for iodine is poorly constrained for I− and virtually unknown for I5+ or I7+. We used I K-edge x-ray absorption spectroscopy conducted at 20 K for determining the local atomic environment of iodine dissolved as I−, I5+, and I7+ in a series of aluminoborosilicate glasses. We determined that I− is surrounded by either Na+ or Ca2+ in agreement with previous studies. The signal collected from EXAFS reveals that I5+ is surrounded invariably by three oxygen atoms forming an IO3− cluster charge compensated by Na+ and/or Ca2+. The I–O distance in iodate dissolved in glass is comparable to the I–O distance in crystalline compounds at ∼1.8 Å. The distance to the second nearest neighbor (Na+ or Ca2+) is also constant at ∼3.2 Å. This derived distance is identical to the distance between I− and Na+ or Ca2+ in the case of iodide local environment. For one sample containing iodate and periodate, the distinction between the local environment of I5+ and I7+ could not be made, suggesting that both environments have comparable EXAFS signals. [ABSTRACT FROM AUTHOR]

Abstract Recent investigation showed that the CO 2 solubility in silicate melts is strongly affected by the #Mg (MgO/MgO + CaO). CO 2 solubility is decreasing with increasing #Mg implying that CO 2 molecules dissolves in the vicinity of Ca atoms to form CO 3 2– molecular groups. We have investigated several CO 2 -bearing (up to 17.2 wt%) silicate glasses using X-ray Absorption Spectroscopy (XAS) at the Mg and Ca K-edge in order to determine the structural environments of Mg2+ and Ca2+ cations. Analyses of the Mg XANES region show that the Mg environment is not affected by the presence of CO 2 dissolved as CO 3 2– groups regardless of the CO 2 content. The Mg K-edge EXAFS simulations and XANES modelling show that the average Mg O distance is close to 2 Å and the average Mg coordination is close to 6. On the contrary, the position of the Ca XANES peak main resonance related to first-coordination shell is negatively correlated with the CO 2 content and shifts from 4051.4 to 4050.8 eV with CO 2 increasing from 0 to 17.2 wt%. The Ca EXAFS simulations showed that Ca O average distance is longer (~2.5 Å) than the Mg O distance. Furthermore, we observed that the Ca coordination number is positively correlated with the CO 2 content: Ca coordination number increases from 7 to 9 for CO 2 content changing from 0 to 17.2 wt%. Mg and Ca XAS results suggest that CO 3 2– groups are dissolved in the vicinity of Ca2+ cations and not in the surrounding of Mg2+ cations which environment remains unaffected by CO 2 dissolution. The tighter Mg atomic environment as well as the lower coordination number for Mg cations as compared to Ca atomic environment could explain such behaviour. One implication of this result is the lower CO 2 transport capacity for Mg-rich silicate melts such as komatiites or kimberlites. [ABSTRACT FROM AUTHOR]

The solubility, speciation, and local atomic environment of chlorine have been determined for aluminoborosilicate glasses equilibrated with various sources of chlorine (NaCl and PdCl2) at high pressure (0.5–1.5 GPa) and high temperature (1350–1400 °C). The Cl solubility reaches up to 11 mol% in borosilicate glass and appears to be strongly influenced by the concentration of network-modifying cations (Ca and Na) and increases with increasing CaO + Na2O content. The Cl solubility is enhanced in Ca-bearing rather than Na-bearing borosilicate glass, suggesting a higher affinity of chlorine for alkaline-earth cations. Cl K-edge XANES and Cl 2p XPS spectra reveal that chlorine dissolves in glasses only as chloride species (Cl–) and no evidence of oxidized species is observed. Using PdCl2 as a chlorine source leads to a pre-edge signal for PdCl2 in the XANES spectra. The EXAFS simulations show that the Cl– local environment is charge compensated by Na+ or Ca2+ at a distance to first neighbor on the order of 2.7 Å, which is comparable to the observed distances in crystalline chloride compounds. The coordination to charge compensating cation is lower in the case of Ca2+ (~1.1) than Na+ (~4.3). [ABSTRACT FROM AUTHOR]

Silicene, a new 2D material has attracted intense research because of the ubiquitous use of silicon in modern technology. However, producing free‐standing silicene has proved to be a huge challenge. Until now, silicene could be synthesized only on metal surfaces where it naturally forms strong interactions with the metal substrate that modify its electronic properties. Here, the authors report the first experimental evidence of silicene nanoribbons on an insulating NaCl thin film. This work represents a major breakthrough, for the study of the intrinsic properties of silicene, and by extension to other 2D materials that have so far only been grown on metal surfaces. [ABSTRACT FROM AUTHOR]

This study investigates the direct and indirect bacterial contributions that influence the dissolution of basaltic glass. In this regard, three different types of glasses – with or without Fe, in the reduced Fe(II) or oxidized Fe(III) states – were prepared on the basis of a simplified basaltic glass composition. In order to prevent the direct contact between the glasses and the model siderophore-producing strain Pseudomonas aeruginosa , the glass samples were isolated in dialysis bags and immersed at 25 °C and pH 6.5 in bacterial cultures. Throughout the dissolution experiments, the following parameters were monitored: determination of bacterial growth, quantification of siderophore (i.e. pyoverdine) production, microscopic observation of the glass surface and determination of dissolution kinetics. Isolating the glass from the bacterial suspension only triggered the biosynthesis of siderophores in the Fe(III)-bearing glass dissolution experiments. Siderophores were produced in the presence of Fe(II)-bearing and Fe-free glass, independently on the experimental setup. The siderophore production appeared to be either continuous in the absence of Fe (glass-free control, Fe-free glass dissolution experiments) or stopped as soon as the bacteria entered their stationary phase when an Fe source was present (Fe(II) and Fe(III)-bearing glass dissolution experiments). The increase in the dissolution rates of each glass was correlated to the complex stability constants of the siderophore with the metallic cations in presence (KFe2+ < KAl3+ ≪ KFe3+). Among the three glasses, only the Fe(III)-bearing one seemed to be significantly impacted by the dialysis process: its dissolution rate was doubled by isolating the glass grains from the cells. These results particularly allow to separate the impact of such bacterial exudates from physical contact effects: they showed the efficiency of pyoverdine in increasing the dissolution of an Fe(III)-bearing glass and evidenced that a direct bacterial cell attachment to the surface of such a glass results in a more moderate enhancement of its dissolution process. This work is a new contribution regarding the high affinity of microorganisms for basaltic glasses as an Fe-source. It highlights the role of Fe(III) accessibility upon the bacterial cells as a key parameter regulating their activity and their efficiency in accelerating the dissolution. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the role of micro-organisms and their siderophores in the first steps of the alteration processes of basaltic glasses in aqueous media. In this regard, three different types of glasses – with or without iron, in the reduced Fe(II) or oxidized Fe(III) states – were prepared on the basis of a simplified basaltic glass composition. Control and Pseudomonas aeruginosa inoculated experiments were performed in a buffered (pH 6.5) nutrient depleted medium to stimulate the production of the pyoverdine siderophore. Results show that the presence of P. aeruginosa has an effect on the dissolution kinetics of all glasses as most of the calculated elemental release rates are increased compared to sterile conditions. Reciprocally, the composition of the glass in contact with P. aeruginosa has an impact on the bacterial growth and siderophore production. As an essential nutrient for this microbial strain, Fe notably appears to play a central role during biotic experiments. Its presence in the glass stimulates the bacterial growth and minimizes the synthesis of pyoverdine. Moreover the initial Fe 2+ /Fe 3+ ratio in the glasses modulates this synthesis, as pyoverdine is not detected at all in the system in contact with Fe(III)-bearing glass. Finally, the dissolution rates appear to be correlated to siderophore concentrations as they increase with respect to sterile experiments in the order Fe(III)-bearing glass < Fe(II)-bearing glass < Fe-free glass. This increase is attributed to complexation reactions between siderophores and Fe or Al for Fe(II)-bearing glass or Fe-free glass, respectively. The dissolution of an Fe-free glass is significantly improved in the presence of bacteria, as initial dissolution rates are increased by a factor of 3. This study attests to the essential role of siderophores in the P. aeruginosa -promoted dissolution processes of basaltic glasses as well as to the complex relationships between the nutritional potential of the glass and its dissolution rates. [ABSTRACT FROM AUTHOR]

From the first initiatives [[1]] to the most recent developments of synchrotron-based techniques for the study of cultural and natural heritage materials, many synchrotron facilities have developed their own scientific programs in this field [[2]]. Ender to hard X-rays 3-23 keVMacro: 250 × 200 µm Micro: 5 to 10 µmXRF, XRD, DANES, DAFS, EXAFS, XANES imaging or punctual measurementsU X-ray tomography Synchrotron X-ray micro- and nanotomography allow the study of the detailed 3D morphology of bulk samples, with a spatial resolution that can go down to the sub-micrometer range for "standard" parallel-beam projection microtomography setups, and down to less than 50 nm in nano-tomography methods using more recent and more complex schemes, such as hard X-ray transmission X-ray microscopy (TXM). D micro spectral imaging with XRF, XANES, and XRD 3D computed tomography with absorption and phase contrast (in the future)T. [Extracted from the article]

This study aims at the characterisation of red and orange glass tesserae from the 4th-century Roman villa of Noheda (Spain). Due to the limited number of analyses available for such ancient materials, many questions remain unanswered about the production processes in the Roman period. Six samples were chosen for their hue variations, including two samples showing banded patterns of red and orange. Differences in copper speciation were investigated by X-ray absorption spectroscopy and compared with colour and compositional variations obtained by EPMA. The shapes and sizes of colouring crystals could be investigated using scanning and transmission electron microscope imaging. The brown-red colour is due to metallic copper nano-particles and corresponds to a low-copper and low-lead group usually described in the literature. The orange samples and bands are coloured by copper oxide C u 2 O nanoparticles with remaining Cu+ in the glass and have greater contents of Cu. Compositional analyses reveal that the same base glass is used in the red and orange bands with additions of Cu, Sn, Pb and probable Fe. Furthermore, based on our results and on the literature review, a high-copper low-lead group of glasses highlights the variability of compositions observed in cuprite colours. [ABSTRACT FROM AUTHOR]

Although microorganisms seem to play an important role in the alteration processes of basaltic glasses in solution, the elementary mechanisms involved remain unclear in particular with regard to the role of organic ligands excreted by the cells. Two glasses, one with Fe and one without Fe were synthesized to model basaltic glass compositions. Fe in the glass was mostly Fe(III) for enhancing interaction with siderophores, yet with small but significant amounts of Fe(II) (between 10% and 30% of iron). The prepared samples were submitted to abiotic alteration experiments in buffered (pH 6.4) diluted solutions of metal-specific ligands, namely oxalic acid (OA, 10 mM), desferrioxamine (DFA, 1 mM) or 2,2′-bipyridyl (BPI, 1 mM). Element release from the glass into the solution after short term alteration (maximum 1 week) was measured by ICP-OES, and normalized mass losses and relative release ratios (with respect to Si) were evaluated for each element in each experimental condition. The presence of organic ligands had a significant effect on the dissolution of both glasses. Trivalent metals chelators (OA, DFA) impacted on the release of Fe 3+ and Al 3+ , and thus on the global dissolution of both glasses, enhancing all release rates and dissolution stoichiometry (release rates were increased up to 7 times for Al or Fe). As expected, the mostly divalent metal chelator BPI interacted preferentially with Ca 2+ , Mg 2+ and Fe 2+ . This study thus allows to highlight the central roles of iron and aluminium in interaction with some organic ligands in the alteration processes of basaltic glasses. It thus provides a step toward understanding the biological contribution of this fundamental geological process. [ABSTRACT FROM AUTHOR]

• Iodine is dissolved as iodide (I−) in high pressure borosilicate glasses. • Both alkali and alkaline-earth cations act as a charge compensator to I− species. • The absence of iodate (I5+) suggests that there is a complex interplay between I− species and oxygen species within the glass structure. The 129I radioactive isotope is a by-product of nuclear plants activity. Owing to its strong volatility, there is currently no ideal protocol to immobilize 129I in nuclear waste borosilicate glasses. Recently, we have proposed the use of high-pressure syntheses to dissolve iodine in various glass compositions; however, I speciation and dissolution mechanism could not be determined. We have adopted an approach combining X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) methods to determine I speciation and molecular environment in glasses containing from 0.5 to 2.5 mol.% I. The XPS spectra reveal that I is mostly dissolved as iodide (>85% I−) with a small proportion of elemental iodine (<15% I0) and the absence of iodate species (I5+). For borosilicate glasses, the XAS results and subsequent spectrum simulations suggested that Na and Ca are involved in the I− vicinity with averaged derived coordination number (CN) of 3.6 and 2.0 and bond length to the nearest neighbour (r X-I) 2.98 and 2.85 Å, respectively. These results suggest that the coexistence of both I− and I5+ species is not requested for electric neutrality but instead, we explain the I speciation by the possible interplay with oxygen species from the borosilicate matrix. In addition, the results imply that the borosilicate network is affected by the I dissolution. [ABSTRACT FROM AUTHOR]

The presence of titanium in ground granulated blast‐furnace slags (GGBS) has been suspected to modify cement properties. This study provides the first evidence of a relation between the TiO2 content of slags and the mechanical properties of mortars based on slag cements. It is observed that only the slags containing less than 1%TiO2 show a compressive strength at 28 days that remains within the 52.5 MPa norm with CEM III cements complying with the European Standard NF EN 197‐1. The structural origin of this chemical dependence of the performance of cements is investigated by determining directly the titanium speciation in various European slags by spectroscopic methods. Electron paramagnetic resonance indicates that about 76% of Ti in slag occurs as Ti4+. The atomic structure around Ti was determined by Ti K‐edge X‐ray absorption near edge structure, which shows that Ti is mainly five‐fold coordinated in square‐based pyramid geometry. Five coordinated Ti acts as network‐stabilizer of the silicate network as it increases the polymerization. Requiring Ca2+ for charge‐compensation of the titanyl bond, it reduces the availability of Ca2+ during glass alteration in a modified random model of glass structure, where Ca2+ atoms are clustered in percolating cationic domains. As a consequence, the presence of five‐coordinated Ti results in a slower dissolution of the slag. These peculiar structural properties of titanium may explain the detrimental role of Ti above a 1% concentration, for many physical and chemical slag properties. This work provides a scientific ground for the technological acceptability of the upper limit of the Ti‐content of GGBS. [ABSTRACT FROM AUTHOR]

Paspalum urvillei and Setaria parviflora are two plant species naturally adapted to iron-rich environments such as around iron mines wastes. The aim of our work was to characterize how these two species cope with these extreme conditions by comparing them with related model species, Oryza sativa and Setaria viridis, that appeared to be much less tolerant to Fe excess. Both Paspalum urvillei and Setaria parviflora were able to limit the amount of Fe accumulated within roots and shoots, compared to the less tolerant species. Perls/DAB staining of Fe in root cross sections indicated that Paspalum urvillei and Setaria parviflora responded through the build-up of the iron plaque (IP), suggesting a role of this structure in the limitation of Fe uptake. Synchrotron μXRF analyses showed the presence of phosphorus, calcium, silicon and sulfur on IP of Paspalum urvillei roots and μXANES analyses identified Fe oxyhydroxide (ferrihydrite) as the main Fe form. Once within roots, high concentrations of Fe were localized in the cell walls and vacuoles of Paspalum urvillei , Setaria parviflora and O. sativa whereas Setaria viridis accumulated Fe in ferritins. The Fe forms translocated to the shoots of Setaria parviflora were identified as tri-iron complexes with citrate and malate. In leaves, all species accumulated Fe in the vacuoles of bundle sheath cells and as ferritin complexes in plastids. Taken together, our results strongly suggest that Paspalum urvillei and Setaria parviflora set up mechanisms of Fe exclusion in roots and shoots to limit the toxicity induced by Fe excess. • Paspalum urvillei and Setaria parviflora are two species naturally adapted to iron-rich environments. • These two species are more tolerant to Fe excess than the model, related species Oryza sativa and Setaria viridis. • Tolerance to Fe excess is achieved by exclusion: formation of iron plaque and vacuolar storage in roots. • The iron plaque is composed mostly of ferrihydrite; Fe is translocated in xylem as tri-Fe citrate-malate complexes. [ABSTRACT FROM AUTHOR]

Chromium (Cr) is at the origin of a wide variety of coloration (green, pink and brown) in porcelain glazes from the French Manufacture de Sèvres . This element was introduced for the first time at the factory in 1804, just a few years after its discovery by Louis-Nicolas Vauquelin. Pigments for glazes were developed at the laboratory of the factory, leading to a palette of 76 references. While the synthesis protocol and the nature of the precursors of these pigments are kept in laboratory notebooks, the products have never been fully studied. In this work, the pigments composed of Cr were characterized by X-ray diffraction (XRD), UV-visible spectroscopy and X-ray absorption near edge structure spectroscopy (XANES). The analyses reveal the presence of common crystalline phases, and open new perspectives for the synthesis of pigments containing chromium at the Manufacture de Sèvres . [ABSTRACT FROM AUTHOR]

Sulfur is one of the main redox sensitive and volatile elements involved in chemical transfers between earth surface and the deep mantle. At mid-oceanic ridges, sulfur cycle is highly influenced by serpentinite formation which acts as a sink of sulfur under various oxidation states (S 2− , S − , S 0 and S 6+ ). Sulfur sequestration in serpentinites is usually attributed to the crystallization of secondary minerals, such as sulfides (e.g. pyrite, pyrrhotite) or sulfates (e.g. anhydrite). However, the role of serpentine minerals as potential sulfur carriers is not constrained. We investigate the distribution and redox state of sulfur at micro-scale combining in situ spectroscopic (X-ray absorption near-edge structure: XANES) and geochemical (SIMS) measurements in abyssal serpentinites from the SWIR (South West Indian Ridge), the Rainbow and the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) areas. These serpentinites are formed in different tectono-metamorphic settings and provide a meaningful database to understand the fate of sulfur during seafloor serpentinization. XANES spectra of serpentinite powders show that the sulfur budget of the studied samples is dominated by oxidized sulfur ( S 6 + / ∑ S = 0.6 – 1 ) although sulfate micro-phases, such as barite and anhydrite, are absent. Indeed, μ-XANES analyses of mesh, bastite and antigorite veins in thin sections and of serpentine grains rather suggest the presence of S 6+ ions incorporated into serpentine minerals. The structural incorporation of S in serpentine minerals is also supported by X-ray fluorescence mapping revealing large areas ( 1600 μm 2 ) of serpentinite where S is homogeneously distributed. Our observations show that serpentine minerals can incorporate high S concentrations, from 140 to 1350 ppm, and that this can account for 60 to 100% of the sulfur budget of abyssal serpentinites. Serpentine minerals thus play an important role in S exchanges between the hydrosphere and the mantle at mid-oceanic ridges and may participate to S recycling in subduction zones. [ABSTRACT FROM AUTHOR]

The corrosion interface of low-alloy carbon steel (C-steel) coupons (P235, ferrite-pearlitic with a columnar microstructure) reacted in clay porewater seeping in a test chamber in situ in the Callovo-Oxfordian formation of the Meuse-Haute Marne Underground laboratory (France) was probed by microscopic and microspectrocopic techniques. Two series of samples were investigated, with extensive and limited corrosion, respectively. For extensively corroded coupons, several layers of inner corrosion products were observed. The innermost layer was made of Cl-rich Fe (hydr)oxide, later evolving to form a massive β-Fe 2 (OH) 3 Cl unit close to C-steel, and sometimes crossed by magnetite ribbons sticking to cementite lamellas, or by patches of green rust. The second inner layer was made of veinlets of Fe hydrated silicate with a sponge-like morphology, a molecular-scale structure reminiscent of clay minerals, and containing nodules of siderite and chukanovite. These (hydroxy)carbonate solids sometimes merged to form a massive layer close to the trace of the original surface. The layers external to this original surface were discontinuous and made of successively Ca-doped siderite (ankerite), Fe sulfide, S‐rich Fe silicate, and finally pyrite nodules and ankerite. For the samples with limited damage, no β-Fe 2 (OH) 3 Cl layer was observed, siderite or chukanovite were in close contact with metal, sometimes with interfacial magnetite, and the veinlets of Fe hydrated silicate were less developed. Only external layers of Fe sulfide and ankerite were observed. This suggests that these slightly corroding samples were in fact confined. Evidence for microbial activity was obtained in the form of a Fe sulfide fringe mixed with ankerite. Microbial activity may have induced some local heterogeneity in corrosion processes, e.g. by changing local pH conditions at mm-scale. [ABSTRACT FROM AUTHOR]

Using large volume press, samples of bridgmanites (Bg) in equilibrium with both silicate melt and liquid Fe-alloy were synthesized to replicate the early period of core-mantle segregation and magma ocean crystallization. We observe that the Fe partition coefficient between Bg and silicate melt (DFeBg/melt) varies strongly with the degree of partial melting (F). It is close to 1 at very low F and adopts a constant value of ~0.3 for F values above 10 wt%. In the context of a partially molten mantle, a larger F (closer to liquidus) should yield Fe-depleted Bg grains floating in the liquid mantle. In contrast, a low F (closer to solidus) should yield buoyant pockets of silicate melt in the dominantly solid mantle. We also determined the valence state of Fe in these Bg phases using X-ray absorption near-edge spectroscopy (XANES). Combining our results with all available data sets, we show a redox state of Fe in Bg more complex than generally accepted. Under the reducing oxygen fugacities (fO2) of this study ranging from IW-1.5 and IW-2, the measured Fe3+ content of Bg is found moderate (Fe3+/ΣFe = 21 ± 4%) and weakly correlated with Al content. When fO2 is comprised between IW-1 and IW, this ratio is correlated with both Al content and oxygen fugacity. When fO2 remains between IW and Re/ReO2 buffers, Fe3+/ΣFe ratio becomes independent of fO2 and exclusively correlated with Al content. Due to the incompatibility of Fe in Bg and the variability of its partition coefficient with the degree of melting, fractional crystallization of the magma ocean can lead to important chemical heterogeneities that will be attenuated ultimately with mantle stirring. In addition, the relatively low-Fe3+ contents found in Bg (21%) at the reducing conditions (IW-2) prevailing during core segregation seem contradictory with the 50% previously suggested for the actual Earth's lower mantle. This suggests the presence of 1.7 wt% Fe3+ in the lower mantle, which reduces the difference with the value observed in the upper mantle (0.3 wt%). Reaching higher concentrations of trivalent Fe requires additional oxidation processes such as the late arrival of relatively oxidized material during the Earth accretion or interaction with oxidized subducting slabs. [ABSTRACT FROM AUTHOR]

Nanotechnology is the new industrial revolution of our century. Its development leads to an increasing use of nanoparticles and thus to their dissemination. Their fate in the environment is of great concern and especially their possible transfer in trophic chains might be an issue for food safety. However, so far our knowledge on this topic has been restricted by the lack of appropriate techniques to characterize their behavior in complex matrices. Here, we present in detail the use of cutting-edge beam-based techniques for nanoparticle in situ localization, quantification and speciation in a crop plant species ( Lactuca sativa ). Lettuce seedlings have been exposed to TiO 2 and Ag nanoparticles and analyzed by inductively coupled plasma spectrometry, micro-particle induced X-ray emission coupled to Rutherford backscattering spectroscopy on nuclear microprobe, micro-X-ray fluorescence spectroscopy and X-ray absorption near edge structure spectroscopy. The benefits and drawbacks of each technique are discussed, and the types of information that can be drawn, for example on the translocation to edible parts, change of speciation within the plant, detoxification mechanisms, or impact on the plant ionome, are highlighted. Such type of coupled approach would be an asset for nanoparticle risk assessment. [ABSTRACT FROM AUTHOR]

In this work, three pieces of historical on-site glass windows dated from the 13th to 16th century and one archeological sample (8th century) showing Mn-rich brown spots at their surface or subsurface have been characterized by optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy. The oxidation state of Mn as well as the Mn environment in the alteration phase have been characterized by X-ray absorption spectroscopy at the Mn K-edge. Results show that the oxidation state of Mn and therefore the nature of the alteration phase varies according to the sample considered and is correlated with the extent of the brown alteration. The larger the brown areas the more oxidized the Mn. However, by contrast with literature, the samples presenting the more extended brown areas are not similar to pyrolusite and contain Mn mainly under a (+III) oxidation state. [ABSTRACT FROM AUTHOR]

The distribution of trivalent and tetravalent cerium, Ce(III) and Ce(IV) respectively, in a lateritic profile from Madagascar, has been characterized by X-ray-absorption near-edge structure (XANES) spectroscopy at the Ce L III -edge on the LUCIA beamline (SOLEIL synchrotron, France). XANES spectra were acquired on bulk-rock samples as well as on specific lateritic minerals or polymineral zones (in-situ measurements) of the tonalite bedrock and the three overlying weathered horizons (C-, B- and A-horizons). Geochemically, the bedrock, and the A- and C-horizons show similar rare earth element content (REE = 363–405 mg/kg). They also display the same positive Ce-anomaly (Ce CN /Ce ∗ = 1.12–1.45), which is therefore likely to be inherited from the bedrock. In the B-horizon, the higher REE content (REE = 2194 mg/kg) and the larger Ce-anomaly (Ce CN /Ce ∗ = 4.26) are consistent with an accumulation zone caused by the evaporation of groundwater during the dry season. There is a good agreement between the Ce(III)/Ce total ratio (X Ce(III) ) deduced from the positive Ce-anomaly (bulk-rock geochemical data) and that derived from XANES spectroscopy on the same bulk-rock samples (BR-X Ce(III) -XANES) in the bedrock, and the C- and B-horizons. In the A-horizon, XANES measurements on bulk rock and minerals revealed a higher BR-X Ce(III) -XANES (up to 100%) compared to the X Ce(III) deduced from geochemical data (X Ce(III) = 79%). The preservation of a positive Ce-anomaly in the A-horizon suggests that the Ce mobilization and redistribution during weathering occurred with no significant Ce fractionation from other trivalent REE. Remarkably, the only investigated sample where cerianite is observed belongs to the B-horizon. Within this horizon, Ce oxidation state varies depending on the microstructural position (porosity, cracks, clay-rich groundmass). The highest Ce(IV) concentrations are measured in cerianite (and aluminophosphates) localized in pores at the vicinity of Mn-rich domains (X Ce(III) -XANES = 30–51%). Therefore, Ce fractionation from other REE is attributed to a Ce oxidation and precipitation potentially assisted by oxyhydroxide scavenging. In the C-horizon, Ce(III) and Ce(IV) are mainly distributed in REE-minerals of the rhabdophane group found in pores and cracks. The similarity between the Ce(III) proportion of rhabdophane grains (X Ce(III) -XANES = 74–89%) with that of the bedrock (BR-X Ce(III) -XANES = 79%) suggests no significant fractionation of Ce(III) and Ce(IV) between solution and mineral during the successive stages of primary REE-mineral alteration, transport in solution and secondary precipitation in the incipient stages of weathering. Overall, our novel spectroscopic approach shows that Ce is not necessarily oxidized nor fractionated from other REE during weathering in lateritic conditions. This implies that like Ce(III), Ce(IV) can be mobilized in aqueous fluids during weathering, possibly thanks to complexation with organic molecules, and can precipitate together with Ce(III) in secondary REE-bearing minerals. The corollary is that (paleo)redox reconstructions in soils and/or sediments based on Ce-anomaly in weathered rocks or minerals must be interpreted with caution. [ABSTRACT FROM AUTHOR]

We have investigated the role of ZrO 2 on the nucleation/crystallization properties of aluminosilicate glasses. A comparison between Zr-free and Zr-bearing glasses shows that adding ZrO 2 favors nucleation in Li-, Mg-, Ca- and Zn-bearing glasses and has no effects in Na-bearing glasses. The Zr environment has been elucidated coupling X-ray absorption spectroscopy at both Zr K- and L 2,3 -edges. The Zr environment corresponds to six-fold coordinated sites (Li and Na glasses) and seven-fold coordinated sites (Mg, Ca and Zn glasses), indicating the coordination number has little influence on the ability to crystallize. Direct Zr–Zr polyhedral linkages are observed for all glasses except the Na-bearing one. Since no correlation between the local Zr site and its ability to promote nucleation can be observed, the origin of the nucleating role of Zr has been interpreted as resulting from the Zr distribution with in the aluminosilicate matrix. The poor crystallization ability for Na-bearing glasses is due to the lack of direct Zr–Zr linkages. Medium range ordering appears as a key parameter to explain properties of Zr-bearing glasses. [ABSTRACT FROM AUTHOR]

Abstract: Serpentinites are an important component of the oceanic lithosphere that formed at slow to ultra-slow spreading centers. Serpentine could thus be one of the most abundant hydrous minerals recycled into the mantle in subduction zones. Prograde metamorphism in subducted serpentinites is characterized by the destabilization of lizardite into antigorite, and then into secondary olivine. The nature of the fluid released during these phase transitions is controlled by redox reactions and can be inferred from oxidation state of Fe in serpentine minerals. We used bulk rock analyses, magnetic measurements, SEM observations and μXANES spectroscopy to establish the evolution of and magnetite content in serpentinite and Fe oxidation state in serpentine minerals from ridge to subduction settings. At mid-ocean ridges, during the alteration of peridotite into serpentinite, iron is mainly redistributed between magnetite and oceanic serpentine (usually lizardite). The Fe3+/FeTotal ratio in lizardite and the modal percentage of magnetite progressively increase with the degree of local serpentinization to maxima of about 0.8 and 7 wt%, respectively, in fully serpentinized peridotites. During subduction, the of serpentinite remains constant (∼7–10 wt%, depending on the initial Fe content of the peridotite) while the modal percentage of magnetite decreases to less than 2% in eclogite facies rocks. The Fe3+/FeTotal ratio in serpentine also decreases down to 0.2–0.4 in antigorite at eclogite facies. Our results show that, in the first 70 km of subduction, the transition from lizardite to antigorite is accompanied by a reduction of Fe in bulk rock samples and in serpentine minerals. This redox reaction might be coupled with the oxidation of reduced oceanic phases such as sulfides, and the formation of oxidized fluids (e.g. SO X , H2O, CO X ). At greater depths, the beginning of antigorite dehydration leads to an increase of Fe3+/FeTotal in relict antigorite, in agreement with the preferential partitioning of ferric iron into serpentine rather than into olivine. [Copyright &y& Elsevier]

Highlights: [•] Pristine TiO2-NPs are internalized inside lettuce leaves after foliar exposure. [•] TiO2-NPs and microparticles from aged paint leachate are detected in plants after foliar exposure. [•] The chemical form of TiO2 particles is unchanged upon internalization. [•] Foliar exposure to pristine TiO2-NPs does not lead to acute phytotoxicity symptoms. [Copyright &y& Elsevier]

Partitioning of sulphur between liquid Fe-rich metals and silicates ( ) was investigated at temperatures from 1800 °C to 2400 °C, pressures from 2 to 23 GPa and oxygen fugacities from 3.5 to 1.5 log units below the iron–wüstite buffer, using multi-anvil apparatus. The results are combined with previous experimental works to refine a multi-variable thermodynamic model of . Sulphur appears to become more siderophile with increasing pressure and FeO content of the silicate melt, and less siderophile with increasing temperature and with Si, C, O, Fe and Ni contents of the metal. We then modelled the behaviour of sulphur in the course of planetary accretion, using different possible scenarios of mantle dynamics and evolution with time of oxygen fugacity. We investigated three end-member models for metal–silicate segregation of the incoming impactors: (i) the planetary mantle does not mix and is kept chemically stratified, (ii) the magma ocean is continuously mixed chemically, and (iii) both the magma ocean and the solid lower mantle are well mixed. We show that if S is accreted along the accretion, whatever the oxidation path, its distribution between core and mantle can lead to the observed S concentration of the mantle ( ) and to the estimations of S content of the core (from its depletion in the mantle relative to the other elements with the same volatility). In the case of an Earth built with reduced material, to explain the present-day S found in the mantle, it is necessary that both the magma ocean and the solid lower mantle mix at each major step of the planetary accretion. S could also be accreted in the last 10 to 20% of Earth's growth and reach its observed present terrestrial abundances if the magma ocean is chemically mixed along the accretion. Consequently, our models show that the S terrestrial abundances do not formally require an S accretion in a late veneer but can be explained by a core–mantle equilibration alone. [ABSTRACT FROM AUTHOR]

The article presents the author's views on the article "Femtosecond laser-induced modification of potassium-magnesium silicate glasses: An analysis of structural changes by near edge x-ray absorption spectroscopy" published in a previous issue. He comments that some deficiencies were present in the x-ray absorption near-edge structure (XANES) analysis although XANES spectroscopy at the Mg K-edge, is well adapted to the study.

Liver is subject to various chronic pathologies, progressively leading to cirrhosis, which is associated with an increased risk of hepatocellular carcinoma. There is an urgent need for diagnostic and prognostic markers of chronic liver diseases and liver cancer. Spectroscopy-based approaches can provide an overview of the chemical composition of a tissue sample offering the possibility of investigating in depth the subtle chemical changes associated with pathological states. In this study, we have addressed the composition of cirrhotic liver tissue by combining synchrotron Fourier transform infrared (FTIR) microspectroscopy and synchrotron micro-X-ray fluorescence (XRF) on the same tissue section using a single sample holder in copper. This allowed investigation of the in situ biochemical as well as elemental composition of cells and tissues at high spatial resolution. Cirrhosis is characterized by regeneration nodules surrounded by annular fibrosis. Hepatocytes within cirrhotic nodules were characterized by high content in esters and sugars as well as in phosphorus and iron compared with fibrotic septa. A high heterogeneity was observed between cirrhotic nodules in their content in sugars and iron. On fibrosis, synchrotron XRF revealed enrichment in calcium compared to cirrhotic hepatocytes. Careful scrutiny of tissue sections led to detection of the presence of microcrystals that were demonstrated as precipitates of calcite using synchrotron FTIR. These results demonstrated that synchrotron FTIR and synchrotron XRF microspectroscopies provide complementary information on the chemical composition of cirrhotic hepatocytes and fibrotic septa in cirrhosis. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy was used to investigate the oxidation state of uranium in various U-and Th-bearing Al-rich CaSiO3 perovskite samples synthesized at high-pressure and high- temperature using a multi-anvil press apparatus. X- ray absorption near edge spectroscopy (XANES) spectra collected at the U LIII- and Th LIII-edges using both micro- and macro-focused beams show U4+ in the Al-rich CaSiO3 perovskite. The structure of the U- and Th-bearing Al-rich CaSiO3 perovskite samples have been cross-checked by XANES spectra collected at the Ca K-, Al K-, and Si K-edges. Al K and Si K spectra suggest that Al incorporates exclusively on the Si site of the CaSiO3 perovskite. Ca K spectra of the (U,Th)-bearing Alrich CaSiO3 perovskite samples were succesfully compared to FEFF8.2 ab initio models of a tetragonal CaSiO3 perovskite with space group P4/mmm. Our results confirm previous assumptions of the coupled substitution of CaSi2 by UAl2 in CaSiO3 perovskite and that U and Th can be incorporated separately or together in CaSiO3 perovskite by means of this mechanism. The possible occurrence of the U- and Th-bearing Al-rich CaSiO3 perovskite are discussed as a potential candidate to locally host a large amount of actinides in the Earth's deep mantle. The study of a phase that can act as a storage mineral for heat-producing actinide elements such as uranium and thorium is fundamental to the understanding of the geodynamics and thermal behavior of Earth. [ABSTRACT FROM AUTHOR]

Smalt was commonly used as a pigment by artists between the 16th and 18th centuries. It is a powdered blue potash glass colored by cobalt ions and often degrades causing dramatic changes in the appearance of paintings. The ann of the work presented in this paper was to investigate the changes in the structure and environment around the cobalt ion on deterioration, to further our understanding of the basis of the loss of color. Particles of well-preserved and altered smalt in microsamples from paintings in the National Gallery, London, and the Louvre, Paris, were analyzed using synchrotron micro-X-ray absorption spectros- copy at the Co K-edge. X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements showed that in intense blue particles the cobalt is predominantly present as Co2+ in tetrahedral coordination, whereas m colorless altered smalt the Co2+ coordination number in the glass structure is increased and there is a shift from tetrahedral toward octahedral coordination. The extent of this shift correlates clearly with the alkali content, indicating that it is caused by leaching of potassium cations, which act as charge compensators and stabilize the tetrahedral coordination of the cobalt ions that is responsible for the blue color. [ABSTRACT FROM AUTHOR]

This study presents a description of the structure of amorphous slags, with particular attention to the Ca local environment and the medium range arrangement of Ca-sites. Using Ca K-edge X -ray absorption spectroscopy (XANES and EXAFS) and pair distribution function (PDF) as well as numerical modeling combining Molecular Dynamics and Reverse Monte-Carlo, we demonstrate that Ca occurs in a complex environment with a distribution between 6- and 7-coordinated sites. Ca atoms are not distributed randomly within the glass structure: the Ca sites are linked by edges and form a complex percolating sub-network of network-modifying cations. The aluminosilicate network in slags is highly depolymerized with, on average, Q2.06 arrangements for Si, indicating the predominance of chain-like structural units and Q2.67 arrangements for Al in more polymerized units cross-linking the Ca-domains. The Ca percolating sub-network forms clusters that may enhance the early dissolution rate of slags in water. [ABSTRACT FROM AUTHOR]

Rare earth elements (REE) speciation in laterites are commonly estimated from sequential extraction procedure (SEP). In this study, the selectivity of a 5-steps SEP protocol was evaluated on individual synthetic Ce-material and applied to a well-characterized lateritic profile developing over a granite bedrock (Madagascar). The synthetic Ce-materials are representative of laterite minerals: Ce-doped oxyhydroxides and kaolinite, cerianite, Ce-rhabdophane and Ce-bastnäsite. The morphology, specific surface area, Ce sorption concentrations were thoroughly characterized prior to SEP. X-Ray absorption spectroscopy on synthetic material indicates that Ce(III) dominates apart for cerianite and Mn-oxide. The evaluation of the 5-steps SEP scheme shows that reagent selectivity is generally good, but the use of hydroxylamine hydrochloride is strongly discouraged. First, distinction between Ce sorbed at the surface of Mn- and amorphous or crystalline Fe-oxyhydroxides remains ambiguous. Second, Ce-rhabdophane (phosphate) and Ce-bastnäsite (carbonate) dissolve partially with this reagent. These experimental results combined with previous mineralogical and geochemical characterization were fundamental to interpret SEP results in the laterite profile from Madagascar. In the three laterite samples from the A-, B- and C-horizons, it is proposed that REE mainly distribute in authigenic phosphates and Fe- and (Mn-)oxyhydroxides. In the oxidized B-horizon, there is a significant LREE/HREE and Ce(IV)/Ce(III) fractionation between laterite minerals. While LREE-Ce is mainly concentrated in phosphates (alunite-jarosite supergroup), it is proposed that HREE and Ce(IV) uptake is dominated by oxyhydroxides. In the A- and C-horizons, the LREE and HREE speciations are similar, indicating no significant LREE/HREE fractionation in laterite minerals and organic matter. In all horizons, the REE ion exchangeable is negligible, although kaolinite is a main mineral of the A- and B-horizons. [ABSTRACT FROM AUTHOR]

In material sciences, spectroscopic approaches combining ab initio calculations with experiments are commonly used to accurately analyze the experimental spectral data. Most state-of-the-art first-principles calculations are usually performed assuming an equilibrium static lattice. Yet, nuclear motion affects spectra even when reduced to the zero-point motion at 0 K. We propose a framework based on density-functional theory that includes quantum thermal fluctuations in theoretical x-ray absorption near-edge structure (XANES) and solid-state nuclear magnetic resonance (NMR) spectroscopies and allows to well describe temperature effects observed experimentally. Within the Born-Oppenheimer and quasiharmonic approximations, we incorporate the nuclear motion by generating several nonequilibrium configurations from the dynamical matrix. The averaged calculated XANES and NMR spectral data have been compared to experiments in MgO. The good agreement obtained between experiments and calculations validates the developed approach, which suggests that calculating the XANES spectra at finite temperature by averaging individual nonequilibrium configurations is a suitable approximation. This study highlights the relevance of phonon renormalization and the relative contributions of thermal expansion and nuclear dynamics on NMR and XANES spectra on a wide range of temperatures. [ABSTRACT FROM AUTHOR]