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Atomistic details about the hydration of ions in aqueous solutions are still debated due to the disordered and statistical nature of the hydration process. However, many processes from biology, physical chemistry to materials sciences rely on the complex interplay between solute and solvent. Oxygen K-edge X-ray excitation spectra provide a sensitive probe of the local atomic and electronic surrounding of the excited sites. We used ab initio molecular dynamics simulations together with extensive spectrum calculations to relate the features found in experimental oxygen K-edge spectra of a concentration series of aqueous NaCl with the induced structural changes upon solvation of the salt and distill the spectral fingerprints of the first hydration shells around the Na+- and Cl--ions. By this combined experimental and theoretical approach, we find the strongest spectral changes to indeed result from the first hydration shells of both ions and relate the observed shift of spectral weight from the post- to the main-edge to the origin of the post-edge as a shape resonance.

Subduction of carbon-bearing phases throughout Earth’s history may be an important mechanism of sourcing carbon to the Earth’s lower mantle. As carbon has very low solubility in mantle silicates, it is primarily present in accessory phases such as carbonates, diamond, or metal carbides. Previous studies indicate that more than half of the carbonate contained in the oceanic crust may survive metamorphism and dehydration in the sub-arc and reach the lower mantle, even though the oxygen fugacity in the deep mantle may not favour their stability [1]. Indeed, the presence of carbonate in ultra-deep diamond inclusions provides evidence for carbonate subduction at least down to the transition zone [2].The carbonate phases present in the lower mantle depend on their bulk composition, the oxygen fugacity, and on their stability at a given pressure and temperature. Results from high-pressure experiments show that magnesite (MgCO3) can be stable up to deep lower mantle conditions (∼80 GPa and 2500 K) [3]. Accordingly, magnesite may be considered the most probable carbonate phase present in the deep Earth. Experimental studies on magnesite decarbonation in presence of SiO2 at lower mantle conditions suggest that magnesite is stable along a cold subducted slab geotherm [4, 5]. However, our understanding of magnesite’s stability in contact with bridgmanite [(Mg,Fe)SiO3], the most abundant mineral in the lower mantle, remains incomplete.Hence, to investigate sub-solidus reactions, melting, decarbonation, and diamond formation in the system MgCO3-(Mg,Fe)SiO3, we conducted a combination of high-pressure experiments using multi-anvil press and laser-heated diamond anvil cells (LH-DAC) at conditions ranging from 25 to 70 GPa and 1300 to 2100 K.Multi-anvil experiments at 25 GPa and temperatures below the mantle geotherm (1700 K) show the formation of carbonate-silicate melt associated with stishovite crystallization, indicating incongruent melting of bridgmanite to stishovite, in accordance with the recent finding of Litasov and Shatskiy [4]. LH-DAC data from in situ X-ray diffraction show crystallization of bridgmanite and stishovite. Diamond crystallization is detected using Raman spectroscopy. A melt phase could not be detected in situ at high temperatures.Our results suggest a two-step process that starts with melting at temperatures below the mantle geotherm, followed by crystallization of diamond from the melt produced. Therefore, we propose that subducted carbonate-bearing silicate rocks will not remain stable in the lower mantle and will instead melt at upper-most lower mantle conditions, fostering diamond formation. Our study also provides additional evidence that diamond production is related to carbonated melt. Consequently, the melting of recycled crust and chemical transfer to the surrounding mantle will hinder the transport of carbon deeper into the lower mantle.[1] Stagno et al. (2015) Contrib. Mineral. Petrol. 169(2), 16.[2] Brenker et al. (2007) EPSL 260(1-2), 1-9.[3] Binck, et al. (2020) Physical Review Materials, 4(5),1-9.[4] Litasov & Shatskiy (2019) Geochemistry International, 57(9), 1024-1033.[5] Drewitt, et al. (2019). EPSL, 511, 213-222.

The pressure stability of the first hydration shell of Y3+ ions in aqueous solution has been investigated by means of extended x-ray absorption fine-structure spectroscopy at the yttrium K-edge for...

The deposition of coatings by means of Physical Vapor Deposition (PVD) is an established process to enhance the lifetime and performance of carbide bulk tools. Although the effect of surface pretreatments on conventional WC-Co surfaces is well known, this investigation examines for the first time, how different surface pretreatments affect the surface integrity of thermally sprayed WC-Co substrates prior a subsequent PVD layer deposition and its resulting properties. Therefore, a WC-12Co feedstock with an average WC particle size of 100 nm was thermally sprayed on AISI M3 steel substrates using High Velocity Oxy-Fuel (HVOF) technique. Hereinafter, the HVOF sprayed WC-Co coatings were grounded and polished, thus serving as substrates for further surface pretreatments and the deposition of a CrAlN PVD hard coating by means of magnetron sputtering. To evaluate the influence of various surface pretreatments on the HVOF sprayed WC-Co coatings, several sequences such as heating, inert gas ion etching, metal ion etching, and High Power Impulse Magnetron Sputtering (HIPIMS)-etching were carried out. With respect to the subsequent PVD layer deposition, the results show that the pretreatment does neither affect the hardness nor Young's modulus of the CrAlN top layer. Yet, different effects on the WC-Co surface and PVD coating adhesion are observed. Inert gas ion etching leads to a faster removal of the carbides than of the Co-binder matrix. In contrast, metal ion etching provides a “micro-blasting” effect and removes the binder matrix as verified by Atomic Force Microscope (AFM) measurements. As a result, a decrease of the compressive residual stress state and an increase of the surface free energy are observed. With respect to HIPIMS-etching, a Cr-nanolayer was applied onto the WC-Co surface, which enhances the adhesion of the CrAlN top layer. Nevertheless, HRC Rockwell adhesion and scratch tests reveal a superior adhesion for samples pretreated with the metal ion etching.

International audience; The understanding of the microstructure of associated liquids promoted by hydrogen-bonding andconstrained by steric hindrance is highly relevant in chemistry physics, biology and for many aspects ofdaily life. In this study we use a combination of X-ray diffraction, dielectric spectroscopy and moleculardynamics simulations to reveal temperature induced changes in the microstructure of different octanolisomers, i.e., linear 1-octanol and branched 2-, 3- and 4-octanol. In all octanols, the hydroxyl groupsform the bases of chain-, cyclic- or loop-like bonded structures that are separated by outwardlydirected alkyl chains. This clustering is analyzed through the scattering pre-peaks observed from X-rayscattering and simulations. The charge ordering which pilots OH aggregation can be linked to thestrength of the Debye process observed in dielectric spectroscopy. Interestingly, all methods used hereconverge to the same interpretation: as one moves from 1-octanol to the branched octanols, thecluster structure evolves from loose large aggregates to a larger number of smaller, tighter aggregates.All alcohols exhibit a peculiar temperature dependence of both the pre-peak and Debye process, whichcan be understood as a change in microstructure promoted by chain association with increased chainlength possibly assisted by ring-opening effects. All these results tend to support the intuitive picture ofthe entropic constraint provided by branching through the alkyl tails and highlight its capital entropicrole in supramolecular assembly.

We determined the intermolecular interaction potential, V(r), of dense lysozyme solutions, which governs the spatial distribution of the protein molecules and the location of its liquid–liquid phase separation (LLPS) region, in various crowding environments applying small-angle X-ray scattering in combination with liquid-state theory. We explored the effect of polyethylene glycol (PEG) on V(r) and the protein’s phase behavior over a wide range of temperatures and pressures, crossing from the dilute to the semidilute polymer regime, thereby mimicking all crowding scenarios encountered in the heterogeneous biological cell. V(r) and hence the protein–protein distances and the phase boundary of the LLPS region strongly depend on the polymer-to-protein size ratio and the polymer concentration. The strongest effect is observed for small-sized PEG molecules, leading to a marked decrease of the mean intermolecular spacing of the protein molecules with increasing crowder concentration. The effect levels off at int...

The hydration and hydrogen-bond topology of small water solvated molecules such as the naturally occurring organic osmolytes trimethylamine N-oxide (TMAO) and urea are under intense investigation. We aim at furthering the understanding of this complex hydration by combining experimental oxygen K-edge excitation spectra with results from spectra calculated via the Bethe-Salpeter equation based on structures obtained from ab initio molecular dynamics simulations. Comparison of experimental and calculated spectra allows us to extract detailed information about the immediate surrounding of the solute molecules in the solvated state. We quantify and localize the influence of the solute on the hydrogen bond network of the water solvent and find spectroscopic fingerprints of a clear directional asymmetry around TMAO with strong and local kosmotropic influence around TMAO's NO head group and slight chaotropic influence around the hydrophobic methyl groups. The influence of urea on the local water network is qualitatively similar to that of TMAO but weaker in magnitude. The strongest influence of both molecules on the shape of the oxygen K-edge spectra is found in the first hydration shells.

We present an X-ray Compton scattering study on aqueous trimethylamine N-oxide (TMAO) and guanidine hydrochloride solutions (GdnHCl) as a function of temperature. Independent from the concentration of the solvent, Compton profiles almost resemble results for liquid water as a function of temperature. However, the number of hydrogen bonds per water molecule extracted from the Compton profiles suggests a decrease of hydrogen bonds with rising temperature for all studied samples, and the differences between water and the solutions are weak. Nevertheless, the data indicate a reduced bond weakening with rising TMAO concentration up to 5 M of 7.2% compared to 8% for pure water. In contrast, the addition of GdnHCl appears to behave differently for concentrations up to 3.1 M with a weaker impact on the temperature response of the hydrogen bond structure.