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The theoretical design of effective metal electrocatalysts for energy conversion and storage devices relies greatly on supposed unilateral effects of catalysts structure on electrocatalyzed reactions. Here, by using high-energy X-ray diffraction from the new Extremely Brilliant Source of the European Synchrotron Radiation Facility (ESRF-EBS) on device-relevant Pd and Pt nanocatalysts during cyclic voltammetry experiments in liquid electrolytes, we reveal the near ubiquitous feedback from various electrochemical processes on nanocatalyst strain. Beyond challenging and extending the current understanding of practical nanocatalysts behavior in electrochemical environment, the reported electrochemical strain provides experimental access to nanocatalysts absorption and adsorption trends (i.e., reactivity and stability descriptors) operando. The ease and power in monitoring such key catalyst properties at new and future beamlines is foreseen to provide a discovery platform toward the study of nanocatalysts encompassing a large variety of applications, from model environments to the device level.

The structure of the planar surface of colloidal solutions of amorphous 27-nm silica sol particles enriched with heavy K+, Rb+, and Cs+ alkali ions is studied by the methods of reflectometry and diffuse (nonspecular) scattering of synchrotron radiation. For liquid-phase systems, we have used a self-consistent approach that makes it possible to reconstruct from experimental data the electron density profiles perpendicular to the hydrosol surface, as well as the spectra of the height–height correlation function in the plane of the surface without using any a priori information about the near-surface structure. Analysis represented here shows that for high values of pH, alkali cations with a large radius and a surface concentration of (5 ± 1) × 1018 m–2 replace Na+ ions with a smaller radius. This result is in qualitative agreement with the dependence of the Kharkats–Ukstrup single-ion electrostatic free energy on the ion radius and in good quantitative agreement with the results obtained by other authors using the capillary-wave approach. The integrated value of the effective height of interface roughness (3.2 ± 0.5 A) coincides to within the measuring error with the prediction of the capillary-wave theory; however, the experimental spectra of the height-to-height correlation function basically differ from the theoretical spectra in the range of low spatial frequencies ν < 10–3 nm–1. The approximation of the spectra by the sum of two K-correlation distributions indicates a transition from the natural roughness of the compact layer of alkali metal ions to the capillary roughness of the liquid surface in the correlation length range of about 1 μm. In our opinion, the aggregate of available data indicates the dispersion of this layer into 2D clusters (Wigner islands).

When one thinks of high-energy X-ray radiation, the first thing that comes to mind is probably the high penetration into materials and therefore the complementarity to neutron probes. Yet there are...

Precious alloys are subjected to a series of mechanical and thermal operations during manufacturing. For 18 carat gold alloys the processing operations can induce L10 ordered nanodomains, known to lead to the build-up of residual stresses, which are the prime cause for shape distortion. Here, in situ high-energy synchrotron X-ray diffraction experiments in combination with electron microscopy observations reveal the influence of the thermo-mechanical history and chemical composition on the ordering kinetics during isochronal heating. Initially, during heating, the elastic lattice strain in the ordered nanodomains increases. The ordering rate and accumulation of lattice strain depend on the cooling rate, predeformation and chemical composition. Above a given temperature, which depends on the deformation state and chemical composition, the lattice strain in the ordered domains relaxes which is ascribed to the formation of a tweed structure.

Blended Elemental powders are an emerging alternative to pre-alloyed powders in metal additive manufacturing due to the wider range of alloys producible with them and the cost savings from not developing novel feedstock. In this study, in situ alloying and concurrent microstructure evolution during SLM are investigated by performing SLM on a BE Ti-185 powder while tracking the surface temperatures via Infra-red imaging and phase transforma- tion via synchrotron X-ray Diffraction. We then performed post-mortem electron microscopy (Backscatter Electron imaging, Energy Dispersive X-ray Spectroscopy and Electron Backscatter Diffraction) to further gain insight into microstructure development. We show that although exothermic mixing aids the melting process, laser melting results only in a mixture of alloyed and unmixed regions. Full alloying and thus a consistent microstructure is only achieved through further thermal cycling in the heat-affected zone.

The processes leading to degradation of Pt nanoparticles inside commercial hydrogen fuel cell catalyst layers are studied in situ, using time-resolved high-energy powder X-ray diffraction. Advances...

The effect of the adsorption of a polypeptide on the lateral interaction of dimyristoylphosphatidylserine molecules in different phase states on the surface of a 10 mM KCl aqueous solution has been studied. Changes in the surface pressure and Volta potential induced by the adsorption of large poly-D-lysine molecules (about 200 links in a chain) have been determined at different areas per lipid molecule in a monolayer. The adsorption of macromolecules noticeably increases the elasticity of the monolayer under lateral compression in the liquid expanded state of lipid and reduces the effective dipole moment from 0.48 to 0.38 D. These properties are in qualitative agreement with X-ray reflectometry data for the lipid monolayer obtained with synchrotron radiation with a photon energy of ≈70 keV. The electron density profiles perpendicular to the surface of the aqueous subphase have been reconstructed from reflectometry data within a model approach to the structure of an interface with two and three layers. These profiles indicate the existence of a wide diffuse polymer layer (150 ± 40) A in width at the interface of the monolayer in both the liquid expanded and liquid condensed states. A decrease in the area per molecule in the monolayer by a factor of 2 results in the doubling of the surface density of the macromolecule film. The adsorption of the polymer also affects the integral density of the layer of polar phospholipid groups, which decreases by a factor of ≈2 in the liquid expanded phase and by ∼30% in the liquid condensed phase.

International audience; Proliferation of hydrogen fuel cell systems is hindered by degradation of the platinum catalyst. Here, we provide a device level assessment of the catalyst degradation phenomena and its coupling to nanoscale hydration gradients, using advanced operando X-ray scattering tomography tailored for device-scale imaging. Gradients formed inside the fuel cell produce heterogeneous degradation of the catalyst nanostructure, which can be linked to the flow field design and water distribution in the cell. Striking differences in catalyst degradation are observed between operating fuel cell devices and the liquid cell routinely used for catalyst stability studies, highlighting the crucial impact of the complex operating environment on the catalyst degradation phenomena. This degradation knowledge gap accentuates the necessity of multimodal, in situ characterization of real devices when assessing the performance and durability of electrocatalysts, and more generally, electrochemically active phases used in energy conversion and storage technologies.

International audience; A Compton spectroscopy investigation is carried out in hydrated Nafion membranes, enabling identification of distortions in the hydrogen-bond distribution of the polymer hydrating water by means of the subtle changes reflected by the Compton profiles. Indeed, deformations of the Compton profiles are observed when varying hydration, and two different bonding kinds are associated with the water molecules: at low hydration, water surrounds the sulfonic groups, while on increasing hydration, water molecules occupy the interstitial cavities formed upon swelling of the membrane. The analysis is proposed in terms of averaged OH bond length variation. A sizable contraction of the OH distance is observed at low hydration (∼0.09 Å), while at higher hydration levels, the contraction is smaller (∼0.02 Å) and the OH bond length is closer to bulk water. An evaluation of the electron kinetic energy indicates that the spatial changes associated with the water distribution correspond to a consistent binding energy increase. Distinct temperature dependences of each water population are observed, which can be straightly related to water desorption into ice on cooling below the freezing point

The theoretical design of effective metal electrocatalysts for energy conversion and storage devices relies on the structure sensitivity of electrochemical processes to their catalyst materials, assuming the structural integrity during operation. However, theoretical predictions do not necessarily match practical performance. Here, by using high-energy X-ray diffraction from the new Extremely Brilliant Source of the European Radiation Synchrotron Facility (ESRF-EBS) on device-relevant Pd and Pt nanocatalysts during cyclic voltammetry experiments in liquid electrolyte, we quantitatively reveal how different electrochemical processes permanently affect the bulk microstructure of nanocatalysts in a distinctive fashion. The reported structural insights provide experimental access to reactivity descriptors such as adsorption and absorption trends operando. The ease and power of such an experimental approach at new and future beamlines is foreseen to guide computational model description of practical nanomaterials in electrochemical environment while providing a discovery platform toward the study of nanocatalysts encompassing a large variety of applications.

We have investigated the formation of lamellar crystals of poly(vinylidene fluoride) (PVDF) in the presence of oriented clay particles with different aspect ratios (ARs) and surface properties. Hot-melt screw extrusion of PVDF with 5 wt % of montmorillonite (AR ≈ 12) or fluoromica (AR ≈ 27) resulted in formation of phase-separated blends. Replacing the clays with their organoclay derivatives, organomontmorillonite or organofluoromica, resulted in the corresponding intercalated nanocomposites. The organoclays induced formation of polar β- and γ-polymorphs of PVDF in contrast to the α-polymorph, which dominates in the pure PVDF and the PVDF/clay blends. Solid-state nuclear magnetic resonance revealed that the content of the α-phase in the nanocomposites was never higher than 7% of the total crystalline phase, whereas the β/γ mass ratio was close to 1:2, irrespective of the AR or crystallization conditions. X-ray diffraction showed that the oriented particles with a larger AR caused orientation of the polar lamellar crystals of PVDF. In the presence of the organofluoromica, PVDF formed a chevron-like lamellar nanostructure, where the polymer chains are extended along the extrusion direction, whereas the lamellar crystals were slanted from normal to the extrusion direction. Time-resolved X-ray diffraction experiments allowed the identification of the formation mechanism of the chevron-like nanostructure.

The structure of the adsorbed layer of alkali ions on the surface of colloidal silica solutions with a particle size of 27 nm has been studied by reflectometry and diffuse scattering of synchrotron radiation with a photon energy of about 71 keV. Electron density profiles in the direction perpendicular to the surface have been reconstructed from experimental data and spectra of the correlation function of heights in the surface plane have been obtained. The revealed deviation of the integral and frequency characteristics of the roughness spectra of the silica sol surface from predictions of the capillary-wave theory is of a fundamental character. This deviation is due to the contribution from roughnesses with low spatial frequencies ν < 10−4 nm–1 and to the interference of diffuse scattering from different layer interfaces of the surface structure.

The use of synchrotron radiation in fundamental and applied materials research is expanding in Europe. Traditionally, synchrotron radiation was used to study the final properties of metal alloys. More recently, due to improvements of the sources, detectors, and experimental techniques themselves, materials processing can be studied in situ on an industrial scale. Various techniques, such as imaging, tomography, and diffraction, are used to study material processing, solidification, thermo-mechanical treatment, shaping, and mechanical behavior under various conditions such as stress and temperature. The use of these techniques in real time during the processing is essential to understand, and furthermore to optimize, the process yielding desired materials properties.

Physical review letters 124(8), 086101 (2020). doi:10.1103/PhysRevLett.124.086101, The equilibrium atomic interface structure between Ga and GaN(0001) is shown to contain substrate surface vacancies followed by substrate-induced layering and preferential lateral ordering in the liquid. The uncovered presence of point defects, in the form of vacancies at both sides of the solid-liquid interface, is an important structural feature which governs the local physical properties. Our x-ray diffraction study reveals that the layering is very stable and persists up to a temperature of 1123 K and a nitrogen pressure of 32 bar. The Ga layer spacing agrees remarkably well with the Friedel oscillation period for this system., Published by APS, College Park, Md.

openaire: EC/H2020/679933/EU//MEMERE We have constructed a 5 cm2 proton exchange membrane hydrogen fuel cell optimized for transparency of high energy X-rays. This cell allows for in situ elastic scattering measurements (WAXS, SAXS) during electrochemical operation with minimal trade-offs in cell performance vs benchtop designs, and is capable of reaching automotive current densities. A key feature is that the beam enters the cell at grazing incidence to the electrodes, massively increasing the effective pathlength and therefore the signal-to-background ratio. The 360∘ transparency in the plane of the sample permits imaging coupled with advanced techniques, such as X-ray diffraction computed tomography.

Hard X-ray transmission microscopy based on refractive X-ray optics can be employed as a tool in material science to investigate buried-in microstructures in two or three dimensions with spatial resolution approaching 100 nm. Switching from monochromatic to radiation with a broader bandwidth, frame rates down to a few milliseconds can be realized, opening new possibilities for in situ studies of microstructure evolution and response to external fields at spatiotemporal resolutions that go well beyond previous benchmarks, demonstrated by ~200 nm resolution tomograms of eutectic microstructures acquired in less than 2 s. The microscope can also be operated in Zernike phase contrast mode, which expands the range of possible applications to cases which otherwise would produce only very faint contrast. A few possible application areas for the microscope are illustrated by a selection of material science test cases.

In this work, the structure of solid-supported lipid multilayers exposed to increased hydrostatic pressure was studied in situ by X-ray reflectometry at the solid-liquid interface between silicon and an aqueous buffer solution. The layers' vertical structure was analyzed up to a maximum pressure of 4500 bar. The multilayers showed phase transitions from the fluid into different gel phases. With increasing pressure, a gradual filling of the sublayers between the hydrophilic head groups with water was observed. This process was inverted when the pressure was decreased, yielding finally smaller water layers than those in the initial state. As is commonly known, water has an abrasive effect on lipid multilayers by the formation of vesicles. We show that increasing pressure can reverse this process so that a controlled switching between multi- and bilayers is possible.

We investigate $K$-shell ionization of ${\mathrm{N}}_{2}$ at 40 keV photon energy. Using a cold target recoil ion momentum spectroscopy reaction microscope, we determine the vector momenta of the photoelectron, the Auger electron, and both ${\mathrm{N}}^{+}$ fragments. These fully differential data show that the dissociation process of the ${\mathrm{N}}_{2}^{2+}$ ion is significantly modified not only by the recoil momentum of the photoelectron but also by the photon momentum and the momentum of the emitted Auger electron. We find that the recoil energy introduced by the photon and the photoelectron momentum is partitioned with a ratio of approximately $30\ensuremath{\mathbin:}70$ between the Auger electron and fragment ion kinetic energies, respectively. We also observe that the photon momentum induces an additional rotation of the molecular ion.

Physical chemistry, chemical physics 21, 3734 - 3741 (2019). doi:10.1039/C8CP05604H, The interfacial premelting in ice/clay nano composites was studied by high energy X-ray diffraction. Below the melting point of bulk water, the formation of liquid water was observed for the ice/ vermiculite and ice/kaolin systems. The liquid fraction is gradually increasing with temperature. For both minerals, similar effective premelting layer thicknesses of 2–3 nm are reached 3 K below the bulk melting point. For the quantitative description of the molten water fraction in wet clay minerals we developed a continuum model for short range interactions and arbitrary pore size distributions. This model quantitatively describes the experimental data over the entire temperature range. Model parameters were obtained by fitting using a maximum entropy (MaxEnt) approach. Pronounced differences in the deviation from Antonow’s rule relating interfacial free energy between ice, water, and clay are observed for the charged vermiculite and uncharged kaolin minerals. The resultant parameters are discussed in terms of their ice nucleation efficiency. Using well defined and characterized ice/clay nano composite samples, this work bridges the gap between studies on single crystalline ice/solid model interfaces and naturally occurring soils and permafrost., Published by RSC Publ., Cambridge

It is shown that high-energy X-ray diffraction allows a fast and accurate texture and microstructure analysis of crystals, which can help to set up optimal industrial procedures for materials manufacturing. This paper presents the experimental and theoretical aspects of quantitative texture analysis using high-energy synchrotron beams. Intensity corrections are less important in this approach than in classical laboratory methods; however, the most important correction, related to the Lorentz factor, can introduce relative fraction changes of up to about 40% compared to the uncorrected case. The resolution of the orientation density function also influences the results. For example, the usual 5° resolution leads to relative deviations of up to 30% in the fraction of some components. The method allowed detection of small changes taking place during the recovery and continuous recrystallization of a cold-rolled Al–TiB2 nanocomposite. Texture information was combined with the results of line profile analysis, evidencing the evolution of the average dislocation density and coherent domain size of the selected grain families. It was found that recovery, as described in terms of dislocation annihilation and coherent domain coarsening, takes place at similar rates in all components.

The properties of the interface between biomaterials and the host tissue play an important role for the process of successful adaptation of implants. Extensive research has focused on shortening the time of osseointegration by modifying the surface in adding a coating such as hydroxyapatite (HAp). We have developed a new type of biocompatible nanohydroxyapatite (n-HAp) coatings, which are characterized before and after deposit on a Ti-6Al-4V substrate using neutron diffraction and scanning electron microscopy. Three months after the implantation in the sheep tibias, high-energy synchrotron radiation (ID15B, ESRF, Grenoble, France) diffraction studies of the cortical bone identify that the c-axes of HAp are preferentially oriented in the direction of the stresses that bone usually withstands. This non destructive analysis of the bone-implant interface proves that bone maturation is achieved successfully with this novel n-HAp coating and demonstrates that the mineralization is completed without spatial organization. None of these findings are obtained with uncoated titanium alloys. The presence of this n-HAp coating on Ti-6Al-4V substrate is decisive in obtaining this mature bone at the interface.

The coating of silicide or nitride layers on U–7 wt%Mo or U–7 wt%Mo–1 wt%Ti particles has been proposed for the minimization of the interaction phase growth in U–Mo/Al dispersion fuel during irradiation. Out-of-pile annealing tests show reduced inter-diffusion by forming silicide or nitride protective layers on U–Mo and U–Mo–Ti particles. To characterize the constituent phases of the coated layers on U–Mo and U–Mo–Ti particles and the interaction phases of coated U–Mo and U–Mo–Ti particle dispersed Al matrix fuel, synchrotron X-ray diffraction experiments have been performed. It was identified that silicide coating layers consisted mainly of U 3 Si 5 and U 4 Mo(Mo x Si 1− x )Si 2 , and nitride coating layers were composed of mainly UN and U 4 N 7 . The interaction phases obtained after annealing of coated U–Mo and U–Mo–Ti particle dispersion samples were identical to those found in U–Mo/Al–Si and U–Mo/Al systems. Nitride-coated particles showed less interaction formation than silicide-coated particles after annealing at 580 °C for 1 h owing to the higher susceptibility to breakage of the silicide coating layers during hot extrusion.

Nanocrystalline (nc) materials possess unique mechanical properties, such as very high strength. However, an understanding of the deformation mechanisms and the succession of related microscopic processes that occur during deformation is still incomplete. We used synchrotron-based in situ compression testing to investigate the sequence of deformation mechanisms emerging in bulk nc nickel with a grain size of 30 nm. The study was accompanied by high-resolution grain size analysis and crystal orientation mapping using transmission electron microscopy. Regardless of the initial microstructure, the deformation behavior of electrodeposited nc Ni is initiated by inhomogeneous elastic lattice straining and its accommodation within the grain boundary network, followed by the onset of dislocation plasticity, which was inferred from texture evolution, and stress-driven grain growth. This observation indicates that deformation in nc metals is governed by a succession of different, partly overlapping mechanisms. It is estimated that intragranular dislocation plasticity contributes only about 40% to the overall deformation.

A new type of high density fuel is needed for the conversion of research and test reactors from high to lower enriched uranium. The most promising one is a dispersion of atomized uranium-molybdenum (U–Mo) particles in an Al matrix. However, during in-pile irradiation the growth of an interaction layer between the U–Mo and the Al matrix strongly limits the fuel’s performance. To improve the in-pile behaviour, the U–Mo particles can be coated with protective layers. The SELENIUM (Surface Engineering of Low ENrIched Uranium–Molybdenum) fuel development project consists of the production, irradiation and post-irradiation examination of 2 flat, full-size dispersion fuel plates containing respectively Si and ZrN coated U–Mo atomized powder dispersed in a pure Al matrix. In this paper X-ray diffraction analyses of the Si and ZrN layers after deposition, fuel plate manufacturing and thermal annealing are reported. It was found for the U–Mo particles coated with ZrN (thickness 1 μm), that the layer is crystalline, and exhibits lower density than the theoretical one. Fuel plate manufacturing does not strongly influence these crystallographic features. For the U–Mo particles coated with Si (thickness 0.6 μm), the measurements of the as received material suggest an amorphous state of the deposited layer. Fuel plate manufacturing strongly modifies its composition: Si reacts with the U–Mo particles and the Al matrix to grow U(Al, Si) 3 and U 3 Si 5 phases. Finally both coatings have shown excellent performances under thermal treatment by limiting drastically the U–Mo/Al interdiffusion.

We describe the only currently available protocol for in situ, real-time monitoring of mechanochemical reactions and intermediates by X-ray powder diffraction. Although mechanochemical reactions (inducing transformations by mechanical forces such as grinding and milling) are normally performed in commercially available milling assemblies, such equipment does not permit direct reaction monitoring. We now describe the design and in-house modification of milling equipment that allows the reaction jars of the operating mill to be placed in the path of a high-energy (∼90 keV) synchrotron X-ray beam while the reaction is taking place. Resulting data are analyzed using conventional software, such as TOPAS. Reaction intermediates and products are identified using the Cambridge Structural Database or Inorganic Crystal Structure Database. Reactions are analyzed by fitting the time-resolved diffractograms using structureless Pawley refinement for crystalline phases that are not fully structurally characterized (such as porous frameworks with disordered guests), or the Rietveld method for solids with fully determined crystal structures (metal oxides, coordination polymers).

UMo-Al based fuel plates prepared with ground U8wt%Mo, ground U8wt%MoX (X = 1 wt%Pt, 1 wt%Ti, 1.5 wt%Nb or 3 wt%Nb) and atomized U7wt%Mo have been examined. The first finding is that that during the fuel plate production the metastable γ-UMo phases partly decomposed into two different γ-UMo phases, U2Mo and α′-U in ground powder or α″-U in atomized powder. Alloying small amounts of a third element to the UMo had no measurable effect on the stability of the γ-UMo phase. Second, the addition of some Si inside the Al matrix and the presence of oxide layers in ground and atomized samples is studied. In the case with at least 2 wt%Si inside the matrix a Silicon rich layer (SiRL) forms at the interface between the UMo and the Al during the fuel plate production. The SiRL forms more easily when an Al–Si alloy matrix – which is characterized by Si precipitates with a diameter ⩽1 μm – is used than when an Al–Si mixed powder matrix – which is characterized by Si particles with some μm diameter – is used. The presence of an oxide layer on the surface of the UMo particles hinders the formation of the SiRL.

Multilayer coatings enhance x-ray mirror performance at incidence angles steeper than the critical angle, allowing for improved flux, design flexibility and facilitating alignment. In an attempt to extend the use of multilayer coatings to photon energies higher than previously achieved, we have developed multilayers with ultra-short periods between 1 and 2 nm based on the material system WC/SiC. This material system was selected because it possesses very sharp and stable interfaces. In this article, we show highlights from a series of experiments performed in order to characterize the stress, microstructure and morphology of the multilayer films, as well as their reflective performance at photon energies from 8 to 384 keV.

Processes at material interfaces to liquids or to high-pressure gases often involve structural changes that are heterogeneous on the micrometer scale. We present a novel in situ X-ray scattering technique that uses high-energy photons and a transmission geometry for atomic-scale studies under these conditions. Transmission surface diffraction gives access to a large fraction of reciprocal space in a single acquisition, allowing direct imaging of the in-plane atomic arrangement at the interface. Experiments with focused X-ray beams enable mapping of these structural properties with micrometer spatial resolution. The potential of this new technique is illustrated by in situ studies of electrochemical surface phase transitions and deposition processes.

Activated carbons (ACs) have a wide range of applications, in which the largely expanded specific surface plays a major role. The question of their structure came back to the limelight with the discovery of nanotubes fullerenes, which suggested that curved surfaces may be present in their structure and which incorporates well into the ideas of ACs porous structure. The source of those curved surfaces is atomic defects present inside the in-plane graphitic honeycomb lattice. Such defects have a crucial influence on the macroscopic morphology as well as physical properties of the material. The activated carbon (AC) in this work was derived from carbonised saccharose by activation with NaOH. Both materials – before and after activation were investigated. The main methods used in this study are wide angle neutron scattering and wide angle X-ray scattering combined with computer simulations. Confirmation of the proposed structures was sought with high-resolution transmission electron microscopy and Ram...

We have studied the decomposition kinetics of the metastable austenite phase present in quenched-and-tempered SAE 52100 steel by in situ high-energy synchrotron X-ray diffraction experiments at elevated temperatures of 200–235 °C under a constant tensile stress. We have observed a continuous decomposition of austenite into ferrite and cementite. The decomposition kinetics is controlled by the long-range diffusion of carbon atoms into the austenite ahead of the moving austenite/ferrite interface. The presence of a tensile stress of 295 MPa favours the carbon diffusion in the remaining austenite, so that the activation energy for the overall process decreases from 138–148 to 82–104 kJ mol−1. Before the austenite starts to decompose, a significant amount of carbon atoms partition from the surrounding martensite phase into the metastable austenite grains. This carbon partitioning takes place simultaneously with the carbide precipitation due to the over-tempering of the martensite phase. As the austenite decomposition proceeds gradually at a constant temperature and stress, the elastic strain in the remaining austenite grains continuously decreases. Consequently, the remaining austenite grains act as a reinforcement of the ferritic matrix at longer isothermal holding times. The texture evolution in the constituent phases reflects both significant grain rotations and crystal orientation relationships between the parent austenite phase and the newly formed ferritic grains.

Chemical and structural transformations have long been carried out by milling. Such mechanochemical steps are now ubiquitous in a number of industries (such as the pharmaceutical, chemical and metallurgical industries), and are emerging as excellent environmentally friendly alternatives to solution-based syntheses. However, mechanochemical transformations are typically difficult to monitor in real time, which leaves a large gap in the mechanistic understanding required for their development. We now report the real-time study of mechanochemical transformations in a ball mill by means of in situ diffraction of high-energy synchrotron X-rays. Focusing on the mechanosynthesis of metal–organic frameworks, we have directly monitored reaction profiles, the formation of intermediates, and interconversions of framework topologies. Our results reveal that mechanochemistry is highly dynamic, with reaction rates comparable to or greater than those in solution. The technique also enabled us to probe directly how catalytic additives recently introduced in the mechanosynthesis of metal–organic frameworks, such as organic liquids or ionic species, change the reactivity pathways and kinetics.

Structural studies of the multi-walled carbon nanotubes obtained using the arc discharge method by high-energy wide-angle X-ray scattering are presented. The diffraction data have been converted to a real-space representation in the form of the pair correlation function via the Fourier transform. The experimental data are compared with model based simulations for atomic arrangements consisting of about 50,000 carbon atoms. Energy of the computer-generated models was optimized using the reactive empirical bond order and the Lennard–Jones potentials for intra- and inter-layer interactions. A comparison of such performed simulations with the experimental data shows a good agreement between them indicating that the model without defects correctly reconstruct the data in a reciprocal and real space. Taking into account previous studies of the defect containing carbon nanotubes the present work provides evidence that the joint diffraction and molecular dynamics techniques can be regarded as an efficient tool for detailed characterization of the atomic scale structure of the carbon nanotubes.

This article describes a single-shot methodology to derive an average coating thickness in multi-particle core–shell systems exhibiting high X-ray absorption. Powder composed of U–Mo alloy particles surrounded by a micrometre-thick UO2protective layer has been used as a test sample. Combining high-energy X-ray diffraction and laser granulometry, the average shell thickness could be accurately characterized. These results have been validated by additional measurements on single particles by two techniques: X-ray nanotomography and high-energy X-ray diffraction. The presented single-shot approach gives rise to many potential applications on core–shell systems and in particular on as-fabricated heterogeneous nuclear fuels.

Circumventing radiation damage remains a major problem for X-ray macromolecular crystallography. Analysis of diffraction data collected from normal-sized cryocooled lysozyme crystals shows that the dose required to collect a data set of prescribed resolution and signal-to-noise ratio, assuming an ideally efficient detector, decreases with increasing photon energy in the investigated 6.5–33 keV range. For example, the data collection efficiency is increased by a factor of ∼8 from 8 to 33 keV. Monte Carlo simulations on lysozyme crystals in the range 5–80 keV, taking into account electron escape from samples of different size, also show a positive effect of high energy (albeit less pronounced than in experiments), especially for micrometre-sized samples, and suggest that the optimum energy range is ∼24–41 keV, depending on crystal size. The importance of counting pixel detectors with a good efficiency at high energy is underlined. Macromolecular crystallography beamlines should be modified, or purposely designed, in order to benefit from higher-energy radiation through reduction of global radiation damage, better data accuracy and extension of phasing by anomalous dispersion.

The optimisation of high density metallic U–Mo/Al(Si) nuclear fuels, developed for use in high neutron flux research reactor without proliferation issues, requires an excellent control of the manufacturing conditions for getting a full benefit of Si powder additions. Eleven full size plates (from the IRIS and E-FUTURE experimental programs) have been analysed by diffraction using synchrotron high energy X-rays. For the first time, both the levels of the γU–Mo phase destabilisation in the U–Mo particle and characteristics (size and composition) of the Si rich protective layers around these particles have been quantified at a macroscopic scale. These results enable to evaluate the influence of the different parameters implied in the manufacturing process and could also provide solutions for producing enhanced fuels.

We present a microstructural investigation of two different pyrocarbons (PyCs), belonging respectively to the rough laminar (RL) and smooth laminar (SL) families. The structure of the materials is analyzed in terms of their pair distribution functions (PDFs) as determined from neutron diffraction experiments. The data are correlated with polarized light optical microscopy, high resolution transmission electron microscopy, Raman microspectrometry, X-ray diffraction, He pycnometry, elastic recoil detection analysis and secondary ion mass spectrometry. Results show that the two materials may be clearly distinguished using the PDF data above a 15 A distance. The PDF of the more ordered carbon (the RL PyC) is also compared to data obtained from an image-guided atomistic reconstruction, showing excellent agreement.

The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10(PO4)6(OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the texture of the reconstituted bone crystals at the interface applying non destructive x-ray diffraction. The required high spatial resolution was achieved utilizing high-energy synchrotron radiation on ID15 at ESRF in Grenoble, France.

Synchrotron X-ray diffraction is reliable to measure residual stresses and characterize existing phases close to substrate/coating interface. In the present study, we focus on the cobalt-alloys coating deposited on stainless steel forging tools via Plasma Transfer Arc (PTA) process. Forging tools always work in high temperature conditions. Since fatigue crack is often detected near to the interface, we used synchrotron radiation to characterize residual stress profiles both in the substrate and coating sides. Also, we defined phases inside diluted substrate layers and in the stellite coating using a Rietveld refinement.

Residual stresses in welds are of major concern for the structure integrity assessment in industrial components. The stresses in the final weld can be determined relatively simple using well established destructive or non-destructive techniques. However, such measurements reflect only the final condition and it remains unclear how stresses built up during the welding process. In order to optimise the final residual stresses in the weld, it is important to monitor the formation of residual strain and stress during the welding process and as such to gain insight into the mechanisms of stress development. In this work non-destructive high energy dispersive synchrotron X-ray diffraction at a high count rate is applied in order to dissolve the welding process in-situ in time and temperature. However, the achievable time resolution at commonly used instruments is restricted by either a limited photon flux or the read out electronics of the detector system resulting in counting times usually much longer than 1sec. We present an energy dispersive detector and read-out-electronics setup realized at the high flux and energy beam line ID15A at the ESRF. The setup allowed for monitoring the strain evolution in two perpendicular directions simultaneously at a sampling rate of 5Hz, resulting in sufficient time and temperature resolution. The change in detector dead time is accounted for by a correction function, which was specifically determined for the detector setup as used for this in-situ experiment.

A novel approach to determine the thermodynamic solubility of tin in indium oxide via the exsolution from tin overdoped nano-ITO powders is presented. High-energy, in situ and ex situ synchrotron X-ray diffraction was utilized to study the solubility limit at temperatures ranging from 900°C to 1375°C. The tin exsolution from overdoped nanopowders and the formation of In4Sn3O12 were observed in situ during the first 4–48 h of high-temperature treatment. Samples annealed between 900°C and 1175°C were also studied ex situ with heat treatments for up to 2060 h. Structural results obtained from Rietveld analysis include compositional phase analysis, atomic positions, and lattice parameters. The tin solubility in In2O3 was determined using the phase analysis compositions from X-ray diffraction and the elemental compositions obtained from X-ray fluorescence. Experimental complications that can lead to incorrect tin solubility values in the literature are discussed.

The transformation of ultra-dispersed diamond nanoparticles of about 50 A in diameter into carbon nano-onions has been studied by high-energy X-ray diffraction and molecular dynamics simulations using the reactive empirical bond order potential. Structural models have been constructed for pristine nano-diamonds and nano-diamonds annealed at 1673 K, 1973 K and 2273 K. These models have been relaxed using the molecular dynamics method and the model based structure factors and the pair correlation functions are compared with the experimental data. All model relaxations and the X-ray diffraction experiments have been carried out at 300 K. Two starting models consisting of 5460 atoms with a single diamond core and an amorphous-like outer shell and for a twinned diamond core and a similar amorphous outer shell containing in total about 13,500 atoms reproduced correctly features of the experimental data. The atomic models of two intermediate and final fully graphitized structures, consisting of the same numbers of atoms and containing the series of defected icosahedral fullerenes describe satisfactorily the atomic arrangements for the samples annealed at 1673 K, 1973 K and 2273 K. The generated models of the nano-diamonds and the nano-onions are related to the previous observations by high-resolution transmission electron microscopy.

X-ray diffuse scattering experiments on single CuO 2 layer Hg high T c superconductors ( HgBa 2 CuO 4 + δ ) near optimal doping level have revealed that the doping oxygen atoms of this system form very long and isolated chains (extending over 75 unit cells in average) in both tetragonal directions, with correlated transverse and longitudinal displacements of at least the nearby pairs of mercury atoms and copper atoms from two coupled CuO 2 layers. Signs of incommensurate periodic lattice distortion have been also observed.

The present study is dedicated to high energy x-ray diffraction measurements of residual stress at bone-implant interfaces. Bone regeneration is different from soft tissue repair as scar formation never occurs and as de novo bone tissue is produced with proliferation and differentiation of mesenchymal cells. To start the bone remodelling, the stress – the most important mechanical factor – should stimulate the osteocytes. Osseointegration is also observed with non-functional implants, in particular with dental implants. This means that a stress similar to a residual stress must exist.

The commercialization of proton exchange membrane (PEM) fuel cells has increasingly demanded lower precious metal catalyst loadings. A better understanding of platinum nanoparticle degradation mechanisms and electrochemistry will be essential in preserving fuel cell performance over increased device lifetimes. In-situ synchrotron x-ray diffraction/scattering is a powerful tool for characterizing commercial catalyst layers in an electrochemical cell1-2. Recent advances in hardware presently allow time-resolved scattering measurements and diffractive imaging3 without compromising electrochemical experiments. New cell designs4 greatly improve the ease and flexibility of measuring membrane electrode assemblies under environmental conditions and Pt loadings relevant for fuel cell operation and degradation. The structural effects and kinetics of platinum electrochemistry on nanoparticles can be directly probed using x-ray diffraction. The evolution of nanoparticle strain, atomic ordering, oxidation, and dissolution are monitored in the presence of adsorbing molecular species under potential control. We show how by monitoring Pt particle size, and Pt lattice strain, it is possible to deconvolute chemical and electrochemical steps in the mechanism of Pt oxidation and reduction. Measurements using conventional single crystal and half cell experiments are compared with x-ray diffraction on an operating PEM fuel cell cathode. Several differences in surface chemistry between these cell configurations are detected, which is directly relevant to the development of better accelerated aging and stress-testing protocols. Particular attention has been given towards developing these advanced synchrotron techniques as useful tools for the non-specialist. Recent advances improving the accessibility of in situ diffraction for the electrochemical community are discussed. Figure 1. X-ray transparent half-cell suitable for high-energy x-ray diffraction of membrane electrode assemblies (left). X-ray powder diffractogram obtained from fuel cell cathode during the oxygen reduction reaction (right). Imai, K. Izumi, M. Matsumoto, Y. Kubo, K. Kato and Y. Imai. J. Am. Chem. Soc., 2009, 131 (17), pp 6293–6300 K. Sasaki, N. Marinkovic, H.S. Isaacs, and R.R. Adzic. ACS Catal., 2016, 6 (1), pp 69–76 F. Reikowski, T. Wiegmann, J. Stettner, J. Drnec, V. Honkimaki, F. Maroun, P. Allongue, O.M. Magnussen. J. Phys. Chem. Lett., 2017, 8 (5), pp 1067–1071 B. Pinaud, A. Bonakdarpour, L. Daniel, J. Sharman and D.P. Wilkinson. J. Electrochem. Soc. 2017, 164 (4), pp F321-F327 Figure 1

The durability of proton exchange membrane fuel cells (PEMFC) is a major barrier to the commercialization of these systems for stationary and transportation power applications. The decrease in the performances is due to irreversible processes in the catalyst layers such as dissolution and contamination and reversible losses which are attributed to the evolution of the cell water distribution [1]. The mechanisms leading to the performance loss under PEMFC operation of individual components (catalyst, membrane, GDL) are well known, however, what is the connection between operating conditions and failure mechanism is still under debate. The degradation in real working conditions may be strongly accelerated and localized since all phenomena are highly inter-correlated and very dependent on the cell design and mode of operation. To provide a long-term stable cell operation, detailed knowledge about the underlying aging mechanisms and their correlation to fluid transport is essential. Here we show, for the first time, that it is possible to obtain simultaneously a space/time resolved information about the catalyst structure, water distribution and microstructural parameters in a running fuel cell using high energy X-ray diffraction techniques. The custom X-ray cell design (area of 5 cm2) allows us to reach current densities up to 4 A/cm2, therefore the performance of the most demanding application such as automotive fuel cells. We use advanced tomography imaging techniques coupled with the full Rietveld analysis of the diffraction (HE-XRD) patterns [2]. This allows us to distinguish (with micron resolution) different materials, their structure and to determine the water distribution as a function of the cell’s operating parameters (humidity, temperature, power output). For example the high resolution and large probed reciprocal space of HE-XRD patterns permit to determine the oxidation state of Pt cathode catalyst at different conditions. This information is then used to distinguish the potential distribution within the cell and to find the parts of the MEA where the Pt nanoparticles are either electrically disconnected from the carbon or they are not reachable by diffusing protons. Both phenomena would effectively lead to a lower performance of the cell. In another example we show that the parallel flowfield geometry of our cell and the defects in the GDL affect the water distribution within the membrane, catalyst layer and GDL. At 2 A/cm2 more water is generated close to the gas inlets of the cell and the defects in the GDL contain relatively less water. At lower current densities the water is much more homogeneously distributed within the MEA and the GDL defects do not play a major role in the water distribution. In conclusion we show that the high energy X-ray diffraction is an interesting non-invasive, relatively simple and robust technique which can be successfully used to study the fuel cell in operando conditions giving unprecedented insight into the working device. Ref.: [1] S. Cherevko et al, ChemElectroChem, 10, 2(2015), 1471–1478; [2] V. Rossi et al., Advanced Materials, 21(2009), 578-583. Fig. 1: (a) The top diagram shows the cross-section sketch of of the cathode side of fuel cell. The H 2 O, Pt and carbon cross-section maps obtained from the analysis of the HE-XRD patterns during the cell operation at 2 A/cm 2 are shown below. (b) The tomographic reconstructions obtained from HE-XRD measurements showing Pt distribution within catalyst layer for four different vertical positions and for three different electrochemical conditions. Figure 1