Synchrotron Experiments Research Articles

Experimental and Model‐Based Analysis of Electrolyte Intrusion Depth in Silver‐Based Gas Diffusion Electrodes

AbstractThe electrolyte distribution is a central point of discussion for understanding the processes inside gas‐diffusion electrodes (GDE) for the oxygen reduction reaction in highly alkaline media. During first radiographic operando synchrotron experiments, the liquid electrolyte was located, however, the through‐plane distribution remains unclear. Therefore, model electrodes consisting of nickel and silver layers are developed to determine the electrolyte intrusion depth. Nickel‐based GDEs are modified to achieve a pore system morphology suitable for the oxygen reduction reaction and subsequently coated with silver‐PTFE catalyst layers. These graded electrodes form gas‐diffusion (nickel) and reaction (silver) layers. The electrodes performance is determined under industrial conditions (80 °C, 30 wt % NaOH electrolyte) as a function of the silver layer thickness and thus of the effective intrusion depth of the electrolyte. The model‐based analysis confirms the experimental determined intrusion depths. Nevertheless, additional operando tomography measurements would help to further improve the understanding of the processes inside GDE.

Synchrotron experiment and simulation studies of magnesium-steel interface manufactured by impact welding

The effective weight reduction in the automotive industry by the wide adoption of lightweight magnesium (Mg) alloys demands high-quality joint between magnesium alloys and massively-used steels in order to wring the excess weight with strength and safety assurance. However, Mg-steel joint is difficult to achieve because there is no mutual solubility between magnesium and steel and huge disparity in physical properties. An impact-based welding method recently showed successful Mg-steel joining. In this work, the characteristics of Mg-steel interface joined by the impact welding method were investigated. Synchrotron high-energy X-ray computed tomography and diffraction were applied to characterize the microstructure across Mg-steel interface. Results revealed a deposit layer formed at the joint interface where Fe-rich particles spread deep into the Mg matrix. High-resolution 3D morphology of Mg-steel interface demonstrated the trapped pores and cracks inside the deposit layer. The formation of the deposit layer and the void/cracking evolution were analyzed by using finite element models. These findings provide insights into the immiscible Mg-steel joining process.

Texture development and dislocation activities in Mg-Nd and Mg-Ca alloy sheets

Texture modification during sheet rolling appears differently in binary Mg-RE (rare-earth) or Mg-Ca alloy, compared to their ternary counterparts containing Zn. The differences in texture development and the active deformation mechanisms under tensile loading were investigated in the binary alloys. These analyses are based on in-situ synchrotron experiments and electron backscatter diffraction measurements to reveal direct experimental evidence of the texture development and the active deformation mechanisms. Higher activations of nonbasal <a> and pyramidal <c+a> dislocations were found in the Nd or Ca containing Mg alloys, compared to the Mg-Zn alloy. The texture development shows an obvious feature, which is a broadening of the basal pole intensity distribution perpendicular to the loading direction and a strengthening of the <101¯0> pole at the loading direction in all examined sheets. This texture development relates to the higher activation of prismatic <a> slip. The addition of Zn in the Mg-RE or Mg-Ca alloys further promotes the activation of nonbasal <a> and pyramidal <c+a> dislocations. This enhanced prismatic <a> slip in the Zn containing ternary alloys is confirmed by EBSD misorientation analysis.

Spatially resolved model of oxygen reduction reaction in silver-based porous gas-diffusion electrodes based on operando measurements

An improved spatially resolved mathematical model for porous, silver-based gas-diffusion electrodes for the oxygen reduction reaction in strongly alkaline electrolyte is presented. For the first time, important parameters describing the distribution of the liquid electrolyte in the electrode were determined via independent operando synchrotron experiments. With the model, a reasonable description of the overvoltage as a function of the current density at 80 °C could be achieved in a range of electrolyte concentrations (27 – 36.6 wt.% NaOH) and oxygen contents (20 – 100 vol.%). Model-based analysis of the processes inside the electrode revealed that a complex water cycle evolves which supports the removal of hydroxide ions and thus boosts the electrode performance. The analysis also showed that additional operando measurement of the electrolyte distribution and investigations with electrodes having a defined thickness of the reaction layer will help to further improve the model.

Synchrotron radiation as a tool for macromolecular X-Ray Crystallography: A XXI century perspective

Intense X-rays available at powerful synchrotron beamlines provide macromolecular crystallographers with an incomparable tool for investigating biological phenomena on an atomic scale. The resulting insights into the mechanism’s underlying biological processes have played an essential role and shaped biomedical sciences during the last 30 years, considered the “golden age” of structural biology. In this review, we analyze selected aspects of the impact of synchrotron radiation on structural biology. Synchrotron beamlines have been used to determine over 70% of all macromolecular structures deposited into the Protein Data Bank (PDB). These structures were deposited by over 13,000 different research groups. Interestingly, despite the impressive advances in synchrotron technologies, the median resolution of macromolecular structures determined using synchrotrons has remained constant throughout the last 30 years, at about 2 Å. Similarly, the median times from the data collection to the deposition and release have not changed significantly. We describe challenges to reproducibility related to recording all relevant data and metadata during the synchrotron experiments, including diffraction images. Finally, we discuss some of the recent opinions suggesting a diminishing importance of X-ray crystallography due to impressive advances in Cryo-EM and theoretical modeling. We believe that synchrotrons of the future will increasingly evolve towards a life science center model, where X-ray crystallography, Cryo-EM, other experimental and computational resources, and knowledge are encompassed within a versatile research facility. The recent response of crystallographers to the COVID-19 pandemic suggests that X-ray crystallography conducted at synchrotron beamlines will continue to play an essential role in structural biology and drug discovery for years to come.

Natural surface oxidation consideration in first principles modeling of the X-ray absorption near edge fine structure of silicon

First-principles calculations of the electronic structure of crystalline silicon and its dioxide were performed on the basis of the density functional theory. The full-potential linearized augmented plane waves method was used with the generalized gradient approximation for the exchange-correlation potential with Perdew, Burke and Ernzerhof functional. X-ray absorption near edge structure of silicon L3 spectra for these materials were calculated with the use of core-hole approach and supercells. These calculated spectra were used as reference for modeling the X-ray absorption L3 spectrum of a real silicon sample covered with a layer of natural SiO2 oxide. Comparison of the spectra obtained by the first principles calculations with the results of a high-resolution synchrotron experiments and the suggested approach to their modeling demonstrated the possibility of a complex silicon-oxygen system prospective materials and structures detailed study.

Computer-controlled liquid-nitrogen drizzling device for removing frost from cryopreserved crystals.

Cryocrystallography is a technique that is used more often than room-temperature data collection in macromolecular crystallography. One of its advantages is the significant reduction in radiation damage, which is especially useful in synchrotron experiments. Another advantage is that cryopreservation provides simple storage of crystals and easy transportation to a synchrotron. However, this technique sometimes results in the undesirable adhesion of frost to mounted crystals. The frost produces noisy diffraction images and reduces the optical visibility of crystals, which is crucial for aligning the crystal position with the incident X-ray position. To resolve these issues, a computer-controlled device has been developed that drizzles liquid nitrogen over a crystal to remove frost. It was confirmed that the device works properly, reduces noise from ice rings in diffraction images and enables the centering of crystals with low visibility owing to frost adhesion.

Dynamic coherent diffractive imaging using unsupervised identification of spatiotemporal constraints.

Dynamic coherent diffractive imaging (CDI) reveals the fine details of structural, chemical, and biological processes occurring at the nanoscale but imposes strict constraints on the object distribution and illumination. Ptychographic CDI relaxes these constraints by exploiting redundant information in data obtained from overlapping regions of an object, but its time resolution is inherently limited. We have extended ptychographic redundancy into the spatiotemporal domain in dynamic CDI, automatically identifying redundant information in time-series coherent diffraction data obtained from dynamic systems. Simulated synchrotron experiments show that high spatiotemporal resolution is achieved without a priori knowledge of the object or its dynamics.

Processing and properties of translucent bismuth sodium titanate ceramics

Lead-free bismuth sodium titanate piezoceramics were processed by a solid-state route with a novel precursor approach. By carefully controlling the processing parameters and sintering atmospheres, translucent ceramics with pore-free, homogeneous microstructures with exceptionally low dielectric loss at elevated temperatures. The pore-free microstructure can influence the operating life of a dielectric device positively, since pores and other microstructural defects are usually responsible for material failures within devices. Synchrotron and surface X-ray diffraction experiments revealed a clear dependence of the crystal structure on sintering parameters and defect chemistry. Microstructural analysis showed a dependency of a secondary phase on the sintering atmosphere. The grain size could be adjusted using a shortened grinding process instead of using the common methods like increasing calcining or sintering temperature.

Design and Precursor-based Solid-State Synthesis of Mixed-Linker Zr-MIL-140A.

Acetic acid, an alternative green solvent, was utilized for the solvothermal synthesis of four 2D materials of composition [Zr2O2(OAc)2(BDC-F)], [Zr2O2(OAc)2(BDC-F4)], [Zr2O2(OAc)2(BDC)], and [Zr2O2(OAc)2(NDC)] (BDC, terephthalate; BDC-F, 2-fluoroterephthalate; BDC-F4, tetrafluoroterephthalate; NDC, 2,6-naphthalenedicarboxylate). The first three compounds were subsequently reacted with terephthalic acid in solid-state reactions to form porous MIL-140A-type metal-organic frameworks and mixed-linker derivatives ([ZrO(BDC)1-x(BDC-Y)x], x = 0-0.18, Y = F, F4). The reaction kinetics of the formation of MIL-140A were investigated with the aid of time-resolved synchrotron and temperature-resolved in-house X-ray powder diffraction experiments. Thorough compositional analyses and solid-state NMR spectroscopic experiments were used to assess the crystallographic ordering of the different linker molecules. Additionally, acetic acid-based routes for the direct synthesis of MIL-140A-NO2 and a novel MIL-140A-(CH3)2 derivative were discovered.

Evidence of an ordered ternary phase in the section Ni–Ti5Sn3 of the ternary Ti–Ni–Sn: Crystal structure and phase stability

In this paper we present the synchrotron and laboratory X-ray powder diffraction (S-XRPD) experiments made at normal conditions and also at different pressures (up to 2 GPa). Then crystal structure and equation of state (EoS) have been determined. These results are discussed together with experimental phase diagram. The binary phases of the Sn–Ti (Ti3Sn, Ti2Sn, Ti5Sn3) are often extended by a ternary addition. This was observed by us many times particularly in the Ga-Sn-Ti system where a ternary phase is observed. In the case of the Ni–Sn–Ti system, the question is still pending. Focusing on D88–Sn3Ti5 let remind that this phase is hexagonal, hP16, P63/mcm, prototype Mn5Si3. The point defect formation energies were obtained from first principles calculations. Four sublattices are introduced to account for the D88 structure and for the possibility of inserting atoms in the 2b sites of the structure P63/mcm. The 2b sites are not occupied in the stoichiometric compound at T 1⁄4 0 K. But the possibility exists that a few atoms occupy these sites at higher temperature or for off-stoichiometric alloys. For stoichiometric D88–Sn3Ti5 alloys, it was shown that the dominant thermal defects are composed of Sn atoms in interstitial positions 2b of the D88 structure and Ti atoms in antisite position on the sites preferentially occupied by Sn atoms. In the Sn-rich D88–Sn3Ti5, the constitutional defects are Sn atoms in interstitial positions. In the Ti-rich D88–Sn3Ti5, the constitutional defects are Ti atoms in antisite position. The chemical potentials as well as the Gibbs energy are obtained as function of composition for various temperatures.

Mechanism of low temperature deformation in aluminium alloys

This study investigates differences in the deformation mechanisms between room temperature (296 K) and cryogenic temperatures (77 K) and their advantages for low temperature formability in alloys EN AW 1085, EN AW 5182 and EN AW 6016. Compared to room temperature behaviour, tensile tests showed an overall increase in yield strength, ultimate tensile strength and uniform elongation with differences among the principal alloy types. In general, the improved mechanical properties result from higher strain hardening rates at lower temperatures. The application of an extended Kocks-Mecking approach showed a significant reduction of the dynamic recovery and suggested higher dislocation densities upon cryogenic deformation. This was confirmed via in-situ synchrotron experiments, which also reveal a higher proportion of screw dislocations. Moreover, kernel average misorientation maps from electron backscattered diffraction and in-situ cryogenic deformation in a transmission electron microscope displayed a more uniform dislocation arrangement with a reduction of slip lines and less highly misaligned areas after deformation at lower temperatures. Supported by a detailed characterization of the microstructure and its dislocation structure, the associated fundamental mechanisms we reveal, which are at the origin of the exceptional improvement in mechanical properties, are extensively discussed.

Fine residual stress distribution measurement of steel materials by SOI pixel detector with synchrotron X-rays

Residual stress is an important factor governing evaluating and controlling the quality of metal materials in industrial products. X-ray measurements provide one of the most effective means of evaluating residual stress without destruction. In such measurements, the effects of residual stress on the crystal structure can be observed through the Debye ring deformation.In previous studies, we developed a residual stress measurement system based on the cosα method, using a two-dimensional (2D) silicon-on-insulator pixel (SOIPIX) detector known as INTPIX4. In a typical laboratory setup, this system requires only 1 s to measure a specified point. This is drastically faster than the conventional system based on the sin2ψ method, which requires more than 10 min, and the cosα-based system using an imaging plate, which requires 1 min. Compared to other systems, it can evaluate the 2D distribution of residual stress faster and provide more detailed information for evaluating materials. We first attempted to measure the 2D distribution in a laboratory setup with a Cr X-ray tube (Cr Kα 5.4 keV) and obtained satisfactory results. We subsequently took measurements using synchrotron monochromatic X-rays to determine the fine accuracy and fine sampling pitch distribution. In this paper, we report the results of the initial synchrotron experiment, including the residual stress distribution of the standard specimen obtained by the first prototype setup. Furthermore, we compare the synchrotron measurements with those from the laboratory.

Load partition during hot deformation of AlSi12 and AlSi10Cu6Ni2 alloys: a quantitative evaluation of the stiffness of Si networks

An eutectic AlSi12 alloy contains a rigid 3D network formed by the eutectic Si in the as-cast condition, which disintegrates during solution treatment. Synchrotron tomography proved that a near eutectic AlSi10Cu6Ni2 alloy also exhibits a 3D network with higher and more stable stiffness due to the presence of aluminides that retain the initial as-cast microstructure during the solubilization treatment and increase the volume fraction of rigid phases. In order to evaluate the load borne by different phases during hot deformation, in situ synchrotron experiments were carried out revealing an underestimation of the load transfer from the soft α-Al matrix to the hard silicon 3D network in the AlSi12 alloy. By taking into account the additional stiffness introduced by the local interconnectivity, the stresses in different phases in the near eutectic AlSi10Cu6Ni2 alloy were calculated. Additionally, the analysis of the aluminide Al2Cu allowed to identify its influence in the global damage of the hybrid 3D network formed by the Si and aluminides in the near eutectic AlSi10Cu6Ni2 alloy.

Synchrotron CT imaging of lattice structures with engineered defects

Understanding mechanical failure, crack propagation, and compressive behavior at the micrometer scale is essential for tailoring material properties for structural performance in cellular materials. Typically, modeling of traditional polymer foam materials is clouded by the lack of control in material morphology and its inherent stochastic structure. Additive manufacturing with sub-micrometer resolution provides a direct path for experimenters to specifically tailor structures needed by modelers to explicitly probe mechanical performance. Using laboratory-based 3D X-ray computed tomographic imaging (CT), the examination of deformation and damage provides a critical path to understand how these soft materials behave. Additionally, synchrotron CT yields realistic information at higher strain rates to directly validate the robustness of our finite element modeling. For this study, nanolithographic printing was employed to generate a series of engineered lattices with increasing levels of defects through the random removal of ligaments. These structures were mechanically tested and imaged with laboratory-based microCT. Additionally, synchrotron experiments were conducted in which the structures were imaged in 3D at 14 Hz during compression at a 0.4 s−1 strain rate. These 3D images show the changes in the structure as the ligaments bend, buckle and fracture in real time. This technique provides a robust framework for developing our methodologies and future exploration of engineered structures.

In situ analysis of cast irons mechanical behaviour using synchrotron x-ray tomography and 3DXRD

When subjecting cast irons to mechanical loading the deformation and damage mechanisms occur on a microstructural level and are dependent on the inherent microstructure. A deeper understanding of the relation between the different microstructural constituents and the macroscopic mechanical behaviour would be beneficial in material development efforts and for the ability to design and cast components with tailored properties. Traditionally, microscopy examinations on sectioned cast iron samples have been used when analysing the microstructure in cast irons. Since all microstructural heterogeneity is in three-dimensions (3D), methods that provide a three-dimensional characterisation are essential for a deeper understanding of, both the microstructural features as well as the deformation and damage of cast irons. Therefore, different cast iron grades have been studied using synchrotron X-ray tomography and 3D x-ray diffraction (3DXRD) at ESRF in Grenoble, France. The samples were stepwise loaded and unloaded in-situ at in the tomography/3DXRD set-up to study the deformation with regard to microstructural constituents and the microstructural evolution in 3D. Based on the 3D tomography image sequences, digital volume correlation (DVC) was used for full strain field analysis and for the analysis of damage and deformation mechanisms. In addition, 3DXRD data were analysed to provide details on the lattice parameters and lattice strain of individual ferrite grains. This work shows the possibilities of such synchrotron experiments for advanced study of the mechanical behaviour of cast iron.

Structure determination of a new cocrystal of carbamazepine and DL-tartaric acid by synchrotron powder X-ray diffraction.

The crystal structure of a new cocrystal of carbamazepine (systematic name: 5H-dibenzo[b,f]azepine-5-carboxamide, C15H12N2O) and DL-tartaric acid (C4H6O6), obtained by liquid-assisted grinding, was solved by powder X-ray diffraction (PXRD). The high-resolution PXRD pattern of this new phase was recorded at room temperature thanks to synchrotron experiments at the European Synchrotron Radiation Facility (Grenoble, France). The starting structural model was generated by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinement and an energy minimization simulation was used to estimate the H-atom positions. The stability of the proposed structure as a function of temperature was also assessed from molecular dynamics simulations. The symmetry is monoclinic (space group P21/c) and contains eight molecules per unit cell, namely, four DL-tartaric acid and four carbamazepine molecules.

Probing Silicon Lithiation in Silicon-Carbon Blended Anodes with a Multi-Scale Porous Electrode Model

Blended negative electrodes with a mix of graphite and silicon are attractive solutions to extend the energy density of lithium-ion batteries. Given the huge volume expansion of silicon, the relative lithiation/delithiation of both active materials upon cycling is crucial to determine the mechanical behavior of the electrode. It is complicated however by the potential hysteresis displayed by silicon. We focus on a blended anode with 16 wt% of silicon carbon composite (SiC-C) at a gravimetric capacity of 1500 mAh.g−1 mixed with 84 wt% graphite. A multi-scale porous electrode model with three different hierarchical units has been developed to account for the morphology of the SiC-C composed of nanoflakes of silicon embedded in a carbon matrix. The developed physics-based model is parametrized with appropriate experiments and validated for two electrodes loadings and various operating conditions. The validated model allows to probe the lithiation competition between the silicon and the carbon within the composite and the graphite. It is able to capture the streaking features revealed by synchrotron experiments. In particular, we show that at higher C-rates, the lithiation of the silicon is delayed and reduced compared to the graphite one. Quantifying this relative competition is valuable as aging effects are significantly accelerated by the expansion of the silicon.

Nanoscale Mapping of Extrinsic Interfaces in Hybrid Solid Electrolytes

Summary Inorganic-organic hybrid solid electrolytes are promising material systems for all solid-state batteries (ASSBs). These electrolytes contain numerous solid | solid interfaces that govern transport pathways, electrode | electrolyte compatibility, and durability. This paper evaluates the role that electrode | electrolyte interfaces and electrolyte structure have on electrochemical performance. Atomic force microscopy techniques reveal how mechanical, adhesion, and morphological properties transform in a series of model hybrid solid electrolytes. These measurements are mapped to sub-surface microstructural features using synchrotron nano-tomography. Hybrid solid electrolytes with shorter polymer chains demonstrate a higher adhesion ( > 100 nN), Young's Modulus (6.4 GPa), capacity (114.6 mAh/g), and capacity retention (92.9%) than hybrid electrolytes with longer polymer chains (i.e., higher molecular weight). Extrinsic interfacial properties largely dictate electrochemical performance in ASSBs. Microstructural control over inorganic constituents may provide a means for tailoring interfacial properties in hybrid solid electrolytes.

Stress localisation in lamellar cementite and ferrite during elastoplastic deformation of pearlitic steel studied using diffraction and modelling

Synchrotron X-ray diffraction was applied to study the evolution of lattice strain and stresses in both phases of pearlitic steel during a tensile test. The advantage of the methodology used in this work is the possibility of experimental study of stress localisation, which is directly determined from measurements and can be used to study the process of strain strengthening of lamellar pearlite. It was found that in the elastic range of deformation, both cementite and ferrite are loaded similarly due to the nearly equal elastic properties of both phases, while plastic deformation leads to significant load transfer from ferrite to cementite. Due to the complexity of the lamellar microstructure of the material, the classical elastic-plastic self-consistent model does not correctly predict the partitioning of the stresses between phases during plastic deformation. Therefore, the grain-matrix interaction given by the self-consistent model was modified and successfully applied to simulate the interaction between phases.The synchrotron experiment allowed us to determine the critical resolved shear stresses of ferrite phase in the pearlitic steel subjected to different thermal treatments. The role of cementite in material strengthening was evaluated on the basis of the evolution of von Mises stress, experimentally determined in both phases. It was found that during plastic deformations, the von Mises stress does not change significantly in ferrite compared to an important increase in elastically deformed cementite. Therefore, the partitioning of stresses between phases is mainly responsible for the strain strengthening of the tested pearlitic steel exhibiting fully lamellar microstructure.