Synchrotron Experiments Research Articles

Understanding the Impact of Gas Diffusion Layer Degradation on Water Inventory in Low Temperature PEM Fuel Cells for Heavy Duty Vehicles Application: Operando X-Ray and Neutron Imaging Study

Samples from two materials representing the condition at begin and end of life, were selected from testing of commercial, state-of-the-art PEM fuel cell stacks. Using small-area single cell setups specifically developed for visualization purposes, operando synchrotron and neutron imaging experiments to visualize water dynamics and distribution within these cells were performed. In this study, the effects of aging on water inventory in the gas diffusion layers throughout the lifespan of the cells are investigated. The findings provide insights into how aging influences water management, which is crucial for optimizing the performance and longevity of PEM fuel cells for heavy-duty applications.

Understanding the Impact of Gas Diffusion Layer Degradation on Water Inventory in Low Temperature PEM Fuel Cells for Heavy Duty Vehicles Application: Operando X-Ray and Neutron Imaging Study

Samples from two materials representing the condition at begin and end of life, were selected from testing of commercial, state-of-the-art PEM fuel cell stacks. Using small-area single cell setups specifically developed for visualization purposes, operando synchrotron and neutron imaging experiments to visualize water dynamics and distribution within these cells were performed. In this study, the effects of aging on water inventory in the gas diffusion layers throughout the lifespan of the cells are investigated. The findings provide insights into how aging influences water management, which is crucial for optimizing the performance and longevity of PEM fuel cells for heavy-duty applications.

Comparison of Full-Field Crystal Plasticity Simulations to Synchrotron Experiments: Detailed Investigation of Mispredictions

Comparison of Full-Field Crystal Plasticity Simulations to Synchrotron Experiments: Detailed Investigation of Mispredictions

Design, construction, and dosimetry of 3D printed heterogeneous phantoms for synchrotron brain cancer radiation therapy quality assurance

Objective. This study aims to design, manufacture, and test 3D printed quality assurance (QA) dosimetry phantoms for synchrotron brain cancer radiation therapy at the Australian synchrotron. Approach. Fabricated 3D printed phantoms from simple slab phantoms, a preclinical rat phantom, and an anthropomorphic head phantom were fabricated and characterized. Attenuation measurements of various polymers, ceramics and metals were acquired using synchrotron monochromatic micro-computed tomography (CT) imaging. Polylactic acid plus, VeroClear, Durable resin, and tricalcium phosphate were used in constructing the phantoms. Furthermore, 3D printed bone equivalent materials were compared relative to ICRU bone and hemihydrate plaster. Homogeneous and heterogeneous rat phantoms were designed and fabricated using tissue-equivalent materials. Geometric accuracy, CT imaging, and consistency were considered. Moreover, synchrotron broad-beam x-rays were delivered using a 3 Tesla superconducting multipole wiggler field for four sets of synchrotron radiation beam qualities. Dose measurements were acquired using a PinPoint ionization chamber and compared relative to a water phantom and a RMI457 Solid Water phantom. Experimental depth doses were compared relative to calculated doses using a Geant4 Monte Carlo simulation. Main results. Polylactic acid (PLA+) shows to have a good match with the attenuation coefficient of ICRU water, while both tricalcium phosphate and hydroxyapatite have good attenuation similarity with ICRU bone cortical. PLA+ material can be used as substitute to RMI457 slabs for reference dosimetry with a maximum difference of 1.84%. Percent depth dose measurement also shows that PLA+ has the best match with water and RMI457 within ±2.2% and ±1.6%, respectively. Overall, PLA+ phantoms match with RMI457 phantoms within ±3%. Significance and conclusion. The fabricated phantoms are excellent tissue equivalent equipment for synchrotron radiation dosimetry QA measurement. Both the rat and the anthropomorphic head phantoms are useful in synchrotron brain cancer radiotherapy dosimetry, experiments, and future clinical translation of synchrotron radiotherapy and imaging.

Relationship between synthesis method-crystal structure-melting properties in cocrystals: the case of caffeine-citric acid.

The influence of the crystal synthesis method on the crystallographic structure of caffeine-citric acid cocrystals was analyzed thanks to the synthesis of a new polymorphic form of the cocrystal. In order to compare the new form to the already known forms, the crystal structure of the new cocrystal (C8H10N4O2·C6H8O7) was solved by powder X-ray diffraction thanks to synchrotron experiments. The structure determination was performed using `GALLOP', a recently developed hybrid approach based on a local optimization with a particle swarm optimizer, particularly powerful when applied to the structure resolution of materials of pharmaceutical interest, compared to classical Monte-Carlo simulated annealing. The final structure was obtained through Rietveld refinement, and first-principles density functional theory (DFT) calculations were used to locate the H atoms. The symmetry is triclinic with the space group P-1 and contains one molecule of caffeine and one molecule of citric acid per asymmetric unit. The crystallographic structure of this cocrystal involves different hydrogen-bond associations compared to the already known structures. The analysis of these hydrogen bonds indicates that the cocrystal obtained here is less stable than the cocrystals already identified in the literature. This analysis is confirmed by the determination of the melting point of this cocrystal, which is lower than that of the previously known cocrystals.

Effect of deformation mode on martensitic transformation in medium Mn steel

In the present work, we have investigated the effect of deformation modes namely uniaxial loading and plane strain loading on martensite transformation in medium Mn TRIP steels, since it plays an important role in influencing formability. Interrupted deformation experiments showed that the martensitic transformation proceeds continuously with plastic strain and is influenced by the specific deformation mode applied. Uniaxially loaded samples underwent a complete austenite to martensite transformation. On the other hand, under plane strain loading, only 70 % of the austenite transformed into martensite, even after fracture had occurred. Through synchrotron and EBSD experiments, we observed that under uniaxial loading, the transformation sequence followed the γ-ε-α′ pathway, whereas, under plane strain, a direct γ-α′ transformation was observed. The intermediate ε-martensite phase is known to facilitate the transformation from austenite to martensite. Consequently, the presence of ε-martensite resulted in a higher degree of austenite transformation in the uniaxial samples. We rationalize the difference in transformation sequences based on resolved shear stress calculations for the two deformation modes.

DFT computation of the electron spectra of thiophene

Recent experiments on thiophene using synchrotron radiation stimulated the present density functional theory (DFT) study of the various types of electron spectroscopy using the DFT methods we developed in our laboratory. Besides the confirmation of the experimental interpretations, the results of the present study strongly validate the methods used for the various types of electron spectroscopy. The average absolute deviations of the DFT results for thiophene from experiment are 0.22 eV for vertical ionization energies of outer valence electrons, 0.10 eV for carbon 1s binding energies, 0.19 eV for vertical valence excitation energies, and 0.18 eV for X-ray absorption energies. The calculated carbon 1s binding energies for bithiophene and terthiophene are also within 0.1 eV of synchrotron experiment. We conclude that workers using synchrotron radiation to study electronic processes of gas-phase molecules can apply our DFT methods for the interpretation of their experimental results.

Proton-conducting membranes based on Nafion® synthesized by using nanodiamond platform

New method of emulsion synthesis of Nafion®-type copolymer composition by using nanodiamond platform has been proposed and implemented. Produced polymeric coagulate saturated with diamonds (4.1 % wt.) possessed increased ionic capacity of the copolymer comparative to the analogue without diamonds. SEM patterns for coagulate membranes showed labyrinthine structures with diamonds integrated into copolymer without any segregation. This structuring provided necessary elastic and strength properties of new type membranes for hydrogen fuel cells. In new membranes synchrotron experiments exhibited a network of ionic channels which ensured a proton conductivity by one order of magnitude higher than that for the analogue produced of premade components.

MULTISCALE ASSESSMENT OF ACHILLES TENDON MECHANICS AND MECHANOBIOLOGY

Achilles tendon mechanical properties depend on a complex hierarchical design, with collagen being the smallest load-bearing unit. At the nanoscale, collagen molecules are organized into fibrils, which at the microscale are assembled into fibers, followed by larger structures such as sub-tendons or fascicles. Degree of in vivo loading affects the collagen content, and organization and consequently the tissue's mechanical response. We aim to unravel how composition, structural organization, and mechanical response are affected by degree of in vivo loading at each length scale. The presentation will outline the results to date about to the use of high-resolution synchrotron-based tissue characterisation methods on several length scales in combination with in situ mechanical tests. We use a rat model, where the tendons are subjected to varying loading in vivo. To characterize the tissue microstructure, phase-contrast enhanced synchrotron micro-tomography is performed. The 3D fiber organization in fully loaded tendons is highly aligned, whereas the fibers in unloaded tendons are significantly more heterogeneously arranged and crimped. To characterize the collagen fibril response, Small Angle X-ray Scattering is performed. Two types of fibril organizations are found; a single population oriented towards the main load direction and two fibril subpopulations with clearly distinct orientations. Scattering during loading showed that the fibrils in unloaded tendons did not strain as much in fully loaded. In situ loading concurrently with high resolution synchrotron experiments show the complex tendon response to in situ load and its relation to in vivo loading and tendon hierarchical structure. Unloading seems to alter the organization of the fibrils and fibers, e.g. increased crimping and more pronounced sub-tendon twists.Acknowledgements: Funding from Knut and Alice Wallenberg Foundation and European Research Council (101002516). Paul Scherrer Institut, Switzerland for beamtime at cSAXS and TOMCAT.

Deep residual networks for crystallography trained on synthetic data.

The use of artificial intelligence to process diffraction images is challenged by the need to assemble large and precisely designed training data sets. To address this, a codebase called Resonet was developed for synthesizing diffraction data and training residual neural networks on these data. Here, two per-pattern capabilities of Resonet are demonstrated: (i) interpretation of crystal resolution and (ii) identification of overlapping lattices. Resonet was tested across a compilation of diffraction images from synchrotron experiments and X-ray free-electron laser experiments. Crucially, these models readily execute on graphics processing units and can thus significantly outperform conventional algorithms. While Resonet is currently utilized to provide real-time feedback for macromolecular crystallography users at the Stanford Synchrotron Radiation Lightsource, its simple Python-based interface makes it easy to embed in other processing frameworks. This work highlights the utility of physics-based simulation for training deep neural networks and lays the groundwork for the development of additional models to enhance diffraction collection and analysis.

Effect of dislocation slip and deformation twinning on the high-pressure phase transformation in Zirconium

Zirconium transforms from the α→ω phase under high hydrostatic pressures. The critical transformation pressure is expected to be affected by internal stresses associated with defects. This study focuses on the effects of dislocations and twins and their associated stress fields on the transformation. Samples are pre-loaded to seed dislocations or twins. In-situ high-hydrostatic-pressure X-ray synchrotron experiments are performed revealing that microstructures with pre-existing prismatic 〈a〉 dislocations and {101¯2} twins promote the transformation more effectively than pyramidal 〈c + a〉 dislocations or {112¯2} twins. Post-mortem electron backscatter diffraction further shows that pre-seeded defects stabilize the ω-phase at ambient conditions. In-situ stress-hold neutron diffraction experiments are also performed combining both hydrostatic and deviatoric stresses capturing the role of deviatoric stresses on phase transformation kinetics. These results support the findings of recent atomistic simulations indicating flow of prismatic 〈a〉 dislocations at an α-ω interface promotes the growth of the ω domain.

Laboratory-based X-ray spectrometer for actinide science.

X-ray absorption and emission spectroscopies nowadays are advanced characterization methods for fundamental and applied actinide research. One of the advantages of these methods is to reveal slight changes in the structural and electronic properties of radionuclides. The experiments are generally carried out at synchrotrons. However, considerable progress has been made to construct laboratory-based X-ray spectrometers for X-ray absorption and emission spectroscopies. Laboratory spectrometers are reliable, effective and accessible alternatives to synchrotrons, especially for actinide research, which allow dispensing with high costs of the radioactive sample transport and synchrotron time. Moreover, data from laboratory spectrometers, obtained within a reasonable time, are comparable with synchrotron results. Thereby, laboratory spectrometers can complement synchrotrons or can be used for preliminary experiments to find perspective samples for synchrotron experiments with better resolution. Here, the construction and implementation of an X-ray spectrometer (LomonosovXAS) in Johann-geometry at a radiochemistry laboratory is reported. Examples are given of the application of LomonosovXAS to actinide systems relevant to the chemistry of f-elements, the physical chemistry of nuclear power engineering and the long-term disposal of spent nuclear fuel.

How Beam Damage Can Skew Synchrotron Operando Studies of Batteries.

With the advent of high-brilliance synchrotron sources, the issue of beam damage on the samples deserves proper attention. It is especially true for operando studies in batteries, since the intense photon fluxes are commonly used to probe ever finer effects. Here we report on the causes and consequences of synchrotron X-ray beam damage in batteries, based on the case study of operando X-ray diffraction. We show that beam damage is caused by the mingled actions of dose and dose rate. The aftereffects can lie in a broad range, from mild modifications of the crystalline structure to artificial phase transitions, and can thus impede or bias the understanding of the mechanisms at play. We estimate the doses at which the different effects appear in two materials, suggesting that it could be expanded to other materials with the same technology. We also provide recommendations for the design of operando synchrotron experiments.

Mechanism of Water Intrusion into Flexible ZIF-8: Liquid Is Not Vapor.

Zeolitic Imidazolate Frameworks (ZIF) find application in storage and dissipation of mechanical energy. Their distinctive properties linked to their (sub)nanometer size and hydrophobicity allow for water intrusion only under high hydrostatic pressure. Here we focus on the popular ZIF-8 material investigating the intrusion mechanism in its nanoscale cages, which is the key to its rational exploitation in target applications. In this work, we used a joint experimental/theoretical approach combining in operando synchrotron experiments during high-pressure intrusion experiments, molecular dynamics simulations, and stochastic models to reveal that water intrusion into ZIF-8 occurs by a cascade filling of connected cages rather than a condensation process as previously assumed. The reported results allowed us to establish structure/function relations in this prototypical microporous material, representing an important step to devise design rules to synthesize porous media.

Modelling needle domains with dislocations: A dislocation pile-up model and comparison with synchrotron experiment

The shape and strain field of a needle domain in a barium titanate single crystal are modelled using a distribution of dislocations and line charges. The arrangement of these dislocations and charges is a result of the balance of modified Peach–Koehler forces acting among the dislocations and a lattice friction assumed to act at each dislocation site. Based on measurements of needle shape by synchrotron X-ray diffraction, dislocation pile-up theory is used to compute the distribution of discrete dislocations along the needle and hence estimate the lattice friction. It is found that the lattice friction in this model is proportional to the opening angle of a wedge-shape needle domain and consistent with the observed magnitude of stress required to mobilize needle domains. The microstrain distribution around an a-a needle domain tip, obtained from X-ray diffraction measurement, is further used to test the dislocation model, with a similar pattern and magnitude of strains identified in the model and the experiment.

Beam damage in operando X-ray diffraction studies of Li-ion batteries.

Operando powder X-ray diffraction (PXRD) is a widely employed method for the investigation of structural evolution and phase transitions in electrodes for rechargeable batteries. Due to the advantages of high brilliance and high X-ray energies, the experiments are often carried out at synchrotron facilities. It is known that the X-ray exposure can cause beam damage in the battery cell, resulting in hindrance of the electrochemical reaction. This study investigates the extent of X-ray beam damage during operando PXRD synchrotron experiments on battery materials with varying X-ray energies, amount of X-ray exposure and battery cell chemistries. Battery cells were exposed to 15, 25 or 35 keV X-rays (with varying dose) during charge or discharge in a battery test cell specially designed for operando experiments. The observed beam damage was probed by µPXRD mapping of the electrodes recovered from the operando battery cell after charge/discharge. The investigation reveals that the beam damage depends strongly on both the X-ray energy and the amount of exposure, and that it also depends strongly on the cell chemistry, i.e. the chemical composition of the electrode.

In‐operando synchrotron experiments of flash sintering carried out in current rate mode

AbstractWe report first‐time results for in‐operando flash sintering synchrotron experiments carried out in current rate mode where the specimen, held at a constant temperature, is fed current that is increased at a constant rate. These experiments are unique because the time dependence of the sintering behavior can be stretched out over a longer period (by changing the current rate) than in voltage‐to‐current experiments in which sintering occurs in a burst at the onset of the flash. Two results are presented: (i) A comparison of temperatures measured with the platinum standard to those predicted by the black body radiation model leading to estimates of the emissivity as a function of porosity whereby emissivity increases from 0.65 to 0.9 as the sample sinters from its green state to full density, and (ii) measurements of the excess lattice expansion as a function of density as the sample sinters continuously while the current is increased. The present work highlights the promise of current rate experiments to obtain results while the sample sinters gradually from its green density to full density (somewhat akin to conventional sintering) for gaining further insights into the mechanisms of flash sintering.

Formation of H3O+ and OH by CO2 and N2O trace gases in the atmospheric environment.

The impact of cosmic rays' energetic subatomic particles on climate and global warming is still controversial and under debate. Cosmic rays produce ions that can trigger fast reactions affecting chemical networks in the troposphere and stratosphere especially when a large amount of relevant trace gases such as carbon dioxide, methane, sulfur dioxide and water are injected by volcanic eruptions. This work focuses on synchrotron experiments and an ab initio theoretical study of the ion chemistry of carbon dioxide and nitrous oxide radical cations reacting with water. These molecules catalyze a fast exothermic formation of hydronium ions H3O+ and the hydroxyl radical OH, the main oxidant in the atmosphere. Moreover, theoretical calculations demonstrate that at the end of the catalytic cycle, CO2 and N2O are produced vibrationally excited and subsequently they quench in the microsecond time scale by collision with the surrounding atmospheric molecules at the pressure and temperature of the upper-troposphere/stratosphere. The chemistry involved in these reactions has a strong impact on the oxidant capacity of the atmosphere, on the sulfate aerosol production, on the cloud formation and eventually on the chemical networks controlling climate and global warming models.

Influence of the deposition process and substrate on microstructure, phase composition, and residual stress state on as-deposited Cr-Al-C coatings

This paper focuses on the influence of the High Power Pulsed Magnetron Sputtering (HPPMS) and Direct Current Magnetron Sputtering (DCMS) coating deposition processes, the bias voltage, deposition temperature, and substrate on various properties of the as-deposited state of Cr-Al-C thin films. Three substrates with different coefficients of thermal expansion and electrical conductivity were used. To investigate the microstructure, phase composition, residual stress state, and mechanical properties, ex-situ and in situ synchrotron experiments were conducted accompanied by electron microscopy and nanoindentation. As-deposited Cr-Al-C coatings consisted of amorphous and crystalline areas, with the ratio highly dependent on the deposition process and substrate. The crystalline phase was identified as metastable (Cr,Al)2C. The highest crystallinity was determined for DCMS coatings. Increasing temperature and decreasing bias voltage increased coating crystallinity for HPPMS coatings. The influence of the deposition process and bias voltage was highly reduced for the substrate with low electrical conductivity. In-situ investigations of the stress state of amorphous areas revealed, that those were acting as a residual stress buffer. The hardness and Young’s modulus of the coatings were found to increase with crystallinity and were slightly increased for crystalline HPPMS coatings compared to DCMS coatings.

Influence of the deposition process on the Cr2AlC phase formation during heat treatment of Cr-Al-C thin films

This paper focuses on the Cr2AlC phase formation during annealing post-treatment, with amorphous Cr-Al-C and (Cr,Al)2C as initial phases in the as-deposited state. The influence of the deposition process on the Cr2AlC formation, texture, and phase composition is investigated and an in-depth discussion of the intermediate phase is carried out. Cr-Al-C thin films were deposited by Direct Current Magnetron Sputtering and High Power Pulsed Magnetron Sputtering with the variation of the deposition temperature. To investigate the microstructure, phase composition, and texture, in situ synchrotron and high-temperature X-ray diffraction experiments were conducted and accompanied by electron microscopy. The Cr2AlC formation can be described as a temperature and time-dependent process with one intermediate state characterized by the formation of the disordered-Cr2AlC phase. Disordered-Cr2AlC shows a similar unit cell to Cr2AlC with an increased c/a ratio. The ratio decreases during the phase formation resulting from an ordering process. Formation temperatures depend on the initial phase, with a decreased formation temperature for (Cr,Al)2C, and the deposition process. While the (002) fiber texture of (Cr,Al)2C inherited to Cr2AlC, Cr2AlC originated from amorphous Cr-Al-C showed no preferred orientation. The coatings contained Cr7C3 as an additional phase, dependent on the deposition process and initial phases.