X-ray Diffraction Mapping Research Articles

The Effects of Electrospinning Structure on the Ion Conductivity of PEO-Based Polymer Solid-State Electrolytes

To overcome the safety hazard of the liquid electrolytes used in traditional lithium batteries, solid electrolytes have drawn more attention because of their advantages such as non-volatility, easy processing, good mechanical properties, and stability. In this paper, sodium alginate (SA) nanofiber membranes were used as the backbone of PEO-based solid electrolytes. SA nanofiber membranes were prepared by electrospinning with assistance from PEO and cross-linked with calcium ions to construct a nanofiber network skeleton, which provided a guarantee for the stability of the subsequent electrolyte preparation process. The effects of spinning conditions and crosslinking time on the structure and performances of the nanofiber membranes were investigated. Meanwhile, the relationship between the skeleton of nanofiber membranes cross-linked with calcium ions and ion conductivity was investigated. The optimal parameters of the electrospinning process including concentration, voltage, distance, and SA content were discussed, and the fiber diameter and its distribution were analyzed. Furthermore, Fourier transform infrared (FTIR) spectrometer, thermal gravimetric analyzer analysis (TGA), X-ray diffraction (XRD), and energy dispersive spectrometer (EDS) maps were used to characterize the nanofiber membranes and electrolytes. The results showed that the thermal performance of cross-linked nanofiber membranes improved and the crystallinity of the PEO matrix decreased. The ion conductivity of the electrolytes was characterized by electrochemical impedance spectroscopy (EIS) testing, and the results showed that the assembled lithium symmetric battery had a good ion conductivity of 6.82 × 10−5 S/cm at 30 °C.

N-doped carbon nanoflakes coordinate with amorphous Fe to activate ozone for degradation of p-nitrophenol

Due to their high catalytic performance, metal nitrogen-doped carbon materials are widely used in the field of environmental restoration of polluted water but there is limited research on metal nitrogen doped carbon composite materials as ozone catalysts. Herein, we report the preparation of amorphous iron-coordinated nitrogen-doped carbon nanosheets as a catalyst for ozone by the coordination of Fe-metal ions at the end of phenol chain in the lignin network. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), powder X-ray diffraction (XRD) and element mapping were used to characterize the Fe/D-NC composite material and investigate its morphology and composition. Highly uniform distribution of iron species was found through characterization. By exploring the degradation performance of composite materials of Fe/D-NC-T (700，800，900 ℃) prepared at different temperatures, it was found that the optimal Fe/D-NC-800 could effectively degrade p-nitrophenol (PNP) within 30 min. Quenching experiments and ESR analysis showed that both free and non-free radicals (•OH, O2•− and 1O2) and intrinsic Lewis acid sites (LAS) of the composite material Fe/D-NC-800 were involved and responsible for the degradation of PNP. This work not only offers new platforms for catalytic ozonation and may drive the development of metal-lignin-based catalytic ozonation for effective water treatment but also opens new avenues toward lignin valorization and biomass economy.

Feedbacks between the formation of secondary minerals and the infiltration of fluids into the regolith of granitic rocks in different climatic zones (Chilean Coastal Cordillera)

Abstract. Subsurface fluid pathways and the climate-dependent infiltration of fluids into the subsurface jointly control the intensity and depth of mineral weathering reactions. The products of these weathering reactions (secondary minerals), such as Fe(III) oxyhydroxides and clay minerals, in turn exert a control on the subsurface fluid flow and hence on the development of weathering profiles. We explored the dependence of mineral transformations on climate during the weathering of granitic rocks in two 6 m deep weathering profiles in Mediterranean and humid climate zones along the Chilean Coastal Cordillera. We used geochemical and mineralogical methods such as (micro-) X-ray fluorescence (μ-XRF and XRF), oxalate and dithionite extractions, X-ray diffraction (XRD), and electron microprobe (EMP) mapping to elucidate the transformations involved during weathering. In the profile of the Mediterranean climate zone, we found a low weathering intensity affecting the profile down to 6 m depth. In the profile of the humid climate zone, we found a high weathering intensity. Based on our results, we propose mechanisms that can intensify the progression of weathering to depth. The most important is weathering-induced fracturing (WIF) by Fe(II) oxidation in biotite and precipitation of Fe(III) oxyhydroxides and by the swelling of interstratified smectitic clay minerals that promotes the formation of fluid pathways. We also propose mechanisms that mitigate the development of a deep weathering zone, like the precipitation of secondary minerals (e.g., clay minerals) and amorphous phases that can impede the subsurface fluid flow. We conclude that the depth and intensity of primary mineral weathering in the profile of the Mediterranean climate zone is significantly controlled by WIF. It generates a surface–subsurface connectivity that allows fluid infiltration to great depth and hence promotes a deep weathering zone. Moreover, the water supply to the subsurface is limited in the Mediterranean climate, and thus, most of the weathering profile is generally characterized by a low weathering intensity. The depth and intensity of weathering processes in the profile of the humid climate zone, on the other hand, are controlled by an intense formation of secondary minerals in the upper section of the weathering profile. This intense formation arises from pronounced dissolution of primary minerals due to the high water infiltration (high precipitation rate) into the subsurface. The secondary minerals, in turn, impede the infiltration of fluids to great depth and thus mitigate the intensity of primary mineral weathering at depth. These two settings illustrate that the depth and intensity of primary mineral weathering in the upper regolith are controlled by positive and negative feedbacks between the formation of secondary minerals and the infiltration of fluids.

Experimental and Modeling Optimization of Strontium Adsorption on Microbial Nanocellulose, Eco-friendly Approach

Green synthesized cellulose nanocrystals (CNCs) was prepared using Neurospora intermedia, characterized, and used to remove Strontium ions (Sr2+) from an aqueous solution with high efficiency. The characterization of CNCs was performed using a UV-Vis Spectrophotometer, Dynamic Light Scattering (DLS), Zeta Potential (ZP), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) mapping, EDX elemental analysis and BET surface analyzer. In this study, Response Surface Methodology (RSM) based on Box-Behnken Design (BBD) was successfully applied for the first time to optimize the dynamic adsorption conditions for the maximum removal of Sr2+ ions from aqueous solutions using CNCs as adsorbent. The effects of parameters, such as initial concentration of Sr2+ (50–500 ppm), adsorbent dosage (0.05–0.2 g/50ml), and contact time (15–120 min.) on removal efficiency were investigated. A mathematical model was studied to predict the removal performance. The significance and adequacy of the model were surveyed using the analysis of variance (ANOVA). The results showed that the second-order polynomial model is suitable for the prediction removal of Sr2+ with regression coefficient (R2 = 97.41%). The highest sorption capacity value of Sr2+ was obtained (281.89 mg/g) at the adsorbent dosage of 0.05 g/50 ml, contact time of 120 min., and the pollutant (Sr2+) concentration of 275 ppm.

Improved polarization retention in epitaxial BiFeO3 thin films induced by strain relaxation

This study investigated the impact of lattice mismatch strain (LMS) on the polarization retention of epitaxial ferroelectric BiFeO3 (BFO) thin films. The application of varying degrees of LMS on the BFO films was achieved by tuning the film thickness, which was verified through X-ray diffraction and reciprocal space mapping. As the strain was gradually eliminated, the film demonstrated a more saturated hysteresis loop with a reduced negative coercive electric field. Additionally, a significant increase in polarization retention was observed with increasing film thickness, strongly indicating the crucial role of LMS in driving the formation of preferred polarization, which is intimately connected with the built-in field induced by oxygen vacancies-relevant space charge alignment. Moreover, the anisotropic LMS state of the BFO films was utilized to horizontally reverse local polarization in a sub-micrometer scale, revealing that strain accelerates the back-switching of polarization to eliminate the artificially created ferroelastic domain walls. To counteract the strain effect, charge injection of electrons was proposed to enhance the retention of switched polarization by fully suppressing the built-in field and pinning the artificially created domain walls. The findings provide valuable insights into the impact of strain on polarization retention for the development of ferroelectric memories.

Formation of strain reduced In0.54Al0.34Ga0.12As layer of vertically coupled QDs arrays for O-band telecom single photon sources

We demonstrate the correlative research on the multi-stacked vertically coupled InAs quantum dots (VCQDs) capped by 15 nm combinational capping layer of In(0.21)Al(0.21)Ga(0.58)As and GaAs layer through Atom probe tomography (APT), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectroscopy (SIMS), High-Resolution X-Ray Diffraction (HRXRD) and Reciprocal Space Mapping (RSM). From the comparative studies, we observed a strain reduction of ∼ 2.3 ± 0.05% in the system, leading to the formation of strain-reduced (SR) In0.54Al0.34Ga0.12As layer with a lattice constant of 5.88 Å, which will work as a shielding layer. We found that the middle portion of the 3rd to 8th layer QDs structure was constant in size, shape, composition, and density, which enhances the carrier confinement in QDs. The computed strain energy values contributed to the overall growth structure of the 30 - layers VCQDs were recorded to be 2.2 meV/atoms. We report the detailed analogy of the in-out flow of In/Ga adatoms in the In0.54Al0.34Ga0.12As layer leading to the evolution of fully developed bigger InAs QDs size. To support the APT results, we also present the outcomes studies of the HRXRD Out-plane and In-Plane symmetric RSM experiment at (002), (004), and (006) reflections to investigate the compressive strain contribution in the SR In0.54Al0.34Ga0.12As shielding layer. This 30-layer VCQDs structure can be employed to fabricate high thermal stability operating at 1.3 µm O-band telecom Single Photon Sources (SPSs).

Room-temperature ferroelectric-like behavior in anatase TiO2 epitaxial films prepared by chemical solution deposition

Ferroelectrics of simple oxides have been of great interest due to they are easy to integrate with silicon semiconductors. The FE hysteresis loop was measured for the first time in pure anatase-phase titanium dioxide is reported, demonstrating that the ferroelectric-like behavior in a-TiO2 epitaxial thin films (7.5 nm to 228.8 nm) prepared by chemical solution deposition method on (001) SrTiO3 based substrates. Synchrotron based X-ray diffraction and reciprocal space mapping analysis prove that we have prepared high-quality epitaxial films. According to the results of the FE hysteresis loop, Pr can reach approximately 0.42 μC/cm2 in a-TiO2 film with a thickness of 14.5 nm. Furthermore, the PFM shows that the ferroelectric-like behavior is exhibited in a-TiO2 film of 7.5 nm and that the PFM polarization switch can be maintained for more than 100 min. All of these seem to indicate the presence of ferroelectric behavior in a-TiO2 films. We recognize that the origin of ferroelectric-like behavior is due to the distortion induced by strain and vacancy. However, since the polarization value is not very large and the PFM decays, the electrochemical effect has a non-negligible influence on the intrinsic ferroelectric performance.

In Vivo Assessment of the Calcium Salt-Forming Ability of a New Calcium Silicate-Based Intracanal Medicament: Bio-C Temp

Calcium salt precipitation induced by intracanal medicaments contributes to the formation of apical hard tissue during apexification. This study compared the calcium salt-forming ability of a new calcium silicate-based intracanal medicament (Bio-C Temp) with that of two commercial calcium hydroxide pastes (Calcipex Plane II and Vitapex) in a rat subcutaneous implantation model. Polytetrafluoroethylene tubes containing each of the three materials were subcutaneously implanted in 4-week-old male Wistar rats. After 28 days, the composition and amount of calcium salts formed at the material-tissue interface were assessed using micro-Raman spectroscopy, X-ray diffraction, and elemental mapping. The tested materials produced white precipitates that had Raman spectra with peaks corresponding to hydroxyapatite and calcite. X-ray diffraction detected hydroxyapatite formation on Calcipex Plane II and Vitapex implants, as well as calcite formation on all three materials. Elemental mapping revealed that Bio-C Temp generated significantly smaller calcium- and phosphorus-rich calcified regions within the subcutaneous connective tissue than Vitapex. These results indicate that Bio-C Temp produced less calcium salt in rat subcutaneous tissue than Vitapex, although all materials formed hydroxyapatite and calcite in rat subcutaneous tissue. Bio-C Temp could be less effective than Vitapex in promoting apical hard tissue formation during apexification.

Alloying Matters for Ordering: Synthesis of Highly Ordered PtCo Intermetallic Catalysts for Fuel Cells.

Porous carbon-supported atomically ordered intermetallic compounds (IMCs) are promising electrocatalysts in boosting oxygen reduction reaction (ORR) for fuel cell applications. However, the formation mechanism of IMC structures under high temperatures is poorly understood, which hampers the synthesis of highly ordered IMC catalysts with promoted ORR performance. Here, we employ high-temperature X-ray diffraction and energy-dispersive spectroscopic elemental mapping techniques to study the formation process of IMCs, by taking PtCo for example, in an industry-relevant impregnation synthesis. We find that high-temperature annealing is crucial in promoting the formation of alloy particles with a stoichiometric Co/Pt ratio, which in turn is the precondition for transforming the disordered alloys to ordered intermetallic structures at a relatively low temperature. Based on the findings, we accordingly synthesize highly ordered L10-type PtCo catalysts with a remarkable ORR performance in fuel cells.

Achieving exceptional wear resistance in a crack-free high-carbon tool steel fabricated by laser powder bed fusion without pre-heating

Laser powder bed fusion (LPBF) for the fabrication of dense components used for tooling applications, is highly challenging. Residual stresses, which evolve in the additively manufactured part, are inherent to LPBF processing. An additional stress contribution in high-carbon steels arises from the austenite-to-martensite phase transformation, which may eventually lead to cracking or even delamination. As an alternative to pre-heating the base plate, which is not striven by industry, lowering the martensite content which forms in the part, is essential for the fabrication of dense parts by LPBF of high-carbon tool steels which are then adapted to LPBF. In this study, a successful strategy demonstrates the processing of the Fe85Cr4Mo1V1W8C1 (wt%) high-carbon steel by LPBF into dense parts (99.8%). The hierarchical microstructure consists of austenitic and martensitic grains separated by elemental segregations in which nanoscopic carbide particles form a network. A high density of microsegregation was observed at the molten pool boundary ultimately forming a superstructure. The LPBF-fabricated steel shows a yield strength, ultimate compressive stress, and total strain of 1210 MPa, 3556 MPa, and 27.4%, respectively. The mechanical and wear performance is rated against the industrially employed and highly wear-resistant 1.2379 tool steel taken as the reference. Despite its lower macro-hardness, the LPBF steel (58.6 HRC, 0.0061 mm3 Nm–1) shows a higher wear resistance than the reference steel (62.6 HRC, 0.0078 mm3 Nm–1). This behavior results from the wear-induced formation of martensite in a microscale thick layer directly at the worn surface, as it was proven via high-energy X-ray diffraction mapping.

Flexible design in the stomatopod dactyl club.

The stomatopod is a fascinating animal that uses its weaponized appendage dactyl clubs for breaking mollusc shells. Dactyl clubs are a well studied example of biomineralized hierarchical structures. Most research has focused on the regions close to the action, namely the impact region and surface composed of chitin and apatite crystallites. Further away from the site of impact, the club has lower mineralization and more amorphous phases; these areas have not been as actively studied as their highly mineralized counterparts. This work focuses on the side of the club, in what is known as the periodic and striated regions. A combination of laboratory micro-computed tomography, synchrotron X-ray diffraction mapping and synchrotron X-ray fluorescence mapping has shown that the mineral in this region undergoes the transition from an amorphous to a crystalline phase in some, but not all, clubs. This means that this side region can be mineralized by either an amorphous phase, calcite crystallites or a mixture of both. It was found that when larger calcite crystallites form, they are organized (textured) with respect to the chitin present in this biocomposite. This suggests that chitin may serve as a template for crystallization when the side of the club is fully mineralized. Further, calcite crystallites were found to form as early as 1 week after moulting of the club. This suggests that the side of the club is designed with a significant safety margin that allows for a variety of phases, i.e. the club can function independently of whether the side region has a crystalline or amorphous mineral phase.

Coherent growth of β-(Al x Ga1−x )2O3 alloy thin films on (010) β-Ga2O3 substrates using mist CVD

Herein, we demonstrate β-(Al x Ga1−x )2O3 thin films that were coherently grown on a (010) β-Ga2O3 substrate using mist chemical vapor deposition (CVD). X-ray diffraction and reciprocal space mapping results revealed that the β-(Al x Ga1−x )2O3 thin films were of high-crystalline quality and were grown coherently to attain an Al content of 18.3% as measured by Rutherford backscattering spectroscopy. Importantly, based on their surface morphologies, the coherently grown β-(Al x Ga1−x )2O3 thin films have atomically flat surfaces. These results indicate that mist CVD is a promising technique for β-(Al x Ga1−x )2O3/β-Ga2O3 heterojunction devices.

Influence of oxygen on performance of multi-principal element alloy as braze filler for Ni-base alloys

In manufacturing of multi-principal element alloys (MPEAs), the casting process is often a primary point of oxygen introduction to the material system, which was demonstrated by the laboratory scale button arc-melting process. Oxygen introduction raises concerns for the mechanical performance of these alloys if employed as structural materials alone or in engineering applications, such as serving as filler materials to enable joining of similar or dissimilar alloy pairs that are conventionally considered difficult to join. In this work, oxide inclusions in an as-cast off-equiatomic MnFeCoNiCu MPEA and Ni-base alloy braze joints made with this MPEA were evaluated by synchrotron x-ray diffraction mapping and electron microscopy. MnO was found to be prevalent throughout the cast MPEA and was chemically reduced during brazing by trace Al from the base material, Ni-base Alloy 600. Incomplete reaction of the MnO with Al, and some alternative reaction with Cr, left a mixture of MnO, Al2O3, and Cr2O3 in the as-brazed joint, with the oxides concentrated near the braze centerline due to directional solidification. In the braze joints, the non-oxide constituent phases detected were an FCC matrix and particles of Cr23C6, Cr7C3, and TiN which are all native to Alloy 600. The evolution of oxides within the brazed joints at elevated service temperatures of 600–800 °C was also evaluated. While MnO and Al2O3 were stable during high-temperature service, Cr2O3 particles grew to several hundred microns, with dissolved oxygen in the MPEA providing a significant source for oxide growth. Comparing tensile performance of the as-brazed condition with post-service conditions showed that the evolution of oxide particles contributed to an increase in strength and decrease in ductility of the brazed joints. Evaluating particle morphologies among fracture surfaces of individual specimens demonstrated that large Cr2O3 particles and continuous cluster networks of Al2O3 were the features most detrimental to total elongation. Hence, unmitigated evolution of oxygen-containing species during brazing and service conditions is detrimental to the ductility of the brazed joints, which highlights the importance of oxygen control in initial manufacturing of MPEAs for engineering applications.

Zirconium hydride phase mapping in Zircaloy-2 cladding after delayed hydride cracking

Hydrogen uptake in zirconium alloys is a major limiting factor of nuclear fuel cladding as subsequent hydride precipitation can lead to potential cladding failure via delayed hydride cracking (DHC). The specific mechanisms of DHC have been a focus in earlier research, however there is still no clear definition of the resulting crystallography and limiting hydride sizes at various temperatures of crack propagation. In this work, a novel thermo-mechanical testing procedure was used to induce radially propagating DHC cracks in thin-walled cladding in a temperature range from 100 to 320 °C. Focused ion beam (FIB)- prepared lamellae were extracted from samples containing the arrested DHC crack for synchrotron micro-beam X-ray diffraction (µXRD) mapping of crystallographic phases. The µXRD phase maps provided information about the required hydride cluster size that would lead to fracture (less than 5 µm), i.e. the critical hydride size. Phase mapping shows that DHC-responsible hydrides primarily consist of the δ phase, with slightly increased ɣ/δ ratios at lower cracking temperatures. In multilayer cladding, the liner material shows significantly increased ratios of ɣ-hydride, while on average, the δ-phase remains predominant. This work also highlights that the ɣ-hydride is indeed a stable zirconium hydride phase, which can precipitate during DHC propagation and within the inner liner of multilayer cladding.

Plastic Deformation in a Molecular Crystal Enables a Piezoresistive Response.

Organic materials are promising candidates for the development of efficient sensors for many medicinal and materials science applications. Single crystals of a small molecule, 4-trifluoromethyl phenyl isothiocyanate (4CFNCS), exhibit plastic deformation when bent, twisted, or coiled. Synchrotron micro-focus X-ray diffraction mapping of the bent region of the crystal confirms the mechanism of deformation. The crystals are incorporated into a flexible piezoresistive sensor using a composite constituting PEDOT: PSS/4CFNCS, which shows an impressive performance at high-pressure ranges (sensitivity 0.08 kPa-1 above 44kPa).

Introducing a bionanocomposite (Ultrasound-assisted synthesis of Ag nanoparticles embedded Aloe vera gel) for the treatment of cervical carcinoma

Regarding applied, facile, green chemical research, a bio-inspired approach is being reported for the sonochemical synthesis of Ag nanoparticles by Aloe vera gel extract as a natural reducing/stabilising and solid support agent without using any toxic and harmful reagent. The biosynthesized Ag NPs/A. vera gel bionanocomposite was characterised by advanced physicochemical techniques like ultraviolet-visible (UV–Vis), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD) and elemental mapping study. It has been established that Aloe vera gel-stabilized silver nanoparticles have a spherical shape with a mean diameter of around 35–40 nm. To investigate the antioxidant potentials of Ag NPs/A. vera gel, one of the common antioxidant techniques i.e. DPPH was used. The results of DPPH test proved the excellent antioxidant properties of Ag NPs/A. vera gel in comparison to the positive control used i.e. butylated hydroxytoluene. The IC50 of Ag NPs/A. vera gel was 42 µg/mL in the antioxidant test. Thereafter, on having a significant IC50 value in radical scavenging assay, we extended the bio-application of the desired nanocomposite in the anticancer study. To survey the cytotoxicity and anti-human cervical carcinoma effects of Ag NPs/A. vera gel, MTT assay was used on CC1-PI19, SiHa, HeLa and HNCF-PI52 cell lines. The IC50 of the Ag NPs/A. vera gel was 16, 13, 15 and 11 µg/mL against CC1-PI19, SiHa, HeLa and HNCF-PI52 cell lines, respectively. As mentioned, the Ag NPs/A. vera gel had significant antioxidant and anti-human cervical cancer effects. After approving the above results in the clinical trial studies, the Ag NPs/A. vera gel can be used as a chemotherapeutic drug for the treatment of several types of cervical cancers. According to the above results, the significant anti-cervical cancer effects of Ag NPs/A. vera gel are confirmed.

Core-shell Au@MIL-100 (Fe) as an enhanced substrate for flunixin meglumine ultra-sensitive detection

This study aimed to develop and validate a simple and efficient surface-enhanced Raman spectroscopy (SERS) method to determine flunixin meglumine (FM) residues in animal tissues through using core-shell Au@MIL-100 (Fe) as enhanced substrate. Au@MIL-100 (Fe) composite material was synthesized by coating metal-organic framework materials (MOFs) on the surface of gold nanoparticles using the solvothermal method. Transmission electron microscopy (TEM), UV–vis spectrum, SERS spectrum, X-ray diffraction (XRD), Infrared spectrum (FT-IR), and EDX elemental mapping results revealed that the structural composition of the compound has good properties with localized surface plasmon resonance (LSPR) properties, high adsorption capacity, excellent SERS sensitivity and stability. When it was used as SERS substrate, the results of quantitative analysis of FM in pork showed a linear range of 0.10–50 mg·L−1 with a correlation coefficient (R2) of 0.9819, the limit of detection (LOD) of 0.15 mg·g−1, the recovery rate of 88.94%∼104.77%, the intra- and inter- batch relative standard deviation (RSD) of 3.57%∼14.22% and 0.18%∼3.44% respectively. Further verification results of the existing standard methods showed no significant difference between the SERS and UV methods (P < 0.05), as well as demonstrating that the SERS method has optimal precision, accuracy, and practicality. These results exposed that Au@MIL-100 (Fe) as a SERS substrate has great potential in rapid and on-site detection analysis.

Understanding the Impact of Microporous Layer Cracks on Pt Catalyst Degradation

As the need for more flexible utilization of renewable energy sources increases, the uses of clean hydrogen and fuel cells are pursued by governments worldwide due to high gravimetric energy density of hydrogen. Polymer electrolyte fuel cells (PEFCs) have demonstrated great potential in passenger light-duty vehicles (LDVs), and their applications in heavy-duty vehicles (HDVs) have recently attracted significant attention due to their unique scalability1. Currently, the micro porous layer (MPL), the side of the gas diffusion layer that faces the catalyst layer in the membrane electrode assembly (MEA), is known to improve the performance of PEFCs at high current densities due to better heat, water management, and electron transport. And there has been an ongoing debate whether changes in water management through having cracks in the MPL will improve the durability of the catalyst. Cracks in the MPL are advantageous as they can facilitate removal of liquid water from the catalyst layer. However, too many cracks can result in poor contact between the MPL and the MEA2. Cracks can also pool water and block oxygen transport.In this study, electrocatalyst accelerated stress tests (ASTs) were performed on the MEAs prepared using MPLs with different density and configuration of cracks. The ASTs had a total of 90 000 cycles, with electrochemical characterization performed at beginning of life, after 10 000, 30 000, 60 000 and 90 000 (end of life). Each cycle consisted of potential cycling between 0.6 V to 0.9 V, with 3 seconds hold time for each. The effect of cracks in MPLs on electrocatalyst degradation was evaluated in both nitrogen (non-reactive) and air (reactive) gas environments at 100% relative humidity, 80oC, and 150 kPa backpressure. In-situ electrochemical characterization and extensive physical characterization was performed to understand the subtle differences in electrocatalyst degradation correlated to the use of crack-free and cracked MPLs. In particular, micro-X-ray fluorescence (XRF) map of identical locations before and after the AST were employed to study in-plane movement of Pt loading over the course of AST. Micro x-ray diffraction (XRD) maps were collected on the MEAs to correlate Pt loadings to Pt particle size distribution.The polarization curves, Tafel plots, and electrochemical surface area (ECSA) for MEAs with and without cracks in the MPLs all demonstrated similar trends in the cells’ durability, revealing that cracks in the MPLs do not significantly affect the performance of the cell at the beginning and also at the end of life. However, the XRF identical location maps showed significant in-plane movement of Pt over the course of the AST: decrease of Pt loading in the mapped region closer to the gas inlet and increase of Pt loading closer to the gas outlet. Moreover, higher degree of cracking was observed at the cell outlet after the AST, indicating that the catalyst layer mechanical aging is not homogeneous.

Soil crusting: New insight from synchrotron 2D micro X-ray diffraction mapping of clay-particle orientation and mineralogy

Our understanding of soil crusting and its detrimental consequences is mainly based on the analysis of morphological changes occurring at the soil surface. Such changes are usually assessed at spatial scales ranging from a few millimeters to that of the field. The inner-reorganisation within the topsoil during soil crusting primarily involves the redistribution of clay particles. Their mineralogy and arrangement remain however delicate to determine by the sole use of microscope observations. To overcome these limitations, we developed an innovative methodology based on synchrotron 2D micro X-ray diffraction (2D-µXRD) to map relevant parameters related to the organisation of all types of soil clay minerals, i.e. relative diffracted intensities, degree of preferential orientation, mean deviation angle from the surface. Our methodological strategy was first validated on a laboratory-made model sample, composed of various pure clay phases with clear preferential orientations. Then, a vertical section of soil crust from long-term bare fallow (LTBF) experiment of the France's National Research Institute for Agriculture, Food and Environment (INRAE, Versailles, France) was studied. Micromorphological features of the soil crust were first described by using conventional scanning electron microscopy. Synchrotron 2D-µXRD analyses were then successfully applied on the same region of interest. The in-depth analysis provided by the synchrotron 2D-µXRD approach revealed the presence of clay microlayers that were not observed on SEM images. Additionally, clay mineralogy as well as preferred clay-particle orientation and overall alignment highlighted specific quantitative structural signatures. These signatures involved the discrimination between clay microlayers associated to the settling of clay particles in microdepressions and clayey microaggregates resulting from transportation of pre-existing soil crusts. This new technique has led to re-interpretation of the deposition mechanisms in the natural soil investigated here and opens wide perspectives for in-depth detailed characterization of clay mineralogy in soil crusts.

Destruction of mesoscopic chemically modulated domains in single phase high entropy alloy via plastic deformation

Chemically modulated mesoscopic domains in a fcc single phase CrMnFeCoNi equi-atomic high entropy alloy (HEA) are detected by small angle diffraction performed at a synchrotron radiation facility, whereas the mesoscopic domains cannot be detected by conventional X-ray diffraction and 2D mappings of energy dispersive X-ray spectroscopy by scanning electron microscopy and scanning transmission electron microscopy. The mesoscopic domains are deformed and shrieked, and finally destructed by plastic deformation, which is supported by the comprehensive observations/measurements, such as electrical resistivity, Vickers hardness, electron backscattering diffraction, and hard X-ray photoemission spectroscopy. The destruction of the mesoscopic domains causes the decrease in electrical resistivity via plastic deformation, so called K-effect, which is completely opposite to the normal trend of metals. We confirmed that the presence and the size of local chemical ordering or short-range order domains in the single phased HEA, and furthermore, Cr and Mn are related to form the domains.