High-energy X-ray Research Articles

Stress Measurement of Stainless Steel Piping Welds by Complementary Use of High-Energy Synchrotron X-rays and Neutrons

Probabilistic fracture mechanics (PFM) is increasingly recognized as a viable approach for evaluating the structural integrity of nuclear components, such as piping, primarily affected by stress corrosion cracking (SCC). PFM analysis requires several input parameters, among which welding residual stress is critically important due to its significant influence on SCC initiation and propagation. Recently, a novel technique involving a double-exposure method (DEM) utilizing synchrotron X-rays was introduced as an effective means for measuring welding residual stress with high spatial resolution. In this paper, we applied DEM to assess the residual stress of a plate specimen, which was extracted from a welded pipe through electrical discharge machining. Consequently, detailed stress maps under a plane stress state were generated. Additionally, the residual stress distributions in the welded pipe under a triaxial stress state were evaluated using neutron diffraction. Based on these findings, we proposed a methodology to acquire detailed stress maps of welded pipes by combining high-energy synchrotron X-rays and neutron diffraction.

Stability of the Fe3O4 (√2 x √2)R 45° Surface in 0.1 M NaOH Investigated by High-Energy Surface X-Ray Diffraction

Transition metal oxides, especially Fe, Co, and Ni oxides, are of great interest as electrocatalysts for the oxygen evolution reaction (OER) in alkaline solution. However, detailed data on the atomic-scale oxide-electrolyte interface structure of these systems are rare. We present studies of a model oxide electrocatalyst, -reconstructed Fe3O4(001). This oxide surface has been extensively investigated under ultrahigh vacuum (UHV) conditions, leading to a detailed understanding of its atomic structure [2]. In previous in situ surface X-ray diffraction studies, we demonstrated that the reconstructed surface can survive transfer into electrochemical environment and determined the stability of the reconstruction as a function of potential [2]. Specifically, we showed that the ()R45° reconstructed Fe3O4(001) surface can be transferred into 0.1 M NaOH at 0.2 V vs. Ag/AgCl while maintaining surface structure and that the reconstruction is irreversibly lifted at sufficiently negative potentials.Here, we present more detailed in situ studies of this system, using the novel technique of High-Energy Surface X-Ray Diffraction (HESXRD) [3,4]. This technique enabled us to measure rapidly a huge reciprocal space volume, which allows to obtain very large sets of crystal truncation rods (CTRs) that can be analysed by surface crystallographic methods. These data provide detailed insights into the temporal stability of the surface at fixed potentials as well as potential-dependent changes in surface structure.In the experiments the Fe3O4(001) single crystal samples were prepared by sputtering and annealing in UHV, followed by sample transfer into the hanging-meniscus cell employed for the HESXRD studies. A new experimental procedure allowed to reduce the time of sample transfer and establishment of potential control to below one minute.The in situ HESXRD measurements were performed at beamline P21.2 of PETRA III at DESY. 7 symmetrically independent CTRs and 2 ()R45° fractional order rods could be measured. These data enabled detailed comparison of the oxide-electrolyte interface with the surface structure under UHV conditions [1]. The potential-dependent data indicate clear structural changes when applying more positive or more negative potentials than 0.2 V vs. Ag/AgCl, as illustrated in part A and B of Fig. 1. However, all surface structures were stable at constant potential over several hours, as indicated in part C of Fig. 1. The quality of the obtained results allows to determine quantitative analysis of the interface structure. First results of this analysis will be presented.We gratefully acknowledge financial support by the German ministry of Science and Education (BMBF) via projects 05K19FK3 and 05K22FK1.

Temperature Dependent Operando High Energy Surface X-Ray Diffraction Studies of Pt(111) Oxidation

Platinum electrocatalysts are still widely used as cathode material in proton-exchange membrane fuel cells (PEMFC) because of their high ORR activity. However, their long-term stability is limited due to degradation processes. This degradation is partly caused by Pt oxidation and oxide reduction, which lead to irreversible surface restructuring and subsequently Pt dissolution. To increase the lifetime of PEMFCs it is mandatory to understand the mechanisms behind the degradation on an atomistic level. This requires studies by structure sensitive in situ methods, in particular, also studies at the elevated temperatures typically employed in PEMFCs operation.Previous studies revealed that in the initial stage of oxide formation Pt atoms are extracted out of the surface and form an ultra-thin oxide layer directly above the surface. This extraction is long known as place exchange [1], but the atomic-scale details of the surface oxide structure, the extraction mechanism, and especially the kinetics of the initial oxide growth were only recently clarified [2-7]. It was found that the structural arrangement of the Pt atoms within the surface oxide on the Pt(111) and the Pt(100) surface is distinctly different, leading to differences in the oxidation/reduction kinetics, the reversibility of the surface oxidation/reduction process, and the amount of Pt dissolution into the electrolyte.Recently, we performed fast operando high-energy surface X-ray diffraction (HESXRD) studies, in which we investigated the initial extraction of Pt atoms on Pt(111) during potential cycles. Surprisingly, it was found that the Pt extraction during the anodic sweep is largely independent of the potential sweep rate, although the peak cyclic voltammograms (CVs) associated with the charge transfer during surface oxidation showed a pronounced shift [7-9]. This suggests that the Pt extraction is a fast process, rather driven by potential and not directly coupled to the slow formation of surface oxygen species. However, the Pt extraction during the anodic sweep and the re-insertion during the cathodic sweep still exhibit significant hysteresis, indicating a complex multistep oxidation kinetics.Previous electrochemical studies of Pt(111) electrodes revealed that the described influence of oxidation/reduction kinetics and the reversibility of the charge transfer processes increase at elevated temperature [10]. However, the temperature dependence of the Pt extraction behavior is currently unknown, because all previous structural studies of oxide growth and reduction have been performed exclusively at room temperature.For the experiments at elevated temperatures we developed a new setup for HESXRD studies of single crystals, which combines a hanging meniscus electrochemical cell for operando X-ray diffraction measurements with an inductive heating device in a joint Ar-filled compartment. This setup allows direct (re-)preparation of the aligned Pt single crystals on the diffractometer. By this, the time between preparation and measurement is reduced down to a few minutes and sample transfer through air is rigorously avoided.Temperature-dependent HESXRD measurements at temperatures up to 343 K were performed at beamline ID31 of the European Synchrotron Radiation Facility. The simultaneously measured electrochemical current and X-ray intensity indicate kinetic shifts in the charge transfer but a rather temperature independent Pt extraction process.We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft via project no. 418603497 and the BMBF via 05K19FK3 and 05K22FK1.

Reveling the orientation preference along with localized Lüders-type deformation in polycrystalline NiTi SMA by in-situ synchrotron-based high energy X-ray diffraction

The stress-induced martensite transformations (SIMTs) in near-equiatomic NiTi shape memory alloys (SMAs) predominantly occur through localized, inhomogeneous, and intense Lüders-type mechanisms, which significantly influence the recoverable strain and mechanical response of the material. An in-depth understanding of the propagation manner and orientation preference of SIMTs is therefore crucial. In this study, we present a unique asymmetric anisotropy of SIMTs and lattice strains induced by Lüders-type deformation in polycrystalline NiTi, achieved through a combination of in-situ synchrotron X-ray diffraction and uniaxial tensile loading experiments. Our experimental findings reveal that in polycrystalline NiTi under uniaxial tensile loading, the austenite with the favored orientation of ⟨110⟩A//loading direction (LD) is consumed faster compared to other orientations, resulting in residual austenite with an orientation of ⟨431⟩//LD within the Lüders banding area. In contrast, the high-strain residual austenite with few favored orientations transforms fairly slowly and remains well beyond the transformational plateau. Our work provides valuable new insights into the microstructural nature of the Lüders-type deformation mechanism of polycrystalline NiTi, and the enhanced understanding of these complex interactions holds promise for optimizing the performance and design of SMAs in practical applications.

Non-Ambient in-Operando X-Ray Diffraction Study of Li-Ion Batteries on Laboratory Diffractometers

A long outstanding issue when pushing the performance of batteries is the degradation during cycling. Understanding the pertinent mechanisms becomes increasingly significant to tackle them and consequently facilitate the discovery of high-performance batteries that meet the requirements for multiple applications. In operando X-ray diffraction (XRD) is a non-destructive technique which can be used to study the non-equilibrium states of a complete battery cell during cycling by essentially tracing the structure changes. In this talk, we will showcase how high-quality XRD data of Li-ion batteries can be quickly collected and analysed during charge-discharge cycles in transmission geometry on the laboratory diffractometer equipped with an X-ray tube with Ag or Mo anode and an area detector optimized for high energy X-rays. Temperature effects on the performance and life of batteries will be discussed based on the temperature-dependent XRD data collected during the charge-discharge cycling of batteries. Quantification of the structural changes from both cathode and anode materials can be done to essentially understand the structure-property relationship of a complete battery cell.

Effect of Asymmetrically Reinforced Membrane on Anion Exchange Membrane Fuel Cell

Anion Exchange Membrane Fuel Cells (AEMFCs) is promising for the generation of electric power from hydrogen, with the expected possible replacement of precious metal catalysts by Earth abundant ones.[1-2] Beyond the independent properties of core materials (AEM, anode and cathode catalysts), the water management during operation is key to achieving high power density, but also high longevity. Thin AEMs are critical to achieve high AEMFC power performance, as the back-diffusion of water from anode to cathode critically helps to mitigate anode flooding. [3] Due to the high swelling of hydrated AEMs, good mechanical durability of thin AEMs however typically requires the introduction of a reinforcement, often a porous polytetrafluoroethylene (PTFE) membrane filled with the anion exchange ionomer.Here, we investigated the structure of different commercial AEMs and their behavior in operating AEMFC. We identified that the position of the reinforced layer (PTFE or other) strongly differs from one type of AEM to another. In the case of strongly asymmetric through-plane position of the PTFE layer (Fig. 1a), the positioning of the PTFE reinforcement close to anode or to cathode has a significant impact on initial power performance (Fig. 1b). A better performance and improved stability was observed with the PTFE layer close to the anode, suggesting that the asymmetric structure can improve the water management in such configuration. The presentation will discuss the results obtained on different commercial AEMs, and whether the asymmetric structure of AEM can be combined with PTFE hydrophobized anodes for even improved performance. The effect of the reinforcement position on the water management was also studied operando by two techniques. With high energy X-ray diffraction technique on an AEMFC under current load, the water distribution profile across the MEA thickness could be obtained from phase deconvolution analysis. With the use of relative humidity sensors at the outlet of anode and cathode of a regular AEMFC setup, [4] the water balance at a given current load could be established and compared for the two different positionings of reinforced AEM.The results shed light on the importance of identifying the position of PTFE reinforcement in commercial or in-house AEM for AEMFC application, with potential implications also for AEM electrolyzers or water-CO2 co-electrolyzers.

The High Energy X-ray Probe (HEX-P): supernova remnants, pulsar wind nebulae, and nuclear astrophysics

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10″ full width at half maximum) and broad spectral coverage (0.2–80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. HEX-P is ideally suited to address important problems in the physics and astrophysics of supernova remnants (SNRs) and pulsar wind nebulae (PWNe). For shell SNRs, HEX-P can greatly improve our understanding via more accurate spectral characterization and localization of non-thermal X-ray emission from both non-thermal-dominated SNRs and those containing both thermal and non-thermal components, and can discover previously unknown non-thermal components in SNRs. Multi-epoch HEX-P observations of several young SNRs (e.g., Cas A and Tycho) are expected to detect year-scale variabilities of X-ray filaments and knots, thus enabling us to determine fundamental parameters related to diffusive shock acceleration, such as local magnetic field strengths and maximum electron energies. For PWNe, HEX-P will provide spatially-resolved, broadband X-ray spectral data separately from their pulsar emission, allowing us to study how particle acceleration, cooling, and propagation operate in different evolution stages of PWNe. HEX-P is also poised to make unique and significant contributions to nuclear astrophysics of Galactic radioactive sources by improving detections of, or limits on, 44Ti in the youngest SNRs and by potentially discovering rare nuclear lines as evidence of double neutron star mergers. Throughout the paper, we present simulations of each class of objects, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of SNRs, PWNe, and nuclear astrophysics.

Li2s-PI3 Cathode for High-Energy-Density All-Solid-State Lithium-Sulfur Batteries

1.Introduction All-solid-state lithium-sulfur batteries (ASSLSBs) are one of the most promising next-generation large scale energy storage devices due to their remarkably high theoretical energy density, which is generated by high capacity of both cathodes, like element S or Li2S and Li metal anode. However, due to insufficient electronic and/or ionic conductivities of element S and Li2S, the low sulfur utilization and correspondingly unsatisfied practical energy density hinder the application of ASSLSBs largely. By heterovalent doping, vacancies in Li2S could be created, leading to higher ionic conductivity [1-2]. In this study, we developed different proportion of PI3-doping Li2S as active material to improve the sulfur utilization. Mixing with CNovel as electronic additive, Li2S-PI3-CNovel as cathode material shows good electrochemical performance. In order to clarify the effect of doping PI3, a detailed analysis of the point defect structure was performed using pair distribution function analysis using high-energy X-ray diffraction, synchrotron X-ray diffraction measurements, and X-ray absorption measurements to correlate with the electrochemical properties. 2. Experimental Li2S-PI3 as active material was synthesized by mixing Li2S and PI3 as raw materials with ball milling method and the proportion of raw materials has been optimized. The characterization of the prepared Li2S-PI3 was conducted by Synchrotron XRD coupled with pair Distribution Function analysis. The ionic conductivities were measured by AC impedance. The cathode materials were prepared based on active materials (90 wt%) and CNovel (10 wt%) as electronic conductor. The batteries composed of Li2S-PI3-CNovel as cathode, Li3PS4 as SSE and Li-In alloy as anode were assembled in the glove box filled with Ar atmosphere. The charge-discharge curves were obtained by galvanostatic measurement. The electronic structure and morphology of the Li2S-PI3-CNovel after electrochemical measurements were examined by X-ray Absorption Spectroscopy (XAS) for S K-edge, P K-edge, and I K-edge. 3.Results and Discussion Pair distribution function (PDF) analysis revealed that with PI3 doping, iodine atoms would occupy sulfur sites and phosphorous atoms would occupy lithium sites, creating lithium vacancies in the antifluorite structure. Figure 1 shows the charge/discharge curves of the Li2S-PI3-CNovel as cathode. The Li2S-PI3-CNovel cathode shows a charge capacity of 440 mAh g-1 and a discharge capacity of 494 mAh g-1 in the first cycle. And the capacities increase to 538 mAh g-1 during the subsequent cycles, with an average voltage of 1.81 V (vs Li/Li+). Even at 1 C (1 C=626 mAh g-1), the cathode without solid-state electrolyte could deliver 207 mAh g-1, corresponding to 38 % capacity retention of that at 0.05 C, which demonstrates good rate performance (Figure 2). The charge compensation is attributed to S, suggesting the conversion reaction between Li2S and element S, which was confirmed by XAS for S K-edge and P K-edge. References H Gamo.et al., Adv. 2022, 3, 2488-2494.NHH Phuc. et al., Energy Res., 2021, 8, 606023. Acknowledgement This research was financially supported by JST ALCA-SPRING Project. Figure 1

A Scalable Approach to Synthesize Cobalt-Free LNMO Cathode Materials for High Energy Density Lithium Ion Batteries

The rapid growing demand for electric vehicles (EVs) has highlighted the need for high-energy-density batteries. The cathode material plays a vital role in achieving this goal[1]. As the limitations of cathode capacity improvement are approached, the pursuit for high-voltage materials becomes a viable option[2]. Lithium nickel manganese oxide LNMO (LiNi0.5Mn1.5O4) stands out due to its remarkable attributes including a substantial reversible capacity, excellent thermal stability, cost-effectiveness, environmental friendliness, and a high energy density[3]. Moreover, its cobalt-free composition aligns with sustainability objectives. Despite extensive research, the large-scale production and deployment of LNMO remain formidable challenges.In this study an industrially applicable co-precipitation method-based scalable synthesis strategy is introduced. The LNMO spheres with controlled various sizes and morphologies were successfully fabricated by adjusting the pH environment during synthesis carefully (Fig. 1A). Scanning electron microscopy (SEM) revealed the presence of uniformly spherical particles with dimensions of appr. 6, 9, and 14 µm and unique morphological characteristics (Fig. 1Ad-f). Synchrotron X-ray diffraction (SXRD) of LNMO samples revealed a deviation from the optimal Ni-to-Mn ratio of 1:3 (Fig. 1B)[4,5]. This variation results from the pH-dependent metal ion precipitation dynamics during synthesis, introducing a fascinating dimension to LNMO material fabrication. As potential cathode materials for lithium-ion batteries, these samples underwent a thorough electrochemical evaluation as part of our research. Among the synthesized LNMO samples, LNMO-9 demonstrated the most promising specific capacity, surpassing approximately 138 mAh/g and working under high voltage of 4.75 V (Fig. 1C). Furthermore, the characterizations of the materials were also thoroughly investigated by a variety of advanced characterization techniques, including Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM).This research reveals a strategy for synthesizing LNMO materials with certain regulated features and presents a successful strategy for industrial manufacturing as well. Particularly in the context of the EV industry, this research acquires critical significance in answering the growing demand for high-performance, sustainable energy storage systems. Fig. 1 (A) Illustration of the synthesis process of LNMO-x samples with SEM images of (a‒c) NiMn-x precursors and (d‒f) LNMO-x products. (B) SXRD patterns with Rietveld refinements and (C) charge/discharge profile of LNMO-x samples. Reference [1] H.-H. Ryu, G.-C. Kang, R. Ismoyojati, G.-T. Park, F. Maglia, Y.-K. Sun, Intrinsic weaknesses of Co-free Ni–Mn layered cathodes for electric vehicles, Materials Today. (2022) S1369702122000645. https://doi.org/10.1016/j.mattod.2022.03.005.[2] T. Liu, A. Dai, J. Lu, Y. Yuan, Y. Xiao, L. Yu, M. Li, J. Gim, L. Ma, J. Liu, C. Zhan, L. Li, J. Zheng, Y. Ren, T. Wu, R. Shahbazian-Yassar, J. Wen, F. Pan, K. Amine, Correlation between manganese dissolution and dynamic phase stability in spinel-based lithium-ion battery, Nat Commun. 10 (2019) 4721. https://doi.org/10.1038/s41467-019-12626-3.[3] Y. Xue, L.-L. Zheng, J. Wang, J.-G. Zhou, F.-D. Yu, G.-J. Zhou, Z.-B. Wang, Improving Electrochemical Performance of High-Voltage Spinel LiNi 0.5 Mn 1.5 O 4 Cathode by Cobalt Surface Modification, ACS Appl. Energy Mater. 2 (2019) 2982–2989. https://doi.org/10.1021/acsaem.9b00564.[4] A. Gomez, G. Dina, S. Kycia, The high-energy x-ray diffraction and scattering beamline at the Canadian Light Source, Review of Scientific Instruments. 89 (2018) 063301. https://doi.org/10.1063/1.5017613.[5] H.M. Rietveld, A profile refinement method for nuclear and magnetic structures, J Appl Crystallogr. 2 (1969) 65–71. https://doi.org/10.1107/S0021889869006558. Figure 1

(Digital Presentation) Operando x-Ray Fluorescence Spectroscopic Study of in-Plane Cerium-Ion Radical Quencher Distribution in Polymer Electrolyte Membranes

One of the challenges for the widespread use of polymer electrolyte fuel cells (PEFCs) is the suppression of chemical degradation in polymer electrolyte membrane (PEM). This degradation is caused by radical species generated due to the reaction of hydrogen peroxide with impurities in the PEM during PEFC operation. One way to suppress the chemical degradation is to add cerium ions to the PEM as radical quencher, 1) which absorbs the radicals through a redox reaction, thereby suppressing PEM degradation caused by radicals. However, it is known that cerium ions move in the in-plane direction due to the humidity and potential distribution, where the depletion of cerium ions causes PEM degradation.2) Therefore, it is required to elucidate the mechanism of cerium ion transport phenomena in the in-plane direction under PEFC operating conditions. High-energy X-ray fluorescence spectroscopy enables operando measurements of cerium distribution by taking advantage of penetration into the fuel cell inside.3) In this study, we have developed operando measurement cells that can observe the distribution phenomenon of cerium ions by using X-ray fluorescence spectroscopy while controlling the humidity gradient in the in-plane direction. Using the developed method, we analyze the cerium ion transport phenomena under the humidity gradient in the membrane electrode assembly (MEA). For the operando X-ray fluorescence measurements, end-plates with an X-ray transmission window and two gas inlets were used to control two different humidity conditions in the PEM. X-ray was incident at 90 degrees from the MEA plane, and a germanium solid-state detector was positioned perpendicular to the incident X-rays to acquire Ce-Ka fluorescence X-ray from the MEA. The catalyst coated membranes composed of a perfluorosulfonic acid-based cation exchange membrane with cerium-ion substitution, coated with a platinum catalyst layer were used. Operando X-ray fluorescence measurements were performed at BL37XU at SPring-8 (Japan). X-rays with incident energy ranging from 40 to 65 keV were used to scan the cell position and detect Ce-Ka fluorescence X-ray. The cell temperature was set at 60°C. Cerium ions in the MEA were found to migrate from the high humidity side to the low humidity side within a range of millimeters in approximately one hour. The migrated cerium ions tended to diffuse into homogeneous state within in a few hours under the uniform humidity condition. Acknowledgments The authors would like to thank M. Toida (Toyota Motor Corporation) for providing samples and for in-depth discussions. References 1) Endoh, ECS Trans., 16, 1229 (2008).2) Y-H. Lai, K. Rahmoeller, J. Hurst, R. Kukreja, M. Atwan, A. Maslyn and C. Gittleman, Electrochem. Soc., 165, F3217 (2018).3) Y. Orikasa, A. Takezawa, K. Amemiya, Y. Tsuji, T. Asaoka, M. Ohki, O. Sekizawa, and K. Nitta, ECS Trans., 109, 109 (2022).

Deterioration of 3D printed multicomponent radiotherapy dosimetry phantom’s properties upon high energy irradiation

Accuracy and realization of the prescribed dose in radiotherapy is one of the crucial ways to ensure the quality of the treatment, which usually is closely related to the use of different types of phantoms. Nowadays 3D printing technology is a promising methodology for the fabrication of phantoms, mimicking different biological tissues. Therefore, analysis of the structural properties of materials and their deterioration due to the irradiation is an important issue. This study is aimed to assess radiation-induced changes of the physical and mechanical properties of 3D printed materials used in the construction of the advanced multicomponent dosimetry phantom for radiotherapy when high energy (6 MeV) X-ray photons were applied for irradiation. Irradiation dose of 70 Gy, representing total dose delivered to the target during the whole treatment procedure prescribed for a patient was applied. Composites filaments with TiO2 additive were extruded using a 3D Devo filament extruder and experimental samples were printed using 3D printer Zortrax M300. Attenuation properties of the samples were simulated using the XCOM database, while mechanical tests were performed using the ElectroPuls® E10000 Linear-Torsion machine. It was observed that 6 MeV photons irradiation of the investigated composites (polyethylene terephthalate glycol (PETG), Polylactic acid (PLA), High Impact Polystyrene (HIPS), ULTRAT ABS and GLASS) and PLA containing various concentrations of TiO2 additives (0 %, 0.5 %, 1.0 % and 2.0 %)) has not induce d significant deterioration of samples’ attenuation and mechanical properties, indicating variations within interval of 5 % − 10 %. However, performed investigation also revealed some improvement of structural and mechanical properties of 3D printed PLA composites with incorporated TiO2.

Unraveling the formation of L12 nano-precipitates within the FCC-phase in AlCoCrFeNi2.1 eutectic high entropy alloy

The present study investigates the formation mechanism of L12 nano-precipitates within the FCC phase during the solidification process of the AlCoCrFeNi2.1 eutectic high entropy alloy. For this purpose, advanced characterization techniques, including high-energy synchrotron X-ray diffraction, transmission electron microscopy, and atom probe tomography were employed, along with CALPHAD calculations. The solidified microstructure of the AlCoCrFeNi2.1 eutectic high entropy alloy consists of five phases: disordered FCC, disordered BCC, ordered B2 BCC, ordered L12 FCC, and sigma (σ). The dendritic regions of the disordered FCC phase were formed due to non-equilibrium solidification, while the L12 nano-precipitates were uniformly embedded within the disordered FCC matrix. These nano-precipitates were enriched with Al and Ni, while being depleted in Co, Cr, and Fe. These nano-precipitates might form around the critical temperature of 600 °C due to short-range diffusion of Al and Ni because of nucleation and growth mechanism during the solidification process.

Impact of interatomic structural characteristics of aluminosilicate hydrate on the mechanical properties of metakaolin-based geopolymer

This study explores the influence of the interatomic structure of sodium aluminosilicate hydrate (N-A-S-H) with varying silica contents on the mechanical properties of metakaolin-based geopolymer. Geopolymer pastes comprising Si/Al ratios between 2.0 and 3.0 were synthesized. A larger number of Si-O-Si linkages compared to Si-O-Al linkages and a higher atomic number density were found in the geopolymers with higher silica contents, which enhanced the compressive strength of the geopolymer pastes up to the optimal Si/Al ratio of 2.5. The paste with a Si/Al = 2.5 exhibited a greater portion of Q4(1Al and 2Al) and denser morphology compared to the other geopolymer pastes. Furthermore, in-situ high-energy synchrotron X-ray scattering experiments were conducted to assess the elastic modulus of the aluminosilicate structure at a local atomic scale. The modulus value in real space decreases with increasing silica contents up to Si/Al = 2.5 and increases with the presence of excessive unreacted silica fume. The modulus value in reciprocal space for the axial and lateral directions both presented a positive value at the geopolymer comprising a Si/Al ratio higher than 2.5, indicating that the load-bearing property of N-A-S-H changed at higher Si/Al ratios. Moreover, the smallest difference between the strains along the axial and lateral directions was detected for the geopolymer with Si/Al = 2.5 in both the real and reciprocal space, owing to the most interconnected and flexible nanostructure, which led to the highest mechanical strength.

Deciphering the glass-forming ability of Al2O3-Y2O3 system from temperature susceptibility of melt structure

Despite its significance in both fundamental science and industrial applications, the glass-forming transition in the Al2O3-Y2O3 (AY) refractory system is not yet fully understood due to the elusive structure evolution upon cooling. Here, atomic-scale structural changes in AY-bearing melts with different compositions and temperatures are tracked by employing in situ high-energy synchrotron X-ray diffraction and empirical potential structure refinement simulation. We find that the glass-forming abilities (GFA) of AY-bearing melts are intriguingly correlated with the dependence of melt structure on temperature. In the case of the Al2O3 and Y3Al5O12 (YAG), the observed large structural changes from superheating to undercooling melt (i.e., higher temperature susceptibility) correspond to a low GFA. Conversely, the 74Al2O3–26Y2O3 (AY26) melt, with the smallest temperature susceptibility, exhibits the highest GFA. Simulation models illustrate that the temperature susceptibility of melt is associated with its atomic arrangement, especially the stability of cation-cation pairs. A balanced network (in AY26 melt), where the unsteady OAl3 tri-clusters are minimized and steady apex-to-apex connections between adjacent network units are abundant, contributes to stabilizing cationic interactions. This, in turn, fosters the formation of large-sized Al-O-Al rings, which topologically facilitates the subsequent glass-forming transition. Our findings provide new structural insight into the GFA of AY-bearing melts and may expand to other unconventional glass-forming systems to accelerate glassy materials design.

Metallic artifacts-free spectral computed tomography angiography based on renal clearable bismuth chelate

Computed tomography angiography (CTA) is one of the most important diagnosis techniques for various vascular diseases in clinic. However, metallic artifacts caused by metal implants and calcified plaques in more and more patients severely hinder its wide applications. Herein, we propose an improved metallic artifacts-free spectral CTA technique based on renal clearable bismuth chelate (Bi-DTPA dimeglumine) for the first time. Bi-DTPA dimeglumine owns the merits of ultra-simple synthetic process, approximately 100% of yield, large-scale production capability, good biocompatibility, and favorable renal clearable ability. More importantly, Bi-DTPA dimeglumine shows superior contrast-enhanced effect in CTA compared with clinical iohexol at a wide range of X-ray energies especially in higher X-ray energy. In rabbits’ model with metallic transplants, Bi-DTPA dimeglumine assisted-spectral CTA can not only effectively mitigate metallic artifacts by reducing beam hardening effect under high X-ray energy, but also enables accurate delineation of vascular structure. Our proposed strategy opens a revolutionary way to solve the bottleneck problem of metallic artifacts in CTA examinations.

Multiscale in-situ observations of the micro- and nanostructure of a PH 13-8 Mo maraging steel during austenitization

The aim of the present work is to elaborate on the microstructural evolution of a PH 13-8 Mo maraging steel during austenitization by using multiscale in-situ techniques, which range from high-temperature electron backscatter diffraction and high-energy X-ray diffraction to high-temperature transmission electron microscopy. In order to supplement these in-situ experiments, samples quenched from different temperatures after isochronal heating are subjected to an in-depth microstructural characterization by means of atom probe tomography.The results indicate diffusion-dominated kinetics for the α’ to γ transformation in the investigated heating rate range. Moreover, high-temperature electron backscatter diffraction experiments confirm the occurrence of the austenite memory effect. In addition to the inheritance of grain size and crystallographic orientation of the prior austenite grains, a lath-like substructure remains in austenite, which consists of thermally stable, geometrically necessary dislocations. It is suggested that these dislocations play the key role for enabling recrystallization at higher temperatures without prior cold deformation. This phenomenon is evidenced for the first time in a PH 13-8 Mo maraging steel. However, it is believed that excessive amounts of carbides at austenite grain boundaries or an alteration of the dislocation structure could impede this abnormal recrystallization.

The high energy X-ray probe (HEX-P): a new window into neutron star accretion

Accreting neutron stars (NSs) represent a unique laboratory for probing the physics of accretion in the presence of strong magnetic fields (B ≳ 108 G). Additionally, the matter inside the NS itself exists in an ultra-dense, cold state that cannot be reproduced in Earth-based laboratories. Hence, observational studies of these objects are a way to probe the most extreme physical regimes. Here we present an overview of the field and discuss the most important outstanding problems related to NS accretion. We show how these open questions regarding accreting NSs in both low-mass and high-mass X-ray binary systems can be addressed with the High-Energy X-ray Probe (HEX-P) via simulated data. In particular, with the broad X-ray passband and improved sensitivity afforded by a low X-ray background, HEX-P will be able to 1) distinguish between competing continuum emission models; 2) provide tighter upper limits on NS radii via reflection modeling techniques that are independent and complementary to other existing methods; 3) constrain magnetic field geometry, plasma parameters, and accretion column emission patterns by characterizing fundamental and harmonic cyclotron lines and exploring their behavior with pulse phase; 4) directly measure the surface magnetic field strength of highly magnetized NSs at the lowest accretion luminosities; as well as 5) detect cyclotron line features in extragalactic sources and probe their dependence on luminosity in the super-Eddington regime in order to distinguish between geometrical evolution and accretion-induced decay of the magnetic field. In these ways HEX-P will provide an essential new tool for exploring the physics of NSs, their magnetic fields, and the physics of extreme accretion.

Achieving near zero-hysteretic superelasticity in a Ni43Fe18Ga27Co12 single-crystalline microwire via Lüders-like phase transformation

Ni43Fe18Ga27Co12 single-crystalline microwires directly fabricated by the Taylor liquid drawing method show the nature of a strong first-order martensitic transformation under external stress or load-biased temperature cycling. By eliminating the nucleation energy barrier through localized plastic deformation, a fully recoverable superelastic strain approaching 11 % with negligible hysteresis is achieved in the course of tensile deformation. Based on in-situ synchrotron high-energy X-ray diffraction analysis, the mechanism of nearly non-hysteretic transformation is unraveled as a sharp, Lüders-like phase transformation. It is found that a single martensitic domain propagates continuously in a monolithic fashion under superelastic cycling with poor crystallographic compatibility of λ2 = 0.950 and small volume change of ∆V = -0.17 % accompanying martensitic transformation. We attributed such near zero-hysteretic transformation characteristics to combining conditions of low crystal defect density, high nucleation barriers but without continual nucleation events, flexibility of the microwire, and small volume change.

Pressure-induced reversal of Peierls-like distortions elicits the polyamorphic transition in GeTe and GeSe

While polymorphism is prevalent in crystalline solids, polyamorphism draws increasing interest in various types of amorphous solids. Recent studies suggested that supercooling of liquid phase-change materials (PCMs) induces Peierls-like distortions in their local structures, underlying their liquid-liquid transitions before vitrification. However, the mechanism of how the vitrified phases undergo a possible polyamorphic transition remains elusive. Here, using high-energy synchrotron X-rays, we can access the precise pair distribution functions under high pressure and provide clear evidence that pressure can reverse the Peierls-like distortions, eliciting a polyamorphic transition in GeTe and GeSe. Combined with simulations based on machine-learned-neural-network potential, our structural analysis reveals a high-pressure state characterized by diminished Peierls-like distortion, greater coherence length, reduced compressibility, and a narrowing bandgap. Our finding underscores the crucial role of Peierls-like distortions in amorphous octahedral systems including PCMs. These distortions can be controlled through pressure and composition, offering potentials for designing properties in PCM-based devices.

A mesoscale crystal plasticity model to predict room-temperature deformation and martensitic transformation of high-strength Quenching and Partitioning (Q&P) Steels and validation with synchrotron X-ray diffraction

Renowned for the superior mechanical properties and adeptness at cold-forming, Quenching and Partitioning (QP) steels have gained prominence as a promising candidate material in fabricating safety-critical components in various industries. The pertinent research on QP steels focus on the martensitic transformation of the Retained Austenite (RA) phase during cold-forming, a crucial mechanism that substantially influences the overall strength and ductility of QP steels. The austenite stability and transformation rate heavily rely on the local strain path and the initial microstructure, which is challenging for analytical prediction. In this paper, a mesoscale model is developed to capture the deformation and transformation kinetics of QP steels inside the microstructure. The model integrates the detailed explicit microstructure, acquired from characterization experiments, into a high-resolution finite element (FE) mesh. It distinctly model the deformation and interaction between the various phases and the effect on the transformation of RA. The model is validated with high energy X-ray diffraction (HEXRD) data, and shows excellent capability in predicting the asymmetric stress-strain behavior under uniaxial tension and compression, as well as the martensitic transformation rate. The model is used to investigate the strain and load partitioning effect of surrounding matrix to the transformation of RA, offering insights into the complex behavior of QP980 and facilitates further material development.