Structural Evolution Process Research Articles

In situ Reconstructured Alloy Nanosheets Heterojunction for Highly Selective Electrochemical CO2 Reduction to Formate.

Tin (Sn)-based materials are expected to realize efficient CO2 electroreduction into formate. Herein, we constructed a heterojunction by depositing Cu on Cu-doped SnS2 nanosheets. During the electrochemical reaction, this heterojunction evolves to a highly active phase of Cu2O@Cu6Sn5 while maintaining its two-dimensional morphology. Specifically, a partial current density of 35 mA cm-2 with an impressive faradaic efficiency of 93 % for formate production was achieved over the evolved heterojunction. In situ and ex situ experiments elucidated the formation mechanism of the Cu₂O@Cu₆Sn₅ heterojunction. Cu₆Sn₅ nanosheets were formed via a stepwise desulfurization process, while Cu₂O was generated through its reaction with hydroxyl radicals. This evolved heterojunction with a high electrochemically active surface area synergistically stabilized the *OCHO intermediate, thereby significantly enhancing the selectivity and activity. Our findings provide insight into the structural evolution process and guide the development of selective electrocatalysts for CO2 reduction.

Unlocking a Fast Track for Magnesium Migration in Cu1.8S1-xSex via Anion-Tuning Chemistry.

Rechargeable magnesium batteries (rMBs) are promising candidates for next-generation batteries in which sulfides are widely used as cathode materials. The slow kinetics, low redox reversibility, and poor magnesium storage stability induced by the large Coulombic resistance and ionic polarization of Mg2+ ions have obstructed the development of high-performance rMBs. Herein, a Cu1.8S1-xSex cathode material with a two-dimensional sheet structure has been prepared by an anion-tuning strategy, achieving improved magnesium storage capacity and cycling stability. Element-specific synchrotron radiation analysis is evidence that selenium incorporation has indeed changed the chemical state of Cu species. Density functional theory calculations combined with kinetics analysis reveal that the anionic substitution endows the Cu1.8S1-xSex electrode with favorable charge-transfer kinetics and low ion diffusion barrier. The principal magnesium storage mechanisms and structural evolution process have been revealed in details based on a series of ex situ investigations. Our findings provide an effective heteroatom-tuning tactic of optimizing electrode structure toward advanced energy storage devices.

Ignition and combustion of AlH3-nanoparticles: A molecular dynamics study

AlH3 has tremendous potential for hydrogen energy storage and energetic applications. The structure and thermodynamic properties of core-shell AHNP with different oxidation degrees from ignition to combustion are studied using ReaxFF molecular dynamics simulations. Two models covered by different alumina shells are built. Results indicate that the thinner shell is ready to form an Al-rich environment, which is crucial for accelerating ignition and subsequent combustion processes. In ignition period, the influence of shell is investigated by comparing surface oxygen adsorption rates, oxidation degree of Al and H atoms, and stress evolution of AHNP. AHNP with thinner shell exhibits a higher O adsorption rate to form an O-rich environment, which accelerates the oxidation process of Al atoms. A thicker shell significantly inhibits the thermal diffusion of core Al and H atoms, while H atoms are still able to penetrate it with a low diffusion rate. Stress analysis shows the thickness of the shell directly affect the thermal diffusion rate of Al atoms. The combustion of AHNP can be divided into three stages: rapid, slow, and self-sustaining combustion. The combustion process is controlled by the particle and external O atoms diffusion behaviors. A detailed structural evolution process during AHNP combustion has also been clarified through the displacement analysis. The findings provide a theoretical foundation for the diffusion-dominated combustion mechanism of AHNP from an atomic view. Novelty and Significance StatementAlH3 has tremendous potential for hydrogen energy storage and energetic applications. At present, the combustion mechanism of AlH3-nanoparticles (AHNP) is still not well understood, and the atomic-scale evolution process and reaction mechanism are also poorly studied, which is difficult to obtain in experiments. In this study, the ignition and combustion mechanisms of AHNP is revealed based on the ReaxFF molecular dynamics simulations, and the influence of oxidation degree on the ignition and combustion of AHNP is also clarified, which can provide theoretical guidance for the application of AHNP as a clean fuel and preparing for the combustion research of AHNP coated with different materials.

Impact structures on Mercury from MESSENGER data: Implications on their formation processes and crustal structure

In this study high-resolution stereo images and Digital Terrain Models (DTMs) from MErcury Surface, Space ENvironment, Geochemistry and Ranging (MESSENGER) mission were utilized to detect impact structures in regions not covered by Mercury’s Laser Altimeter (MLA), while gravitational data was utilized as a supported data set. We have established an inventory of 314 impact structures ≥150 km, classified on their morphological and gravitational characteristics. 24 basins ≥300 km have been newly discovered. Additionally, we have identified significant surface modifications in impact structures of smooth material infill, which can be either impact-induced or volcanic in origin. The Bouguer anomaly and crustal thinning in the center are displaying an interplay of predominant change of crustal structure in impact basins. Further, this study reveals a common impact history of Mercury and the Moon. Nevertheless, cumulative density distributions suggest the possibility of either a divergence in impactor populations responsible for forming large basins on both celestial bodies or a significant shift in impactor rates. This work holds important implications not only for understanding impact structure formation and evolution processes but also for interpreting the crustal structure. It presents an updated and expanded catalog of impact structures on Mercury, encompassing buried basins, and identifies new areas of interest, potentially serving as target sites for the forthcoming BepiColombo mission.

Room-temperature synthesis of VO(OH)2 as a high capacity cathode material for aqueous zinc ion batteries

The development of satisfactory cathodes plays a key role in the widespread utilization of aqueous zinc ion batteries. Cathode materials with high specific capacity and long cycling life are still urgently needed for aqueous zinc ion batteries. Herein, a new cathode material VO(OH)2 is synthesized by a facile room-temperature precipitation approach, and its electrochemical characteristics and structural evolution process are investigated. Benefiting from its intrinsic electrochemical activity, the VO(OH)2 cathode exhibits a remarkable specific capacity of 488 mAh g−1 at 0.1 A g−1, retains a high capacity of 219.1 mAh g−1 at the increased current density of 10 A g−1, and provides a maximum energy density of 439.2 Wh kg−1. In addition, when subjected to a 12,000 cycles charge/discharge test at 10 A g−1, the cathode retains a capacity of 185.8 mAh g−1, highlighting durable cycling performance. The structural evolution analysis reveals that of VO(OH)2 cathode may be in-situ transformed to an amorphous vanadium oxide V2O5-x in the first charging process, which could reversibly intercalate/deintercalate zinc ions. This research supplies a promising cathode material for aqueous zinc ion batteries and enhances understanding of vanadium oxyhydroxide in metal ion storage.

Early-age hydration of tricalcium aluminate in chloride solutions

Understanding the kinetics and mechanisms involved in early-age hydration of tricalcium aluminate (C3A) in chloride solutions holds promise for implementing seawater-mixed concrete in the marine environment, as C3A remains the most reactive component of Portland cement (PC), affecting both PC and concrete's early-age hardening and long-term durability. Herein, we conducted a series of meticulously designed ex-situ and in-situ experiments to elucidate the intricate hydration behaviors of C3A in various chloride solutions. The results reveal that C3A exhibits distinct hydration kinetics and structural evolution processes in different solutions. The rapid precipitation of alumino-ferrite-mono (AFm) and C3AH6 phases contributes to the swift development of hydration heat and storage modulus in water and NaCl solutions, with a slight acceleration observed in the later one. Conversely, the formation of C3AH6 is delayed in CaCl2 and MgCl2 solutions before 20 min, with the subsequent precipitation of Cl-AFm enhancing its later production, particularly in CaCl2 solutions. Ab-initio calculations further elucidate that the acceleration effect of Cl ions originates from the ionization and structurization of hydrated surface Ca ions. However, this positive effect is significantly offset by Cl pairing with counterions, resulting in a dramatic adverse effect of solution Ca ions originated from the negative entropy effect of structuralized water molecules and electrostatic repulsion with like-charged surface Ca ions and solvent dipoles. Our findings provide valuable insights for sustainable and durable designs on cement-based materials mixed with seawater.

Evolution mechanism of rapid solidification microstructure of an undercooled copper-based single phase alloy

Using undercooling technology combined with melt purification of glass and recirculation overheating, different undercoolings were successfully obtained for Cu60Ni38Co2 alloy samples. Applying high speed photography technique, the physical process of undercooled solidification was observed and relationship between undercooling and solidification rate was analyzed. Experimental results indicate the critical undercoolings exist in the structure evolution process. Electron backscatter diffraction (EBSD) analysis was applied to characterize the Cu60Ni38Co2 alloy sample with a maximum undercooling of 255K, revealing grain orientation and the corresponding orientation difference distribution. In addition, transmission electron microscopy (TEM) showed high density dislocation networks. Combining EBSD and TEM data analysis, an important conclusion was drawn: recrystallization is the main factor for grain refinement at high undercooling. This finding is of great significance for a deeper understanding of the structure evolution in the physical process of undercooled alloys.

Vortices Evolution Characteristics and Pressure Pulsations of Variable-speed Francis Turbine

Abstract The stability of Francis turbine under low load conditions has become the focus in the power grid dominated by variable renewable energy. In this paper, the variable-speed approach is used to explore the operating characteristics of the Francis turbine, the RANS/LES hybrid turbulent model is adopted to investigate the fluid structure evolution process, and using the Q-criterion depicts the vortex cores. The results show that the numerical simulation agrees well with the experimental data acquired from the model test. It is found that the variable-speed operation can effectively eliminate the vortex ropes in the draft tube. Unexpectedly, the vortices in the runner will evolve from the separated vortices at the runner outlet for the fixed-speed Francis turbine to the inter-blade vortices at the runner inlet for the variable-speed Francis turbine in the case of small guide vane opening. It is concluded that the optimum operating range of a variable-speed Francis turbine (VSFT) should be within ±30% rated speed and 60% to 100% opening, and the pressure pulsation coefficient in the draft tube can be reduced from 7% to 1% at minimum water head, the output and efficiency of the turbine are increased by about 30% and 10% respectively.

Study on the performances of epoxy asphalt binders influenced by the dosage of epoxy resin and its application to steel bridge deck pavement

The concentration of epoxy resin can outstandingly affect the performance of hot-mixed epoxy asphalt binders. A standard measuring procedure of tensile performance for plastics is applied to investigate epoxy asphalt binders influenced by different dosages of epoxy. The rheological performances and microscope structure evolution process influenced by hot mixed epoxy dosage are investigated by dynamic shear rheometer and laser scanning confocal microscopy respectively. The consequences manifest that the flexibility and anti-rutting ability of epoxy asphalt binders is raised accompanied by raising the dosage of epoxy resin are founded by long time of creep, creep and recovery. Dynamic shear rheometer temperature scans showed that epoxy asphalt binders exhibited excellent thermal stability within the scope of −20 °C and 120 °C, when the amount of epoxy resin is no less than 40%. It was observed by laser scanning confocal microscopy that the three-dimensional crosslinked network structure was gradually shaped when the epoxy resin concentration was no less than 40%. These experimental results demonstrated that the excellent performances of epoxy asphalt binders are obtained when the concentration of epoxy resin is no less than 40%. From the viewpoint of epoxy asphalt mixtures, the optimal mixture performances are acquired, when the concentration of epoxy resin is no less than 40%. Finally, when the concentration of epoxy resin is 40%, the excellent cost-performance of epoxy asphalt is obtained, which can be used in steel bridge deck pavement.

Study on rotating stall characteristics of centrifugal pumps based on gamma transition model

The phenomenon of rotating stall in centrifugal pumps is closely associated with the evolution of the blade boundary layer. Aiming to accurately predict the characteristics of the boundary layer, this study investigates the phenomenon of rotating stall in centrifugal pump impellers using the gamma (γ) transition model. The accuracy of the numerical simulation was confirmed by comparing its conclusions with the results of the testing. In calculations considering transition characteristics, the distribution of low-pressure areas inside the impeller is relatively discontinuous, while the pressure distribution is more uniform. However, in calculations without considering transition, the low-pressure regions in neighboring flow channels exhibit a tendency to be interconnected, resulting in a more variable pressure distribution, and the pressure contour at the outlet is closer to parallel. The dynamic characteristics of the centrifugal pump impeller rotating stall were obtained through the dynamic mode decomposition method, including the frequency, structure, and dynamic evolution process of the stall vortex. Through modal reconstruction, it was discovered that the impeller's rotation causes the stall vortex to undergo periodic fluctuations. The stall vortex is not stationary but moves synchronously with the rotation of the blades. At different time points, the stall vortex exhibits periodic changes. At the blade suction entrance, the stall vortex initially appears. Subsequently, multiple vortex structures resulted in channel blockage. After a period of development, the excess vortex structures merge to generate a typical “8” shaped vortex structure and move toward the exit. Finally, the exit stall vortex disappears, and a new vortex structure is generated at the inlet of the blade suction surface.

Tracking the role of compressive strain in bowl-Like Co-MOFs structural evolution in water oxidation reaction

Dynamic structural evolution of catalyst active sites is crucial to for transition metal-catalyzed oxygen evolution reaction (OER). Yet, the elucidation of their mechanism behind the compressive-strain-induced reconstruction during OER process remains enigmatic. Here, we construct a bowl-like cobalt-based metal-organic frameworks (BL-Co-MOFs) catalyst with compressive strain to investigate the effect of strain on the structural evolution process and the OER mechanism. In situ techniques directly observe that compressive strain exists in the reconstruction of the potential-driven CoOOH-like active phase with contractile interatomic CoCo distance, promoting a direct OO radical coupling over the Co sites (Co−O−O−Co) during the OER process. This disrupts the constrains of the inherent linear scaling relationship and achieves the kinetic-faster oxide path mechanism (OPM) during OER process. Consequently, the BL-Co-MOFs exhibit a huge mass activity of 12516 A gmetal−1 and a large turnover frequency of 6888 h−1 at a low overpotential of 275 mV (300 mA cm−2).

Structure evolution analysis of asphalt mixtures during compaction based on particle tracking and granular properties

Pavement compaction is a process of structure evolution of materials accompanied by energy dissipation, which is closely related to the inherent granular properties of asphalt mixture. This research achieved dynamic characterization of particle migration energy and contact force development through particle tracking technique and discrete element simulation. Analytical theories for multi-stage structure evolution and compaction mechanisms were proposed based on granular properties. Results indicate that kinetic, dissipative, and potential energies dynamically represent stages of structure evolution, determined by particle collisions, self-organization into arches, and interlocking reinforcement. The initial density state is established after interparticle collisions, while self-organization occurs as particles adaptively rearrange spatially by rotation in response to unbalanced forces, accompanied by a cyclical strengthening trend of arch formation and collapse. Arches facilitate stress redistribution toward isotropy, with strong contact forces exhibiting a top-down and side-center trend, progressively supported by particles larger than 4.75 mm. Theoretical measures for compaction control were proposed, including pre-calculation of IC, selection of compaction temperature corresponding to the optimum energy efficiency, and control of principal stress deflection within the friction cone. This research aims to provide insight into granular properties and compaction dynamics, thereby contributing to intelligent compaction.

Investigating the effects of base oil type on microstructure and tribological properties of polyurea grease

The soaring prices and physiological toxicity of lithium-based grease make polyurea grease a promising alternative due to its balanced cost and performance. Employing preformed thickeners to avoid toxic raw materials has become a preferred method for eco-friendly preparation of polyurea grease. However, the underlying mechanism of base oil modulates the microstructure of polyurea greases prepared with preformed thickeners, subsequently influencing their macroscopic performance remains unclear. Herein, three polyurea greases were synthesized by regulating the base oil types ((poly(α-olefin) oil (PAO40), alkyl naphthalene oil (AN30), and polyether oil (OSP320)) with the same preformed thickener. The real-time polarizing microscope observation of the grease structure evolution process revealed that the preformed thickeners gradually expanded in the base oil and formed a fiber structure. An increased polarity disparity between thickener and base oil leads to a reduced swelling rate and increased fiber length. As a result, compared with high polarity OSP320 and low polarity AN30, non-polar PAO40 induces a more interconnected 3D network composed of long fiber in obtained grease (PG). Low field nuclear magnetic resonance characterization and molecular simulations reveal this network exhibits significant binding ability towards base oil, reducing the movement ability of the base oil, endowing PG with the highest structural strength, achieving effective lubrication and low noise performance. These in-depth understandings will help promote the research and development of polyurea greases.

Pseudotetrahedral Organotin-Capped Chalcogenidometalate Supermolecules with Optical Limiting Performance.

The rational design of crystalline clusters with adjustable compositions and dimensions is highly sought after but quite challenging as it is important to understand their structural evolution processes and to systematically establish structure-property relationships. Herein, a family of organotin-based sulfidometalate supertetrahedral clusters has been prepared via mixed metal and organotin strategies at low temperatures (60-120 °C). By engineering the metal composition, we can effectively control the size of the clusters, which ranges from 8 to 35, accompanied by variable configurations: P1-[(RSn)4M4S13], T3-[(RSn)4In4M2S16] (R = nbutyl-Bu and phenyl-Ph; M = Cd, Zn, and Mn), T4-[(BuSn)4In13Cu3S31], truncated P2, viz. TP2-[(BuSn)6In10Cu6S31], and even T5-[(BuSn)4In22Zn6Cu3S52], all of which are the largest organometallic supertetrahedral clusters known to date. Of note, the arylstannane approach plays a critical role in regulating the peripheral ligands and further enriching geometric structures of the supertetrahedral clusters. This is demonstrated by the formation of tin-oxysulfide clusters, such as T3-[(RSn)4Sn6O4S16] (R = Bu, Ph, and benzyl = Be) and its variants, truncated T3, viz., TT3-[(BuSn)6Sn3O4S13] and augmented T3, viz., T3-[(Bu3SnS)4Sn6O4S16]. Especially, two extraordinary truncated clusters break the tetrahedral symmetry observed in typical supertetrahedral clusters, further substantiating the advantages offered by the arylstannane approach in expanding cluster chemistry. These organometallic supertetrahedral clusters are highly soluble and stable in common solvents. Additionally, they have tunable third-order nonlinear optical behaviors by controlling the size, heterometallic combination, organic modification, and intercluster interaction.

Three-dimensional temperature field inversion in the northern South China Sea

A Swin Transformer oceanic three-dimensional temperature field inversion model is established for the northern South China Sea and its surrounding waters based on satellite observation data and ocean reanalysis data from 1993 to 2018. The inversion results are tested using Argo observation data. The root-mean-square errors of the monthly average temperature fields for 2017 and 2018 are 0.10 to 1.98°C and 0.11 to 1.92°C, respectively, with the maximum values mainly located near the mixing layer. The temperature inversion root-mean-square errors are generally less than 1 °C. Additionally, this article analyzes the three-dimensional structural characteristics and evolution process of a typical anticyclone eddy in the study area. The results show that the inversion results can clearly demonstrate the three-dimensional structure of the eddy and continuously and completely reproduce the process of eddy persistence and movement.

In situ TEM study of pulse-enhanced plasticity of monatomic metallic glasses

The electropulsing process can be used to tailor the microstructure and deformability of metallic glasses (MGs). Here, we report the microstructural origin of enhanced electroplasticity of monatomic Ta MG nanowires. Under electromechanical loading, the Ta MG nanowire exhibits improved ductility and obvious necking behavior. By evaluating the dynamic structural evolution via in situ diffraction, it is found that the atomic mobility in flow units of Ta MG can be improved significantly under the stimulation of pulse current, mainly through the athermal electron-atom interaction, which results in the fast annihilation of flow units and, thereby, fast structural relaxation. These structural evolution processes can help to eliminate the formation of the obvious shear band. These findings provide insight into the origin of electroplasticity in amorphous materials, which is of scientific and technological significance for the design and processing of a variety of MGs.

Simultaneous secondary electron microscopy in the scanning transmission electron microscope with applications for in situ studies.

Scanning/transmission electron microscopy (STEM) is a powerful characterization tool for a wide range of materials. Over the years, STEMs have been extensively used for in situ studies of structural evolution and dynamic processes. A limited number of STEM instruments are equipped with a secondary electron (SE) detector in addition to the conventional transmitted electron detectors, i.e. the bright-field (BF) and annular dark-field (ADF) detectors. Such instruments are capable of simultaneous BF-STEM, ADF-STEM and SE-STEM imaging. These methods can reveal the 'bulk' information from BF and ADF signals and the surface information from SE signals for materials <200 nm thick. This review first summarizes the field of in situ STEM research, followed by the generation of SE signals, SE-STEM instrumentation and applications of SE-STEM analysis. Combining with various in situ heating, gas reaction and mechanical testing stages based on microelectromechanical systems (MEMS), we show that simultaneous SE-STEM imaging has found applications in studying the dynamics and transient phenomena of surface reconstructions, exsolution of catalysts, lunar and planetary materials and mechanical properties of 2D thin films. Finally, we provide an outlook on the potential advancements in SE-STEM from the perspective of sample-related factors, instrument-related factors and data acquisition and processing.

Nanocrystallization Behaviour of Amorphous Co&lt;sub&gt;67&lt;/sub&gt;Fe&lt;sub&gt;4&lt;/sub&gt;Cr&lt;sub&gt;7&lt;/sub&gt;Si&lt;sub&gt;8&lt;/sub&gt;B&lt;sub&gt;14&lt;/sub&gt; Alloy

The investigation addresses the structure of a Co-based alloy and its magnetic properties. The major applications of these materials are in the development of different sensors, which require materials with high permeability. The structure evolution processes need to be explored to clarify the main parameters determining the time-temperature stability. In the present paper, a nanocrystallization behavior of Co67Fe4Cr7Si8B14 amorphous alloy manufactured in the form of a ribbon was studied using X-ray diffraction and sample vibromagnetometry methods. The structure evolution induced by the 30min isothermal annealing at a temperature range of 450 - 700 °C was studied by the X-ray diffraction method, and crystallization with hcp-Co, fcc-Co, and Co2B nanophases was revealed depending on the annealing temperature. According to thermomagnetic measurements, the nanocrystallization process corresponds to a three-stage crystallization model. The crystallization onset temperature of the amorphous alloy was observed to be to equal540 °C. The Curie point and saturation magnetization of the as-quenched alloy were defined as 305 °C and 76 Am2/kg, respectively.

Efficient photo-thermal catalytic CO2 methanation and dynamic structural evolution over Ru/Mg-CeO2 single-atom catalyst

It is a promising green technology to reduce CO2 to CH4 by using renewable solar energy driving photo-thermal catalysis route. However, the efficiency of photo-thermal catalytic CO2 methanation remained to be improved, and the mechanism of this reaction still required further investigation. In this paper, a Ru/Mg-CeO2 catalyst was designed based on the concepts of single atom catalyst and photo-thermal catalysis concept. The catalyst achieved the CH4 formation rate of 469 mmol·gcat−1·h−1 at 400 °C under photo-thermal conditions with good catalytic stability. Besides, the superiority of the single-atom of Ru, Ru-O-Ce structure and doping of alkaline metals in catalytic process was proved by a series of physicochemical and optical characterization, and electron migration direction from Ce and Mg elements to Ru sites through Ru-O-Ce and Ru-O-Mg path under photo-thermal catalysis was determined by ISI-XPS experiment. Finally, the comprehensive reaction mechanism and reversible dynamic structural evolution process between Ru-O-Ce and Ru-Ov-Ce structures were investigated by in situ DRIFTs experiments, and the source of the excellent performance and structure-function relationship of the catalyst was explored, which provided the theoretical and practical basis for the development of catalyst and industrial application of the reaction.

Insights into the Structural Evolution Process of Na/ZnFe2O4 Spinel Catalyst in CO2 Hydrogenation

AbstractThe CO2 hydrogenation to olefins process over Fe‐based catalysts offer a promising route for the production of high‐value chemicals from non‐fossil route. Herein, we present a Na promoted ZnFe2O4 spinel catalyst and their structural evolution from fresh state to reduction and to reaction period was elucidated. The clear phase segregation between Fe and Zn occurred after reduction/reaction because of crystalline phase transformation in the order of ZnFe2O4→ZnO+Fe7C3+χ‐Fe5C2→FeO+ZnO+Fe7C3+χ‐Fe5C2. The formation of iron carbide phases (Fe7C3 and χ‐Fe5C2) was enhanced dramatically by Na promoter. The adjacent Na promoter increase the electron density in Fe−Zn interfaces and enhance its ability to dissociate CO* to form adsorbed CHx* species, thus promoting the formation of olefins. This Na promoted rich electronic Fe−Zn interfaces alters the balance between iron oxides and iron carbides on the catalyst surface, which accelerate the chain growth reaction and facilitate the coupling efficiency of tandem reaction. The various catalysts were characterized by N2 physisorption, SEM, HR‐TEM, HAADF‐STEM, ex‐situ /in situ XRD, Mössbauer spectra, ICP, in situ XPS, and operando DRIFTs.