Coordination Number Research Articles

Insight into the initiation and propagation mechanism of desiccation cracking in clayey soil from DEM simulations

Desiccation cracking, a common natural phenomenon, significantly affects the mechanical and hydraulic properties of clayey soils. This study employs 3D Discrete Element Method (DEM) to investigate the initiation and propagation mechanisms of soil desiccation cracking. By integrating water evaporation at the soil surface and water transportation between soil grains into a traditional DEM model, we unveil a sequential and hierarchical pattern in the development of desiccation cracks. Initially, micro cracks proliferate and coalesce in regions of soil defects characterized by the lowest coordination numbers, leading to the genesis of primary cracks. Subsequently, a complex network of cracks propagates, governed by the interplay between cracking and the redistribution of the tensile stress field. As desiccation advances, the detachment of soil from the bottom wall and an increase in soil strength contribute to the stabilization of the crack network. Notably, the hierarchical nature of desiccation cracking is predominantly shaped by initial soil defects and subsequently refined by stress concentration within the soil clods, correlating with changes in the length-to-height ratio of the soil clods.

Impact of initial gradation on compaction characteristics and particle crushing behavior of gravel under dynamic loading

Gravel is a widely used construction material due to its versatility and cost-effectiveness. However, gravel particles are prone to crushing under dynamic loading, causing changes in gradation. The evolution of gradation and its effects on physical properties are not well understood. This study investigates the physical properties of gravel, such as dry density, void ratio, and relative crushing index, under different initial gradations (uniformity coefficient, Cu), using surface vibration compaction tests. A hyperbolic relationship was established between initial Cu and dry density, showing that an increase in Cu can result in a decrease in the void ratio and an increase in the coordination number until stabilization. Particle crushing increases with higher initial Cu, correlating quantitatively with relative crushing indexes. Maximum dry density, minimum void ratio, and fractal dimension also correlate with these relative crushing indexes, suggesting intrinsic relationships among these properties and particle crushing. The size effect can be eliminated by establishing empirical relationships between crushing parameter and particle size.

2D Discrete Element Simulation of Electrode Structural Evolutions in Li‐Ion Battery During Drying and Calendering

Drying and calendering are critical steps in the manufacture of electrodes for lithium‐ion battery that affect their mechanical and electrochemical properties. A 2D representative volume element (RVE) model, including active material and carbon binder domain particles of different shapes and sizes, is developed. The evolution of the RVE structure is simulated using the discrete element method, providing insight into changes in velocity, coordination number, porosity, pore size distribution, tortuosity, and stress. Based on this analysis, a three‐step drying scheme is proposed in accordance with the experimental drying results. In addition, the calendering process significantly improves the mechanical integrity and electronic conductivity of the electrode. Through simulations and experimental observations of changes in surface morphology and porosity, an optimal compression ratio of about 20% is determined for the electrode.

Predicting social experience from dyadic interaction dynamics: the BallGame, a novel paradigm to study social engagement

Theories of embodied cognition suggest that a shared environment and ongoing sensorimotor interaction are central for interpersonal learning and engagement. To investigate the embodied, distributed and hence dynamically unfolding nature of social cognitive capacities, we present a novel laboratory-based coordination task: the BallGame. Our paradigm requires continuous sensing and acting between two players who jointly steer a virtual ball around obstacles towards as many targets as possible. By analysing highly resolved measures of movement coordination and gaming behaviour, game-concurrent experience ratings, semi-structured interviews, and personality questionnaires, we reveal contributions from different levels of observation on social experience. In particular, successful coordination (number of targets collected) and intermittent periods of high versus low movement coordination (variability of relation) emerged as prominent predictors of social experience. Importantly, having the same (but incomplete) view on the game environment strengthened interpersonal coordination, whereas complementary views enhanced engagement and tended to generate more complex interactive behaviour. Overall, we find evidence for a critical balance between similarity and synchrony on the one hand, and variability and difference on the other, for successful engagement in social interactions. Finally, following participant reports, we highlight how interpersonal experience emerges from specific histories of coordination that are closely related to the interaction context in both space and time.

Characterization of Pore Structure and Fluid Mobility of Shale Reservoirs.

Accompanying the commercial exploitation of shale oil and gas in North America, shale oil has gradually become an important resource, sparking great interest among countries around the world in recent years. In this study, focusing on the Paleogene Shahejie Formation in Bohai Bay (Eastern China), techniques such as CT, nitrogen adsorption, mercury injection capillary pressure (MICP), and nuclear magnetic resonance (NMR) were used to characterize the pore structure and mobility of the shale reservoir. Based on the X-ray CT data, the pore radius of the shale reservoir is in the range 0.5-65 μm, and the pore coordination number is concentrated in the range of 1-4. The shale reservoir is poorly connected. The minimum size of the unit body for establishing the digital core model is 380 μm. Based on the experimental data of nitrogen adsorption and MICP, the pores of shale in the study area are mainly classified as ink-bottle-shaped pores, transition-shaped pores, and flat plate slit-shaped pores. The specific surface area and volume of pores are mainly attributed to meso- and macropores. The movable fluid saturation of shale is distributed from 23.59 to 44.42%, the pore throat radius is distributed from 0.001 to 6 μm, and the lower limit of the movable pore throat radius of shale is distributed between 9.0 and 20.1 nm. The movable fluid porosity is mainly distributed between 0.84 and 4.08%, with an average movable fluid porosity of 2.37%. The findings provide a theoretical basis for the efficient development of shale oil resources.

Structure Sensitive Reaction Kinetics of Chiral Molecules on Intrinsically Chiral Surfaces.

Enantiospecific heterogeneous catalysis utilizes chiral surfaces to resolve enantiomers via structure sensitive surface chemistry. The catalyst design challenge is the identification of chiral surface structures that maximize enantiospecificity. Herein, we develop data driven models for the enantiospecificity of tartaric acid reactions on chiral Cu(hkl)R&S surfaces. Measurements of enantiospecific rate constants were obtained by using curved Cu(hkl)R&S surfaces that enable kinetic measurements on hundreds of chiral surface orientations. One model uses feature vectors derived from generalized coordination numbers to capture the local structure around Cu atoms exposed by the Cu(hkl)R&S surfaces. The second model introduces the use of chiral cubic harmonic functions to capture the symmetry constraints of the face-centered cubic Cu structure. The model using 58 generalized coordination numbers has a fitting error similar to that of the model using only 5 cubic harmonic functions. The two models predict maxima in the enantiospecificity on surfaces with very similar surface orientations. The models developed in this work are applicable for any enantiospecific reaction happening on any chiral material with a cubic lattice structure, opening the way to understanding the surface structure sensitivity of the enantiospecific reaction kinetics.

Fine-tuning Pt nanoparticle and coordination for enhanced catalytic efficiency in microwave-assisted methylcyclohexane dehydrogenation over Pt/Al2O3 catalysts

The advancement of microwave-assisted catalysis technology will play a crucial role in the realms of energy conversion and catalysis. In this study, we developed a series of Pt/Al2O3-H catalysts by varying the reduction temperature and duration to control the Pt particle size, aiming to optimize the catalytic performance for microwave-assisted methylcyclohexane (MCH) dehydrogenation. Among the synthesized catalysts, Pt/Al2O3-H-400–15 emerged as the most effective, characterized by Pt particles of 1.5 nm and a Pt-Pt coordination number of 2.8. This particular catalyst demonstrated a high metal-support interaction, which significantly enhanced its activity and stability during the dehydrogenation process. Notably, it showed superior performance in MCH dehydrogenation under microwave irradiation, maintaining high stability and minimal methane formation over 626 h. The enhanced catalytic behavior under microwave irradiation is attributed to the elimination of low-temperature dead zones, which are commonly observed in traditional thermal catalysis, resulting in higher efficiency, greater activity, and reduced by-product and coke formation. This study underscores the potential of microwave-assisted catalysis as a more effective alternative to conventional thermal methods for the dehydrogenation of MCH.

Slowdown of solvent structural dynamics in aqueous DMF solutions

This study presents a comprehensive investigation into the molecular dynamics of solvation environments through an integrated approach combining Fourier-transform infrared (FTIR) spectroscopy, molecular dynamics (MD) simulations, and two-dimensional infrared (2D IR) spectroscopy. We explore the solvation of an ionic solute (ammonium thiocyanate) in various solvent systems, including N,N-dimethylformamide (DMF), water, and a 0.5 mole fraction of DMF in water, aiming to unravel the intricate interplay between solute-solvent interactions and solvent dynamics across diverse solvation environments. By integrating FTIR spectral analysis with radial distribution functions and coordination numbers obtained from MD simulations, we decipher the solvent composition around the solute molecule. Analysis of 2D IR spectra and hydrogen bond, as well as dipolar autocorrelation function from MD simulations, further elucidates the nuances of solute-solvent interactions, highlighting the impact of solvent dynamics on solvation structures. Our results reveal a significant slowdown of the solvent structural dynamics in the equimolar binary solvent mixture compared to the neat solvents. This slowdown underscores the complex relationship between solute-solvent interactions and solvent dynamics. The integration of FTIR, MD simulations, and 2D IR spectroscopy provides a unified framework for obtaining a holistic understanding of solvation dynamics, offering valuable insights into the underlying molecular mechanisms governing solute-solvent interactions in complex systems. These results pave the way for future studies to delve deeper into the molecular intricacies of solvation phenomena.

Transformations to the aluminum coordination environment and network polymerization in amorphous aluminosilicates under pressure.

The structure of calcium aluminosilicate glasses (CaO)x(Al2O3)y(SiO2)1-x-y with the near tectosilicate compositions x ≃ 0.19 and 1 - x - y ≃ 0.61 or x ≃ 0.26 and 1 - x - y ≃ 0.49 was investigated by in situ high-pressure neutron diffraction and 27Al nuclear magnetic resonance (NMR) spectroscopy. The results show three distinct pressure regimes for the transformation of the aluminum coordination environment from tetrahedral to octahedral, which map onto the deformations observed in the production of permanently densified materials. The oxygen packing fraction serves as a marker for signaling a change to the coordination number of the network forming motifs. For a wide variety of permanently densified aluminosilicates, the aluminum speciation shares a common dependence on the reduced density ρ' = ρ/ρ0, where ρ is the density and ρ0 is its value for the uncompressed material. The observed increase in the Al-O coordination number with ρ' originates primarily from the formation of six-coordinated aluminum Al(VI) species, the fraction of which increases rapidly beyond a threshold ρthr'∼ 1.1. The findings are combined to produce a self-consistent model for pressure-induced structural change. Provided the glass network is depolymerized, one-coordinated non-bridging oxygen atoms are consumed to produce two-coordinated bridging oxygen atoms, thus increasing the network connectivity in accordance with the results from 17O NMR experiments. Otherwise, three-coordinated oxygen atoms or triclusters appear, and their fraction is quantified by reference to the mean coordination number of the silicon plus aluminum species. The impact of treating Al(VI) as a network modifier is discussed.

Quantitative study on the selective depressing effect of polysaccharides on some polar minerals

This study presents a systematic summary on the depressing effect of polysaccharides on some polar minerals, revealing that the order of their depressing strength on some polar minerals was primarily associated with the surface properties of the minerals, showing a limited correlation with the structure of polysaccharides. Subsequently, the selective depressing mechanism of polysaccharides on polar minerals was quantitatively explained from the perspective of acid–base interaction mechanism, and a criterion system for determining the depressing effect of polysaccharide on minerals was proposed. Specifically, it was found that the hydroxylation reaction of metal sites on mineral surface was a prerequisite for polysaccharide adsorption. Under the above–mentioned conditions, the selective depressing effect of polysaccharides on these minerals with different metal sites could be assessed through a parameter system in which the ion potential φ of surface metal sites served as the primary determinant, and the solubility product constant of metal hydroxides played a secondary role. In cases where minerals shared identical surface metal sites, the selective depressing effect of polysaccharides was analyzed by comparing the coordination numbers of these sites. Specifically, minerals with a higher number of coordinated surface metal sites tend to show a weaker response to depressing effect of polysaccharide. Consequently, this study theoretically elucidated the selective depressing effect of polysaccharides on polar minerals, and the criterion system proposed in this study outperforms the prediction results based on the isoelectric point (pHiep). These research findings have important guiding significance for a deeper understanding of the selective depressing mechanism of polysaccharides and the regulation of flotation.

Powder bed fusion with electron beam: The interplay of sintering, porosity, and coordination number in modelling the powder thermal conductivity through a novel tortuosity formulation

For the powder bed fusion with electron beam (PBF-EB) additive manufacturing, properties such as the thermal conductivity of the material surrounding the melting area are critical. Thermal conductivity is influenced by the extremely high temperature reached in a short time and distributed in the building area. This fast temperature growth produces sintering phenomena and the creation of a neck between the particles. Because of this sintering, measuring the thermal conductivity at the process conditions is challenging.This paper proposes an analytical formulation for estimating the effective powder bed thermal conductivity at the PBF-EB conditions, introducing a novel modelling strategy for the tortuosity factor. In a changing net of sintered powder particles, the proposed model for the tortuosity factor considers the neck evolution and the complexity of the heat transfer due to the several heat paths possible through the particle net. To show the effectiveness of the proposed model, the thermal conductivity is evaluated for three 3D structures characterised by an increasing number of powder particles and heat path complexity: a simple cubic, a body centred cubic and a portion of a powder bed. It is shown that thermal conductivity strongly depends on the arrangement of the particles in 3D space, the structure density and the complexity of the heat diffusion path (tortuosity). Also, the numerical results from the proposed model show good agreement when compared with finite element analysis and experimental literature data.

Jamming is a first-order transition with quenched disorder in amorphous materials sheared by cyclic quasistatic deformations

Jamming is an athermal transition between flowing and rigid states in amorphous systems such as granular matter, colloidal suspensions, complex fluids and cells. The jamming transition seems to display mixed aspects of a first-order transition, evidenced by a discontinuity in the coordination number, and a second-order transition, indicated by power-law scalings and diverging lengths. Here we demonstrate that jamming is a first-order transition with quenched disorder in cyclically sheared systems with quasistatic deformations, in two and three dimensions. Based on scaling analyses, we show that fluctuations of the jamming density in finite-sized systems have important consequences on the finite-size effects of various quantities, resulting in a square relationship between disconnected and connected susceptibilities, a key signature of the first-order transition with quenched disorder. This study puts the jamming transition into the category of a broad class of transitions in disordered systems where sample-to-sample fluctuations dominate over thermal fluctuations, suggesting that the nature and behavior of the jamming transition might be better understood within the developed theoretical framework of the athermally driven random-field Ising model.

Antimony sorption to schwertmannite in acid sulfate environments

Schwertmannite is a poorly-crystalline Fe(III) oxyhydroxysulfate mineral that may control Sb(V) mobility in acid sulfate environments, including acid mine drainage and acid sulfate soils. However, the mechanisms that govern uptake of aqueous Sb(V) by schwertmannite in such environments are poorly understood. To address this issue, we examined Sb(V) sorption to schwertmannite across a range of environmentally-relevant Sb(V) loadings at pH 3 in sulfate-rich solutions. Antimony K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that Sb(V) sorption (at all loadings) involved edge and double-corner sharing linkages between SbVO6 and FeIIIO6 octahedra. The coordination numbers for these linkages indicate that sorption occurred by Sb(V) incorporation into the schwertmannite structure via heterovalent Sb(V)-for-Fe(III) substitution. As such, Sb(V) sorption to schwertmannite was not limited by the abundance of surface complexation sites and was strongly resistant to desorption when exposed to 0.1 M PO43-. Sorption of Sb(V) also conferred increased stability to schwertmannite, based on changes in the schwertmannite dissolution rate during extraction with an acidic ammonium oxalate solution. This study provides new insights into Sb(V) sorption to schwertmannite in acid sulfate environments, and highlights the role that schwertmannite can play in immobilizing Sb(V) within its crystal structure.

Dendritic Pt Aerogel for Highly Efficient Electrocatalytic Methanol Oxidation Reaction

AbstractMetallic aerogels, as featured by high surface area, porosity, and self‐supported metal skeleton, are regarded as an ideal platform for developing next‐generation electrocatalysts. However, the precise adjustment of their skeleton nanostructure to enhance catalytic properties remains significantly underexplored. Herein, inspired by the impact of the metal atoms’ coordination number on their reactivity, we devised and prepared dendritic Pt aerogels (DPAs) via a facile sol‐gel method. The synergy of aerogel structure and coordinatively distinct catalytic sites from dendritic morphology enables DPAs to exhibit markedly improved electrocatalytic activity and stability for methanol oxidation reaction. The mass activity and specific activity of DPAs are 1.28 A mgPt−1 and 1.5 mA cmPt−2, which are 4.1 and 3.2 times higher than those of commercial Pt/C, respectively.

Comparing the MP2, DKH2‐MP2 and SCAN Hybrid Forces Molecular Dynamics Simulation on the Structure and Dynamics of Hydrated Ion Ba2+ in Aqueous Solution

AbstractThe study investigated the structural and dynamical properties of hydrated ion Barium (Ba2+) in aqueous solution using quantum mechanical/molecular mechanical molecular dynamics simulations (QM/MM MD simulation). The primary objective was to assess the performance of the SCAN functional in describing the structure and dynamics of formed Ba2+ hydration shells in aqueous solution. The SCAN/MM MD simulation demonstrated the closest agreement with previously reported experimental data regarding the structural and dynamical properties of hydrated ion Ba2+. Specifically, the Ba2+ and surrounding water molecules distance was determined to be 2.79 Å, with equal distribution of coordination numbers of 8 and 9 in the first hydration shell. Moreover, the stretching frequency of 232.21 cm−1 closely matched the CCSD(T) results. The obtained results from SCAN/MM MD has a better agreement than results from MP2/MM and DKH2 MP2/MM molecular dynamics simulation. These findings underscore the potential of SCAN/MM MD simulation as a promising method for investigating the structural and dynamical properties of hydrated ions.

Soft and diffusion-controlled Sr-MOF for efficient separation of H2O/D2O

Heavy water (D2O) electrolysis is the primary technology for D2 production, playing an irreplaceable role in fields such as nuclear fusion research and isotope tracing. However, the inherent similarity in chemical properties between H2O and D2O (with only a 1.4 °C difference in boiling points) poses significant challenges to their separation. Furthermore, the extremely low natural abundance of D2O (0.015 %) increases the difficulty and cost of separation, while traditional electrolysis and distillation techniques are highly energy intensive. Therefore, there is an urgent need to develop novel adsorbents for efficient and environmentally sustainable H2O/D2O separation. Herein, we used polydentate ligand 2, 5-dihydroxyterephthalic acid (DOBDC) and its derivatives 4,4́-(anthracene-9,10-diyl) bis (2-hydroxybenzoic acid (ABHB) as raw materials to prepare two novel high coordination Sr-MOFs namely IPE-1 and IPE-2, respectively. These MOFs were applied for efficient separation of H2O and D2O at room temperature. X-ray diffraction results reveal that one Sr atom in IPE-1 is coordinated with 9 oxygen atoms. This high coordination number results in the formation of ultra-small rectangular pores of approximately 2.5 Å. Adsorption isotherms of N2, CO2, H2O, and D2O indicate that the ultramicroporous structure of IPE-1 precludes efficient diffusion of CO2 and H2O molecules into the MOF channels. In contrast, the activated IPE-2 exhibits good CO2, H2O, and D2O uptake capacities of 3 mmol/g, 8.38 mmol/g, and 6.51 mmol/g at 298 K, respectively. The Qst values and Ksap values of H2O and D2O indicate that the adsorption rates of H2O were much higher than D2O under 0.2 < P/P0 < 0.7, with a calculated ratio of approximately 1.26. This study not only provides appealing MOFs materials for efficient H2O/D2O separation at room temperature but also provides a new avenue for preparing adsorbents with high stability and high separation performance.

Strength and fabric anisotropy of granular materials under true triaxial configurations using DEM

This paper investigates the strength and fabric anisotropy of granular materials under true triaxial configurations using the discrete element method. A clump logic based on the multi-sphere approach was utilized to replicate realistic particle shapes. The evolutions of deviatoric stress and volumetric strains were found to be independent of mean effective stress, and intermediate principal stress parameter (b). From a macroscopic viewpoint, all samples exhibited initial strain hardening followed by softening behaviour, stabilizing at large deviatoric strains due to the dense state of assemblies. The peak state friction angles showed dependency on the b-value, aligning closely with experimental findings. Microscopic parameters such as mechanical coordination number and sliding fraction were found to be approximately independent of b-values. Additionally, non-coaxiality was observed for various b-values except for specific shear modes, aligning with previous findings using spherical particles. These results highlight the capability of clumped particles to simulate the true mechanical behaviour of granular materials and contribute to our understanding of their complex response under different loading conditions.

Dense Hydrated Magnesium Carbonate MgCO3·3H2O Phases.

The study of the structural stability of carbonates under different pressure and temperature conditions is important for modeling the carbon budget in the Earth's interior and the stability of carbonation products of carbon capture and storage (CCS) solutions. In this work, we confirm the existence of the two dense polymorphs of the hydrated magnesium carbonate MgCO3·3H2O nesquehonite mineral previously reported, and we characterize their structures using synchrotron single-crystal X-ray diffraction at 3.1 and 11.6 GPa. Phase transitions entail the distortion and atomic rearrangement of the Mg-centered polyhedra and the tilting of the [CO3] carbonate units. In particular, the Mg coordination number increases from 6 in nesquehonite to 7 in the second high-pressure phase, while maintaining a topology based on complex MgCO3(H2O)2 chains. We also studied their vibrational behavior upon compression using Raman spectroscopy and complemented the experimental results with density-functional theory (DFT) calculations. The role played by hydrogen bonds in the compressibility and the polymorphism of this hydrated carbonate is also discussed.

Enhancing mechanical strength and porosity of alumina extrudates through composite processing

Industrial alumina supports need to possess both high mechanical strength and porosity, but these requirements often conflict with each other. In this work, differences in powder properties such as particle shape, flowability, and peptizability were utilized to composite for extrusion. When globoid pseudo-boehmite was composited with sheet-like alumina at a mass ratio of 3:1, the extrudate exhibited a mechanical strength of 183 N·cm−1 and a porosity of 62.24%, representing a 46.4% and 4.5% increase, respectively, when compared to using globoid alone. Multiscale characterizations revealed that the composite extrudate possessed rich and interconnected mesopores and macropores. The outcome of DEM indicated that the composited extrudates had higher porosity and particle average coordination numbers than the single powder extrudates. This study revealed a correlation between powder properties and extrudate structures, providing design insights for the targeted control of mechanical strength and pore structure.

Synthesis, crystal Structure, theoretical calculation and luminescence properties of Cu(Ⅱ), Co(Ⅱ), Ni(Ⅱ) and Zn(Ⅱ) quinolinyl benzimidazole complexes with multiple coordination number induced by proton

The innovative ligand H2L, featuring a benzimidazole structure substituted with 8-hydroxyquinoline and equipped with N,O donor sites, underwent successful synthesis and meticulous characterization. Notably, this ligand was exclusively synthesized through catalysis under protonated conditions, accompanied by an in-depth exploration of the catalytic mechanism. Employing single-crystal X-ray diffraction, we acquired and authenticated four distinct asymmetric double-decker sandwich mononuclear transition metal complexes: [Cu(HL)2]·2H2O, [Co(HL)2]·CH3OH, [Ni(HL)2] and [Zn(HL)2]·CH2Cl2. Among these, complex 1 revealed an intriguing five-coordinate Cu(II) center adopting a distorted square pyramidal geometry, whereas the central metal ions in complexes 2–4 exhibited a six-coordinate configuration, characterized by a distorted octahedral geometry. Noteworthy is the observation that the dihedral angles within the crystal structures of complexes 2–4 approached approximately 90° to a significant extent. To delve deeper into the electronic properties and transitions, meticulous DFT and TD-DFT calculations were performed on both the ligand H2L and complexes 1–4. Furthermore, a comprehensive investigation into the luminescence properties of both H2L and its complexes was conducted, revealing a pronounced luminescence quenching effect in the complexes compared to the ligand. Through thorough analysis utilizing Hirshfeld surface examination and IRI analysis, various weak intermolecular interactions within the system were elucidated.