Explore the vast range of titles available.

HighlightsThe reaction mechanisms of hydrogen evolution reaction (HER) on various crystal surfaces of zinc anode have been systematically investigated by first-principle calculations.Both the thermodynamic and kinetic aspects of HER have been studied to reveal the relative HER activity of several crystal surface of zinc anode.The generalized coordination number of surface Zn atoms are proposed as a key descriptor of HER activity of Zn anode.Hydrogen evolution reaction (HER) has become a key factor affecting the cycling stability of aqueous Zn-ion batteries, while the corresponding fundamental issues involving HER are still unclear. Herein, the reaction mechanisms of HER on various crystalline surfaces have been investigated by first-principle calculations based on density functional theory. It is found that the Volmer step is the rate-limiting step of HER on the Zn (002) and (100) surfaces, while, the reaction rates of HER on the Zn (101), (102) and (103) surfaces are determined by the Tafel step. Moreover, the correlation between HER activity and the generalized coordination number (CN¯) of Zn at the surfaces has been revealed. The relatively weaker HER activity on Zn (002) surface can be attributed to the higher CN¯ of surface Zn atom. The atomically uneven Zn (002) surface shows significantly higher HER activity than the flat Zn (002) surface as the CN¯ of the surface Zn atom is lowered. The CN¯ of surface Zn atom is proposed as a key descriptor of HER activity. Tuning the CN¯ of surface Zn atom would be a vital strategy to inhibit HER on the Zn anode surface based on the presented theoretical studies. Furthermore, this work provides a theoretical basis for the in-depth understanding of HER on the Zn surface.

We have carried out in situ high‐pressure acoustic velocity measurements of (Fe2+, Al)‐bearing MgSiO3 glass up to pressures of 155 GPa, which confirmed a distinct pressure‐induced trend change in the transverse acoustic velocity (VS) profile around 98 GPa, likely caused by the Si‐O coordination number (CN) change from 6 to 6+. Although it has been reported that the substitution of Fe2+ in MgSiO3 glass induces almost linear velocity reduction up to ∼160 GPa, we revealed that the VS profile of (Fe2+, Al)‐bearing MgSiO3 becomes anomalously steeper above ∼100 GPa and eventually came to be equivalent to MgSiO3 glass above ∼125 GPa. This implies the incorporation of Al into Fe‐bearing MgSiO3 glass significantly facilitates making it far elastically stiffer and thus the densification under pressures well within the Earth's lower mantle. Our results indicate the possible presence of stiff and highly dense silicate melts in deep MOs in the rocky terrestrial planets. Plain Language Summary Since the terrestrial planets are thought to have gone through multiple episodes of magma ocean (MO) in their formation processes, clarifying the structure and physical properties of silicate melts under relevant deep MO conditions is crucial to understanding the internal structure and evolution of the terrestrial planets. Our in situ high‐pressure acoustic velocity measurements of (Fe2+, Al)‐bearing MgSiO3 glass, used as a structural analog of silicate melts, shows both Al and Fe2+ are very effective to reduce the pressure corresponding to the Si‐O CN change from 6 to 6+. In addition, a few percentages of Al incorporation could make the Fe‐bearing MgSiO3 glass significantly far elastically stiff and thus dense with 6+ CN in Si‐O in the deep terrestrial interiors. The presence of stiff and highly dense silicate melts in deep MOs in the terrestrial planets would offer essential insights into the MO convection, gravitational stability of silicate melts in the course of MO crystallization, and the mantle stratification of the terrestrial planets. Key Points We have carried out acoustic wave velocity measurements of (Fe2+, Al)‐bearing MgSiO3 glass up to 155 GPa VS profile displays a change at 98 GPa induced by the Si‐O coordination number change from 6 to 6+ followed by anomalously steeper trend Results indicate the possible presence of highly dense Al, Fe2+‐bearing Si‐rich melts in the deep terrestrial magma oceans

Extended X‐ray absorption fine structure (EXAFS) is a comprehensive and usable method for characterizing the structures of various materials, including radioactive and nuclear materials. Unceasing discussions about the interpretation of EXAFS results for actinide nanoparticles (NPs) or colloids were still present during the last decade. In this study, new experimental data for PuO2 and CeO2 NPs with different average sizes were compared with published data on AnO2 NPs that highlight the best fit and interpretation of the structural data. In terms of the structure, PuO2, CeO2, ThO2, and UO2 NPs exhibit similar behaviors. Only ThO2 NPs have a more disordered and even partly amorphous structure, which results in EXAFS characteristics. The proposed new core‐shell model for NPs with calculated effective coordination number perfectly fits the results of the variations in a metal–metal shell with a decrease in NP size. New experimental EXAFS results for PuO2 and CeO2 nanoparticles in the size range of 2 nm were compared with published data for other lanthanide and actinide dioxides. A conceptual core‐shell model with a calculated effective coordination number is proposed to fit the changes in EXAFS.

An accurate understanding of the breakage mechanism of broken coal and rock mass and its coupling relationship with stress and porosity is important for achieving efficient and safe production in coal mines, storage and utilisation of gas and water resources in goafs, and environmental ecological protection. In this study, a novel 3D simulation method is proposed for broken rock and coal granule compaction and breakage. This method can simulate the re-breakage characteristics of broken rock and coal granules during laterally confined compression (LCS). On this basis, numerical simulations combined with laboratory tests are conducted to quantitatively analyse the stress, porosity, and breakage rate evolution characteristics of broken rock granules during LCS. The entire loading process of broken rock granules is divided into three stages: self-adjustment, broken, and elastic. The stress evolution and breakage evolution characteristics of the broken rock granules during each loading stage are delineated. The breakage characteristics of broken rock granules are the main reasons for the evolution of stress, porosity, and breaking rate. In the elastic stage, only uniform compressive stress acts on the broken rock granule, inhibiting further breakage of the sample. When the loading stress reaches the tensile strength of the broken rock granules, the breakage rate of the models increases the fastest. The effects of the broken sample strength and sample size on the breakage characteristics and stress evolution law of the broken models during loading are further discussed. The secant modulus of the broken models in the elastic stages is approximately equal to the elastic modulus of the coal and rock samples. The coordination number evolution law of the broken granules during loading is the main factor affecting its breakage.

Understanding the correlation between coordination number and permeability is crucial for predicting fluid flow behavior in hydrocarbon reservoirs. In this study, we investigated the influence of coordination number on permeability in three-dimensional (3D) rock models. The research methodology involved the creation of synthetic 3D rock models, incorporating pores networks with varying coordination numbers. Utilizing the Lattice Boltzmann Methods (LBM), a computational fluid dynamics approach, we simulated fluid flow through these synthetic rock models and quantified their permeability. Our findings demonstrated a strong dependency of permeability on the coordination number of synthetic rock models. The application of the Lattice Boltzmann Method (LBM) proved to be an effective tool for understanding fluid flow behavior in porous rock formations and can serve as a basis for further optimization of reservoir management strategies to maximize hydrocarbon exploitation.

The macroscopic response of a geomaterial is entirely determined by changes at the particle scale. It has been established that particle crushing is affected by particle size, shape and mineral composition and initial density; and the initiation of breakage has often been related to the onset of yielding. Encouraged by the success of X-ray tomography in revealing particle-scale mechanisms of deformation, we present our findings regarding the onset of particle breakage, deriving from our study of 3D images of a dry granular assembly undergoing crushing. We propose two bespoke image analysis algorithms, which allow us to track breakage and identify contacts prior to breakage. The combination of the two algorithms, along with the high resolution of the 3D images enables us for the first time to track breakage of individual particles, identify different breakage modes for each particle and simultaneously study the effect of particle morphology and coordination number on breakage. Three different breakage types are identified: chipping, splitting and fragmentation. We have found that particle heterogeneity and sphericity mainly contribute to fragmentation, whereas the coordination number also affects chipping. The confining stress state within the particles with high coordination number made them more resistive to fragmentation, whereas particles with low coordination number mainly undergo fragmentation. The shearing of the particles at their contact points, leads to local stress concentrations resulting into surface chipping. Finally, we discuss the relation between the initiation of breakage and yielding, showing that some breakage occurs before the point where yielding is traditionally defined.

As a non-renewable resource, oil faces increasing demand, and the remaining oil recovery rates in existing oil fields still require improvement. The primary objective of this study is to investigate the impact of pore structure parameters on the distribution and recovery of residual oil after polymer flooding by constructing a digital pore network model. Using this model, the study visualizes the post-flooding state of the model with 3DMAX-9.0 software and employs a range of simulation methods, including a detailed analysis of the pore size, coordination number, pore–throat ratio, and wettability, to quantitatively assess how these parameters affect the residual oil distribution and recovery. The research shows that the change in the distribution of pore sizes leads to a decrease in cluster-shaped residual oil and an increase in columnar residual oil. An increase in the coordination number increases the core permeability and reduces the residual oil; for example, when the coordination number increases from 4.3 to 6, the polymer flooding recovery rate increases from 24.57% to 30.44%. An increase in the pore–throat ratio reduces the permeability and causes more residual oil to remain in the throat; for example, when the pore–throat ratio increases from 3.2 to 6.3, the total recovery rate decreases from 74.34% to 63.72%. When the wettability changes from oil-wet to water-wet, the type of residual oil gradually changes from the difficult-to-drive-out columnar and film-shaped to the more easily recoverable cluster-shaped; for example, when the proportion of water-wet throats increases from 0.1:0.9 to 0.6:0.4, the water flooding recovery rate increases from 35.63% to 51.35%. Both qualitative and quantitative results suggest that the digital pore network model developed in this study effectively predicts the residual oil distribution under different pore structures and provides a crucial basis for optimizing residual oil recovery strategies.

Roundness/angularity is a vital shape descriptor that significantly impacts the mechanical response of granular materials and is closely associated with many geotechnical problems, such as liquefaction, slope stability, and bearing capacity. In this study, a series of biaxial shearing tests are conducted on dual-size aluminum circular and hexagonal rod material. A novel image analysis technique is used to estimate particle kinematics. A discrete element model (DEM) of the biaxial shearing test is then developed and validated by comparing it with the complete experimental data set. To systematically investigate the effect of roundness/angularity on granular behavior, the DEM model is then used to simulate eight non-elongated convex polygonal-shaped particles. Macroscopically, it is observed that angular assemblies exhibit higher shear strengths and volumetric deformations, i.e., dilations. Moreover, a unique relationship is observed between the critical state stress ratio and particle roundness. Microscopically, the roundness shows a considerable effect on rotational behavior such that the absolute mean cumulative rotation at the same strain level increases with roundness. A decrease in roundness results in relatively stronger interlocking, restricting an individual particle’s free rotation. Furthermore, the particles inside the shear band exhibit significantly higher rotations and are always associated with low coordination numbers. Generally, the geometrical shape of a particle is found to have a dominant effect on rotational behavior than coordination number.

Particle breakage in sands can cause significant changes in particle-scale characteristics and is associated with many geotechnical engineering applications. The breakage behavior of loose silica sands sheared under high-pressure loading is studied using X-ray microtomography. Increases in confining pressure cause a significant strain hardening throughout the stress–strain curve, which is directly related to the successive particle breakage. A variety of particle-scale characteristics are quantitatively analyzed based on the CT images, including particle fracture, particle size, fractal dimension, particle shape, and coordination number. Splitting and chipping failure modes are more likely to occur by the external force bridging fewer particles. The fractal condition for particles smaller than 0.4 mm demonstrated that more breakage events occur in the smaller particles rather than larger particles. Particle shape shows an exponential relationship with the breakage indices regardless of the stress path. Meanwhile, the influence of particle breakage is more sensitive to sphericity and convexity than the aspect ratio. The evolution of the coordination number is quite size-dependent, and the larger particles tend to have a higher coordination number for all scans. In the shear stage, significant particle breakage causes a decrease in the mean coordination number, indicating that smaller particles with lower coordination numbers exist in the manner of filling the gaps between the larger particles.

In the field of nano energy, investigating the specific heat capacity and coordination number of nano-confined water is highly significant for gaining a better understanding of the energy and microstructure of confined water. In this work, we employed the method of molecular dynamics (MD) simulation to calculate the specific heat capacity at constant volume and coordination number of water molecules confined in carbon nanotubes (CNTs) under different conditions ( T =600–700 K, P =21.776 and 25 MPa, CNT diameter=0.949–5.017 nm). The results showed that near the critical point, the specific heat capacity at constant volume of confined water was lower than that of bulk water, and the energy fluctuation showed a trend of first increasing and then remaining unchanged with the increase of temperature and CNT diameter. Among them, the saturation point of temperature is 650 K (reduced pressure P r =1) and 660 K ( P r =1.15), and the saturation point of CNT diameter is 2.034 nm. Additionally, the pseudo-critical temperature of confined water was the same as bulk water, and it increased with the increase of critical pressure. Moreover, with the increase of CNT diameter, the coordination number of confined water increased rapidly, and reaches the saturation state when the CNT diameter is 2.034 nm. This investigation revealed the mass and energy characteristics of nano-confined water near the critical point, which could provide guidance for the critical phase transition of nano-confined water.