Adjacent Particles Research Articles

In Situ Investigation of the Phase Transition at the Surface of Thermoelectric PbTe with van der Waals Control.

The structure of thermoelectric materials largely determines the thermoelectric characteristics. Hence, a better understanding of the details of the structural transformation process/conditions can open doors for new applications. In this study, the structural transformation of PbTe (a typical thermoelectric material) is studied at the atomic scale, and both nucleation and growth are analyzed. We found that the phase transition mainly occurs at the surface of the material, and it is mainly determined by the surface energy and the degree of freedom the atoms have. After exposure to an electron beam and high temperature, high-density crystal-nuclei appear on the surface, which continue to grow into large particles. The particle formation is consistent with the known oriented-attachment growth mode. In addition, the geometric structure changes during the transformation process. The growth of nanoparticles is largely determined by the van der Waals force, due to which adjacent particles gradually move closer. During this movement, as the relative position of the particles changes, the direction of the interaction force changes too, which causes the particles to rotate by a certain angle.

Electropolymerization of 1,5-naphthalenediamine monomers and redox activity in aqueous zinc batteries

More organic molecules have been found to be applicable to zinc-ion batteries (ZIBs). The active monomers usually need a beforehand polymerization to overcome dissolution. In this work, organic 1,5-naphthalenediamine (1,5-NAPD) monomers were used directly as cathode material and electropolymerized by the first oxidation in Zn-ion batteries (ZIBs). Fourier-transform infrared spectra confirmed the polymerization and the most likely polymerization pattern of conformational isomerism was proposed. Scanning electron microscopy reveals the agglomeration occurs among adjacent particles in electrode. The electropolymerization of monomers eliminates beforehand polymerization steps. The initial discharge capacity achieves 134 mAh g−1 at 0.05 A g−1 without obvious capacity decay after 1000 cycles at different rates.

Membrane Distillation: Pre-Treatment Effects on Fouling Dynamics.

In the research reported in this paper, membrane distillation was employed to recover water from a concentrated saline petrochemical effluent. According to the results, the use of membrane distillation is technically feasible when pre-treatments are employed to mitigate fouling. A mathematical model was used to evaluate the fouling mechanism, showing that the deposition of particulate and precipitated material occurred in all tests; however, the fouling dynamic depends on the pre-treatment employed (filtration, or filtration associated with a pH adjustment). The deposit layer formed by particles is not cohesive, allowing its entrainment to the bulk flow. The precipitate fouling showed a minimal tendency to entrainment. Also, precipitate fouling served as a coupling agent among adjacent particles, increasing the fouling layer cohesion.

Synthesis and consequence of Zn modified ZSM-5 zeolite supported Ni catalyst for catalytic aromatization of olefin/paraffin

Zn modified ZSM-5 zeolite supported Ni bifunctional catalysts were prepared by in-situ hydrothermal synthesis (Zn-Ni-ZSM-5), co-impregnation method (Zn-Ni/ZSM-5) as well as combining in-situ hydrothermal synthesis of Zn-ZSM-5 and sequential impregnation of Ni (Ni/Zn-ZSM-5) and used for the selective converting olefin to aromatics applicable for FCC gasoline hydro-upgrading. The Lewis (L) acid sites generated by ZnOH+ species and hydrogenation active sites from Ni0 species were varied with preparation method, in which their locations at the external surface or micropores of zeolite changed the acid properties of catalysts. Comparing to the Zn-Ni/ZSM-5 from the co-impregnation method, direct in-situ hydrothermal method could incorporate Zn and Ni species within zeolite, which makes the strong interaction between the metal species and the framework Al to form medium-strong L acids (ZnOH+/NiOH+). This leads to the decrease of ratio of Brønsted acid sites to L acid sites (B/L) from 0.40 to 0.12 and the difficulty in reducing of Ni cations to Ni0 from 57% to 30% Ni0 percent. Ni/Zn-ZSM-5 sample prepared by incorporating Zn species into micropores and sequential depositing Ni species at the external surface of zeolite possesses a low B/L ratio similar to Zn-Ni-ZSM-5 (0.20 versus 0.12) but a much higher Ni0 percent (52% versus 30%). Zn-Ni-ZSM-5 shows closer intimacy between Zn and Ni species comparing to Zn-Ni/ZSM-5 and Ni/Zn-ZSM-5. For the 1-hexene aromatization, the formed iso-alkene at acid sites was quickly saturated to iso-alkanes by the adjacent Ni0 particles over Ni-Zn-ZSM-5 catalyst in hydrogen steam. However, the location of aromatization active sites (ZnOH+, L acid sites) in micropores and hydrogenation active sites (Ni0 species) on external surface of Ni/Zn-ZSM-5 makes the tandem conversion of n-alkene → iso-alkene → aromatics, rather than the n-alkene → iso-alkene → iso-alkane. Thus, Zn-Ni-ZSM-5 with close intimacy of ZnOH+ and Ni0 particles shows a high iso-alkane selectivity (27.9% iC4+), while Ni/Zn-ZSM-5 exhibits a high aromatics selectivity (39.6 %) in the conversion of 1-hexene in hydrogen steam. Similar results have also found in the conversion of n-heptane. Here, the control of the intimacy of Zn and Ni in ZSM-5 zeolites has been realized to be a good protocol to adjust the selective conversion of olefins/alkanes to aromatics versus iso-alkanes.

Microstructure-optimized concentration-gradient NCM cathode for long-life Li-ion batteries

Herein, a comprehensive investigation of the effect of calcination temperature on the physicochemical properties of full-concentration-gradient Li[Ni0.78Co0.10Mn0.12]O2 (FCG NCM78) and the electrochemical performance of FCG NCM78 cathodes was conducted. The electrochemical performance of the FCG NCM78 cathode was significantly influenced by the physical properties of FCG NCM78, such as crystallinity, compositional gradient, and morphology. The crystallinity of FCG NCM78 increased with increasing calcination temperature; however, the compositional gradient and radial alignment of rod-shaped primary particles increasingly disappeared at calcination temperatures exceeding the optimal calcination temperature. FCG NCM78 calcined at the optimal calcination temperature retained the morphological texture of its precursor and demonstrated high crystallinity; the resulting cathode exhibited remarkable cycling stability, thereby retaining 86.3% of its initial capacity after 4000 cycles, and superior rate capability due to the availability of nearly straight diffusion paths for Li-ion transport across adjacent primary particles. In contrast, excessively coarsened FCG NCM78 cathode particles, which are obtained at high calcination temperatures, develop permanent microcracks during cycling, thereby facilitating severe structural damage of the cathode material by parasitic surface reactions and the rapid deterioration of the solid electrolyte interphase layer on the graphite anode surface due to the crossover of dissolved transition-metal ions. Therefore, for superior electrochemical performance, the physicochemical properties of FCG cathode materials should be carefully optimized by controlling the calcination process.

The influence of particle chain-magnetic field spatial location, frequency, dynamic strain amplitude and the prestrain on the mechanical performance of anisotropic magneto-rheological elastomer

Although there are literatures to characterize the properties of anisotropic magneto-rheological elastomer (MRE), more attention is paid when the particle chain is parallel to the applied magnetic field. However, in prospective of modeling and application design, mechanical characterization of anisotropic MRE under other particle chain-magnetic field spatial locations is needed. Herein, mechanical properties of anisotropic MRE with four kinds of particle chain-magnetic field spatial locations under varies frequencies, strain amplitudes and prestrains are tested. It shows that even the particle chain is perpendicular to the magnetic field, there exists an obvious MR effect. Besides the attraction of adjacent magnetized particles, the Maxwell stress tensor also contribute to the MR effect. Furthermore, an obvious strain amplitude dependent viscoelastic behavior is exhibited for anisotropic MRE. Moreover, the MR effect and the loss factor decrease as the increase of prestrain. The investigation contributes to the designing, modeling and applications of anisotropic MRE.

Thermal effect of high temperatures on the physical and mechanical properties of a granite used in UNESCO World Heritage sites in north Portugal

This work discusses the results from a set of physical and mechanical test conducted on 46 cubic samples of a granite from the north of Portugal widely used in local granite-built UNESCO World Heritage sites, heated in a furnace at temperatures ranging from 105 to 700 °C and cooled under different conditions. Then, the obtained results are compared with an extensive database of published case studies, showing that porosity, unit weight, ultrasonic waves velocities, elastic modulus and uniaxial compressive stress variations are mostly related to the induced thermal-stress caused by the anisotropic thermal expansion of the mineral grains. Only mineralogy and specific gravity do not exhibit changes for the studied range of temperatures. For specimens heated to above 500 °C, degradation processes predominate due to alpha-beta phase transition in quartz grains, considerably increasing the linear crack density, length and width and degrading the rock properties. Regarding the influence of the cooling method, thermal effects are amplified when cooling is performed by water immersion because of the inhomogeneous shrinkage and the subsequent tension stress between adjacent particles due to temperature decrease that develop at different pace within the samples. Scanning electron microscopy confirms the increase of damage and the negative effect on the granite properties caused by thermal treatment from 500 °C and by water cooling. For temperatures lower than 500 °C a hardening effect slightly improving elastic modulus and uniaxial compressive strength is observed in slowly and quickly cooled samples. The derived conclusions considerably improve the knowledge about the behaviour against temperature of this type of granite, with the purpose of evaluating the integrity level of granite-built UNESCO cultural heritage sites in northern Portugal.

Linear optical properties of 2d assembly of interacting gold nanoparticles: analytical approach in dipole approximation

Using a Drude-like model for the conduction electrons of Metal Nanoparticles (MNPs) assembled in a periodic two-dimensional (2D) array, considering dipole-dipole interactions of adjacent particles, an analytical expression is achieved for the MNP permittivity where the functionality of interaction term on the different geometric and physical parameters is evident. A numerical analysis is carried out for a gold NP array for two different sizes of NPs and two different host media of water and glass. It is shown that, interaction of NPs leads to a substantial increase in the extinction cross section, the red-shift of the Surface Plasmon Resonance (SPR) wavelength and decrease in the full width at half maximum (FWHM) of cross section. The absolute values of the real and imaginary parts of complex permittivity of each MNP decrease in comparison with the single particle case.

A quantitative model to understand the microflow-controlled sintering mechanism of metal particles at nanometer to micron scale

In this paper, the particle size effect on the sintering behaviors of Cu particles at nanometer to micron scale is explored. The results show that micron-sized particles could form obvious sintering necks at a low temperature of 260 °C, exhibiting a shear strength as high as 64 MPa. A power relation of x ∝ a 0.8 between sintering neck radius (x) and particle radius (a) is discovered, and a sintering model with a quantitative relational expression of (x/a)5 = 160γδDt/3akT is proposed by considering the surface tension driven microflow process between adjacent particles to predict the growth of sintering necks. It is concluded that the sintering process of particles at nanometer to micron scale is controlled by microflow mechanism instead of diffusion mechanism. Our proposed model provides a new theoretical basis for understanding the kinetic growth mechanism of sintering necks of metal particles.

Impact of Al2O3 Particle Size on the Open Porosity of Ni/Al2O3 Composites Prepared by the Thermal Oxidation at Moderate Temperatures

The performance of attractive Ni-based composites can be affected by changing their microstructures, e.g., introducing pores. Here, we report a novel, relatively low-cost process to fabricate Ni/Al2O3 composites with open porosity modified by the size of Al2O3 particles. The mixture of powders was subjected to thermal oxidation twice in air after a maximal temperature of 800 °C was reached in a stepwise manner and maintained for 120 min. The oxidation kinetics were determined thermogravimetrically. The open porosity was evaluated by an Archimedes’ principle-based method. Localization and quantification of NiO, newly formed on the Ni particle surface and acting as a mechanical bonding agent, were explored by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffractometry. Larger ceramic particles prevented merging of NiO layers on adjacent Ni particles more efficiently; therefore, the open porosity increased from 21% to 24.2% when the Al2O3 particle diameter was increased from 5–20 µm to 32–45 µm. Because both Ni/Al2O3 composites exhibited similar flexural strength, the composite with larger Al2O3 particles and the higher open porosity could be a better candidate for infiltration by molten metal, or it can be directly used in a variety of filtration applications.

Influences of sintering temperature on pore morphology, porosity, and mechanical behavior of porous Ti

The purpose of this study was to determine the influences of the sintering temperature on the pore morphology, porosity, and mechanical behavior of titanium foams. Porous Ti samples were successfully manufactured using the metal powder metallurgy method in conjunction with sintering at the four temperatures (900, 1000, 1100, and 1200 °C). The sintering temperature significantly influenced the pore morphology, porosity, and mechanical behavior of the titanium foams. The titanium foams were characterized using an optical microscope in conjunction with scanning electron microscopy. A fracture showed the appearance and growth of a sintering neck between adjacent particles. As the sintering temperature increased, the sintering necks gradually became clearer. The porosity decreased from 56.48% to 46.83% as the sintering temperature increased from 900 °C to 1200 °C, while the initial yield strength of the porous titanium increased from 101.81 to 208.01 MPa. The porous titanium foams produced by the metal powder metallurgy method have a significant utilization potential in hard-tissue engineering.

Efficient image segmentation based on deep learning for mineral image classification

Mineral image segmentation plays a vital role in the realization of machine vision based intelligent ore sorting equipment. However, the existing image segmentation methods still cannot effectively solve the problem of adhesion and overlap between mineral particles, and the segmentation performance of small and irregular particles still needs to be improved. To overcome these bottlenecks, we propose a deep learning based image segmentation method to segment the key areas in mineral images using morphological transformation to process mineral image masks. This investigation explores four aspects of the deep learning-based mineral image segmentation model, including backbone selection, module configuration, loss function construction, and its application in mineral image classification. Specifically, referring to the designs of U-Net, FCN, Seg Net, PSP Net, and DeepLab Net, this experiment uses different backbones as Encoder to building ten mineral image segmentation models with different layers, structures, and sampling methods. Simultaneously, we propose a new loss function suitable for mineral image segmentation and compare CNNs-based segmentation models' training performance under different loss functions. The experiment results show that the proposed mineral image segmentation has excellent segmentation performance, effectively solves adhesion and overlap between adjacent particles without affecting the classification accuracy. By using the Mobile Net as backbone, the PSP Net and DeepLab can achieve a high segmentation performance in mineral image segmentation tasks, and the 15 × 15 is the most suitable size for erosion element structure to process the mask images of the segmentation models.

Strength improvement of rock fractures and aggregates cemented with bio-slurry

Microbially induced carbonate precipitation (MICP) is a new environmentally friendly technique for grouting rock fractures and aggregates. However, this method can achieve only a limited degree of strength increase and low treatment efficiency. To address these limitations, an improved treatment method was designed and tested using bio-slurry (i.e., bacterial suspension with fine calcite particles), and the treatment effectiveness and strength of cemented rock fractures and aggregates were enhanced. The experimental results show that the rock specimens with fractures grouted using bio-slurry exhibited significantly higher shear strength values than those treated using the conventional MICP method, owing to a nearly six times higher filling ratio. The uniaxial compressive strength of the rock aggregates cemented using bio-slurry was two times higher than that treated using the conventional method, owing to the formation of more calcite crystals near the contact points between adjacent particles. The proposed bio-slurry method was demonstrated as an effective technique for cementation of rock fractures and aggregates with a higher efficiency than the traditional method.

Preparation and optimization of the environmental dust suppressant with agricultural waste straw.

In order to reduce the dust pollution caused by the coal mining process, a novel composite environmental dust suppressant for coal dust control was synthesized by corn straw, sodium carboxymethyl cellulose (CMC), and additives. This study focused on the preparation conditions of the dust suppressant, and the performances of which were investigated systematically. Response surface method (RSM) was used to optimize the raw material formulation and preparation parameters. The optimum mass ratio of straw, CMC, and alkali of the dust suppression was 65:20:15 (m/m), which was prepared under the conditions of the reaction time being 1.5 h and the rotation speed being 300 r/min. The pH of the dust suppressant was 8.0, and the state of which was suspension. Additives were benefited to enhance the suppressant performance, and the surface tension and the contact angle could decrease to 32.4 mN/m and 32.0°. The suppressant has a maximum viscosity of 363.6 mPa·s, and the compressive strength could be up to 200 kPa. The hygroscopic rate could reach more than 4%. The wind erosion resistance could be up to 99 % at the wind speed of 14 m/s. After spraying the dust suppressant, the gap between particles was filled with dust suppressant, and the adjacent particles were bound by strong mechanical action.

Liquid-Bridge Contact Model of Unsaturated Granular Materials and its Application in Discrete-Element Method

In the past, the capillary effect is rarely considered for microcontact models when two adjacent particles are separated by a certain distance. In this paper, a liquid-bridge contact model of unsaturated particles is presented, which is applied to the discrete-element software PFC. Based on this, simulations of uniaxial tensile for unsaturated soils under (2D) situation are carried out, and influence of a water retention angle on uniaxial tensile strength are studied. The simulation results show that the uniaxial tensile strength of unsaturated soil decreases gradually with the increase of the water retention angle, obvious cracks generate at both ends of the soil samples, and the soil sample possesses a residual strength. According to the particle displacement field, velocity field, and contact force chain, the failure forms of samples with different water retention angles are determined. Based on the rose diagram of normal contact force, the changes of its direction and value during failure process are observed directly, so as to analyze the evolution law of contact force for unsaturated soils.

Chase-escape with death on trees

Chase-escape is a competitive growth process in which red particles spread to adjacent uncolored sites, while blue particles overtake adjacent red particles. We introduce the variant in which red particles die and describe the phase diagram for the resulting process on infinite d-ary trees. A novel connection to weighted Catalan numbers makes it possible to characterize the critical behavior.

Synthesis and characterization of graphene nanosheet-modified polycrystalline diamond compact

Graphene nanosheets were used as additives in the preparation of polycrystalline diamond compact (PDC) composites to overcome the low fracture toughness and heat resistance of PDC composites. The PDC composites were then sintered at a pressure of 5.8 GPa and a temperature of 1500 °C. Subsequently, the mechanical properties, microstructure, and toughness mechanism of PDC composites modified by graphene nanosheets were studied. The PDC sample prepared by adding 0.2 wt% graphene nanosheets had the best comprehensive performance. Compared with the sample without graphene nanosheets, the impact toughness of the sample with 0.2 wt% graphene nanosheets improved by 29.78%, while the heat-resistant temperature increased by 34.5 °C. The hardness and wear resistance of the sample did not show any significant decrease and were essentially the same as those of the unmodified PDC composite sample. Two factors were found to influence the toughening mechanism. On the one hand, the lubricating effect of graphene promoted particle rearrangement, pore filling, and mutual sliding between adjacent diamond particles, which resulted in a denser and more uniform PDC composite material. On the other hand, the graphene nanosheets at the triangular grain boundaries were interspersed in the cobalt binder and led to the formation of a unique structure of “cobalt-graphene nanosheets”. This unique structure acted as the skeletal structure and effectively prevented fracture crack propagation.

Localization in the kicked Ising chain

Determining the border between ergodic and localized behavior is of central interest for interacting many-body systems. We consider here the recently quite popular kicked Ising chain. A convenient description of such a many-body system is achieved by the dual operator that evolves the system in contrast to the time-evolution operator not in time but particle direction. We focus in this paper on the largest eigenvalue of a function of the dual operator. It is identified to be a convenient tool to determine if the system shows ergodic or many-body localized features. We analytically explain the eigenvalue structure by perturbation theory in the vicinity of the noninteracting system. This result agrees with the numerics for small times in a previous work [Braun et al., Phys. Rev. E 101, 052201 (2020)]. Given that a direct numerical computation of this largest eigenvalue is only possible for small times, another achievement of this paper is to provide a way to determine this eigenvalue by the ratio of spectral form factors for adjacent particle numbers. By extensive large-time numerical computations of the spectral form factor, we can then distinguish between localized and ergodic system features and compute the Thouless time, i.e., the transition time between these regimes in the thermodynamic limit.

Informative light pulses of indicating polymer fiber-optic piezoelectroluminescent coatings upon indentation of rigid globular particles

A mathematical model of operation of an indicating polymer coating with an embedded fiber-optic piezoelectroluminescent (PEL) sensor is developed for diagnosing multiple mechanical force actions by digital processing of an informative luminous flux at the output of the optical fiber of the sensor. Distributed force action is caused by a multipoint low-velocity impact of multiple rigid particles, e.g., hail impacts, and the indentation of particles across the outer surface of the coating. The results of the numerical modeling of the sequence of informative light pulses at the output of the optical fiber of the PEL sensor are presented. The effects of the amplitude of the control voltage at the sensor contacts and the possible intersections of the “perturbation zones” of the adjacent globular particles on the amplitude and shape of light pulses are identified via numerical analysis. The filtering of informative signals of the indicating PEL coating based on the control sensor voltage is studied to exclude the effect of insignificant (outside of the operational range) external mechanical actions on the detected informative light signal.

Hierarchical Structured Multidimensional Nano Carbon Bowl @MoS2/Graphene Electrodes with Enhanced Electrochemical Capacitance Performances

Hierarchical structured ‘0D+ 2D+ 2D’ multidimensional nano carbon bowl (CB)-Molybdenum Disulfide (MoS2)-Graphene ([email protected]2/Graphene) hybrid is a promising electrode material for high-performance energy storage. The semiconcave hollow carbon bowl (CB) with a high specific surface area can increase more active sites for uniform growth of MoS2 nanosheets. The unique bowl-shaped structure also helps to increase the contact area between adjacent particles, shorten the transmission distance of electrolyte ions and improve the rapid charge and discharge performance of the material. To further overcome the poor conductivity of pure MoS2 and efficiently display its energy storage performance, the hierarchical [email protected]2/Graphene ‘0D+ 2D+ 2D’ multidimensional structured electrodes were synthesized by the hydrothermal method. As a ‘conductive bridge’, graphene was wrapped outside the surface of the [email protected]2 to form a continuous conductive network channel in the GO-MoS2-CB hierarchical structure for better charge and ion transport. Moreover, the [email protected]2 can also be used as a ‘spacer’ for graphene, alleviating the agglomeration of graphene sheets and providing part of the electric double-layer capacitance. When was used as the electrode material for supercapacitors, [email protected]2/Graphene can obtain a better electrochemical property than [email protected]2 and CB. The specific capacitance of [email protected]2/Graphene can reach 588 F g−1 at a current density of 0.2 A g−1 and 398 F g−1 at high current density of 10 A g−1, respectively. In addition, the 2D graphene nanosheets can not only improve the electrical conductivity, but also can be used as a buffer to alleviate structural changes during the long-term charging and discharging process, improving the cycling performance. The capacitance retention of [email protected]2/Graphene is enhanced to 83.9% after 5000 cycles.