Granular Crystals Research Articles

Study on dispersion and wave velocity in 2D elliptic granular crystals by a micromechanics-based micromorphic model

This study considers two-dimensional elliptic granular crystals respectively with different aspect ratios. Using a micromechanics-based micromorphic model, macroscopic micromorphic constitutive modulus tensors of elliptic granular crystals are obtained. Two modes of Taylor expansion of relative displacements are used to establish contact relation between particles. This study obtains micromorphic transverse-rotational and longitudinal waves. Obvious dispersions of micromorphic waves are given in 2D elliptic granular crystals. With increase of aspect ratio, width of frequency band gap increases when wave propagates along [Formula: see text] direction but decreases when wave propagates along [Formula: see text] direction. Two modes of Taylor expansion of relative displacements only have influence on dispersions and frequency band gap of transverse-rotational waves. Velocities of longitudinal and transverse-rotational waves first decrease to zero, keep zero for a range of frequency and then increase to a larger wave velocity with increase of frequency for different aspect ratios. The situation with a larger aspect ratio leads to larger transverse-rotational and longitudinal velocities, and ratio between transverse-rotational and longitudinal velocities decreases from 0.7 to 0.59, when wave propagates along [Formula: see text] direction. However, it leads to smaller transverse-rotational and longitudinal velocities, and ratio between two velocities decreases from 0.88 to 0.56, when wave propagates along [Formula: see text] direction.

Isothermal experiments on steam oxidation of magnetron-sputtered chromium-coated zirconium alloy cladding at 1200 ℃

The isothermal steam oxidation behavior of chromium-coated zirconium alloy cladding at 1200 ℃ is studied. The cladding substrate is Zr-1 Nb alloy with outer diameter of 9.5 mm and thickness of 0.57 mm. The Cr coating is prepared by magnetron sputtering method with thickness of about 11 µm. The oxidation durations are 300 s~14,400 s. After oxidation, blisters are formed on the surface due to the compressive stress in coating, and the coating surfaces are porous or exhibit a morphology with ravines and granular crystals. A four-layer structure (Cr2O3, Cr, Zr(Cr,Fe)2 and Zr from outside to inside) is formed in the early stage of oxidation. However, Zr4+ can migrate into Cr coating through grain boundaries and reacts with Cr2O3. The redox reaction between Zr and Cr2O3 leads to the coating failure, resulting in the oxidation of Zr alloy substrate. Due to selective oxidation, a certain thickness of Cr coating is retained during the thickening of outer ZrO2. The emergence of outer ZrO2 layer is significantly delayed by Cr coating, and Cr coating is able to reduce the growth rate of outer ZrO2 layer. Therefore, Cr coating has a protective effect in 1,200 ℃ steam environment and can improve the oxidation resistance of Zr alloy cladding.

Phases and Morphology of CuFeSe2 Films Prepared by Electrodeposition

In order to prepare CuFeSe2 films at a low cost, the electrochemical behavior of the plating solution with different pH, and the effects of different electrodeposition potential, electrodeposition temperature and electrodeposition time on the phase formation and morphology of the electrodeposited CuFeSe2 films were investigated. CuFeSe2 films were prepared by electrodeposition using copper sulfate, ammonium ferrous sulfate, selenium dioxide and sodium citrate as raw materials. When the pH is 2.5, the electrodeposition potential is −0.6 V, electrodeposition time is 30 min and the electrodeposition temperature is 30 °C, the thin films are well crystallized, compact and uniform, and the micromorphology of the samples is granular crystal. In this paper, electrochemical workstation was used to test the electrochemical performance of the bath, XRD was used to characterize the phase of the sample, SEM was used to characterize the morphology of the sample.

Processes of Obtaining Granular Materials from Al–Zn–Mg–Cu Aluminum Alloys Using Ultra-Fast Granular Crystallization

Processes of Obtaining Granular Materials from Al–Zn–Mg–Cu Aluminum Alloys Using Ultra-Fast Granular Crystallization

Simulation-guided optimization of granular phononic crystal structure using the discrete element method

The paper describes a novel methodology of designing granular phononic crystals for acoustic wave manipulations. A discrete element method is utilized to model the dynamics of a pulse wave propagating through the densely packed assembly of elastic spherical particles with an embedded phononic crystal — the region consisting of a certain arrangement of particles with varying densities. We suggest an optimization strategy that extremizes the useful properties of a granular phononic crystal, which are described in terms of a noise-proof functional based on frequency–wavenumber summation of spectral energy density. Few types of efficient phononic crystals are identified. The suggested methodology is of interest for a number of applications, in particular, for seismic shielding and selective sound absorption.

On the mechanism of pattern transformations in soft granular crystals

Tunable nonlinear characteristics of granular crystals can be potentially useful to a wide range of applications. Several diatomic two-dimensional granular crystals are reported showing compression-driven pattern transformations, but their underlying mechanisms are not explained. In this study, we investigate the veiled underlying mechanisms of compression-driven pattern transformations in 2-D soft granular crystals. In order to adopt a linear perturbation approach, we employ a simplified mass–spring model derived from the granular contact network and perform a series of numerical analyses including quasi-static analysis and microscopic/macroscopic instability analyses. The results show that the pattern transformation of the considered granular crystals are closely relating to instability. Furthermore, the effects of Young’s modulus and radius on the pattern transformations are studied by using the mass–spring model. We confirm the significance of instabilities in pattern transformations and the effectiveness of the simple mass–spring model by performing the corresponding finite element analyses where granular particles are modeled by continuum elements. In motions of continuum solids, instability is well known to serve as a symmetry-breaking mechanism. This study demonstrates that instability also plays a critical role to break the symmetry of deformed patterns in granular crystals.

Studies on the Electrodeposition of UO2 Production in UO2Cl2-LiCl-KCl Melt

UO2 is an important nuclear fuel, also has potentials in the field of functional materials. In this work, the electrochemical behavior of UO2 2+ in LiCl-KCl molten salt (500 °C) and the effects of reduction potential (−0.1 to −1.0 V) and uranyl concentration (0.5 wt% to 4.0 wt%) on morphology and grain size of electrolytic products were studied. The reduction potential was found playing a decisive role in the morphology of cathodic products. When the potential was ≤−0.4 V (vs Pt(II)/Pt), dendritic and cracked characteristic of the UO2 crystal appeared. The average current density had a positive correlation with the grain size of cathodic products, and it increased first and then decreased with the increase of overpotential, having a maximum at −0.6 V (vs Pt(II)/Pt). On the other hand, the uranyl concentration also had a positive correlation with the grain size of the cathodic product without changing the integrity of grain morphology. For the preparation of large and granular UO2 crystal, the reduction potential of −0.2to−0.3 V (vs Pt(II)/Pt), as well as the uranyl concentration of greater than 2.0 wt% were recommended, and UO2 crystal with average grain size greater than 500 μm and high uniformity could be finally obtained.

Some new wave profiles and conservation laws in a Pre-compressed one-dimensional granular crystal by Lie group analysis

Some new wave profiles and conservation laws in a Pre-compressed one-dimensional granular crystal by Lie group analysis

Analysis of purple urine bag syndrome by low vacuum scanning electron microscopy

Purple urine bag syndrome (PUBS) is seen in the prolonged indwelling bladder catheters, and the mechanism of its onset was investigated using low vacuum scanning electron microscopy (LVSEM), which enables us to study the 3D structure of urinary sediments and urine bag walls. The urinary sediment and urine bags of 2 cases of PUBS were observed by LVSEM. The urine was brown turbid urine with a pH of 8.5, and magnesium phosphate stones and granules were observed in the urinary sediment together with Gram-positive and Gram-negative bacilli. Bacteria that moved by Brownian motion were observed with a dark-field microscope. LVSEM showed granular crystals around the bacilli, cocci, or mycelium that adhered to the walls of the bag. Granular crystals were dissolved in chloroform and presumed to be a mixture of the bacterial metabolites indigo blue and indirubin red. LVSEM also detected unusual tubular and honeycomb-like graphene in the urinary sediments, which were derived from the inner layer of the silicon elastomer-coated rubber catheter. LVSEM revealed purple crystals produced by bacteria or fungi attached to the urine bag that caused PUBS.

Direct observation of edge modes in zigzag granular chains

As a new class of artificial elastic materials, granular crystals are mechanical structures of elastic beads arranged in contact through a lattice. One important feature of wave dynamics in granular crystals is that it highly relies on the contact mechanics, allowing for exotic wave transport properties such as rotational waves, solitary waves, slow edge waves, topological edge waves, etc. Realizing granular structures with well-predicted wave physics not only renders these new properties to mechanical systems, but provides also significant possibilities for advanced elastic wave control scenarios. Here, we theoretically and experimentally study the linear wave dynamics in one-dimensional (1D) zigzag granular chains constructed with macroscopic spherical stainless steel/tungsten beads. A spring–mass model including normal, shear and bending mechanical couplings between beads is proposed to characterize the wave dynamics in the chain, which turns out to exhibit remarkable agreement with the experimental measurements. Our work confirms the existence of localized translational–rotational coupled modes at the ends of granular chains, and it might motivate future studies for novel topological wave effects in granular structures.

Preparation and characterization of novel CuS / SiO 2 @n‐octadecane phase‐change nanocapsules enhanced photothermal conversion for solar energy utilization

The design of CuS/SiO2@n-octadecane nanocapsules with high sensitivity to light and heat is being conducive to photothermal conversion and efficient utilization of solar energy. In this work, CuS was deposited on the surface of the SiO2 shell by the chemical bath deposition method. Through the characterization of microstructure and chemical composition, the granular CuS crystal was uniformly coated on the SiO2 shell. The synthesized nanocapsules are spherical and have a perfect core-shell structure. The quantity, distribution, and size of CuS deposited on the shell can be adjusted by regulating the synthesis parameters. The prepared CuS/SiO2@n-octadecane nanocapsules have a melting temperature of 26.85°C and melting enthalpy of 65.0 J/g at the optimum preparation condition (10 mmol/L cetyltrimethylammonium bromide, 70°C, 0.02 mol/L Cu2+) and have excellent durability. The light absorption performance of CuS/SiO2 nanocapsules in the Vis-NIR was significantly enhanced, photothermal conversion efficiency reached 52.7%. In addition, the CuS/SiO2 nanocapsules also showed good photocatalytic performance, and the degradation degree of methyl orange reached 71% within 3 hours. These results show that the designed photo-driven nanocapsules have excellent performance and great potential in solar energy utilization and intelligent fabric. Highlights We have creatively synthesized PCM nanocapsules with CuS/SiO2 shells. The melting enthalpy and melting temperature are 65.0 J/g and 26.85°C, respectively. The activity of the SiO2 shell was increased by amino coupling agent modification. CuS has increased 4-5 times of photothermal conversion efficiency in Vis-NIR.

In-situ grown bilayer MOF from robust wood aerogel with aligned microchannel arrays toward selective extraction of uranium from seawater

Metal-organic frameworks (MOFs) have been widely applied in the recovery of specific guest molecules due to their excellent properties including high porosities, adjustable pore size and abundant chelating functions. However, the granular MOF crystals bring a great challenge to the recycling and reusing from aqueous media, and thus seriously limit their practical application. In this work, MOF bonded wood aerogel prepared by means of in-situ growth strategy was developed for uranium extraction from natural seawater. Eco-friendly and biocompatible wood aerogel possesses run-through microchannel arrays enclosed by aligned cellulose nanofibers (CNFs), contributing to the free and fast diffusion of uranyl ions (UO22+), and thus result in the sufficient coordination with active chelation sites of MOF crystals. To increase the loading content of MOF, bilayer MOF architecture (CMPM) was prepared by using hydroxyl functional groups in CNFs and polydopamine (PDA) coating as nucleation centers of MOF, respectively. The resultant CMPM adsorbents exhibited good reversible compressibility and fragility resistance, which were critical to extend its service life. Moreover, the excellent photothermal conversion capability of PDA enabled CMPM to acquire high temperature under simulated sunlight irradiation. Owing to the apparently endothermic behavior of UO22+, light-irradiated CMPM achieved high adsorption capacity (5.81 mg-U/g-Ads) together with excellent UO22+ selectivity in natural seawater after 30 days. Therefore, this work provides a feasible solution in promoting the practical application of MOF adsorbents.

Topographic Control of Order in Quasi-2D Granular Phase Transitions.

We experimentally investigate the nature of 2D phase transitions in a quasi-2D granular fluid. Using a surface decorated with periodically spaced dimples we observe interfacial tension between coexisting granular liquid and crystal phases. Measurements of the orientational and translational order parameters and associated susceptibilities indicate that the surface topography alters the order of the phase transition from a two-step continuous one to a first-order liquid-solid one. The interplay of boundary inelasticity and geometry, either order promoting or inhibiting, controls whether it is the granular crystal or the granular fluid which makes contact with the edge. This order induced wetting has important consequences, determining how coexisting phases separate spatially.

Synthesis of cesium bismuth iodide perovskite using toluene as anti-solvent with higher photocurrent response

Cesium bismuth iodide (Cs3Bi2I9) perovskite exhibits low toxicity and comprises air-stable materials with promising photo-absorber properties. However, the morphology of a Cs3Bi2I9 film fabricated via spin coating contains micro-/nano-structured flakes, which is not ideal for constructing an optoelectronic device. In this work, we fabricated and compared the Cs3Bi2I9 film by implementing spin-coating using different anti-solvent dripping techniques. The Cs3Bi2I9 film fabricated using toluene as an anti-solvent exhibits maximum uniformity, comprises small granular crystals, and demonstrates a significantly increased photocurrent response.

Precursor nuclei on the bottom of a vibrating container: The onset of granular self-assembly crystallization

Kinetic energy is transferred through collisions to the millimeter particles that are in contact with the base of a vertically vibrated 3D container. In the early stages of a vibrational annealing process where the dimensionless acceleration is kept constant, the spontaneous appearance and disappearance of unstable clusters of ordered particles near the bottom surface of the container is observed. In later stages of this vibrational annealing process, the precursor nuclei stabilize becoming stable crystal seeds which resembles a thermal phase transition. Molecular Dynamics simulations based on these experimental observations are used to study the unstable–stable transition. The Ornstein–Zernike equation using the Percus–Yevick closure is applied to the stages before and after the observation of the stable crystal seeds in order to extract the effective potentials associated with the phase transition. Both the radial distribution function and the effective potentials show a clear correspondence of the spatial correlation as the crystallization phase begins to appear.

Scalable processing of granular crystals by high-frequency oscillation

High-frequency vibration proves a fundamental step towards scalable growth in colloidal crystals. Various experimentally-replicable vibration mechanisms are hereby devised and exerted on randomly generated silicoid particles to explore geometric and dynamic effects on the induced crystal at equilibrium state. The Discrete Element Method is employed, with inter-particle contact idealized by a linear mass–spring–dashpot system with Coulomb sliding friction. With the vertical (Z) direction determined by gravity, the mechanisms comprise vertical, circular, and angular oscillation, with the latter realized in the plane normal to gravity. Characterization of the generated crystal is quantified by a hybrid machine-learning algorithm developed upon direct correlation between the coordinate data, crystallinity and grain-surface parameters. Parametric analysis is carried out in terms of vibration parameters (frequency, amplitude and duration) and the square-prismatic box aspect ratio. Results manifest optimum values of box aspect ratio, vibration amplitude and frequency, with crystallinity parameters mostly saturating after 2 minutes of vibration.

Quantifying surface free energy of molecular crystal β-HMX using non-equilibrium molecular dynamics methods

Granular molecular crystals show a large variation in the orientation, length, shape, and cohesive interactions of interfaces when embedded in a polymer matrix. But the determination of the associated excess of free energy is not straightforward, especially due to the entropic contribution which is not negligible for molecular compounds. The surface free energy (SFE) is also important to predict crystal shapes and growth or to prove crucial insights into the mesoscale interfaces in the granular composites often with interfacial defects, voids, and pores. In this paper, we use Molecular Dynamics (MD) and assess and adapt two non-equilibrium methods, namely, non-equilibrium thermodynamic integration (NETI) and modified steered MD (SMD), to determine the SFE of various facets of a high-energy molecular crystal of interest: β-HMX. Starting with defect-free surfaces, both methods agree well with experiment concerning the most stable facets, whose energy is further lowered by a large entropic contribution. For some facets, surface creation (debonding process) and annihilation (bonding process) show fundamentally different paths, henceforth irreversible. Then, we discuss some sources of discrepancy between theoretical and experimental SFE, considering non-reversible dissipative events, surface roughness, and differences between various experimental techniques. These non-equilibrium methods can be applied to a wide range of molecular crystals and to study interface stability in polycrystals or with binding polymers, including the effects of various defects.

Disorder-induced vibrational anomalies from crystalline to amorphous solids

The origin of boson peak -- an excess of density of states over Debye's model in glassy solids -- is still under intense debate, among which some theories and experiments suggest that boson peak is related to van-Hove singularity. Here we show that boson peak and van-Hove singularity are well separated identities, by measuring the vibrational density of states of a two-dimensional granular system, where packings are tuned gradually from a crystalline, to polycrystals, and to an amorphous material. We observe a coexistence of well separated boson peak and van-Hove singularities in polycrystals, in which the van-Hove singularities gradually shift to higher frequency values while broadening their shapes and eventually disappear completely when the structural disorder $\eta$ becomes sufficiently high. By analyzing firstly the strongly disordered system ($\eta=1$) and the disordered granular crystals ($\eta=0$), and then systems of intermediate disorder with $\eta$ in between, we find that boson peak is associated with spatially uncorrelated random flucutations of shear modulus $\delta G/\langle G \rangle$ whereas the smearing of van-Hove singularities is associated with spatially correlated fluctuations of shear modulus $\delta G/\langle G \rangle$.

The micromorphic constitutive parameters and dispersion behaviors in different granular crystals

This study considers granular crystals respectively with different three-dimensional microstructures categorized into a medium dense microstructure and two dense microstructures in one-sized and two-sized particles. Macroscopic micromorphic constitutive parameters are obtained for different granular crystals based on the micromechanics-based micromorphic model. Furthermore, two micromorphic wave modes are predicted for a plane strain problem, including coupled transverse-rotational and longitudinal waves. This study predicts obvious dispersions of micromorphic waves in different granular crystals. The widest frequency band gap is predicted for granular crystals with medium dense microstructure, and granular crystals with two dense microstructures have the same frequency band gap. The correlations are respectively obtained between frequency band gaps and void ratios, coordination numbers, characteristic lengths and micromorphic parameters. According to dispersion behaviors, correspondences between micromorphic and Cosserat waves are obtained. The simulations of dispersion curves based on the discrete element model are obtained to compare with the theoretical mircomorphic dispersion ones.

Effect of Cr2O3 on the crystallization, structure, and properties of Ti-bearing blast furnace slag-based glass ceramics

ABSTRACT The effects of Cr2O3 on the crystallization, structure, and properties of Ti-bearing blast furnace slag-based glass ceramics were investigated. The results show that the transition temperature and crystallization temperature decreased with introduction of Cr2O3 as a while. Specifically, the crystallization temperature first decreased, then increased with the increase Cr2O3 concentration from 0.2 wt% to 0.8 wt%, and finally decreased with further increased in Cr2O3 concentration. The crystal phases were identified as anorthite, diopside, and akermanite. As the content of Cr2O3 increased to 0.8 wt%, the dendrites gradually decreased and the granular crystals gradually increased. When the Cr2O3 concentration further increased, the number of granular crystals gradually decreased and the dendrites gradually accumulated. With the increase of Cr2O3 from 0.2 wt% to 0.8 wt%, the structure of the investigated glass gradually depolymerized, while the opposite trend was presented with further increased in Cr2O3 content. With increasing Cr2O3 content from 0.2 wt% to 2 wt%, the flexural strength values and Vickers hardness values of the glass ceramics first increased and then decreased, and the maximum values of flexural strength and Vickers hardness were obtained as 94.371MPa and 974.43MPa, respectively. The prepared Ti-bearing blast furnace slag-based glass ceramics showed good acid and alkali resistance.