Granular Crystals Research Articles

ZnO Films Incorporation Study on Macroporous Silicon Structure.

In the present work, we developed hybrid nanostructures based on ZnO films deposited on macroporous silicon substrates using the sol–gel spin coating and ultrasonic spray pyrolysis (USP) techniques. The changes in the growth of ZnO films on macroporous silicon were studied using a UV-visible spectrometer, an X-ray diffractometer (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). XRD analysis revealed the beneficial influence of macroporous silicon on the structural properties of ZnO films. SEM micrographs showed the growth and coverage of ZnO granular and flake-like crystals inside the pores of the substrate. The root mean square roughness (RMS) measured by AFM in the ZnO grown on the macroporous silicon substrate was up to one order of magnitude higher than reference samples. These results prove that the methods used in this work are effective to cover porous and obtain nano-morphologies of ZnO. These morphologies could be useful for making highly sensitive gas sensors.

Flow-induced surface crystallization of granular particles in cylindrical confinement

An interesting phenomenon that a layer of crystallized shell formed at the container wall during an orifice flow in a cylinder is observed experimentally and is investigated in DEM simulation. Different from shear or vibration driven granular crystallization, our simulation shows during the flow the shell layer is formed spontaneously from stagnant zone at the base and grows at a constant rate to the top with no external drive. Roughness of the shell surface is defined as a standard deviation of the surface height and its development is found to disobey existed growth models. The growth rate of the shell is found linearly proportional to the flow rate. This shell is static and served as a rough wall in an orifice flow with frictionless sidewall, which changes the flow profiles and its stress properties, and in turn guarantees a constant flow rate.

Analytical solutions of solitary waves and their collision stability in a pre-compressed one-dimensional granular crystal

In this paper, a pre-compressed one-dimensional granular crystal model is studied. The bright analytic single and multiple solitary wave solutions in more general forms than those obtained the KdV system in the previous studies are derived by using the homogeneous balance principle and Hirota’s bilinear method. The difference between the present solutions and those from the KdV system are investigated both analytically and numerically. By analyzing the dispersion relation and the collision process of solitary waves, we find that there are two types of double-solitary waves in the pre-compressed granular crystal model. The geometric and numerical analysis of dynamic behaviors of the solutions is presented with emphasis on the relation between the double-solitary waves and elastic collision between single-solitary waves. We find that the opposite collision between single-solitary waves may be stable and thus generate a stable double-solitary wave. It is concluded that the collision is a special stable double-solitary wave solution. We further propose a possible way to determine the stability of multiple solitary waves qualitatively. The results of this paper provide a theoretical basis for finding stable multiple solitary wave solutions.

Wave self-interactions in continuum phononic materials with periodic contact nonlinearity

The existence of nonlinearity within materials manifests richer wave propagation compared to their linear counterpart in the form of amplitude-dependent material response and energy transfer between frequencies. While these properties have been extensively studied in the case of continuous and discrete nonlinear phononic materials (PMs), individually, the behavior of continuum PMs with discrete nonlinearities, which could open new opportunities for wave propagation control via discrete–continuum coupling, is relatively unexplored. In this article, we investigate nonlinear wave propagation through one-dimensional continuum PMs with periodic contacts. Specifically, the periodicity is in the form of pre-compressed rough contacts resulting in nonlinearly coupled linear finite thickness elastic layers. We analyze the system using full-scale time-domain finite element simulations by treating the contacts as spring-equivalent nonlinear thin elastic layers. The model considers a power-law pressure-gap relationship at the rough contacts. The evolution of propagating nonlinear waves within the weakly nonlinear regime is illustrated, emphasizing the generation of zero (DC), self-demodulated low, and second harmonic frequencies for excitation in different zones of the dispersion relation. The continuum between discrete contact nonlinearities exhibits local DC reduction and second harmonic increment, not observed in discrete PMs such as granular phononic crystals. The intertwined effects of nonlinearity, periodicity, and finiteness on nonlinear wave propagation are also explored, which results in maximum DC amplitude at the finite boundaries of the PMs and mode-based second harmonic characteristics. Finally, we demonstrate the flexibility of the proposed nonlinear PMs by characterizing the dependence of nonlinear wave propagation on different arrangements of embedded contacts. The concept of discretely embedding nonlinear interfaces, such as rough contacts, within an elastic continuum, opens opportunities to control the global nonlinear response of the PMs through local microstructural nonlinearities.

Isotropic pressure promoted collective self-healing response in granular molecular crystals

自愈合材料具有修复损坏并改善产品寿命、 安全性和功能的能力. 但自愈合效应在有序分子晶体中却很少被报道, 且自愈效率较低. 在本研究中, 我们首次报告了常温下N-甲基脲(NMU)晶体颗粒中各向同性压力触发的集体性自愈行为. 其中, 自愈率最高可以达到100%, 并伴随着“粉晶-单晶”转变. 自愈后的晶体会在更高压力作用下破裂, 并在卸压过程中再次愈合. 原位光学显微镜、 单晶X射线衍射、 粉末晶体X射线衍射和拉曼实验表明, 在0.3 GPa附近的各向异性相变和晶粒间的紧密接触是NMU晶体颗粒产生集体性自愈响应的两个先决条件. 该集体性自愈行为的高自愈率来源于在自愈合过程中外部压力被持续不断地消耗并转化为氢键重组的化学能, 这也为提高其他分子晶体中自愈合效率提供了思路.

Contact model for elastically anisotropic bodies and efficient implementation into the discrete element method

We introduce a contact law for the normal force generated between two contacting, elastically anisotropic bodies of arbitrary geometry. The only requirement is that their surfaces be smooth and frictionless. This anisotropic contact law is obtained from a simplification of the exact solution to the continuum elasticity problem and takes the familiar form of Hertz’ contact law, with the only difference being the orientation-dependence of the material-specific contact modulus. The contact law is remarkably accurate when compared with the exact solution, for a wide range of materials and surface geometries. We describe a computationally efficient implementation of the contact law into a discrete element method code, taking advantage of the precomputation of the contact modulus over all possible orientations. Finally, we showcase two application examples based on real materials where elastic anisotropy of the particles induces noticeable effects on macroscopic behavior. Notably, the second example demonstrates the ability to engineer tunable vibrational band gaps in a one-dimensional granular crystal by mere rotation of the constituent spherical particles.Graphic abstract

Viscosity of CaO-MgO-Al2O3-SiO2-TiO2-FeO slag with varying TiO2 content: The Effect of Crystallization on Viscosity Abrupt Behavior

Reasonable slag fluidity is essential for stable HIsmelt process operation. During the slag-tapping process, crystallization will cause the slag viscosity to rise sharply, which is not conducive to stable slag-tapping operation, especially for smelting high-titanium slag. In this paper, the viscosity of the CaO-MgO-Al2O3-SiO2-TiO2-FeO slag with varying 10–50% TiO2 content was studied in the laboratory. The crystalline phases of water quenched slag samples at different temperatures were determined by XRD, and it was verified with the results of Factsage thermodynamic calculations. In addition, the effects of crystalline phase, crystalline morphology and crystal size on the critical viscosity of slag were discussed through SEM-EDS analysis. The results show that the proper TiO2 content in the slag is below 40%, the temperature of critical viscosity (Tcv) of the slag is between 1336 °C and 1360 °C, and the Tcv of the slag with a TiO2 content of 50% increases to 1500 °C. The sudden increase in viscosity is related to the crystallization behavior of the slag. With the increase of TiO2 content, the main precipitated titanium-rich phase in the slag changed from dendritic perovskite to plate-shaped pseudobrookite. Among them, when the TiO2 content is 10%, the sharp increase in viscosity of the slag is mainly determined by the precipitation amount of melilite. The amount of crystals in the slag between 20% and 43% causes the viscosity of the slag to rise rapidly, which is mainly due to the fact that the granular crystals have a greater influence on the viscosity than the plate crystals. Compared with the experimental results, it is found that Factsage software cannot accurately calculate the phase equilibrium of slag with a TiO2 content of 40–50%.

Difference between Internal and External Hydration of Hardened Cement Paste under Microwave Curing

In order to investigate the difference between internal and external hydration of hardened cement paste under microwave curing, a comparative study on the hydration products, hydration degree, fracture morphology, and pore structure between the inner part and outer part of hardened cement paste (Φ120 mm × 120 mm) under microwave curing was carried out by XRD‐Rietveld refinement, TG‐DSC, SEM, and MIP methods. The results show that the total hydration degree of the inner part is lower at early ages, but with the hydration, there is little difference in the hydration degree between inner and outer parts at later ages. Apart from granular AFt crystal formed in the inner part of hardened cement paste, there is little difference in the fracture morphology between internal and external hydration. The total porosity of the outer part is lower than that of the inner part.

Stimuli-responsive granular crystals assembled by dipolar and multipolar interactions.

This work describes granular crystals held together by unusual, multipolar interactions and, under the application of an external bias, undergoing reversible structural transitions between closed and open forms. The system comprises two types of polymeric beads agitated on one or between two conductive plates and gradually acquiring charges by contact electrification. The charges thus developed induce a series of electrostatic images in the conductive supports and, in effect, the beads interact via dipolar or multipolar interactions, enabling the stabilization of non-electroneutral crystals. Furthermore, under an applied bias, the beads become polarized and their complex interactions (due to the series of image charges as well as series of image dipoles) result in open-pore crystals which return to compact forms upon bias removal. These effects are rationalized by analytical calculations, and the crystal structures observed in the experiments are reproduced by molecular dynamics simulations.

Toward understanding solitary wave propagation in composite-cylinders-based 1D granular crystals

One-dimensional (1D) granular crystals are demonstrated to be outstanding nonlinear systems for supporting various types of novel stress waves. This letter reports on the investigation of solitary wave propagation within 1D granular crystals based on composite cylinders. We design two types of composite particles by creating a material mismatch within the granular, i.e., core–shell and sandwich types. We discover that such 1D composite granular chains support the formation of strongly nonlinear solitary waves. A finite element model is constructed to describe wave propagation behaviors fully validated by experiments. We conduct a theoretical analysis that agrees with numerical results and uncovers the physical mechanisms of solitary wave propagation in 1D composite granular chains through the parametric study. Finally, the fundamental understanding of dynamic responses is extended to more generalized composite granular chains with sandwich configurations. Results provide in-depth physical understanding and engineering design guidance to quantitatively tailor wave properties through simple 1D granular structures.

Wave propagation through submerged granular media over a wide range of fluid viscosities

The low-velocity impact response of 2D granular crystals immersed in various fluids over a wide range of viscosities (1–106 cP) was investigated. The drag effects in the immersed crystals results in significantly higher wave attenuation as compared to dry granular crystals. In order to quantify the spatial dependence of the wave decay characteristics, the coefficients of attenuation were computed for the dry granular crystals and granular crystals immersed in various fluids. The coefficient of attenuation for immersed granular crystals was significantly larger than the coefficient of attenuation for dry granular crystals. As the viscosity increased, the coefficient of attenuation also increased due to the additional drag effects followed by an unexpected decrease for the highest viscosity fluids. The ratio of kinetic energy to strain energy for immersed granular crystals decreases initially as a function of viscosity but increases again for the fluids with the highest viscosities.

Granular crystallization using CFBC ash for phosphorus removal via hydroxyapatite

Abstract To prevent eutrophication and remove phosphorus, circulating fluidized bed combustion (CFBC) ash was utilized to elute Ca2＋ and OH − for hydroxyapatite (HAP) crystallization. CFBC ash was compared with the gypsum byproduct of a domestic waste incineration plant and pure CaO reagent. CFBC ash proved to be a suitable raw material to supply Ca2＋ and OH − for HAP crystallization. CFBC ash was reprocessed as a granular crystallization agent (GCA) to improve its applicability to non-point pollution source control. In addition, a manufacturing procedure for a GCA utilizing 4.8% blast furnace slag as a binder was developed based on durability and the ion elution rate in water. Column tests with sedimentation showed that 93% and 98% of T-P and PO4-P were removed after 12 h of settling, respectively. In on-site filtration trench tests, filtration following crystallization with a 4 h retention time achieved a 63.5% and 52.8% removal efficiency with respect to T-P and PO4-P, respectively. After operation for 13 d, an increase in porosity with pore distribution on the surface of the GCA was observed. Through their long-term on-site operation, crystallization–filtration trenches using GCA provide an effective alternative process for the management of agricultural non-point source pollution.

Experimental Investigation on Uniaxial Unconfined Compressive Properties of Ice on Asphalt Pavement Surface

Mechanical deicing is a method to remove the ice on the pavement surface, and the ice strength directly affects the difficulty and effectiveness of the mechanical deicing. This paper aims to investigate the compression strength of ice to facilitate the deicing equipment to crush ice. In this paper, a large-scale freezing laboratory is employed to simulate low temperature environment, and the uniaxial unconfined compressive tests of artificial fresh-water ice under different temperature conditions are carried out through the uniaxial loading system. The compressive strength and modulus of ice are obtained when the substrate is asphalt pavement. The test result shows that the ice compressive strength and modulus respectively distribute from 0.36 MPa to 3.67 MPa and 11.7 MPa to 359.1 MPa when ice temperature varies from -0.7℃ to -7.5℃. The relations between ice temperature and compressive strength are approximately in linear manner, while the relation of compressive modulus and ice temperature shows good power function and exponential relationships respectively when ice temperature ranges from -8℃ to -5℃ and from -5℃ to 0℃. Furthermore, the failure mechanism of ice under relatively lower temperature is due to the development of cut-through cracks inside the ice. The failure mode divides into shear failure and ductile failure and the failure ice is mainly composed of large ice strips and bulks. For the ice with relatively higher temperature especially the ice close to melting point temperature, the ice failure mode is compressive and ductile, and the failure ice is mainly composed of granular ice crystals.

Effects of Erosion Form and Admixture on Cement Mortar Performances Exposed to Sulfate Environment

The effects of the admixtures, erosion age, concentration of sulfate solution, and erosion form of sulfate attack on the mechanical properties of mortar were investigated. Simultaneously, the microstructure, pore characteristics, kinds and morphologies of erosion products of mortar before and after sulfate attacks were performed by Mercury Intrusion Porosimetry (MIP), Environment Scanning Electronic Microscope and Energy Dispersive Spectrometer (ESEM-EDS). In addition, the crystal form and morphology characteristics of crystallization on mortar surfaces attacked by partial immersion form were studied. The results showed that the compressive and flexural strengths of mortar attacked by sulfate for four months decreased with the increase of the replacement of cement with fly ash, and the corresponding strength of mortar containing slag first increased and then decreased. The admixtures can improve the microstructure and mechanical properties of mortar within the replacement ratio of 10%. Although the change laws of the mortar specimens containing different admixtures were similar, the mortar containing slag had an excellent sulfate resistance under the same condition. Compared with the complete immersion form, the strength variation of the mortar containing fly ash attacked by semi-immersion form was less. The porosity and average pore diameter of mortar attacked by sulfate for four months increased, and the percentage of micropore with the pore diameter less than 200 nm increased. Plenty of rod-like and plate-like erosion products were generated in mortar attacked by a sulfate solution with a high concentration. A larger number of fibrous and flocculent crystallization covered the mortar’s surface containing fly ash, but it was a granular and dense crystallization formed on the mortar’s surface containing slag. Much dendritic erosion product was generated in the mortar attacked by semi-immersion form, and ESEM-EDS analysis revealed that it may be scawtite, spurrite, and residue of the decomposed calcium silicate hydrate (CSH) in the inner mortar; however, the crystallization sodium sulfate was crystallized on mortar surface.

Effect of P2O5 and Al2O3 on crystallization, structure, microstructure and properties of Li2O–MgO–Al2O3–SiO2–TiO2–ZrO2 glass ceramics

The structure, microstructure, thermal and mechanical properties of glasses and glass-ceramics in the LMAS (Li2O, MgO, Al2O3, SiO2) system and the effect of P2O5 and Al2O3 additives have been studied. The transition temperatures of both glasses and glass-ceramics increase with the P2O5 and Al2O3 concentration, but at high temperatures the melt viscosity decreases. The main crystalline phases formed are lithium aluminium silicate, enstatite and β-spodumene, being the growth of β-spodumene favoured by fluorine ions, P2O5 and the heat treatment temperature as well. Raman and FT-IR spectroscopies have shown the formation a silica-rich glass phase which acts as a matrix of the crystallites containing Al2O3 and P2O5 in its composition. The shape and aspect ratio of the crystallites depend on the Al2O3 concentration. For low Al2O3 concentration a variety of tubular, granular and plate-like crystals appear, while for high Al2O3 concentration the main shape of the crystals is spherical or globular. Hv, E and CTE properties are related to the crystalline phases formed during the crystallization treatment, and their variations are in accordance with the increase of the crystal aspect ratio. The CTE values of the GCs decrease as the P2O5 content increases up to 3%, while for the Al2O3 concentration of 16% the minimum CTE value is obtained. Hv and E values of the GCs are higher than those corresponding to their respective parent glasses. According to these values, these glasses and glass-ceramics are not appropriate for machining.

The effects of limonene on the crystallization of palm oil

This study aimed to evaluate how the addition of limonene in different concentrations (1–10 g/100 g) influences the crystallization of palm oil (PO). An extensive study of the crystallization behavior of PO and its blends was performed using nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), polarized light microscopy (PLM), and X-ray diffraction. Adding limonene to PO reduced its solid fat content (SFC) and delayed crystallization, with a more pronounced effect at higher concentrations (7.5 and 10 g/100 g). The samples’ microstructure changed from spherulites in pure PO to agglomerated granular crystals at higher concentrations (7.5 and 10 g/100 g). Regarding polymorphism, the samples containing limonene showed a slight sign of acceleration over time, and after 60 days all samples, including PO, had predominance of the β form. It can be affirmed that reducing the SFC of PO substantially contributes to mitigating its post-hardening.

Effects of Temperature and Water on Mechanical Properties, Energy Dissipation, and Microstructure of Argillaceous Sandstone under Static and Dynamic Loads

RMT-150B rock mechanics and split Hopkinson pressure bar (SHPB) devices were adopted to investigate the physical and mechanical properties, energy dissipation, and failure modes of argillaceous sandstone after different high temperatures under air-dried and saturation states. In addition, SEM and EDS tests were conducted to investigate its microstructure characteristics. Results showed that both the P-wave velocity and density of argillaceous sandstone specimen decreased with the increase of high temperature, while its porosity increased. Compared with static stress-strain curves, there was no obvious compaction stage for dynamic stress-strain curves, and the decrease rate of dynamic curves after peak strain was obviously slow compared with static curves. Both the static and dynamic strengths of argillaceous sandstone specimens decreased with increasing temperature, and the critical temperature point for the strength of argillaceous sandstone was 400°C. At the same temperature, the specific energy absorption under air-dried state was generally smaller compared with that under saturated state. Both the strain rate and temperature showed significant effect on the failure mode. After 100∼1000°C heat treatment, the granular crystals of the clastic structure gradually became larger, and both the number and average size of the original pores decreased, resulting in the deterioration of mechanical properties of argillaceous sandstone specimen.

Small Mass Nanopteron Traveling Waves in Mass-in-Mass Lattices with Cubic FPUT Potential

The mass-in-mass (MiM) lattice consists of an infinite chain of identical beads that are both nonlinearly coupled to their nearest neighbors and linearly coupled to a distinct resonator particle; it serves as a prototypical model of wave propagation in granular crystals and metamaterials. We study traveling waves in an MiM lattice whose bead interaction is governed by the cubic Fermi–Pasta–Ulam–Tsingou potential and whose resonator mass is small compared to the bead mass. Excluding a countable number of “antiresonance” resonator masses accumulating at 0, we prove the existence of nanopteron traveling waves in this small mass limit. The profiles of these waves consist of the superposition of an exponentially localized core and a small amplitude periodic oscillation that itself is a traveling wave profile for the lattice. Our arguments use functional analytic techniques originally developed by Beale for a capillary–gravity water wave problem and recently employed in a number of related nanopteron constructions in diatomic Fermi–Pasta–Ulam–Tsingou lattices.

Stickiness of sugar syrups with and without particles

Stickiness of sugar solutions causes problems in various food products and operations. In this study, the effects of glucose syrup type (dextrose equivalent) and crystalline particles on stickiness of sugar solutions with water contents from 10 to 20% were determined. Four different corn syrups with varying dextrose equivalence (DE) were used to determine the effects of polysaccharide distribution on sugar syrup stickiness. The effects of particles (zirconium oxide beads (Zr 2 O 3 ), fondant sucrose and granular sucrose crystals) on the surface were then evaluated to gain a better understanding of their role in reducing syrup stickiness. Stickiness was measured as tack force and work of adhesion with a texture analyzer and correlated with water content and glass transition temperature ( T g ). Both tack force and work of adhesion increased to a maximum as moisture content decreased from 20% down to between 11 and 13%. Below this water content, work of adhesion decreased as syrups underwent a transition from cohesive to adhesive failure. Similar behavior was shown for T-T g . In general, lower DE caused a reduction in both tack force and work of adhesion without a significant change in T g . Particles at the surface, regardless of their size or origin, decreased stickiness approximately linearly with increasing surface coverage, verifying the hypothesis that a reduction in the surface area of amorphous sugar in contact with the probe causes a direct reduction in stickiness. Stickiness of a partially-crystalline coating layer was correlated to moisture content and the extent of surface coverage of particles. • Stickiness of sugar syrups is directly correlated with syrup moisture content. • Syrups made with higher DE corn syrup had higher tack force and work of adhesion. • Particles added to the bulk of sugar syrups did not affect stickiness. • Surface particle addition significantly decreased sugar syrup stickiness.

Fat crystallization of blends of palm oil and anhydrous milk fat: A comparison between static and dynamic-crystallization

The application of dynamic-crystallization (a combination of shear with rapid cooling) often plays an important role in the production of industrial fat-based products such as shortenings/margarines but has been rarely reported. In this study, three blends of palm oil (PO) with anhydrous milk fat (AMF) (0, 25 and 50% AMF, w/w) were rapidly crystallized under static (using freezer) and dynamic conditions (using a benchtop scraped surface heat exchanger). Various techniques including differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarized light microscopy (PLM), rheology and texture analysis were applied to investigate physicochemical properties of fat blends as well as their crystal morphology upon the long-term storage (4 weeks) at 5 °C and 15 °C. The results revealed that high cooling rate of dynamic-crystallization not only affected melting behavior of fat blends but also prevented the polymorphic transformation from β’ to β crystals. Besides, the application of shear during fat crystallization helped to improve significantly the gel strength of produced shortenings. Although post-crystallization of low melting triacylglycerols (TAGs) occurred for all produced shortenings during storage at 5 °C which was accompanying with a firmness increase, it was more considerable for samples owning higher AMF content. Moreover, this phenomenon promoted the sintering as well as Ostwald ripening between fat crystals of dynamic-crystallized fat blends resulting in the formation of unwanted large aggregates (or granular crystals) with the size ranging from 100 to 500 μm.