Composite Spheres Research Articles

Carbon/Li4Ti5O12 Composite Spheres Prepared Using Chinese Yam as Carbon Source with Ultrahigh Capacity as Anode Materials for Lithium Ion Batteries

AbstractSpinel structured Li4Ti5O12 (LTO) spheres modified with carbon (Carbon/LTO composites) using Chinese yam (CY) as carbon source have been obtained by a hydrothermal method combining with a calcining at 700 °C in N2 atmosphere. The influences of the additions of CY on the morphology, structure, carbon content and also the electrochemical properties of the resulted carbon/LTO composite spheres have been investigated in details. SEM and TEM investigations show that all the composites possess spherical morphology and consist of nanosized Li4Ti5O12 crystals modified with carbon. With the increase of CY additions, the size of Li4Ti5O12 primary crystals decrease gradually, and reach to a turn over point and then the crystal size turn to large ones when the CY content increased further. It has been demonstrated that carbon modification of Li4Ti5O12 with Chinese yam as carbon source could efficiently improve the electrochemical performance of Li4Ti5O12. One of the composite sample named as C/LTO‐10 shows an ultrahigh initial specific capacity of about 211.9 mAh ⋅ g−1 at a current density of 1 C. It shows excellent cycle performance and maintains a specific capacity of 184.5 mAh ⋅ g−1 even after 300 cycles. A specific capacity of 123.5 mAh ⋅ g−1 still could be delivered at a high current density of 30 C, exhibiting also superior rate capability.

Study on cellulose microfilaments based composite spheres: Microwave-assisted synthesis, characterization, and application in pollutant removal

A novel study of synthesizing the temperature-responsive polymer grafted cellulose filaments/Poly (N-isopropylacrylamide) (NIPAM) spheres (P-MCCBs) was carried out for the removal of dyes and heavy metal ions. The novelty of the presented work consists of the application of the nano-sized pore-forming agent (Calcium Carbonate) and the introduction of a temperature-responsive monomer (NIPAM) while preparing the adsorbents. In addition, the spherical adsorbents were synthesized through an in-situ free radical polymerization using a microwave-assisted heating approach. The morphology, chemical structure, pH, and thermal sensitivity of P-MCCBs were characterized properly. The adsorption and desorption behaviors of dyes and heavy metal ions on P-MCCBs were also investigated. The results showed that P-MCCBs exhibited a fast adsorption rate, the adsorption equilibrium reached within 80 min and 40 min for MB and Pb2+, respectively (25 °C). Moreover, around 5–8% and 20% of adsorbed MB and Pb2+ were released at the temperature above 45 °C. The adsorption kinetics followed pseudo-second-order model, and the desorption process was fit well using Higuchi and Korsmeyer-Peppas models. These results indicated that P-MCCBs could be served as a novel material for controllable adsorption and desorption processes of various contaminants.

Dynamic interaction of refractory and molten steel: Effect of alumina-magnesia castables on alloy steel cleanness

High quality alloy steel is an important material needed for social and economic development. It is of great significance to major national projects and defence security. Refractories are used in the smelting process of steel; they are some of the main sources of impurities which have an important effect on the quality of steel. As alumina-magnesia refractories are the main lining materials used for steel refining, the influence of these refractories on the cleanliness of molten steel under dynamic smelting conditions has been studied. The size, quantity, composition, and structure evolution of inclusions in steel are analysed. The results show that after smelting, the content of alloy elements in the steel is stable, and that the total oxygen content and inclusions in the steel are increased by the corrosion of the alumina-magnesia castables. However, the maximum average particle size of the inclusions in the steel was limited to 20 µm, which did not cause large inclusions in the steel or seriously affect the quality of steel. During the dynamic melting process, because of the presence of Si and Mn in the alloy steel, the inclusions changed from homogeneous CaS wrapped Al2O3-MgO composite sphere to MnS wrapped egg-shaped structure. The alloy elements in steel were found to be beneficial, as they reduced the effect of alumina and magnesia inclusions on the quality of steel. The results indicate that it is feasible to smelt high quality alloy steel using alumina-magnesia carbon-free castable, and that it would be better to limit the refining time to 45 min during smelting.

Defect nucleation modelling

The purpose of this article is to compare concepts of defect nucleation based on bifurcation of equilibrium solution and on damage modelling. The nucleation criterion is defined as a bifurcation of the equilibrium solutions of the perfect body and of the imperfect one when the size of the defect vanishes. The defect is considered as a small volume which evolves as a damaged zone. To study the influence of geometry of the defect on the critical loading governing its initiation, we consider the particular cases of a linear elastic composite sphere and of a linear elastic composite cylinder, for which the equilibrium solutions are known when the radial distribution of elastic bulk modulus is given simultaneously with a uniform shear modulus. The initial defect is a small sphere or a small cylinder, respectively, it can be a cavity or a kernel made with an elastic material with lower mechanical properties.

Synthesis of Core‐Shell Structured MnO2 Petal Nanosheet@Carbon Sphere Composites and Their Application as Supercapacitor Electrodes

AbstractA novel MnO2 petal nanosheet@carbon sphere core‐shell structure was successfully fabricated by adjusting the quantity of the KMnO4 precursor employed during the in situ growth of MnO2 on the surface of carbon spheres via a facile hydrothermal method. In the presence of low KMnO4 contents, only MnOOH was generated. In contrast, upon increasing the quantity of KMnO4, δ‐MnO2 nanorods and petal nanosheets were obtained, thereby allowing the formation of the core‐shell structured δ‐MnO2 petal nanosheet@carbon sphere composites. However, beyond a certain point, further increases in the KMnO4 content were unfavorable. Although, prepared MnO2/carbon sphere composites of different morphologies can be used for supercapacitors (SCs) electrode materials, we found that the core‐shell structured MnO2 petal nanosheet@carbon sphere composites exhibited the optimal capacitance performances in all the composites. These composites exhibited an excellent specific capacitance of 231 F⋅g−1 under a current density of 0.5 A⋅g−1. Furthermore, they also demonstrated an impressive cycling stability. Indeed, after 1,000 cycles at 10 A⋅g−1, the MnO2 petal nanosheet@carbon spheres exhibited 96% of their initial capacitance in a 1 M Na2SO4 aqueous electrolyte. The synergistic effect between δ‐MnO2 and the porous carbon spheres in the unique core‐shell structured is responsible for the excellent cycle life.

Synthesize of large-sized porous carbon spheres with controllable N-content via spray-drying and photo-induced RAFT polymerization

A method combined spray-drying process with light-induced reversible addition fragmentation chain transfer (RAFT) polymerization was used to synthesize N-doped carbon spheres (N-CS). Firstly, the common used carbon precursor phenolic resin which called Resol was modified with a chain transfer agent (CTA). Then, the mixed ethanol solution of CTA modified Resol, F127, TEOS, and HCl was used as starting material. After a typical spray-drying process, uniformed and discrete composite spheres in regular size (70 μm) were obtained. The RAFT polymerization of acrylonitrile was initiated under the irradiation of blue LED at the surface of spheres. Through such manner, controlled amount of polyacrylonitrile was introduced onto the surface of carbon sphere. After calcination at 900 °C and etching, the obtained porous N-CS (60 μm) showed controllable total N content up to 10.8 wt%, tunable high surface area up to 1130 m2/g and good CO2 absorptivity which can up to 4.34 mmol/g at 273 K and 4.13 mmol/g at 298 K at 1.0 bar.

Characterization and compressive property of Mg alloy-ceramic sphere composites

Magnesium matrix composites reinforced with Al2O3 ceramic sphere (i.e., AZ91D-Al2O3 sphere composites) were prepared by infiltration casting method. The morphology, microstructure, elements, phase compositions of the composites were observed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD), respectively. And the compressive properties at room temperature and elevated temperatures were investigated. The experimental results show that the ceramic spheres are uniformly distributed in the AZ91D matrix alloy. The surface of the ceramic sphere provides a site for heterogeneous nucleation of Mg17Al12 phase. The compressive strengths of the composites and AZ91D alloy are reduced with the increase of temperature. However, the composites show the higher compressive strength than the AZ91D alloy at evaluated temperatures. The deformation behaviors were observed and the failure mechanisms at room temperature and elevated temperatures were discussed.

Control of pore size in shell of hollow silica–alumina composite spheres for hydrolytic dehydrogenation of ammonia borane

In the present study, we attempted to control the shell pore size of hollow spheres and investigated the resulting effect on their acidic properties and activity for the acid-promoted hydrolytic dehydrogenation of ammonia borane. Silica shells were formed on polystyrene template particles via sol–gel method, followed by calcination. For controlling the pore structure, surfactants with various molecular lengths (decyltrimethylammonium bromide (DeTAB), cethyltrimethylammonium bromide (CTAB), and stearyltrimethylammonium bromide (STAB)) were used. The shells of all the hollow spheres included monodispersed and well-ordered pores, and the pore size increased with increase in the molecular length of the surfactant. In particular, the hollow spheres prepared with CTAB and STAB consisted of numerous well-ordered mesopores with sharp peaks centered at approximately 2.4 and 2.8 nm, respectively. The molar ratios of the hydrolytically evolved hydrogen to the initial NH3BH3 in the presence of the hollow spheres prepared with DeTAB, CTAB, and STAB were 0.9, 3.0, and 2.7, respectively, which indicated the stoichiometric amount of hydrogen was evolved in the presence of the hollow spheres prepared with CTAB and STAB. The amount and rate of hydrogen evolution depended on the pore structure, and the hollow spheres with well-ordered and appropriate-sized mesopores in the shells showed a large amount and high rate of hydrogen evolution.

Unsteady rotational motion of a composite sphere in a viscous fluid using stress jump condition

ABSTRACTThe unsteady rotational motion of a composite sphere, consisting of a solid core surrounded by a porous shell, in an incompressible viscous fluid is discussed using Brinkman’s formula. The composite sphere is assumed to rotate about z-axis with time-dependent angular velocity. Laplace transform technique is utilized to obtain the solution of the problem. The inversion of Laplace transform is obtained analytically using contour integration. An analytical and numerical interpretation of the Torque exerted by the fluid on the porous surface is obtained. The effect of stress jump condition and permeability coefficient is discussed and some special cases are deduced.

A least squares approach for effective shear properties in an $${{\varvec{n}}}$$ n -layered sphere model

This work presents the derivation of the effective shear modulus for a heterogeneous material composed of multilayered composite spheres embedded in a linear elastic matrix. It is based on the composite spheres model known from the literature. In contrast to Herve and Zaoui (Int J Eng Sci 31:1–10, 1993), the effective shear modulus is obtained by equating the results of two models: In the first model, a heterogeneous sphere is embedded in an equivalent homogeneous material, whereas in the second model, the heterogeneous sphere is replaced by an equivalent homogeneous sphere. In the context of both, a shear stress approach and a shear deformation approach, this results in an overdetermined system of equations which is solved with the least squares method. In a numerical study, our results are compared to effective moduli and bounds from the literature. Furthermore, a convincing agreement with experimental data for glass microspheres embedded in a polyester matrix is demonstrated.

Electrochemistry of SmCl3 and SmF3 in Molten NaCl-KCl

Lanthanide elements, which are present in spent fuel from fast nuclear reactors, can be converted into molten salts by anodic dissolution. Electrolysis of molten salts is promising for separation of lanthanides and actinides. To solve this problem, it is necessary to have experimental data on the electrochemical behavior of various lanthanides in molten salts. The aim of this study is determine the influence of the first coordination sphere composition of samarium complexes on its electrochemistry in molten equimolar mixture NaCl-KCl. Electrochemical investigations were carried out in a temperature range of 973-1173 K by cyclic voltammetry using an AUTOLAB PGSTAT 20 potentiostat with a package of application programs GPES (version 4.4.). The melt container was a glassy carbon crucible of SU-2000 brand, which also served as an auxiliary electrode. Tungsten wire was used as working electrode and Pt wire was utilized as a quasi-reference electrode. In the NaCl-KCl-SmCl3 melt it was found that peak current of the recharge process of Sm(III) to Sm(II) is directly proportional to the square root of the polarization rate, while the peak potential does not depend on the polarization rate up to v=0.1 V s-1. According to the theory of linear sweep voltammetry, up to the polarization rate 0.1 V s-1, the electrode process is reversible. However, in the NaCl-KCl-SmF3 molten system the recharge process was reversible up to the scan rate 1.0 V s-1. Diffusion coefficients of Sm(III) in chloride and chloride-fluoride melts were determined by cyclic voltammetry using the Randels–Sevchik equation. The quasi-reversible process for the Sm(III)/Sm(II) redox couple was determined in NaCl-KCl-SmCl3 melt at a sweep rate 0.1<v<0.3 V s-1. This mechanism is clearly evidenced by the deviation of the experimental points from linearity in the IC p vs. v 1/2 plot, by the dependence EC p on v and by the magnitude of the difference between EA p and EC p, which is larger than is required for a reversible process. A transition from a reversible to a quasi–reversible process was found at v > 1.0 V s-1 in the NaCl-KCl-SmF3 melt. The standard rate constants of charge transfer (k s) of the Sm(III)/Sm(II) redox couple were determined by cyclic voltammetry both in NaCl-KCl-SmCl3 and NaCl-KCl-SmF3 molten salts using the Nicholson’s equation, which is valid for quasi-reversible processes. The higher values of k s were obtained in chloride melt than in chloride-fluoride molten system.

A novel graphite-PCM composite sphere with enhanced thermo-physical properties

Cooling is one of the major energy consuming processes in industry; thus the design of efficient and reliable cold energy storage system based on phase change material is an important requirement in many fields. However, the performance of such system is limited by the poor thermal conductivity of most phase change material. This paper provides a novel graphite-phase change material composite sphere, having high thermal conductivity. In this study, two different types of phase change material were used, organic (PureTemp4) and inorganic (water) phase change materials. The measured thermal conductivity of graphite-water and graphite-PureTemp4 composite spheres were 12 and 30 times higher than those of pure water and PureTemp4, respectively. The microstructure of the compressed expanded graphite and graphite-phase change material composites were examined using a scanning electron microscope. The result shows that the phase change material was completely filled the pores and adhered as a thin layer on the graphite surfaces. Differential scanning calorimeter and thermal cycling tests showed no significant changes in thermal properties of the graphite-phase change material composite spheres after 200 thermal cycles. The measured average freezing rates for graphite-phase change material composite and hollow plastic spheres containing the same amount of PCM are 14.42 W and 4.58 W respectively, while for melting are 31.34 and 10.28 W respectively. The super-cooling of water was reduced 2 °C by the effect of graphite, however it was totally eliminated in the presence of small amount of silver iodide as a nucleating agent. The use of compressed graphite matrix decreases little the energy density of the phase change material spheres, however the significant heat transfer enhancement override such small decrease in energy density.

Synthesis and photo-thermal property of alginate/gold nanorod composite spheres

Gold nanorods (GNRs) have received considerable attention in the development of novel photo-thermal materials because of their unique optical property. In this paper, alginate/GNR composite microspheres were synthesized through emulsification of the aqueous alginate/GNR mixture in the paraffin oil via a water/oil emulsion technique followed by cross-linking process in the solution of CaCl2. Microstructure and near-infrared (NIR) responsive photo-thermal property of the resultant composite spheres were investigated. SEM observations showed that the composite spheres were spherical in morphology and had the diameter of 5-40 μm. XRD patterns showed that the typical diffraction bands of GNRs were observed at 38° and 44° in the composite spheres. Under the 808 nm-NIR irradiation, the composite spheres were NIR-responsive and the temperature of the aqueous suspension of the composite spheres increased from 28°C to 39°C. It was found that their photo-thermal property could be well adjusted through controlling the content of GNRs in the composite spheres and irradiation time.

Synthesis and in vitro biodegradability of carbonatedhydroxyapatite/chitosan composite spheres

Hydroxyapatite(HAp)/biopolymer composites have been extensively applied as bone tissue regenerative materials because of their excellent biocompatibility and osteo-conductivity. However, the low biodegradability of HAp highly limited their practical applications. In this study, the carbonated hydroxyapatite(CHAp)/chitosan composite spheres with the size range of 100-200 μm and 300-400 μm were synthesized from CHAp and chitosan via a water/oil emulsion technique and their microstructure and biodegradability were evaluated. SEM observations showed that the resultant spheres were spherical in shape and had a rough surface. FT-IR spectrum showed that the composite spheres were derived from CHAp and chitosan due to the presence of the characteristic bands of phosphorous groups, carbonate groups and amide groups. XRD patterns showed that the composite spheres maintained the crystalline structure of CHAp crystals after combination of CHAp with chitosan. In vitro biodegradation was performed as the composite spheres were separately soaked in the buffer saline with the pH of 4.5 and 7.4. It was found that the biodegradation of the composite spheres was not affected by the size range of the composite spheres, but highly influenced by the pH value of the buffer saline. The composite spheres little degraded under the neutral condition, while around 25% of the composite spheres degraded after 7 days of incubation under acidic condition. Our results indicate that the present composite spheres are biodegradable and suitable as potential bone regenerative fillers.

Drag Experienced by a Composite Sphere in an Axisymmetric Creeping Flow of Micropolar Fluid

Drag Experienced by a Composite Sphere in an Axisymmetric Creeping Flow of Micropolar Fluid

Fabrication of β‐tricalcium phosphate composite ceramic scaffolds based on spheres prepared by extrusion‐spheronization

AbstractIn this study, β‐tricalcium phosphate/phosphate‐based glass (β‐TCP/PG) composite spheres were prepared by an extrusion‐spheronization method featuring high production and fine control of sphere size. Subsequently, fully interconnected β‐TCP composite ceramic sphere‐based (TCCS) scaffolds were fabricated by sintering the randomly packed β‐TCP/PG composite spheres. The results manifested that at least 20% microcrystalline cellulose (MCC) was required to obtain β‐TCP/PG composite spheres in good spherical shape. The prepared TCCS scaffolds showed hierarchical pore architecture, which consisted of interconnected macropores among the spheres, a hollow core in the sphere, plentiful medium‐sized pores in the sphere shell and micropores among the grains. The pore architecture and mechanical strength of the TCCS scaffolds could be tailored by adjusting the sintering temperature, sphere size, and amounts of PG and MCC in the β‐TCP/PG composite spheres. This work is believed to open up new paths for the design and fabrication of interconnected bioceramic scaffolds for application in bone regeneration.

In situ coherent X-ray diffraction imaging of radiation-induced mass loss in metal-polymer composite spheres.

A major limitation to the use of coherent X-ray diffraction imaging (CXDI) for imaging soft materials like polymers and biological tissue is that the radiation can cause extensive damage to the sample under investigation. In this study, CXDI has been used to monitor radiation-induced structural changes in metal-coated poly(methyl methacrylate) microspheres. Using a coherent undulator X-ray beam with 8.10 keV photon energy, 14 tomograms at a resolution of ∼30 nm were measured consecutively, which resulted in an accumulated dose of 30 GGy. The three-dimensional images confirmed that the polymer core was strongly affected by the absorbed dose, giving pronounced mass loss. Specifically, as the metal-polymer composite was exposed to the X-ray beam, a bubble-like region of reduced density grew within the composite, almost filling the entire volume within the thin metallic shell in the last tomogram. The bubble seemed to have its initiation point at a hole in the metal coating, emphasizing that the free polymer surface plays an important role in the degradation process. The irradiation of an uncoated polystyrene microsphere gave further evidence for mass loss at the free surface as the radius decreased with increased dose. The CXDI study was complemented by X-ray photon correlation spectroscopy, which proved efficient in establishing exposure dose limits. Our results demonstrate that radiation-induced structural changes at the tens of nanometer scale in soft materials can be followed as a function of dose, which is important for the further development of soft-matter technology.

Preparation of porous carbon nanotube/carbon composite spheres and their adsorption properties

Carbon nanotubes (CNTs) are considered precursors to efficient adsorbents in many fields, including medical hemoperfusion; however, such adsorbents have not yet been realized, mainly because of the lack of scalable processing technologies to transform as-produced CNTs into applicable bulk materials. In this study, an extrusion–spheronization process followed by carbonization was developed to synthesize CNT/carbon composite spheres. A freeze-casting post-treatment in liquid nitrogen was explored to tailor the pore structures. In the freeze-casted tailored composite spheres, hierarchical pore structures with more developed meso- and macro-pores were formed compared to the untreated samples. Scanning electron microscopy observations demonstrated the generation of abundant laminar slit-like macropores after freeze-casting. Nitrogen adsorption-desorption tests and mercury porosimetry analyses indicated that the spheres had pore width distributions ranging from 100 nm to 1000 nm, in addition to highly developed mesopores. The adsorption capacities of the freeze-casted spheres for Vitamin B12 and lysozyme were 52.8 mg/g and 47.1 mg/g, respectively, which were remarkably higher than those of traditional adsorbents such as activated carbon or macroporous resin; the adsorption rates were also significantly higher with the composites. Energy-dispersive X-ray spectral mapping analyses confirmed that the macropores developed by freeze-casting acted as diffusion throughways during the adsorption process.

Exact solutions for the effective nonlinear viscoelastic (or elasto-viscoplastic) behaviour of particulate composites under isotropic loading

Abstract We consider a composite sphere which consists of a spherical inclusion embedded in a concentric spherical matrix, the inclusion and matrix phases obeying an isotropic nonlinear viscoelastic behaviour . For different isotropic loadings (macroscopic stress or dilatation, swelling of the inclusion phase), the general solutions are shown to depend on the shear stress distribution in the matrix. This shear stress distribution is solution of a first-order nonlinear integro-differential equation, regardless of the inclusion viscoplastic behaviour. When the viscous strain rate potentiel in the matrix is a power-law function of the von Mises equivalent stress, closed-form solutions are given for some special cases clearly identified. Full-field calculations of representative volume elements of particulate composites are also reported. For a moderate volume fraction of inclusions, the composite sphere model turns out to be in excellent agreement with these full-field calculations.

Synthesis of composite of ZnO spheres with polyaniline and their microwave absorption properties

Three-dimensional (3D) ZnO microspheres with the composite of polyaniline (PANI) have been successfully synthesized by one-pot solvothermal and in-suit polymerization method. The obtained microspheres were uniform having the diameter of 4 μm–7 μm. These microspheres, inside cushion of PANI polymer, exhibit excellent microwave absorption properties. Composite of ZnO microspheres with PANI increased the complex permeability and enhanced the dielectric loss. Thus, the microwave absorption properties of the composite have been intensified. Despite the fact that the composite of ZnO with PANI herein dissipate the microwaves by dielectric loss, their performance is admirable compared to most of PANI-based composites reported. The morphological, structural and spectral properties have been investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and the Fourier transform infrared (FT-IR). It is found that the maximum reflection loss value of ZnO@PANI reaches −41 dB at 14 GHz with a thickness of 3.5 mm that is superior to the previously reported composite of PANI with other materials.