A new perspective on carbon nano-onion/nickel hydroxide/oxide composites: Physicochemical properties and application in hybrid electrochemical systems

Carbon nano-onion (CNO) and Ni(OH)₂ or NiO composites were prepared by chemical loading of Ni(OH)₂ on the carbon surface. The samples were characterized by transmission electron microscopic (TEM) and scanning electron microscopic (SEM) methods, powder X-ray diffraction (XRD) technique and by differential-thermogravimetric analyses (TGA-DTG). The porosity properties were characterized by using nitrogen gas adsorption analyses. Pristine inorganic samples of NiO and Ni(OH)₂ revealed different morphologies and porous characteristics when compared to those of the CNO composites, which showed unique electrochemical properties. The electrochemical performance of the CNO/Ni(OH)₂ or CNO/NiO composites is largely affected by the mass, the morphology, the crystal phases of the inorganic component and the distribution of the Ni(OH)₂/NiO phase. The CNO composites were used as materials for hybrid charge-storage devices.     

Carbon nanotube-reinforced composites: frequency analysis theories based on the matrix stiffness

Strong and versatile carbon nanotubes are finding new applications in improving conventional polymer-based fibers and films. This paper studies the influence of matrix stiffness and the intertube radial displacements on free vibration of an individual double-walled carbon nanotube (DWNT). For this, a double elastic beam model is presented for frequency analysis in a DWNT embedded in an elastic matrix. The analysis is based on both Euler–Bernoulli and Timoshenko beam theories which considers shear deformation and rotary inertia and for both concentric and non-concentric assumptions considering intertube radial displacements and the related internal degrees of freedom. New intertube resonant frequencies and the associated non-coaxial vibrational modes are calculated. Detailed results are demonstrated for the dependence of resonant frequencies and mode shapes on the matrix stiffness. The results indicate that internal radial displacement and surrounding matrix stiffness could substantially affect resonant frequencies especially for longer double-walled carbon nanotubes of larger innermost radius at higher resonant frequencies, and thus the latter does not keep the otherwise concentric structure at ultrahigh frequencies. Therefore, depending on the matrix stiffness, for carbon nanotubes reinforced composites, different analysis techniques should be used while the aspect ratio of carbon nanotubes has a little effect on the analysis theory which should be selected.     

Dielectric properties and morphologies of composites filled with whisker and nanosized zinc oxide

Two kinds of zinc oxide (ZnO) powders, which are ZnO whisker (w-ZnO) and nanosized ZnO (n-ZnO), were used to prepare the composites with a matrix of low-density polyethylene (LDPE). Dielectric constants and losses of the composites were measured in a frequency range of 1-10 MHz. The dielectric constants and losses increase with increasing w-ZnO content in composites. Modified w-ZnO has a remarkable effect on dielectric properties of the composites. Dielectric constants and losses of the composites containing n-ZnO are larger than those containing w-ZnO under the same content. The results can be explained by nanoscale effects. Some theories of mixing laws are also referred to the dielectric properties of composites in this paper.     

CNT composites for aerospace applications

Carbon nanotubes were synthesized by thermal arc plasma process after optimization of the synthesis parameters. These samples were then analysed by scanning and transmission electron microscopes (SEM and TEM), in order to establish the morphology of the nanostructures. Atomic force microscopy (AFM) and electron diffraction studies were also carried out before using the sample for the composite material preparation. Composites of epoxy resin with curing agent as well as a mixture of graphite and carbon nanotubes were prepared with varying proportions of the mixture. The electrical resistivity of the material was studied under varying pressure and voltage conditions. Preliminary results of these studies present interesting features which are reported here.     

Preparation and study of carbon nano-onion for lithium storage

Carbon nano-onions were prepared by burning castor oil. The as-prepared carbon nano-onions were characterized by scanning electron microscopy and transmission electron microscope to confirm the nano-onion structures. The carbon nano-onions were used as anodes for rechargeable Li-ion batteries and demonstrated high reversible capacity and relatively good rate capability. The electrochemical performance can be attributed to the unusual surface properties and unique structural features of the carbon nano-onion anode, which amplify both surface area and extensive intermingling between curved graphite layer over small length scales, thereby leading to fast kinetics and short pathways for both Li ions and electrons.     

Synthesis of polyoxometalates-functionalized carbon nanotubes composites and relevant electrochemical properties study

Carbon nanotubes (CNTs)-based polyoxometalates (POMs)-functionalized nanocomposites were synthesized by simply functionalizing CNTs with Keggin and Dawson-type POMs. The positively charged polyelectrolyte poly (diallyldimethylammonium chloride) (PDDA) was introduced to assemble negatively charged POMs and CNTs. The composition, structure and morphology were investigated by UV-visible (UV-vis), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Cyclic voltammetry (CV) was employed to investigate the electrochemical properties of the resulting nanocomposites. The cyclic voltammograms indicate that the electrochemical properties of POMs are fully maintained. Functionalizing CNTs with POMs not only retains the unique properties of nanotubes, but also endows CNTs with the reversible redox activity of POMs.     

Polydiphenylamine/carbon nanotube composites for applications in rechargeable lithium batteries

Polydiphenylamine/single walled carbon nanotube (PDPA/SWNT) composites were synthesized electrochemically aiming at their application as active electrode materials for rechargeable lithium batteries. The electrochemical polymerization of diphenylamine (DPA) on a SWNT film immersed in a 1 M HCl solution was studied by cyclic voltammetry. Comparing cyclic voltammograms recorded on a blank Pt electrode with those obtained for a SWNT film deposited on Pt electrode one observes in the latter case a decrease of the DPA reduction potential. To elucidate electrochemical polymerization mechanism, photoluminescence studies on DPA/SWNT and PDPA/SWNT systems were carried out. Additional information concerning the functionalization process of SWNT with PDPA was obtained by Raman and IR spectroscopy. Using the PDPA/SWNT composite as active material for the positive electrode of a rechargeable lithium cell (LiPF₆ electrolyte), the charge-discharge tests show a specific discharge capacity of ca. 245 mA h g⁻¹, much higher than the 35 mA h g⁻¹ for pure PDPA.     

Damping properties of thermoplastic-elastomer interleaved carbon fiber-reinforced epoxy composites

The aim of this study is to characterize the damping properties of carbon fiber-reinforced interleaved epoxy composites. Several types of thermoplastic-elastomer films, such as polyurethane elastomers, polyethylene-based ionomers and polyamide elastomers were used as the interleaving materials. The damping properties of the composite laminates with/without the interleaf films were evaluated by the mechanical impedance method. Also, the effects of the lay-up arrangements of the carbon-fiber prepregs on the damping properties of the interleaved laminates were examined. The viscoelastic properties of interleaved polymer films were reflected in the damping properties of the corresponding interleaved laminates. The loss tangent of the interleaf films at the test temperature played an important roll in the loss factor of the interleaved laminates. Also, the stiffness of the films at the resonant frequency of the laminates was another important parameter that controlled the loss factor of the interleaved laminates.     

Carbon nanotube reinforced metal binder for diamond cutting tools

The potential of carbon nanotube reinforcement of metallic binders for the improvement of quality and efficiency of diamond cutting wheels is studied. The effect of multi-walled carbon nanotube (MWCNT) reinforcement on the mechanical properties i.e. hardness, Young modulus, strength and deformation behavior of copper and iron based binder for diamond cutting wheels is investigated experimentally and numerically. Computational micromechanical studies were carried out to clarify the mechanisms of the MWCNT material strengthening. It is demonstrated that the adding of MWCNTs leads to the decrease of grain size of the structural constituents of the binder, what in turn leads to the improved simultaneously hardness, Young modulus, plastic extension, bending strength and performances of the metallic binders. Comparing service properties of diamond end-cutting drill bits with and without MWCNT one observed the drastic increase of the cutting speed as a result of MWCNT reinforcement.     

Processing and characterization of nanostructured Cu-carbon nanotube composites

Carbon nanotube (CNT) reinforced nanostructured Cu matrix composite with a grain size less than 25 nm has been successfully fabricated via a combination of ball milling and high-pressure torsion. CNTs were found to be homogeneously dispersed into the metal matrix, leading to grain refinement with a narrow grain size distribution and significant increase in hardness.     

纳米洋葱碳的制备及其纯化研究

以甲烷为碳源,316号不锈钢网为催化剂,800℃下催化裂解甲烷,采用化学气相沉积法制备平均粒径为70~100nm纳米洋葱碳,通过酸洗-低温煅烧-磁选方法对洋葱碳进行纯化处理。X射线衍射、扫描电子显微镜、透射电子显微镜、红外吸收光谱、拉曼光谱和振动样品磁强计对样品的形貌结构、物相组成及磁性能进行表征分析。结果表明,酸洗-低温煅烧能有效去除初产物中裸露的催化剂颗粒及无定型碳,磁选则实现将内包有[Fe-Ni]磁性催化剂的洋葱碳与空心的洋葱碳分离,最终获得纯净的空心纳米洋葱碳。     

Gd2O3:Eu@mesoporous SiO2 bifunctional core-shell composites: Fluorescence label and drug release

A novel kind of core-shell nanocomposite Gd₂O₃:Eu³⁺@mesoporous SiO₂ was successfully fabricated, which consisted of a solvothermal synthesized Gd₂O₃:Eu³⁺ nanospheres core, a thin nonporous silica midterm layer and an ordered mesoporous silica shell. The XRD, SEM, TEM, FTIR, N₂ adsorption/desorption and PL spectra were employed to characterize the composites. The cytotoxicity of Gd₂O₃:Eu³⁺@mesoporous SiO₂ and Gd₂O₃:Eu³⁺ was assessed by the standard MTT assay. The composites had spherically monodisperse morphology and a narrow size distribution around 180 nm in diameter. Furthermore, they also demonstrated the strong photoluminescence of ⁵D₀-⁷F_J emissions. In addition, the composites exhibited good property of sustained drug release by using ibuprofen (IBU) as model drug in the drug delivery process. Therefore, the drug release process could be easily tracked and identified through photoluminescence. Overall, the present composites have potential significant biomedical application as ideal bifunctional materials.     

Microstructure and abrasive wear characteristics of in situ vanadium carbide particulate-reinforced iron matrix composites

In this work, in situ synthesis with infiltration casting and subsequent heat treatment was applied to fabricate vanadium carbide (V₈C₇) particulate-reinforced iron matrix composites. The microstructure and wear-resistance of V₈C₇ particulate-reinforced iron matrix composites with different volume fraction were studied using scanning electron microscopy, X-ray diffraction, and wear testing. The V₈C₇ particles were uniformly distributed in the matrix, and the size of the V₈C₇ reinforcement was 2–12 μm. The relative wear resistance of the composites initially increases decreases with higher V₈C₇ volume fractions. The best wear resistance of the composites was 21.2 times higher than that of gray cast iron under a 20 N load. This was achieved at 24% V₈C₇ volume fraction. Wear of the composites manifests as grooves, broken carbide particles, and re-embedment of wear debris.