Influence of nano-SiO<Subscript>2</Subscript> and carbon fibers on the mechanical properties of POM composites

Polyoxymethylene/carbon fiber(POM/CF)composites containing nano-SiO₂ were prepared, and their mechanical properties were investigated. At a content of 1-5 vol.%, the nano-SiO₂ exerted an obvious reinforcing effect on POM, leading to an increase in the elastic modulus and stiffness of the composites.     

The effect of CNT modification on the mechanical properties of polyimide composites with and without MoS<Subscript>2</Subscript>

The aim of this work was to investigate the effect of surface modification of carbon nanotubes (CNTs) on the mechanical properties of polyimide (PI) composites with and without MoS₂. A three-phase system of CNT/PI/ MoS₂ laminates were fabricated with an extrusion-grade PI to produce CNT-reinforced laminates with MoS₂ volume fractions of 1–5%. The tensile and impact properties of CNT/PI composites and CNT/PI/MoS₂ laminates were also measured and compared. Results showed that the introduction of CNTs as reinforcing additives improved the tensile properties of the composites, but worsened their impact properties. Furthermore, the addition of MoS₂ increased the impact strength of the CNT/PI composites greatly. The optimum contents of CNT and MoS₂ have been found.     

Fabrication of Pt deposited on carbon nanotubes and performance of its polymer electrolyte membrane fuel cells

A new method of depositing nano-sized Pt particles on the surface of the carbon nanotubes was introduced, and the performance of Pt/carbon nanotube compound on polymer electrolyte membrane fuel cells was measured. The experimental results show that the fine platinum particles (about 3 nm) were well dispersed on carbon nanotubes, which demonstrates the excellent catalytic properties of the Pt/CNTs compound in polymer electrolyte membrane fuel cells.     

Energetic modelling for carbon fibre reinforced carbon

In this contribution an energetic model for multi-phase materials is developed describing the influence of microstructure on different length scales as well as the evolution of phase changes. Restrictions on the energy functional are discussed. In such a non-convex framework, interfacial contributions serve for relaxing the total energy. Such models can be applied to describe the macroscopic material properties of carbon fibre reinforced carbon where phase transitions between regions of different texture of the carbon matrix are observed on nanoscale as well as columnar microstructures on microscale [2]. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Estimation of the optimal distribution of the fibers in carbon/carbon composite

Carbon/carbon (C/C) composites are widely represented in the industry and are utilized for extreme thermal and mechanical loading. Optimization of the fibers distribution allows by still high stiffness to provide reducing of the weight of the components that has crucial importance in aircraft and aerospace industry. A microstructure optimization problem for estimation of the microstructure with minimal compliance is formulated. The design variables of the posed problem are the local fibers distribution and porosity. The volume fractions of the fibers and pores in the whole microstructure are fixed. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of surface treatment of carbon fibers on the strength properties of carbon fiber plastics

Conclusions The strength characteristics of composites based on carbon fibers having a coating of silicon carbide are in direct dependence on the coating thickness and on the porosity, which makes it possible to assume the possibility of increasing the degree of realization of the strength characteristics of fibers having a coating in a composite by increasing the degree of impregnation of the carbon cord with the binder. The latter finds confirmation also in the fact that at a small coating thickness on the carbon fiber (of the order of 5 nm) the porosity of the composite obtained is equal to the porosity of the material based on the carbon fiber without coating. Moreover, as is evident from Fig. 3c, the casing of silicon carbide does not form a continuous coatting over the whole perimeter of the cord. The presence of these prerequisites, and also the high resistance of carbon fibers having a silicon carbide coating to oxidation [9], open up wide prospects for creating new composite materials based on them.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 603–606, July–August, 1979.     

土体残余强度的PSO-LSSVM模型

利用最小二乘支持向量机(LSSVM)建立土体残余强度模型,以液限、塑性指数、粘粒含量和偏差等为输入变量,通过改变输入变量的结构建立2个LSSVM模型,并采用粒子群优化(PSO)算法设定模型参数,分别预测残余摩擦角值,并与实验值、人工神经网络(ANN)模型作比较,得出LSSVM模型具有较好的效果,另外对LSSVM的输入变量进行敏感性分析,得出偏差对模型的影响最大,印证文献中结论并说明模型的合理性。     

Transnational remanufacturing decisions under carbon taxes and tariffs

Considering the influence of carbon taxes and tariffs on transnational closed-loop supply chains, this paper establishes three remanufacturing modes of an original equipment manufacturer (OEM) in an exporting country. In one remanufacturing mode, the OEM conducts remanufacturing itself, and in the other two modes, the OEM authorizes a retailer in the importing country to engage in remanufacturing. Next, we analyse the optimal pricing and carbon emissions reduction decisions of the OEM and retailer in the different modes and further study how different levels of carbon tax and tariff combinations impact OEM remanufacturing decisions, the social welfare of importing countries and the environment. The results show the following. (1) When the carbon tariff is high, the optimal sales of remanufactured products increase. However, this does not contribute to the continuation of the product system; thus, it is short sighted for the government to hastily set high carbon tariffs to discourage the import of new products to protect domestic enterprises. (2) Carbon tariffs cannot effectively encourage the OEM to invest in emission reduction because carbon tariffs are passed on to consumers in importing countries through price adjustment. However, carbon tax may be an indirect factor affecting the OEM's willingness to invest in emission reduction. (3) The OEM favours allowing the retailer to remanufacture when the carbon emissions of the remanufactured products are similar to those of new products. Co-investment in emission reduction has the potential to align the profit maximization of the OEM with the social welfare maximization of the importing country. (4) It is not profitable for the importing government to set high carbon tariffs to protect its own enterprises.     

A comparative study on the mechanical and barrier characteristics of polyimide nanocomposite films filled with nanoparticles of planar and tubular morphology

Polyimide (PI) films based on poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PI-PM) were filled with different nanoparticles, such as organically modified montmorillonite (MMT), vapor-grown carbon nanofibers (VGCF), and silicate nanotubes (SNT) of different concentration.. Rheological measurements and structural investigations showed a relatively good dispersion of the nanoparticles in the PI matrix to an extent that depended on the type and morphology of the nanoparticles used. The mechanical (tensile modulus, strength, and deformation at break) and the barrier (oxygen permeability) properties of PI-PM nanocomposite films were investigated. The polyimide nanocomposites filled with SNT and tubular VGCF nanoparticles showed an increased tensile modulus with increasing volume concentration of the nanoparticles without a catastrophic decrease in the elongation at break. In addition, the MMT particles, chemically modified with 4,4'-bis-(4′′-aminophenoxy)diphenylsulfone, significantly improved the barrier properties of the PI-PM films, which exceeded those of the nanocomposites filled with VGCF or SNT. The relative poor oxygen barrier and mechanical properties of the PI-PM/VGCF nanocomposite films are ascribed to the relative weak adhesion between the VGCF and the polyimide matrix, which was confirmed by scanning electron microscopy of the fracture surface of these films.     

Multiwall carbon nanotube/epoxy composites produced by a masterbatch process

A masterbatch process based on a minicalander (three-roller mill) and a vacuum dissolver was developed in order to produce multiwall carbon nanotube/epoxy composites with loading fractions of 0.5, 1.0, and 2.0 wt.%. TEM and SEM analyses were performed to investigate the dispersion results. A contrast imaging in the SEM backscattering mode revealed a homogeneous distribution of carbon nanotubes in the whole volume of the material. Furthermore, an interesting correlation was found to exist between the network structure formed by the nanotubes in the epoxy matrix and the appearance of fracture surface of the nanocomposites. Furthermore, the nanocomposites exhibited an electrical conductivity in the regime of some 10⁻² S/m. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 567–582, September–October, 2006.     

Alteration of the mechanical behaviour of polypropylene owing to successive introduction of multiwall carbon nanotubes and stretching

Stretching effects on the morphology of polypropylene/carbon nanotube composites is the focus of this work. The material under investigation was composed of isotactic polypropy lene (iPP) and multiwall car bon nanotubes (MWCNTs) in amount of 0.5 wt.%. The iPP and CNTs were mixed under sonication in a solvent, and the homogenized mixture was melted and pressed. The rectangular plates produced from the material were stretched by a constant load at a fixed temperature in order to obtain extended specimens. The scanning electron microscopy, a thermal gravimetric analysis, and the differential scanning calorimetry were employed to study variations in the structural morphology of the material. A dynamic mechanical analysis showed that the strain-induced crystallization of polypropylene and the possible Stone–Wales transformation of the carbon nanotubes due to stretching improved the mechanical performance of the nanocomposites considered.     

Tensile and tribological properties of a short-carbon-fiber-reinforced peek composite doped with carbon nanotubes

The main objective of this paper is to develop a high-wear-resistant short-carbon-fiber-reinforced polyetheretherketone (PEEK) composite by introducing additional multiwall carbon nanotubes (MWCNTs) into it. The compounds were mixed in a Haake batch mixer and fabricated into sheets by compression molding. Samples with different aspect ratios and concentrations of fillers were tested for wear resistance. The worn surfaces of the samples were examined by using a scanning electron microscope (SEM), and the photomicrographs revealed a higher wear resistance of the samples containing the additional carbon nanotubes. Also, a better interfacial adhesion between the short carbon fibers and vinyl ester in the composite was observed.     

Modelling the growth of soil-borne fungi in response to carbon and nitrogen

Email: Angelique.Lamour{at}medew.fyto.wau.nl Growth of soil-borne fungi is poorly described and understood,largely because non-destructive observations on hyphae in soilare difficult to make. Mathematical modelling can help in theunderstanding of fungal growth. Except for a model by Paustian& Schnürer (1987a), fungal growth models do not considercarbon and nitrogen contents of the supplied substrate, althoughthese nutrients have considerable effects on hyphal extensionin soil. We introduce a fungal growth model in relation to soilorganic matter decomposition dealing with the detailed dynamicsof carbon and nitrogen. Substrate with a certain carbon: nitrogenratio is supplied at a constant rate, broken down and then takenup by fungal mycelium. The nutrients are first stored internallyin metabolic pools and then incorporated into structural fungalbiomass. Standard mathematical procedures were used to obtainoverall-steady states of the variables (implicitly from a cubicequation) and the conditions for existence. Numerical computationsfor a wide range of parameter combinations show that at mostone solution for the steady state is biologically meaningful,specified by the conditions for existence. These conditionsspecify a constraint, namely that the ‘energy’ (interms of carbon) invested in breakdown of substrate should beless than the ‘energy’ resulting from breakdownof substrate, leading to a positive carbon balance. The biologicalinterpretation of the conditions for existence is that for growththe ‘energy’ necessary for production of structuralfungal biomass and for maintenance should be less than the mentionedpositive carbon balance in the situation where all substrateis colonized. In summary, the analysis of this complicated fungalgrowth model gave results with a clear biological interpretation.     

Properties of a composite prepared using a concentrate of carbon nanotubes in polyethylene

Results of an investigation into the properties of polyethylene (PE) with small, no more than 5 wt.%, additions of multiwall carbon nanotubes (CNTs) are reported. Specimens of the composite were prepared using a concentrate containing 31.6 wt.% of nanotubes in the polyethylene matrix. The concentrate was fabricated by a patent in situ polymerization method. Experimental data on the influence of CNT additions on the thermograms of differential scanning calorimetry, the crystallinity of the polyethylene matrix, and the indices of mechanical properties (yield stress, strength, elastic modulus, ultimate elongation, and long-term creep) of PE/CNT composite are obtained. A theoretical analysis of elastic properties of the PE/CNT composite was carried out by using the Mori–Tanaka theory of an equivalent medium. The calculation results are compared with experimental data.     

Well-aligned carbon nanotube array membrane and its field emission properties

Ensembles of aligned and monodispersed carbon nanotubes (CNTs) can be prepared by templating method which involves fabrication of porous anodic aluminum oxide (AAO) template, control of catalytic iron particle size and chemical vapor deposition of carbon in the cylindrical pores of AAO. Here we show that template-synthesized CNTs can be fabricated as well-aligned nanoporous CNTs membrane, which can be directly used as an electron field emitter. A low threshold electric field of 2-4 V/μm and maximum emission current density of - 12 mA/cm² are observed. The results also show that the electron emission current is a function of the applied electrical field and the Fowler-Nord-heim (F-N) plot almost follows a linear relationship which indicates a Fowler-Nordheim tunneling mechanism, and the field enhancement factor estimated is about 1100-7500. The simple and convenient approach should be significant for the development of nanotube devices integrated into field emission displays (FEDs) technology.     

TEM and Raman scattering investigation of carbon in annealed Co/C soft X-ray multilayers

The structures of the carbon sublayers in the annealed Co/C soft X-ray multilayers fabricated by using a dual-facing-target sputtering system have been characterized by transmission electron microscopy (TEM) and Raman spectroscopy (RS). The results suggest that the structural variations in the carbon layers can be roughly divided into three stages, i.e. ordering, crystalline and grain growth stages. At the ordering stage with annealing temperatures below 400°C, the amorphous carbon layers change from ones of bond-angle disorder and fourfold-bonding only to ones of threefold-bonding. At the crystalline stage, the amorphous carbon layers in the as-deposited multilayers crystallize to graphite crystallites in the annealing temperature range of 500–600°C. At the grain growth stage, the specimens are annealed at temperatures higher than 700°C. A growth in the graphite crystallite dimensions is observed, which is consistent with the TEM results. Project supported by the National Natural Science Foundation of China and Beijing Zhongguancun Associated Center of Analysis and Measurement.     

Systems accounting for energy consumption and carbon emission by building

The method of systems accounting for overall energy consumption and carbon emission induced by a building is illustrated in terms of a combination of process and input–output analyses with a concrete procedure to cover various material, equipment, energy and manpower inputs. A detailed case study based on raw project data in the Bill of Quantities (BOQ) is performed for the structure engineering of the landmark buildings in E-town, Beijing (Beijing Economic–Technological Development Area). Based on the embodied energy and carbon emission intensity database for the Chinese economy in 2007, the energy consumption and the carbon emission of the structure engineering of the case buildings are quantified as 4.15E+14 J and 4.83E+04 t CO₂ Eq., corresponding to intensities of 6.91E+09 J/m² and 0.81 t CO₂ Eq./m² floor area. Steel and concrete contribute respectively about 50% and 30% of the energy consumption and the carbon emission, as a result of the reinforced-concrete structure of the case buildings. Materials contribute up to about 90% of the total energy consumption and carbon emission, in contrast to manpower, energy and equipment around 8%, 1% and 0.1%, respectively.     

Morphology, structure and Raman scattering of carbon nanotubes produced by using mesoporous materials

Carbon nanotubes were prepared by chemical vapor deposition (CVD) of hydrocarbon gas on various substrates. The effect of substrates on the growth, morphology and structure of carbon nanotubes were investigated. Aligned carbon nanotubes with high density and purity were achieved by CVD on mesoporous silica substrate. The Raman scattering of aligned carbon nanotubes was carried out, and the dependence of the phonon properties on the microstructure of the nanotubes has been discussed.     

Single wall carbon nanotubes and their electrical properties

Single-wall carbon nanotubes (SWCNTs) were synthesized and purified. A water colloid of SWCNTs was prepared and used to assemble SWCNTs onto a gold film surface. Scanning tunneling microscopy (STM) images showed that short SWCNTs stood on gold film surfaces. Using STM tips made of SWCNTs, a crystal grain image of a gold thin film and an atomic resolution image of highly oriented pyrolytic graphite were successfully obtained. The electrical properties of short SWCNTs, which stood on the surface of gold film, were measured using STM. That SWCNTs stand on gold thin films is a promising technique for studying structures and properties of carbon nanotubes, as well as assembling and fabricating high-intensity coherent electron sources, field emission flat panel display, tips for scanning probe microscopes, new nanoelectronic devices, etc.     

Noncoaxial vibration of fluid-filled multi-walled carbon nanotubes

This paper is concerned with the free vibration of the fluid-filled multi-walled carbon nanotubes (MWCNTs) with simply supported ends. Based on simplified Donnell’s cylindrical shell model and potential flow theory, the effect of internal fluid on the coupling vibration of the MWCNTs-fluid system is discussed in detail. The results show that the resonant frequencies are decreased due to the effect of the fluid, and the fluid has only a little influence on the associated amplitude ratio in MWCNTs corresponding to the natural resonant frequency (frequency of the innermost tube), while plays a significant role in the associated amplitude ratios corresponding to the intertube resonant frequency. For the natural resonant frequency, the vibration mode is coaxial. However, for the intertube resonant frequency, the system shows complex noncoaxial vibration, which plays a critical role in electronic and transport properties of carbon nanotubes (CNTs).