原位增强羟基磷灰石/壳聚糖复合棒材

利用低温水溶液均相沉积法制备了磷酸钙盐微纤维; 应用原位沉析法制备了壳聚糖(CS)三维棒材及羟基磷灰石(HA*)/CS复合棒材。XRD证实应用原位沉析法制备HA*/CS复合棒材过程中, 磷酸钙盐转化为羟基磷灰石结构, 尺寸为10~60 μm, 并用SEM对晶体形貌进行了表征, 分析了转化机制。HA*/CS复合材料的微观形貌表明, HA*晶体在CS凝胶棒原位沉析的过程中析出而与CS基体形成镶嵌、 相互咬合结构, 且在基体中分散均匀, 有效地提高了HA*与CS基体的界面连接作用, 使力学性能显著提高。所制备的HA*/CS棒材随HA*含量的增大(在其饱和溶解度3.3 wt%范围内), 复合材料的弯曲性能逐渐提高, 当羟基磷灰石质量分数为3.3%时, 复合材料的弯曲强度达到159.6 MPa, 弯曲模量达到5.1 GPa, 比CS基体分别提高85.6%和54.5%。HA*/CS复合棒材的弯曲强度和弯曲模量远高于松质骨, 弯曲强度也比密质骨高。      

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.     

碳纤维增强木材复合材料

碳纤维增强木材复合材料(CFRW)是新一代建筑材料、修补材料和装饰材料之一。在土木工程建筑、旧建筑的加固修补等方面得到广泛应用。CFRW不仅可提高材料的抗拉强度、压缩强度等,而且还赋予木材防菌防蚁、防水防腐、导电和电磁波屏蔽等新的功能。同时,可综合利用破碎木材及边角料,通过复合使其变废为宝。本文主要论述CFRW的制造、性质及其应用。     

纳米碳管/聚合物功能复合材料

纳米碳管(Carbonnanotubes,CNT)具有π π共轭电子结构,可与结构相似的聚合物(Polymer)通过范德华力结合形成复合材料。导电聚合物(Electricallyconductingpolymer,ECP)包覆多壁纳米碳管(Multi walledcarbonnanotubes,MWNT)后,可用于诸如超级电容器等电子器件。共轭发光聚合物修饰纳米碳管形成的CNT polymer复合材料,具有很强的发光性能,有望用于电子接收器和光电器件。通过连结氨基聚合物,可使多壁纳米碳管溶解和功能化,从而将纳米碳管引入生物学系统中。研究结果表明,CNT polymer复合物有许多潜在的应用,有待进一步发展。     

In vitro evaluation of hydroxyapatite reinforced polyhydroxybutyrate composite

Particulate hydroxyapatite (HA) was incorporated into polyhydroxybutyrate (PHB) to form a bioactive and biodegradable composite for applications in hard tissue replacement and regeneration. HA/PHB composite containing 10, 20, and 30 vol.% of HA was made for in vitro evaluation. In vitro studies were conducted using an acellular simulated body fluid (SBF). Composite specimens were immersed in SBF at 37 °C for various periods of time prior to surface analysis and mechanical testing. Results obtained from scanning electron microscopic (SEM) examination, thin film X-ray diffraction (TF-XRD) analysis, and Fourier transform infrared (FTIR) spectroscopy showed that a layer of bone-like apatite formed within a short period on HA/PHB composite after its immersion in SBF, demonstrating high in vitro bioactivity of the composite. The bioactivity and mechanical properties of the composite could be changed by varying the amount of HA in the composite. Dynamic mechanical analysis (DMA) revealed that the storage modulus (E′) of HA/PHB composite increased initially with immersion time in SBF, due to apatite formation on composite surface and decreased after prolonged immersion in SBF, indicating degradation of the composite in a simulated body environment. HA/PHB composite thus has the potential for its intended applications.     

Damping characteristics of carbon nanotube reinforced aluminum composite

A multi-walled carbon nanotube (MWNTs) reinforced 2024Al composite was successfully fabricated by a procedure of mixing 2024Al powders and CNTs, cold isostatic press and hot extrusion. The damping behaviors of the composite were investigated with frequency of 0.5, 1.0, 5.0, 10, 30 Hz, at a temperature of 25–400 °C. The experimental results show that the frequency significantly affects the damping capacity of the composite when the temperature is above 230 °C; meanwhile, the damping capacity of the composite with a frequency of 0.5 Hz reaches 975 × 10^− 3, and the storage modulus is 82.3 GPa when the temperature is 400 °C, which shows that CNTs are a promising reinforcement for metal matrix composites to obtain high damping capabilities at an elevated temperature without sacrificing the mechanical strength and stiffness of a metal matrix.     

Carbon nanotube reinforced polymer composites—A state of the art

Because of their high mechanical strength, carbon nanotubes (CNTs) are being considered as nanoscale fibres to enhance the performance of polymer composite materials. Novel CNT-based composites have been fabricated using different methods, expecting that the resulting composites would possess enhanced or completely new set of physical properties due to the addition of CNTs. However, the physics of interactions between CNT and its surrounding matrix material in such nano-composites has yet to be elucidated and methods for determining the parameters controlling interfacial characteristics such as interfacial shear stress, is still challenging. An improvement of the physical properties of polymer nanocomposites, based on carbon nanotubes (CNTs), is addicted to a good dispersion and strong interactions between the matrix and the filler.     

Carbon nanotube composite films with switchable transparency

A composite film with switchable transparency is fabricated by sandwiching a carbon nanotube (CNT) sheet within polyurethane (PU) films. The introduction of CNTs not only makes the composite film electrically conductive but also induces a rapid crystal melting of soft segments in the PU. As a result, the film can be switched from opaque to transparent in just several seconds after turning on voltage, and reversed back to opaque after turning off voltage. The film also possesses several other attractive properties, including excellent flexibility, low energy consumption, switching speed insensitivity to ambient temperature, and easy coloration, which make the film promising for a wide variety of practical applications.     

Carbon fiber reinforced hafnium carbide composite

Hafnium carbide is proposed as a structural material for aerospace applications at ultra high temperatures. The chemical vapor deposition technique was used as a method to produce monolithic hafnium carbide (HfC) and tantalum carbide (TaC). The microstructure of HfC and TaC were studied using analytical techniques. The addition of tantalum carbide (TaC) in the HfC matrix was studied to improve the microstructure. The microstructure of HfC, TaC and co-deposited hafnium carbide-tantalum carbide (HfC/TaC) were comparable and consisted of large columnar grains. Two major problems associated with HfC, TaC, and HfC/TaC as a monolithic are lack of damage tolerance (toughness) and insufficient strength at very high temperatures. A carbon fiber reinforced HfC matrix composite has been developed to promote graceful failure using a pyrolytic graphite interface between the reinforcement and the matrix. The advantages of using carbon fiber reinforcement with a pyrolytic graphite interface are reflected in superior strain capability reaching up to 2%. The tensile strength of the composite was 26 MPa and needs further improvement. Heat treatment of the composite showed that HfC did not undergo any phase transformations and that the phases comprising composite were are thermochemically compatible.     

Investigation of carbon nanotube reinforced aluminum matrix composite materials

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.     

Carbon nanotube reinforced small diameter polyacrylonitrile based carbon fiber

Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) composite (99/1) based carbon fibers with an effective diameter of about 1 μm have been processed using island-in-a-sea bi-component cross-sectional geometry and gel spinning. PAN/CNT (99/1) based carbon fibers processed using this approach exhibited a tensile strength of 4.5 GPa (2.5 N/tex) and tensile modulus of 463 GPa (257 N/tex), while these values for the control PAN-based carbon fiber processed under the similar conditions were 3.2 GPa (1.8 N/tex) and 337 GPa (187 N/tex), respectively. Properties of these 1 μm diameter carbon fibers have been compared to the properties of the larger diameter (>6 μm) PAN and PAN/CNT based carbon fibers.     

Carbon nanotube/polyaniline composite nanofibers: facile synthesis and chemosensors

An initiator is applied to synthesize single-walled carbon nanotube/polyaniline composite nanofibers for use as high-performance chemosensors. The composite nanofibers possess widely tunable conductivities (10(-4) to 10(2) S/cm) with up to 5.0 wt % single-walled carbon nanotube (SWCNT) loadings. Chemosensors fabricated from the composite nanofibers synthesized with a 1.0 wt % SWCNT loading respond much more rapidly to low concentrations (100 ppb) of HCl and NH(3) vapors compared to polyaniline nanofibers alone (120 s vs 1000 s). These nanofibrillar SWCNT/polyaniline composite nanostructures are promising materials for use as low-cost disposable sensors and as electrodes due to their widely tunable conductivities.     

Elastic response of a carbon nanotube fiber reinforced polymeric composite: A numerical and experimental study

Premature failure due to low mechanical properties in the transverse direction to the fiber constitutes a fundamental weakness of fiber reinforced polymeric composites. A solution to this problem is being addressed through the creation of nanoreinforced laminated composites where carbon nanotubes are grown on the surface of fiber filaments to improve the matrix-dominated composite properties. The carbon nanotubes increase the effective diameter of the fiber and provide a larger interface area for the polymeric matrix to wet the fiber. A study was conducted to numerically predict the elastic properties of the nanoreinforced composites. A multiscale modeling approach and the Finite Element Method were used to evaluate the effective mechanical properties of the nanoreinforced laminated composite. The cohesive zone approach was used to model the interface between the nanotubes and the polymer matrix. The elastic properties of the nanoreinforced laminated composites including the elastic moduli, the shear modulus, and the Poisson’s ratios were predicted and correlated with iso-strain and iso-stress models. An experimental program was also conducted to determine the elastic moduli of the nanoreinforced laminated composite and correlate them with the numerical values.     

Carbon nanotube/teflon composite electrochemical sensors and biosensors

The fabrication and attractive performance of carbon nanotube (CNT)/Teflon composite electrodes, based on the dispersion of CNT within a Teflon binder, are described. The resulting CNT/Teflon material brings new capabilities for electrochemical devices by combining the advantages of CNT and "bulk" composite electrodes. The electrocatalytic properties of CNT are not impaired by their association with the Teflon binder. The marked electrocatalytic activity toward hydrogen peroxide and NADH permits effective low-potential amperometric biosensing of glucose and ethanol, respectively, in connection with the incorporation of glucose oxidase and alcohol dehydrogenase/NAD(+) within the three-dimensional CNT/Teflon matrix. The accelerated electron transfer is coupled with minimization of surface fouling and surface renewability. These advantages of CNT-based composite devices are illustrated from comparison to their graphite/Teflon counterparts. The influence of the CNT loading upon the amperometric and voltammetric data, as well as the electrode resistance, is examined. SEM images offer insights into the nature of the CNT/Teflon surface. The preparation of CNT/Teflon composites overcomes a major obstacle for creating CNT-based biosensing devices and expands the scope of CNT-based electrochemical devices.     

Carbon nanotube reinforced hybrid composites: Computational modeling of environmental fatigue and usability for wind blades

The potential of advanced carbon/glass hybrid reinforced composites with secondary carbon nanotube reinforcement for wind energy applications is investigated here with the use of computational experiments. Fatigue behavior of hybrid as well as glass and carbon fiber reinforced composites with and without secondary CNT reinforcement is simulated using multiscale 3D unit cells. The materials behavior under both mechanical cyclic loading and combined mechanical and environmental loading (with phase properties degraded due to the moisture effects) is studied. The multiscale unit cells are generated automatically using the Python based code. 3D computational studies of environment and fatigue analyses of multiscale composites with secondary nano-scale reinforcement in different material phases and different CNTs arrangements are carried out systematically in this paper. It was demonstrated that composites with the secondary CNT reinforcements (especially, aligned tubes) present superior fatigue performances than those without reinforcements, also under combined environmental and cyclic mechanical loading. This effect is stronger for carbon composites, than for hybrid and glass composites.     

Carbon nanotube composite optoacoustic transmitters for strong and high frequency ultrasound generation

We demonstrate carbon nanotube (CNT) composite-based optoacoustic transmitters that generate strong and high frequency ultrasound. The composite consists of CNTs grown on a substrate, which are embedded in elastomeric polymer used as an acoustic transfer medium. Under pulsed laser excitation, the composite generates very strong optoacoustic pressure: 18 times stronger than a Cr film reference and five times stronger than a gold nanoparticle composite with the same polymer. This enhancement persists over a broadband frequency range of up to 120 MHz and is confirmed by calculation. We suggest the CNT-polymer composites as highly efficient optoacoustic transmitters for high resolution ultrasound imaging.     

Carbon fiber knitted fabric reinforced copper composite for sliding contact material

A novel carbon fiber knitted fabric reinforced copper (C/C–Cu) composite was fabricated by a pressureless infiltration technique. The microstructure of the composite was characterized by scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The mechanical, electrical and tribological properties of the C/C–Cu composite were compared with those of a carbon/copper contact strip. The experimental results showed that the C/C–Cu composite formed an interpenetrating network structure. It exhibited a high bending strength of 186 MPa, excellent impact strength of 4.7 J/cm² and a particularly low electrical resistivity of 0.58 μΩ m, giving it advantages over the C/Cu strip in terms of both mechanical and electrical properties. Friction and wear experiments were conducted for the C/C–Cu composite and the C/Cu strip on a hemisphere pin-on-block apparatus, using cooper pins against polished specimens in dry sliding conditions. It was found that the C/C–Cu composite exhibited greater wear resistance than the C/Cu strip and did less damage to the copper pin.     

Carbon nanotube (CNT)-based composites as electrode material for rechargeable Li-ion batteries: A review

The ever-increasing demands for higher energy density and higher power capacity of Li-ion secondary batteries have led to search for electrode materials whose capacities and performance are better than those available today. Carbon nanotubes (CNTs), because of their unique 1D tubular structure, high electrical and thermal conductivities and extremely large surface area, have been considered as ideal additive materials to improve the electrochemical characteristics of both the anode and cathode of Li-ion batteries with much enhanced energy conversion and storage capacities. Recent development of electrode materials for LIBs has been driven mainly by hybrid nanostructures consisting of Li storage compounds and CNTs. In this paper, recent advances are reviewed of the use of CNTs and the methodologies developed to synthesize CNT-based composites for electrode materials. The physical, transport and electrochemical behaviors of the electrodes made from composites containing CNTs are discussed. The electrochemical performance of LIBs affected by the presence of CNTs in terms of energy and power densities, rate capacity, cyclic life and safety are highlighted in comparison with those without or containing other types of carbonaceous materials. The challenges that remain in using CNTs and CNT-based composites, as well as the prospects for exploiting them in the future are discussed.     

Polyisoprene-multi wall carbon nanotube composite structure for flexible pressure sensor application

The major problem of conventional rigid sensor materials is difficulty to integer them into soft flexible structures. Piezoresistive polyisoprene/nanostructured carbon composite appears as promising materials for such application. Previous research approved high structure carbon black and carbon nanotube filled composites as finger pressure sensitive piezoresistive materials. Carbon nanotubes originate with variable length to width ratio and high electric conductivity in longitudinal direction of the tubes, which theoretically should make it possible to obtain electric percolation in polymercarbon nanotube composites at very low loads of filler. However recent experience with mechanically dispersed carbon nanotubes shows quite high values of percolation threshold and specific sensing properties. In this work we present an attempt to use ultrasound for improved dispersion of the filler in a piezoresistive polyisoprene-multi wall carbon nanotube composite as well polyisoprene-high structure carbon black composite. The noticeable shift of percolation threshold for both types of composites have been achieved. The piezoresistive behavior of sonicated composites have been determined and compared with mechanically mixed ones. The differences have been evaluated and explained.     

Friction and wear behavior of hydroxyapatite based composite ceramics reinforced with fibers

The HA-based composites reinforced with multi-component fibers were prepared by hot pressing. The friction properties of the composite at different temperatures were investigated by a block-on-disc tester. The results show that the addition of Cu has a significant positive effect on the friction and wear behaviors of HA-based composites. The improvements in the friction and wear properties of HA-based composites depend on the formation of an interfacial layer. The plastic deformation and the mending effect of Cu benefit the formation of the interfacial layer. The wear mechanism of the composites changes from the delamination and abrasive wear to the adhesive wear with increasing Cu.