Impact behavior and fractographic study of carbon nanotubes grafted carbon fiber-reinforced epoxy matrix multi-scale hybrid composites

Carbon nanotubes are the most promising reinforcement for high performance composites. Multiwall carbon nanotubes were directly grown onto the carbon fiber surface by catalytic thermal chemical vapor deposition technique. Multi-scale hybrid composites were fabricated using the carbon nanotubes grown fibers with epoxy matrix. Morphology of the grown carbon nanotubes was investigated using field emission scanning electron microscopy and transmission electron microscopy. The fabricated composites were subjected to impact tests which showed 48.7% and 42.2% higher energy absorption in Charpy and Izod impact tests respectively. Fractographic analysis of the impact tested specimens revealed the presence of carbon nanotubes both at the fiber surface and within the matrix which explained the reason for improved energy absorption capability of these composites. Carbon nanotubes presence at various cracks formed during loading provided a direct evidence of micro crack bridging. Thus the enhanced fracture strength of these composites is attributed to stronger fiber–matrix interfacial bonding and simultaneous matrix strengthening due to the grown carbon nanotubes.     

碳前驱体对LiFePO_4/C复合材料的形貌及电化学性能的影响

采用葡萄糖、环氧树脂、酚醛树脂为碳源制备了LiFePO4/C复合材料。利用X射线衍射、扫描电镜等方法对复合材料进行研究。结果表明,葡萄糖获得了碳包覆复合材料,而环氧树脂、酚醛树脂则得到了碳芯结构复合材料。碳芯结构复合材料的电化学性能优于碳包覆复合材料,电流密度为15mA/g时,试样C、D的放电容量分别为165、167mAh/g;电流密度为600mA/g时,试样C、D的放电容量分别为139.4、145.5mAh/g,经过50循环后容量保持率分别高达99.2%、99.5%。     

单分散镍碳复合纳米球和碳微球的制备

以脱油沥青(deoiled asphalt)为碳源,采用化学气相沉积法(CVD)制备碳微球,其裂解后的残渣经真空热处理制得单分散镍碳复合纳米球.用场发射扫描电镜(FESEM)、高分辨透射电镜(HRTEM)和X射线衍射仪(XRD)对产物进行表征.结果表明,碳微球高纯,属无定型碳结构,大小分布在1～2μm范围内;镍碳复合纳米球为准球形核壳结构,核为镍,壳为碳,尺寸在10～30nm范围,晶化程度较高,结构较完善.     

镍/碳微球复合材料的制备和表征

碳微球与微米镍粉按一定比例混合后,经过6h机械球磨并在1600℃真空热处理,合成了微米镍/碳复合材料。通过场发射扫描电镜(FESME)、高分辨透射电镜(HRTEM)和X射线衍射仪(XRD)对产物进行表征。结果表明,产物为碳包覆镍金属颗粒,粒径200～400nm的镍颗粒被30～100nm的碳层包覆,碳层的石墨化程度较高;产物石墨化碳层的形成缘于Ni3C的形成和分解。     

Fabrication and Properties of SiB6-B4C with Phenolic Resin as a Carbon Source

Si-B-C ceramic composites were synthesized using SiB6, B4C, and phenolic resin as a carbon source by pressureless sintering in an Ar atmosphere. Then, the Si-B-C ceramic composites were fabricated to determine their potential for applications as high hardness and high temperature composites. The X-ray diffraction patterns of sintered bodies of SiB6-B4C with carbonized phenolic resin can be seen that SiB6 and C changed to B4C and SiC. In this study, it is obtained that carbonized phenolic resin is good addition material as a reaction material comparing to carbon powder at 1683 K for 1 h by pressureless sintering in an Ar atmosphere.     

Effects of the size of nano-copper catalysts and reaction temperature on the morphology of carbon fibers

In this study, carbon fibers with different morphologies, including coiled carbon nanofibers and straight carbon fibers, were obtained by the chemical vapor deposition using a Cu-catalytic pyrolysis of acetylene at 250 °C. The influences of nano-copper catalyst particle size and the reaction temperature on the morphology of carbon fibers were investigated. Under the same reaction condition, coiled carbon nanofibers generally were synthesized using nano-copper catalyst with smaller particles size, and bigger copper particles are apt to produce straight carbon fibers. With decreasing of reaction temperature to 200 °C, straight carbon fibers were obtained, instead of coiled carbon nanofibers at 250 °C. The product was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD).     

Effects of Current Frequency on the Microstructure and Wear Resistance of Ceramic Coatings Embedded with SiC Nano-particles Produced by Micro-arc Oxidation on AZ91D Magnesium Alloy

To improve the surface wear resistance of the ceramic coating fabricated by micro-arc oxidation (MAO) on AZ91D magnesium alloy,ceramic coatings embedded with SiC nano-particles at different current frequency (500 Hz,700 Hz,and 900 Hz) were produced during the MAO process.The morphology and phase composition of the coatings were investigated by scanning electron microscopy (SEM),field emission scanning electron microscopy (FESEM),and X-ray diffraction (XRD).The surface roughness of the coatings was character...     

Cu2O-WO3复合物的制备及其光催化性质研究

采用室温液相还原法制备了Cu2O微米立方块和Cu2O-WO3复合物,利用XRD和FESEM对产物进行了表征。研究了太阳光照下氧化亚铜微米立方块对不同染料的光催化降解性能,结果表明合成产物对阴离子染料有较好的降解效果,对阳离子染料降解效果不明显。Cu2O-WO3复合物对阳离子染料亚甲基蓝的光催化活性明显高于纯的Cu2O,其中10%Cu2O-WO3复合物的光催化效果最好。借助荧光光谱分析了复合物提高阳离子染料亚甲基蓝的光催化效果的原因。     

碳模板转化法制备管状SiC/Si复合陶瓷

利用纸作为原材料,通过卷曲、树脂浸渍、碳化预制备出具有层状结构的管状碳模板,之后在1550℃通过原位反应液相渗Si0.5-1h,在常压烧结条件下制备出具有层状结构特征的SiC/Si管状陶瓷复合材料.采用XRD、SEM对碳模板反应前后的物相变化和显微结构进行了研究.结果表明了该材料的最终产物为β-SiC和Si,且两者分布表现出明显的交替成层现象,呈现出层状陶瓷的结构特征.     

In-situ One-pot Preparation of LiFePO4/Carbon-Nanofibers Composites and Their Electrochemical Performance

A novel in-situ route was employed to synthesize LiFePO4/carbon-nanofibers (CNFs) composites. The route combined high-temperature solid phase reaction with chemical vapor deposition (CVD) using Fe2O3 and LiH2PO4 as the precursors for LiFePO4 growth and acetylene (C2H2) as the carbon source for CNFs growth. The composites were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The electrochemical performance of the composites was studied by galvanostatic cycling and cyclic voltammetry (CV). The results showed that the in-situ CNFs growth could be realized by the catalytic effect of the Fe2O3 precursor. The sample after 80 min CVD reaction showed the best electrochemical performance, indicating a promising application in high-power Li-ion batteries.     

Paraffin/carbon aerogel phase change materials with high enthalpy and thermal conductivity

Two kinds of carbon aerogels, graphene aerogels (GA) and carbon nanotubes-graphene aerogels (CGA), were prepared by modified hydrothermal method. The form-stable phase change materials (PCMs) were fabricated by adsorbing paraffin into carbon aerogels. Morphology, structure, form stability and thermal property were characterized by scanning electron microscope (SEM), in situ X-ray diffraction (in situ XRD) and differential scanning calorimeter (DSC). The results showed that GA presented wrinkled surface textures with curling edges, and carbon nanotubes (CNTs) were interspersed or attached to GA sheets. The phase transition temperature and the phase change enthalpy of the GA/paraffin PCM composite were 48.7 °C and 223.2 J/g, respectively. Thermal and mechanical properties of PCM composites achieved a qualitative leap with the adding of carbon aerogels. The PCM composites had a thermal conductivity of about 2.182 W/m K at the carbon aerogels loading fraction of 2 wt%. The form-stable PCM composites with high thermal conductivity and high enthalpy could be promising for thermal energy storage applications in construction field.     

Microstructural characterization and fracture properties of SiC-based fibers annealed at elevated temperatures

Ceramic matrix composites (CMCs) have been proposed as potential structural materials for application of high temperature technologies. Excellent high temperature performance of CMCs requires that fibers must have high enough thermal stability and sufficient mechanical properties throughout the service life. In order to clarify the correlation between the mechanical properties and the microstructure of SiC-based fibers, SiC-based fibers were annealed at elevated temperatures in Ar for 1 h. After annealing, the fracture strengths on these fibers were evaluated at room temperature by tensile test; the microstructural features were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Furthermore, the fracture mechanics was applied to estimate the fracture toughness and the critical fracture energy of these fibers. As a result, excellent microstructure and mechanical stabilities were observed for SiC fibers with near-stoichiometric composition and high-crystallite structure. Combining the microstructure examination with tensile test indicates that the thermal and mechanical stabilities of SiC fibers at high temperatures were mainly controlled by their crystallization and composition as well as other factors.     

Press-Fit Sheathing for Ceramic Gun Liners

Ceramic materials are being investigated by the Army for use in gun tubes. Compared to gun steels, ceramics possess superior wear resistance at ballistic temperatures, thus enabling improved lifetime for gun tubes. In order to survive the ballistic event, however, it is necessary to prestress the ceramic components with external sheathing to offset the tensile stresses in the tube wall that occur during the ballistic event. Previous sheathing designs for ceramic liners have included thermal shrink fits of tubular metallic components, steel wire overwrapped under high tension, and advanced fibrous composites overwrapped under high tension. In the present investigation, press-fitted composite sheaths are fabricated and tested with the purpose of validating a computer model applicable to the design of ceramic gun barrel liners.     

Dislocations in plastically deformed apatite

Dislocations were introduced at room temperature by a Vickers indentation into a biological ceramic, apatite. Two types of apatite, a single crystal of fluorapatite and a sintered polycrystal of hydroxyapatite, were studied. Specimens prepared using a focused-ion-beam technique were examined by transmission electron microscopy. Natures of dislocations were determined by the conventional g · b criterion, where the weak-beam method was also applied. The slip system in fluorapatite apatite was determined to be      

Processing aspects of glass-nicalon fibre and interconnected porous aluminium nitride ceramic and glass composites

Glass matrix-fibre and glass infiltrated ceramic composites with interconnected phases have been shown to have the potential for displaying optimum thermal conductivity and dielectric constant at 1 MHz making them useful as substrates for electronic packaging. Ceramic (Nicalon and silicon carbide grade (SCS)) fibre-borosilicate glass composites were fabricated using tape casting processes combined with pressure and pressureless sintering techniques. Experiments were also conducted to process AIN ceramics with interconnected porous channels which were then hot infiltrated with borosilicate glass. Results of optical characterization of the composites indicate that infiltration of Nicalon cloth with glass is achieved by hot pressing, while the tape casting and lamination approach followed by sintering is useful for fabricating composites of glass and Nicalon tows. The sintered aluminium nitride ceramics are comprised of 28% (volume fraction) interconnected pores. Hot infiltration yielded 100 m penetration of borosilicate glass into the pores of the nitride ceramic. The paper discusses the various scientific aspects involved in processing the glass-fibre and porous AIN composites containing 3-d interconnected pores. Results of the microstructural characterization of these composites are discussed particularly in regards to the desired microstructure essential for these composites to be useful as substrates in electronic packaging.     

Electron field emitters based on multi-walled carbon nanotubes coated with conducting polymer/metal/metal-oxide composites

The present work describes the field emission properties of multi-walled nanotubes (MWNTs)-based conducting polymer/metal-oxide/metal/MWNTs composites (polyaniline (PANI)/SnO₂/Sn/MWNTs). MWNTs were synthesised by chemical vapour deposition technique. SnO₂/Sn/MWNTs were prepared by using chemical reduction followed by calcination. By in situ polymerisation method, surface of SnO₂/Sn/MWNTs were coated with PANI. PANI/SnO₂/Sn/MWNTs field emitters were fabricated over flexible graphitised carbon fabric substrate by spin coating technique. High-resolution transmission electron microscopy and scanning electron microscopy were used to characterise the field emitters. Field emission properties have been studied using an indigenously made facility. The fabricated PANI/SnO₂/Sn/MWNTs field emitters exhibited excellent field emission properties with a turn on field of 1.83 V µm^?1 and a field enhancement factor of 4800.     

Optical and dielectric properties of lanthanide titanium tantalate and niobate ceramic composites

The xPrTiTaO₆ (1 − x) YTiNbO₆ dielectric ceramic composites are fabricated through the solid state ceramic route. The compositions are calcined in the temperature range 1,200–1,260 °C and sintered in the range 1,350–1,410 °C. Structural analysis of the materials is done using X-ray Diffraction analysis. The composites contain both aeschynite and euxenite orthorhombic phases. The surface morphology of the sintered pellets is examined by scanning electron microscopy. The dielectric constant, conductance and loss factor are measured in the radio frequency region. The UV–visible spectra are recorded and the band gap is calculated. The photoluminescence spectra of the compositions are recorded and the transitions causing emission are identified. The elemental composition of the composites is confirmed using energy dispersive spectroscopy. The materials are suitable for substrate and optoelectronic applications.     

Vacuum-deposited carbon coatings

In recent years, highly favorable results have been obtained using low temperature isotropic pyrolytic carbons in prosthetic devices requiring a high degree of thromboresistance. The development of vacuum-deposited carbon coatings was undertaken to extend the application of carbon to geometries and configurations that cannot be fabricated from low temperature isotropic carbon. Vacuum-deposited coatings have been produced on a variety of metallic and polymeric substrates.The different vacuum deposition processes which have been investigated include electron beam gun evaporation using high vacuum, gas scattering and ion- plating conditions. In addition, sputtering processes using ion beams and magnetically confined plasmas were studied.The surface morphology, structure and preferred orientation of the coatings produced by the different processes were characterized by scanning and transmission electron microscopy. Film purity and interfacial characteristics were examined by Auger electron spectroscopy.The scanning electron microscopy study shows that thin carbon films generally have a smooth and featureless surface morphology. However, other surface morphology features are obtained in thicker films, depending on the processing conditions. The transmission electron micrographs show the absence of structure and growth features. Electron diffraction indicates that the films consist of a turbostratic phase and a non-crystalline phase. The apparent crystallite sizes are small, and there is no three-dimensional ordering. Generally, the films are isotropic and consist of relatively pure carbon, with the degree of disorder dependent on the process conditions.     

电泳沉积制备平行栅碳纳米管场发射阴极的研究

利用磁控溅射、光刻、湿法刻蚀和电泳技术在玻璃基片上成功制备平行栅场发射阴极阵列,用光学显微镜、场发射扫描电镜和拉曼光谱观察了碳纳米管的形貌和结构,并测试所制备的平行栅碳纳米管阴极的场发射性能.光学显微镜和场发射电子显微镜测试表明,平行栅结构阴极和栅极交替地分布,同一个平面内,CNTs有选择性地沉积在平行栅结构中的阴极表...     

Preparation of multiwalled carbon nanotubes-platinum-Nafion-glucose oxidase nanobiocomposite and its application to glucose biosensor

Platinum (Pt) nanoparticles were electrodeposited within multiwalled carbon nanotubes-Nafion-glucose oxidase (MWNTs-Nafion-GOx) nanobiocomposite by a potentiostatic method. The morphology and nature of the resulting MWNTs-Pt-Nafion-GOx nanobiocomposite were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The electrocatalytic properties of the MWNTs-Pt-Nafion-GOx nanobiocomposite film modified glassy carbon electrode were characterized by cyclic voltammetry and amperometry in the presence of hydrogen peroxide. The glucose biosensor sensitivity was strongly influenced by the deposits of Pt nanoparticles and amount of GOx concentration within the MWNTs-Pt-Nafion-GOx nanobiocomposite film. The optimized glucose biosensor displayed a sensitivity of 640 nA mM(-1), a linear range of up to 4 mM, a detection limit of 4 microM, and a response time of less than 4 s at an operating potential of +500 mV versus Ag/AgCl (3 M KCl).