Key Engineering Materials Vols. 334-335

Abstract: The applications of carbon nanotubes benefit to a wide range of engineering, applied physics and biomaterials areas for their superior mechanical and electrical properties. Recently, coiled carbon nanotube (CCNT) has opened a new alternative to reinforce traditional advanced composites. Their coiled shapes are considered to induce mechanical interlocking between the nanotubes and matrix which result in the enhancement of fracture toughness and mechanical strength of the composites. In this study, nanomechanical properties of CCNT reinforced epoxy composites with varying weight percentages (0, 1, 3, and 5 wt %) of nanotubes were measured by the nanoindentation technique. Hardness and elastic modulus measurement of the composites were conducted.

Abstract: The carbon nanotubes were prepared by catalytic decompose of benzene using floating transition method at 1100~1200°C. Benzene was used as carbon source and iron as catalyst with sulfur. The carbon nanotubes are straight with diameter 30~80nm, internal diameter 10~50nm and length 50~100μm. The carbon nanotubes and epoxy resin were sufficiently mixed. The mixture was smeared on to a pure aluminum plate layer by layer until the thickness of the composite layer reached 1.0 mm. The coating resin was cured by heating under infrared radiation. Complex permittivity, permeability and microwave reflectivity of carbon nanotubes reinforced epoxy resin coating had been investigated at the frequency ranges of 8.2~12.4GHz and 2~18GHz respectively. The real part (ε′) of complex permittivity of this coating ranges from 14.87 to 13.86, and the imaginary part (ε″), from 6.42 to 5.87, the loss tangent tgδε (ε″/ε′), from 0.42 to 0.45. The real part (μ′) of complex permeability of this coating ranges from 1.02 to 1.14, and the imaginary part (μ″), from 0.08 to 0.11, the loss tangent tgδμ (μ″/μ′), from 0.06 to 0.11. The maximum absorbing peak of the carbon nanotube reinforced epoxy resin coating is 22.89 dB at 11.40GHz. The band width (R<-10dB) of this coating with thickness of 1.0 mm is 3.0GHz, band width (R<-5dB) is 4.7GHz at the frequency range of 8~18GHz. This carbon nanotube reinforced epoxy resin coating would be a good candidate for microwave absorbing material.

Abstract: The filling of multi-walled carbon nanotubes (MWNTs) with metallic silver nanowires via wet chemistry method was investigated. The carbon nanotubes were filled with long continuous silver nanowires. The carbon nanotubes were almost opened and cut after being treated with concentrated nitric acid. Silver nitrate solution filled carbon nanotubes by capillarity. Carbon nanotubes were filled with silver nanowires after calcinations by hydrogen. The diameters of silver nanowires were in the range of 20-40nm, and lengths of 100nm-10μm. We studied the micromorphology of the silver nanowires filled in carbon nanotubes by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on the experimental results, a formation mechanism of the Ag nanowire-filled carbon nanotubes was proposed. And the microwave permittivity of the carbon nanotubes filled with metallic silver nanowires was measured in the frequency range from 2 GHz to 18 GHz. The loss tangent of the carbon nanotubes filled with metallic silver nanowires is high. So the carbon nanotubes filled with metallic silver nanowires would be a good candidate for microwave absorbent.

Abstract: The tribological and mechanical properties of polytetrafluoroethylene (PTFE) composites filled with carbon nano-fiber (CNF), short carbon fiber (SCF) and the combination of them were studied. The results indicate that the wear volume loss of the PTFE composite filled with CNF or SCF, in comparison with that of pure PTFE, decreases by 1~2 orders of magnitude. And the best wear resistant composition is achieved by the combination of SCF with CNF; as an example, PTFE+2 wt% CNF+18 wt% SCF exhibits a specific wear volume loss of 0.88 mm3, which is about 11 times lower when compared to the PTFE composite filled with 18 wt% SCF. Meanwhile, the results also show that the tensile strength of SCF or CNF filled PTFE composites is better than that of pure PTFE. However, the combination of the two fillers decreases the tensile strength of PTFE composites. Worn surfaces were investigated using a scanning electron microscope, from which it is assumed that a mechanism of rolling effect, due to the filling of nanoparticles, which has a positive protective effect for PTFE matrix.

Abstract: A series of nanocomposites, SiCN/A3S2 ceramics, were prepared by hot-pressing method. The nanometer SiCN powder is characterized of high dielectric dissipation. The dielectric properties of the SiCN/A3S2 nanocomposites were investigated. XRD and SEM were conducted to study the phases and microstructure of the nanocomposites. Compared with the pure A3S2 ceramic, the grain size in the nanocomposites is reduced due to the addition of nanometer SiCN powder. The relative densities of the nanocomposites are also lower than that of the pure A3S2 ceramic. Both the real and imaginary parts of the complex permittivity of nanocomposites in X band increase as the content of SCN powder in the samples rises obviously. When the contents of SiCN powder in samples are same, the real and imaginary parts of the samples vary with the sintering temperature. The tanδ of the nanocomposites reduces from 1.9 to 1.4 when sintering temperature increases from 1450OC to 1650 OC. SAED pattern reveals that structure of the SiCN in SiCN/ A3S2 sintered at higher temperatures tend to crystallize. The real, imaginary parts and dissipation factor of the nanocomposites sintered at higher temperature is lower than those sintered at 1450 °C.

Abstract: Hydroxyapatite reinforced ultrahigh molecular weight polyethylene (HA/UHMWPE) nanocomposites with HA volume fraction 0.1~0.5 are processed by twin-screw extrusion compounding and compression molding followed by hot drawing. SEM micrographs show that HA nano-particles are homogeneously dispersed in the highly oriented UHMWPE inter-fibrils. Tensile tests show that the modulus increases, while the strength and ductility decrease, with the increase of HA content. A good combination of mechanical properties can be obtained in the composite with HA nano-particles volume fraction 0.3.

Abstract: Although many studies have been conducted in the past few years on the possibility of using carbon nanotube (CNT) to improve the performance of polymer-based materials, some of the results were contradictory and lack of coherence. Thus, the in-depth understanding of CNT composites is required. In this paper, single-walled carbon nanotubes (SWNTs), which were functionalized by sonicating with nitric and sulfuric acids, will be used to fabricate a SWNT/epoxy composite. There are two reasons for functionalizing the SWNTs, they are (i) to improve the dispersion of the SWNTs in polymer, and (ii) to improve the interfacial bonding properties between the SWNTs and polymer matrix. Tensile property test and micro-hardness test will be carried out to examine the mechanical properties of the composites with different SWNT contents. Thermogravimetry Analysis (TGA) will be used to evaluate the thermal properties of the composites. Scanning Electron Microscope (SEM) will also be used to investigate the failure mechanism of the composites after tensile test. A comparison of the composites with functionalized and non-functionalized SWNTs will be given to elaborate the effect of nanotube functionalization.

Abstract: The dynamic properties of multi-walled carbon nanotubes (MWNTS)/epoxy nanocomposite beams were investigated experimentally and numerically. The MWNTs/epoxy nanocomposite beams were fabricated by hot press method. In experiment, the dynamic properties of the nanocomposite beams, such as natural frequency, and damping ratio, were obtained. A shaker was used to provide the vibration source at the fixed base of the specimens. The vibration signals of the nanocomposite beams were detected by a laser sensor, and the frequency responses were obtained by a computer-aided signal analyzer. The half power method was used to find the damping ratios of the nanocomposite beams for each mode. In analysis, the mechanical properties of MWNTs/epoxy nanocomposites were obtained and used in the free vibration analysis by the finite element method. The natural frequencies and mode shapes of the nanocomposite beams were calculated numerically. The effect of the weight percentage of MWNTs on the dynamic properties of the nanocomposite beams was investigated. The numerical results were found to be in good agreement with the experimental ones.