Processing and characterization of syntactic carbon foams containing hollow carbon microspheres

The effects of heat-treatment on the properties of carbon foams were studied. The carbon foam was first prepared by adding hollow carbon microspheres to phenolic resin, followed by post-curing, pre-carbonization and carbonization. The mechanisms of failure behaviour and the increase of electrical and thermal conductivities showed that the properties of the foams were influenced by the heat-treatment temperature. Results showed that the introduction of more interval voids during carbonization resulting in a reduction of the mechanical properties. Carbon foams with electrical conductivity of 1.20 S/cm and thermal conductivity of 12.85 W/mK were obtained.     

Preparation and properties of the three-dimensional highly thermal conductive carbon/carbon-silicon carbide composite using the mesophase-pitch-based carbon fibers and pyrocarbon as thermal diffusion channels

The novel three dimensional highly thermal conductive carbon/carbon-silicon carbide (C/C-SiC) composite was successfully prepared using the mesophase-pitch-based carbon fibers and pyrocarbon as the thermal diffusion channels. The results show that the highly thermal conductive C/C-SiC composite with 221.1 W m^?1K^?1 in the ablation direction exhibits a smaller temperature gradient, and the surface temperature is 470 °C lower than that of the lowly thermal conductive C/C-SiC composite. The mass and linear ablation rates of the highly thermal conductive C/C-SiC composite are 0.56 mg·cm^?2 s^?1 and 0.11 μm·s^?1, respectively.     

Processing and mechanical properties of magnesium foams

An open-cellular magnesium foam has been manufactured by using powder metallurgy technology basing on space holder fillers in the present study. Depending on the volume fraction and the diameter of the carbamide particles, the porosity and pore size can be controlled in the range of 40–80% and 0.5–2.0 mm, respectively. Quasi-static compressive tests indicate that the mechanical behavior of the present magnesium foam is in good agreement with the Gibson–Ashby model when the porosity is over 45%. The most outstanding mechanical feature, however, may be its long and flat plateau region that is favorable for energy absorbing applications.     

泡沫炭的最新研究进展

泡沫炭是一种新型的炭材料,具有密度小、强度高、导电、导热、热稳定、化学稳定等良好的物理和化学性能。制备泡沫炭的前驱体主要包括有机聚合物和中间相沥青,不同前驱体所制备的泡沫炭结构和性能也有一定差异。本文从泡沫炭的制备、改性、性能及应用等方面综述了近年来泡沫炭的最新研究进展,重点阐述了中间相沥青基泡沫炭的制备和性能,并指出了泡沫炭的未来研究方向。     

Continuous electrodeposition for lightweight, highly conducting and strong carbon nanotube-copper composite fibers

Carbon nanotube (CNT) fiber is a promising candidate for lightweight cables. The introduction of metal particles on a CNT fiber can effectively improve its electrical conductivity. However, the decrease in strength is observed in CNT-metal composite fibers. Here we demonstrate a continuous process, which combines fiber spinning, CNT anodization and metal deposition, to fabricate lightweight and high-strength CNT-Cu fibers with metal-like conductivities. The composite fiber with anodized CNTs exhibits a conductivity of 4.08 × 10(4)-1.84 × 10(5) S cm(-1) and a mass density of 1.87-3.08 g cm(-3), as the Cu thickness is changed from 1 to 3 μm. It can be 600-811 MPa in strength, as strong as the un-anodized pure CNT fiber (656 MPa). We also find that during the tensile tests there are slips between the inner CNTs and the outer Cu layer, leading to the drops in electrical conductivity. Therefore, there is an effective fiber strength before which the Cu layer is robust. Due to the improved interfacial bonding between the Cu layer and the anodized CNT surfaces, such effective strength is still high, up to 490-570 MPa.     

Processing of nanocomposite foams in supercritical carbon dioxide. Part I: Effect of surfactant

Polystyrene-clay nanocomposites were prepared by in situ polymerization to achieve the better dispersion of lamellar silicates i.e. montmorillonite and fluorohectorite and were used to process foams with supercritical CO₂. Clay-Polymer interactions were modulated by varying the surface treatment of clays: a physical interface was formed with the compatible surfactant showing aromatic groups (MMT-benz) and a chemical interface was created after reaction of methacrylate group (MMT-MHAB) with the styrene monomer. The dispersion of nanocomposites and the microstructure of resulting foams are very dependent on the quality of the clay/matrix interface. With the compatible clay, exfoliation of aromatic clay in polystyrene matrix is obtained at all scales. On the other hand, with the reactive clay, intercalated primary particles are obtained but the size of foam cells is the smallest and cell density is the highest. Our results suggest that the nucleation occurs primarily on physico-chemical nucleation sites that are the carbonyl group of the tethered copolymers synthesized on reactive clay and that present a strong affinity for CO₂. The relaxation times determined by using solid-state NMR spectroscopy are consistent with the formation of the in situ copolymers.     

泡沫炭的研究进展

介绍了泡沫炭的基本性质及制备方法:泡沫炭是一种性能优异,用途广泛的新型炭材料;不同的制备原料和方法所得泡沫炭的结构和性能也有所不同.通常用于制备泡沫炭的原料包括有机聚合物、中间相沥青以及煤和煤系物.重点阐述了以煤和煤系物作为前体制备泡沫炭的相关工作,综述了泡沫炭的结构、性能及近年来国内外的研究进展,并对其潜在的应用和发展趋势做了初步总结.     

Preparation and characterization of highly conductive transparent films with single-walled carbon nanotubes for flexible display applications

Dense, aligned single-walled carbon nanotubes (SWCNTs) were obtained by nitric acid treatment and the subsequent removal of metal impurities by HCl. The highly purified SWCNTs were dispersed with sodium dodecyl sulfate in order to obtain a stabilized suspension for spray coating on flexible polyethylene terephthalate (PET) substrate. The low sheet resistance of the resulting thin conductive film on the PET substrate was due to the interconnecting networks of highly purified SWCNT bundles. These bundles formed strong crisscross networks of nanotubes clustered together with well defined channels, thus improving the electrical and optical properties of the film. Its sheet resistance varied from 956 to 472 Ω/square with 85% optical transmittance at a wavelength of 550 nm. The films may be potential candidates for flexible display applications.     

Strong,conductive carbon nanotube fibers as efficient hole collectors

We present the photovoltaic properties of heterojunctions made from single-walled carbon nanotube (SWNT) fibers and n-type silicon wafers. The use of the opaque SWNT fiber allows photo-generated holes to transport along the axis direction of the fiber. The heterojunction solar cells show conversion efficiencies of up to 3.1% (actual) and 10.6% (nominal) at AM1.5 condition. In addition, the use of strong, environmentally benign carbon nanotube fibers provides excellent structural stability of the photovoltaic devices.     

Graphitized boron-doped carbon foams: Performance as anodes in lithium-ion batteries

The electrochemical performance as potential anodes in lithium-ion batteries of several boron-doped and non-doped graphitic foams with different degree of structural order was investigated by galvanostatic cycling. The boron-doped foams were prepared by the co-pyrolysis of a coal and two boron sources (boron oxide and a borane–pyridine complex), followed by heat treatment in the 2400–2800 °C temperature interval. The extent of the graphitization process of the carbon foams depends on boron concentration and source. Because of the catalytic effect of boron, lightweight graphite-like foams were prepared. Boron in the foams was found to be present as carbide (B₄C), in substitutional positions in the carbon lattice (B–C), bonded to nitrogen (B–N) and forming clusters. Larger reversible lithium storage capacities with values up to ∼310 mA h g⁻¹ were achieved by using the boron oxide-based carbon foams. Moreover, since the electrochemical anodic performance of these boron-doped foams with different degree of structural order is similar, the beneficial effect of the presence of the B–C boron phase was inferred. However, the bonding of boron with nitrogen in the pyridine borane-based has a negative effect on lithium intercalation.     

Mechanical properties of copper-coated carbon foams

The mechanical properties of copper-coated carbon foam were investigated. Reticulated vitreous carbon cell type foams, with 97% porosity and 10 ppi pore size, were electroplated with copper for different periods of time to obtain coatings with different thicknesses and foams with different porosities. Compression tests were performed to determine the Young’s modulus and the plateau stress. The copper electroplating technique improved these two properties, with the modulus increasing from 4.5 to 8.6 MPa for the sample electroplated for 40 min and the plateau stress increasing from 54 to 171 kPa for the foam coated for 80 min. The relationships between the measured properties and the copper weight ratio were determined.     

Thermal properties of copper-coated carbon foams

Carbon foams, with 97% porosity, were electroplated with copper for different periods of time to achieve desired copper thicknesses and foam porosity. A light flash diffusivity instrument was used to measure the thermal conductivity of the coated samples. An analytical model was developed to calculate the effective thermal conductivity of the coated foams. It was observed that the copper-coated carbon foam with 50% porosity can attain a thermal conductivity of 180 W/m K. The results from the analytical model were compared to the experimental results and they were in a very good agreement. The above analyses demonstrated the significance of copper coating in tailoring carbon foam thermal properties. The developed analytical model was adopted to predict the thermal conductivity of the copper-coated carbon foams.     

Electromagnetic shielding performance of carbon foams

The electromagnetic shielding performance of carbon foams is measured using the nested reverberation chamber method in the frequency band 1–4 GHz, which is the frequency range of most cellular phones and microwave ovens. Good values of shielding effectiveness are obtained even with a small thickness of carbon foam. The results are used to assess the correct electrical conductivity values for the investigated materials using a multiple reflection model to compute the material transmission coefficient. The potential applications of such materials are in the lightweight microwave shielding structures that are partially transparent to optical frequencies.     

Anisotropy of mesophase pitch-derived carbon foams

Carbon foams with uniform pore size were produced from mesophase pitch in a high-pressure chamber. The morphologies, crystal structure and mechanical properties of as-grown carbon foams, carbonized and graphitic foams were investigated. The microwave absorbing properties of carbon foam sandwich composites at 2-18 GHz were also examined. It was found that the extension of pores in the xz-plane direction (parallel to the direction of gravitational force) was larger than that in the xy-plane direction (perpendicular to the direction of gravitational force). The compressive strength and modulus of resultant foams in the xz-plane direction were higher than those in the xy-plane direction. Further, the reflection loss of the sandwich composites composed of xy-plane carbon foam slabs was lower than that of xz-plane composites. The results of this work showed that carbon foam was a kind of anisotropic material.     

The electromagnetic characteristics of carbon foams

Three different pore size carbon foams with variable electric conductivities were prepared by a polymer sponge replication method. The electromagnetic parameters of these carbon foams and their corresponding pulverized powders were measured by a resonant cavity perturbation technique at a frequency of 2450 MHz. The results show that carbon foams have smaller dielectric constants but several times larger dielectric loss compared with their corresponding pulverized powders. Moreover, carbon foams show magnetic loss while no magnetic loss can be observed from their corresponding pulverized powders. The magnetic loss of carbon foams is apparently a kind of extrinsically magnetic loss and believed to be able to maintain at high temperatures. The electromagnetic characteristics of carbon foams demonstrate that macrostructure modification is an effective way to modulate electromagnetic properties of such materials.     

Polystyrene-based carbon spheres as electrode for electrochemical capacitors

A series of carbon spheres with various porous texture parameters were prepared from polystyrene-based macroreticular resin spheres by carbonization and activation. The as-prepared carbon spheres had a maximum specific surface area of 996 m² g^?1, total pore volume of 1.34 cm³ g^?1 and average pore size of 5.39 nm. Moreover, these carbon spheres showed a mesopore size distributed mainly in about 40 nm. A high specific capacitance of 153 F g^?1 for carbon sphere by carbonization, 164 F g^?1 for carbon sphere by activation for 1 h and 182 F g^?1 for carbon sphere by activation for 2 h can be obtained. Moreover, a specific energy between 2.3 and 5.1 Wh kg^?1 for these carbon spheres can be obtained in 6 mol L^?1 KOH electrolyte.     

Effective post treatment for preparing highly conductive carbon nanotube/reduced graphite oxide hybrid films

SWCNT-reduced graphite oxide hybrid films were prepared by a filtration method. An efficient post-treatment procedure was designed to reduce GO and remove dispersants simultaneously. The sheet resistance decreased significantly after treatment, by a factor of 4-13 times. Films with excellent performance (95.6%, 655 Ω per square) were obtained and had great potential applications.