B.Q. Wei

Processing and properties of carbon nanotubes-nano-SiC ceramic

Carbon nanotubes–nano-SiC ceramic has been fabricated by the hot-press method. The preparation steps involved the use of dispersing nano-SiC powders and carbon nanotubes in butylalcohol using an ultrasonic shaker. The reasonable relative density of about 95% has been achieved by hot-pressing at 2273 K (at 25 MPa in Ar for 1 h). The three-point bending strength and fracture toughness of the composite has about 10% increment over monolithic SiC ceramic which was fabricated under the same process. The reasons for the increment are the strengthening and toughening role of carbon nanotubes occuring in the matrix.

Fabrication of aluminum-carbon nanotube composites and their electrical properties

Abstract Aluminum–carbon nanotube (CNT) composites were fabricated by hot-pressing the respective powders. The microstructural characteristics and the distribution of carbon nanotubes in the aluminum matrix were investigated. The electrical resistivities of the composites were measured from room temperature down to 4.2 K. The electrical resistivity at room temperature increases slightly with increasing volume fraction of the carbon nanotubes in the aluminum. From room temperature to ∼80 K all the composites exhibit the typical metallic decrease of the electrical resistivity upon lowering the temperature. At about 80 K their resistivities abruptly drop by more than 90%; at lower temperatures the resistivity does not show any fluctuation.

Study of electrochemical capacitors utilizing carbon nanotube electrodes

Several types of block-form porous tablets of carbon nanotubes are fabricated to use as polarizable electrodes in electrochemical capacitors (ECs). These tablets are prepared by using moulded mixtures comprising carbon nanotubes and phenolic resin powders. Comparison of the effect of different processing on the performance of the capacitors is specifically investigated. Using these polarizable electrodes, ECs with a specific capacitance of about 15 to 25 F cm−3 are obtained with 38 wt.% H2SO4 as the electrolyte.

Transformation of carbon nanotubes to nanoparticles by ball milling process

Abstract Carbon nanotubes were treated by high-energy ball milling processing for different milling times, and the samples were observed by HRTEM. The broken nanotubes and lots of carbon onion-like particles were obtained in the sample milled for 15 min. When the milling time was up to 60 min, carbon nanotubes turned into amorphous carbon. On the basis of HRTEM observation of carbon nanotubes and carbon nanoparticles, we discuss the possible formation mechanism of nanoparticles under the impact acting as driving force.

Hydrogen storage of dense-aligned carbon nanotubes

Abstract It has been considered so far that the inner cavities of carbon nanotubes are the desired place for the storage of hydrogen molecules. Here we show that the inter-nanotube space between densely aligned carbon nanotubes, produced by catalytic pyrolysis of ferrocene, could also contribute to the effective uptake of molecular hydrogen. This provides a new way to improve the properties of carbon nanotubes in storing hydrogen or other elemental molecules.

Electric double-layer capacitors using carbon nanotube electrodes and organic electrolyte

Porous tablets of carbon nanotubes were used as polarizable electrodes in electric double-layer capacitors (EDLC). The specific surface area and pore specific volume of the carbon nanotube materials were measured. An energy density of about 20 W h/kg of EDLC using these polarizable electrodes were obtained on a single cell device with an organic liquid solvent as electrolyte.

The mechanism of phase transformation from carbon nanotube to diamond

Abstract The transitional model from carbon nanotube to diamond has been established. The transition has Leen accomplished from carbon nanotube to carbon onion and then to diamond through laser irradiation. The transition from tube to onion under laser irradiation experiences the process of structure collapse of the tube and re-organization of carbon clusters. Carbon atoms in onions have some sp 3 character due to the insertion of pentagons in hexagon networks and curling of the structure. So onions are easier than graphite to transform into diamond. Laser irradiation can give rise to the loss of atoms by sputtering and interstitial atoms among shells. Because of the surface tension a state of self-compression is formed in carbon onions and the pressure can induce the transition from onion to diamond.

The effect of surface treatments on hydrogen storage of carbon nanotubes

： Carbon nanotubes used in this experiment were grown from a acetylene－ hydrogen mixture on a support using different catalyst precursors. The surface characteristics of carbon nanotubes determined the interaction with hydrogen, so the materials thus produced were submitted to two different treatments, namely nitric acid and alkali solution to gain favorable adsorption surface, these treatments improved surface area and surface activity effectively. At last it can absorb 5％ of hydrogen at room temperature under 10 MPa, and the result is stable.

Vertical aligned carbon nanotubes grown on Au film and reduction of threshold field in field emission

Vertical aligned carbon nanotubes were synthesized on quartz glass and Au film by catalytic decompositon of ferrocene and xylene. Morphological differences between aligned nanotubes grown on the two substrates are studied and discussed through SEM images. Field emission testing shows that aligned nanotubes grown on Au have a lower threshold field than those grown on quartz glass. This reduction of threshold field indicates a new way to improve field emission properties through the selection of a highly conductive growth substrate for carbon nanotubes.

Electrical conductivity and field emission characteristics of hot-pressed sintered carbon nanotubes

A soft sinter of pure carbon nanotubes was fabricated by hot-pressing under the conditions of 2273K/25MPa/Ar/1h. Four-probe resistance measurements showed that the resistivity of the sinter was about (2--3) {times} 10{sup {minus}4} {Omega}{center_dot}cm. The temperature dependence of the electrical resistance was also studied. Field emission properties of the sinter indicate that it is a good candidate for practical field emission applications.