Many routes have been developed for the synthesis of carbon nanotubes, but their assembly into continuous fibers has been achieved only through postprocessing methods. We spun fibers and ribbons of carbon nanotubes directly from the chemical vapor deposition (CVD) synthesis zone of a furnace using a liquid source of carbon and an iron nanocatalyst. This process was realized through the appropriate choice of reactants, control of the reaction conditions, and continuous withdrawal of the product with a rotating spindle used in various geometries. This direct spinning from a CVD reaction zone is extendable to other types of fiber and to the spin coating of rotating objects in general.

We report on the mechanical properties of fibers consisting of pure carbon nanotube fibers directly spun from an aerogel formed during synthesis by chemical vapor deposition. The continuous withdrawal of product from the gas phase imparts a high commercial potential to the process, either for the production of particularly strong fibers or for the economic production of bulk quantities of carbon nanotubes. Tensile tests were performed on fibers produced from the dissociation of three different hydrocarbons, namely, ethanol, ethylene glycol, and hexane, with a range of iron (catalyst) concentrations. The conditions were chosen to lie within the range known to enable satisfactory continuous spinning, the iron concentration being varied within this range. Increasing proportions of single wall nanotubes were found as the iron concentration was decreased, conditions which also produced fibers of best strength and stiffness. The maximum tensile strength obtained was 1.46 GPa (equivalent to 0.70 N/tex assuming a density of 2.1 g/cm(3)). The experiments indicate that significant improvements in the mechanical properties can be accomplished by optimizing the process conditions.

No abstract

Single-walled carbon nanotubes (SWNTs) have been synthesized by the rapid injection of a nickel formate/silica gel catalyst/support into a hot fluidized-bed reactor. The initial rapid heating of the catalyst in the hydrocarbon feedstock was found to be essential for the nucleation of SWNTs since only amorphous or graphitic carbon particles were formed without it. These results suggest that the rapid heating of the catalyst precursor enables the formation of the small metal particles required for SWNT growth, probably due to the accelerated thermal decomposition of the catalyst precursor and enhanced nucleation rate. The growth of the SWNTs was investigated by the adoption of different methods for introducing the catalyst, and by varying the synthesis parameters including the catalyst loading, hydrocarbon gas flow rate, and concentration. The results found that SWNTs formed only under certain reaction conditions. The nanotubes produced were characterized by electron microscopy and Raman spectroscopy.

By tensile tests on GFRP rebar after high temperature, the change regularity and influent factor are analyzed. The results show that: With the temperature increasing, vitrification, carbonization, decomposition at high temperature test section of the GFRP rebar are aggravating , and their mechanical properties are deteriorating. At the same time, the limited tensile strength and ultimate tensile elastic modulus decreased in different degree.