Synthesis and Properties of Carbon Nanotube Yarns and Textiles
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Synthesis and Properties of Carbon Nanotube Yarns and Textiles Mark W. Schauer, David Lashmore, and Brian White Nanocomp Technologies, 162 Pembroke Rd, Concord, NH, 03301 INTRODUCTION Many facilities around the world are producing metric tons of carbon nanotubes (CNTs). These nanotubes are typically suspended in a solvent, compounded with various materials, and formed into products [1, 2]. The result is a low concentration (typically less than 3%) of carbon nanotubes in the matrix, since larger concentrations tend to clump and precipitate. Also, the nanotubes used are relatively short (less than 1 micron) as longer nanotubes will not disperse into a solvent and harsh processing techniques typically shorten CNTs [3-6]. This low concentration of short nanotubes results in poor tensile load transfer between nanotubes [1, 6-8], and it is impossible to take advantage of the tremendous strength possessed by individual nanotubes. At Nanocomp Technologies, a very different approach to the production of macroscopic carbon nanotube materials is used. Relatively long (most likely 10 to 100 microns long), small diameter carbon nanotubes (either single-walled or dual-walled) are produced by chemical vapor deposition (CVD). This aerogel-like pure nanotube material is collected onto a moving belt to form a non-woven textile, or spun into a continuous yarn. This product is then post-processed to form a desired product. Tensile strength and other properties can be improved by stretching the material, thus aligning the nanotube bundles. A small amount of binder (5% to 30% by weight) can be incorporated to form a composite. The resulting products have tensile strengths unprecedented in macroscopic nanotube materials. EXPERIMENT Carbon nanotubes are produced by a gas phase pyrolysis method [7-13], similar to CVD, using a floating iron catalyst and ethanol as the primary carbon source. The ethanol based fuel contains ferrocene as the iron source, as well as thiophene and other fuel conditioners to facilitate the chemical processes. This fuel mixture is introduced through a nebulizer into an injector tube
Figure 1. Schematic of the CVD apparatus used to produce macroscopic CNT materials.
using hydrogen or helium as a carrier gas (Figure 1). The injector is specially designed to optimize the formation of catalyst particles of a specific size distribution by controlling the thermal gradient, gas flow, and chemical concentrations. Once created, the catalyst particles exit the injector and enter the CVD furnace where the fuel is thermally decomposed and the nanotubes begin to form. The material is collected at the exit of the furnace, either on a moving belt to create a non-woven textile, or by an anchor from which a continuous yarn is spun. Subsequently the material is taken out of the furnace environment for post-processing. The non-woven textiles and yarns can be post-processed in various ways. They can be condensed with a volatile solvent such as acetone. They can be mechanically stretched, usually in the presence of some
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