Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
2002-03-04
2004-07-20
Mayes, Melvin C. (Department: 1734)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S108000, C264S171260, C264S172170, C264SDIG001, C264SDIG002
Reexamination Certificate
active
06764628
ABSTRACT:
FIELD OF THE INVENTION
Methods are described for the spinning of carbon nanotube fibers containing a high loading of nanotubes in a fiber component; the stabilization of spun materials by post-spinning processes; and the application of such materials made by spinning.
DESCRIPTION OF THE RELATED ART
Since the discovery of carbon nanotubes by Iijima and coworkers (Nature 354, 56-58, (1991) and Nature 361, 603-605 (1993)) various types of carbon nanotubes (NTs) have been synthesized. A single-wall carbon nanotube (SWNT) consists of a single layer of graphite that has been wound into a seamless tube having a nanoscale diameter. A multi-wall carbon nanotube (MWNT), on the other hand, comprises two or more such cylindrical graphite layers that are coaxial. Both single-wall and multi-wall nanotubes have been obtained using various synthetic routes, which typically involve the use of metallic catalysts and very high processing temperatures. Typical synthesis routes are those employing a carbon arc, laser evaporation of carbon targets, and chemical vapor deposition (CVD).
SWNTs are produced by the carbon-arc discharge technique using a pure carbon cathode and a carbon anode containing a mixture of graphite powder and catalytic metal(s), like Fe, Ni, Co and Cu (D. S. Bethune et al. Nature 363, 605-7 (1993) and S. Iijima and T. Ichihashi, Nature 363, 603-5 (1993)). C. Journet et al. (Nature 388, 756-758 (1997)) have described an improved carbon-arc method for the synthesis of SWNTs which uses Ni/Y (4.2/1 atom %) as the catalyst. Co-vaporization of carbon and the metal catalyst in the arc generator produced a web-like deposit of SWNTs that is intimately mixed with fullerene-containing soot.
Smalley's group (A. Thess et al., Science 273, 483-487(1996)) developed a pulsed laser vaporization technique for synthesis of SWNT bundles from a carbon target containing 1 to 2% (w/w) Ni/Co. The dual laser synthesis, purification and processing of single-wall nanotubes has been described in the following references: J. Liu et al., Science 280, 1253 (1998); A. G. Rinzler et al., Applied Physics A 67, 29 (1998); A. G. Rinzler et al., Science 269, 1550 (1995); and H. Dai, et al., Nature 384, 147 (1996).
The CVD method described by Cheng et al. (Appl. Phys. Lett. 72, 3282 (1998)) involves the pyrolysis of a mixture of benzene with 1 to 5% thiophene or methane, using ferrocene as a floating catalyst and 10% hydrogen in argon as the carrier gas. The nanotubes form in the reaction zone of a cylindrical furnace held at 1100-1200° C. Depending on the thiophene concentration, the nanotubes form as either multi-wall nanotubes or bundles of single-wall nanotubes. Another useful method for growing single-wall nanotubes uses methane as the precursor, ferric nitrate contained on an alumina catalyst bed, and a reaction temperature of 1000° C.
Another CVD synthesis process was described by R. E. Smalley et al. in PCT International Application No. WO 99-US25702, WO 99-US21367 and by P. Nikolaev et al. in Chem. Phys. Lett. 313, 91-97 (1999). This process, known as the HiPco process, utilizes high pressure (typically 10-100 atm) carbon monoxide gas as the carbon source, and nanometer sized metal particles (formed in-situ within the gas stream from organo-metallic precursors) to catalyze the growth of single-wall carbon nanotubes. The preferred catalyst precursors are iron carbonyl (Fe(CO)
5
) and mixtures of iron carbonyl and nickel carbonyl (Ni(CO)
4
). The HiPco process produces a SWNT product that is essentially free of carbonaceous impurities, which are the major component of the laser-evaporation and carbon-arc products. The process enables control of the range of nanotube diameters produced, by controlling the nucleation and size of the metal cluster catalyst particles. In this way, it is possible to produce unusually small nanotube diameters, about 0.6 to 0.9 nm.
The nanotube-containing products of the laser-evaporation and carbon-arc processes invariably contain a variety of carbonaceous impurities, including various fullerenes and less ordered forms of carbon soot. The carbonaceous impurity content in the raw products of the laser and carbon arc processes typically exceeds 50 weight %. Purification of these products generally relies on selective dissolution of the catalyst metals and highly ordered carbon clusters (called fullerenes) followed by selective oxidation of the less ordered carbonaceous impurities. A typical purification process is described by Lui et al. in Science 280, 1253 (1998). This method involves refluxing the crude product in 2.6 M nitric acid for 45 hours, suspending the nanotubes in pH 10 NaOH aqueous solution using a surfactant (e.g, Triton X-100 from Aldrich, Milwaukee, Wis.), followed by filtration using a cross-flow filtration system. While the effects of these purification processes on the nanotubes themselves are not completely understood, it is believed that the nanotubes are shortened by oxidation.
As discussed by B. I. Jakobson and R. E. Smalley (American Scientist 85, 325, 1997) SWNT and MWNT materials are promising for a wide variety of potential applications because of the exceptional physical and chemical properties exhibited by the individual nanotubes or nanotube bundles. Some SWNT properties of particular relevance include metallic and semiconducting electrical conductivity, depending on the specific molecular structure, extensional elastic modulus of 0.6 TPa or higher, tensile strengths on the order of ten to one hundred GPa, and surface areas that can exceed 300 m
2
/g.
The proposed applications of carbon nanotubes include mechanical applications, such as in high-strength composites, electrical applications, and multifunctional applications in which different properties aspects of the carbon nanotubes are simultaneously utilized. Tennent et al. in U.S. Pat. No. 6,031,711 describe the application of sheets of carbon nanotubes as high performance supercapacitors. In this application, a voltage difference is applied to two high-surface-area carbon nanotube electrodes that are immersed in a solid or liquid electrolyte. Current flows in the charging circuit, thereby injecting charge in the nanotubes, by creating an electrostatic double layer near the nanotube surfaces.
The application of carbon nanotube sheets as electromechanical actuators has been recently described (R. H. Baughman et al., Science 284, 1340 (1999)). These actuators utilize dimension changes that result from the double-layer electrochemical charge injection into high-surface-area carbon nanotube electrodes. If carbon nanotubes can be assembled into high modulus and high strength assemblies (such as filaments, ribbons, yarns, or sheets) that maintain their ability to electrochemically store charge, then superior actuator performance should be obtainable. The problem has been that no methods are presently available for the manufacture of nanotube articles that have these needed characteristics.
These and other promising applications require assembling the individual nanotubes into macroscopic arrays that effectively use the attractive properties of the individual nanotubes. This obstacle has so far hindered applications development. The problem is that MWNTs and SWNTs are insoluble in ordinary aqueous solvents and do not form melts even at very high temperatures. Under certain conditions, and with the aid of surfactants and ultrasonic dispersion, bundles of SWNTs can be made to form a stable colloidal suspension in an aqueous medium. Filtration of these suspensions on a fine-pore filter medium, as described by Lui et al. in Science 280, 1253 (1998), results in the production of a paper-like sheet which has been called “bucky paper” (in reference to buckminsterfullerene, or C
60
, the first member of the fullerene family of carbon cluster molecules). Such sheets, which can range in conveniently obtainable thickness from 10-100 microns, possess mechanical strength derived from the micro-scale entanglement of the nanotube bundles. Bucky paper preserves the large accessible surface area of the nanotube bundle
Baughman Ray H.
Golecki Ilan
Lobovsky Alex
Matrunich James
Palley Igor
Honeywell International , Inc.
Mayes Melvin C.
Palguta Larry J.
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