Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
2001-07-24
2004-09-14
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C423S44500R, C423S447200
Reexamination Certificate
active
06790425
ABSTRACT:
BACKGROUND OF THE INVENTION
Fullerenes are closed-cage molecules composed entirely of sp
2
-hybridized carbons, arranged in hexagons and pentagons. Fullerenes (e.g., C60) were first identified as closed spheroidal cages produced by condensation from vaporized carbon.
Fullerene tubes are produced in carbon deposits on the cathode in carbon arc methods of producing spheroidal fullerenes from vaporized carbon. Ebbesen et al. (Ebbesen 1), “Large-Scale Synthesis Of Carbon Nanotubes,”
Nature
, Vol. 358, p. 220 (Jul. 16, 1992) and Ebbesen et al., (Ebbesen II), “Carbon Nanotubes,”
Annual Review of Materials Science
, Vol. 24, p. 235 (1994). Such tubes are referred to herein as carbon nanotubes. Many of the carbon nanotubes made by these processes were multi-wall nanotubes, i.e., the carbon nanotubes resembled concentric cylinders. Carbon nanotubes having up to seven walls have been described in the prior art. Ebbesen II; Iijima et al., “Helical Microtubules Of Graphitic Carbon,”
Nature
, Vol. 354, p. 56 (Nov. 7, 1991).
In defining carbon nanotubes, it is helpful to use a recognized system of nomenclature. In this application, the carbon nanotube nomenclature described by M. S. Dresselhaus, G. Dresselhaus, and P. C. Eklund,
Science of Fullerenes and Carbon Nanotubes
, Chap. 19, especially pp. 756-760, (1996), published by Academic Press, 525 B Street, Suite 1900, San Diego, Calif. 92101-4495 or 6277 Sea Harbor Drive, Orlando, Fla. 32877 (ISBN 0-12-221820-5), which is hereby incorporated by reference, will be used. The single wall tubular fullerenes are distinguished from each other by double index (n,m) where n and m are integers that describe how to cut a single strip of hexagonal “chicken-wire” graphite so that its edges join seamlessly when it is wrapped onto the surface of a cylinder. When the two indices are the same, m=n, the resultant tube is said to be of the “arm-chair” (or n,n) type, since when the tube is cut perpendicular to the tube axis, only the sides of the hexagons are exposed and their pattern around the periphery of the tube edge resembles the arm and seat of an arm chair repeated n times. Arm-chair tubes are a preferred form of single-wall carbon nanotubes since they are metallic, and have extremely high electrical conductivity. In addition, all single-wall nanotubes have extremely high thermal conductivity and tensile strength.
Single-wall carbon nanotubes (SWNT) have been made in a DC arc discharge apparatus of the type used in fullerene production by simultaneously evaporating carbon and a small percentage of Group VIII transition metal from the anode of the arc discharge apparatus. See Iijima et al., “Single-Shell Carbon Nanotubes of 1 nm Diameter,”
Nature
, Vol. 363, p.603 (1993); Bethune et al., “Cobalt Catalyzed Growth of Carbon Nanotubes with Single Atomic Layer Walls,”
Nature
, Vol. 63, p. 605 (1993); Ajayan et al., “Growth Morphologies During Cobalt Catalyzed Single-Shell Carbon Nanotube Synthesis,”
Chem. Phys. Lett
., Vol. 215, p. 509 (1993); Zhou et al., “Single-Walled Carbon Nanotubes Growing Radially From YC
2
Particles,”
Appl. Phys. Lett
., Vol. 65, p.1593 (1994); Seraphin et al., “Single-Walled Tubes and Encapsulation of Nanocrystals Into Carbon Clusters,”
Electrochem. Soc
., Vol. 142, p. 290 (1995); Saito et al., “Carbon Nanocapsules Encaging Metals and Carbides,”
J. Phys. Chem. Solids
, Vol. 54, p. 1849 (1993); Saito et al., “Extrusion of Single-Wall Carbon Nanotubes Via Formation of Small Particles Condensed Near an Evaporation Source,”
Chem. Phys. Lett
., Vol. 236, p. 419 (1995). It is also known that the use of mixtures of such transition metals can significantly enhance the yield of single-wall carbon nanotubes in the arc discharge apparatus. See Lambert et al., “Improving Conditions Toward Isolating Single-Shell Carbon Nanotubes,”
Chem. Phys. Lett
., Vol. 226, p. 364 (1994).
While this arc discharge process can produce single-wall nanotubes, the yield of nanotubes is low and the tubes exhibit significant variations in structure and size between individual tubes in the mixture. Individual carbon nanotubes are difficult to separate from the other reaction products and purify.
An improved method of producing single-wall nanotubes is described in U.S. patent application Ser. No. 08/687,665, entitled “Ropes of Single-Walled Carbon Nanotubes” incorporated herein by reference in its entirety. This method uses, inter alia, laser vaporization of a graphite substrate doped with transition metal atoms, preferably nickel, cobalt, or a mixture thereof, to produce single-wall carbon nanotubes in yields of at least 50% of the condensed carbon. The single-wall nanotubes produced by this method tend to be formed in clusters, termed “ropes,” of 10 to 1000 single-wall carbon nanotubes in parallel alignment, held together by van der Waals forces in a closely packed triangular lattice. Nanotubes produced by this method vary in structure, although one structure tends to predominate.
PCT/US/98/04513 entitled “Carbon Fibers Formed From Single-Wall Carbon Nanotubes” and which is incorporated by reference, in its entirety, discloses, inter alia, methods for producing single-wall carbon nanotubes, nanotube ropes, nanotube fibers, and nanotube devices. A method for making single-wall carbon nanotubes is disclosed, in which a laser beam vaporizes material from a target comprising, consisting essentially of, or consisting of a mixture of carbon and one or more Group VI or Group VIII transition metals. The vapor from the target forms carbon nanotubes that are predominantly single-wall carbon nanotubes, and of those, the (10, 10) tube is predominant. The method also produces significant amounts of single-wall carbon nanotubes that are arranged as ropes, i.e., the single-wall carbon nanotubes run parallel to each other. The laser vaporization method provides several advantages over the arc discharge method of making carbon nanotubes: laser vaporization allows much greater control over the conditions favoring growth of single-wall carbon nanotubes and the laser vaporization method produces single-wall carbon nanotubes in higher yield and of better quality. The laser vaporization method may also be used to produce longer carbon nanotubes and longer ropes.
PCT US99/25702 entitled “Gas-phase process for production of single-wall carbon nanotubes from high pressure CO” and which is incorporated by reference, in its entirety, discloses, inter alia, methods for producing single-wall carbon nanotubes, nanotube ropes, nanotube fibers, and nanotube devices. A method for making single-wall carbon nanotubes is therein disclosed, which invention comprises the process of supplying high pressure (e.g., 30 atmospheres) CO that has been preheated (e.g., to about 1000° C.) and a catalyst precursor gas (e.g., Fe(CO)
5
) in CO that is kept below the catalyst precursor decomposition temperature to a mixing zone. In this mixing zone, the catalyst precursor is rapidly heated to a temperature that results in (1) precursor decomposition, (2) formation of active catalyst metal atom clusters of the appropriate size, and (3) favorable growth of SWNTs on the catalyst clusters. Preferably a catalyst cluster nucleation agency is employed to enable rapid reaction of the catalyst precursor gas to form many small, active catalyst particles instead of a few large, inactive ones. Such nucleation agencies can include auxiliary metal precursors that cluster more rapidly than the primary catalyst, or through provision of additional energy inputs (e.g., from a pulsed or CW laser) directed precisely at the region where cluster formation is desired. Under these conditions SWNTs nucleate and grow according to the Boudouard reaction. The SWNTs thus formed may be recovered directly or passed through a growth and annealing zone maintained at an elevated temperature (e.g., 1000° C.) in which tubes may continue to grow and coalesce into ropes.
Carbon nanotubes, ropes of carbon nanotubes, and in particular, single-wall carbon nanotubes and ropes thereof, are useful for making electrical connectors in mi
Casavant Michael J.
Chiang Wan-Ting
Colbert Daniel T.
Hague Robert H.
Huffman Chad B.
Hendrickson Stuart L.
Lish Peter J
Ross Spencer Garsson Winstead Sechrest & Minick P.C.
Wiliam Marsh Rice University
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