WO2005068067A1

WO2005068067A1 - Electric arc apparatus for making fullerenes

Info

Publication number: WO2005068067A1
Application number: PCT/US2004/006886
Authority: WO
Inventors: Michael Joseph Pepka
Original assignee: Michael Joseph Pepka
Priority date: 2003-12-23
Filing date: 2004-03-04
Publication date: 2005-07-28

Abstract

A high temperature, electric arc reactor chamber between a consumable carbon anode and a cooled cathode produces atomized carbon ejected from the chamber in gaseous velocity visible streams in which single wall nanohorns form as the gaseous carbon cools away from the chamber. To achieve a pressurized atomized carbon atmosphere in the reactor chamber between the anode and cathode and to achieve an arc over the entire electrode areal surfaces, the anode and cathode have matching surfaces maintained with a constant gap across the surfaces. By design, the gap is very small, resulting in the white-hot anode that is consumed at a high anode feed rate. A non-air gas envelopes the reactor chamber and surrounding regions, which isolates the reactor chamber and jet streams from surrounding air. The gas also carries the formed nanohorns into a reduced ('vacuum') that collects and sorts nanhorns by size.

Description

ELECTRIC ARC APPARATUS FOR MAKING FULLERENES

BACKGROUND Field of the Invention This invention relates to production of fullerenes, and more specifically to the apparatus and method of producing single wall carbon nanotubes, particularly in nanohorn clusters, in commercially viable quantities. Prior Art A fullerene is a third form of pure carbon and is different from graphite and diamond, the only two forms known before 1985. A fullerene structure is generally characterized as a two-dimensional carbon array, each carbon atom bonded to three other carbon atoms. The carbon array curves around to meet and j oin with itself as a molecule with cage-like structure and aromatic compound properties. One such fullerene molecule, referred to as "buckminsterfuUerene," or "buckyball" contains 60 carbon atoms bonded together in a spherical surface relationship, a structural diagram of which resembles the familiar shape of a soccer ball. Buckyballs often occur in multilayers, that is, a fullerene with multiple concentric spherical surfaces. Single-wall carbon nanotubes (SWNT) are fullerenes of closed-cage carbon molecules typically arranged in cross sectional hexagons and pentagons. Commonly known as "buckytubes," these cylindrical carbon structures have extraordinary properties, including high electrical and thermal conductivity, as well as high strength and stiffness. Concentric, or nested, single-wall carbon cylinders, known as multi-wall carbon nanotubes (MWNT) also occur ~ carbon nanotubes having two or more walls have been described. Multi-wall nanotubes possess properties similar to the single- wall carbon nanotubes; however, single-wall carbon nanotubes have fewer defects, rendering them stronger, more conductive, and typically more useful than multi-wall carbon nanotubes. Single-wall carbon nanotubes are believed to be much more free of defects than are multi-wall carbon nanotubes because multi-wall carbon nanotubes can survive occasional defects by forming bridges between the unsaturated carbon of the neighboring cylinders, whereas single-wall carbon nanotubes have no neighboring walls for defect compensation. Multi-wall nanotubes occur more commonly than single wall nanotubes. In fact, multi-wall nanotubes are readily produced, though in small volumes, in various processes previously disclosed in the art, including laser ablation, electric arc and vapor deposition. Single wall nanotubes are difficult to obtain and occur in these same processes mixed in small portions with MWNT. They are difficult to separate from the MWNT and therefore presently little more than a research novelty. A further form of fullerene is termed a nanohorn, comprising a single wall fullerene in a conal shape with conical walls at 20° from its longitudinal axis expanding from a smaller end closed by a cap of about 1 nm. diameter to a larger open end of about 2 nm diameter, much like a thimble. Previously, nanohorns were found among MWNT produced by laser ablation. They are found in clusters of hundreds or thousands of individual nanohorns apparently held together by van der

Waal forces. The clusters appear as nearly homogeneous puffballs, averaging over about 80 nanometers (nm) in diameters, having no preferred or defined growth center, that is, a point from which the nanohorn cluster grows. Characteristically, the nanohorns appear to orient somewhat with their smaller, capped end directed outward. At about 600° K the nanohorn cap closing the smaller end breaks off or opens leaving a frusto-conical single wall carbon nanostructure. Being both single wall carbon nanostructures, nanohorns and SWNT generally share the same properties and advantages, especially the nanohorns without its cap. In many applications such as a catalyst, the nanohorn structure may be more advantageous than the SWNT structure due to its vast surface area; a typical nanohorn surface area in a nanohorn cluster is approximately 250 square meters per gram. With an intrinsic strength estimated to be on the order of 100 times that of steel, single-wall carbon nanotubes and nanohorns are a possible strengthening reinforcement in composite materials. The intrinsic electronic properties of single- wall carbon nanotubes and nanohorns also make them electrical conductors and useful in applications involving field emission devices, such as flat-panel displays and in polymers used for radiofrequency interference and electromagnetic shielding that require electrical conductance properties. In other applications involving electrical conduction, single- wall carbon nanotubes, ropes of single- wall carbon nanotubes and nanohorns are useful in electrically conductive coatings, polymers, paints, solders, fibers, electrical circuitry, and electronic devices, including batteries, capacitors, transistors, memory elements, current control elements, switches and electrical connectors in micro-devices such as integrated circuits and semiconductor chips used in computers. The single wall nanotubes and nanohorns are also useful as antennas at optical frequencies as constituents of non-linear optical devices and as probes for 2 scanning probe microscopy such as are used in scanning tunneling microscopes (STM) and atomic force microscopes (AFM). Their exceptional thermal conductivity 4 properties render single-wall carbon nanotubes and nanohorns useful in composites, coatings, pastes, paints and other materials where heat transfer is a desired property. «* 6 hi composite materials, aligned single-wall carbon nanotubes and nanohorns can provide enhanced electrical, mechanical, optical, and/or thermal properties. Single- 8 wall carbon nanotubes and nanohorns can be used as replacement for, or in conjunction with, carbon black in tires for motor vehicles, and as elements of LO composite materials to elicit specific physical, chemical or mechanical properties in those materials, such as electrical and/or thermal conductivity, chemical inertness, L2 mechanical toughness, etc. The nanotubes and nanqhorns themselves and materials and structures comprising carbon these nanostractures are also useful as supports for t4 catalysts in chemical processes, such as hydrogenation, polymerization and cracking, and in devices such as fuel cells. L6 All known processes for formation of single-wall nanotubes involve a transition- metal catalyst, residues of which are invariably present in the resulting fullerenes. L 8 Likewise, these processes also result in production of varying amounts of carbon material that are not in the form of single-wall nanotubes. In the following, this non- 10 nanotube carbon material is referred to as "amorphous carbon." One of several methods of synthesizing fullerenes is by DC arc discharge. 12 Fullerene tubes are found to be produced from vaporized carbon in carbon deposits on the cathode while producing spheroidal buckyball fullerenes. However, historically arc discharge methods produce only small amounts of carbon nanotubes, and almost all of those multi-wall nanotubes, intermingled with other non-nanotube carbon forms, and individual carbon nanotubes are difficult to separate and purify from the other reaction products. While this arc discharge process can produce single wall nanotubes, the yield of single wall nanotubes is low and the tubes exhibit significant variations in structure and size between individual tubes in the mixture.

Improvement in the relative yield and structural consistency of single wall carbon nanotubes has been made in the arc discharge process by simultaneously evaporating carbon and a small amount of Group VIIIB transition metal from the anode of the arc discharge apparatus but still the total yield remains small. Another disadvantage of the prior art is the relative difficulty with which large amounts of carbon are vaporized continuously and then condensed into soot comprising fullerenes. Although fullerene production methods are suitable for relatively low rates, e.g. 10 grams per hour, they have not been efficiently scaled up to produce a soot comprising fullerenes at high rates, and having a high yield of fullerenes. An intrinsic difficulty with vaporizing carbon to produce fullerenes is that the carbon source must be heated to over 2800° C. At these temperatures, black body emission is intense. The intense light produced by black body emission in the electric arc method causes a photochemical reaction that diminishes the yields of fullerenes by forming large carbon clusters in the carbon vapor near the electrodes where the vaporized carbon concentration is high and close to the intense light. With relatively small carbon electrodes, the fullerenes are exposed to extremely intense UV radiation only briefly, and if carbon rods are heated resistively, only small amounts of UV radiation are produced. However, with larger electrodes that would be used to make fullerenes at high rates by vaporizing more anodic carbon, large amounts of UV radiation is produced, which causes the unwanted photochemical reaction of the newly formed fullerenes with the carbon vapors. An improved method of producing single-wall nanotubes is described in U.S. Pat. No. 6,183,714, entitled "Ropes of Single- Wall Carbon Nanotubes". This method uses 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 generally 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. Although the laser vaporization process produces an improved yield of single- wall carbon nanotubes, the product is still heterogeneous, and the nanotubes tend to be too tangled for many potential uses of these materials. In addition, the laser vaporization of carbon is a high-energy process, requiring substantial power input for vaporization of graphite. Another way to synthesize carbon nanotubes is by catalytic decomposition of a carbon-containing gas by nanometer-scale metal particles supported on a substrate.

The carbon feedstock molecules dissociate on the metal particle surface and the resulting carbon atoms combine to form nanotubes. The method typically produces imperfect multi-walled carbon nanotubes, but under the certain reaction conditions, can produce excellent single- wall carbon nanotubes. One example of this method involves the disproportionation of CO to form single-wall carbon nanotubes and CO₂ catalyzed by transition metal catalyst particles comprising Mo, Fe, Ni, Co, or mixtures thereof residing on a support, such as alumina. Although the method can use inexpensive feedstocks and moderate temperatures, the yield of single- wall carbon nanotubes is limited due to rapid surrounding of the catalyst particles by a dense tangle of single- wall carbon nanotubes, which acts as a barrier to diffusion of the feedstock gas to the catalyst surface, limiting further nanotube growth. Large amounts of other forms of carbon, such as amorphous carbon and multi-wall carbon nanotubes are also present in the resulting product. The process also requires the removal of the support material for many applications. All-gas phase processes can be used to form single-wall carbon nanotubes. In one example of an all gas-phase process, single-wall carbon nanotubes are synthesized using benzene as the carbon-containing feedstock and ferrocene as a transition metal catalyst precursor. By controlling the partial pressures of benzene and ferrocene and by adding thiophene as a catalyst promoter, single-wall carbon nanotubes can be produced. However, this method also suffers from simultaneous production of multi- wall carbon nanotubes, amorphous carbon, and other products of hydrocarbon pyrolysis under the high temperature conditions necessary to produce high quality single-wall carbon nanotubes. Another method for producing single- wall carbon nanotubes involves an all-gas phase method using high pressure CO as the carbon feedstock and a gaseous transition metal catalyst precursor. This method is effective in making single wall carbon nanotubes without simultaneously making multi-wall nanotubes. Furthermore, the method produces single- wall carbon nanotubes in high purity; less than about 10 wt % of the carbon in the solid product is attributable to other carbon-containing species, including both graphitic and amorphous carbon. Although the carbon nanotubes from this product are of high quality and purity, there is still a need for a method for producing single- wall carbon nanotubes at higher catalyst productivity and feedstock yields in order to improve the process economics and produce high quality single-wall carbon nanotubes at lower cost. The search for methods to produce single- wall carbon nanotubes and nanohorn clusters at high yield and high catalyst productivity has been an on-going need in order to make nanotubes and nanohorns economically viable in various applications.

Besides improving economics, higher process and catalyst yields provide routes to increased availability of larger amounts of single- wall carbon nanotubes. In conventional chemical processes, higher product yields can often be achieved with higher temperatures, pressures, catalysts and feed concentrations. Contrary to convention, these techniques have not been effective in making single-wall carbon nanotubes in the gas phase using CO as the carbon-containing feedstock. Although somewhat higher yields are observed at higher pressures, the higher yields can often be attributed to higher associated catalyst concentrations. In the gas phase, using CO as the carbon-containing feedstock, single-wall carbon nanotube yield decreases at temperatures above 1050° C, possibly due to metal cluster evaporation and chemical attack of the metal catalyst clusters by CO. Accordingly, there remains a need for a method for producing single-wall carbon nanotubes at high yield and high catalyst productivity. Therefore, a primary object of the invention is enhanced production of fullerenes, and more specifically single wall nanotubes. Another object is the enhanced production of clusters of nanohorns. A further object is efficient production of single wall nanotubes. A yet further object is custom production of a preferred diameter and length of single wall nanotubes and nanohorns. SUMMARY OF THE INVENTION The present invention enhances production of single wall nanostructures over multiwall nanotube production with a high temperature, electric arc reactor chamber, a significant portion of which collects as agglomerate accumulations, or cores, on the cathode. The remainder of the atomized carbon escapes the reactor chamber sides as a gaseous ejection and forms single wall nanohorns that combine apparently under van der Waal forces into nanohorn clusters. Nanohorn production volume is much improved over any previously known process, yielding an amount approximately equal to 10% of the core deposits by weight. The reactor chamber comprises a cooled cathode with a surface presented to an end of at least one anode bar. Each of the cathode and the anode end mutually present a broad areal surface to the other. For purposes herein, the term "areal," "areally," or "areal surface" is meant to indicate a functional two-dimensional surface, that is, exploiting the two-dimensional nature of the surface. In contrast, as applied to arc discharge anodes, the typical arc welding rod is 1/8" inch diameter and is functionally employed as a point during operation with its end directed at a welding target, an electrical cathode. The carbon bar of the present invention, however, has an end and typical cross-section of 1 cm by 1 cm for the purpose of establishing a two- dimensional reactor chamber wall and therefore has an areal extent to contain a plasma of atomized carbon together with an opposing cathode wall. In previously disclosed arc discharge nanostructure production processes, the anode end is intentionally small to avoid photochemical reactions caused by anode blackbody emission. The present invention by design ignores the black body emission and exploits the confining nature of the areal surface of the large anode end that enables a pressurized atmosphere of atomized carbon to be maintained between the anode areal surface and the cathode, also with an areal surface opposite the anode end. The cathode and anode are electrically connected to a high amperage power source such that when the anode is brought in near contact with the cathode an electric arc strikes between them over a gap. To achieve a pressurized atomized carbon atmosphere in the reactor chamber between the anode and cathode and to achieve an arc over the entire electrode areal surfaces, the anode and cathode have matching surfaces maintained with a constant gap across the surfaces. By design, the gap is very small, resulting in a white-hot anode opposite a cooled cathode. The carbon anode end vaporizes under the electric arc to produce a pressurized reactor chamber. As the anode end is consumed in the reactor chamber, the anode is fed toward the cathode to maintain the preferred gap, which adds to the carbon plasma pressure. Under pressure of the reactor chamber, gaseous carbon is ejected in high velocity visible jet streams from the reactor chamber open chamber sides. It is suspected that the rate of ejection from the reactor chamber overcomes the photochemical reaction that occurs when the atomized carbon is allowed to dwell around the anode with high blackbody emission. The required carbon plasma pressure is maintained by feeding the anode longitudinally toward the cathode to replenish the plasma at the rate that carbon is expelled from the reactor chamber both in the visible jets and the core deposits (and any other process that exhausts carbon from the reactor chamber, such as in invisible oxides of carbon). The required rate, referred to herein (including in the claims below) as the anode feed rate, is that rate that generates and maintains the visible jet streams of atomized carbon. The anode feed rate is a range of rates, all of which include the defining characteristic of generating the visible jets of carbon from the sides of the reactor chamber. It has been determined experimentally that when an initial anode feed rate, the rate at which the visible jet streams are first generated, is increased, the rate of production of nanohorns also increases. The range of anode feed rate therefore extends between the initial anode feed rate and that rate at which reactor chamber collapses and the anode is driven into physical contact with the cathode. It has been found that a typical feed rate for a carbon bar of 1 cm. by 1 cm. is typically approximately 2.5 cm per minute. The cathode is typically cylindrical rotatable on a cylinder axis to present a change of surface to the anode. The cylinder is a container holding water that circulates into and out of the cylinder. The cathode can also be planar, equivalently presenting a change of surface to the anode by laterally translating the cathode. The anode is mounted on a carriage adjustable in two dimensions useful in maintaining the gap and in aligning the anode end smaller than the cathode with a preferred cathode location. The carriage may also be vertically adjustable to locate the anode along the cathode longitudinally. Gaseous carbon ejected from the reactor chamber from open chamber sides cools in a nonair gas enveloping the reactor chamber and surrounding regions into single wall nanohorn clusters that are collected by a reduced pressure tube ("vacuum") that collects and sorts nanohorns by size. A portion of the ejected carbon accumulates along the ejection path, forming deposits of fullerenes, refened to as cores, on the cooled cathode that are dislodged when the cathode rotates to a new position. (The actual process of obtaining accumulations of fullerenes on the cathode about the reactor chamber is not clearly understood. Therefore, representation of deposits of atomized carbon or generally accumulation is meant to include all other processes for achieving the agglomerate accumulations.) The cores are found to comprise 50%

MWNT and 50% other SP2 nanoparticles. To produce commercial quantities of the fullerenes, the process is scaled with multiple anodes forming multiple reactor chambers with a common cathode. Each anode is mounted to a common carriage that feeds the anodes concurrently toward the cathode in first forming arcs in each reactor chamber and then in maintaining a very hot atmosphere of vaporized carbon in each reactor chamber with an arc gap of only approximately 1-2 mm. As the anode is continuously feed into each reactor chamber matching the rate the anode is consumed, vaporized carbon is expelled from the chamber. The temperature in the reactor is uniformly hot such that formations of amorphous carbon within the chamber do not occur. Rather, the carbon remains atomized until it is ejected from the chamber sides where it immediately cools outside the influence of black body radiation into single walled carbon nanohorns that assemble substantially into nanohorn clusters before they are collected by a low- pressure tube, or "vacuum" and sorted by size. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the apparatus, including the anode carriage, cathode, and nanohorn collector. FIG. 2 is perspective view of the collector opposite the gas conduit with the anode therebetween presented to the cathode FIG. 3 is a top planar view of a flat end anode presented to a convex curved cathode forming a reactor chamber therebetween. FIG. 4 is a cut-away cross sectional view of the reactor chamber. FIG. 5 is a perspective view of the cylindrical cathode also showing a plurality of anode bars presented orthogonal to the cathode side. FIG. 6a is a perspective view of a planar cathode shown with typical accumulations of fullerene deposits. The figure shows a plurality of anodes aligned vertically with ends presented to the cathode. FIG. 6b is a perspective view of the planar cathode of FIG. 6a, also shown with typical accumulations of fullerene deposits after the anodes have been repositioned at the cathode. The anodes are aligned horizontally, intended to be repositioned together vertically at the cathode as fullerene deposits accumulate on the cathode. FIG. 7 is a cut-away view of the nanohorn collector. FIG. 8 is an artistic representation of a single wall nanotube depicting carbon atoms as balls interconnected hexagonally by electron bonds. FIG. 9 is an artistic representation of a multi-wall nanotube, shown with two concentric single wall tubes. FIG. 10 is an artistic representation of a single wall nanotube of hexagonally interconnected SP2 carbons shown growing from catalysts of metal atoms. FIG. 1 la is an artistic representation of a single nanohorn, shown in side and end views. FIG. 1 lb is an artistic representation of the nanohorn of FIG. 11a, shown in a circular closed end view from front, back and side views. FIG. 12a is an artistic representation of a single nanohorn after it has been heated to remove the cap that closes its small end, shown in side and end views FIG. 12b is an artistic representation of the single nanohorn of FIG. 12a, shown in a circular closed end view from front, back and side views. FIG. 13 is a scan of actual nanohorn clusters using a scanning electron microscope. Clusters are seen as three ball-like structures apparently adhering together. The scan is valuable to show the nature of the cluster; individual nanohorns cannot be discerned. Actual nanohorn walls are thin and largely transparent to the image except when the electron scan passes through multiple nanohorn walls. The apparent dark lines in the image therefore do not delineate a nanohorn but represent an area where multiple nanohorn walls absorb scanning electrons. FIG. 14 is a scan of actual nanostructures. The icicle-like elongated growths are believed to be multi-wall nanotubes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The fullerene production apparatus 10 of the present invention shown in FIG. 1 comprises a cathode 12, which may or may not be carbon 100, and an anode 14 comprised of carbon spaced apart from the cathode 12 by a small gap 16 of approximately 0.1-2 mm. The cathode 12 and the anode 14 at the gap 16 have opposing matching areal surfaces 12a and 14a with an extent 18 that defines an open- sided broad reactor chamber 20 between the extended anode and cathode opposing surfaces 12a, 14a. As shown in FIG. 3 and 4, the cathode 12 and anode 14 electrically connect to a power source 22, typically 20 to 70 volts at between 30 and 500 amps, such that an electric arc 24 is formed across the gap 16 that vaporizes anodic carbon 102, therein creating a pressurized reactor chamber 20 that exhausts vaporized carbon 102 under pressure in visible jets streams 26 of carbon from reactor chamber sides 28. As provided above, the reactor chamber 20 remains pressurized and jet streams 26 continue to flow as the anode 14 is fed into the reactor chamber 20 at an anode feed rate. The amperage level and anode feed rate can be varied to produce several different mixes of fullerenes, including single wall nanotubes 30, multi-wall nanotubes 32, and nanohorns 34 and nanohorn clusters 36, shown in FIG. 9-14. A typical range of power is 25 to 30 volts at 90 to 500 amps. Nanohorn production in gaseous reaction chamber exhaust jets 26 is found to maximize with 190 amps with a high feed rate, which yields short multi-wall nanotubes of 5 to 20 nm diameters. The electric arc 24 causes a high reactor chamber temperature, which, together with bombarding electrons from the cathode, continuously consumes the anode 14 and pressurizes the reactor chamber 20 with atomized carbon 102 as the anodic carbon is vaporized. The chamber pressure causes the ejection the atomized carbon

102 in the visible jets 26 through the open chamber reactor sides 28. The ejected atomized carbon 102 in the visible jets 26 then combines into fullerenes, mostly nanohorns 34, outside of the chamber 20, upon ejection from the reactor chamber. The reactor chamber 20 is replenished as additional anodic carbon 102 is vaporized into the reactor chamber maintaining an effective constant pressure. The opposing matching surfaces 12a and 14a forming the reactor chamber 20 typically comprise a concave cathodic surface 12b matching a convex anodic surface 14b. Preferably, the cathode 12 is cylindrical with a cylinder side 38 presented to the anode 14. The anode 14 typically is an elongate rod 40 with a rectangular cross section of 1-2 cm per side. The anode end 42, often flat initially, presents to the cathode 12. Mismatched anodic and cathodic surfaces evolve into matched surfaces 12a and 14a as the anode 14 is advanced toward the cathode 12 initially in the reactor chamber 20. The actual process involved is not yet clear. It is suspected that anode and cathode matching surfaces 12a, 14a of areal extent 18 are formed from initial mismatched anode and cathode surfaces as fullerenes from vaporized anodic carbon extend the cathode as the expelled carbon grows carbon deposits 44 onto the cathode surface. Gaseous carbon ejected from the reactor chamber is deflected by the deposits as it in turn carves a smooth curved cathode surface in the deposits matching a smooth curved surface on the anode also carved by the stream of ejected gaseous carbon between the close cathode and anode surfaces separated by an equidistant gap throughout the surfaces of only approximately 0.1-2 mm. Typically, the arc 24 is struck initially and moves between the anode and cathode surfaces 14a and 12b between closest electrode locations. Anodic carbon 102 is vaporized and deposited on the cooled cathode 12 within the reactor chamber 20, accumulating until the cathode surface with deposits 44 matches the anode surface even as the anode 14 is vaporized. This initial surface step is obviated by commencing the process with a cathodic surface comprising a section presented to the anode 14 with a concave surface 12b and an anode 14 with a convex surface 14b matching the cathodic section concave surface 12b. The anode 14 mounts on a carriage 50 typically with two orthogonal axes of adjustment 52 and 54, a first axis 54 of which is aligned orthogonal to the cathode 12.

The carriage 50 may also be vertically adjustable to locate the anode 14 at a preferred position on the cathode 14. Adjustment of the anode 14 on the first axis 54 feeds the anode 14 toward the cathode 12. In operation, the anode 14 is adjusted toward the cathode 12 on the first axis 54 to maintain a preferred gap 16 as the anode 14 is consumed. The preferred gap 16 is that which maintains the anode surface opposite the cathode 12 during operation in white-hot condition, which is approximately 0.1-2 mm. It has been experimentally determined that the atmospheric environment about the reactor 20 influences fullerene production. Therefore, a selective non-air gas 56 such as nitrogen or argon routed through a gas conduit 58 directed generally at the reactor chamber 20 envelopes the reactor chamber 20 and atomized carbon ejected in jets 26 from the reactor chamber 20, shielding the reactor chamber and the atomized carbon from ambient air and water vapor, which may be detrimental to the fullerene production process. One or more collectors 60 directed at the jet streams 26 collect nanohorns 1036 formed in the jet streams 26 as they cool away from the reactor chamber 20. The collectors 60 are positioned to substantially collect the non-air gas 56 that envelops the jet streams 26, typically opposite the gas conduit 58 so the non-air gas 56 shields the jets 26 of ejected carbon 102 from air, which minimizes formation of oxides of carbon, as it sweeps the formed nanohorns 34 into the collector 60. The collectors 60 comprise a low-pressure tube 62, or "vacuum," adapted to draw ejected fullerenes into a collector reservoir 64. Commonly, the collector 60 further comprises a separator 66 that sorts collected nanohorn fullerenes by size. The separator 66 comprises a series of bags 66' of ever smaller filtering mesh. Each bag typically envelops a bag of a smaller mesh down to a first, or finest mesh bag. It has also been experimentally determined that production efficiency and size of single wall nanotubes 30 and nanohorns 34 is enhanced by certain metal catalysts 68, usually a Group VIIIB transition metal such as Mo, Fe, Ni, Co, or mixtures thereof.

Therefore, optionally, one or more metal catalysts 68 are integrated into the carbon anode 14. The catalyst may be homogeneous throughout the anode or it may be filled in a groove longitudinal with the anode (not shown). As provided above, during operation, fullerenes of carbon are discharged from the reactor chamber 20 and grow loosely in deposits 44 attached to the cathodic surface 12. These fullerenes, mostly MWNT, continue to accumulate at the sides of the reactor chamber 20, pushing the accumulation outward as new fullerenes accumulate. As the accumulations tend to block the reactor chamber sides 28, the discharge of atomized carbon jets 26 tends to divert back along the anode 14, causing fullerenes deposits to accumulate alongside the anode 14, slightly spaced apart as an exhaust of gaseous carbon from the reactor chamber 20. Thus the reactor chamber 20 evolves to include a reactor portion 45 extending from the opposing cathodic and anodic surfaces toward and around the anode, spaced therefrom such that vaporized anodic carbon exhausts the reactor between the cathodic deposit and alongside said anode. Fullerene deposits 44, or cores, are harvested by dislodging them from the cathode 12. To do so, the anode 14 is withdrawn from the cathode 12 thereby ending the electric arc 24 and defeating the reactor chamber 20. The cathode 12 is then shifted from a first cathode section opposite the anode having deposit accumulations of fullerenes to a second section opposite the anode, moving a prior cathodic surface opposite the anode away from the anode. For a cylindrical cathode, the cylinder is rotated on its axis 19. For a planar cathode, it is translated laterally from the anode.

Equivalently, this may be achieved by translating the anode on its second axis 52. The deposits are then dislodged from the cathode. The cathode therein presents a new surface opposite the anode, and the anode is again moved toward the cathode to reestablish a reactor chamber at the second cathode section. Preferably, the cathode comprises a cylindrical container 70 holding a coolant 71, typically water. To assure that the cathode 12 remains cool, water (or other coolant) is continuously circulated into and out of the cylindrical container 70 through pipes 73. It was noted above that water, or water vapor, may be detrimental to fullerene production. Therefore, the cathode container 70, cylindrical or planar, is closed with a lid 72 that prevents escape of water. As shown in FIG. 5, for more efficient fullerene production, the anode comprises a plurality of parallel anode bars 14' all connected to the carriage 50 and each opposing a section of a common cathode 12 such that the carriage 50 translates the anode bars 14' together toward the common cathode, each spaced apart therefrom by a respective gap, and each forming a reactor chamber with the cathode. Each is connected to an independent power source 22' such that an electric arc 24 is formed across the respective gaps 18 to each produce fullerenes. The respective gaps 18 are a common separation between respective anodes and the common cathode.

Claims

CLAIMS Having described the invention, what is claimed is as follows:

1. Electric arc apparatus for making fullerenes, comprising a cathode with an areal surface, a carbon anode with an areal surface opposing the cathode areal surface and spaced apart therefrom by a small operational gap and forming a broad reactor chamber therebetween, wherein the cathode and anode electrically connect to a power source such that an electric arc forms across the gap causing a high reactor chamber temperature, the anode being continuously consumed as anodic carbon is vaporized in the reactor chamber resulting in a pressurized atmosphere of atomized carbon in the reactor chamber that ej ects visible j et streams of gaseous carbon from reactor chamber sides, the ejected atomized carbon combining into fullerenes upon ej ection from the reactor chamber, a carriage on which the anode is mounted feeding the anode toward the cathode at an anode feed rate that maintains the operational gap of the reactor chamber and the visible jet streams of carbon as the anode is consumed.

2. The apparatus of claim 1 further comprising a collector collecting fullerenes formed in the visible jet streams ejected from the reactor chamber, the collector comprising a low-pressure tube adapted to draw ejected fullerenes.

3. The apparatus of claim 2 wherein the collector further comprises a separator sorting collected fullerenes by size.

4. The apparatus of claim 3 wherein the collector further comprises a plurality of bags, an outer bag enveloping a bag of a smaller mesh.

5. The apparatus of claim 1 further comprising a non-air gas conduit disposed to deliver non-air gas that envelops the reactor chamber and jet streams of ejected atomized carbon, shielding the reactor chamber and regions closely around the reactor chamber including the visible jet streams from ambient air and water vapor.

6. The apparatus of claim 5 further comprising a collector collecting fullerenes formed in the visible jet streams ejected from the reactor chamber, the collector comprising a low-pressure tube positioned to draw said fullerenes and at least a portion of the non-air gas into the collector.

7. The apparatus of claim 6 wherein the collector is opposite the non-air gas conduit with the jet streams therebetween.

8. The apparatus of claim 6 further comprising a dry box in which are contained said anode, cathode, and carriage into wherein the non-air gas fills the dry box exclusive of other gases, including air and water vapor, controlling the ambient environment of the reactor chamber and regions closely surrounding it.

9. The apparatus of claim 1 wherein the anode feed rate is a range of rates, all of which generate the visible jets of carbon from the sides of the reactor chamber.

10. The apparatus of claim 1 wherein the anode is a bar of approximately 1 cm by 1 cm and the anode feed rate is approximately 2.5 cm per minute.

11. The apparatus of claim 1 in which the opposing areal surfaces forming the reactor chamber comprise a concave cathodic surface matching a convex anodic surface.

12. The apparatus of claim 11 in which the reactor chamber comprises fullerene deposits extending from the cathode toward and around the anode, spaced apart therefrom, with said visible jet streams directed alongside the anode.

13. The apparatus of claim 11 in which opposing matching surfaces self-form upon initiation of the electric arc, depositing carbon on the cathode from the reactor chamber, ejected gaseous carbon forming said matching curved surfaces.

14. The apparatus of claim 1 wherein the cathode comprises a cylindrical outer surface opposing the anode.

15. The apparatus of claim 12 wherein the cathode cylinder rotatable on a cylinder axis therein presenting a new cathodic surface opposite the anode upon rotation and moving a prior cathodic surface opposite the anode away from the anode for dislodging of fullerene deposits on the cathode accumulated during consumption of the anode.

16. The apparatus of claim 14 wherein the cathode comprises a cylinder containing a coolant.

17. The apparatus of claim 16 wherein the coolant comprises circulating water.

18. The apparatus of claim 16 wherein the cylinder is closed to prevent coolant vapor from escaping toward the reactor chamber except for possible sealed coolant recirculation into and out of the cylinder.

19. The apparatus of claim 1 wherein the cathode comprises a planar surface opposing the anode adapted to translate before the anode moving a prior cathodic surface opposite the anode away from the anode for dislodging of fullerene deposits on the cathode accumulated during consumption of the anode.

20. The apparatus of claim 1 wherein said power source comprises an amperage of between 90 and 500 amps.

21. The apparatus of claim 1 wherein the anode has a cross section of between 1 and 4 square centimeters.

22. The apparatus of claim 1 wherein the anode comprises a plurality of parallel anode bars all connected to the carriage and each opposing a section of a same, or common cathode such that the carriage translates the anode bars together toward the common cathode each spaced apart therefrom by a respective gap, each forming a reactor chamber with the cathode and each connected to a power source such that an electric arc is formed across the respective gaps.

23. The apparatus of claim 21 in which the respective gaps are a common separation between respective anodes and the common cathode.

24. The apparatus of claim 21 in which the respective anodes are electrically connected to independent power sources.

25. The apparatus of claim 1 wherein the anode comprises a catalyst and carbon.

26. The apparatus of claim 24 wherein the catalyst is at least one Group VIIIB transition metal.

27. Electric arc apparatus for making fullerenes, comprising a cooled cathode with an areal surface, a carbon anode with an areal surface matching and opposing the cathode areal surface and spaced apart therefrom by a small operational gap and forming a broad reactor chamber therebetween, wherein the cathode and anode electrically connect to a power source such that an electric arc forms across the gap causing a high reactor chamber temperature, the anode being continuously consumed as anodic carbon is vaporized in the reactor chamber resulting in a pressurized atmosphere of atomized carbon in the reactor chamber that ejects visible jet streams of gaseous carbon from reactor chamber sides, the ejected atomized carbon combining into fullerenes upon ejection from the reactor chamber, a carriage on which the anode is mounted feeding the anode toward the cathode at an anode feed rate that maintains the operational gap of the reactor chamber and the visible jet streams of carbon as the anode is consumed, a non-air gas conduit disposed to deliver non-air gas that envelops the reactor chamber and jet streams of ejected atomized carbon, shielding the reactor chamber and regions closely around the reactor chamber including the visible jet streams from ambient air and water vapor, a collector collecting fullerenes formed in the visible jet streams ejected from the reactor chamber, the collector comprising a low-pressure tube positioned to draw said fullerenes and at least a portion of the non-air gas into the collector.

28. Employing an electric arc apparatus for making fullerenes that comprises a cathode with an areal surface, a carbon anode with an areal surface opposing the cathode areal surface and spaced apart therefrom by a small operational gap and forming a broad reactor chamber therebetween, and a carriage on which the anode is mounted, the method of producing fullerenes comprising the following steps: (1) Electrically connecting cathode and anode to a power source, (2) Moving the anode toward the cathode until an electric arc is struck between the anode and the cathode causing a high reactor chamber temperature; (3) Consuming the anode as anodic carbon is vaporized in the reactor chamber resulting in a pressurized atmosphere of atomized carbon in the reactor chamber that ej ects visible jet streams of gaseous carbon from reactor chamber sides, the ejected atomized carbon combining into fullerenes upon ejection from the reactor chamber; (4) Continuously advancing the anode toward the cathode at an anode feed rate that continuously generates said visible jet streams; (5) Enveloping the reactor chamber and ejected atomized carbon with non-air gas, shielding the reactor chamber and the atomized carbon from ambient air, fullerenes forming in the ejected jet streams; (6) Capturing fullerenes ejected from the reactor chamber.

29. The method of claim 28 further including the step of capturing ejected fullerenes in a low-pressure collector tube adapted.

30. The method of claim 28 further including the step of filtering nanohorns in the captured fullerenes by nanohorn cluster size.

31. The method of claim 28 further including the method of forming a plurality of accumulations of fullerene deposits on the cathode through the following steps: (1) Withdrawing the anode from the cathode, thereby ending the electric arc and defeating the reactor chamber; (2) Shifting the cathode from a first cathode section opposite the anode having accumulations of fullerenes to a second section opposite the anode; (3) Reestablishing an operational reactor chamber by repeating steps (1) - (5) of claim 28.

32. The method of claim 31 further including the steps of dislodging and capturing accumulations of fullerenes from the cathode.

33. The method of claim 31 in which the step of shifting the cathode further includes the step of rotating a cylindrical cathode on a cathode axis.

34. The method of claim 28 further including the step of cooling the cathode by maintaining water within the cathode.

35. The method of claim 34 further including the step of circulating water through the cathode.

36. The method of claim 28 further including the step of forming anode and cathode matching surfaces of areal extent from mismatched anode and cathode surfaces by vaporizing the anode surface and accumulating fullerenes from vaporized anodic carbon onto the cathode surface forming curved matching surfaces with an equidistant gap throughout the surfaces.

37. The method of claim 28 including the step of selecting a preferred anode that incorporates a catalyst that derives desired nanotube characteristics.