Patent application title: SHEAR REACTOR FOR VORTEX SYNTHESIS OF NANOTUBES
David J. Mccutchen (Portland, OR, US)
David J. Mccutchen (Portland, OR, US)
Wilmot H. Mccutchen (Orinda, CA, US)
IPC8 Class: AD01F912FI
Class name: Carbon or compound thereof elemental carbon fiber, fabric, or textile
Publication date: 2009-10-22
Patent application number: 20090263309
Continuous nanotube synthesis by vortex deposition occurs in an
axially-fed shear reactor comprising coaxial counter-rotating disk
impeller/electrodes charged as anodes. Nanotube evolving ends, charged as
cathodes, point toward the anode axis of rotation and protrude into the
space between the anodes. Radial vortices in a shear layer of the space,
between the boundary layers on the impeller/electrodes, spin cations to
be deposited on evolving nanotube ends approximately at the vortex axis,
so deposition is by swirling cathode fall. The evolved nanotubes are
extracted mechanically, and they conduct electrons from charging means to
charge the evolving ends as cathodes. The preferential synthesis of
metallic carbon nanotubes is due to the greater resistance of
non-metallic structures such as graphite or semiconductive structures.
Ozone serves to oxidize non-metallic structures and to functionalize the
loose ends of nanotube fragments. Dopants can be added to the evolving
nanotubes by introduction of dopants at the periphery because the
evolving ends are maintained in stable locations. Or dopants can be added
by the simultaneous decomposition of gases (for example, carbon dioxide
and nitrogen gas) within the reactor or in an external reactor.
1. A shear reactor for the continuous synthesis of nanotubes,
comprisingcounter-rotatable spaced-apart coaxial impeller/electrodes
defining between them a space, the space comprising a shear layer when
said disk impeller/electrodes are in counter-rotation;means for
counter-rotation connected to said impeller/electrodes;means for charging
said impeller/electrodes as anodes, said anode charging means
electrically connected to said impeller/electrodes;a peripheral wall
enclosing said space, the peripheral wall comprising at least one opening
therethrough, the opening providing means for communicating with said
space from outside the peripheral wall;means for feeding a source gas
into said space at approximately the axis of rotation of the disk
impeller/electrodes, the source gas comprising cations for deposition on
evolving nanotube ends within the space;means for extracting nanotubes
from the space, said extracting means disposed outside of the peripheral
wall, and said extracting means connected to nanotubes evolving in the
space; andmeans for charging said evolving ends of nanotubes as cathodes
protruding into the space.
2. The shear reactor of claim 1, wherein the source gas comprises cations created in an external reactor.
3. The shear reactor of claim 1, wherein the source gas comprises a carbonaceous gas.
4. The shear reactor of claim 1, wherein the source gas comprises vapor.
5. The shear reactor of claim 1, wherein the source gas provides dopant ions.
6. The shear reactor of claim 1, wherein said disk impeller/electrodes comprise openings therethrough, said openings providing means for gas to exit the space.
7. The shear reactor of claim 1, wherein the opening at the periphery is a gap between narrowly-spaced disk impeller/electrodes and the peripheral wall comprises the convergent surfaces of said disk impeller/electrodes.
8. The shear reactor of claim 1, wherein said means for extracting nanotubes includes an exposure of said nanotubes to ozone.
9. The shear reactor of claim 1, wherein the peripheral wall is a static shrouding wall comprising at least one opening therethrough for the extraction of nanotubes from the space.
10. The shear reactor of claim 9, wherein the peripheral wall comprises at least one concave vortex reflector centered on said opening.
11. The shear reactor of claim 10, wherein said opening is through a conical protrusion extending from the center of said vortex reflector into the space.
12. The shear reactor of claim 1, further comprising means for doping evolving nanotubes by dopants introduced in the vicinity of the periphery.
13. The shear reactor of claim 1, further comprising means for maintaining evolving ends of nanotubes at a certain distance from the peripheral wall and within a formation zone within the space.
14. The shear reactor of claim 13, wherein said maintaining means comprise a stepper motor connected to a takeup reel.
15. The shear reactor of claim 14, wherein said maintaining means comprise sensing means connected to said stepper motor for changing the motor speed in response to the position of the evolving end.
16. A method for preferential synthesis of conductive nanotubes, comprising the simultaneous steps ofcreating a vortex of cations in a formation zone between counter-rotating anodes;charging a nanotube stub as a cathode, the stub being disposed in the formation zone; andwithdrawing the nanotube stub away from the anode axis so as to maintain the evolving end of the nanotube within the formation zone.
17. The method of claim 16, further comprising the simultaneous step of controlling the speed of withdrawal by sensing means.
18. Apparatus for producing doped nanotubes, comprisingcounter-rotatable spaced-apart coaxial impeller/electrodes defining between them a space, the space comprising a shear layer when said disk impeller/electrodes are in counter-rotation;means for counter-rotation connected to said impeller/electrodes;means for charging said impeller/electrodes as anodes, said anode charging means electrically connected to said impeller/electrodes;a peripheral wall enclosing said space, the peripheral wall comprising at least one opening therethrough, the opening providing means for communicating with said space from outside the peripheral wall;means for feeding a source gas into said space at approximately the axis of rotation of the disk impeller/electrodes, the source gas providing cations for deposition on an evolving nanotube end;means for extracting nanotubes from the space, said extracting means disposed outside of the peripheral wall, and said extracting means connected to nanotubes evolving in the space; andmeans for charging said evolving ends of nanotubes as cathodes protruding into the space.
19. The apparatus of claim 18, wherein dopants are not present in the source gas, but are introduced into the space in the immediate vicinity of said evolving nanotube end.
20. The apparatus of claim 19, wherein dopants are extracted from said space in the immediate vicinity of said evolving end to prevent their deposition on said evolving nanotube end.
The applicants claim the benefit of provisional application 61/026,963 entitled "Continuous Synthesis of Carbon Nanotubes by Vortex Turbulence" filed Feb. 7, 2008 by Wilmot H. McCutchen and David J. McCutchen, as well as provisional application 61/034,242 entitled "Dual Disk Dynamo High Shear Reactor" by Wilmot H. McCutchen and David J. McCutchen, filed Mar. 6, 2008.
FIELD OF THE INVENTION
This invention applies to the synthesis of carbon or other nanotubes and to electrolysis in turbulent reactors.
BACKGROUND OF THE INVENTION
Nanotubes have been synthesized from many materials, including boron nitride, tungsten disulfide, titanium dioxide, molybdenum disulfide, bismuth, copper, and gold.
Carbon nanotubes in particular are a commercially valuable form of carbon that has many remarkable properties. The fibers are 100 times stronger in tensile strength than steel, and are the most efficient heat conductors known. These nanotubes have a high degree of stiffness, due to their molecular structure. They can theoretically be formed in any length, but present methods of formation include a random direction of formation, and this limits the resulting length the nanotube to a couple of centimeters as best.
Chemical vapor deposition is a method currently used by commercial companies creating quantities of nanotubes. The formation of the nanotubes is made from the evaporation of a solution of carbon or other ions suspended in alcohol or another solvent. This makes the tubes form in random directions to a length of at most a few millimeters. The solvent with the forming tubes can be in the form of an aerogel, and the final step of deposition can be as the aerogel is being drawn into a cable. This can achieve speeds of deposition of up to 2 meters a minute, but the cable is a grouping of short nanotube lengths, and lacks the tensile strength that would come from a single long nanotube.
Laser ablation and arc discharge are other synthesis methods. In laser ablation for carbon nanotubes, a high energy laser vaporizes a carbonaceous target to produces carbon ions, whereas arc discharge vaporizes carbon electrodes. Isotropic turbulence spins some of these carbon ions into nanotubes, which are very short in length due to the chaotic orientation and short duration of any formation vortices.
Depending on their structure, carbon nanotubes can be electrical superconductors, also known as metallic nanotubes, or semiconductors. Conventional synthesis methods produce a mixture of conductive and semiconductor nanotubes, which must later be separated by suitable means outside of the reactor.
SUMMARY AND OBJECTS AND ADVANTAGES OF THE PRESENT INVENTION
The present invention represents a scalable approach to continuous synthesis of long nanotubes. A flow of carbon ions is organized into radial vortices which feed the formation of continuously evolving nanotubes. The ion vortices are mechanically forced by counter-rotating disk impeller/electrodes, and the vortices create a solenoidal magnetic field which causes self-tightening of the vortex. Turbulence is anisotropic, or directionally oriented, instead of the random isotropic turbulence of conventional reactors, so the vortices are coherent and radially arranged. The formation process within these vortices favors the creation of longer strands that can be spooled up to an external reel continuously. This can make the production of long nanotube strands in large quantities a commercial reality.
Another advantage is that the formation process tends to favor the production of metallic instead of semiconducting nanotubes. The evolving nanotubes are charged as cathodes, and the current will flow easily through the metallic nanotubes to their evolving ends, but does not flow easily through semiconductive nanotubes due to their higher resistance. Therefore semiconductive nanotubes tend not to evolve because their evolving ends are starved of electrons by their resistance.
A further advantage is the production of doped nanotubes with variations along their length, produced by changing the conditions in which the evolving end of the nanotube is formed.
The ion source may be electrolysis within the shear reactor, or an external source. In the case of an external source, the source gas fed into the shear reactor is a mixture of a carrier gas and the ions which will be rolled into nanotubes by coherent directed turbulence and swirling cathode fall. The nanotubes could therefore be of gold or other conventional nanotube materials, as well as of carbon.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of one half of the preferred embodiment of the vortex synthesis shear reactor of the present invention.
FIG. 2 is a cross section close-up of the area of the formation zone.
FIG. 3 is a front view of the peripheral wall, seen from the space in the reactor.
FIG. 4 is a top view of the reactor, showing the array of radial vortices.
FIG. 5 is a cross section of one half of an alternative embodiment, comprising converging anodes.
2. Top disk impeller/electrode 4. Bottom disk impeller/electrode 5. Peripheral wall 6. Source gas 7. Space 8. Axial source gas vent 9. Support spindle 10. Axis of rotation of the disk impeller/electrodes 2,4 12. Charging means 14. Carbon ions 16. Hole in sintered metal anode 17. Exhaust port 18. Radial vortex 20. Curved vortex reflector 21. Pressure vent in reflector surface 22. Conical protrusion 24. Evolving end of nanotube 26. Central opening in conical protrusion 22 28. Ozone feed 30. Electrons from cathode 32. Carbon ion outer vortex 34. Withdrawal of nanotube 36. Formation zone 38. Rebound vortex 40. Dopant source 42. Control for dopant source 44. Dopant ion 46. Dopant ion in nanotube structure 48. Dopant exhaust vent 50. Dopant exhaust 52. Reflector vent negative pressure 54. Reflector vent positive pressure 56. Nanotube cable 58. Takeup reel 60. Seal between peripheral wall and disk impeller 62. Disk pinch section 64. Slit opening 66. Ozone chamber 68. Nanotube yarn 70. Precision extraction means
The following description is directed toward the production of carbon nanotubes, but the present invention can be used to synthesize nanotubes and other tubular fullerene structures from other suitable compounds.
Controlled turbulence is used in a shear reactor to create coherent radial vortices of carbon ions in a shear layer between counter-rotating and coaxial disk anodes. Residence time of ions in the reactor is long, and the ion vortices deposit ions in swirling cathode fall on evolving nanotube ends during this residence time. The nanotubes are then withdrawn from the reactor.
Carbon or other metal ions (cations) concentrate in the shear layer because they are repelled from the anodes. Because of the counter-rotation of the disk impeller/electrodes, the radial vortices 18 in the shear layer are radially oriented like spokes of a wheel with respect to the disk axis of rotation 10. Each vortex contains a formation zone at its core where carbon ions are concentrated at the point of formation of an evolving nanotube. Each nanotube has a captive end and an evolving end. The evolving end is charged as a cathode and grows as more carbon ions aggregate to it to form the characteristic pattern of connections of a nanotube. The captive end is used to pull the nanotube out from the periphery of the reactor continuously to prevent the evolving end from leaving the formation zone, and the captive end is a conductor of electrons to the evolving end. To improve the quality and functionalize the nanotubes, they preferably should be exposed to ozone as they leave the formation zone and are withdrawn from the reactor.
As shown in the schematic cross sectional view of one half of the shear reactor in FIG. 1, the controlled turbulence vortex is forced by two approximately parallel and coaxial counter-rotating disk impeller/electrodes 2 and 4 which act as centrifugal impellers of a source gas 6 axially injected to the space 7 between them. The top impeller 2 rotates into the page, and the bottom impeller 4 rotates out of the page. Their common axis of rotation 10 is approximately at the centerline of the reactor.
By the term counter-rotating is meant simultaneous rotation other than exactly co-rotating, as for example, where both impeller/electrodes rotate in the same direction but at different angular velocities, or where one rotates and the other is static. Preferably, there is exact counter-rotation, where the opposed coaxial impeller/electrodes 2,4 rotate in opposite directions at approximately the same angular velocity. Suitable means, not shown, connected to the impeller/electrodes cause them to counter-rotate.
The counter-rotating disk electrode/impellers 2,4 in combination with a peripheral wall 5 define a space 7 where vortex synthesis of nanotubes is forced. Axial feed of a source gas 6 to the space 7 between the impellers 2,4 is caused by positive pressure through axial source gas vents 8 in a cylindrical support spindle 9 which supports the impellers 2,4 and maintains them in a coaxial orientation around their common disk axis of rotation 10.
The support spindle is connected to external charging means 12 and acts as a conductor between the charging means and the impellers, making the spindle and each impeller/electrode 2,4 an anode. The external charging means 12 for the anodes are coupled to the static support spindle, and through its seals to the disks, with the seals being mercury seals or other electrically conductive seals. Alternatively, the disks, spindle and peripheral wall can all be charged as anodes separately. The charging means provides constant or pulsed sonic or radio frequency direct current. A conventional current (positive ions) flows into the evolving end as an electron current flows out of it. Intermittent current would serve to soften the impact of the ions on the nanotube end.
A source gas is 14 is axially fed into the space between the anodes. The term source gas includes a plasma created in an external reactor. Preferably the source gas comprises ions produced by an external source. The source gas may comprise cations mixed with and an inert carrier gas such nitrogen, argon or xenon.
Alternatively, the source gas could be a carbonaceous gas such as carbon monoxide which has not yet been ionized. The source gas may comprise carbonaceous molecules such as methane (CH4), acetylene (C2H2), carbon monoxide (CO) or carbon dioxide (CO2). It may also comprise molecules of a volatile organic compound (VOC). The source gas may include sulfur dioxide. What will be described below is a shear reactor for the electrolytic decomposition of carbon monoxide to form metallic carbon nanotubes.
The carbon ions can be produced in the reactor by the decomposition of a carbonaceous source gas, preferably carbon monoxide because it is abundant and because dissociation produces carbon and ozone. Ozone surrounding the nanotubes serves to functionalize loose ends and to oxidize non-nanotube structures which would clutter the product of the reactor.
The source gas, whether an externally created plasma or a gas to be dissociated by electrolysis within the reactor, is injected through at least one axial source gas vent 8 and is advected radially outward from the disk axis of rotation in boundary layers against the anodes. The anodes repel cations, such as carbon ions, into a shear layer between the boundary layers.
Evolving nanotube ends 24, which are charged as cathodes, extend into the shear layer. Arcing between the anodes 2,4 and cathodes 24 is prevented by the continuous rotation of the anodes, breaking incipient arcs and causing a diffuse, or corona, discharge in the space 7. Therefore a high amount of energy can be pumped into the space 7 to decompose the source gas. Not only electrical energy but also mechanical energy is transferred to the source gas by the high shear of the reactor.
If the source gas is carbon monoxide (CO), the bond dissociation energy is 9.144 eV. Because the shear reactor of the present invention has high residence time, there is time to pump the required dissociation energy into the space 7 between the disk impeller/electrodes 2,4. High pressure in the space 7 is caused by positive feed pressure through the axial feed gas vents 8 and the added enthalpy due to the work of the rotating impeller/electrodes on the source gas.
Decomposition of the carbonaceous source gas creates a cloud of carbon ions 14 in the shear layer between the impeller/electrodes, while oxygen or other electrolysis product gases are evolved at the anode impeller surfaces. Preferably the impellers are of sintered metal so as to present a large surface area to the source gas and to provide many holes 16 for the exit of electrolysis product gases.
In the case of a source gas comprising cations mixed with a carrier gas, such as nitrogen, argon, or xenon, the cations are repelled by the anodes and the carrier gas flows through boundary layers against the impeller/electrodes and out of the reactor through the holes 16 in the anodes and through exhaust ports 17 in the periphery 5. Some of the oxygen gas becomes ozone, which because it has a heavier molecular weight than the source gas flows radially outward to the peripheral wall 5.
The shear layer comprises a multi-scale network of radial vortices. At the periphery of the reactor, the radius of the radial vortices is small. The turbulence within the reactor is organized and anisotropic due to the forcing of the counter-rotating disk impeller/electrodes 2,4 and the continuous mass flow in and out of the reactor. The axes of the radial vortices 18 are approximately orthogonal to the disk axis of rotation 10.
Impingement of the vortex end on the peripheral wall 5 causes contraction of the radial vortex 18 due to the mechanics of the vortex-wall interaction. A resultant rebound directed away from the peripheral wall along the vortex axis of rotation pulls the evolving end 24 of the nanotube back toward the disk axis of rotation 10 in a tighter rebound vortex 38.
Within this small radius rebound vortex 38 is a concentrated rapid swirl of cations, which by their vortex motion create a solenoidal magnetic field that causes the cation vortex to self-tighten into an even smaller radius. At the core of the vortex is a region with the optimal conditions for nanotube assembly, called the formation zone. The evolving end 24, charged as a cathode dangles in the formation zone, and cations deposit on the evolving end continuously in swirling cathode fall.
The rotation of carbon ions in a radial vortex in the shear layer produces a solenoidal magnetic field, because charges in motion always produce a magnetic field. Here we have positive charges in coherent vortex motion, which, according to the right hand rule, will produce a solenoidal magnetic field having a North pole pointing at the peripheral wall 5. Carbon ions rotating through this mechanically forced magnetic field experience a magnetic force squeezing them into the vortex axis. The self-tightening of the carbon ion vortices due to mechanically forced anisotropic turbulence also acts to knit the carbon ions into a nanotube structure.
As the nanotube lengthens toward the disk axis of rotation 10, extraction means such as a takeup reel 58 pull the evolving end back toward the peripheral wall and thus maintain the evolving end in the formation zone at an optimal distance from the peripheral wall. Charging means 12 connected to the takeup reel 58 charge it as a cathode, and nanotubes pulled by it conduct electrons to the formation zone. Metallic, or conductive, nanotube structures are favored in formation because they conduct electrons with less resistance than semiconductive nanotube structures. Therefore the nanotube evolving ends 24 dangling in the formation zone will preferentially be ends of metallic carbon nanotubes.
Tension in the nanotube due to the pull of the takeup reel 58 versus the force of the rebound from the vortex-wall interaction acts to stretch and anneal the nanotube and provides means for maintaining the evolving end in the formation zone.
The optimal withdrawal speed for the evolving end is determined by the monitoring or conditions inside the reactor such as feed pressure, temperature, charge and ion density. It may also be determined by a measurement of the piezoelectric activity of the nanotube as it flexes in the swirl of the vortex or remains calm in the vortex core. Suitable means known to the art, such as stepper motors and gearing for precision movement, may connect to the takeup reel 58 and the nanotube cable 56 itself and control its speed, both into and out of the shear reactor, so as to maintain the evolving end 24 at an optimal location in the space 7. Experiment using constant reactor conditions could also determine an optimal constant takeup reel speed. The withdrawal means closest to the reactor should preferably include precision extraction means for gripping and advancing a nanotube in a linear motion as needed.
Preferably the peripheral wall 5 comprises one or more concave cavities facing the space 7. Each cavity is a curved vortex reflector 20 to focus and tighten the rebound vortex to make a tighter concentration or carbon ions. At the center of the vortex reflector 20, is an approximately conical protrusion 22, comprising a central opening 26 for the cathode to extend into the space 7. Preferably, the peripheral wall 5 should be charged as an anode, to prevent carbon coking, but the vortex reflector 20 should be dielectric, to prevent arcing between the cathode evolving end 24 and the anode peripheral wall 5.
Alternatively, the peripheral wall could be without vortex reflectors or conical protrusions but having one or more holes through it. Alternatively, the peripheral wall could be not static, but part of the impellers, with half of the peripheral wall on each impeller, as in the alternative embodiment comprising converging anodes, as shown in FIG. 5.
Vapor source gas could be ionized by arc discharge between the evolving nanotube ends and the counter-rotating anodes. The arc discharge would be a corona because arc dwelling on the anodes is broken continuously by rotation of the anode arc site away from the cathode. Shear plus corona discharge pumps sufficient energy into the vapor for ionization. The vapor could be of an organic compound, of metals, of carbon, or of other cation sources.
Carbonaceous source gas could provide cations for carbon nanotube synthesis by dissociation within the shear reactor according to the present invention. The evolving nanotube ends are cathodes, and the disk impeller/electrodes are anodes. Discharges in the space are in the nature of corona discharges rather than dwelling arcs because the rotation of the anodes breaks incipient arcs and prevents them from dwelling. For example, carbon monoxide, is decomposed in the reactor, providing carbon cations for nanotube deposition and oxygen for ozone.
Von Karman swirling flow in an open system occurs in the space 7 of a shear reactor according to the present invention because there is high shear between counter-rotating coaxial disk impeller/electrodes 2,4 and there is simultaneous and continuous mass flow in (through the axial source flow vents 8) and out (through the impeller holes 16 and the exhaust ports 17). The flow is not disordered, as in closed system setups, but comprises a multiscale array of branched radial vortices due to the fact that this is an open system. Radial counterflow is forced in the space 7 by counter-rotation of the disk impeller/electrodes 2,4. Against each disk impeller/electrode is a boundary layer. Source gas and gaseous electrolysis products, such as ozone, flow radially outward from the axis of rotation 10. Radially inward flow toward the axis 10 occurs in the shear layer between the counter-rotating boundary layers. Recirculating flow radially inward through the shear layer toward the impeller axis of rotation is caused by the rebound resulting from the vortex-wall interaction as vortices in the shear layer encounter the periphery wall 5 enclosing the space 7 between the impellers.
As shown in the schematic cross section of the area of the formation zone in FIG. 2, at the center of each curved reflector 20 for a shear layer carbon ion vortex 32, a protruding central cone 22 extends into the axis of the tightened rebound vortex 38. The evolving end 24 of the nanotube extends from a small opening 26 in the tip of this cone and radially inward toward the disk axis. Here the opening is shown larger for purposes of clarity; the opening 26 for the nanotube should be narrow to allow better control of the positioning of the nanotube evolving end 24. In the vicinity of the evolving end 24 is a formation zone 36 including the core of the carbon ion rebound vortex 38. The formation zone in the vortex core is a space of relative calm having a dense and evenly distributed concentration of carbon ions orbiting in close proximity to the evolving end 24, which favors balanced and rapid growth. Preferably, the opening 26 comprises insulating material so as to prevent the nanotube evolving end 24 from shorting. For example, the conical protrusions could be of ceramic insulating material.
Unlike the counter-rotating disk impeller/electrodes 2,4, which are charged as anodes, the evolving nanotube tip is charged as a cathode by charging means 12. The charging means 12 connect to the takeup reel 58 and the nanotubes conduct electrons to the evolving ends. Nanotubes are known to be very efficient field emitters of electrons, due to the sharpness of their points. The carbon ion vortices have an electron deficiency. The cathode source of electrons 30 attracts the carbon ions 14 in a dense cloud around the evolving end 24, continuously drawing in carbon ions in swirling cathode fall for continuous vortex deposition, allowing the synthesis of very long nanotubes. As the length of the nanotube grows, it is withdrawn 34 back through the cone, to prevent the evolving end 24 from leaving the formation zone 36.
Any ozone (O3) resulting from electrolysis functionalizes the ends of nanotube fragments and any sites of defective formation, which is where nanotubes are vulnerable to oxidation. If ozone is not present from electrolysis, it should be supplied in an ozone feed 28 outside the peripheral wall, which bathes the emerging nanotube and extends through the opening 26 toward the formation zone. Graphitic or coke solid carbon is oxidized by the ozone and recycled in the reactor, so these impurities are minimized in the solid carbon structures produced by the present invention. Semiconductive and nonconductive damaged nanotubes are also excluded from production because their evolving ends are starved of electrons due to their high resistance, whereas metallic nanotubes, which are excellent conductors, are better able to suck the electrons from the charging means to augment their evolving ends.
Nanotube cables 56 are grown from a captive stub extending into the formation zone. For starting the growth process, the nanotube stub can be short, and attached if necessary to a wire that attaches to the takeup reel or other withdrawal means and extends the stub into the formation zone. Nanotube stubs could be metal wires connected to the takeup reel 58 and extending into the space 7. On startup of the reactor, carbon nanotubes begin to deposit on the end of the wire, and the wire is drawn out of the space 7 along with the nanotubes attached to it. The type of nanotube stub can influence the type of growth produced, since the growth will tend to duplicate the structure available. The stub can be single wall, multiwall or multistrand. If several nanotube ends are presented together as a stub, then a multistrand cable will be the result.
A charged cathode wire can also attract nanotube growth in the form of a tangle of shorter nanotubes, which in turn are charged as a cathode to encourage further growth. This nanotube "yarn" can also be formed and withdrawn continuously. Loose ends dangling from the nanotube yarn should be functionalized by passage of the yarn through ozone in a chamber disposed outside of the peripheral wall 5. The ozone does not attack the length of a well-formed nanotube, but defective structures such as graphite are oxidized. Thus the nanotube yarn produced is clean of impurities.
Doping of Nanotubes
The structure of a nanotube is a regular lattice that can be altered at specific points and still maintain most of its strength. Other atoms can be embedded in the lattice, or captured inside the tube. Special sequences of these atoms in the nanotubes can act as diodes or other electronic components. Other sequences of atoms in a nanotube can be used to store information. An analogy is the strand of information that is the DNA molecule, but in this case the molecule is not expected to duplicate, and can contain a more complex sequence of elements.
Nitrogen-doped carbon nanotubes have been discovered to have excellent oxygen reduction properties, making them suitable substitutes for platinum in fuel cells. Nitrogen-doped carbon nanotubes could be produced by the simultaneous electrolysis of nitrogen and a carbonaceous gas such as carbon monoxide.
Products of decomposition of other constituents, such as sulfur ions from decomposition of SO2, can also be dopants. Sulfur atoms incorporated into nanotubes would provide means for linking nanotubes together, as with rubber, into a durable macrostructure. Sulfur dioxide is a troublesome trace pollutant in carbon dioxide from coal emissions, so simultaneous electrolytic decomposition of CO2 and SO2 would save an expensive scrubbing step and would produce a valuable material from waste.
The present invention provides means for precisely doping long nanotubes as well as doping them by simultaneous bulk decomposition as mentioned above in the case of CO2 and SO2. Because the location of the evolving end is controllable, dopant sources, such as heated wires, can be placed near the evolving end. One useful material which might be produced by such means would be silver-doped carbon nanotubes, which would be strong and bactericidal as well.
As shown in FIG. 2, the introduction of dopant atoms into the evolving nanotube end may be done through precisely controlled heated wires 40, with the dopant atoms coming off by sublimation due to heating supplied according to a control for the dopant source 42. Since these ends are charged as anodes, they do not tend to attract carbon ions. By making use of a known rate of growth of the main tube or tubes, doping at precise intervals leads to increasing value in the finished nanotube cable. The dopant atoms 44 are introduced into the core vortex, which takes then into the formation zone 36 where they become part of the nanotube structure 46. To stop the dopants from being added further to the structure, a dopant exhaust vent 48 is used to exhaust the gas in the formation zone containing the dopant atoms 50. In this way the dopants can be turned on and off, or different dopants may be added in sequence.
Because of the counter-rotation of the disk impellers, the radial vortices tend to be relatively stable radial spokes. But if internal conditions cause the vortices to wobble in their position as they impact the peripheral wall, then pressure vents 21 in the reflector surface can stabilize and center the location of the vortex in the curved reflector, for better reflection of the carbon ions into the formation zone. Negative pressure 52 tends to suck the carbon ion vortex in that direction, while positive pressure 54 creates a pressure ridge that will push the vortex away. The shape of the vents may be elongated to create the effect of a circular pressure ridge or trough within the vortex reflector. Measurement of the gases coming out of the shear reactor through these vents can indicate the density of carbon ions inside, the amount of carbon dioxide and carbon monoxide from the oxidation of carbon deposits by ozone, and the level of dopant ions.
FIG. 3 shows a front view of the peripheral wall 5 seen from the space 7 within the reactor, showing a vortex reflector 20 and the approximate outline of the central conical protrusion 22 with the central opening 26 for the evolving end 24. The outer ion vortex 32 and rebound vortex 38 are shown, based on the motion of the upper disk impeller 2 and the lower disk impeller 4. The exhaust vents 17 are primarily used to exhaust the non-carbon ion components and carbon dust, and the reflector pressure vents 21 control the position of the vortex as it impacts the reflector. A dopant source 40 ions is shown, as well as dopant exhaust vents 48.
FIG. 4 is an top view of the multiple radial spoke vortices between the counter-rotating disks. Each spoke vertex represents a formation zone, so many nanotube cables 56 can be formed at once according to the present invention. Each of the cables can be drawn out from the periphery and wound onto a takeup reel 58. The multitude of radial carbon nanotube cables can then easily be bundled into nanostring or even nanocable, materials which would have extremely good conductivity at high temperature and also very high tensile strength.
FIG. 5 shows an embodiment comprising convergent anodes. The peripheral wall 5 is the convergent portions of the anodes 2,4. The anodes in this example are narrowed first by a disk pinch section 62 and at their periphery are separated by a narrow slit opening 64. Beyond this opening is an ozone chamber 66 to clean up and functionalize the emerging nanotubes, which may emerge as nanotube yarn 68, charged by charging means 12 as a cathode at the evolving end 24. The parallel currents cause the conductors to attract, so the parallel currents in the multitude of nanotubes coming out of the shear reactor would cause them to draw together into nanoyarn and stick together by van der Waals forces. The growing nanotube yarn 68 is and withdrawn from the reactor by precision extraction means 70 and eventually wound onto the takeup reel 58.
The present invention for the vortex synthesis of nanotubes can be applied to any material or compound which lends itself to this kind of self assembly, in addition to the materials mentioned above. Temperature, carrier gas, electrolysis and cathode charge can be varied as needed, and the components of the shear reactor itself can feature coatings with catalysts or manufactured surfaces to improve electrolysis or prevent unwanted buildup of coatings.
It will be evident to artisans that features and details given above are exemplary only. Except where expressly indicated, it should be understood that none of the given details is essential; each is generally susceptible to variation, or omission. It should be apparent to those of ordinary skill what particular applications of the novel ideas presented here may be made given the description of the embodiments. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments described, which are merely illustrative of the present invention and not intended to have the effect of limiting the scope of the claims.
Instructed hindsight on the part of those of more than ordinary skill in the particular art of desalination should not be admitted as ex post facto evidence that the present invention was obvious or that they could easily have done it had they bothered, when the problem of mass production of nanotubes with extended length and variable composition has remained unsolved for so long.
Patent applications by David J. Mccutchen, Portland, OR US
Patent applications by Wilmot H. Mccutchen, Orinda, CA US
Patent applications by MCCUTCHEN CO.
Patent applications in class Fiber, fabric, or textile
Patent applications in all subclasses Fiber, fabric, or textile