Shear reactor for vortex synthesis of nanotubes

Abstract

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, comprising
 counter-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; and   means 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 of
 creating 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; and   withdrawing 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, comprising
 counter-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; and   means 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.