Continuous method for producing inorganic nanotubes

Abstract

Production of nanotubes of carbon or of other inorganic material by moving a carbon-containing substrate ( 8 ), such as a tape or belt of carbon fibres, within a reaction chamber ( 1 ) either through an electric arc in a gap between two electrodes ( 2, 3 ) or adjacent an electrode so that an electric arc exists between the electrode and the substrate, to cause the nanotubes to form on the substrate ( 8 ). The method enables the continuous or semi-continuous production of nanotubes. Preferably, the process is carried out at atmospheric pressure and nanotubes of high purity are produced.

1 . A method for producing nanoscale hollow inorganic fibrils or nanotubes, including moving a carbon-containing substrate within a reaction chamber either through an electric arc in a gap between two electrodes or adjacent an electrode so that an electric arc exists between the electrode and the substrate, to cause the nanotubes to form on the substrate.  
     
     
         2 . A method according to  claim 1  including moving the substrate at a substantially steady speed through the arc.  
     
     
         3 . A method according to  claim 1  including moving the substrate through the arc in steps.  
     
     
         4 . A method according to  claim 1  wherein at least one electrode is a carbon containing electrode.  
     
     
         5 . A method according to  claim 4  wherein the substrate is composed of carbon fibres.  
     
     
         6 . A method according to  claim 5  wherein the substrate is a tape or belt woven from carbon fibres.  
     
     
         7 . A method according to  claim 5  wherein the substrate is a paper of carbon fibres.  
     
     
         8 . A method according to  claim 1  including tensioning the substrate against the anode of the electrodes.  
     
     
         9 . A method according to  claim 1  including moving the substrate at a speed such that the substrate has a residence time in the arc of at least three seconds.  
     
     
         10 . A method according to  claim 1  including moving the substrate at a speed of less than 5 mm per second.  
     
     
         11 . A method according to  claim 1  wherein the arc current is sufficiently low to form nanotubes on the substrate but avoid structural damage to the substrate.  
     
     
         12 . A method according to  claim 1  wherein the arc current is set at a level which causes some vaporisation of the substrate without structurally damaging the substrate.  
     
     
         13 . A method according to  claim 1  wherein the arc has a current density in the range 0.1 to 1 Amps/mm2.  
     
     
         14 . A method according to  claim 1  wherein a catalyst is present which will favour the production of single wall nanotubes.  
     
     
         15 . A method according to  claim 1  including flushing a gas through the reaction chamber which contains sufficient oxygen to react with other species without oxidising the nanotubes on cool down.  
     
     
         16 . A method according to  claim 1  including directing a flow of gas to cool one or both of the electrodes and/or the substrate.  
     
     
         17 . A method according to  claim 1  including directing a flow of gas onto the substrate after it has passed through the arc to cool the substrate and/or clear it of carbon vapour.  
     
     
         18 . A method according to  claim 1  wherein the nanotubes are carbon nanotubes.  
     
     
         19 . A method according to  claim 1  wherein the electrodes and the substrate have a carbon purity in excess of 99.5%.  
     
     
         20 . A method according to  claim 1  wherein the nanotubes are composed of BC 2 N and/or BC 3 .  
     
     
         21 . A method of producing nanoscale hollow carbon fibrils or nanotubes, comprising moving a tape or belt composed of carbon filaments having a carbon purity in excess of 99.5% through an electric arc in a gap between two carbon containing electrodes having a carbon purity in excess of 99.5% at a speed sufficient relative to the arc current to form carbon nanotubes on the fibres or filaments of the substrate without damaging the substrate.  
     
     
         22 . Carbon nanotubes formed by the method of any one of  claims 1  to  21 .  
     
     
         23 . A method according to any one of  claims 1  to  21  wherein a power supply which supplies the arc current has a rms voltage ripple of less than 1 volt and current ripple of less than 0.5 Amps.