Apparatus and method for plasma synthesis of carbon nanotubes
Apparatus and method for plasma synthesis of carbon nanotubes couple a plasma nozzle to a reaction tube/chamber. A process gas comprising a carbon-containing species is supplied to the plasma nozzle. Radio frequency radiation is supplied to the process gas within the plasma nozzle, so as to sustain a plasma within the nozzle in use, and thereby cause cracking of the carbon-containing species. The plasma nozzle is arranged such that an afterglow of the plasma extends into the reaction tube/chamber. The cracked carbon-containing species also pass into the reaction tube/chamber. The cracked carbon-containing species recombine within the afterglow, so as to form carbon nanotubes in the presence of a catalyst.
1. A method of synthesising carbon nanotubes, the method comprising:
supplying a process gas to a plasma nozzle that is coupled to a reaction tube or chamber, the process gas comprising a carbon-containing species, wherein the carbon-containing species comprises a gaseous hydrocarbon, natural gas, CH 4 , C 2 H 6 , C 2 H 4 , C 3 H 8 , C 4 H 10 , a liquid hydrocarbon, a liquefied hydrocarbon, toluene, or ethanol;
supplying radio frequency radiation to the process gas within the plasma nozzle, so as to sustain a plasma within the plasma nozzle, and thereby cause cracking of the carbon-containing species, wherein the plasma is generated at atmospheric pressure; and
providing a catalyst;
wherein the plasma nozzle is arranged such that an afterglow of the plasma extends into the reaction tube/chamber, the cracked carbon-containing species also passes into the reaction tube/chamber, and the cracked carbon-containing species recombines within the afterglow, so as to form carbon nanotubes in the presence of the catalyst; and
wherein the method further comprises applying cooling to the afterglow on exiting the plasma nozzle.
2. The method according to claim 1 , further comprising forming at least one vortex in the process gas within the plasma nozzle, and subjecting said at least one vortex to said radio frequency radiation.
3. The method according to claim 1 , wherein the radio frequency radiation comprises microwave radiation.
4. The method according to claim 1 , wherein the cooling comprises water cooling or gas cooling.
5. The method according to claim 1 , wherein the process gas further comprises a buffer gas, the buffer gas comprising argon, nitrogen, or helium.
6. The method according to claim 1 , wherein the process gas further comprises a buffer gas, the buffer gas comprising carbon dioxide.
7. The method according to claim 1 , wherein the afterglow within the reaction tube/chamber has an operating temperature of lower than 3500° C., lower than 2000° C., or around 1000° C.
8. The method according to claim 1 , further comprising extracting the carbon nanotubes using a continuous extraction process.
9. The method according to claim 1 , wherein the carbon-containing species is cracked without the process gas being introduced into a thermal zone; and wherein no external heating is applied during the formation of the carbon nanotubes.