Low temperature cnt growth using gas-preheat method

Abstract

A method for synthesizing carbon nanotubes (CNT) comprises the steps of providing a growth chamber, the growth chamber being heated to a first temperature sufficiently high to facilitate a growth of carbon nanotubes; and passing a substrate through the growth chamber; and introducing a feed gas into the growth chamber pre-heated to a second temperature sufficient to dissociate at least some of the feed gas into at least free carbon radicals to thereby initiate formation of carbon nanotubes onto the substrate.

1 . A system for synthesizing carbon nanotubes (CNT) comprising:
 a growth chamber that receives a substrate having a catalyst disposed thereon;   a heater for heating the growth chamber to a first temperature, the first temperature sufficiently high to facilitate a growth of carbon nanotubes on the substrate; and   a gas pre-heater that heats a feed gas to a second temperature and introduces the feed gas into the growth chamber to synthesize carbon nanotubes on the substrate.   
     
     
         2 . The system of  claim 1 , wherein the second temperature is sufficient to dissociate at least some of the feed gas into at least free carbon radicals. 
     
     
         3 . The system of  claim 1 , wherein the second temperature is within about 40% of the first temperature and is sufficient to achieve a desired temperature profile within the growth chamber. 
     
     
         4 . The system of  claim 1 , wherein the gas pre-heater comprises a heater external to the growth chamber that controllably heats the feed gas to the second temperature. 
     
     
         5 . The system of  claim 1 , wherein the gas pre-heater comprises a heater external to the growth chamber that controllably heats a process gas to a temperature exceeding the second temperature; and a diffuser having an input for receiving the heated process gas and an input for receiving the feed gas at a lower temperature and combining the heated process gas and the feed gas to provide a diffused output into the growth chamber including feed gas at the second temperature. 
     
     
         6 . The system of  claim 1 , wherein the substrate comprises at least one material selected from the group consisting of: a carbon fiber, a graphite fiber, a cellulosic fiber, a glass fiber, a metal fiber, a ceramic fiber, an aramid fiber, and any combination thereof. 
     
     
         7 . The system of  claim 1 , further comprising a controller for controlling one or more of the rate at which the growth chamber receives the substrate, the first temperature, the second temperature, and the feed gas supply. 
     
     
         8 . The system of  claim 1 , wherein the first temperature is in a range of from about 450° C. to about 650° C. 
     
     
         9 . The method of  claim 1 , wherein the second temperature is in a range of from about 550° C. to about 1000° C. 
     
     
         10 . The system of  claim 1 , wherein the substrate is a fiber tow having a sizing and an iron based catalyst thereon. 
     
     
         11 . The system of  claim 1 , wherein the feed gas comprises at least one gas selected from the group consisting of: acetylene, methanol, ethylene, methane, propane, benzene, and natural gas. 
     
     
         12 . The system of  claim 5 , wherein the process gas comprises at least one gas selected from the group consisting of: nitrogen, helium and argon.