Arrays of long carbon nanotubes for fiber spinning

Abstract

An array of long carbon nanotubes (i.e. an array where the average length of the nanotubes is greater than 0.5 millimeters) is prepared by exposing a supported catalyst at elevated temperature to a gas mixture of hydrocarbon, inert gas, and a relatively low percentage of hydrogen. Addition of water vapor to the gas mixture may result in an increase in the length of the nanotubes, an increase the rate of growth, and a decrease in contamination of the array by amorphous carbon. The temperature and growth time are also chosen to minimize the amount of amorphous carbon that forms on the array. Fibers spun from the array have a higher tensile strength compared to known CNT fibers.

1 . A method for preparing an array of long nanotubes, comprising: 
 exposing a catalyst structure to a gaseous mixture for a chosen amount of time within a chosen temperature range, wherein the gaseous mixture comprises hydrocarbon, inert gas, and hydrogen, wherein the percentage of hydrogen in the gaseous mixture is P, and wherein P<20%, whereby an array of substantially aligned carbon nanotubes forms on the catalyst, the carbon nanotubes of the array having an average length of greater than about 0.5 millimeter.    
     
     
         2 . The method of  claim 1 , wherein the catalyst structure comprises a silicon substrate, a layer of silicon dioxide on the silicon substrate, a layer of aluminum oxide deposited by ion beam assisted deposition on the silicon dioxide layer, and a layer of metal on the aluminum oxide layer.  
     
     
         3 . The method of  claim 1 , wherein the layer of aluminum oxide is amorphous.  
     
     
         4 . The method of  claim 1 , wherein the layer of metal comprises iron.  
     
     
         5 . The method of  claim 1 , wherein the hydrocarbon in the gaseous mixture is present in an amount in the range of from about 20 percent to about 80 percent.  
     
     
         6 . The method of  claim 1 , wherein the hydrocarbon comprises ethylene, acetylene, hexane, acetone, or mixtures thereof.  
     
     
         7 . The method of  claim 1 , wherein the inert gas is present in an amount in the range of from about 20 percent to about 80 percent.  
     
     
         8 . The method of  claim 1 , wherein the inert gas comprises argon.  
     
     
         9 . The method of  claim 1 , wherein P≦10%.  
     
     
         10 . The method of  claim 1 , wherein P≦6%.  
     
     
         11 . The method of  claim 1 , wherein P≦5%.  
     
     
         12 . The method of  claim 1 , wherein P≦4%.  
     
     
         13 . The method of  claim 1 , wherein P≦3%.  
     
     
         14 . The method of  claim 1 , wherein the gaseous mixture further comprises water vapor.  
     
     
         15 . The method of  claim 1 , wherein the gaseous mixture is a flowing gaseous mixture.  
     
     
         16 . The method of  claim 1 , wherein the chosen amount of time and the chosen temperature are selected to minimize the formation of amorphous carbon on the array of substantially aligned carbon nanotubes.  
     
     
         17 . The method of  claim 1 , wherein the chosen amount of time is in the range of from about 5 minutes to about 2 hours.  
     
     
         18 . The method of  claim 1 , wherein the chosen amount of time is in the range of from about 10 minutes to about one hour.  
     
     
         19 . The method of  claim 1 , wherein the chosen amount of time is in the range of from about 15 minutes to about 30 minutes.  
     
     
         20 . The method of  claim 1 , wherein the chosen temperature range is from about 700 degrees Celsius to about 800 degrees Celsius.  
     
     
         21 . The method of  claim 1 , wherein the chosen temperature range is from about 730 degrees Celsius to about 780 degrees Celsius.  
     
     
         22 . The method of  claim 1 , wherein the temperature is about 750 degrees Celsius.  
     
     
         23 . The method of  claim 1 , wherein the array of substantially aligned carbon nanotubes comprises a length of from about 20 μm to about 4.5 mm.  
     
     
         24 . An array of carbon nanotubes prepared by a method comprising exposing a catalyst structure to a gaseous mixture for a chosen amount of time within a chosen temperature range, wherein the gaseous mixture comprises hydrocarbon, inert gas, and hydrogen, wherein the percentage of hydrogen in the gaseous mixture is P, wherein P<20%, whereby an array of substantially aligned carbon nanotubes forms on the catalyst, the carbon nanotubes of the array having an average length of greater than about 0.5 millimeters.  
     
     
         25 . A densely packed array of substantially straight and aligned carbon nanotubes comprising an average nanotube length of at least 2.5 millimeters.  
     
     
         26 . The array of  claim 25 , wherein the average nanotube length is at least 4 millimeters.  
     
     
         27 . The array of  claim 25 , wherein the average nanotube length is at least 4.5 millimeters.  
     
     
         28 . A method for preparing a fiber, comprising: 
 exposing a catalyst structure to a gaseous mixture for a chosen amount of time at a temperature in a chosen temperature range, wherein the gaseous mixture comprises hydrocarbon, inert gas, and hydrogen, wherein the percentage of hydrogen in the gaseous mixture is P, wherein P<20%, whereby an array of substantially aligned carbon nanotubes forms on the catalyst, the carbon nanotubes of the array having an average length of greater than about 0.5 millimeters; and    spinning a fiber from the array.    
     
     
         29 . A fiber prepared by a method comprising: 
 exposing a catalyst structure to a gaseous mixture for a chosen amount of time at a temperature in a chosen temperature range, wherein the gaseous mixture comprises hydrocarbon, inert gas, and hydrogen, wherein the percentage of hydrogen in the gaseous mixture is P, wherein P<20%, whereby an array of substantially aligned carbon nanotubes forms on the catalyst, the carbon nanotubes of the array having an average length of greater than about 0.5 millimeters; and    spinning a fiber from the array.    
     
     
         30 . The fiber of  claim 29 , wherein said fiber has a tensile strength S, wherein S≧1 GPa.  
     
     
         31 . A spun fiber of carbon nanotubes having a tensile strength T, wherein S≧1 GPa.  
     
     
         32 . A ribbon prepared by a method comprising: 
 exposing a catalyst structure to a gaseous mixture for a chosen amount of time within a chosen temperature range, wherein the gaseous mixture comprises hydrocarbon, inert gas, and hydrogen, wherein the percentage of hydrogen in the gaseous mixture is P, wherein P<20%, whereby an array of substantially aligned carbon nanotubes forms on the catalyst, the carbon nanotubes of the array having an average length of greater than about 0.5 millimeters; and    pulling a ribbon from the array.    
     
     
         33 . A composite structure, comprising: 
 a silicon substrate;    a layer of silicon dioxide on the silicon substrate;    a layer of aluminum oxide having a thickness of from about 2 nanometers to about 20 nanometers deposited by ion beam assisted deposition on said layer of silicon dioxide; and    a layer of iron having a thickness of from about 0.1 nanometers to about 5 nanometers on said layer of aluminum oxide.    
     
     
         34 . The structure of  claim 33 , wherein the aluminum oxide layer is at least partially amorphous.  
     
     
         35 . The structure of  claim 33 , wherein the aluminum oxide layer is completely amorphous.  
     
     
         36 . The structure of  claim 33 , wherein the aluminum oxide layer is comprised of fine grains.