Patent ID: 8026100

Claim:
A method of measuring the lifetime of a catalyst for producing carbon nanotubes comprising: providing first and second independent samples of a catalyst suitable to produce carbon nanotubes; exposing independently each of the first and second independent catalyst samples to a first hydrocarbon source containing predominantly a first isotope of carbon therein for a first and a second time period, respectively; allowing the first hydrocarbon source to react to produce a first portion of carbon nanotubes containing the first isotope of carbon at each of the first and second independent catalyst samples; exposing independently each of the first and second independent catalyst samples to a second hydrocarbon source containing predominantly a second isotope of carbon therein for a third and fourth time period, respectively; allowing the second hydrocarbon source to react to produce a second portion of carbon nanotubes containing the second isotope of carbon at each of the first and second independent catalyst samples; and measuring the physical properties of the carbon nanotubes grown at the first and second independent catalyst samples to determine the lifetime of the catalyst, wherein the lengths of the first, second, third and fourth time periods are independently varied, and the first and the second catalyst are each exposed to a hydrocarbon source until carbon nanotubes are no longer produced.