Several metal alloys have shown promise as improved catalysts for catalytic thermal decomposition of hydrocarbon gases to produce carbon nanotubes (CNTs). Heretofore almost every experiment on the production of carbon nanotubes by this method has involved the use of iron, nickel, or cobalt as the catalyst. However, the catalytic-conversion efficiencies of these metals have been observed to be limited. The identification of better catalysts is part of a continuing program to develop means of mass production of high-quality carbon nanotubes at costs lower than those achieved thus far (as much as $100/g for purified multi-wall CNTs or $1,000/g for single-wall CNTs in year 2002).
The main effort thus far in this program has been the design and implementation of a process tailored specifically for high-throughput screening of alloys for catalyzing the growth of CNTs. The process includes an integral combination of (1) formulation of libraries of catalysts, (2) synthesis of CNTs from decomposition of ethylene on powders of the alloys in a pyrolytic chemical-vapor-decomposition reactor, and (3) scanning-electron-microscope screening of the CNTs thus synthesized to evaluate the catalytic efficiencies of the alloys. Information gained in this process is put into a database and analyzed to identify promising alloy compositions, which are to be subjected to further evaluation in a subsequent round of testing.
The promising alloys identified thus far have been the following (compositions in atomic percentages): 90 Co, 10 Ti; 20 Co, 70 Ni, 5 Ti, 5 Ta; 90 Co, 10 Mo; 20 Co, 75 Ni, 5 Mo; 80 Co, 10 Ti, 10 Al; 70 Co, 15 Ni, 15 Ti; 80 Co, 10 Ni, 10 Ti; 70 Co, 5 Ta, 5 Mo, 20 Mn; 80 Ni, 10 Mo, 10 A; 80 Co, 12 Ni, 8 Al; and 80 Co, 20 Cr.
Some of these alloys have been found to catalyze the formation of carbon nanotubes from ethylene at temperatures as low as 350 to 400 °C. In contrast, the temperatures typically required for prior catalysts range from 550 to 750 °C.
This work was done by Ted X. Sun and Yi Dong of Intermatix Corp. for Johnson Space Center.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
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Refer to MSC-23477-1, volume and number of this NASA Tech Briefs issue, and the page number.