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TechFront Research and Development in Manufacturing and Technology


New Process Allows Nanofibers to Grow at Room Temperature


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esearchers at North Carolina State University (Raleigh, NC) have devised a safer method of growing vertically aligned carbon nanofibers (VACNF) with ambient air, rather than using toxic chemicals like ammonia at very high temperatures in a vacuum chamber. VACNFs, which hold promise for gene- delivery tools, sensors, batteries and other technologies, are typically manufactured by placing a substrate coated with nickel nanopar- ticles in a vacuum chamber heated to 700°C (1292°F). The chamber is filled with ammonia gas and either acetylene or acetone gas, which contain carbon, and a voltage is applied to the substrate and an anode in the chamber to ionize the gas, creating plasma that directs the nanofiber growth.


“This discovery makes VACNF manufac- ture safer and cheaper, because you don’t need to account for the risks and costs associated with ammonia gas,” said Anatoli Melechko, an adjunct associate professor of materials science and engineering at NC State and senior author of a paper on the work. “This also raises the possibility of growing VACNF on a much larger scale.” Ammonia has been used in the process to keep carbon from forming a crust on the nanoparticles, which would prevent the formation of VACNF. “We didn’t think we could grow VACNFs without ammonia or a hydrogen gas,” Melechko said. The team tried the conventional vacuum technique, using acetone gas. When they replaced the ammonia gas with ambient air, it worked. The size, shape and alignment of the nanofibers also were consistent with the fibers produced using conventional techniques. “We did this using the vacuum technique without ammo- nia,” Melechko said. “But it creates the theoretical possibility of growing VACNF without a vacuum chamber. If that can be


done, you would be able to create VACNF on a much larger scale.” Melechko also credited the role of two high school stu- dents involved in the work, A. Kodumagulla and V. Varanasi,


Researchers demonstrated that they can grow vertically-aligned carbon nanofibers using ambient air, rather than ammonia gas.


who are lead authors of the paper. “This discovery would not have happened if not for their approach to the problem, which was free from any preconceptions,” Melechko said. “I think they’re future materials engineers.” The paper, “Aerosynthesis: Growth of Vertically-aligned Carbon Nanofibres with Air DC Plasma,” is published online in the journal Nanomaterials and Nanotechnology. Co-authors include former NC State doctoral student R.C. Pearce; NC State doctoral student W.C. Wu; Dr. Joseph Tracy, an associate professor of materials science and engineering at NC State; and D.K. Hensley and T.E. McKnight of Oak Ridge National Laboratory. The work was partially supported by a National Science Foundation grant. For more information, see www.ncsu.edu. ME


June 2014 | ManufacturingEngineeringMedia.com 31


Image courtesy Anatoli Melechko, North Carolina State University


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