A new ammonia-free means of manufacturing vertically aligned carbon nanofibers (VACNFs) has been developed by researchers at North Carolina State University.
This new process is based instead on the use of ambient air — allowing for the phasing out of the use of toxic ammonia gas, as well as reducing of costs.
VACNFs are currently being investigated as a material of potential use in everything from batteries, to energy generation, to gene-delivery tools. But, until now, the methods used for creating VACNFs was relatively expensive and relied on toxic materials.
“This discovery makes VACNF manufacture safer and cheaper, because you don’t need to account for the risks and costs associated with ammonia gas,” states Dr Anatoli Melechko, an adjunct associate professor of materials science and engineering at NC State, and lead author of a new paper describing the work. “This also raises the possibility of growing VACNFs on a much larger scale.”
North Carolina State University provides more:
In the most common method for VACNF manufacture, a substrate coated with nickel nanoparticles is placed in a vacuum chamber and heated to 700 degrees Celsius. The chamber is then filled with ammonia gas and either acetylene or acetone gas, which contain carbon. When a voltage is applied to the substrate and a corresponding anode in the chamber, the gas is ionized. This creates plasma that directs the nanofiber growth. The nickel nanoparticles free carbon atoms, which begin forming VACNFs beneath the nickel catalyst nanoparticles. However, if too much carbon forms on the nanoparticles it can pile up and clog the passage of carbon atoms to the growing nanofibers.
Ammonia’s role in this process is to keep carbon from forming a crust on the nanoparticles, which would prevent the formation of VACNFs.
“We didn’t think we could grow VACNFs without ammonia or a hydrogen gas,” Melechko explains.
But, despite that, they tried anyways. And the size, shape, and alignment of the VACNFs was consistent with those produced via conventional processes.
“We did this using the vacuum technique without ammonia,” Melechko states. “But it creates the theoretical possibility of growing VACNFs without a vacuum chamber. If that can be done, you would be able to create VACNFs on a much larger scale.”
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