Saturday, 26 July 2014
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Ambient air manufacture for vertical carbon nanofibres

Researchers from North Carolina State University have demonstrated that vertically aligned carbon nanofibres (VACNFs) can be manufactured using ambient air, making the manufacturing process safer and less expensive. 

VACNFs hold promise for use in gene-delivery tools, sensors, batteries and other technologies.

Conventional techniques for creating VACNFs rely on the use of ammonia gas, which is toxic.

‘This discovery makes VACNF manufacture safer and cheaper, because you don’t need to account for the risks and costs associated with ammonia gas,’ said Dr 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 VACNFs on a much larger scale.’

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 nanofibre 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 clog the passage of carbon atoms to the growing nanofibres.

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 said in a statement.

Melechko’s team tried the conventional vacuum technique, using acetone gas. However, they found that the process worked when ambient air replaced the ammonia gas.

The size, shape and alignment of the VACNFs were said to be consistent with the VACNFs produced using conventional techniques.

‘We did this using the vacuum technique without ammonia,’ Melechko said. ‘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.’

The paper, “Aerosynthesis: Growth of Vertically-aligned Carbon Nanofibres with Air DC Plasma,” is published online in Nanomaterials and Nanotechnology


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