There are a lot of grown-up ways I might have chosen to write that headline, but when you watch this video you'll see why I resorted to talking like my five-year-old neighbor. Though what you're watching are simple chemical reactions under a transmission electron microscope (TEM), it's tempting to describe them in animalistic terms. The carbon nanotube really looks like a living, wiggling creature being consumed by a dark lumpy menace (the iron), which then appears to suddenly start vomiting the worm back up. What's really happening here?
First of all, this film demonstrates a somewhat novel discovery about carbon nanotubes (CNTs), which is that they can grow, shrink, and then grow again. Physicist Xiaofeng Feng and his colleagues discovered that they could control this growth by pumping acetylene gas in and out of the CNT growth chamber. Pump in the gas, and the CNT grows. Pump it out, and the CNT's iron catalyst starts eating its ass. Sadly for those of us rooting for iron flakes to take over the nanosphere, slaying CNTs with great vengeance, it turns out that this reaction is all because of water. When the acetylene leaves the growth chamber, water molecules start removing carbon atoms from the CNT, making it appear to be eaten by the iron.
In Nano Research, the authors offer a more technical explanation:
It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out.
Here's the iron eating that CNT in in super-upcloso-vision. Read the scientific paper in Nano Research.