Chain molecules, which only exist as nitrogen, are among the most energetic substances of all – but this makes this polymeric nitrogen too unstable to have any practical use. A research group led by Chi Ding from Nanjing University is now reporting that carbon nanotubes could potentially solve this problem. According to their recent publication in the journal “Chinese Physics Letters”, previously unknown structures made of pure nitrogen are formed inside carbon nanotubes, which are very energetic but most likely stable at room temperature. The team studied the possible structures of nitrogen in the tubes using two simulation methods to determine their stability. However, it is still unclear whether and how the stable super explosives can be produced in practice.
The fact that chain molecules of nitrogen are so well suited as explosives is due to the diatomic nitrogen (N2). This molecule, which also makes up around four-fifths of the Earth’s atmosphere, is one of the most stable molecules there is because of the triple bond between the two atoms. Polymeric nitrogen, in which the atoms are linked by single and double bonds, tends to form N2 rearrange and give off a lot of excess energy. This and the fact that only a non-toxic gas is produced in the process makes such molecules desirable as technical explosives.
Therefore, for research into very nitrogen-rich molecules such as isocyanogentetraazide (C2N14) strong nerves and good protective clothing. Or, like the team at Ding, you do it on the computer. The working group modeled the energy landscape inside carbon nanotubes and created potentially stable structures from nitrogen using a machine learning algorithm. The team finally tested whether they really work using a classic molecular dynamics program.
In addition to two known structures, the working group discovered three other previously unknown ways in which nitrogen atoms in carbon nanotubes can arrange themselves into chains or tubes. Not only do they fit into the carbon nanotubes, they also deform them, according to the simulations, so that they are no longer round but oval. The data indicate that the nitrogen molecules encapsulated in this way are stable even under everyday conditions, but at the same time have twice the energy density of the explosive TNT.