Today, most rockets are fueled by hydrazine, a toxic and hazardous chemical comprised of nitrogen and hydrogen. Those who work with it must be kitted up in protective clothing. Even so, around 12,000t of hydrazine is released into the atmosphere every year by the aerospace industry
Now, researchers are in the process of developing a greener, safer rocket fuel based on metal organic frameworks (MOFs), a porous solid material made up of clusters of metal ions joined by an organic linker molecule. Hundreds of millions of connections join in a modular structure.
Robin Rogers, formerly at McGill University, US, has worked with the US Air Force on hypergolic liquids that will burn when placed in contact with oxidisers, to try get rid of hydrazine. He teamed up with Tomislav Friščić at McGill who has developed ways to react chemicals ‘mechanochemically’ – without the use of toxic solvents.
The pair were interested in a common class of MOFs called zeolitic imidazole frameworks, or ZIFs, which show high thermal stability and are usually not thought of as energetic materials.
They discussed the potential of using ZIFs with the imidazolate linkers containing trigger groups. These trigger groups allowed them to take advantage of the usually not accessible energetic content of these MOFs.
The resulting ZIF is safe and does not explode, and it does not ignite unless placed in contact with certain oxidising materials, such as nitric acid, in this case.
Authorities continue to use hydrazine because it could cost millions of dollars to requalify new rocket fuels, says Rogers. MOF fuel would not work in current rocket engines, so he and Friščić would like to get funding or collaborate with another company to build a small prototype engine that can use it.