Synthesis of polynitrogen materials using nanosecond-pulsed plasmas in liquid nitrogen*

Novel energetic materials based on nitrogen (polymeric nitrogen) are of interest as an efficient and clean fuels, explosives and energy storage. An all-nitrogen material, however, was shown to be difficult to synthesize (for example, cubic gauche polynitrogen synthesis requires pressure up to 120 GPa and ~2000 K of temperature), and almost impossible to stabilize at normal conditions.

Electrical discharges in liquid have been used extensively for generation of nanostructured materials. In-liquid discharges are an attractive tool for material synthesis dues to a unique set of characteristics: relative high temperatures and pressure, radiation (UV, visible and IR range) and high densities of reactive species. Ignition of these types of discharges in cryogenic environment presents even more possibilities for generation of unconventional materials due to extremely fast quenching outside of discharge zone. In our recent studies, we have employed nanosecond-pulsed plasmas ignited in liquid nitrogen as a tool for production and fast quenching of nitrogen-rich materials. Nanosecond-pulsed plasma treatment of liquid nitrogen results in generation of fluorescent material, which closely resembles the Raman spectra of amorphous nitrogen previously obtained using high pressure compression of molecular nitrogen. Shadow imaging of the shock wave propagation from the exploded material allowed us to estimate its energy density to be about 13.3±3.5 kJ/g (3.2±0.8 in TNT equivalent), close to the predicted number for the polymeric nitrogen network of ~11.3 kJ/g.