Nanosecond-pulses Create PolyNitrogen for Future Clean Energy Source

Scientists have long theorized that the energy stored in the atomic bonds of nitrogen could one day be a source of clean energy. But coaxing the nitrogen atoms into linking up has been a daunting task. Researchers at Drexel University’s C&J Nyheim Plasma Institute have finally proven that it’s experimentally possible — with some encouragement from a liquid plasma spark.

Reported in the Journal of Physics D: Applied Physics, the production of pure polymeric nitrogen — polynitrogen — is possible by zapping a compound called sodium azide with a jet of plasma in the middle of a super-cooling cloud of liquid nitrogen. The result is six nitrogen atoms bonded together — a compound called ionic, or neutral, nitrogen-six — that is predicted to be an extremely energy-dense material.

“Polynitrogen is being explored for use as a ‘green’ fuel source, for energy storage, or as an explosive,” said Danil Dobrynin, PhD, an associated research professor at the Nyheim Institute and lead author of the paper. “Versions of it have been experimentally synthesized — though never in a way that was stable enough to recover to ambient conditions or in pure nitrogen-six form. Our discovery using liquid plasma opens a new avenue for this research that could lead to a stable polynitrogen.”

Previous attempts to generate the energetic polymer have used high pressure and high temperature to entice bonding of nitrogen atoms. But neither of those methods provided enough energy to excite the requisite ions — atomic bonding agents — to produce a stable form of nitrogen-six. And the polymeric nitrogen created in these experiments could not be maintained at a pressure and temperature close to normal, ambient conditions.

It’s something like trying to glue together two heavy objects but only being strong enough to squeeze a few drops of glue out of the bottle. To make a bond strong enough to hold up, it takes a force strong enough to squeeze out a lot of glue.

That force, according to the researchers, is a concentrated ion blast provided by liquid plasma.

Liquid plasma is the name given to an emission of an ion-dense matter generated by a pulsed electrical spark discharged in a liquid environment — kind of like lightning in a bottle. Liquid plasma technology has barely been around for a decade though it already holds a great deal of promise. It was pioneered by researchers at the Nyheim Institute who have explored is use in a variety of applications, from health care to food treatment.

Because the plasma is encased in liquid it is possible to pressurize the environment, as well as controlling its temperature. This level of control is the key advantage that the researchers needed to synthesize polynitrogen because it allowed them to more precisely start and stop the reaction in order to preserve the material it produced. Dobrynin and his collaborators first reported their successful attempt to produce polynitrogen using plasma discharges in liquid nitrogen in a letter in the Journal of Physics D: Applied Physics over the summer.

In their most recent findings, the plasma spark sent a concentrated shower of ions toward the sodium azide — which contains nitrogen-three molecules. The blast of ions splits the nitrogen-three molecules from the sodium and, in the excited state, the nitrogen molecules can bond with each other. Not surprisingly, the reaction produces a good bit of heat, so putting the brakes on it requires an incredible blast of cold — the one provided by liquid nitrogen.

“We believe this procedure was successful at producing pure polynitrogen where others fell short, because of the density of ions involved and the presence of liquid nitrogen as a quenching agent for the reaction,” Dobrynin said. “Other experiments introduced high temperatures and high pressures as catalysts, but our experiment was a more precise combination of energy, temperature, electrons and ions.”

Journal of Physics D: Applied Physics – Nanosecond-pulsed spark discharge plasma in liquid nitrogen: synthesis of polynitrogen from NaN3

Abstract
Nanosecond-pulsed plasma ignited in liquid nitrogen is a unique tool for the synthesis of unconventional materials due to a combination of energetic properties of the discharge itself (high densities of reactive species, pressures and radiation) with the low temperature of the surrounding dense liquid. Here, we report on applications of such plasma for synthesis of a polymeric nitrogen compound, preliminarily identified as neutral or ionic N6, from sodium azide precursors.

17 thoughts on “Nanosecond-pulses Create PolyNitrogen for Future Clean Energy Source”

  1. Methalox avg is 26.7. N2 is 28. Depending on the energy content, polynitrogen may have a higher Isp than methalox (or a lower one). But I agree that monopropellants are often bad news.

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  2. If you’re not rounding water to 20, you shouldn’t be rounding N2 and CO2 either. N2 is 28, CO2 is 44.
    As it happens, the average molecular weight of methalox exhaust (2 H2O for every CO2) is 26.7. N2 is only a little heavier.

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  3. Actually, the average molecular weight of burnt methalox is about 25; There are two water molecules for every CO2 molecule, after all.

    Mono-propellants that consist of a single compound are just generally bad news. Even if you keep them cold, all you’d really need is a good cosmic ray going through the tank to set them off.

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  4. This, note that dynamite is not use by the military as it blow up way to easy. Military want explosives you can shoot out an cannon at 20K g and don’t detonate if hit by enemy shells.
    This was solved long ago. Tank turret popping an magazine explosions is cordite buring in an closed space.
    Military also want stuff they can store for decades as wars are rare.

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  5. But nitroglycerin is NOT worth keeping around to blow stuff up.
    It’s far too unstable. The cost and risks make it far cheaper to use something with less kJ/g but safer and easier to handle.

    It’s only used as an ingredient in far more stable explosives. And medicine.

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  6. The exhaust would be N2 (reaction product) not N6 (reactant). N2 is lighter (30) than the exhaust from methalox and the like, which is CO2 (40) and water (18). Could not find hypothetical energy content of hexazine but it should be much larger than tetrazine (N4). As for stability, they claim it is stable at minus 50C. Presumably blows up if warms to ambient. Does sound dodgy to handle.

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  7. Looking at the details of this technical innovation, it make we wonder if it could be the basis for something resembling a micro-fusion reactor. After all, the pressures and perhaps heat management involved might be the path to such fusion.

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  8. If it was at least as stable as the primary explosives used in primers, it might find a market there, to reduce lead exposure.

    But this was more of a theoretical demonstration that the compound could actually be stable. It’s certainly not a practical means of manufacture.

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  9. There are many compounds that are a better explosive than the commonly used octogen (HMX) and hexogen (RDX), but these two are still commonly used, while others are not. Hexanitrohexaazaisowurtzitane (or humanely CL-20) has been around for 30+ years, yet it costs a pretty penny, and is not stable enough to shock. If it is made stable, it loses its main advantage. Same, in extreme, may be the outcome for pure nitrogen: very interesting, but no way.

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  10. Yeah, if this is as stable and well behaved as nitroglycerin, it’s not worth to keep around except for blowing up stuff.

    And probably not even for that, given explosives need to have some tolerance to be manipulated and displaced.

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  11. If anyone is interested, a stable enough nitrogen polymer has been the sweetest dream of the military explosives R&D. It would cost arm, leg and three kidneys, which is acceptable for some military work, but clean energy my ass.

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  12. It wouldn’t be useful for rocket fuel anyway; You want both high energy AND low molecular weight, to get the average speed of the molecules as high as possible. While N6 might solve the energy end of this, it would have a high molecular weight, lowering the exhaust velocity.

    On top of that, you don’t want unstable monopropellants, they tend to blow up before they reach the combustion chamber.

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  13. Based on a little googling, N6 hasn’t been made yet but people think it will be pretty unstable. N4 has the same energy per mole as methane, but would be 48 g/mol while methane is only 16 g/mol. If N4 is less energy per gram than methane and N6 isn’t stable, this doesn’t seem that useful for rocket fuel.

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