[Enthalpy]

Hello everybody!

The choice of a rocket odixiser is even narrower than for rocket fuels:

• Solid stages use NH₄ClO₄ for decades. Improvement is credible but unclear.
• The efficient cold liquid is O₂. End of game.
• Satellite micro-thruster and even a few launchers still use the "storable" (liquid on Earth) N₂O₄ with hydrazines. Operators want to get rid of them all. Research on ionic liquids has provided no alternative as efficient, and non-chemical propulsion will terminate the whole storable option.

This is what survived from thousands of investigated miracle oxidisers, so new claims meet scepticism. It shouldn't prevent trying: aeroplanes flew after many disappointments.

The PhD thesis of Martin Rahm is a source of data for nitramides:
http://kth.diva-portal.org/smash/get/diva2:360054/FULLTEXT01
Ammonium dinitramide NH₄N(NO₂)₂ page 14/87
Trinitramide N(NO₂)₃ page 64/87, he synthesized it.

[Enthalpy]

The only composition used in solid launcher stages is ammonium perchlorate, aluminium and polybutadiene. Progress results from graphite fibre casings and from more powder volume mixed in the prepolymer.

One promising solid oxidiser, ammonium dinitramide, has already a production plant. Replacing the perchlorate, it would emit no HCl. It would gain interesting 12s if even more powder volume could fit in the prepolymer than now, so the gain in real life is unclear to me.

This is very far from liquids' performance, sorry. Claims by the proponents base on the "impulse density" which is little relevant for space transport.

[Enthalpy]

One other oxidiser is trinitramide. Detected in minute concentration in solution, so bigger amounts will probably show drawbacks as a propellant, say if they detonate. But the compound can have uses for synthesis or as a test for a theory - or as a publication before being forgotten.

The heat of formation is only estimated by software: +203kJ/mol for the solid at 298K, according to Montgomery cited by Rahm.

The mix would beat perchlorate by 26s, nice. As trinitramide contains no fuel, less oxidiser is needed in the prepolymer, and less aluminium too as it happens, so the solid volume fraction is no barrier.

The proponents suggest that trinitramide, whose stability at room temperature is uh-doubtful, could make cryogenic solid propellants. My answer: if accepting cold, we could mix liquid oxygen with powder of methane or ethylene and freeze everything in a graphite fibre casing. Performance unbeatable by any nitramide whatsoever.

[Enthalpy]

For the synthesis of trinitramide, I've already suggested atomic nitrogen in NO₂
http://www.chemicalforums.com/index.php?topic=72951.msg338230#msg338230
whose most probable result is nitrogen, oxygen and their mundane compounds, plus oxidized tantalum. Worth a try?

Here is a different attempt, with NX₃ in NO₂.

While NO₂ reacts easily with X₂, bonds are stronger in NX₃, in kJ/mol according to
www.nist.gov/data/nsrds/NSRDS-NBS31.pdf:
   243     F-NF2
   188     F-NO2
   158     F-F
   381     Cl-NCl2
   142     Cl-NO2
   243     Cl-Cl
so light shall break X-NX₂ to let the fragments react with NO₂. Advantageously, the compounds can be cold and diluted.

One unknown is the fragile O₂N-N(NO₂)₂ bond. A software estimate is 110kJ/mol, less than mean 168kJ/mol for I-N in NI₃. This favours a big halogen in NX₃, alas, and the wavelength should excite the trihalide rather than the nitramide if this is possible, and pass through XNO₂.

The only NX₃ spectra I have
http://satellite.mpic.de/spectral_atlas
are for NF₃ (absorbs too little) and NCl₃, which absorbs better than NO₂ at 254nm (8*10^-19cm²/mol). NBr₃ and NI₃ should be more sensitive to this wavelength.

So the procedure would be: cool and evacuate the reactor, fill it with NO₂ and a carrier gas, switch the lamp, sublimate NX₃, separate the lab debris by sedimentation, analyze.

Marc Schaefer, aka Enthalpy