deltaH
Dangerous source of unreferenced speculation
Posts: 1663
Registered: 30-9-2013
Location: South Africa
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Mood: Heavily protonated
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Super propellants: hydrazinium azide hydrazinate and boron
I'm theoretically studying propellants that target the formation of hydrogen, since hydrogen being a light gas can be used to fire projectiles at
extremely high velocity, for example, as exploited in a light gas gun [1]. Unlike a light gas gun, however, I'm focusing on chemical propellants that
generate the hydrogen directly and not using a propellant to compress hydrogen, indirectly.
Since any solids produced by the chemical reaction can be very abrasive to the barrel of such hypothetical cannons, I am furthermore trying to focus
on reactions that produce dry lubricating solids as their product of combustion, for example, solids such as:
hexagonal boron nitride
molybdenum disulfide
carbon nitride
Out of all of these, boron nitride is very attractive. Hexagonal boron nitride is a white high melting solid that has similar physical properties to
graphite. It is a most excellent dry lubricant that is already commercially exploited for this purpose [2]. However, the main other benefit is that it
allows one to use amorphous boron, a very energetic fuel, in preparing the propellant.
I started by considering what I consider to be the benchmark for energetic hydrogen producing reactions, the so-called 'ALICE' reaction [3][4] between
aluminium nanopowders and water... well ice to be more precise 
Now the analogous reaction for boron targeting boron nitride would be to use boron powder and ammonia. However, ammonia is not very energetic, so I
turned to considering hydrazine and then progressed to hydrazinium azide hydrazinate (HAH). This is a low melting solid (m.p. 65C) that is remarkably
insensitive to friction (but not heat) and electrostatic discharge, all things considered [5].
My idea would be for a stoichiometric mixture of HAH and amorphous boron powder, then gently melting the HAH to fuse it intimately into the boron
powder and granulate. This idea though, is not novel and described in US patent 3309248 [6], "Solid propellants containing hydrazonium azide and boron
compounds", except that they describe using a polyurethane binder with the particular combo of boron powder and HAH.
Anyhow, I've done a thermodynamic calculation in EXCEL (attached) to work out the adiabatic temperature of a reaction between HAH and boron:
2[N2H5[+]N3[-].N2H4] + 14B => 14BN + 9H2
I've used NIST data for enthalpies and have had to extrapolate for BN because of the very high temperatures.
The flame temperature is a remarkable 4300°C, provided I haven't messed it up as I'm prone to doing 
Anyhow, the neat thing is that after firing such a cannon, the barrel wall should have a thin dusting of lubricating boron nitride, ready for the next
hypervelocity shot 
References:
[1] http://en.wikipedia.org/wiki/Light-gas_gun
[2] http://www.bn.saint-gobain.com/uploadedFiles/SGbn/Documents/...
[3] http://en.wikipedia.org/wiki/ALICE_(propellant)
[4] https://www.youtube.com/watch?v=-b7siH1Ausc
[5] Anton Hammerl et al, Synthesis and Characterization of Hydrazinium Azide Hydrazinate, Propellants, Explosives, Pyrotechnics, (2001), 26,
161–164.
[6] http://www.google.com/patents/US3309248
Attachment: adiabatic flame temperature calc for boron and HAH.xlsx (11kB)
This file has been downloaded 447 times
[Edited on 21-12-2014 by deltaH]
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PHILOU Zrealone
International Hazard
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Good ideas!
Also interesting:
*boran-ammonia solid (H3B-NH3 (H3B(-)-NH3(+))
and eventually
*boran-hydrazine H3B-NH2-NH2 or even H3B-NH2-NH2-BH3
Edit:
If hydrazine is too acidic for the BH3..there is a chance one get:
1°)H2B-NH-NH2, HB(-NH-NH2)2 and B(-NH-NH2)3
2°)and eventually H2N-NH-NH-BH2, HB(-NH-NH-)2BH and B(NH-NH)3B or polymers of the two last kind...
[Edited on 21-12-2014 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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deltaH
Dangerous source of unreferenced speculation
Posts: 1663
Registered: 30-9-2013
Location: South Africa
Member Is Offline
Mood: Heavily protonated
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Thanks PHILOU (flattered). In fact, I had considered ammonia borane, but found that while it would make a huge amount of hydrogen, it
wasn't energetic enough. For a while I considered the hypothetical use of an exploding metal wire in the chamber where vaporised metal would heat the
ammonia borane rapidly (something like an exploding bridge wire), using the extremely high heats of vaporisation of metals (well heat liberated upon
condensing), but then started considering more energetic versions that don't require the complexity of those particular type of power supplies and
also that wouldn't introduce metal powder into the barrel (abrasive).
First after ammonia is hydrazine (but perhaps not as practical because one component is a liquid), but the nice thing about that version is the ease
of preparation.
Then I progressed to considering even more energetic and solid combinations with hydrazoic acid. That's when I read about HAH salts and their
stability, though admittedly, harder to synthesise.
Then again, this not you're 'everyday' type of cannon 
Out of curiosity, I was wondering what the ISP of the HAH/boron propellant would be, but I don't know as of yet how to calculate ISP's when solids are
involved 
I have the flame temperature worked out and normally I would use the equation:
Ve = SQRT[(2*k/(k-1))*(R'*Tc/M)*(1-(Pe/Pc)(k-1)/k)]
where,
k = specific heat ratio
R' = universal gas constant = 8,314.51 N-m/kg-oK
M = exhaust gas molecular weight
Tc = combustion chamber temperature
Pc = combustion chamber pressure
Pe = pressure at the nozzle exit
but not to sure how to employ it in the presence of solids, someone please help!
Possibly instead of a conventional gun setup, the projectile could be fired in a self-propelled artillery fashion?
If using a conventional bullet setup, I would imagine the projectile would be best made out of a light metal to attain very high velocity... perhaps
aeronautic aluminium alloys?
****
Okay, went ahead and calculated an ISP using the Ve from the above formula assuming the solids don't have a very large effect.
The result is unbelievable, Ve = 13.5km/s with ISP=1300/s  ???
This is surely nonsense, no?
Thanks Dornier for your thoughts on this.
Attachment: ISP calculation for HAH boron propellant.xlsx (11kB)
This file has been downloaded 450 times
****
PHILOU, just saw your edits now... are those longer nitrogenic salts not frightfully unstable?
[Edited on 21-12-2014 by deltaH]
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