Fulmen
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Metal diamine salts for PSAN
It looks like Nakka might have come across something close to the holy grail of amateur propellants, a fast burning, 200+ Isp ammonium nitrate
composition with only OTC ingredients: http://nakka-rocketry.net/anexp.html
And while phase stabilization isn't an absolute requirement it is nice to know that the fuel can be stored for for extensive periods. Besides, it's a
fun challenge.
The simplest method seems to be 10-15% KNO3, but it will reduce Isp and probably change the burn properties compared to straight AN. So my first focus
is on more powerful stabilizers like zinc diamine nitrate. This one only requires 1-2% and seems to be one of the best documented stabilizers.
This patent seems to cover everything needed: https://www.google.com/patents/US5071630
Basically zinc diamine nitrate is produced by adding zinc oxide to molten AN according to this reaction:
ZnO + 2NH4NO3 = Zn(NH3)2(NO3)2 + H2O
Unfortunately the water can cause the diamine to decompose into zinc nitrate, so dry ammonia must be passed through the dried melt to replace lost
ammonia. This must be assayed as an excess will produce the tetraamine complex which isn't a good stabilizer. While fine for commercial mfg it's not
really suited for the amateur, so a better method must be found.
The first major obstacle is the lack of info on these compounds, if anyone has more knowledge please feel free to share them. But from what I can
gather it should be possible to produce the diamine by mixing equal molar amounts of zinc nitrate and zinc tetraamine nitrate, and the tetraamine can
be made by passing ammonia into molten AN containing zinc nitrate.
This still require a somewhat complicated setup, so I was wondering if the tetraamine salt could be isolated from aqueous chemistry somehow.
There might be other options as well, it seems that Zn can be substituted with either Ni or Cu (http://www.google.com.pg/patents/US6508995). Perhaps one of those diamines are less likely to decompose?
This patent also mentions hydroxides and carbonates, if the carbonates can react with AN to form the diamine no water would be produced. Then the
question becomes whether or not the pure carbonate can be isolated. Copper only forms the basic carbonate from aqueous reactions, I'm not even sure if
it can be isolated at all. I haven't found anything conclusive on Zn or Ni yet.
Any thoughts?
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nitro-genes
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Both zinc nitrate and ammonia are very soluble in ethanol, (maybe isopropanol as well) if the di/tetramine complex isn t, adding together cold
solutions of both may precipitate the complex salts directly maybe? Maybe adding strong ammonia to a solution of zinc nitrate in ethanol would also
work, simplifying things.
[Edited on 23-11-2017 by nitro-genes]
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Fulmen
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Good idea. Even if it is soluble it could be possible to prepare the amine by passing ammonia through the nitrate dissolved in ethanol. Just wish I
could find some more info on those salts. At some point I need to verify their presence, do they make any interesting reactions? I guess an acid
titration is the simplest test.
We're not banging rocks together here. We know how to put a man back together.
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Fulmen
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After thinking it through I realized that the carbonates will release exactly the same amount of water, so that's not going to work any better.
I have however found several references to copper diamine nitrate (https://www.google.com/patents/US6372191), it also mentions mixing the tetraamine with the nitrate to produce the diamine. It seems like it's
possible to produce the diamine directly from CuO and AN, but I'm unsure if this will cause the same problems as with the zinc compound (loss of
ammonia due to aqueous conditions). But luckily there are a ton of information on copper tetraamine nitrate available, guess I have some more reading
to do.
I haven't found too much data on the performance of Cu-stabilized PSAN, so this might be another wild goose chase. But it's the most promising
candidate so far.
We're not banging rocks together here. We know how to put a man back together.
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Fulmen
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Good news everybody. It seems like CuO makes for a good stabilizer (see attached PDF). This raises the hope of finding a direct route.
I must admit it would be fun to characterize these compositions myself, rather than relying on others results. DTA seems to be a good, simple analysis
for this, and it's not outside the realm of DIY. I think I'll borrow an arduino and see if I can jerry-rig something together. I already have a couple
of peltiers that would be perfect for temperature control.
Attachment: engel1985.pdf (222kB)
This file has been downloaded 437 times
We're not banging rocks together here. We know how to put a man back together.
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Fulmen
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A DTA seems like a doable project. I'm waiting for an arduino, first project will be temperature control. That's useful for a number of projects and
there are ready made software for this. Next would be the differential measurement. I'm thinking K-element fed to an instrumental amplifier should
work?
We're not banging rocks together here. We know how to put a man back together.
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underground
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Pls keep us update Fulmen, i am interested in this subject too!
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Fulmen
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Nice to hear.
Feel free to read up on what's out there, if you start digging through the research and patents you'll find a lot of info.
I have taken a step back to designing a DTA for this project (/viewthread.php?tid=78663). Reading papers is fine, but I want to develop a method that
produces consistent results with a minimum of equipment and effort. And the only way to verify this is to test it.
We're not banging rocks together here. We know how to put a man back together.
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