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Author: Subject: Metal diamine salts for PSAN
Fulmen
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[*] posted on 23-11-2017 at 07:09
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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[*] posted on 23-11-2017 at 09:19


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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[*] posted on 23-11-2017 at 09:42


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.



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[*] posted on 24-11-2017 at 09:01


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.




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[*] posted on 26-11-2017 at 02:07


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)
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[*] posted on 28-11-2017 at 05:17


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?



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[*] posted on 7-12-2017 at 11:00


Pls keep us update Fulmen, i am interested in this subject too!
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[*] posted on 7-12-2017 at 12:26


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.




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