hossam6006
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Urea Nitrate + Aluminium Reactivity
I tested a mixture of UN:AL / 12:1 many times without problems, but yesterday after 4 hours, the mixture was reacting producing heat and bad smell, so
I disposed the charge immediately.
I know many who mix UN+AL and detonate it without problems.
checkout this one: https://www.youtube.com/watch?v=5SpTofaUY0I
Some people reported similar accidents when mixing UN with AL powder.
My guesses are:
- Bad washing of UN: I wash my UN after nitrating under a stream of cold water, shouldn't that be sufficient? I also tried washing
with sodium bicarbonate, but I was advised not to do so because UN solution is acidic and that would result in the decomposition of sodium
bicarbonate.
- Al shouldn't be mixed with UN at all: UN is acidic and it would react with aluminium powder producing Al(no3)2 ?! and the
passivization layer (https://en.wikipedia.org/wiki/Aluminium_nitrate) is not sufficient to stop the reaction because of the large surface of powdered aluminium?!
- summer heat is the reason: mixtures I prepared earlier was is winter?
My questions are:
- Is my washing process sufficient? should I use sodium bicarbonate for washing?
- what's the reaction that's taking place here (UN+AL)?
- what's the best way to prepare the mixture?
[Edited on 21-8-2013 by hossam6006]
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Nicodem
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Thread Moved
21-8-2013 at 09:09 |
Marvin
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Aluminium and Nitrates are usually a problem combination, when nitrates are reduced they turn into ammonia which increases the pH and accelerates the
reaction by removing the passivating oxide layer. Might be what is going on. In pyrotechnics boric acid is sometimes used to stabilise the mixtures
but that is for alkali nitrates and may not be an option.
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hossam6006
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that's true Marvin
But AL powder is a very common additive to many explosives, propellants and oxidizers including nitrates. (e.g ANFO, KNAL, ...)
should that be a mistake too, due to the reduction you mentioned? are there ways to minimize this reaction to a safe/stable level?
and what about nitro- explosives (e.g NC, NG) ? can I safely mix them with AL powder ?
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AndersHoveland
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Urea nitrate may be a little more acidic than ammonium nitrate, and also it is quite possible that the urea may be facilitating dissolution of the
passivating layer, whereas with ammonium nitrate all the ammonia is tied up in the form of the ion and cannot complex.
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Marvin
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Water alone causes problems with fine aluminium powder but it's generally more stable with mild acid than mild base. Magnesium mixtures are the other
way around and you can spot this in the formulations. All the components of commercial ANFO are very highly processed, powder density, impurities and
are generally mixed just before use. Ammonium nitrate is a hygroscopic nightmare and I would expect aluminium used to have additional protection,
plastic, chromium, laquer. Must be something in Urbanski about this. I don't know that Urea Nitrate is not a nightmare, the only time I've heard of
it being used is the 1993 WTC bombing.
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hossam6006
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Thanks guys, problem solved.
Both AN and UN are acidic, but sodium bicarbonate should never be used for washing!
I tested 2 samples: 1 washed with pure water and the other with 5% sodium bicarbonate solution, the latter had a huge heat after 4-6 hours.
I thought It would vanish HNO3 traces and result some good NaNo3, but it looks like it's working as a catalyst accelerating the reaction and removing
passivation layer
| Quote: | | Ammonium nitrate is a hygroscopic nightmare and I would expect aluminium used to have additional protection, plastic, chromium, laquer.
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UN is as powerful as AN, it's not hygroscopic nightmare but it has a negative oxygen balance.
And no, AL powder should never be coated with anything! it should be as fine as it can be. if coated you could end up with a deflagration instead of
an explosion.
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