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caterpillar
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[*] posted on 22-1-2012 at 01:33
Unexpected reactions


I think, some of you, folks, met reactions, that you was not waiting for. It would be useful to share this experience, because when you are working with energetic materials most of such situations are of potential danger. Once I prepared R-salt. Preparation was simple and gave me 20-30 gr of thin and light yellow crystals. I mixed it with AN. This mixture, been ignited, burned violently. It was rather interesting, because most of mixtures of AN with reducing agents burned slowly (and this is why I failed, trying to use AN as oxidizer in solid propellants). I was in doubt, or to use AN+R-salt as a rocket propellant, or to simply explode it. I thought for some days, and once at the morning something happened. It was not an explosion nor open flame arose, but within one second the plastic bottle with aforementioned mixture transformed into gray clouds of smoke. I have a solid guess now, that this reaction was caused by trace amount of nitric acid, normally presenting in AN. I met another unexpected reaction (not so violent) during my attempts to replace mixed acid by H2SO4 +Me(NO3). I made picric acid, and all was good with Me=K or Me=Na. But I met problem with NH4NO3. At the final stage entire reacting mixture must be kept for one our at 100 Celsius by mean of boiling water bath. It produces very small amount of red fumes, but when I used NH4NO3 instead of KNO3, intensity of generation of nitrogen oxides began to increase. Finally I had to stop this process and threw reacting mixture into large volume of cold water. Generation of nitrogen oxides had another unpleased result: reacting mixture increased in volume and overwhelmed my flask. May be, these reactions are described somewhere, but I've never met such info.




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[*] posted on 22-1-2012 at 02:13


Quote: Originally posted by caterpillar  
I think, some of you, folks, met reactions, that you was not waiting for. It would be useful to share this experience, because when you are working with energetic materials most of such situations are of potential danger. Once I prepared R-salt. Preparation was simple and gave me 20-30 gr of thin and light yellow crystals. I mixed it with AN. This mixture, been ignited, burned violently. It was rather interesting, because most of mixtures of AN with reducing agents burned slowly (and this is why I failed, trying to use AN as oxidizer in solid propellants). I was in doubt, or to use AN+R-salt as a rocket propellant, or to simply explode it. I thought for some days, and once at the morning something happened. It was not an explosion nor open flame arose, but within one second the plastic bottle with aforementioned mixture transformed into gray clouds of smoke. I have a solid guess now, that this reaction was caused by trace amount of nitric acid, normally presenting in AN.


Dude, escuse me.. Its just my humble opinion, but r-salt is a extremely dangerous stuff. The real safety-concerning unexpected reactions are nitrosamine reacting with substances in your body to give you cancer. Know highly carcinogen stuff.. Simple to make though..

Hope you (or anyone around you) didnt have inhalated any of the gray smoke, neither from rocket propellant composition nor from plastic bottle.. Most probably contained some r-salt as aerosol/or in gas phase.

Quote:
I met another unexpected reaction (not so violent) during my attempts to replace mixed acid by H2SO4 +Me(NO3). I made picric acid, and all was good with Me=K or Me=Na. But I met problem with NH4NO3. At the final stage entire reacting mixture must be kept for one our at 100 Celsius by mean of boiling water bath. It produces very small amount of red fumes, but when I used NH4NO3 instead of KNO3, intensity of generation of nitrogen oxides began to increase. Finally I had to stop this process and threw reacting mixture into large volume of cold water. Generation of nitrogen oxides had another unpleased result: reacting mixture increased in volume and overwhelmed my flask.


As for ammonium nitrate problems, see attached paper, it was already posted, unfortunatelly I didnt succeed to find it. According to it and to your picric acid synthesis report:

- impurities (chlorides, etc)
- very low pH (H2SO4)
- high temperatures
- organic stuff

All of this combined could be the reason of your NOx runaway.

Remember N2O could be made too with NH4NO3/H2SO4 system (in different reaction conditions).

Quote: Originally posted by AndersHoveland  
There must be impurities, because as much as I know there should not be any bright red color in the reaction of concentrated H2SO4 and NH4NO3. Nitrogen dioxide, however, can give the solution a redish-brown color.

I have also read that the use of ammonium nitrate, rather than sodium or potassium nitrate, in nitrations can sometimes be problematic. NH4NO3 has the advantage that it is much more soluble. But reaction with concentrated sulfuric acid can also cause some decomposition.

When ammonium nitrate is heated with concentrated sulfuric acid, about 85% of its nitrogen is given off as nitrous oxide. Most of the remainder as nitrogen gas. Typically, ammonium nitrate is only dehydrated when a large excess (50 times as much) of sulfuric acid is used and the temperature is raised to 150degC.
http://pubs.acs.org/doi/abs/10.1021/ja01681a501

Attachment: NH4NO3.pdf (104kB)
This file has been downloaded 448 times

[Edited on 22-1-2012 by Aqua_Fortis_100%]




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[*] posted on 22-1-2012 at 15:21


About R-salt: when I made it, I did not know about properties of nitrozamines. But, due to the fact that I'm still alive (described situation occured many years ago) it did no harm for me. Fast and exotermic reaction between R-salt and NH4NO3 surely destroyed all N-NO groups, thus inhalation of gray smoke was not very dangerous. About NH4NO3: I did same process with KNO3 without any problem. Amount of NO2 was very small. Dehidratation of NH4NO3 gives N2O, which is colorless. Therefore, oxidation was caused by NH4+ (?) or concentrration of HNO3 or... I do not know. But, I think, H2SO4 + NH4NO3 may be used at low temperature as a nitrating agent.



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[*] posted on 22-1-2012 at 15:43


Gray smoke is a sure sign of incomplete reactions in compositions (negative OB and/or not very efficient mixing of components), so probably most of the R-salt were destroyed and some was carried with by-products by smoke. And note that most cancers will take years to fully develop. Hope you is really ok. (Sorry, Im not trying to discourage you, but cancer is one of the biggest killer today and all, rich and poor people is exposed to it, more or less.. So, trying to avoid it, is the best one could do.)
You could of course oxidate nitrosamine group to nitroamine, giving you RDX in this case, but of course yields are low (specially when based on starting hexamine).


Yeah, about NH4NO3 I dont believe too in great amounts of N2O formed (if any) in your nitrating mix, but still there is a close 'window' of parameters (temperature, contaminants, etc) that could lead to much greater N2O yields.. And I too give my bet, for safety sake, to use NH4NO3 nitrating system only at low temperatures..

Cheers.

[Edited on 22-1-2012 by Aqua_Fortis_100%]




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[*] posted on 22-1-2012 at 21:01


Oh, yeah, you are asolutely right about using H2SO4+NH4NO3 only at low temperature (for example, for preparing nitrourea or hexamine dinitate). That incident, that I narrated about, took place at 1971-73, I cannot tell more precisely. I think, now I can sleep well- R-salt will not be cause of my death. My nitrating mix generated not N2O, but NO2. And all what was in reaction vessel (is it a proper term for a glass from-under cucumbers in marinade?) was fulfield with red bubbles and started to move away.



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[*] posted on 23-1-2012 at 11:44


Hello caterpillar, Im glad you ok.

I suspect Ive found the reason of your r-salt incident:

Maybe you have already readed this, from r-salt thread:
http://www.sciencemadness.org/talk/files.php?pid=59793&a...
(pdb's translation of memorial des poudres)

Quote:
Both TMTN and DNPMT are both decomposed by acids, the latter violently with
concentrated acids. A way to separate mixed products in to dissolve them in hot 25%
acetic acid: DNPMT decomposes very rapidly, while TMTN is only slightly attacked. The high sensitivity of DNPMT to acids explains why spontaneous and violent decomposition of DNPMT+NH4NO3 mixtures have been observed.


This means your r-salt could be impure when you made it (lack of acid, or weak acid - pH not low enough - in the procedure, giving a mixed product CTMTNA-DNPMT).

[Edited on 23-1-2012 by Aqua_Fortis_100%]




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[*] posted on 23-1-2012 at 13:11


Making more than very small batches of "R-salt" is potentially hazardous because of the toxic/carcinogenic nature of nitrosamines. Use appropriate precautions and ventilation.
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[*] posted on 23-1-2012 at 14:59


Oh, yeah, oxidation of R-salt to RDX requires low temperature (-30 Celsius). it means, of course, that oxidation at higher temperature will go violently. Well, thanks to you all: I will make R-salt no more!



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