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Author: Subject: How to verify/identify sodium azide?
Junk_Enginerd
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[*] posted on 31-10-2019 at 11:03
How to verify/identify sodium azide?


I am in the process of making lead azide, from sodium azide and lead nitrate. I'm stuck, however, on a point that makes me a bit uncertain.

For my sodium azide, I've disassembled a vehicle airbag. Yes, I know it's dangerous and a delicate procedure, but I know what I'm doing. The extraction went just fine. Anyway, I was under the impression that pretty much all airbags use sodium azide. I watched a few youtube vids to get a feeling for what I should expect etc, and tore out the airbag from my retired crappy old car. The sodium azide is mixed with some amount of silicon carbide, to take care of the sodium that azide forms on decomposition.

What I was expecting was silicon carbide black prills. What I got out of it was red prills. This makes me suspicious. The color looks very much like red iron oxide, and it makes up quite a large amount of the total mass. Now, why would they couple sodium azide with lots of iron oxide? That doesn't make sense to me.

The prills burn very vigorously and quickly. Not fast enough for a "poof" or any kind of explosion though. I'd compare it to a sugar/nitrate mix but maybe 3-4 times faster. The prills, if ignited on only one side, like to pick up some speed and fly away like a tiny rocket. They leave surprisingly little solid residue. Maybe 5-10% of the original volume remains as a solid.

I dissolved and crushed the prills in warm water and filtered off all the solids. I noted that it seemed to generate gas when it dissolved in the water, which I found odd. No large amounts, but there was definitely some light bubbling happening.

I made a very small scale test of my intended synthesis, and mixed 1-2 ml of this solution with a lead nitrate solution. Glittering crystals formed quite rapidly, which is what I would expect if it was done with sodium azide, but I suppose the same would happen with a lot of other compounds since most lead compounds aren't water soluble.

I read some more and apparently there's quite the diversity in gas generator propellants for air bags. So, now I'm quite skeptical that it is indeed sodium azide that I've gotten.

Wikipedia has some info:
"The azide-containing pyrotechnic gas generators contain a substantial amount of the propellant. The driver-side airbag would contain a canister containing about 50 grams of sodium azide. The passenger side container holds about 200 grams of sodium azide.[100][better source needed]

The alternative propellants may incorporate, for example, a combination of nitroguanidine, phase-stabilized ammonium nitrate (NH4NO3) or other nonmetallic oxidizer, and a nitrogen-rich fuel different from azide (e.g. tetrazoles, triazoles, and their salts). The burn rate modifiers in the mixture may be an alkaline metal nitrate (NO3-) or nitrite (NO2-), dicyanamide or its salts, sodium borohydride (NaBH4), etc. The coolants and slag formers may be e.g. clay, silica, alumina, glass, etc.[101][non-primary source needed][original research?] Other alternatives are e.g. nitrocellulose based propellants (which have high gas yield but bad storage stability, and their oxygen balance requires secondary oxidation of the reaction products to avoid buildup of carbon monoxide), or high-oxygen nitrogen-free organic compounds with inorganic oxidizers (e.g., di or tricarboxylic acids with chlorates (ClO3-) or perchlorates (ClO4-) and eventually metallic oxides; the nitrogen-free formulation avoids formation of toxic nitrogen oxides)."


I guess the only thing that seems to fit with my observation is the last part which at least mentions metal oxides.

Does anyone have any helpful tips on how to be sure what it is I have, or maybe some insight into what it's likely to be? I suppose it may be relevant that the car I tore apart is a 2002 Citro├źn.
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DavidJR
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[*] posted on 31-10-2019 at 12:26


They aren't always sodium azide nowadays due to the extreme toxicity.
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[*] posted on 31-10-2019 at 16:50


My sodium azide is off-white, and looks a little like sodium nitrite.

I don't know if the stuff from azide based airbags looks like that though.
Mine is from Aldrich or somebody like that.

You probably shouldn't dissolve what you think might be sodium azide in water.
It can release Azoic(EDIT: make that hydrazoic) acid, which is poisonous, but not stinky enough to drive you out of the lab before you get a lungfull.

There are nitrate based bags too, as you said.
There's a thread on here somewhere that discusses which are which to some limited extent.


[Edited on 1-11-2019 by SWIM]





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[*] posted on 31-10-2019 at 22:44


Well, the most obvious test is to isolate and dry a small amount of the lead precipitate. If it detonates in the open in milligram amounts from flame contact, then it is probably azide.
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[*] posted on 31-10-2019 at 22:50


The azide I have now is as SWIM has described it, slightly off white crystalline powder.

I once disassembled an early model 1990s air bag before to obtain the sodium azide and it was in the form of almost black pressed pills.
They also contained potassium nitrate and a metallic powder (iron?) which was responsible for the dark colouration. When I dissolved them to synthesize lead azide for caps, this dark metal powder did not dissolve and magnetized to my stir bar instead.

There should be a warning on the airbag as well that says "danger contains sodium azide" or something similar. Mine had it on the base.





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[*] posted on 1-11-2019 at 04:13


I work in the airbag industry. I am more on the mechanical engineering side of airbags, but obviously as a chemistry enthusiast I have great interest in our inflators and their pyrotechnic composition.

Calls to eliminate azide from airbags were widespread by around 1995 and shortly thereafter all but the smallest manufacturers had reformulated their propellants.

The company I work for uses mainly nitroguanidine, biuret, dicyanamide, and tetrazoles. Another (now defunct) company made use of phase stabilized ammonium nitrate as a cost save which backfired when environmental conditioning data was faked. Eventually the foil seals on the inflators failed and swings in humidity caused phase changes in the AN which crumbled the tablets. Like gunpowder, the tablet shape and size is crucial to control burn rate, and these pulverized tablets would generate excessive pressure, bursting the casing, and resulting in a number of fatalities.

The nonproprietary side of our eBOM system shows me that our propellants also contain things like potassium perchloate, basic copper II nitrate, and titanium hydride. We also own patents on polymer bonded RDX and HMX propellant tablets although I do not know if these are in use at all.

Be extremely careful opening airbag inflators. Many modern inflators are not all pyrotechnic. We make extensive use of "hybrid" inflators which contain stored gas under high pressure, which is released through a burst disk by a small squib. Our typical fill pressure is 9045 psi, a mixture of helium and argon. These inflators run much cooler than pyrotechnic models which allows us to use nylon and PET fabrics as opposed to Nomex and Kevlar as has been used in the past. It is gentler on the fabric and gentler on the occupant, and generates far less irritating exhaust. These came about with revisions to FMVSS 226 which demand occupant protection in a rollover for up to 6 seconds post-crash, necessitating a cool-gas fill since all-pyro inflators have high exhaust gas temperatures and the gas cools quickly, causing the bag to deflate quickly in turn.

So, unfortunately airbags containing azide are rare as hens' teeth these days, which is just as well considering the danger involved with opening one. I'd recommend an alternative azide prep using an alkyl nitrate and hydrazine sulfate, which (aside from toxicity) is a pretty basic prep by wet chemistry standards.
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[*] posted on 1-11-2019 at 09:56


Moisture crumbling ammonium nitrate based powder grains.

Some guys had the exact same problem back in the late 19th or early 20th century trying to adapt ammonium nitrate to use in firearms.

The cartridge had like 1 huge grain in there, but it'd crumble burn way too fast.

Never heard of hybrid initiators before.
Sounds pretty clever.

Kinda brings to mind Bert's hypothesizing on whether Prince Rupert's drops could be used to initiate a really sensitive primer.





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[*] posted on 1-11-2019 at 10:01


I haven't looked at it in a while but I'm pretty sure my sodium azide is pure white. I may be misremembering though but I'm away from my lab and can't check at the moment.
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[*] posted on 1-11-2019 at 10:29


Yes, NaN3 is a pure white powder. I bought some from a member here about 4 years ago.
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[*] posted on 1-11-2019 at 12:51


Had a look at mine, and it is pretty white.

Maybe I actually was picturing the sodium nitrite.

EDIT: Yes, I should've actually looked at the stuff first.





[Edited on 1-11-2019 by SWIM]





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[*] posted on 1-11-2019 at 13:47


Both sodium azide and nitrite are colorless powders. For some reason colorless lead nitrate and sodium azide make a light brown, sort of orange lead azide, I don't know why.

Identification of sodium azide could be done by heating a little of it in a test tube. At around 300 degrees it decomposes quite violently, shooting molten sodium around, you will recognize it when it does so.

[Edited on 1-11-2019 by Tsjerk]
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[*] posted on 1-11-2019 at 14:59


My nitrite is very slightly yellowish which seems to be normal, but I guess this could be impurities.
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[*] posted on 1-11-2019 at 20:19


Damn, i was sure it was slightly off white too, I didnt check mine just had it pictured in my head that way as well.

If it is a sodium azide containing airbag it should have a warning stating this somewhere on it.
I found a picture of the casing of the one I took apart for you to compare the design.
The azide pellets were contained in the metal disc on left which is made of very thin metal. This sat in the vented metal conainer on the right with the initiator in the middle.

[Edited on 2-11-2019 by greenlight]

20191101_171056.jpg - 2.3MB

[Edited on 2-11-2019 by greenlight]




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[*] posted on 2-11-2019 at 13:18


Why don't you just buy reagent grade sodium azide on amazon?

https://www.amazon.com/HiMedia-GRM123-100G-Sodium-Azide-100/...

100 grams for 17 bucks isn't bad at all.
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[*] posted on 2-11-2019 at 13:52


Quote: Originally posted by Deathunter88  
Why don't you just buy reagent grade sodium azide on amazon?


In anticipation of your next 4 posts: (you're welcome)

https://www.amazon.com/Laliva-Tungsten-trioxide-WO3-microspheres/dp/B07SM5P2ZV
https://www.amazon.com/CGOLDENWALL-Spectrophotometer-Spectrometer-Laboratory-Wavelength/dp/B07YDL4C4D
https://www.amazon.com/Calcium-Metal-Irregular-Pieces-ampoule/dp/B07MJHCNJK
https://www.amazon.com/Potassium-Nitrate-Reagent-Purity-Granulated/dp/B07XK9RMFY

[Edited on 2-11-2019 by S.C. Wack]




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