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Author: Subject: Stability of sodium azide in solution?
Douchermann
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[*] posted on 10-12-2007 at 21:23
Stability of sodium azide in solution?


Hey guys, I was wondering if sodium azide would decompose if it was in boiling distilled water. I have an air bag module (I seperated the firing chamber from the actual bag) and it's impossible to open. I was hoping to let it sit in boiling water for some time to hopefully dissolve all the sodium azide out. And also, would boiling down to reduce the volume decompose it? What is the solubility at those temperatures, I can only find 17C. I would be using distilled water by the way. Thanks guys.



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[*] posted on 11-12-2007 at 13:31


I don't have much to add other than the solubility data.

Edit:

These references should have the data on the stability of sodium azide.

Thermochimica Acta. 284 (2): 441-444.

Gakkaishi. 51(3):148.



[Edited on 11-12-2007 by PainKilla]

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[*] posted on 11-12-2007 at 13:34


More info on azides, and the references:

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[*] posted on 11-12-2007 at 13:43


Thermal Stability of Sodium Azide (Gakkaishi. 51(3):148.)

Yasuhiro FUJIMOTO, Takayuki ANDO and Shigeru MORISAKI

Abstract : Though chemical accidents have occured over and over, some part of these accidents are based on unstable chemical substances. These chemicals easily decomose or igniteby heats or mechanical shocks under an atmosphere of not so much high temperature.

In this paper, sodium azide was chosen as an example of unstable chemical substances. Sodium azide is used in the preparation of hydrazoic acid, lead azide, pure sodium or as propellant for inflating automotive safety bags, etc. It is no doubt that sodium azide is more stable than other azides, however, the danger not been assessed satisfactorily.
Thermal decomposition of sodium azide is shown as follows.

2NaN3 ==> 2Na + 3N2 (1)

It is known that the decomposition takes place at 300*C. In addition, the heat of decomposition has been reported. However, these results were obtained about half a century ago and the other thermal analytical results, in particular under an adiabatic condition, have seldom been reported ever since.

And sodium azide reacts chemically active organic halides as follows.

RCl + NaN3 ==> RN3 + NaCl (2)

But reactions between sodium azide and organic halide polymers have not been reported yet. Hence, this paper describes the results of the following two subjects about thermal stability of sodium azide.

1. Thermal decomposition of sodium azide

(1) Decomposition temperature and heat of decomposition

The experiments were carried out by DSC in air and argon atmosphere. The decomposition temperatures were about 430 *C in air and about 400*C in argon atmosphere. The heats of decomposition were about 90 kcal/mol in air and about 10 kcal/mol in argon. Obviously, the mechanism of thermal decomposition in air is different from that in argon. This is because metal sodium, which is produced through thermal decompositon of sodium azide, is oxidized by oxygen in air.

(2) Weight decrease by thermal decomposition
The experiments were conducted with TG-DTA in the above two different atmospheres. In air, the weight goes back considerably after a decrease in the weight by the decomposition of sodium azide to pure sodium and nitrogen. But in argon, such a phenomenon was not observed.
These results show that the sodium is certainly oxidized in air after decomposing of sodium azide. The following reaction scheme is estimated according to the above results.

4NaN3 + 02 ==> 2Na2O + 6N2 (3)

(3) Self-heat rate and pressure under an adiabatic condition
The experiment under an adiabatic condition was carried by ARC only in an inert gas. Beginning of self-heat of sodium azide was observed at around 335*C, and the following decomposition was too fast to follow the increase in the self-heat rate with ARC.

2. Reactions between sodium azide and organic halide polymers

(1) Measurements under programmed temperature
DSC was also used for the experiments in an atmosphere of air. The decomposition temperatures of any organic polymers, such as polyethylene, polypropylene, polyvinylchloride and polytetrafluoroethylene, were not changed in the presence of sodium azide, and no DSC-peaks due to exothermic decomposition were observed.

(2) Measurements under fixed temperatures

The experiments were carried out by DSC for providing another evidence in confirmation of no reactions between organic halide polymers and sodium azide. No exotherms were observed at the constant temperature of 300*C for 2 hrs which might arize by the reactions between the polymers and the azide. The above results show surely that sodium azide may be thermally stable with organic polymers at relatively high temperature.

[Edited on 11-12-2007 by PainKilla]
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[*] posted on 11-12-2007 at 14:58


I wonder how relevant these data are considering he proposes to place the material in boiling water? It doesn't seem likely that thermal decomposition at 300 deg. is going to happen at 100 deg in water. It is an ionic substance so trinitride ion is the species involved as soon as water gets to work on it. I suppose since it's an airbag the material could get heated a bit before solvation but not to anywhere near 300. Isn't there some safety data on it? What is supposed to happen to it if a car catches fire? Must be a lot less of an issue than the fuel.



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[*] posted on 11-12-2007 at 17:45


When I got azide from airbags I just used a saw to get it out... 30 mins of careful sawing and it'll be done (assuming they're all more or less standard in their construction). That's less time than it'll take you to boil down the water and crystalise the sodium azide using your poposed method (although I don't doubt that what you suggest will work).
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[*] posted on 11-12-2007 at 17:47


P.S. - http://en.wikipedia.org/wiki/Solubility_table

It's quite useful, although in this case it doesn't give much info.
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[*] posted on 11-12-2007 at 18:56


I wouldnt recommend it.
NaN3 is used in biochem for preventing fungal/bacterial growth. Usually a 0.1% solution is used. It is always said though that these solutions don't last long, a few weeks at the very most, at 4 deg. I wouldnt want to think about what happens when you boil it.
Try to precipitate it with i.e. Pb and resolubilise with (without ever working with the dry material) NaOH? The PbOH2 thus formed is insoluble.




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[*] posted on 11-12-2007 at 18:57


and there is this

http://www.geneseo.edu/~ehs/Lab%20and%20Art%20Studio%20Safet...

http://www.ehs.neu.edu/hazardous_waste/fact_sheets/sodium_az...
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[*] posted on 16-12-2007 at 20:05


NaN3 forms small amounts of hydrogen azide with water. Actually i've heard NaN3 + H2O is used to produce HN3, but I've also heard that only trace amounts of HN3 are produced.

Apparently a KNO3/NaN3 mixure is used, not just NaN3

I'm sorry I couldn't give you something more useful, like a solubility table.

But, just out of amateur curiosity, why not use a ketone or alcohol as the solvent?




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