| Pages:
1
2 |
Vomaturge
Hazard to Others
Posts: 286
Registered: 21-1-2018
Member Is Offline
Mood: thermodynamic
|
|
I think AJKOER is talking about the warning of SDIC or TCCA forming traces of NCl3 with water. As far as wg48's original accident, I think it was
caused by the self-sustaining exothermic thermal decomposition of SDIC.
[rquote] it appeared to be in thermal runner way with steam rapidly issuing from the loose cap. I was about to dump the tube when its contents
rapidly decomposed propelling at least part of tube into the side of a small oven.
[rquote]
assuming that the tube had a cap that had not yet been removed when it burst, this is exactly what I'd expect. I don't know what the cap was like
(rubber stopper? Threaded?), but the fact that a big portion of the tube flew apparently in one piece like a rocket, busted a hole in the oven, then
shattered? That seems like a deflagration to me. The exact details of the incident are important, but now that we know SDIC creates enough heat to
sustain its own decomposition, it seems plausible that no other energetic materials were present.
Quote: Originally posted by wg48  |
Probagation testing:
From DOI: 10.1002/prs.680220202
Estimated decomposition enthalpy -1000cal/g
self-sustaining thermal decomposition reaction approximately .06 to 0.1 cm/s. Max temperature 600C
Onset of decomposition approximately 90C, with maximum rate at 150 to 200C
Decomposition products
From https://pubs.acs.org/doi/pdf/10.1021/ie502154b
"Starting from these results, we have characterized two decomposition reactions for SDIC, both giving two molecules of chlorine isocyanate (Cl-N=C=O)
and one molecule of sodium isocyanate (Na-N=C=O). However the first path corresponds to a two steps mechanism while the second is composed by a single
step. The first reaction, shown in Scheme 1, involves an initial breaking of two nitrogen - carbon bonds (G≠ = 44.1 kcal mol-1) to form a molecule
of chlorine isocyanate. The rest of the initial cycle decomposes with a low energetic barrier (G# = 12.6 kcal mol-1) to form another chlorine
isocyanate and a sodium isocyanate molecule. The second path involves a concerted breaking of N1-C2, N3-C4 and N5-C6 bonds of SDIC (see Figure 1) but
its energy is too high to be competitive (G = 48.0 kcal mol-1) with the first proposed reaction."
[Edited on 12-2-2018 by wg48] |
parameters like burn rate also depend on wether the material is a solid block, wether the burning surface is able to vent gases (or wether the gas
gets forced deeper into the powder, heating it further), what pressure the reactant is under, etc. It seems logical that preheating the material would
make it burn faster too, because it would require less heat transfer to reach ignition temperature deeper in the powder. It is my uneducated opinion
that preheating made less than a gram of ETN DDT in an open test tube, causing this accident here:
https://www.sciencemadness.org/whisper/viewthread.php?tid=16...
By getting a large piece of energetic material within a few degrees of its ignition point, you make it more sensitive to further temperature increase.
When one part does ignite the burst of heat/pressure effects the rest of the sample much more than it would at room temperature.
By the way, I would kind of expect the same damage pattern from a NCL3 accident as from ETN. The glass would probably fly in all directions, with a
stronger explosion making smaller, much faster fragments. It would be more radial, and less coherent. Of course, I don't know. Maybe the tube was
against the oven, and the big hole was made by a dense shower of fragments, or even the blast pressure itself?
[Edited on 24-2-2018 by Vomaturge]
|
|
|
wg48
National Hazard
Posts: 821
Registered: 21-11-2015
Member Is Offline
Mood: No Mood
|
|
The oven was 2 to 3ft away. Only three fragments of glass (two with threads) and one piece of the threaded cap were found in the opposite direction of
the oven. That suggests the capped end failed first injuring my finger and propelled a mostly intact tube into the oven where the all but the three
pieces of the tube were found. The oven is old. I suspect the plastic is brittle from repeated heating cycles.
I think tests will confirm rapid decomposition due to the temperature and partial confinement of the decomposition products. I may perform some
outside tests soon undercover of burning garden rubbish. I don't want to alarm my neighbours.
I guess the morale of the story is if this experiment unexpectedly goes bang have I mitigated the risks. I think I was lucky my hand or more could
have been seriously injured. I only had eye protection.
An other one would be don't use a loose screw cap as a vent use a cottwool or glass wool plug or none.
From my camping days: If you wrap a strike anywhere match head in Al foil then throw it in to a camp fire it does not go pop. If you place it near the
edge of the fire in just the right position such that it heats up slowly, it will frequently make a bang. Occasionally matches thrown in to a camp
fire that land near the fire or on the cooler side of wood such that they heat up slowly can ignite so quickly that they are propelled out of the
fire.
[Edited on 24-2-2018 by wg48]
|
|
|
Vomaturge
Hazard to Others
Posts: 286
Registered: 21-1-2018
Member Is Offline
Mood: thermodynamic
|
|
Thanks. Sounds like the stuff deflagrated as described in the link you gave. Heating the substance to 90-250 C makes it produce gases, and more than
enough heat (600C! ~4 kj/gm!) to propagate the reaction. Like a fuel/oxidizer mixture, or an unstable compound like nitrocellulose, this substance has
variable burn rate. The experience with match heads supports the theory that burn rates can be increased by preheating. The fact that a propellant/low
explosive can cause a closed container to explode is hardly surprising. A loose cap is probably good enough for an experiment involving slow
endothermic decomposition or evaporation, but energetic materials (including slow burning thermites and KNO3/sugar mixes) if they must be heated,
likely need to be in an open pan, preferably well away from the operator!
What did surprise me, though, is that this material decomposes energetically, and that this property is not well known. The Wikipedia page on sodium
dichloroisocyanurate talks about it as a cleaning agent, mentions a luminescent reaction with hydrogen peroxide, but says nothing about the fact that
it is a low explosive! Of course, nitrocellulose, ammonium nitrate, and picric acid all have (or had) non explosive uses. I still wish the MSDS would
let you know when something is known to decompose violently on heating:
http://www.essef.be/images/documenten/004800_vf1_E.pdf
They describe it as producing toxic fumes on heating, but nothing about how it decomposes, or what to do if a not-quite-sealed barrel or shipping
container of it is hissing and smoking. Run!
|
|
|
wg48
National Hazard
Posts: 821
Registered: 21-11-2015
Member Is Offline
Mood: No Mood
|
|
Vomaturge: The MSDS was written in 2015 and states that it is “presented in good faith and believed to be correct as of the date of publication”
but that accident report was written in 2003!!!
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by Vomaturge | I think AJKOER is talking about the warning of SDIC or TCCA forming traces of NCl3 with water. As far as wg48's original accident, I think it was
caused by the self-sustaining exothermic thermal decomposition of SDIC.......
[Edited on 24-2-2018 by Vomaturge] |
I found a prior comment by Woelen relating to some NH2Cl formation, which is described as, not normally expected, and which I have suggested as a
possible minor reaction path upon hydrolysis:
| Quote: Originally posted by woelen | The TCCA is pure. The bottle says "92% active chlorine" and this is near the theoretical value for 100% pure TCCA.
I also have severe doubts about CO. CO is strongly reducing and how could such a gas be formed in such a strongly oxidizing environment? I myself tend
to believe more and more that it is NH2Cl, but unfortunately very little information can be found about this compound. Most information is about
swimming pools and about water treatment with very dilute solutions of NH2Cl, but of course that information does not tell anything about flammable or
explosive properties of the more or less pure gas.
The smell of the gas mix is really bad. It is not as strong as the smell of chlorine, but its strength comes close to it (the actual smell, however,
is quite different from the smell of chlorine). You must very carefully whiff some of the gas to your nose and certainly should not stick your nose in
the test tube. If you do that, then you'll certainly get the mother of all caughs.
I can imagine formation of NH2Cl from TCCA as follows:
TCCA contains -N(-Cl)-C(=O)- chains. These could hydrolyze to NH2Cl and H2CO3, but normally this does not occur. The oxidizing nature of the
hypochlorite may lead to oxidative breakage of the ring and then the above mentioned hydrolysis may occur. At the same time, part of the N-atoms must
end up in oxidized species, most likely N2. The -C(=O)- part would end up in carbonate ion, while the -N(-Cl)- part hydrolyzes and picks up hydrogen
from water, the OH-group from the water then goes to the -C(=O)- part and becomes part of a (bi)carbonate ion. So, the gas produced would be a mix of
N2 and NH2Cl, with at least one molecule of N2 for 4 molecules of NH2Cl, but probably more of the N-atoms are oxidized and a larger part of the
nitrogen ends up as N2. What remains behind in solution is carbonate ion and chloride.
Cyanuric acid does not contain -N(-Cl)- parts. Its triol-form contains -N(-H)- parts and its triketol-form contains aromatic -N-C-N chains. I can only
imagine oxidative cleavage of the ring structure to occur with formation of N2 and hydrolysis to NH3 and carbonate ion. The NH3 then immediately is
destroyed by excess bleach and nearly all is converted to N2.
[Edited on 18-6-13 by woelen] |
Link: http://www.sciencemadness.org/talk/viewthread.php?tid=24659
[Edited on 27-2-2018 by AJKOER]
|
|
|
| Pages:
1
2 |
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
