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Adas
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[*] posted on 8-1-2012 at 04:03
Strange flash powder residue


Hello SM,
Yesterday I made my first FP (KNO3 + S + Al). When I ignited it, it burned slowly, because I used excess KNO3, I didn't measure anything. After burning, there was strange green residue on one place. It was green like, idk, K<sub>2</sub>MnO<sub>4</sub>.

I have no idea what it was. Any ideas?
Thanks




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Pulverulescent
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[*] posted on 8-1-2012 at 04:40


Quote:
After burning, there was strange green residue on one place. It was green like, idk, K<sub>2</sub>MnO<sub>4</sub>.
I have no idea what it was. Any ideas?
Thanks

Well it could hardly be potassium manganate unless Mn was present!
Al<sub>2</sub>(SO<sub>4</sub>;)<sub>3</sub> which can be yellowish may have formed and just looked greenish!
Nitrates, BTW, make very poor flash powders with Al!
Chlorates are much preferred for Al-based FP - but sulphur (for obvious reasons) should not be a part of these compositions!

P
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Adas
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[*] posted on 8-1-2012 at 05:36


I know, that manganate was just an example! That idea with aluminium sulfate seems interesting. And I have no chlorates, nor perchlorates, because my father always says how dangerous they are and shit... But it makes really nice light, though :D



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Pulverulescent
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[*] posted on 8-1-2012 at 06:08


Perchlorates are (quite a bit?) safer to handle than chlorates - just in case you ever find yourself in a position to make that choice!

P
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Adas
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[*] posted on 8-1-2012 at 07:20


Quote: Originally posted by Pulverulescent  
Perchlorates are (quite a bit?) safer to handle than chlorates - just in case you ever find yourself in a position to make that choice!

P


Yeah, I know this fact very well, that's why I don't like chlorates. Once I made a perchlorate cell and let it run for like a month on 5A, but the current wasn't fully used because of the graphite electrodes (I will not talk about details now). I filtered and dried it.

I was very stupid, but I put this stuff into mortar with sugar! And I started grinding hardly to see if it self-ignites. hopefully, no ignition occured. It was probably impure (Na2CO3, NaOH, other stuff...).

EDIT: and when I ignited it mixed with sugar, the reaction was fast, but NO FLAME was present! really

[Edited on 8-1-2012 by Adas]




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Pulverulescent
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[*] posted on 8-1-2012 at 07:42


Back in the day, I put a couple of ounces, mixed with dried graphite anode-sludge into a good-sized stone mortar and gave it a vigorous grinding, and to test, put the lighted end of my cigarette to some powder which had collected on the flat rim of the vessel!
The sparks went into the mortar (naturally!) and just as the deflagration began, I swung myself around to try to avoid the worst of it!
I ended up losing half a beard and one eyelash and eyebrow and weathering a tongue-lashing from my then-wife, who'd seen the cloud of smoke billowing from the shed . . .
It, the shed, still bears some of the scars inside its tin roof --- ~30 years later!

P
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blogfast25
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[*] posted on 8-1-2012 at 10:11


Quote: Originally posted by Adas  
Hello SM,
Yesterday I made my first FP (KNO3 + S + Al). When I ignited it, it burned slowly, because I used excess KNO3, I didn't measure anything. After burning, there was strange green residue on one place. It was green like, idk, K<sub>2</sub>MnO<sub>4</sub>.

I have no idea what it was. Any ideas?
Thanks


If it burns slowly it's not a flash powder, now is it??? That's a complete oxymoron. A real flash powder provides an almost instantaneous reaction, usually with very fast development of gaseous reaction products so that no or little ash is left behind.

You need to respect stoichiometry to get that type of flash powder to... erm... flash! The reactions are:

KNO3 + 2 Al === > K + 1/2 N2 + Al2O3

and

2 Al + 3 S === > Al2S3

and with an excess of sulphur:

2 KNO3 + 3 S === > 2 K + N2 + 2 SO3

All are very highly exothermic.

No sulphates are formed, as far as I'm aware.

Al/KClO3/S is certainly reported to flash, but I'm not sure about Al/KNO3/S. If I recall well, in the Al/KClO3/S flash powder, sulphur is only a minority constituent. The mixture has also been reported to be shock sensitive.

Carefully read up on these things before you experiment with them.

[Edited on 8-1-2012 by blogfast25]




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Lambda-Eyde
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[*] posted on 8-1-2012 at 10:51


KNO<sub>3</sub>/Al/S is called "slow flash" and is used as a mild break charge in pyrotechnics. Chlorates and sulfur don't mix well, and are notoriously sensitive. The number one rule of pyrotechnics is not to mix those two under any circumstances.



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Adas
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[*] posted on 8-1-2012 at 11:14


Quote: Originally posted by blogfast25  

KNO3 + 2 Al === > K + 1/2 N2 + Al2O3

and with an excess of sulphur:

2 KNO3 + 3 S === > 2 K + N2 + 2 SO3



I see no reason why potassium should be formed.




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[*] posted on 8-1-2012 at 12:09


Quote: Originally posted by Pulverulescent  
Quote:
After burning, there was strange green residue on one place. It was green like, idk, K<sub>2</sub>MnO<sub>4</sub>.
I have no idea what it was. Any ideas?
Thanks

Well it could hardly be potassium manganate unless Mn was present!
Al<sub>2</sub>(SO<sub>4</sub>;)<sub>3</sub> which can be yellowish may have formed and just looked greenish!
Nitrates, BTW, make very poor flash powders with Al!
Chlorates are much preferred for Al-based FP - but sulphur (for obvious reasons) should not be a part of these compositions!

P


Al sulphate is white. If it looks yellowish it's not pure. Once you allow for the possible presence of impurities then the green colour could be any of a whole bunch of things.
Mn isn't a rare element
http://en.wikipedia.org/wiki/File:Elemental_abundances.svg
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Pulverulescent
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[*] posted on 8-1-2012 at 13:31


Yes, the anhydrous and the hydrated salts are white!
The anhydrous salt, though, is occasionally found as yellowish crystals in the vicinity of volcanoes (or spent KNO<sub>3</sub>/S/Al FPs) as a mineral called millosevichite so the yellow tinge would, indeed, appear to be from the sulphur-impurity . . .

P
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[*] posted on 8-1-2012 at 14:53


Quote: Originally posted by Pulverulescent  
Back in the day, I put a couple of ounces, mixed with dried graphite anode-sludge into a good-sized stone mortar and gave it a vigorous grinding, and to test, put the lighted end of my cigarette to some powder which had collected on the flat rim of the vessel!
The sparks went into the mortar (naturally!) and just as the deflagration began, I swung myself around to try to avoid the worst of it!
I ended up losing half a beard and one eyelash and eyebrow and weathering a tongue-lashing from my then-wife, who'd seen the cloud of smoke billowing from the shed . . .
It, the shed, still bears some of the scars inside its tin roof --- ~30 years later!

P


That's a great story. I would love to see a film adaptation of it. Slow motion. :D




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[*] posted on 9-1-2012 at 05:58


What were you burning the flash powder on?

Could the green be external contamination?
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Adas
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[*] posted on 9-1-2012 at 08:47


Quote: Originally posted by lavenatti  
What were you burning the flash powder on?

Could the green be external contamination?


Possibly yes, it was done on a piece of concrete.. but I doubt concrete reacted anyhow.




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[*] posted on 9-1-2012 at 09:28


Was the aluminium contaminated with iron and somehow iron(II) sulfate formed?



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Adas
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[*] posted on 9-1-2012 at 10:05


Quote: Originally posted by LanthanumK  
Was the aluminium contaminated with iron and somehow iron(II) sulfate formed?


Fe <0.2%

And it was more like K2MnO4, the green colour was very nice.




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[*] posted on 26-10-2019 at 13:36


As I found out by chance, equal volumes of Aluminum powder and potassium permaganate makes a nice flash powder. And yes, there was green specs in the residue, which made beautiful green water streams when I hosed away the leftovers.
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