Sciencemadness Discussion Board

Flash Powder

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densest - 15-10-2009 at 13:12

Quote: Originally posted by Mossydie  

... and it means I don't have to use my equally unreliable fuse. It's a KNO3 / sugar one and burns well but sometimes just stops, unpredictably. I think I need three strands braided together to prevent this.

Maimed? It would need a pretty huge amount to do much damage surely? - even if I had been right next to the bit I set off, I think the danger would have been the glass flying rather than the explosion itself.

There are a number of sets of instructions on how to make blackmatch. Yes, you need to braid or twist a number of strands together to get a reliable fuse. Very quickly and approximately: Blackmatch is made by dredging a set of thin strings through a mixture of 95% black powder & 5% dextrin in an alcohol/water mixture (25% alcohol is common) then twisting and drying them. They should be somewhat flexible due to the dextrin even when fully dry. The black powder need only be KNO3/C/S finely powdered and mixed.

The danger is mostly that the deflagration gets close to detonation and the shock wave generated can shred and shatter rather than just push. Flash powder burns so quickly that a pile of it self-confines i.e. the outer layers act as wrappers or confinement causing the event to be more intense. 10 grams makes a much bigger bang than 2 x 5 grams. The American PGA usually demonstrates a pound of flash in a wooden hut - the hut is turned into toothpicks scattered for quite a distance. A pound is quite a bit, true, but the principle is similar even with 25 gram quantities.

Furthermore, KMnO4 is an extremely inconsistent and unpredictable oxidizer, much more so than KClO3 which, with S, has caused many accidents (though some people and organizations have used those together with other fuels for many years, go figure). KClO4 is usually safer still, though with benzene ring containing compounds it too can approach detonation.

1281371269 - 15-10-2009 at 14:41

Thanks for the info - I'll be sure to take more care with it. I don't have any KClO3 and though there are plenty of instructions on making it, going out of my way to produce energetics would make uncomfortable whereas I just happened to have the components of the KMnO4 one. Could you possibly elaborate on why / how KMnO4 is an unpredictable oxidiser? What's the chemistry behind this, and what are the results of the lack of predictability other than differing ignition times?

densest - 15-10-2009 at 16:39

@mossydie - I'm not sure why KMnO4 is so likely to start reacting, other than that it is a very powerful oxidizer and that MnO2 and MnO4- are both catalytic accelerators of decomposition of other oxidizers and combustion of fuels. My guess is that one or more of the following is true: the threshold energy to start KMnO4 decomposing is small, the energy released when it decomposes is large, the crystals are strained and when broken tend to initiate decomposition, the catalytic effect of Mn on combustion causes quick initiation from a small amount of energy, MnO4 directly attacks Al given a very small amount of water, and so on.

I'm pretty sure that moist KMnO4 attacks Al pretty violently. The combination can deflagrate without warning just sitting there (very rare, but it has happened) or on mixing or other friction (often enough that I wouldn't do it). A tiny drop of sweat could be enough.

If you have good dark aluminum flake, even KNO3 will make respectable flashes and moderate bangs. I would recommend making reliable fuse - a fuse that appears to go out is the first step to a disaster.

As pyrotechnics people say, "Stay green". It's supposedly from hundreds of years ago when leafy branches were uses as shields - if they were green, they didn't catch fire. Or so the legend goes.

1281371269 - 16-10-2009 at 10:24

Thanks - KNO3 is a good idea actually and I'll stick to the folding paper method of mixing.

Incidentally, here is the original formula in grams:
10.8g KMnO4 to
5.4g Al to
2g S

For KNO3 the recommended amounts seem to be 5g KNO3 to 3g S to 2g Al

Bikemaster - 16-10-2009 at 12:11

Yes, this is the good formulas.
I think it is one of the more stable flash powder, but it has some bad point, like to be not very powderful (compare to kclo3 flash) and it smell chit went much sulphur. But it is a really good flash to start .
For the mixing, start by mixing the kno3 and the sulphur togetter in a motar to get an homogene mixture. After add the alluminum powder and mix gentily with a wodden spoon.
You can use the paper method, but to get the same result, it will be much longer.

[Edited on 16-10-2009 by Bikemaster]

Formatik - 23-10-2009 at 00:11

Quote: Originally posted by densest  
@mossydie - I'm not sure why KMnO4 is so likely to start reacting, other than that it is a very powerful oxidizer and that MnO2 and MnO4- are both catalytic accelerators of decomposition of other oxidizers and combustion of fuels. My guess is that one or more of the following is true: the threshold energy to start KMnO4 decomposing is small, the energy released when it decomposes is large, the crystals are strained and when broken tend to initiate decomposition, the catalytic effect of Mn on combustion causes quick initiation from a small amount of energy, MnO4 directly attacks Al given a very small amount of water, and so on.

I'm pretty sure that moist KMnO4 attacks Al pretty violently. The combination can deflagrate without warning just sitting there (very rare, but it has happened) or on mixing or other friction (often enough that I wouldn't do it). A tiny drop of sweat could be enough.

Just gave some more thoughts on this. Note also that moist sulfur in air builds some sulfuric acid. I can see this making sulfur and permanganate unstable. Sulfur and chlorate also*. E.g. the formation of H2SO4 which has been observed: by letting well-washed sulfur flowers sit in air for several weeks eventually forms some sulfuric acid according to John (J. für Chem. u. Phys., 14,417), Wagenmann (Pogg. Ann. 24, 601). Though sulfur milk which was kept dry for 18 years was shown to be entierly free of sulfuric acid (Wackenroder, Arch. Pharm. [2] 26, 180). There might also be some additional factors also.

Metal powders and dusts with oxidants can be quite moisture sensitive. With some systems responding immediatley, like AgNO3 and Mg (flash mixture), or other similar mixtures like NH4NO3 + NH4Cl and Zn, etc. I would think those kind of issues also plague mixtures like KMnO4, Al, and sulfur.

*Spontaneous ignition of chlorate and sulfur has been noted in some literature, e.g. the Encyclopedia Americana on fireworks (of course, saftey issues like the increased sensitivity eventually replaced the chlorate with perchlorates):

Chlorates, discovered by the French chemist Claude Louis Berthollet in 1786, were first disclosed in firework compositions by James Cutbush in 1823. Other chlorate color formulas were published by Moritz Meyer (Leipzig, 1833) and F. M. Chertier (Paris, 1843). Most of them proved to be friction-sensitive and subject to spontaneous ignition because of the instability of sulfur in the presence of potassium chlorate. To avoid this problem, modern color formulas contain shellac or vegetable gum in place of sulfur.

[Edited on 23-10-2009 by Formatik]

1281371269 - 24-10-2009 at 12:59

I tried the KNO3 flash today using Mg wire as fuse and wasn't too impressed, it seems to burn much slower than the KMnO4 one. It wasn't contained, I tried .8g amount first and then a 7g amount in an open tin. It's harder to contain than the KMnO4 one because one can't simply shove it in a tin with some glycerol. What is the advantage of it over gunpowder?

Bikemaster - 24-10-2009 at 13:43

As i said, it is not a really fast burning flash. Compare to my black powder, it burn slower, but it have a big difference between this flash and black powder went the flash is contained, the explosion is much more powerful with the flash.

An other small thing, for you safety, stop using improvise fuse...
You can simply buy some on the internet for not too much (pyrodirect), or if you want someting much better,make you own e-macht. It is the cost less and the safest way to ingnite charge.
If you are not sure how to make some i can make a small turial to show.

good luck and safe your finger...they are important

1281371269 - 24-10-2009 at 13:49

Mg ribbon works surprisingly well actually with good reliability / burn rate. I'd make some but I don't have any dextrin - is it possible to do it without?

densest - 25-10-2009 at 07:41

Quote: Originally posted by Mossydie  
Mg ribbon works surprisingly well actually with good reliability / burn rate. I'd make some but I don't have any dextrin - is it possible to do it without?

You can make dextrin(e) in a home oven. Use a pure starch if you can (corn(maize)starch, tapioca starch, arrowroot starch, rice starch or powder, etc) or wheat flour if you must. Spread it out on aluminum foil or a wide metal cooking sheet in a thin layer. Heat to 125C or so (not very hot) for (say) 30-45 minutes, stirring every 5 or 10 minutes. Check frequently and remove from heat when it turns yellowish to very very light brown.

What you are doing is breaking the very long starch molecules into medium length molecules. Overheating degrades the starch too far and it is not adhesive.

Cheap (maybe $0.10 of starch) and easy.

[Edited on 25-10-2009 by densest]

1281371269 - 25-10-2009 at 09:15

I'll try this - why does the length of the molecule in this case affect the adhesive properties?

densest - 25-10-2009 at 09:59

@mossydie - this is my understanding of starchy adhesives. More knowledgeable people can add or correct as necessary.

dextrine is adhesive because the polysaccharide (polyglucose) molecules are somewhat/partially soluble and have functional groups which attract or attach to surfaces. Starches are less soluble because the molecules are long and partially crystalline and often branched so that water can't get in. Some natural starches are adhesive - glutinous/sticky rice, for instance. Dextrine is less branched and less crystalline than starch and shorter so that water can get in and lots of ends are exposed. Dextrine also has some of the glucose units charred so that they have more active functional groups exposed, increasing the attraction to other objects. The molecules bridge and tangle to bind things together in a non-crystalline way which is flexible.

If the molecules are too short, then they don't bridge gaps and don't tangle together.

Wheat flour can be boiled to make a paste - the gluten (protein) gives it most of its adhesive power. It doesn't seem to burn as well as dextrine so it isn't often used in pyrotechnic mixtures. It does bind paper well so it's used to make cases, tubes, etc.

Also, you asked what flash is good for - it's primary uses are as a very fast burning or very bright mixture. Gunpowder makes much safer bangs but requires more powder. Flash is used in firecrackers because the CPSC in its bizarre wisdom limits them to 50 mg powder each and some people like the flashes. I don't know where you live, so I don't know what laws apply. Look up "triangle salutes" for an easy and quick way to make gunpowder bangs. No matter where you are, be very careful!

[Edited on 25-10-2009 by densest]

Making e-macth

Bikemaster - 26-10-2009 at 16:54

Yes you can make e-macth without any binder. All depent on what type of e-macth that you want to make.

So has i said, i will show you how i make my e-macth.

These e-macth are really constant, cost almost nothing, can be set of but a 9V batterie,small and they are really fast to make.

Firtst, you need to find some stuff:

1. shooting wire : speaker wire are really good, and you can get 100ft for 9,99$ at the dollar store.
2. bridge wire : for my e-macht, i use 41 awg nichrome wire, and you can this for cheap there
3. pyrothecnique mixture of your choose
4.Nitrocellulose lacker: Can be made from ping pong balls and acetone.

There the nircrome and the shooting wire.

Take the end of the shooting wire and take off a small par of the protective layer, and bend the wire like on the picture. This will help to put the brige wire.

The quality of the picture is really bad, but what i made is that I put the nichrome wire from one wire ofthe shooting wire to the other, and i bend these wire completly at 180° on each side of the wire.
I put a real e-macht just to compare the size of it.
At this stage, if you want to set a charge, you don't need to put any pyrogen mixture on it.

But if you want to add some powder to your e-match, you can use this way.

With this way, it is much faster that the e-macth dipping way, because you don't have to wait until it dry.

But with this method, it will not work for fountain and rocket. Because the macth need to burn during more time. it you want to set off these stuff, you need to make you macth by the dipping way.
1.Just use the same base e-macth.
2.Make a slug with black powder and 50/50 water/methanol mix.
3.Dip the tip of the e-macth in this mix two or three time in it (let it dry between each dipping).
4.Let the macth completly dry under a light.
5.Dip the black powder tip in nitrocellulose lacker two time.(it will protect the macht from being crush from shock and prevent the water absortion.
6.Let dry the macht until it completry dry.

This macth will work for all propose, but it will be longer to make.

Good Luck

[Edited on 27-10-2009 by Bikemaster]

1281371269 - 30-10-2009 at 07:49

Thanks to both Bikemaster and densest for all the help - I think if I try any pyro again in the future I'll go for an electric fuse as it seems the easiest to time precisely and thus the safest.

User - 30-10-2009 at 09:51

Another easy method which i came up with a while ago.
Take some good quality visco fuse.
A needle (for fixing clothes)
Nichrome or constante wire.

Put the wire through the eye of the needle and give it a couple of twists.
Stick the needle through the fuse so it comes out at the other end.
Take some speaker wire and attach it to the ends of the bridge wire.
Hold the thing tightly together end apply some pvc-glue.

A big advantage is that this is very water proof if the visco is NC coated.
Also the wire ignites the fuse immediately and I found this to be very reliable.
If one is using this to set off energetics there is a visual aspect.
If for whatever reason it wont go off one can determen whether the bridge failed or not.

If course this is schematic.
One could twist the bridge around the fuse.

vis.jpg - 11kB

[Edited on 30-10-2009 by User]

quicksilver - 16-3-2010 at 13:36

Unfortunately this was made by a young fellow who did not document what he was doing (& I'm using it as an illustration only) but it's interesting. So far the only "flash" I have ever seen that explodes unconfined in that small of a weight (aside from Armstrong's & Realgar) has been this combination:

Shimizu once postulated that his strongest perchlorate flash exploded unconfined at the level of approx 50gr. However this permanganate flash design produced an explosion dropping down to the sub gram level. Although I have ;little desire to test it as the video showed a very crude test; it may be in line w/ flash made as an initiator for (or in place of) a primary. The issue here is that if such a thing occurs unconfined & permanganate designs would function w/ some stability (a might BIG "IF"), the potential for it's use in fireworks may be substantial.

Shimizu's #11 was KCLO4 64%
Al 23%
S 13%

KMnO4 60%
Al/ Mg 30%
S 10%

This individual claims it's 50%30%10%*

"An intriguing property of potassium perchlorate is it's ability to form isomorphous crystal mixtures with potassium permanganate in an apparent continuous series, reported from 3-96 mole % potassium permanganate & sited my Melor. A similar behavior is reported with Rubidium permanganate & with potassium periodate(KlO4). To this author's knowledge this possibility of influencing the reactivity of the perchlorate by "built-in" permanganate has never been pryochemically exploited".
(Ellern pp338)

* Unfortunately the author of the video did not explore this issue in a manner that would have made it useful to Ellern's dialog of Melor's work. But within H. Ellern's book is sited a few places to explore isomorphous crystal mixtures.

[Edited on 17-3-2010 by quicksilver]

Formatik - 27-3-2010 at 10:39

Maybe is there a flash possible with lead dioxide? Some flash formulas using BaO2 are known and have been used in photo flash mixtures, but none with PbO2.

Some time ago I made some PbO2 by mixing aq. lead nitrate (any soluble lead salt probably works) with excess commercial NaClO and then heating this under the bunsen burner for several minutes to convert the red-orange precipitate to dark brown, and when washed well and dry, finely powdered nearly black, partly clumpy PbO2. I looked to see if it forms a flash and investigated some of its pyrotechnic properties.

A fine mixture of PbO2 with cane sugar powder with the PbO2 in excess deflagrated weakly if it's wrapped in a tissue paper (entwined using fingers) and ignited through conc. H2SO4 (by dipping one end in it) or a match flame (it's also been claimed to ignite from friction (8 parts PbO2 to 1 part cane sugar per: A manual of elementary chemistry by G. Fownes), but I couldn't get an ignition this way). The burning was slow and without any visible flame, but the glowing and gas release was visible.

Something like 3 vol. PbO2 and 1 vol. sulfur flowers ignites easier and burned a lot faster (as well as more complete) than the sugar admixture, burning with a visible pale bluish flame. Dripping in conc. H2SO4 didn't ignite it (Bretherick's handbook claims H2SO4 does ignite it). Chemistry, inorganic & organic by Bloxam says PbO2 and sulfur in 6:1 respective mass ratio ignites from friction. Mixed with some solid fuel, PbO2 usually ignites from friction, hence past use of PbO2 in matches (e.g. old French matches).

I couldn't get mixtures of PbO2 with Al or Zn dust to ignite from flame, water or acid. Brethericks claims PbO2 "reacts violently" with magnesium or aluminium (PbO also said to "react violently" with aluminium). But if starting from magnesium dust, then yeah simpler flashes are possible with even less obvious oxidants.

Around 3 vol. PbO2, 1 vol. sulfur flowers, 1 vol. aluminium dust mixture burns lively with a flame (it's no flash powder, burning speed is similar to black powder) from a burning match. Small piles with H2O or H2SO4 showed no reaction, and no gas evolution visible.

The PbO2 looks very similar to KMnO4 except that it's dark brown and not soluble. But it also doesn't have equal reactions to that oxidant. For example, moistening PbO2 with acetone, turpentine, glycerol, or DMSO when a drop H2SO4 was added, no ignition occurred. Although in some cases like with acetone or most especially turpentine there was hefty gas evolution, but in small amounts the reaction certainly fell short of any ignition.

Powerful flash

mnick12 - 27-3-2010 at 10:56

Back in my pyro days I did quite a lot of experimentation with magnesium based flash powders. And through trial and error I have come up with a very powerful flash composition. Sadly I do not remember the exact ratio but it was some like this (by weight) 55% 250mesh mg powder, 30%KClO4, and 15% BaSO4. All I did was diaper these together then use it. This mix was very strong and gave a very satisfying thud when lit .3g quantities. It also exploded with little confinement I once took about .5g and placed it on the patio then I took a piece of masking tape and taped the powder down, lit the fuse then BOOM!-scared me. Another scary and perhaps funny thing was I took an empty center wound rocket engine filled it up lit it in my backyard, and there was a massive boom which made a crater in my back yard. Needless to say I quickly left the house and on my way down the street I saw THREE cop cars cruising down.
Ahh enough reminiscing of my kewlish pyro days. One last thing both oxidizers are needed I tried without BaSO4 and KClO4, and neither were as good.

12AX7 - 27-3-2010 at 14:43

I haven't tried BaSO4, but Ba(NO3)2 burns very hot indeed with MgAl. KClO4 would have the effect of accelerating it, being suitable for flash alone.

I'm going to guess the reason you found KClO4 alone didn't work very well is your metal was fairly coarse. Dunno, 250 mesh Mg should take a spark pretty well.


Formatik - 27-3-2010 at 17:15

If one has magnesium dust then even much milder oxidizers work for flashes. German patent 101528 describes a flash using 1 part Mg and 1 part silicic or boric acid as mixtures which burn extremely rapidly with a flash under weak thin smoke evolution (Shimizu says boric acid corrodes magnesium). Brethericks described MgSO4 mixed with Mg dust as a "noisy but low power bursting charge for pyrotechny".

[Edited on 28-3-2010 by Formatik]

quicksilver - 30-3-2010 at 08:36

It's been said that unlike Al, Mg is quite brittle and mills in a continually smaller but irregular shape. When the particulate reaches (approx) 20 micrograms or less, it's tendency to cake and clump together is such that quite a bit of care is needed aside from an anti-caking agent for a complete & intimate mix with other powdered materials. The tendency to cling and cake may also be caused by a variety of factors but super fine Mg is difficult to work with & can be extremely sensitive to static.
Under a microscope the particulates look very sharp with a huge variety of shapes. It's easy to see how this material would "clump-up" and bind to a larger mass. Mixing would be quite challenging as it could settle and bind once again. I have seen it settle as it's density is different than other materials it may have been mixed with & actually become less volatile than the equivalent aluminum (non-flake).
Seems extremely useful for stars and pyrotechnics that are mixed and then maintain that mixture through some glue-like addition. Some military flares use NC lacquer and KCLO4/Mg. As a side note there was a tragedy in Nevada awhile back from that very same mixture but the details were very sparse.

It's corrosive issues may stem from the sharp edges breaking down again & again: this may be why some treat w/ linseed oil.
It does not seem to "air float" as much as similar sized AL; especially flake. Mg simply does not appear to flake. It just breaks smaller and smaller. However it DOES float & (IMO) may be a really problematic issue. One challenge is that to bring it smaller, there are few ball-mill materials that would be safe. Milling does present some serious safety issues in that regard.

[Edited on 30-3-2010 by quicksilver]

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