economical flash.

[scarletmanuka]

Cost is a very important part of our hobby, yet it is not often mentioned. I have been interested in the best composition to use to mass manufacture small fire crackers so I conducted a test of flash compositions from easily available chemicals in Australia. The 'crackers' are small equilateral triangle firecrackers made from a paper strip about 2cm across and thirty cm long. It was not taped or glued.The fuse is about 1mm thick. Generally, they contain about 1/4 to 1/2 gm flash. I filled the casings completely due to the fluffy nature of the Al. I used electronic balance accurate to 0.001 grams and weighed out 1 gram of composition at a time. they were mixed on paper. KNO3, KMnO4 and S grinded seperately before use to a talc like consistency.

I tested five different comps:
To save time I have designated the compositions with a number.
1. KNO3 70
S 10
Al 20

2. KNO3 50
S 20
Al 30

3. KMnO4 70
S 10
Al 20

4. KNO3 50
S 20
Al 30
KMnO4 10
( I know the % doesn't add up)

5. Straight AP

The KNO3 was 2$ for 1 kilo and was 100% (and made in israel). Found in a perth hydroponics store.
The KMnO4 was $4.30 for 50g and 1g/g, found at chemmart
Sulfur was $12.50 for 1 kg at hardware, says 100% on packet but probably contains alot of acid. Also large crystals.
Al was 5$ for 50gm of "Aluminium lining" at art supply store, very very fine, but has some oil added i think. Tried drying in oven at 250C for an hour, but didn't do much. Expensive, but worth it for it's v.small particle size. For some reason it is quite fluffy, so adds good filling for your composition. It can be removed with acetone, but it is too hard and messy.
An expensive day out, but I have enough to last me for a long time now.

The test
Composition 1. This is obviously the cheapest comp, but if you pay peanuts you get monkeys, and this was pretty poor. It mostly failed to ignite, and when it did, it just flared up, no report at all.
$2.29 for 100gm

Comp 2. This was closer to good flash with a loud report and a v.bright flash, however it failed to break the triangle cracker, and just expanded the fuse hole.
$3.40 for 100gm

Comp 3. I discovered this flash long before i could get KNO3, and it has excellent performance. It never failed to ignite with a loud report, and rip the paper casing to shreds. However, the flame is not as bright as the KNO3 comps.
$8.17 for 100gm

Comp 4. This was an attempt to catalyse the comp 2, which was just a tad to slow for use in such small amounts. It worked v.well in the triangle firecrackers with same result as Comp 3. ie. loud report and shredding of the casing. It also has a cleaner flame.
$4.11 for 110gm.

Comp 5. This probably doesn't need explaining, no trace of the casing left, drilled hole through the flower pot it was resting against. Not really suitable for fire cracker. No flash.
$1.50 for 100gm

Additional testing.
Comp 3,4 and 5 ignite after being struck by hammer.
None of the comps ignite with water.
Compositions with KMnO4 and S can be mixed with acetone, and then dried to improve burn rate (or so i am told). Sounds messy though.

Conclusion: the best comp was undoubtedly comp 3, but it may have some sensitivity issues, and is also the most expensive of the lot. Comp 1. has no purpose in ife, while comp 2. would be an ideal low cost flash for larger casings. Comp 4. was fine for the triangle firecrackers, but probably not usefull for anything less than 1/4 gm well confined. BP was not able to perform in such small amounts. For those without scales, comp 3. is ideal because just about any amount works.

[T_Pyro]

Try BaNO3 in compositions 1 and 2 instead of KNO3. I get far better results with that. Also, there's a thread in the pyrotechnics section on compositions like 1 and 2 on your list. Go ahead and read it if you haven't already.

[scarletmanuka]

I'm sure it has already been mentioned, can Ba(NO3)2 be obtained from fractional crystillisation of KNO3 and BaCl2. Do the percentages need to be changed to acount for the Ba(NO3)2? The compositions are non stoich any way.

[PanMaster]

A very cheap flash composition 8x as powerful as blackpowder is yellow powder, 3 parts KNO3, 2 parts K2CO3, 1 part S, melt them together and BANG

[Speakle]

I have made a good bit of flash over the last couple of years. I always use the 70/30 mix of pot.perchlorate and german dark alum. I havent seen too many people in here talking about using that mixture. I have been nothing but pleased with it, so I am curios why people use all of these other mixtures especially since I have read that sulfur makes the mixes more sensitive and unpredictable.

[devilassassin]

Im able to get Calcium Nitrate(NZ$4.50kg) even cheaper than Potassium Nitrate. So I was wondering if anyone has found that Ca(NO3)2 performs better in that Comp 2 flash mixture than KNO3.

[0EZ0]

Ca(NO3)2 is very hygroscopic. Much more so than NH4NO3. I think you will find it very hard to keep the composition dry at all. Aside from that, I'm not too sure that Calcium Nitrate would even be a potent enough oxidizer for this type of application.

Speakle, many members can not afford rare and expensive (in most regions) materials like German Dark Al and Potassium Perchlorate. Those that can rarely document their use of it as it has already been discussed many times before in the archives and previous threads. People use other flash formulas as they use more readily and cheaply available materials. Unfortunately almost all alternative flash compositions are more dangerous/sensitive/reactive than the commercially standard 70/30 Perchlorate/Al.

PanMaster, Fulminating powder (the composition you speak of) is not a flash powder and it does not find any practical application as a replacement for it. It's rate of combustion far exceeds any deflagrating flash mixes and is quite dangerous to produce via the mix and melt method. That aside it is quite hygroscopic from what I have heard. Not the most attractive characteristics of a salute composition.

[Blackhawk]

As I have said before I will be doing some testing on cheap flash and when I do it will go here, but it may be some time from now, they will be in standard (however small) cardboard cases with epoxy endplugs and visco. I have KNO3, S (Some), Mg, Al, KMnO4, I have tried the stoichiometry of the different mixes I will try, can you see anything wrong with them?

2KNO3 + 5Mg - 5MgO + K2O + N2
63% to 37%

2KMnO4 + 5Mg - 5MgO + K2O + 2MnO
72% to 28%

12KMnO4 + 20Al - 10Al2O3 + 6K2O + 12MnO
79% to 21%

I attempted to end up with just oxides but for the first however I thought the N2 would likely not react.

[blindreeper]

Firstly why could this not have gone in the pyrotechnics section?
Secondly, I don't think you will ever work ouyt the stiochemistry for flashes or BP. Simply because there is so many decomposition products, it is almost impossible to work out.

[Blackhawk]

Yes well this is just a very simplistic view to get some roundabout ratios, the combustion products are really not important in the long run as you won't be using them for anything and you will eventually get the best ratios with trial and error. Don't know why this isn't in the pyrotechnics section, I guess he didn't want to add to one of the other flash pages for fear of going OT and he didn't want to start a new flash topic when there are already a few.

[xyz]

Flash powder doesn't use stoichometric ratios, the reason for this is that it will make the best flash if it is deficient in oxygen (a small amount of very hot but still unburnt metal powder oxidising in the atmoshpheric oxygen creates the flash).

[Blackhawk]

Of course, if you want to use the flash powder for the flash, however if you are going for the bang I would think complete internal combustion might be a better thing, that and my Al is so crappy that if it was shot out of the salute it would simply give a shower of sparks instead of a fireball.

[scarletmanuka]

OK Blackhawk, try this one. First of all use stoich Mg/KMnO4 in a salute and then try it 50/50. The 50/50 mix should still be much louder and faster. I think this is because the Mg particles are not so far apart, allowing faster propogation of the flame front. Therefore the ideal ratios should not be dependent on stoich but rather how well you can have the particles integrate together. For instance, Stoich KMnO4 and large Al filings will be very tricky to ignite as the Al particles are drowned by the KMnO4 and are not able to ignite the other particles.
Blackhawk: I would be very interested if you could compare mixes with and with out sulfur inside decent salute casings. My guess is that the Sulfur wont really add anything. If your poor grade Al performs well, it will undoubtly mean a reduction in cost for the higher fuelled mixes. The Al was my most expensive ingredient.

[T_Pyro]

Mg and KMnO4? If I had access to Mg, I wouldn't be messing around with KMnO4! Further, sulfur helps to sensitize certain mixtures. If you want some proof, try the KNO3/Al mixture with, and without S.

blindreeper:
I think scarletmanuka was trying to play it safe by posting in the WC, since he's comparatively new here. I think such a move is commendable, and should not be discouraged. If the topic is worthy enough, the moderators will move it to the appropriate section.

[Blackhawk]

heh, well the question is do I really have access to Mg, Infact I only have about a foot of ribbon, which I am grinding into powder ATM, but it is really a one off thing for gathering info, I don't have the supplies to make it regularly. I will try and get some pics of the raw chems and cases in the coming 2weeks, although I won't mix and seal them untill I am ready to use them seeing as they are realitively untested mixtures (I can never find any mention of KMnO4/Mg flash). All told I will have te full comparisson wrapped up in about 3 weeks, hope you can wait ;)

[scarletmanuka]

Just a little OT...

Well I do feel that I really need to mention this. For all of you scrounging around for Mg, go with the metal pencil sharpners. The body is made out of Mg to stop the blades rusting. 99% of the metal pencil sharpners are made of Mg. To test this, simply put your tongue over the blade and the body of the sharpner and you should feel a tingle of the current going through your tongue.

NB T_Pyro, I have a metal sharpner on my desk made in India. Should be a viable option if you were to experiment with flash.

[T_Pyro]

For all of you scrounging around for Mg, go with the metal pencil sharpners.

Hmm... That sounds (very) interesting! I have a couple of metal pencil sharpeners lying about, but never thought that they could be made of Mg! But isn't it odd that the metal just beneath Ca in the electronegativity series (and above Aluminium!) should be used in such a manner? I'll have to do some tests, I think...

[Bert]

To test a light metal/alloy for Mg: Take a file and make a clean spot. Put a drop of strong white vinegar on the clean area- if it quickly develops bubbles, it is either Mg or a reasonably high Mg/Al alloy. This is a bit more definitive than licking it, as well as more hygenic.

[scarletmanuka]

Still OT...
The reason Al can't be used in pencil sharpners is because of it's protective oxide coating. This means it can not be used as a sacrificial anode. I suppose zinc could be used, but Mg is also light weight and nice and shiny. A more fun test besides the acid one would be to cut of a strip with a hacksaw and ignite it like standard ribbon. In my younger days, all my Mg for flash came from these.

[T_Pyro]

Put a drop of strong white vinegar on the clean area- if it quickly develops bubbles, it is either Mg or a reasonably high Mg/Al alloy.

Er, I was thinking of dissolving a bit of the metal in dil. HCl, adding liq. NH3 till alkaline, and testing it with NaHPO4. A white ppt is a positive test for the Mg++ cation.

[Bert]

Yeah, the "vinegar test" is what the guys down at the scrap yard would do. It's a meatball test, if you've got the knowledge and reagents, by all means be more elegant! Hereabouts, small pencil sharpeners are all made out of plastic... I got a bit chunk of Mg from the tailgate of a wrecked delivery truck years ago, before I could buy ready made Mg and Mg/Al powders. Still got 20# or so left I think. Hard work to turn it into powder. Alloying it 50:50 with Al makes it easy to pulverize, but has its own set of difficulties...

[T_Pyro]

Ok, I just tested a sliver of metal from my metal sharpener, and I found the presence of copper and aluminium only. No magnesium present. My search for a source of Mg continues.:confused:

[Bert]

Mg is used for light alloy castings in aircraft, truck parts, lawnmower decks and other apps where weight is critical. Try going to a scrap yard and just asking them if they have any. They probably do- That's how I got mine, years ago. Also, some printing methods use pure Mg plates. I found a supplier years ago, but new they were too pricy. However, if they are scrapping out the old ones you might score a few.