Question about KNO3/Al flash powder.

[Brightthermite]

So I milled up some aluminum that is very fine. It will burn with the touch of a match. However when I try and make any flash powder with it, it will hardy ignite. I have tired ratios of KNO3/Al, 7/3, 50/50, 3/2, and 2/3. 2/3 proved to be the best which is odd considering the fuel is in excess in this ratio. When the oxidizer is added it makes it significantly harder to ignite. I know most flash powder comps contain some amount of sulfur and I know KNO3 isnt the best oxidizer you can get.

 

I hear that sulfur catalyzes the reaction (by providing heat??) as I have seen just Mg and Sulfur in a 4/1 be ignited and burn nearly as fast as flash powder. When my KNO3 is mixed with Mg powder in a 50/50 it nearly explodes, burns with a nice thump.

 

So has anyone made a successful flash powder with just KNO3 and Al? And if not is Sulfur really that important?

[greenlight]

I have some 400 mesh aluminium powder that I can mix with potassium perchlorate in stoichiometric ratio and it barely burns. This is because of the spherical shape of the particles (less surface area tjan other forms like flaked).

Even though you have milled the Al it sounds like it is still in the spherical form or some of it is. It is unusual that it burns on it's own though, mine doesn't

 

Potassium nitrate flash is never going to be super fast regardless I think. The Mg is a much more reactive (and dangerous) fuel owing to the fast loud thump it burns with you describe.

 

The sulfur, I believe is there to lower the ignition temperature of the mixture when it melts first and mixes more i intimately with the KNO3 making for easier ignitability.

KNO3 melting point = 300.C

S melting point = Around 100.C

[greenlight]

I don't think the KNO3 flash has much use outside of being a booster for shells called slow flash I think.

Once it is confined the burn rate would increase significantly and provides a nice bursting effect.

A lot of sluggish burning comps completeling change when confined with hot gases and nowhere for them to go.

[Wiley]

2;1:1 kno3:s:IBA is what I used to break my 1.91" multis up to 7 breaks. 2g in a small paper flash bag with the stars packed in around it with polverone gave very nice breaks. I've used it by itself in bottom shots, and it works OK there.

[Brightthermite]

I don't think the KNO3 flash has much use outside of being a booster for shells called slow flash I think.

Once it is confined the burn rate would increase significantly and provides a nice bursting effect.

A lot of sluggish burning comps completeling change when confined with hot gases and nowhere for them to go.

So would you say the slow burn has a lot to do with the oxidizer? Ive been told that Perchlorate and chlorate are much better but I never knew to this degree.

[Brightthermite]

I have some 400 mesh aluminium powder that I can mix with potassium perchlorate in stoichiometric ratio and it barely burns. This is because of the spherical shape of the particles (less surface area tjan other forms like flaked).

Even though you have milled the Al it sounds like it is still in the spherical form or some of it is. It is unusual that it burns on it's own though, mine doesn't

 

Potassium nitrate flash is never going to be super fast regardless I think. The Mg is a much more reactive (and dangerous) fuel owing to the fast loud thump it burns with you describe.

 

The sulfur, I believe is there to lower the ignition temperature of the mixture when it melts first and mixes more i intimately with the KNO3 making for easier ignitability.

KNO3 melting point = 300.C

S melting point = Around 100.C

The Al should be in small flake form since it was ball milled. After doing some research I believe I found the problem to be the oxidizer itself. Thanks for the insight tho!

[MrB]

Flash on KNO3 can be noisy / powerful enough, but KNO3 / Al alone isn't commonly used. Typically it has, as you said, sulfur added. KNO3 / Mg works very well, as you discovered.

 

I exclusively use KNO3 /MgAl / S for my flash, but from the little testing i've done i've decided that the tiny amounts people use to make timed inserts isn't enough for a good sound. Not really a problem for me, but it pretty much proves that it is a slower / less powerful alternative. It breaks crosettes nicely, and in salutes it makes a good noise, and that pretty much covers all my flash needs. KClO4 supply is rather limited here, so i try to save it for colored stars... But pretty much all KClO4 based flash beats KNO3 based stuff hands down. Please don't use KClO3. It's kinda easy to piss of, and you wont like it when it's angry.

;- )

[greenlight]

@ brightthermite, I have never really got a fast burn rate out of any flash compositions with potassium nitrate as the oxidizer.

You say you found the problem to be the oxidizer. What was the problem exactly?

Was it not powdered or was it fertilizer grade and causing problems?

 

Perchlorate and chlorate oxidized flash compositions are much more powerful yes indeed. Perchlorate flash would be the safest any day over chlorate based though.

 

Potassium chlorate gives off heat (exothermic) when it decomposes as well as oxygen which lowers ignition temperature conpared to perchlorate mixtures and I think contributes to its instability and makes it "easy to piss off" haha.

Edited August 23, 2017 by greenlight

[Brightthermite]

@ brightthermite, I have never really got a fast burn rate out of any flash compositions with potassium nitrate as the oxidizer.

You say you found the problem to be the oxidizer. What was the problem exactly?

Was it not powdered or was it fertilizer grade and causing problems?

 

Perchlorate and chlorate oxidized flash compositions are much more powerful yes indeed. Perchlorate flash would be the safest any day over chlorate based though.

 

Potassium chlorate gives off heat (exothermic) when it decomposes as well as oxygen which lowers ignition temperature conpared to perchlorate mixtures and I think contributes to its instability and makes it "easy to piss off" haha.

Oh nothing was wrong with the KNO3 quality wise, its pretty pure, was powdered well in a mortar and pestle, and works great for rocket fuels and such. As you said you have never got a fast burn form potassium nitrate, I believe the KNO3 just does not have what it takes to make a fast flash without sulfur. I found a few videos of people making flash with homemade Al powder and perchlorate and saw that it has a much faster burn then mine with KNO3. So I just figured KNO3 "wasnt powerful enough" or doesnt oxidizes it as rapidly (dont really know the chemistry as of why).

Edited August 23, 2017 by Brightthermite

[OrganicPolyCHEM]

KNO3 is a very powerful oxidizer in most cases when it comes to combustion, but as a general, true "oxidizer" in the sense of electron transfer and the ability to rip electrons from other atoms not so much... It works very effectively in most any fuel explosive by providing oxygen we all know, however, this only applies to organic fuel. The "fuel" in flash is unoxidized Al metal, which reduces fairly easily but provides no source of other atoms to recombine with the nitrogen (which is also fairly electronegative). In carbon/hydrocarbon explosives as the fuel is burned O combines with C and H both releasing tremendous heat, also N can recombine with O forming much more stable NO2 gas (thus pulling energy out of system), as well as H forming ammonia or other combinations of N containing species that absorb much less energy leaving more energy driving rapid combustion (see energy of formation for NO2 vs NH3 and other N,C,O,H species). Also, if NO2 is generated then less oxygen is actually available to "burn" the fuel.

 

K perchlorate is a much stronger oxidizer chemically becauso unlike nitrates, the Cl-O bond is rather weak and with Cl being more electronegative than O, its actually a strong oxidizer itself. So when it reacts, no new Cl-O species reform (in most cases) leaving much more O to burn as well as active Cl atoms desperately searching for an electron to steal (ususally from the K of the salt). If you look at the electron structure of ClO4, you see Cl can only accept one e- so how can it bond 4 O atoms?? Its lone pairs act as a lewis base (as ammonia acts as base to form ammonium ion) donating its 3 lone pairs to 3 O atoms, with the 4th O bonded the same way since Cl stripped an e- from K giving ClO4 its negative charge. During thermal breakdown, this easily decomposes to KCl salt and two O2 molecules providing large amounts of O with very little activation energy. NO3 however, must absorb energy in order to break N-O bonds to release O thus providing less overall energy and reactive oxygen.

 

Also, ClO4 is a tetrahedral molecule which is non-polar so it is quite stable. KClO3 on the other hand, though an extremely reactive oxidizer more so than perchlorate, should be avoided at all cost especially in use with metals and sulfur. ClO3 is a polar molecule with the Cl having a negatively charged lone pair on one side like NH3. Its quite unstable because of this, is very susceptible to shock ignition, can self-ignite in presence of fuels or friction, dangerous when mixed with moisture and acids, and very dangerous in presence of sulfur. Most S contains S-based acidic impurities which can react with ClO3 spontaneously generating heat and highly unstable chloric acid (nasty acid will "eat almost anything). This can propigate to burn S into S-oxides which reform S acids with moisture...you get the picture...boom! Metals are easily reduced, can spark w friction or static, so combining with an unstable, powerful oxidizer and churning them together is a bad idea unless there is a specific reaction that calls for ClO3 specifically and the person involved is knowledgeable of the detailed chemistry and hazards. Otherwise, you may as well play with raw nitroglycerine (ive made nitro in small amounts only because its one thing im scared of as a chemist, even knowing how to control it one mistake with a large amount and my parents would be washing me off whats left of the walls of my lab....)

 

I hope someone actually reads this and gets something out of it; i tend to go in depth for people who like to know the "why" of the chemistry behind questions like this. Mechanisms are too complex to try and type out in a forum, but I hope I brought someone a little better understanding of the "why" chlorates work better burning metals. This took some time to put together, so please let me know if anyone enjoyed it and any other question about anything chemistry feel free to ask. I have a masters in chem. engineering and do experiments daily to further my understanding; my information isnt just pulled from wiki....lol

[Arthur]

Aluminium behaves badly in a ball mill. Initially it becomes finer than it started, BUT there is a limiting value where no more milling makes it finer. After more milling particles are milled and separately agglomerated at balancing rates, leading to no progress in milling fineness being apparent. The fastest flash aluminiums have extra ingredients in small amounts to prevent particle agglomeration. Also they have very different particle shapes... A spherical ball of Al is hard to fire but a ragged lump of the same overall size is much easier to ignite.

 

In short not all aluminiums are equal!

[robbo]

Hey OrganicPolyCHem:

Please do feel free to hold forth on the chem digressions. Much appreciated.

[greenlight]

@ OrganicpolyCHEM, the was very well explained and I enjoyed reading it. The chemistry of pyrotechnics is very interesting.

[Baldor]

Aluminium behaves badly in a ball mill. Initially it becomes finer than it started, BUT there is a limiting value where no more milling makes it finer.

Hi Arthur.

 

Will adding some charcoal help with a better milling of aluminium, other than protecting from oxidation? And changing media size? Say, starting with 12mm balls, and change to 5mm when there seems to not be any improvement.

[Arthur]

Firstly I've never personally experimented with this. Several books I've read over the years have formed my opinion.

 

I'm completely unsure what method is used commercially to produce the special aluminiums of high reactivity. One electron micrograph I saw was particles but they were actually balls of aluminium fluff -looked like balls of paper from a shredder on a micro scale. There were expressions of particle area suggesting that a 5 micron particle could have a surface area measured in square metres which is impossible for a 5 micron sphere, so while the particle falls through a 5u hole it must be very fluffy in construction.

[WillowPineAndBoom]

Let's open eye's again.. hallo to all pyro guys! I test this composition kno3 al s so much times that i lost count of tests(and thats beacuse i cant get kcio4 to make it). So some basic staff about it. The al must be ball mill antil it stick to the jar. I personal mill it 3 days with stainless steel balls 16mm and 3mm equals amounts of balls in thick pvc homemade jar mill!!! The kno3 must be make crystallized method(boiling method see in ytoub) to be pure clear white! And sulfur must be as ore clear yellow colour and dry! The comp is 6.3.1 kno3 al s... the comp must be mix in the ball mill empty of media about 1 hour at least but the jar walls must have stopers to move the powder and mix it! Have fun and be safe always!

[Piccaso]

Are you saying that the final step of your milling is with all the chems mixed? I hope not as this would be a very fast way to kill yourself or someone else. You need to stop messing with flash before you hurt someone. Your experimenting shows a lack of knowledge that will end up hurting you. There is plenty of good info out there for free, please educate yourself before you kill yourself.

[GrassyKnollShooter]

OP there's nothing in flash powder other than Potassium Perchlorate and Aluminum powder. No sulfur.

You won't get much from KNO3 it's pretty average as an oxidizer.

 

Ball mill it to death. Always.

[WillowPineAndBoom]

Are you saying that the final step of your milling is with all the chems mixed? I hope not as this would be a very fast way to kill yourself or someone else. You need to stop messing with flash before you hurt someone. Your experimenting shows a lack of knowledge that will end up hurting you. There is plenty of good info out there for free, please educate yourself before you kill yourself.

First as i said before piccaso i mill it al chems in ball mill "WITHOUT MEDIA INSIDE" that is! Second you can't even read my post correct, and my knowledge is enough trust me i am not an idiot! I make this hobby 12 years etc now and i know the basic

information at least! And third you "look" some guy that came here with 25 posts only to make safety training without to ask first! You don't know me as i don't know you that's a fact yes but i don't want to offend people like you! First i read and then i talk... And fourth, "if you don't respect something, you won't respect it back" He says a proverb, here in our places! I am not saying that your speak is not right for God's sake but you must respect someone and learn about him! THUMPS UP TO YOU PICCASO!!!

[BetICouldMake1]

OP there's nothing in flash powder other than Potassium Perchlorate and Aluminum powder. No sulfur.

You won't get much from KNO3 it's pretty average as an oxidizer.

 

Ball mill it to death. Always.

 

Since the OP was asking specifically about KNO3 "flash" I assume he was referring to the common nitrate booster which does contain sulfur. That aside, there is not just one formula for flash. 70/30 perc/Al is standard, but there are formulas that call for sulfur (or antimony) in addition to the perc/al.

[Piccaso]

 

First as i said before piccaso i mill it al chems in ball mill "WITHOUT MEDIA INSIDE" that is! Second you can't even read my post correct, and my knowledge is enough trust me i am not an idiot! I make this hobby 12 years etc now and i know the basic

information at least! And third you "look" some guy that came here with 25 posts only to make safety training without to ask first! You don't know me as i don't know you that's a fact yes but i don't want to offend people like you! First i read and then i talk... And fourth, "if you don't respect something, you won't respect it back" He says a proverb, here in our places! I am not saying that your speak is not right for God's sake but you must respect someone and learn about him! THUMPS UP TO YOU PICCASO!!!

 

I was not trying to upset you but trying to help keep you safe. I worked as an EMT for 5 years and do not like seeing people get hurt. In the future I will be sure to reread your posts a few times before responding. Yes, I have trouble reading your post correctly because of the way it is written and the spelling. There have been plenty of milling accidents from blending completed comps with or without the media. So, since you obviously do not want others insight, I will leave you be in the future and good luck to you keeping both of your thumbs to put up.