I made flash powder, not thermite?

[Spoz]

Just thought Id share an interesting experience with you.

Today I attempted to make some KNO3/S/Al flash in the ratio 50:30:20. Ive made this before and it burnt very brightly unconfined, I did not test it confined.

Todays batch though, made in exactly the same way, when ignited unconfined burnt much like thermite. It was difficult to ignite, and when it did it sputtered alot before it finally got going.

After it had cooled it left blobs of metal, presumably aluminium, most of the powder seemed to be reacted. It was done on a roofing tile, and the molten metal seems very strongly stuck to it.

Is this known to happen with this flash powder mix? Last time I made this flash, I didnt notice the molten metal - if it formed. Could it be that I am not using enough oxidizer, or perhaps too much sulphur?

[nbk2000]

Burning metal powder with an oxidizer is not thermite.

The 'Thermite' reaction is typically the reduction of a metal oxide with a more reactive metal. Iron oxide with magnesium, for instance.

Perhaps your nitrate was damp, or the sulfur wasn't finely powered? Or the aluminium got an oxide coating.

[Spoz]

I realise it isnt a thermite reaction, I said thermite because it behaved exactly as thermite does.

The nitrate being damp is the probable cause, its been fairly humid here the past few days. I cant tell if my aluminium has an oxide coating or not, as far as I can tell it looks the same as when I bought it (it is 325 mesh). I'll try drying the nitrate and giving it another go then, thanks for the tip.

[The_Duke]

Aluminum and atmospheric Oxygen react with each other to form thin protective layers of Oxides on all exposed Aluminum surfaces. These thin layers of Oxides conveniently prevent further oxidation and corrosion of the metal (this includes your Al powder).

A lot of the time Al is added to brass alloys to take advantage of this property to enhance the corrosion protection of said alloys.

[Spoz]

Yeah, aluminium is handy like that.

Does the oxide layer on fine powders have an effect on pyrotechnic compositions only because of the high surface to volume ratio, or for some other reason?

[quicksilver]

I realise it isnt a thermite reaction, I said thermite because it behaved exactly as thermite does.
.

I have used thermite (Thermate WeldFor) professionally. I don't think you mean that it weld-sealed cracks in Back-Hoe thickness steel, do you? ;-)

"Does the oxide layer on fine powders have an effect on pyrotechnic compositions only because of the high surface to volume ratio, or for some other reason?"

Fine powders are a whole world unto themselves. They differ in reactivity depending on not only their compostion per se' but their manufacturing process. Al is a unique species as the processes of mfg. are numerous. With some of the sub-sieve particulate Al is produced aluminum carbide; making it uniquely reactive! In other processes a percentage of carbon exists on the particulate matter. Aluminum oxide however is not more than a percentage of a micron thick when formed on sieve sized Al and for the most part would not affect it's _pyrotechnic_ interaction to a great degree. The shape of the particulate is the predominate factor. And in so saying if the particulate is spherical there is generally less oxide than flake material. The flake or other non-spherical shape has an edge or point therein the burn can begin with greater speed than to consume the whole ball [as it exists]. That is why grindings, or other non-spheroidals are used in Thermite. A professional level Thermite reaction is something to behold. Basically, once you have seen it you can understand the utility in using it in weldments.
However to address your question specifically; the level of actual oxide is very minor and actually difficult to achieve. The oxide would make little difference, if it's actual oxide and not carbon or a carbide that is in place. The Al would need to be exposed in pure form in a sheet-flat large area for oxide to exist on (let's say) a Kg of material. There may be some oxide on a top level of some material but not the under-lying portion. And we are assuming that stearates have not been mixed at the factory with that batch; a pure Al powder is not sold via pyrotechnic suppliers. There are mil-spec powders that may be obtained as surplus but NOT from pyro suppliers. Nickel, tin, copper, aluminum, & zinc have all appeared on the surplus market. And in single mircon (2-9uM) sizes! When a non-pure product exists it's labled as such...even oxided material.

I know you are aware of most of this but some folks don't know about the carbon / carbide issue....

[tmp]

Carbon and carbides do get into German Dark Al powder as a results of
the charring before stamping process. I shook some German Dark on a
piece of paper and it left behind a carbon stain. BTW, I make my own
Al powder and KClO4 for flash. It doesn't burn - it goes BOOM !

Spoz, KNO3 is not as reactive as the chlorates/perchlorates. It you
can't buy chlorates/perchorates, search this forum for procedures to
make them. There are plenty of threads !

[quicksilver]

A very interesting tool adjuntive to this discussion is a microscope. With a mid-level quality microscope you can determine what you are dealing with and often it is not what you may have thought you bought.
Purchases made on a pyrotechnic market are frought with mis-labled material. It is not often mentioned but some "pyro-grade" Al is fine-flitter with a large percentage of quality (5413, etc) Al and will generally act the same for report purposes. The issue is one of overall quality and of course getting what you pay for. A mircoscope doesn't lie. After negotiating a large purchase of Indian Black a club member some many years back found that an unusually high percentage of carbon in the unit level bags (one pound). He then looked carefully and discovered that the Al had much too high a percentage of "free" carbon in it. When this was brought to the broker's attention he became overly defensive about it and refused to even look at the slide. Additionally: it seems that a sample of "German Black" from another well known mail order firm had a percentage of spherical, granulated, and flake Al all in the same 5mg sample.* When you are spending that much money on something or putting your reputation on the line it's best to know what you are dealing with and Al is EASY to degrade.
*A unique experiment is to use a gram of flitter-grade Al and mix it with .25% high quality Al then use it as it were ALL high quality Al....it will respond the same! It is said that a well known supplier had done this or simply looked the other way when someone brought this to his attention some years back.
There is also some VERY expensive Al on the surplus market with a microscopic Teflon coating that is extremely reactive and sold as such. There is a surplus Mg and Teflon mix that is very reactive and must be sold as per Zirconium packaging (in the wet) from a mil flare mfg. All of them would be determined via a mircoscope.....it's like a jewler's loop for reactive metal powders.

[NoltaiR]

Various things could have gone wrong in your little experiment.

For one.. since when do you have 50% fuel and 50% oxidizer.. especially when you are using potassium nitrate?!?

Flash powder is very powerful and as its name implies.. it should NEVER be hard to ignite... after all you can make fuses with flash powder... and cheap commercially made fireworks use many forms and grades of flash powder.

In my experience with flash powder back in the day, I have used KNO3 (amidst other things) as my oxidizer. It is not the best.. honestly its not even close the being the best, but if it is what you have available then it will do.

If there is any molten metal left over then 90% of the time you probably just didn't have your ratios correct. I don't mean to misjudge you but those ratios you provide are from some sort of [ligitimate] text right? And you measured by mass and not volume right?

Simply put...

Al = fuel
KNO3 = Oxidizer
S = can count as a fuel but mainly it just helps the reaction

If you see ANY metal left then you didn't use enough oxidizer or quite possibly you didn't powder it enough? I would recommend playing around with different ratios.. and as always the amounts will change based on if you are testing confined or unconfined.

I don't know how you are mixing these but ball milling is probably the best but any improvised method of refining the chemicals to the smallest possible grain size is always the best.

Lastly, if you still have problems with ignition, considering using a small amount of black powder as your primary ignition. Also try getting a hold of better oxizers like KClO3 or KClO4.

[tomu]

Various things could have gone wrong in your little experiment.

. . . snip . . .



I don't know how you are mixing these but ball milling is probably the best but any improvised method of refining the chemicals to the smallest possible grain size is always the best.

Lastly, if you still have problems with ignition, considering using a small amount of black powder as your primary ignition. Also try getting a hold of better oxizers like KClO3 or KClO4.

Uhm, you are not talking about ball milling flash powder, don't you?

I guess you meant ball milling the oxydizer alone (straight) just with some anti-caking agent like aerosil or cab-o-sil (about 0.5% - 1%) just to make it a fine powder. But seriously you don't meant to ball mill the alu powder with any kind of oxydizer (nitrates, chlorates or perchlorates etc.) together, which would of course lead to desaster (KABOOM).

[NoltaiR]

Well take this with a grain of salt...

Obviously for safety reasons, any sort of refining or milling process should be done with the ingredients separated.. and in this case only the oxidizer is needing to be milled (since S is already available in a very fine form and you would never mill a metal).

But having the precaution stated... I have milled it altogether. I am not even saying that I recommend doing that but I am saying that it is possible. HOWEVER, just so that no one dies and blames me for it, there is always a VERY real chance of the mix heating and inducing combustion.. and with something like flash in a confined space, nothing good can happen.

All-in-all, just watch the ratios and at least refine your oxidizer and/or non metal fuels to their most favorable form.

[tomu]

Well, you might get away with ball milling KNO3 and Alu powder for a short period but certainly not with ball milling any chlorate or perchlorate composition.

Anyway, there is absolutely no need to ball mill flash powder and it's certainly an unsafe procedure, in case of chlorate or perchlorate compositions it's outright suicidal.

[quicksilver]

The more intimate your mixture the better. A whetted mixing does wonders. As you know you would reduce in size the individual particulate (ball milling the individual components) and using ethanol to make a slurry. Evaporate the slurry and use a grounded medium such as a brush and piece of cardboard to actually break up and mix the components (after you ground yourself) making sure there is no static prior. A stiff brush with no exposed metalic parts will allow the components to break up further and more intimatly mix the composition, or use diapering. It would be possable to reduce the oxidizer to sub-sieve particulate with a ball mill. The sulfur would serve as both a reducing agent and a fuel but if you can get quality sulfur if may be ground very small to begin with. Water is a lesser choice as sulfur doesn't mix well w/ water but does better with alcohol. Drying is faster. Here is where particulate shape makes a real difference and if you do have an Al that has some carbide in it you want to avoid water especially. If the Al is granulated ball milling will flatten the shape for a more effective burn. The original "cocca powder" black powder corning process produced some of the best propellant in Europe and still stands unique as the strongest black powder concept used in history. Some research on that process will reveal some of the best ways to produce an intimate mixture of solids.

[tomu]

What the heck are you babbling about?

You don't wet mix flash powder neither with ethanol nor with water or anything else. It would be totally useless. In case of a nitrate based flash powder it would be counterproductive or even dangerous if you wet it with water, because a hydration reaction will start and the stuff will heat up even if you buffered it with boric acid. Ethanol on the other hand will dissolve nothing neither a nitrate nor any chlorate or perchlorate, needless to say certainly not the Al, so it's pointless to use it.

The sulfur will lower the ignition temperature and so facilitate easier ignition also it will produce some gas at combustion, thats it. Sulfur is usually sold as a very fine powder or dust, sulfur sticks are no longer common. So normally there is no need to ball mill sulfur. BTW. you can't judge the quality/purity of sulfur by looking if it's sold in powdered form or not.

Only the oxydizer needs to be finely powdered, and if this is done in a ball mill the oxydizer is dry milled and not wet. It helps tremendously to add some anti-caking agent like aerosil or cab-o-sil to the oxydizer before milling and of course it should be bone dry to mill it succesfully.

BTW. flash powder and black powder are two totally different things! We are talking about flash powder here.

Anyway, just to straighten things up, I guess with "cocca" powder you meant cocoa powder a gun powder made with charbon roux. The remarkable thing about this cocoa powder was certainly not the corning process but the charcoal used to make it, which was made of a only partially charred soft wood.

You better use the search function of this forum and on the internet and read a lot more, after that get some practice and first hand experience, before posting BS.

[quicksilver]

You better use the search function of this forum and on the internet and read a lot more, after that get some practice and first hand experience, before posting BS.
You should read the post in context before getting so worked up. Both flash and black powder are analogous; oxidizer / fuel & or reducing agent compositions. Various methods of intimate mixing have been utilized with flash, including whetting (and drying, as that is part of whetting). The concept of 'whetting" HAS been utilized with flash (see Kosanke '98). Chemically S does act as a reducing agent & fuel. If you want to nit-pick at posts; realize that will come back to haunt you, especially here. There WAS a corning process utilized with cocca powder; quite a unique one. But then I suppose a "Gunmith" would know that, right?
I haven't got the faintist idea why you are lashing out at a discussion wherein there are various subjects brought up on a central theme; but it seems just a bit too immature to continue. ....later pal.

[NoltaiR]

Tomu, as long as your name has 'amateur' next to it, you have no place to be cutting down someone like quicksilver. With as little activity as there has been around here, we don't need to lose what precious few members that we have.

Also, I hope that both of you are speaking about things you have experience with rather than argueing over your version of some text file.