Regarding Oxidizer/Reducer Formulation Ratios

[jeffreyschultz]

I am just getting started in pyrotechnics and formulation, and have a question regarding something I encountered when testing out compositions for sparklers and eventually a gerb. I can't recall the specific ratio I was using at the time, as it was the result of several tweaked tests attempting to increase the amount of sparks created upon decomposition using a bernzomatic torch. I was using potassium perchlorate, mixed aluminum flake, firefly (+40-325 mesh), atomized spherical aluminum (400 mesh), titanium hydride (-120 mesh), and charcoal (was trying to see if it would down the burn rate).

 

The question I have for you guys, and I am not sure if I have provided enough information, but I am sure this is a problem that has been seen many times before, but when the composition finished burning it left behind what looked like a piece of "sponge" that was clearly metal. I realize this isn't really a creative composition and was me toying around really, but I'm curious if this was the result of not having enough oxidizer in the mix? I can see where this would be an issue when I go to create a gerb and this "sponge" blocks the nozzle, possibly causing it to confine the pressurized gases and causing it to pop!

 

Any information is appreciated as I would like to know if it's something more, and if this is remedied simply by having a more stoichiometric formulation.

[mabuse00]

Well, to answer your question we need to know what ratios you used.

 

Usually creating metallic sparks is achieved by introducing some rather coarse metal particles into a gas producing composition, like blackpowder ect. The gasses will propel the burning metal parts away thus creating the effect.

If this is the case, you don't need to include the metal into your stoichiometry, or it's at least not crucial.

 

A mixture like you described - only metal fuels - will not produce any gas, and if it's slow burning the reaction products, salts and metal oxides, wont be propelled anywhere, producing slag.

 

I don't know how far you've allready gone into pyro, but be aware that what you described could be called some kind of flashpowder that can react very violently. Loading this kind of composition into a gerb will create stimuli that may set it of when done improperly. Basically it cannot be done safely without a press and blast shield.

 

For making a simple gerb I suggest using something like blackpowder + 20% titanium.

If you cannot make decent blackpowder, greenmix would also work.

Edited August 12, 2013 by mabuse00

[jeffreyschultz]

I started with the Steel Powder Sparklers post on the Skylighter blog (http://blog.skylight...-sparklers.html) and went from there substituting additional aluminum and titanium in where steel was originally included. I tried to keep those ratios, but towards the end of experimenting I know the ratios were skewed a bit from more rapid testing. I am aware of flash powder, and wasn't intending on creating it as I have read warnings against creating it until you are fully legal'd up and have some experience working with it.

 

I forgot to mention I had also bound the mixture the day before using the ratio listed in the blog with dextrin, so it wasn't a powder at this point, but a thick paste that had dried that I had dry stirred and started tweaking to see the effect it had.

 

The dried composition didn't behave like a flash powder in my opinion, where an amount of about 1/4 in^3 would produce a shower of sparks about in a hemispherical fashion with an approximate range of 1 1/2 ft for about 3-4 seconds. It wasn't an instantaneous deflagration, but a slow burn that seems to have generated gas from the distance the single sparks flew. I know that both charcoal and dextrin are fuels, so I am not sure if it is an accurate statement that it was "metal-only", unless smaller ratios would have deamed it metal-only. At no point did I feel the reaction was out of control or that my safety was in question, or that it was decomposing too rapidly, for use in a sparkler. I would say that I wouldn't want to use it in a sparkler because the distance the sparks flew would be too much to hold in your hand without getting burned by the slag!

 

You could say this was my first attempt at creating something. I made small amount before this to see what the color would be and what size the sparks would be, which represented the composition before I started tweaking it. I have been doing a bit of reading too, so my next few attempts will like be more "by the books" than my trail-blazing first attempt! (not saying I wasn't reading before this attempt, because I have been for the last three months while building up my confidence to give it a try)

 

I didn't have any Strontium Nitrate on hand, and had read elsewhere about the usage of KP in sparklers, so that's is why its in there.

Edited August 12, 2013 by jeffreyschultz

[jeffreyschultz]

Well, to answer your question we need to know what ratios you used.

 

Usually creating metallic sparks is achieved by introducing some rather coarse metal particles into a gas producing composition, like blackpowder ect. The gasses will propel the burning metal parts away thus creating the effect.

If this is the case, you don't need to include the metal into your stoichiometry, or it's at least not crucial.

 

A mixture like you described - only metal fuels - will not produce any gas, and if it's slow burning the reaction products, salts and metal oxides, wont be propelled anywhere, producing slag.

 

I don't know how far you've allready gone into pyro, but be aware that what you described could be called some kind of flashpowder that can react very violently. Loading this kind of composition into a gerb will create stimuli that may set it of when done improperly. Basically it cannot be done safely without a press and blast shield.

 

For making a simple gerb I suggest using something like blackpowder + 20% titanium.

If you cannot make decent blackpowder, greenmix would also work.

 

Sounds a lot simpler than what I was going for initially and might satisfy the first attempt itch. I am trying to get a ball mill together to start milling my own BP, so unless I use commercial I would have to go with an alternative. I have read about a couple different types that don't need a mill, like one called red gum black powder. Would that be ok?

[LTUPyro]

You don't need fast BP for gerbs, screened BP (Green mix) will work just fine, fast BP can cause very fast burn rate and nozzle blow out. I don't recommend using Commercial BP for gerbs since it usually have additional chems like KCLO4 wich is not safe to ram.

 

It wasn't an instantaneous deflagration, but a slow burn that seems to have generated gas from the distance the single sparks flew. I know that both charcoal and dextrin are fuels, so I am not sure if it is an accurate statement that it was "metal-only", unless smaller ratios would have deamed it metal-only

Dextrin is not fuel, it's binder wich can be activated by water or water-alc mix.

[jeffreyschultz]

I could have sworn that dextrin was a fuel. I knew it was a binder, but some chemicals play multiple roles in a composition, such as in rockets where the binders also tend to be fuels to increase mass-energy and specific-impulse of the motor.

 

In my mix, it was used as a binder, but being a starch I figured it was also a fuel.

[Seymour]

Jeffrey, you are right. Many substances have multiple roles, and Dextrin is for sure a fuel and a binder. When using it as a binder, it's fuel value must be considered if you are considering the fuel/oxygen ballance.

 

Occasionally it is used as a fuel only, when no binder, or some other binder is used. This is probably uncommon because it can be a bit hygroscopic, especially if you have a high percentage.

 

I don't recommend using Commercial BP for gerbs since it usually have additional chems like KCLO4 wich is not safe to ram.

 

I agree that one should exercise caution with modifying bought explosives, for the obvious reason that you don't know what exactly in it. I also am well aware that certain black powder like propellants have KCLO4 in them (to improve power, reduce smoke and barrel fouling), however these should never be called "black powder". I've always come across them with some other name (Pyrodex for example) or called "Black powder substitute".

 

While of course misleading mislabeling occurs, have you really come across most of the time you have encountered commercial BP LTU?

 

A mixture like you described - only metal fuels - will not produce any gas, and if it's slow burning the reaction products, salts and metal oxides, wont be propelled anywhere, producing slag.

 

Mabuse, note the Titanium hydride and the Charcoal. While the Titanium will likely produce solid products, I expect that a majority of hydrogen will in the promiscuous excitement become steamy water vapor. And the Charcoal of course, becomes the full mix of wood burning type products, most of which are gasses like CO2, CO and H2O.

 

The question I have for you guys, and I am not sure if I have provided enough information, but I am sure this is a problem that has been seen many times before, but when the composition finished burning it left behind what looked like a piece of "sponge" that was clearly metal. I realize this isn't really a creative composition and was me toying around really, but I'm curious if this was the result of not having enough oxidizer in the mix? I can see where this would be an issue when I go to create a gerb and this "sponge" blocks the nozzle, possibly causing it to confine the pressurized gases and causing it to pop!

 

Yeah I fully think that the slag will have metal in it because it has such a large excess of metal in it. However this may or may not be the cause of this sponge-like slag. You get that from all sorts of compositions that are not burning cleanly, and the slag is made up from whatever they are producing, which like the compositions themselves, varies very widely.

 

You also have compositions that have an absolutely huge excess of metal in them, but still don't do this, which is why I don't blame the metal content for the problem. Essentially you just need to get it burning with sufficient vigour for whatever gas that is produced to entirely carry away all the solids and liquids as it leaves, and before they have time to aggregate together.

 

While ultimately Mabuse is right and BP + 20% Ti (or less, perhaps - though I approve!) is probably the easiest and quite safe, in the interests of continuing messing around with what you've got I'd suggest something like 5 KP, 3 Al, 2 Charcoal by weight. Both Aluminiums will, of course, give very different effects. Mixing them can be fun.

 

While certainly these mixes in theory are not far off flash powder, I'm not sure that flash powder like caution is really required. Obviously given the sufficient confinement they will go bang quite devastatingly, I'd say they are on par with your average purple star mix in that regard. And of course when making unknown mixes, all outcomes should be expected possible when they are tested.

[LTUPyro]

Sorry for misleading information . Never heard or thought that dextrin is also fuel

[jeffreyschultz]

Thank you, Seymour! That was a very helpful response. I will move forward with your suggestion.

 

I was starting to get the feeling I should just start over and drop down to BP, which I have "some" (very loose term) experience with homemade BP from hunting with family when I was younger, but was looking for something a bit more "interesting." I feel that I am somewhat intelligent, and have interests spanning many fields of study to include chemistry, and with a loosely gathered precept I have a few intended places where I want to go with pyrotechnics. I have a bit more general knowledge than I think I let on, but this issue was something I had considered beforehand and is why I went with KP instead of a number of the other oxidizers I have on hand, which was to reach a more exothermic decomp. to ensure the materials reached their flash point. To be honest, I didn't know what effects the mixture would have on the required temperatures or if it would have any effect at all other than possibly lowering them. If I recall correctly, I remember somewhere in my reading that Shimizu stated there was a rough inverse relationship between BP and KP with regards to the rate of deflagration and heat generation. I am also familiar with azeotropic properties of some liquid solutions, and must have been keeping that in the back of my mind when I was starting out--thinking about it now, I am not sure that applies in this particular case.

 

I think I need to also get out of a purely deterministic mindset and leave somethings out of the equation when approaching this in the future, as I was trying to account for everything.

 

Thanks again!

Edited August 13, 2013 by jeffreyschultz

[Jonathan]

When I want chem ratios, I go to an online calculator (there are a number) to get the balanced equation for reactants and products. Then I do my own stoichiometric calcs using an Excel spreadsheet and atomic weight values from the Periodic Table. For an actual stoichiometric reaction, there should be no reactant (e.g., un-oxidized metal) among the products.

[Mumbles]

Except simple 2 part mixtures, like for flash powder formulas and thermites, online calculators are basically useless for pyrotechnic reactions. Even going to 3 component mixtures makes the reactions needlessly complicated. Something like black powder, which has purely inorganic components, yields over 30 reaction products. When you start adding in anything containing even the simplest organic molecules, the product distribution goes even higher.

[Jonathan]

Mumbles,

 

I've found a calculator that will handle three reactants and any number of products. The user has to guess correctly as to the products, but the calculator will do the balance. No guarantee, however, the proposed reaction will proceed. The calculator, IOW, is just a tool with limitations on its usefulness.