14 replies to this topic

[Potassium chlorate]

As we all know the perchlorate molecule has one oxygen atom more than the corresponding chlorate molecule. Theoretically this would mean that the perchlorate is:

1. More energetic

2. A better oxygen donor

But due to another fact, namely that the chlorine atom in the perchlorate is a "closed shell" atom, it is more stable and thus less inclined to give off its oxygen, at least as long as we are talking about LE, i.e. our kind of pyrotechnics.

So, what to do about it? Can one compensate for this outside the laboratory? There are potassium dichromate, manganese dioxide and zirkonium. The first two are catalysts and the third accelerates reactions by giving off tremendous amounts of heat when mixed with a composition and ignited together with it.

Suggestions?

Edited by Pyroswede, 30 August 2010 - 10:10 AM.

[vaslop2005]

I've been thinking about this fact for a while, but there are some issues.

1, When you make a perchlorate decompose at the same rate as a chlorate, it is roughly the same sensitivity. (this is perfectly shown by sulfur and phosphorous, where they are almost as sensitive as the chlorate versions of the same mix)

2, perchlorates loose all their oxygen (typically speaking) when used in pyrotechnic combustion anyway.

but for a faster decomposition, their are of course catalysts (including Fe2O3 as-well as the other two you mentioned) also their are high energy fuel additives, like dark flake Al (at small percentages) fine magnesium, charcoal/lampblack (which also acts as an opacifier)

do you have a specific need for this? or just for interest..?

[Potassium chlorate]

Right now my stars are chlorate based, though I'm thinking of making them perchlorate based instead for safety, but then I will have to "tune them up" a little to get the same result.

[vaslop2005]

ahh, i wish i could use chlorates for coloured stars, i just worry that i will contaminate my ammonium perchlorate...

But i find that just making the stars a little smaller than you'd imagine, and a two step prime (hot prime, followed by full speed meal) makes the stars burn relatively fast as they are burning on all surfaces, i use this technique with slow ammonium perchlorate stars and have no problems at all...

also, if you are after colours youll find that increasing the burn rate can ruin your colour, especially blues.

on a side note, how do you cope with sulfer contamination?

[Potassium chlorate]

I never mix sulfur and chlorates, though sulfur and percholrates is OK.

[vaslop2005]

sulfur and percholrates is OK.

dont be too sure, sulfer always has acid present, and mixing this with chlorates forms HClO3 which is incredibly dangerous.

but with perchlorates it forms anhydrous HClO4 (which is worth looking at online) as it very easily detonates, when mixed with fuels this makes the situation worse. It may be a common practise to do, but i try and avoid using them in the same composition, but for things like primes its fine

i know i sound like a compulsive worrier, but somethings i think are just un-necessary

[Potassium chlorate]

The whole point with using potassium perchlorate instead of potassium chlorate is that the closed shell structure makes it less sensitive to sulfur and other stuff that might make chlorates self-ignite.

Sulfur of today is usually incredibly pure compared to what they used 50-100 years ago.

From a pretty well known pyro supplier's homepage. His sulfur contains:

" moisture 0,03%
- org.comp. 0,02%
- H₂SO₄ 0,002%"

1 kilo of that sulfur contains only 20 mg of sulfuric acid.

[Mumbles]

You'd want to get SO2 content too, as it can be turned into acid and actually more of an issue that free acid. It all also comes down to how much you trust your supplier too.

Anyway, the acid content is a moot point anyway as sulfuric acid isn't strong enough to make perchloric acid. Besides that there have been studies done that show that it isn't chloric acid that causes issues, it's chlorine dioxide. Sulfur dioxide can form it, but I suppose it's all acid based. I don't know what causes the sensitivity with (per)chlorates and sulfur exactly, but I'd rely more on experimental data with my chemical stocks rather than untested beliefs based upon stuff I've read. Grinding perchlorate/sulfur in a mortar and pestle causes sizzling with little more pressure than with chlorate/sulfur. Whether this means perc/sulfur danger is understated, or chlorate/sulfur danger is overstated is up to you to believe.

Much of the sulfur on the market is that which is produced from petroleum product desulfurization. It's both incredibly pure, and they practically have to pay people to take it away. I will not argue that todays sulfur is much cleaner than that which was used long ago. I think this was certainly a player in the almost religious aversion to chlorate/sulfur. Personally, I have nothing against them coming in contact with each other such as priming chlorate stars with meal. If I can help it, I will not actually integrate them into the same mixture though.

Perchlorate color stars are pretty easy to do. While I am sure your chlorate star formulas are quite good, you may find it easiest to start from scratch with known good perc colors, and tweak from there, or at least use them to compare. One thing you will probably come to realize is that perchlorate based stars frequently will require external chlorine donors. Under normal circumstances the chlorine from perc doesn't get donated like it does in chlorate. Sulfur can make it do so though. I can try to suggest some formulas if you'd like. You may also find that perc based colors are less forgiving in terms of formulation and color, so chemical purity comes into play. There are plenty of people who think their chemicals are perfectly fine, yet get a rude awakening. This isn't as critical with metallic stars.

[vaslop2005]

Actually sulfuric acid is used in producing analytical perchloric acid from barium perchlorate, and the way that chloric acid decomposes forms chlorine dioxide, spontaniously

4HClO3--->4ClO2+O2+2H2O

Its a tricky situation, but I've had enough of situations where i sit on the sofa and listen to my heart pounding and my ears ringing, and think of what could have happened if... its just a shame that the best chemicals are the dangerous ones...

if anything I'd advise ammonium perchlorate colours, its well worth the time and effort (and money) because i cant for the life of me get a good enough blue from potassium perchlorate, might be something to do with me being a perfectionist...

[Mumbles]

Well yeah, you can probably make it from silver perchlorate and HCl too. It gets formed by the thermodynamic driving force of the Barium Sulfate dropping out, not H2SO4 being a stronger acid. It's unlikely the same sort of reaction would happen with potassium. I've read you can actually make perchloric acid from sodium perchlorate and HCl, again due to a solubility manipulation. As you boil off the water, the NaCl precipitates out forming the acid because it is so much more insoluble than sodium perchlorate.

Edited by Mumbles, 31 August 2010 - 01:51 AM.

[Potassium chlorate]

My red stars, for example, are actually made of strontium nitrate, potassium chlorate, magnesium and some other stuff and already have parlon both as a second chlorine donor as well as a binder. As a binder it also inhibits reactions between magnesium and the potassium chlorate. It would probably be pretty easy to change the formulation into one with potassium perchlorate, where I add sulfur to help to get the chlorine out of the perchlorate as well. With this slight change my red star formula would actually be pretty much like Ruby Red.

I actually also agree with Mumbles that the sensisivity of sulfur/chlorate is overrated due to impurities in sulfur in the past, though I also think that it's unnecessary to increase the risk by mixing them, when perchlorate is available.

Edited by Pyroswede, 31 August 2010 - 07:56 AM.

[MDH]

Part of it is the stability of KClO4 vs. NH4ClO4 - which seems to decompose more easily, though with a more saturated flame. Hence why AP makes such huge flame envelopes. AP + Hexamine + Sulfur colors are wonderful, and also stable.

[Mumbles]

Surely it's the hexamine if you think AP stars have a huge flame envelope. They are well known to burn slowly and with small flame envelopes, almost requiring hexamine to approach that of chlorate or to a lesser extent potassium perchlorate. You could probably get the same flame envelope with hexamine + potassium perchlorate. I heard Robert Winokur talking about how chlorate + Hexamine was remarkably sensitive. Perhaps, much like the perchlorate/sulfur, you should do a little test yourself just to make sure you're comfortable with it before trying it extensively.

[seymour]

If I remember correctly, the cause for sensitivity between hexamine and chlorates, was suspected to be some hexamine reverting back to Formaldehyde and Ammonia, which is not to be mixed with chlorates.

In my experience AP is rather unreliable. I've had compositions with it burn fast, or not at all at atmospheric pressure. I've had fast burn rates with huge flames, and very small flames with long burn times.

Different fuels react very differently, and a well formulated AP coloured star can burn fast, bright, saturated, with a large flame, and with a high resistance to being blown blind.

Often, however, a composition that looks like it has promise can burn terribly, in all ways, including colour saturation.

[Potassium chlorate]

AP is actually a secondary explosive completely on its own, so no wonder that it might react in an unsuspected way depending on mesh size, other reactants etc.

Ammonia and chlorates form ammonium chlorate, which is extremely instable and dangerous. Hence the risk with mixing hexamine with chlorates.