12 replies to this topic

[digger]

Right then it has been a little bit of time since I have done any experimentation so I thought I would give it a go.

I thought I would look for a new cheaper crackling microstar mix. So here is my first try at a formula

MnO2 18.7
CuO 18.7
MgAl 12.5 (325 mesh)
10% NC solution 12

So they are sat drying at the mo. I lit a wet one which gave a very bright white flash, so there is some hope.

Does anyone have any experience or practical advice to add on this type of thermit reaction as I have not had allot of experience with crackling microstars to date.

[dr thrust]

i'll look forward to the results, the only thing ive used mnO2 but mixed with german dark in was a experimental rocket motor, it was ferocious to say the least and a small loose batch 2g acted like a flash mix with the same bright flash as you described lol, in fact it made me jump back

Edited by chris m, 16 November 2009 - 06:52 PM.

[a_bab]

I once made a mix made of MnO2/Al powder and made a salute out of it. The report was quite deep, indicating a lower reaction speed compared to Pb3O4/Al mix, that works great for salutes (comparable to flash). It was impressive nevertheless.

Also, I looks like it would melt around 500 degrees C with decomp. Bi2O3/Pb2O4 melt around 800 degrees, which is apparently needed for the delay but I can't wait for the results. It would make indeed a nice, even OTC replacement (from batteries). I would have never thought about this, but rather about Sb2O3 as a replacement for Bi salts known to work in dragon eggs (trioxide, subcarbonate, subnitrate).

It's not a bad idea to use the microstar as a flash core for round stars (japonese style stars).

Edited by a_bab, 17 November 2009 - 07:06 AM.

[seymour]

In my experience Manganese dioxide/aluminium thermite has been a moderate speed, clean burning mixture, due to the gaseous state of the metal emitted by the reaction.

With Magnalium I know it's used as a rocket fuel. Seeing that copper oxide burns much faster with metals than manganese dioxide, but still does not pop like a dragon eg, I am not very confident that it will work as intended. Still, the addition of the NC changes things a fair bit. I hope I'm wrong

Just noticed that a_bab got in way ahead of me. You seem to have had more promising results than me. In the salute you described, what Aluminium was used?

Edited by seymour, 17 November 2009 - 08:58 AM.

[Gary]

I wonder whether substituting lead tetraoxide or bismuth compounds for tin dioxide (SnO2) would work in a crackle formula? After all, tin is similar to lead in its physical properties; like lead, it melts at a relatively low temperature, and both tin and lead have similar (although not identical, of course) chemistries. Tin is in the same group as lead in the periodic table (group 14). If tin dioxide produces a good crackle effect in a microstar formula, it has the added bonus of being a little less toxic than lead. I might order a small batch of tin dioxide from a ceramic dealer, just to see if it is any good. Even if the effect is not exactly the same as the loud report produced in lead or bismuth crackling microstars, it still might be worthwhile. A new, novel effect might be 'discovered'!

[Mortartube]

If using tin in mixes, you must be very careful to avoid the formation of Stannic Acid, which is undesireable in pyro mixes. This is the reason it is not used commercially. Best avoided.

[a_bab]

The aluminium I used in the MnO2 based salute mix was paint grade aluminium (flake, 300+ mesh I suppose). It works decently in a KP based flash.
But with magnalium it should work better.

Actually I remember now I discovered the flash-like reaction when I tried to get manganese metal via aluminothermic reduction. I only got vapors of it, that's for sure (reoxidised to something else, or maybe back to MnO2 ).

Edited by a_bab, 17 November 2009 - 04:17 PM.

[digger]

Ok then chaps. Thanks for the input.

The initial formula shows promise as a flash core. Bright white flash without any delay with 1mm x 1mm cut stars. When I tried a 3mm x 3mm x 1mm square it strobed quickly and brightly (The fast strobing made the misses feel ill) . I will try it with a larger mesh MgAl to see if I can slow down the strobing.

OK next formula

MnO2 20
CuO 7
MgAl 325 mesh 8
KNO3 3
S 3
NC 10% 10

More promising quicker flash with a slight pop. So I will up the Sulphur drop the MnO2 a little and remove the KNO3 to see what effect this has.

Maybe do a star gun test at the weekend.

[a_bab]

I'd start from a basic dragon egg formula and tune it.

Besides, I can't see why potassium nitrate would help for crackling. It is known to even destroy the crackle effect.

Edited by a_bab, 17 November 2009 - 06:51 PM.

[digger]

I'd start from a basic dragon egg formula and tune it.

Besides, I can't see why potassium nitrate would help for crackling. It is known to even destroy the crackle effect.

Although there are a few published compositions with it in. Such as the one I used as the second formula to which I replaced the PbO4 with the MnO2. Which I have tried as a microstar using modified synthetic NC which made earsplitting bangs.

[a_bab]

Oh, didn't know about that one. Sorry...

[pyrotrev]

I looked at MnO2 for crackle/flash compositions a while back, primarily because MnO has some spectral lines in the yellow-green part of the spectrum and was hoping some coloured flashes might be forthcoming. In general I found it less reactive than CuO, though it does seem to have a useful delay. Results were as follows:

A 70/30 mix of MnO2 with dark Al gives a gentle slow flash, slightly yellowish.

A 70/30 mix of MnO2 with MgAl gave an even slower flash, but the composition in powder form didn't all burn at once - sometimes there were 3 or 4 flashes at 3....5 sec intervals. Interesting that Digger found some strobe effects.

Replacing lead oxide in the Pb3O4/CuO/MgAl/KNO3/S mix in Lancaster gave microstars with a good delay and a decent flash, but only a gentle pop rather than the sharp crack you get with lead - nice effect in a fountain though.

[MDH]

I have a generally more laborous way of producing flash cores. Essentially, I just take a flash composition and make a number of small crackers (2/4 by 1/4) and hand roll them in a fast burning black powder based star. There is very little fuse once the burning star composition reaches the small report.

Colors are amusing and simple once you learn how to effectively produce them - Most of the time it is nearly equal parts of a nitrate and magnesium with a small amount of parlon. Perchlorates are never included.