10 replies to this topic

[Gary]

Magnalium (MgAl) alloy seems to be included in every crackle formula in combination with CuO, lead tetroxide or bismuth subcarbonate/oxide.
Is there any particular reason for this? I mean, why can't either of the parent aluminium or magnesium metals be used instead of the MgAl alloy? Could a 50/50 mixture of fine magnesium and aluminium be used, or is it essential for it to be in alloy form?

[Mumbles]

I can't speak for the equal parts thing, but I have my doubts if it would work.

MgAl is required because it can burn vibrationally. Dragon eggs, like strobes require an on and off phase. The off phase is the smoulder phase. You will see the dragon egg burn bright orange/red. The on phase is the crack at the end. As I understand it, the metals react separately. If using a mixture I'm not sure if you could get as distinct of a delay. Strobes can be done in the same was as dragon eggs with vibrationally burning MgAl, or two separate oxidizers with AP and a sulfate. In theory something could be done with dragon eggs, but I've never seen anything violent enough. I think the CuO kind of plays on this, but more serves as an additive to make the crackle louder.

[Gary]

[quote name='Mumbles' date='06 November 2009 - 02:25 PM' timestamp='1257517540' post='61520']
I can't speak for the equal parts thing, but I have my doubts if it would work.

MgAl is required because it can burn vibrationally. Dragon eggs, like strobes require an on and off phase. The off phase is the smoulder phase. You will see the dragon egg burn bright orange/red. The on phase is the crack at the end. As I understand it, the metals react separately. If using a mixture I'm not sure if you could get as distinct of a delay. Strobes can be done in the same was as dragon eggs with vibrationally burning MgAl, or two separate oxidizers with AP and a sulfate. In theory something could be done with dragon eggs, but I've never seen anything violent enough.

Perhaps there is a violent thermite-type reaction occuring? I have read that CuO-Al thermite reacts with almost explosive ferocity.
Regarding a 'vibrational burn', that reminds me of oscillatory chemical reactions, such as the 'iodine clock' or Belousov-Zhabotinsky reaction.

[a_bab]

I'm sure Mg powder will work just as well as magnalium. But, some issues may arise with the known problems associated with the use of Mg. So the "vibrational" burning doesn't explain the reaction (besides, magnalium burns "vibrationally" with barium/strontium nitrate and it is a different thing there; so does mag,nesium with AP/sulphates. So it's irrelevant to dragon eggs.)

Once touched by a flame, a exothermical reaction melts the star first, and (if large) will stay like this for some time and then suddenly go bang. Even a large amount (10's of grams) is capable of exploding if proper conditions are met (like heating the mix evenly and being prepared for a deafening report)

There are things like NC laquer known to be absolutely necesary for the cracke to occur. It's not the case BUT if potassium nitrate from the prime gets soaked in the star it will ruin it. So does water. That's why acetone is needed as a wetting/solvent agent.

Not even copper oxide is needed to get a loud crackle. The only things really needed are:
1. magnalium/magnesium (somewhat coarse, 30-60 mesh)
2. lead tetraoxide/bismuth trioxide/bismuth subnitrate/bismuth subcarbonate (as for now, new chems may be discovered)

Each other component has it's role (NC - for better incorporation, water protection and inflamability; copper oxide - diluant, delay agent, may help on loudness as it reacts too in thermite fashion as stated before)

What it is well known for now is that it must be a thermite kind of reaction.

Because the coarseness is a must, I have this theory of what happends. The reaction is obvious (explosive reduction to lead/bismuth metal).
Basically I think that in the first phase, when the mixture melts (delay step), the magnalium particules start to "dissolve" in the melted mix till the optimum concentration is reached. This is the delay. Once the concentration is achieved, the melt will explode with so much violence due to the speed of the reaction, greatly increased by the molten state (better mixture, and extra energy).

Edited by a_bab, 06 November 2009 - 04:26 PM.

[Mumbles]

Coarseness is not required. You can make fully functional dragon eggs with -200 mesh MgAl. The only difference is the delay. At some point the delay between smoulder and bang becomes shorter than the time required to turn the whole granule into a fully molten blob. At this point it turns into kind of a sizzle.

You may also be surprised to find out that NC is not required. I've seen crackle successfully made with water and dextrin in a commercial manufacturing facility. The key is to seal the granules after this step to prevent other chemicals from entering the granule. They will disrupt the proper burn pattern.

[CCH Concepts]

what do they seal them with, wax?

also the dragon eggs ive made so far have been about 2 or 3mm am i going to get a much better effect if i go bigger?

[Mumbles]

I've seen wax and deck wood sealer used. I don't know if I am at liberty to give away their process, but it is a typical crackle formula.

When you go too big you run into the above problem of the crackle part out running the delay. It will break apart into kind of a cascade of additional crackles. I've seen them go as large as 6mm or so if you are good and careful. I think it may have been pressed.

[CCH Concepts]

i have been ricing them, with cotton coat, glasses and gloves. as i use lead tetra-oxide and I'm not going to risk finding out if it is a poisonous as people say. i tend to make my bigger stars by cutting them and once they have dried a little rolling them by hand to i guess 6-10 mm depending on application. would this be a suitable method?

[pyrotechnist]

What does a draggon eggs mix burn like when burned as a free flowing powder without any binder or being turned into micro-stars? My personal theory of how they work is that the Nitrocellulose and magnesium burn off creating a thick molten layer that surrounds the core which then leaves the oxide and aluminum to burn which turns into a violent aluminum based flash that explodes due to the surrounding crust encapsulating it.

The problem with using dextrin as a binder is the fact that the micro-stars will start mixing with any sort of matrix mix you may use when pumping them as a matrix star etc. This is where the NC comes into play as it seems to act as some sort of delay fuel as well as it protects the micro-stars from alcohol and water unless you use acetone lol. It seems that the potassium nitrate seeping into the crackle mix may just be a bit of over hype as this has never seemed to be a real problem.

[jayden]

Does the pingpong ball nitrocellulose lacquer have any downfall in comparison to proper nitrocellulose lacquer
in dragon egg stars (esp. in the Bismuth subcarbonate version)?

[tamaldas]

Magnalium (MgAl) alloy seems to be included in every crackle formula in combination with CuO, lead tetroxide or bismuth subcarbonate/oxide.
Is there any particular reason for this? I mean, why can't either of the parent aluminium or magnesium metals be used instead of the MgAl alloy? Could a 50/50 mixture of fine magnesium and aluminium be used, or is it essential for it to be in alloy form?

The cracklig star formulae are basically thermite mixtures in which a metal oxide eg.Pb3O4,Sb2S3,Cu(ll)O orFe2O3 reacts with a reactive metal such as Mg or Al. In the reaction metal oxides break into their corresponding metals with explosion producing lots of heat called Thermite reaction. . CuO reacts readily with Al & Mg.Hence CuO is used in small amounts in the crackling formulae to start the initial reaction first to produce the heat, the heat evolved in the reaction further initiates decomposition of Pb3O4 or Sb2S3 which is present in a higher percentage in the composition. Thus MgAl is a must in crackling compositions.