hillbilly Posted July 22, 2014 Posted July 22, 2014 I'm not new to the hobby but I've never tried making crackling micro stars. I orderd some bismuth trioxide, 200m mg/al and I have black co and nc I'm a little confused on how greatly the ratios vary on the amount of bismuth trioxide on some of the formulas I've read any help on a starter formula with the chems I have?
Tommy Posted July 23, 2014 Posted July 23, 2014 Show here www.creagan.net/fireworks/compositions.html#dragonseggs
Mumbles Posted July 23, 2014 Posted July 23, 2014 I like the first formula he posted. It's worth a read. The information of NC, and getting enough of it in there, is really the key to making these work well. You can also use a blend of different sized MgAl, but straight 200 mesh works well to start off. The more coarser MgAl you use, the longer the delay, but louder they tend to be. Bismuth Trioxide - 3Copper Oxide - 3Magnalium - 2
hillbilly Posted July 24, 2014 Author Posted July 24, 2014 Thank you, I will give Mumbles formula a try. The chemestry of what is going on in crackle has me a little confused. I'm thinking the bismuth trioxide must be acting as both an oxidizer and part of the fuel. Everything I read about it discusses procedure and formula but I like to understand the basic chemestry before I do too much experimentation
Mumbles Posted July 24, 2014 Posted July 24, 2014 As far as I understand it, the reaction itself is similar to a strobe. There is a smoulder phase and a flash phase. Strobes make a little more logical sense since there are two oxidizers, one low temp and one high temp. Some of the Pyrotechnica journals may have information. To the best of my knowledge, the oxidizer or oxidizer mix reacts with the aluminum portion of MgAl. This builds up some sort of intermediate oxidizer, likely Copper (I) oxide and Bi (II) Oxide, or at least some sort of complex mixed valent compounds, which eventually undergo an explosive reaction with the magnesium.
hillbilly Posted July 24, 2014 Author Posted July 24, 2014 (edited) Interesting, i wonder if the reaction would be the same in a vacume or if maybe it gets part of its oxygen from the air? Gonna do some experimenting carefully (on the ground) too dry for anything in the air for a few more months thanks for the info Edited July 24, 2014 by hillbilly
Yus Posted March 17, 2016 Posted March 17, 2016 I have found that light/bright Al-Mg powder works well in crackling microstars with different mixtures of Bi and Pb and Cu oxides. But grey or dark Al-Mg powder does not work. Why this happen? How to resume crackling effect with dark Al-Mg powder? And, why Al-Mg powder becomes dark if Al2O3 and MgO have white colour? P.S. Sory for my bad English.
lloyd Posted March 17, 2016 Posted March 17, 2016 (edited) Yus,The dark color is an indication of surface oxidization. I do not know this to be the case, but that may inhibit the reaction from proceeding as it should. I do know that the oxides of aluminum are high-temperature "refractory" substances that may take substantial energy to decompose, and thus rob energy from the smoulder reaction. Lloyd Edited March 17, 2016 by lloyd
Mumbles Posted March 18, 2016 Posted March 18, 2016 The darkness is an uneven surface effect. The oxidation is probably not all that deep, potentially to the point that the surface oxide can't absorb all of the light. That's not important though. As the metal is slowly corroded, it wont oxidize evenly. Even if you started with a perfectly smooth piece of metal, it'd soon start looking like sandpaper microscopically. This rough surface scatters light more, so less is reflected. This has the effect of appearing darker than one would expect. Very small particles of matter interact with light differently as well. It's probably not at play here, but can have very unexpected results sometimes.
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