I've never posted any of my work on this forum, but decided to do so as it definately falls into the realm of amateur pyrotechnics. The formulas I post are flash-type reactions, so if you are not familiar with any of these, please be warned: Easy does not mean safe. Here goes...
Being fasinated by pyro-chemistry and particularly the use of easily obtainable, safe chemicals to make pyro, i started fiddling around with a strobe mix made up of Plaster of Paris, Sulfur and MgAl (50/50). The idea for this came from an article by Shimizu where he discribes the strobe mechanism. In this he suggested various chemical pairs for the "flash" reaction and some for the "smoulder/dark" reaction. Two of these pairs caught my attension. BaSO4/Al for the flash- and S/Mg for the smoulder-reaction. Having done some experiments with CaSO4 (Plaster of Paris) and MgAl, I knew that this made a pretty decent flash if the CaSO4 was completely dry, so i wondered if it would be possible to make a strobe mix using MgAl, CaSO4 and S.
I started by writing the reaction equations for CaSO4/MgAl and S/MgAl assuming sulfide products and came up with:
A) CaSO4/MgAl = 63/37 (wt%)
S/MgAl = 61/39 (wt%)
I tested these. The CaSO4 reacted as expected. Flash! The S/MgAl surprised me a bit. This mix "burns" with a flash&pop! Scary stuff and definately not a smoulder reaction, but i decide to continue...
Next I mixed a 1:1 ratio of A and B. As i couldn't use a waterbased binder with the CaSO4, i decided to bind with +10% NC made from ping-pong balls dissolved in acetone. I let it dry and then tried to light a small pellet wearing leather gloves, leather apron, face shield and ear plugs. Nothing happend except when heating for a while in which case it would flash and go out abruptly. Not exatly what i was expecting and after thinking on it for a while, i guessed the problem might be that there is not enough of the "smouldering" reactiong going on to initiate the "flash" reaction.
Next i tried A:B = 1:2. Garbed in my chicken-suite, i tried again. It worked! The mix burnt with beautiful small sparks and then would flash unexpectedly leaving me completely blinded. The flashes were irregular between 10 end 15seconds and would sometimes go out after a few flashes due to the intensity of the reaction. Still seeing black spots everywhere, i cracked open a beer and celebrated my success. It was a good day.
Next i decided to increase the amount of B to A to see if i could get a stable reaction. I tried A:B = 1:3 and A:B = 1:4. The 1:3 mix performed the best with stable flashes around 4sec. The 1:4 mix flashed irregularly between 3 and 5sec throwing of a lot of sparks.
Sticking to the 1:3 mix i decided to add some KNO3 to the mix in an attempt to increase the flash rate. I added +10%wt KNO3 to B and this worked, but the flashes came more irregular and burning longer. At this point my experimentation was interupted by life, so i decided to share what i have hoping to pass the baton.
Currently the best mix is:
S (#70) 47%
MgAl (<45um) 37%
Bind with +10%NC from ping-pong balls
The Plaster of Paris (CaSO4) is for modeling and is super fine. I bake this for 1hr @ 200oC to drive off as much moisture as possible (CaSO4.1/2H2O -> CaSO4). The ingredients are sieve-mixed 3times using a #30 sieve. NC is mixed with Acetone and incorporated into the mix. Acetone is evaporateded during mixing until a putty is obtained that can be made into pellets. Fast drying gives the best results.
Note: 5%NC is probably sufficient to bind this mix, but i add the extra 5% to prevent the absorption of moisture. This seems to work as i've tested pellets left outside and these seem to perform the same as stored ones. I would recommend using a drying box as there is some chance of moisture absorption during the drying process.
I've not made stars or grains from this so have no data on it's performance during flight. It does give a very novel experience as this burns with a beautiful volcano like effect until the flash which is absolutely blinding! :-) The repeat rate is about 0.25Hz (4sec).
I look forward to hear if any of you have done work on this and look forward to any follow-ups on my work.
If you can't be good, be good at it.
P.S. The pellets light quite easily, but if you are making them into stars, i guess a prime would be neccesary. One could also granulate this and add them as micro-stars to a willow-mix. The binder probably needs to be replaced by an alcohol-based binder (shellac/red gum) to prevent water getting into the CaSO4. A chlorine doner (PVC, Parlon) can also be added to the mix to get orange-flashes. I've not done any of this, so have no idea what the resuls will be.