Qubedworks
Smoke bombs (spring - summer 2011)
I started off by messing around with the two basic smoke bomb ingredients: potassium nitrate (KNO3) and icing sugar. Although I made various things during my pyrotechnics phase such as rockets, explosives and thermite, I spent a lot of time perfecting smoke bombs. My first tests were definitely not the most elegant but I quickly refined my products.
Good smoke bombs consist of KNO3 and sugar uniformly and finely mixed at a ratio of around 3:2.
If you've ever tried following some online tutorials you'll quickly realize that cooking KNO3 and sugar in a pot over a fire is not only a hassle to clean up (caramelized sugar) but also borderline dangerous. You don't want this thing going off in your kitchen. I'm speaking from experience here.
Another method used was wet mixing which consisted of dissolving the ingredients in water and then letting everything dry out. The dry crust obtained from this has to be powdered and squashed into a solid shape or otherwise into a cannister. Compressing this powder into anything half solid however, is not possible without a big press and is likely to crumble apart.
At first I made a press myself. I custom cut pieces of wood to fit a PE pipe section. The photos show the full setup: base, shaft, pipe and plunger.
I thought this pipe would have good non stick properties and would also resist a fair amount of heat against the hot slurry coming right out of the kitchen pot. Even though I was right, this ended up being quite a hot mess with me burning my fingers.
I ran eventually into a tutorial with a better recipe for more smoke consisting of 3:2:2 KNO3, icing sugar, paraffin. The preparation in the tutorial was done by cooking over a fire, so again making a nice mess this time with paraffin wax instead of caramelized sugar. The downside to this mix is that it requires a much higher temperature to set the mix off. A simple firework fuse wouldn't be hot enough to set the reaction off but instead I'd need to implement a second "hotter fuse" next to the mix.
The part of interest however here was the use of paraffin to suspend the KNO3 and sugar and the lower preparation temperature (sugar caramelizes at 186°C whereas paraffin already melts above 37°C). So I thought I'd do the preparation in the oven, where the temperature is much easier to control, directly in the cannisters. This meant less cleanup, less handling, more safety and a higer production capacity.
Below I have broken the preparation down into 5 steps:
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Premelt 2 parts of paraffin within the cannister in the oven. Then add 2 parts sugar and 3 parts KNO3 and stir until a uniform slurry is obtained (amount of ingredients depends on cannister size).
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Take the cannister out to cool and insert plunger (diameter 1 cm) in the middle at the top
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Remove plunger and wait till everything has cooled to ambient temperature. This is important as paraffin expands a lot with heat. The shape of the mix will therefore deform quite significantly while cooling.
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Insert the firework fuse into the pocket created by the plunger and fill the gaps with a secondary fuse. For the secondary fuse I used "sugar rocket fuel" which is basically 64% KNO3, 35% sugar and 1% iron oxide or rust. This is a fast burning, high temperature powder.
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Close the cannister.
Except for the KNO3, I got my hands on the rest of the ingredients locally and also ended up making my own.
To make gunpowder for example carbon is needed. I basically collected my own carbon powder by rubbing coal against sandpaper.
I also made my own rust by electrolysis. To obtain significant quantities, I accelerated the rusting of nails by connecting them to the anode. This just creates pure oxygen to form on the nails while immersed in a saline solution, ideal conditions for quick rusting
I made each cannister out of 2 cut aluminium beer cans. I drilled the exhaust holes using a mini drill and stretched one over the other as to deform it into a lid. It's important to not have too many holes as when the mix is exposed to too much oxygen when burning it has a tendency to catch fire. A flame uses up the mix in a different way and creates much less smoke.
Each of my cannisters is quickly sealed with an aluminium wire. It's pretty cheap and works well. The best part is that if you make your cannisters properly you'll even be able to reuse them.
Once ignited the mix continues to burn/release smoke even if immersed in water.
...This is all of course for educational purposes only, under controlled scientific conditions. Make them at your own risk and remember, safety first. Don't put any of this stuff in the microwave either, I've had a bad experience.
