So the other week I was fortunate to witness Guy Fawkes’ Day/Bonfire Night. As I was watching the different coloured fireworks and effects, I began to wonder how fireworks work.
The art of chemistry
The art of pyrotechnics comes down to basic chemistry, oxidation (if anyone remembers previous posts on oxidation, it is the process of losing or gaining electrons) and the addition of chemicals which create heat (exothermic reactions). In the case of fireworks, a fuel source (usually a metal) is oxidised by an oxygen source other than atmospheric oxygen. Traditionally, nitrates, perchlorates and chlorates are used as oxidisers.
So what about the colours? The range of colours that we see during a fireworks display are due to the addition of metal salts. Sodium is used for yellow, strontium for red, barium salts for green, and copper for blue. The white/incandescent effects are due to white hot burning metals such as magnesium (does anyone remember during Chemistry class watching Mg burn when it came into contact with air??!!).
A little bit of timing, a little bit of engineering
The chemistry is actually the easiest part of creating fireworks. The next step is to send the fireworks into the sky. This is where the engineering comes into it. Fireworks are traditionally shaped like a missile, with a long stick, a fuse, a charge, and a head that contains the pyrotechnic chemicals (sometimes with several housing units making up the head).
The fireworks also normally contain several fuses attached to different housing heads. The fuses are timed, so as to create the differently timed explosions that we see. Gunpowder is most often used as a charge, which propels the missile into the air and creates the first explosion that promotes the secondary reactions containing the coloured salts. Et voilà!
Simple chemistry, a little bit dangerous
Although the principle behind fireworks is simple and it seems relatively straightforward to make them, they are explosives and are therefore dangerous. The ratio of chemicals, the amount of gunpowder used, and fuse and tail length all need to be precise. If not, premature explosions can occur which can result in injuries.
So my take home message? Enjoy the show, appreciate the chemistry and the feats of engineering, but don’t try it at home!!