The Science of fireworks
Year eight students were very lucky to be able to visit the Royal Institution and watch a wonderful lecture on fireworks.
Fireworks consultant, author and former Oxford chemist Dr Tom Smith explained the basic chemistry and construction of fireworks, and their use in modern fireworks displays. The talk included spectacular demonstrations of bangs, whistles and colours that certainly appealed to Rooks Heath’s year eight. Tom has travelled the world acting as pyrotechnic consultant to the Olympic and Commonwealth Games and, closer to home, working on the London New Year celebrations since 1999. He has lectured widely on pyrotechnic chemistry and has recently published a book on firework displays.
Fireworks were first made in China over 1,000 years ago! Gunpowder is what makes gunpowder explode. Potassium nitrate is the most important part of gunpowder. This is what propels the firework into the sky. A fuse is used to light the gunpowder, which ignites to send the firework skyward. Once the firework is in the air, more gunpowder inside it causes it to explode with a BANG! The colours are produced by the metal salts in the mixture burning.
The fuse sets off a charge, which ignites the gunpowder. This propels the firework into the sky.
Once the firework is in the sky, the gunpowder within the firework ignites. This causes the ‘stars’, which contain metal salts and iron filings, to explode in different colours and sparkles. If the firework is in sections, the stars can be in different compartments. These compartments explode at different times, making different patterns.
The pattern of stars around the central gun powder charge creates different patterns of fireworks. For example, if the stars are in a circle around the black powder charge, you get a circle display of colour.
A simple shell used in an aerial fireworks display. The blue balls are the stars, and the grey is black powder. The powder is packed into the centre tube, which is the bursting charge. It is also sprinkled between the stars to help ignite them.
For most fireworks the hotter the firework the nearer the colour is to white. Red fireworks have one of the lowest temperatures.
Red fireworks get their colour from strontium salts such as strontium carbonate (bright red) and lithium salts such as lithium carbonate (red).
Green colours get their colour from barium compounds + chlorine producer such as barium chloride (bright green).
Blue fireworks get their colour from copper compounds + chlorine producer such as copper acetoarsenite, known as Paris Green (blue) and copper (I) chloride, (turquoise blue).
Orange fireworks get their colour from calcium salts such as calcium chloride, calcium sulphate.
Gold fireworks get their colour from incandescence of iron (with carbon), charcoal, or lampblack as well as some sodium compounds.
To understand why the fireworks produce different coloured lights think about electrons of the atom sitting on the bottom rung of a “step ladder”. Each rung is an energy level and the electrons remain on the low energy rung unless they are given some energy.
However the electrons don’t remain at the higher energy level forever. They drop back down and light is emitted. The bigger the drop the more energy is released and the shorter wavelength light is produced.
Our year eight students enjoying the show.