In the Olympic opening, Beijing used fireworks with the shape of footprint bring us to the stadium from Tian An Men. Then, before all the performance start, amazing, and great fireworks colored the whole dark sky.
The opening ceremony!!!
The formation of fireworks actually is based on the theory of combustion. There are 6 major ingredients in the composition of fireworks:
Fuel is use to start the fireworks through combustion. Fuel used in fireworks is charcoal, which also known as black powder in pyrotechnic industry. Normally, fuels that use in fireworks will contain organic element such as charcoal or thermite.
Fuel in fireworks is to lose electrons to atoms within the oxidizer and releasing atoms from the oxidizer. During this process, between fuel and oxygen will form a bond and produce a product which in stable stage. However, only a little amount of fuel-oxidiser compound required to start the combustion. After fuel-oxidiser compound start combust, it will produce and release solid mixture liquefies and vaporises into the flame of ignition.
The function of oxidizing agent is to produce oxygen needed for mixture inside the fireworks to burn. The most commonly oxidizers are nitrates. Nitrates are composed by nitrate ions ( NO3-) with metal ions. However, the most common oxidizer is potassium nitrate; it will decompose to potassium oxide, nitrogen gas and oxygen gas.
2KNO3 → K2O + N2 + 5/2 O2
From the equation above, we can observe that nitrate just releases 2.5 oxygen out of 3, so because of nitrates never release off all available oxygen, the reaction would not vigorous. In fact, nitrates not use in star explosions because the reactions of nitrates do not produce high enough of temperature to energize more colourful metal salts.
Chlorates, which contain chlorate ion ( CIO3-). It gives out all oxygen in the reaction, in fact it will have more explosive energy and produce about 1700 to 2000˚C temperature.
2KCIO3→ 2KCI + 3O2
Although chlorates have an extreme explosive, but it is very dangerous to handle because it is less stable. This is because chloride atom have the potential to form bond with four oxygen atoms but now it just bond with three oxygen atoms, so made the chlorine atom become unsaturated and non-stable. Instead, perchlorates are now been use in fireworks because it is more stable than chlorates and also release all the oxygen.
Perchlorates contain perchlorate ion (CIO4-) and each chlorine atom is bounded to four oxygen atoms which bonded with the maximum number of oxygen atoms, therefore perchlorates are more stable than chlorates.
KCIO4 →KCl + 2O2
The next element of fireworks is reducing agent. Reducing agent is use to burn with the oxygen that provided by oxidizing agent to produce hot gasses. Normally, sulphur and carbon would be used as reducing agent.
S + O2→SO2
C + O2→CO2
By following, regulator like metal that add into fireworks is to control the rate of reaction by speeding up or slowing the reaction. Based on collision theory, the larger surface area will increase the rate of reaction. So, the larger surface area of metal will increase or speed up the rate of reaction. Therefore, the finer the powder of metal, the faster the rate of reaction.
As we seem that the fireworks at Olympic got a lot of colour, so to produce different types of colour, different types of metal compound would be use in fireworks. In addition, different amount of energy release when reactions occur will characterized the colour of fireworks.
The metal compound and wavelength of colour of fireworks are listed in the table below:
The last element is binders. Binders are used to hold mixture of the fireworks together in a lump. There are two main elements used as binder, which are dextrin that dampened by water and shellac compound that dampened by alcohol. The binders actually do not begin work until it found that the fireworks has been lit and unstable for storage which potentially dangerous.