Science of FIREWORKS

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Fireworks function by the rapid, highly exothermic chemical reaction (burning) of a fuel with oxygen.  The hot gases generated by this process can emit light by themselves, or transfer the energy to other compounds that emit light.  The heat also serves to further release oxygen from the solid oxidizer, so it can combine with the fuel, ignite, and continue the reaction.  All pyrotechnic compositions contain for main ingredients – a fuel, and oxidizer, color/effect producing chemicals, additives, and binders.  Each of these will be explained more in-depth below.

Oxidizer

The word “burning” describes the oxidation of a fuel in air.  A campfire, for instance, uses oxygen from the air to turn wood (cellulose) into steam (H2O) and carbon dioxide (CO2), among other things.  This reaction releases a fair amount of heat – perfect for warming your hands, roasting marshmallow, or incinerating AOL “trial” CDs.  So why do fireworks need an oxidizer?  Simply because our atmosphere doesn’t provide  the chemicals with enough oxygen (O2) to sustain the rapid rate of burning that fireworks require in order to give off color, shoot into the air, or explode.  Only about 20% of the air we breathe is oxygen, which is only good for slow burning reactions like campfires.  If you throw a log on a campfire, you’ll notice that sometimes it takes hours for it to burn.  So fireworks compositions must include their own oxygen.  But because oxygen is a gas, it must be carried in a solid, powdered form – that is, chemically bound to another chemical.  Though there are hundreds of such compositions, the vast majority of these are useless for pyrotechnics because they require too much heat energy to release the oxygen.  Oxidizers much be compositions that will release their oxygen at low temperatures (hundreds of degrees ranther than thousands).

There are many compounds which make good oxidizers: potassium nitrate (KNO3), strontium nitrate (Sr(NO3)2), barium nitrate (Ba(NO3)2), potassium perchlorate (KClO4), ammonium perchlorate (NH4ClO4), potassium chlorate (KClO3), and barium chlorate (Ba(ClO3)2).

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