Chemistry of pyrotechnics
Pyrotechnics use a variety of chemistry concepts, which produce different effects of sound and color. Although fireworks are pyrotechnics, not all pyrotechnics are fireworks. Pyrotechnics include any effect that uses rapid oxidization to produce an effect of light or sound. This excludes almost all high explosives except for a very few used in pyrotechnics such as picric acid. Thermite reactions and decomposition of ammonium dichromate2 are never used in commercial fireworks but they can be pyrotechnic displays.
An important part of pyrotechnics to the amateur is synthesis of different chemicals to be used in certain reactions. |
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Often chemicals cannot be acquired for reasonable prices, so the chemicals are manufactured at a home lab. There are a wide variety of chemistry principals that apply to pyrotechnics and making different chemicals for pyrotechnic use.
These include the use of the periodic table and of course the elements,polyatomic ions and compounds, ionic, molecular compounds, hydrocarbons, synthetic substances, and sometimes balancing equations. They also include synthesis and decomposition reactions, double and single displacement reactions, controlling rates of reactions, endothermic and exothermic reactions, acids and bases, and element oxides. Of course combustion is a central part of pyrotechnics and is dealt with throughout the other topics instead of being given its own section.
Chlorates are useful in most types of colored fire composition.
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Their large oxygen content is useful for starting the chemical reaction, and the ions they yield produce the color that is desired. For instance: mixing barium chlorate and orange shellac, a binder / fuel resin that is basically a complex carbohydrate with some trace elements, can produce a green flame. Potassium chlorate, orange shellac and strontium compounds can produce red flames.Stable, safe formula for white, blue and purple flames were developed in the 20th century. Before this time, the majority of recipes was unsafe and needed to be precisely mixed for them to work properly. The modern firework generates white flames with the addition of antimony and aluminum dust to potassium nitrates and some sort of fuel, such as charcoal or shellac. Blue coloration is generally achieved with the use of copper, sulfur and potassium compounds. |
Oxidizers
The first thing in a firework is the oxidizing agent. These produce the Oxygen to burn the mixture. Oxidizers are usually nitrates, chlorates or perchlorates. The common oxidizers are nitrates. These are made up of a metal ion and the nitrate ion. I'll use potassium nitrate as an example. Nitrates only give up 1/3 of their oxygen. The resulting equation would look something like this:
2XClO3 -› 2XCl + 3O2
The next Oxidizers are chlorates are also made up of a metal ion and then the chlorate ion. Chlorates give up all of their oxygen, causing a more spectacular reaction. Unfortunately this also makes the chemicals EXTREMELY explosive. An example of a chlorate giving up its oxygen would look something like this:
XClO4 -› XCl + 2O2
Perchlorates have more oxygen in them, but are less likely to explode if you drop them than are chlorates. Again these are made up of a metal ion and then the perchlorate polyatomic ion. An example of a typical perclorate giving up its oxygen would look something like this, (graphic).
Reducing Agents
The second elements of fireworks are the reducing agents. The reducing agents burn the oxygen produced by the oxidizers to produce hot gasses. Two examples of reducing agents are Sulfur and Charcoal(carbon). These react with the oxygen to form respectively Sulfur Dioxide and Carbon Dioxide.
Binders
The fourth element of fireworks are the binders. Binders hold the mixture in
a lump. This lump is a star. In order to form a star, two main elements
are used. These two are dextrine dampened by water, or a shellac
compound dampened by alcohol. These are rolled and then cut, or
the mixture is forced into a paper tube, and pushed out with a dowel.
Then the stars are cut as they come out.
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