Requirements
In addition to an oxidizer, pyrotechnic mixtures will also contain a good fuel - or electron donor - that oxygen to produce an oxidized product plus heat. This heat will enable the high-energy chemist to produce any of a variety of possible effects - color, motion, light, smoke, or noise.
The desired pyrotechnic effect must be carefully considered when a fuel is selected to pair with an oxidizer for a high-energy mixture. Both the flame temperature that will be produced and the nature of the reaction products are important factors. The requirements for some of the major pyrotechnic categories are:
1. Propellants: A combination producing high temperature, a large volume of low
molecular weight gas, and a rapid burnning rate is needed. Charcoal and organic
compounds are often found in these compositions because of the gaseous products
formed upon their combustion.
2. Illuminating compositions: A high reaction temperature is mandatory to achieve
intense light emission, as is the presence in the flame of strong light-emitting
species. Magne- sium is commonly found in such mixtures due to its good heat output.
The production of incandescent magnesium oxide particles in the flame aids in achieving
good light in- tensity. Atomic sodium, present in vapor form in a flame, is a very
strong light emitter, and sodium emission domi- nates the light output from the
widely used sodium nitrate/ magnesium compositions.
3. Colored flame compositions : A high reaction temperature produces maximum light
intensity, but color quality depends upon having the proper emitters present in
the flame, with a minimum of solid and liquid particles present that are emitting
a broad spectrum of "white" light. Magnesium is sometimes added to colored flame
mixtures to obtain higher intensity, but the color quality may suffer due to broad
emission from MgO particles. Organic fuels (red gum, dextrine, etc.) are found in
most color mixtures used in the fireworks industry.
4. Colored smoke compositions: Gas evolution is needed to disperse the smoke particles.
High temperatures are not desirable here because decomposition of the organic dye
molecules will occur. Metals are not found in these mixtures. Low heat fuels such
as sulfur and sugars are commonly employed.
5. Ignition compositions: Hot solid or liquid particles are desirable in igniter
and first-fire compositions to insure the transfer of sufficient heat to ignite
the main composition. Fuels producing mainly gaseous products are not commonly used.
A good fuel will react with oxygen (or a halogen like fluorine or chlorine) to form a stable compound, and substantial heat will be evolved. The considerable strength of the metal-oxygen and metal-halogen bonds in the reaction products accounts for the excellent fuel properties of many of the metallic elements.
A variety of materials can be used, and the choice of material will depend on a variety of factors - the amount of heat output required, rate of heat release needed, cost of the materials, stability of the fuel and fuel /oxidizer pair, and amount of gaseous product desired. Fuels can be divided into three main categories. metals, non-metallic elements, and organic compounds.