Pyrotechnic composition

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date=April 2017 A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas/smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions. Pyrotechnic substances do not rely on oxygen from external sources to sustain the reaction.

Contents

Types

Basic types of pyrotechnic compositions are:

Some pyrotechnic compositions are used in industry and aerospace for generation of large volumes of gas in gas generators (e.g. in airbags), in pyrotechnic fasteners, and in other similar applications. They are also used in military pyrotechnics, when production of large amount of noise, light, or infrared radiation is required; e.g. missile decoy flares, flash powders, and stun grenades. A new class of reactive material compositions is now under investigation by military.

Many pyrotechnic compositions – especially involving aluminium and perchlorates – are often highly sensitive to friction, impact, and static electricity. Even as little as 0.1–10 millijoules spark can set off certain mixtures.

Materials used

Pyrotechnic compositions are usually homogenized mixtures of small particles of fuels and oxidizers. The particles can be grains or flakes. Generally, the higher the surface area of the particles, the higher the reaction rate and burning speed. For some purposes, binders are used to turn the powder into a solid material.

Fuels

Typical fuels are based on metal or metalloid powders. A flash powder composition may specify multiple different fuels. Some fuels can also serve as binders. Common fuels include:

When metallic fuels are used, the metal particle size is important. A larger surface area to volume ratio leads to a faster reaction; this means that smaller particle sizes produce a faster-burning composition. The shape also matters. Spherical particles, like those produced by atomizing molten metal, are undesirable. Thin and flat particles, like those produced by milling metal foil, have higher reaction surface and therefore are ideal when faster reaction is desired. Using nanoparticles can drastically affect the reaction rates; metastable intermolecular composites exploit this.

A suitable metal fuel may be dangerous on its own, even before it is mixed with an oxidizer. Careful handling is required to avoid the production of pyrophoric metal powders.

Oxidizers

Perchlorates, chlorates and nitrates are the most commonly used oxidizers for flash powders. Other possibilities include permanganates, chromates, and some oxides. Generally, the less the oxidizer, the slower the burning and the more light produced. For use at very high temperatures, sulfates can be used as oxidizers in combination with very strongly reducing fuels.

Oxidizers in use include:

Corresponding sodium salts can be substituted for potassium ones.

Additives

See also

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<span class="mw-page-title-main">Ammonium perchlorate</span> Chemical compound

Ammonium perchlorate ("AP") is an inorganic compound with the formula NH4ClO4. It is a colorless or white solid that is soluble in water. It is a powerful oxidizer. Combined with a fuel, it can be used as a rocket propellant called ammonium perchlorate composite propellant. Its instability has involved it in a number of accidents, such as the PEPCON disaster.

<span class="mw-page-title-main">Potassium chlorate</span> Chemical compound

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<span class="mw-page-title-main">Flash powder</span> Pyrotechnic mixture

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A pyrotechnic colorant is a chemical compound which causes a flame to burn with a particular color. These are used to create the colors in pyrotechnic compositions like fireworks and colored fires. The color-producing species are usually created from other chemicals during the reaction. Metal salts are commonly used; elemental metals are used rarely.

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<span class="mw-page-title-main">Colored fire</span> Pyrotechnic effect

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<span class="mw-page-title-main">Barium oxalate</span> Chemical compound

Barium oxalate is a chemical compound with the chemical formula BaC2O4. It is a barium salt of oxalic acid. It consists of barium cations Ba2+ and oxalate anions C2O2−4. It is a white odorless powder that is sometimes used as a green pyrotechnic colorant generally in specialized pyrotechnic compositions containing magnesium metal powder. Flame color is rich and vivid without additional chlorine donors. Such compositions burn rate is satisfied without commonly used oxidizers as nitrates, chlorates and perchlorates.

Ammonium perchlorate composite propellant (APCP) is a solid rocket propellant. It differs from many traditional solid rocket propellants such as black powder or zinc-sulfur, not only in chemical composition and overall performance but also by being cast into shape, as opposed to powder pressing as with black powder. This provides manufacturing regularity and repeatability, which are necessary requirements for use in the aerospace industry.

<span class="mw-page-title-main">Flare (countermeasure)</span> Aerial defence against heat-seeking missiles

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In pyrotechnics, a pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, such as thermites, gas generators, and solid-fuel rockets. The name is often used also for the compositions themselves.

A smoke composition is a pyrotechnic composition designed primarily to generate smoke. Smoke compositions are used as obscurants or for generation of signaling smokes. Some are used as a payload of smoke bombs and smoke grenades.

<span class="mw-page-title-main">Nitronium perchlorate</span> Chemical compound

Nitronium perchlorate, NO2ClO4, also known as nitryl perchlorate and nitroxyl perchlorate, is an inorganic chemical, the salt of the perchlorate anion and the nitronium cation. It forms colorless monoclinic crystals. It is hygroscopic, and is a strong oxidizing and nitrating agent. It may become hypergolic in contact with organic materials.

Delay composition, also called delay charge or delay train, is a pyrotechnic composition, a sort of pyrotechnic initiator, a mixture of oxidizer and fuel that burns in a slow, constant rate that should not be significantly dependent on temperature and pressure. Delay compositions are used to introduce a delay into the firing train, e.g. to properly sequence firing of fireworks, to delay firing of ejection charges in e.g. model rockets, or to introduce a few seconds of time between triggering a hand grenade and its explosion. Typical delay times range between several milliseconds and several seconds.

A pyrotechnic heat source, also called heat pellet, is a pyrotechnic device based on a pyrotechnic composition with a suitable igniter. Its role is to produce controlled amount of heat. Pyrotechnic heat sources are usually based on thermite-like fuel-oxidizer compositions with slow burn rate, high production of heat at desired temperature, and low to zero production of gases.

<span class="mw-page-title-main">Rocket propellant</span> Chemical or mixture used as fuel for a rocket engine

Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical rocket, or from an external source, as with ion engines.

References

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