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NASA Standard Initiator

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NASA Standard Initiator

A pyrotechnic initiator (also initiator or igniter) is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, e.g. thermites, gas generators, and solid-fuel rockets. The name is often used also for the compositions themselves.

Pyrotechnic initiators are often controlled electrically (called electro-pyrotechnic initiators), e.g. using a heated bridgewire or a bridge resistor. They are somewhat similar to blasting caps or other detonators, but they differ in that there is no intention to produce a shock wave. An example of such pyrotechnic initiator is an electric match.

Composition

The energetic material used, often called pyrogen, is usually a pyrotechnic composition made of a fuel and oxidizer, where the fuel produces a significant amount of hot particles that cause/promote the ignition of the desired material.

Initiator compositions are similar to flash powders, but they differ in burning speed, as explosion is not intended, and have intentionally high production of hot particles. They also tend to be easier to ignite than thermites, with whom they also share similarities.

Common oxidizers used are potassium perchlorate and potassium nitrate. Common fuels used are titanium, titanium(II) hydride, zirconium, zirconium hydride, and boron. The size of the fuel particles is determined to produce hot particles with the required burning time.

More exotic materials can be used, e.g. [1]

For special applications, pyrophoric igniters can be used which burst into flame in contact with air. Triethylborane was used as an igniter for the Lockheed SR-71 jet engines.

Common compositions

Metal-oxidizer

ZPP

One of the most common initiators is ZPP, or zirconium – potassium perchlorate – a mixture of metallic zirconium and potassium perchlorate. It is also known as NASA Standard Initiator. It yields rapid pressure rise, generates little gas, emits hot particles when ignited, is thermally stable, has long shelf life, and is stable under vacuum. It is sensitive to static electricity.

BPN

Another common igniter formula is BPN, BKNO3, or boron – potassium nitrate, a mixture of 25% boron and 75% potassium nitrate by weight. It is used e.g. by NASA. It is thermally stable, stable in vacuum, and its burn rate is independent of pressure.

In comparison with black powder, BPN burns significantly hotter and leaves more of solid residues, therefore black powder is favored for multiple-use systems.

BPN's high temperature makes it suitable for uses where rapid and reproducible initiation is critical, e.g. for airbags, rocket engines, and decoy flares. It is however relatively expensive.

BPN can be also used as an ingredient of [2]

BPN can be ignited by a laser. [4]

Others

Other mixtures encountered are [5]

Metal hydride-oxidizer

Metal hydride-oxidizer mixtures replace the metal with its corresponding hydride. They are generally safer to handle than the corresponding metal-oxidizer compositions. During burning they also release hydrogen, which can act as a secondary fuel. Zirconium hydride, titanium hydride, and boron hydride are commonly used.

ZHPP

ZHPP (zirconium hydride – potassium perchlorate) is a variant of ZPP that uses [6]

THPP

THPP (titanium hydride potassium perchlorate) is a mixture of [7]

Intermetallics

Formation of an intermetallic compound can be a strongly exothermic reaction, usable as an initiator.

Titanium-boron

[8]

Nickel-aluminium

Nickel-aluminium laminates can be used as electrically initiated pyrotechnic initiators. NanoFoil is such material, commercially available.

Palladium-aluminium

[10]

Pyrofuze comes as a solid wire of different diameters (from 0.002" to 0.02"), braided wire, ribbon, foil, and granules. Palladium, [14]

Others

BNCP

BNCP, (cis-bis-(5-nitrotetrazolato)tetraminecobalt(III) perchlorate) is another common initiator material. It is relatively insensitive. It undergoes laser diode.

Lead azide

Lead azide (Pb(N3)2, or PbN6) is occasionally used in pyrotechnic initiators.

Others

Other materials sensitive to heat can be used as well, e.g. [16]

See also

References

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