A pyrotechnic initiator
) 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.
The energetic material used is usually a pyrotechnic composition
made of a fuel and oxidizer, where the fuel produces a copious 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. carboranes.
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.
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
Another common igniter formula is BPN
, 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 on pressure.
-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.
(zirconium hydride - potassium perchlorate
) is a variant of ZPP that uses zirconium hydride
instead of pure zirconium. It is significantly safer to handle than ZPP.
(titanium hydride potassium perchlorate) is a mixture of titanium(II) hydride
and potassium perchlorate. It is similar to ZHPP. Like ZHPP, it is safer to handle than titanium-potassium perchlorate.
, (cis-bis-(5-nitrotetrazolato)tetraminecobalt(III) perchlorate
) is another common initiator material. It is relatively insensitive. It undergoes deflagration
transition in a relatively short distance, allowing its use in detonators
. Its burning byproducts are of relatively little harm to environment.
It can be ignited by a laser diode
, or PbN6
) is occasionally used in pyrotechnic initiators.
Other materials sensitive to heat can be used as well, e.g. tetrazene explosive
, lead mononitro-resorcinates, lead dinitro-resorcinates, and lead trinitro-resorcinates.