Pyrotechnic initiator

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 which 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.{{cite patent |country=EP |number=1128994B1 |status=expired |title=Carborane-containing airbag inflator |pubdate=2001-09-05 |gdate=2004-08-11 |fdate=1999-11-09 |pridate=1998-11-16 |inventor=Karl K. Rink |assign1=Autoliv ASP Inc.}}

For special applications, pyrophoric igniters can be used which burst into flame in contact with air. Triethylborane/TEA-TEB was used as an igniter for the Lockheed SR-71 jet engines, the Rocketdyne F-1 engine on the first stage of the Saturn V, NPO Energomash's RD-180 engine used on the first stage of the Atlas V, and SpaceX's Merlin engine used on the first stage of the Falcon 9.

One of the most common initiators is ZPP, or zirconium – potassium perchlorate – a mixture of metallic zirconium and potassium perchlorate. This mixture is used in the NASA Standard Initiator,{{cite book

|date=1 January 1995

|title=Applications catalog of pyrotechnically actuated devices/systems

|url=https://ntrs.nasa.gov/api/citations/19950011972/downloads/19950011972.pdf

|location=Cleveland, OH

|publisher=NASA Lewis Research Center

|pages= 66 - 67

|archive-url=https://web.archive.org/web/20220822092153/https://ntrs.nasa.gov/api/citations/19950011972/downloads/19950011972.pdf

|archive-date=22 August 2022

}} which is used to ignite various pyrotechnic systems, including the NASA standard detonator.{{cite book

|date=1 October 1963

|title=Proceedings of Electric Initiator Symposium - 1963

|url=https://apps.dtic.mil/sti/pdfs/AD0440764.pdf

|location=Franklin Institute, Philadelphia, Pennsylvania

|publisher=U.S. Army Materiel Command

|pages= 3-17

|archive-url=https://web.archive.org/web/20180528000000/https://apps.dtic.mil/sti/pdfs/AD0440764.pdf

|archive-date=28 May 2018

}} [https://archive.org/details/DTIC_AD0440764/mode/2up Alt URL] 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, 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 solid rocket propellants.

BPN can be ignited by a laser.{{cite patent |country=ES |number=2160485B1 |status=expired |title= Neuron exocytosis inhibitory peptide and cosmetic and pharmaceutical compositions containing the peptide |pubdate=2001-11-01 |gdate=2002-05-16 |fdate=1999-04-23 |pridate=1999-04-23 |inventor=Blanes Mira Maria Clara; Carbonell Castell Teresa; Fernandez Ballester Gregorio J; Ferrer Montiel Antonio Vicente; Gil Tebar Ana Isabel; Gutierrez Perez Luis Miguel; Llobregat Hernandez M Mercedes; Perez Paya Enrique; Planell Cases Rosa M; Viniegra Bover Salvador |assign1=Lipotec SA}} A semiconductor laser of at least 0.4 watts output can be used for ignition in vacuum.{{Cite journal |last=Koizumi |first=Hiroyuki |last2=Nakano |first2=Masakatsu |last3=Inoue |first3=Takayoshi |last4=Watanabe |first4=Masashi |last5=Komurasaki |first5=Kimiya |last6=Arakawa |first6=Yoshihiro |year=2006 |title=Study on laser ignition of boron/potassium nitrate in vacuum |url=http://www.jes.or.jp/mag/stem/Vol.67/documents/Vol.67,No.6,p.193-198.pdf |journal=Science and Technology of Energetic Materials |volume=67 |issue=6 |pages=193-198}}

Other mixtures encountered are aluminium-potassium perchlorate and titanium-aluminium-potassium perchlorate.{{cite patent |country=US |number=4391196 |status=expired |title= Add-on igniter for pyrogen type igniter |pubdate=1983-07-05 |gdate=1983-07-05 |fdate=1981-04-20 |pridate=1981-04-20 |inventor=Robert E. Betts |assign1=US Department of Army}}

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 (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.{{cite patent |country=US |number=6117254 |status=expired |title= Initiator for airbag inflation gas generation via dissociation |pubdate=2000-09-12 |gdate=2000-09-12 |fdate=1998-02-20 |pridate=1998-02-20 |inventor=Karl K. Rink, William B. Richardson, David J. Green |assign1=Autoliv ASP Inc.}}

THPP (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.

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

Titanium-boron composition is one of the hottest pyrotechnic reactions in common usage. It is solid-state, gasless. It can be used as a pyrotechnic initiator or for heating confined gas to perform mechanical work.{{Cite conference |last=Begeal |first=D. R. |last2=Munger |first2=A. C. |orig-year=1990 |title=Titanium-boron mixtures as variable heat sources |url=https://www.osti.gov/biblio/6912971 |conference=Sandia National Lab., Albuquerque, USA |language=English}}

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

Palladium-clad aluminium wires can be used as a fuse wire, known as Pyrofuze.{{Cite web |title=PYROFUZE® |url=http://www.sigmundcohn.com/pdf/EN/pyrofuze.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110716070538/http://www.sigmundcohn.com/pdf/EN/pyrofuze.pdf |archive-date=2011-07-16 |website=Sigmund Cohn Corp.}} The reaction is initiated by heat, typically supplied by electric current pulse. The reaction begins at 600 °C, the melting point of aluminium, and proceeds violently to temperature of 2200–2800 °C. The reaction does not need presence of oxygen, and the wire is consumed.{{Cite report |url=https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-74-0743 |title=Improved Hot-Wire Electroexplosive Devices |last=Joppa |first=Richard M. |date=1974 |publisher=Los Alamos Scientific Laboratory of the University of California |access-date=2021-09-30}}

Pyrofuze comes as a solid wire of different diameters (from 0.002" to 0.02"), braided wire, ribbon, foil, and granules. Palladium, platinum, or palladium alloyed with 5% ruthenium can be used together with aluminium.{{cite patent |country=US |number=4208967 |status=expired |title= Squib design |pubdate=1991-08-06 |gdate=1991-08-06 |fdate=1990-03-09 |pridate=1990-03-09 |inventor=Robert E. Betts |assign1=US Department of Army}}{{cite patent |country=US |number=5036769 |status=expired |title= Pyrofuze pin for ordnance activation|pubdate=1983-07-05 |gdate=1983-07-05 |fdate=1981-04-20 |pridate=1981-04-20 |inventor=James M. Schaff, Amos J. Diede |assign1=US Department of Navy}} Pyrofuze bridgewires can be used in squibs and electric matches. Pyrofuze foils can be used for e.g. sealing of various dispensers or fire extinguishing systems.{{Cite report |url=https://apps.dtic.mil/sti/citations/ADD004692 |archive-url=https://web.archive.org/web/20210930175326/https://apps.dtic.mil/sti/citations/ADD004692 |url-status=live |archive-date=September 30, 2021 |title=Containment and Release Device for Fluids. |last=Carignan |first=D. J.|last2=Willian |first2=L. |date=1978-01-03 |publisher=Department of the Air Force |language=en}} Palladium-magnesium composition can also be used, but is not commercially available or not at least as common.{{cite patent |country=US |number=3889755 |status=expired |title= Electrical appliance fire extinguisher |pubdate=1975-06-17 |gdate=1975-06-17 |fdate=1973-11-19 |pridate=1973-11-19 |inventor=Byron G Dunn |assign1=Fire Fox Corp.}}

BNCP, (cis-bis-(5-nitrotetrazolato)tetraminecobalt(III) perchlorate) is another common initiator material. It is relatively insensitive. It undergoes deflagration to detonation transition in a relatively short distance, allowing its use in detonators. Its burning byproducts are of relatively little harm to environment.{{cite patent |country=US |number=6672215 |status=patent |title= Constant output high-precision microcapillary pyrotechnic initiator|pubdate=2004-01-06 |gdate=2004-01-06 |fdate=2001-10-17 |pridate=2001-10-17 |inventor=Sami Daoud |assign1=Textron Innovations Inc.}} It can be ignited by a laser diode.

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

Other materials sensitive to heat can be used as well, e.g. HMTD,{{Cite web |date=2009-07-01 |title=How to Create an ANNM Detonator from scratch. |url=http://www.pyronfo.com/high-explosives/how-to-create-an-annm-detonator.html |url-status=usurped |archive-url=https://web.archive.org/web/20160309153206/http://www.pyronfo.com/high-explosives/how-to-create-an-annm-detonator.html |archive-date=2016-03-09 |website=Pyronfo}} tetrazene explosive, lead mononitro-resorcinates, lead dinitro-resorcinates, and lead trinitro-resorcinates.{{cite patent |country=US |number=5942717 |status=expired |title= Electro-pyrotechnic initiator, method for making same, and vehicle safety system|pubdate=1999-08-24 |gdate=1999-08-24 |fdate=1996-04-01 |pridate=1999-08-24 |inventor=Claude Pathe, Raphael Trousselle |assign1=Davey Bickford SAS}}

• Sprengel explosive

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Category:Pyrotechnic compositions