flash powder
{{Short description|Pyrotechnic mixture}}
{{multiple issues|{{more citations needed|date=November 2013}}{{original research|date=November 2013}}{{howto|date=November 2013}}}}
Flash powder is a pyrotechnic composition, a mixture of oxidizer and metallic fuel, which burns quickly (deflagrates) and produces a loud noise, regardless of confinement in some formulations. It is widely used in theatrical and display pyrotechnics and consumer fireworks (namely firecrackers, professional salutes, and formerly in banned items such as cherry bombs and M-80s) and was once used for flashes in photography.
Image:Flash Powders.JPG (A) powder for some types of fuels (B).]]
Different varieties of flash powder are made from different compositions; most common are potassium perchlorate and aluminium powder. Early formulations used potassium chlorate instead of potassium perchlorate.
Flash powder compositions are also used in military pyrotechnics when production of large amount of noise or light is required, e.g., stun grenades, battle simulator devices, and photoflash bombs.
History
Lycopodium powder is a yellow-tan dust-like powder historically used as a flash powder.{{cite book|title=Photographic Times and American Photographer, vol.18|date=1888|publisher=Scovill Manufacturing Company|page=26|url=https://books.google.com/books?id=8zlJAQAAMAAJ&q=lycopodium+powder+photography&pg=PA26|access-date=23 October 2017|language=en}} Today, the principal use of the powder is to create flashes or flames that are large and impressive but relatively easy to manage safely in magic acts and for cinema and theatrical special effects.
Mixtures
Normally, flash powder mixtures are compounded to achieve a particular purpose. These mixtures range from extremely fast-burning mixtures designed to produce a maximum audio report, to mixtures designed to burn slowly and provide large amounts of illumination, to mixtures that were formerly used in photography.{{citation needed|date=June 2025}}
=Photo-flash powders=
For photography, fuel-rich mixtures containing magnesium and nitrates were used. The excess magnesium is volatilized by the reaction and burns in air providing additional light. In addition, the higher concentration of fuel results in a slower burn, providing more of a "poof" and less of a "bang" when ignited. Various formulas from 1917 include: {{convert|1|oz|g|abbr=on}} potassium nitrate to {{convert|1|oz|g|abbr=on}} magnesium, {{convert|2|oz|g|abbr=on}} magnesium to {{convert|0.5|oz|g|abbr=on}} chrome alum, and {{convert|2|oz|g|abbr=on}} magnesium to {{convert|0.5|oz|g|abbr=on}} potassium chlorate.{{cite journal |editor1-last=Watkins |editor1-first=T. C. |journal=The Photographic Journal of America |title=Flashlight Powders |date=1917 |volume=54 |page=384 |url=https://archive.org/details/photographicjo541917phil/page/384/mode/2up |publisher=Edward L. Wilson Company, Inc. |location=Philadelphia, PA}} Fuel rich flash powders are also used in theatrical flash pots.{{citation needed|date=June 2025}}
Magnesium based compositions degrade over long periods, meaning the metallic Mg will slowly react with atmospheric moisture. Commercial photographic flash powders are sold as two-part mixtures, to be combined immediately before use.{{citation needed|date=June 2025}}
=Aluminium and chlorate=
The combination of aluminium powder and potassium chlorate is unstable, and a poor choice for flash powder that is to be stored for more than a very short period.{{citation needed|date=June 2025}} For that reason, it has been largely replaced by the potassium perchlorate mixtures.
The simplest is a two-component chlorate mix, although this is rarely used.
:{{chem2|KClO3 + 2 Al -> Al2O3 + KCl}}
The composition is approximately 70% {{chem2|KClO3}} : 30% Al by weight for the reactants of the above stoichiometrically balanced equation.
Sometimes a few percent of bicarbonate or carbonate buffer is added to the mixture to ensure the absence of acidic impurities.
Sulfur is often added as a third component to this mixture{{cite book |last1=Davis |first1=Tenney L. |title=The chemistry of powder and explosives: complete in one volume |date=1941 |publisher=Angriff Press |location=Hollywood, CA |isbn=0913022004 |page=116 |url=https://archive.org/details/the-chemistry-of-powder-and-explosives-angriff-press/page/116/mode/2up}} in order to reduce the activation energy. Antimony trisulfide may be used as an alternative, and is more stable in storage.{{citation needed|date=June 2025}}
=Potassium nitrate, aluminium and sulfur=
{{uncited section|date=June 2025}}
This composition, usually in a ratio of 5 parts potassium nitrate, to 3 parts aluminum powder, to 2 parts sulfur, is especially popular with hobbyists.{{who?|date=June 2025}} It is not very quick-burning unless exceptionally fine ingredients are used. Adding 2% by weight boric acid can potentially improve shelf-life.
:{{chem2|2 KNO3 + 4 Al + S -> K2S + N2 + 2 Al2O3}}
The composition is approximately 59% {{chem2|KNO3}} : 31.6% Al : 9.4% S by weight for the reactants of the above stoichiometrically balanced equation.
=Aluminium and perchlorate=
{{uncited section|date=June 2025}}
Aluminium powder and potassium perchlorate are the only two components of the pyrotechnic industry standard flash powder.
The balanced equation for the reaction is:
:{{chem2|3 KClO4 + 8 Al -> 3 KCl + 4 Al2O3}}
The stoichiometric ratio is 34.2% aluminum and 65.8% perchlorate by mass.
A ratio of seven parts potassium perchlorate to three parts dark pyro aluminium is the composition used by most pyrotechnicians.{{who?|date=June 2025}}
=Magnesium and nitrate=
{{uncited section|date=June 2025}}
Another flash composition consists of magnesium powder and potassium nitrate. Other metal nitrates have been used, including barium and strontium nitrates.
:{{chem2|2 KNO3 + 5 Mg -> K2O + N2 + 5 MgO}}
The composition is 62.4% {{chem2|KNO3}} and 37.6% Mg by weight for the reactants of the above stoichiometrically balanced equation.
Safety and handling
{{uncited section|date=June 2025}}
Flash powders even within intended usages{{which?|date=June 2025}} often release deadly amounts of explosive force. Nearly all flash powder mixtures are sensitive to shock, friction and electrostatic discharge. Additionally, accidental contaminants such as strong acids or sulfur compounds can sensitise some of them even more. Because flash powder mixtures are so easy to initiate, there is a high risk of accidental explosion which can inflict severe blast/fragmentation injuries, e.g. blindness, explosive amputation, permanent maiming, or disfigurement. Fatalities have occurred.
Flash powders are often highly sensitive to friction, heat/flame and static electricity. A spark of as little as 0.1–10 millijoules can set off certain mixtures.
Most flash powder formulations (especially those that use micrometre flake aluminium powder or fine magnesium powder as their fuel) can self-confine and explode in relatively small quantities. This makes flash powder dangerous to handle, as it can cause severe hearing damage and amputation injury even when sitting in the open.
Self-confinement occurs when the mass of the pile provides sufficient inertia to allow high pressure to build within it as the mixture reacts. This is referred to as inertial confinement, and it is not to be confused with a detonation.