Flash powder
Encyclopedia
Flash powder is a pyrotechnic composition
Pyrotechnic composition
A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...

, a mixture of oxidizer and metallic fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

, which burns quickly and if confined produces a loud report. It is widely used in theatrical pyrotechnics
Pyrotechnics
Pyrotechnics is the science of using materials capable of undergoing self-contained and self-sustained exothermic chemical reactions for the production of heat, light, gas, smoke and/or sound...

 and fireworks
Fireworks
Fireworks are a class of explosive pyrotechnic devices used for aesthetic and entertainment purposes. The most common use of a firework is as part of a fireworks display. A fireworks event is a display of the effects produced by firework devices...

 (namely salutes
Salute (pyrotechnics)
In pyrotechnics a salute is a device primarily designed to make a loud report , and may or may not have a visual effect. Most salutes will also have a very bright flash and are made from many different formulas depending on manufacturer and desired effect. They may have aluminum, antimony,...

, e.g., cherry bomb
Cherry bomb
Cherry Bombs are approximately spherical shaped exploding fireworks, ranging in size from three-quarters-inch to one-and-one-half-inch in diameter...

s, M-80
M-80 (explosive)
M-80s are a class of large firecrackers, sometimes called salutes. The Simulator, Artillery, M80, was originally made in the early 20th century by the U.S. Military to simulate explosives or artillery fire; Later, M-80s were manufactured as fireworks...

s, firecracker
Firecracker
A firecracker is a small explosive device primarily designed to produce a large amount of noise, especially in the form of a loud bang; any visual effect is incidental to this goal. They have fuses, and are wrapped in a heavy paper casing to contain the explosive compound...

s, and cap gun
Cap gun
A cap gun is a toy gun that creates a loud sound simulating a gunshot and a puff of smoke when the trigger is pulled. Cap guns were originally made of cast iron, but after World War II were made of zinc alloy, and most newer models are made of plastic....

 shots) and was once used for flash
Flash (photography)
A flash is a device used in photography producing a flash of artificial light at a color temperature of about 5500 K to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light...

es in photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

.
Different varieties of flash powder are made from different compositions; most common are potassium perchlorate
Potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...

 and aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 powder. Sometimes, sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 is included in the mixture to increase the sensitivity. Early formulations used potassium chlorate
Potassium chlorate
Potassium chlorate is a compound containing potassium, chlorine and oxygen atoms, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. It is the most common chlorate in industrial use...

 instead of Potassium Perchlorate.

Flash powder compositions are also used in military pyrotechnics, when production of large amount of noise, light, or infrared radiation is required; e.g. missile decoy flares
Flare (countermeasure)
A flare is an aerial infrared countermeasure to counter an infrared homing surface-to-air missile or air-to-air missile. Flares are commonly composed of a pyrotechnic composition based on magnesium or another hot-burning metal, with burning temperature equal to or hotter than engine exhaust...

 and stun grenade
Stun grenade
A stun grenade, also known as a flash grenade or a flashbang, is a non-lethal weapon. The first devices like this were created in the 1960s at the order of the British Special Air Service as an incapacitant....

s.

Safety and handling

Flash-powder mixtures are highly sensitive to shock, friction and electrostatic-discharge. Additionally, accidental contaminants such as strong acids or sulphur compounds can sensitise them even more. Because flash-powder mixtures are so easy to initiate, there is a high risk of accidental explosions which can inflict severe blast/fragmentation injuries e.g., traumatic amputation of body parts. Fatalities have occurred. Flash powder compositions should therefore not be handled by anyone who is unfamiliar with their properties, or the handling techniques required to maintain safety. Flash powder and flash-powder devices pose exceptionally high risks to children, who typically cannot understand the danger and may be less adept with safe handling techniques. As a result, children tend to suffer more severe injuries than adults.

Flash powders—especially those that use chlorate
Chlorate
The chlorate anion has the formula ClO. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by a roman numeral in parentheses, e.g...

—are often highly sensitive to friction, heat/flame and static electricity
Static electricity
Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...

. A spark of as little as 0.1-10 millijoules can set off certain mixtures. Certain formulations prominent in the underground press contain both sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 and potassium chlorate
Potassium chlorate
Potassium chlorate is a compound containing potassium, chlorine and oxygen atoms, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. It is the most common chlorate in industrial use...

. These mixtures are shock and friction sensitive. Modern pyrotechnic practices call for never using sulfur in a mix containing chlorate salts.

Some flash powder formulations (those that use single-digit micrometre flake aluminum powder or fine magnesium powder as their fuel) can self-confine and explode in 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.

Flash powder of any formulation should not be mixed in large quantities by the amateur pyrotechnician. Beginners should start with sub-gram quantities, and refrain from making large devices. Flash powder should only be made at the site at which it will be used. Additionally, the mixture should be made immediately before use.

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.

Aluminium and chlorate

Because of the above mentioned instability, the combination of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 powder and potassium chlorate
Potassium chlorate
Potassium chlorate is a compound containing potassium, chlorine and oxygen atoms, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. It is the most common chlorate in industrial use...

 is a poor choice for flash powder that is to be stored for more than a very short period of time. For that reason it has been largely replaced by the potassium perchlorate mixtures. Chlorate mixes are used when cost is the overriding concern, because potassium chlorate is less expensive than perchlorate. By mass the composition is seven parts of KClO3 to three parts of pyro aluminum. It is critically important to exclude sulphur and any acidic components from these mixtures. Sometimes a few percent of bicarbonate buffer is added to the mixture to ensure the absence of acidic impurities.
KClO3 + 2 Al → Al2O3 + KCl

Aluminum - nitrate with sulfur

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. It is not very quick burning, unless exceptionally fine ingredients are used. Although it incorporates sulfur, it is in fact fairly stable, sustaining multiple hits from a hammer onto a hard surface. Adding 2% of its weight with boric acid is reputed to significantly increase stability and shelf life, through resistance to dampening through ambient humidity. Other ratios such as 6 KNO3/3 Al/2 S and 5 KNO3/2 Al/3 S also exist and work. All ratios have similar burn times and strength, although 5 KNO3/3 Al/2 S seems to be dominant.
2 KNO3 + 4 Al + S → K2S + N2 + 2 Al2O3


For best results, "German Dark" aluminum should be used, with airfloat sulfur, and finely ball milled pure potassium nitrate. The finished mixture should never be ball milled together.

Aluminum and perchlorate

Aluminum powder and potassium perchlorate
Potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...

 are the only two components of the pyrotechnic industry standard flash powder. It provides a great balance of stability and power, and is the composition used in most commercial exploding fireworks.

The balanced equation for the reaction is:
3 KClO4 + 8 Al → 4 Al2O3 + 3 KCl


Although not stoichiometrically
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...

 balanced, a ratio of seven parts Potassium Perchlorate to three parts Dark Pyro Aluminum is the composition used by most pyrotechnicians. However, a ratio of 2 mass units potassium perchlorate to 1 mass unit Dark Pyro Aluminum is closer to stoichiometric, and may produce a louder report.

For best results, the aluminum powder should be "Dark Pyro" grade, with a flake particle shape, and a particle size of less than 10 micrometres. The KClO4 should be in powder form, free from clumps. It can be sieved through a screen if necessary to remove any clumps prior to use. The particle size of the perchlorate is not as critical as that of the aluminum component, as much less energy is required to decompose the KClO4 than is needed to melt the aluminum into the liquid state required for the reaction.

Although this composition is fairly insensitive, it should be treated with care and respect. Hobbyist pyrotechnicians usually use a method called diapering, in which the materials are poured separately onto a large piece of paper, which is then alternately lifted at each corner to roll the composition over itself and mix the components. Some amateur pyrotechnicians choose to mix the composition by shaking in a closed paper container, as this is much quicker and more effective than diapering. Paper/cardboard is chosen over other materials such as plastic as a result of its favorable triboelectric properties.

Large quantities should never be mixed in a single batch. Large quantities are not only more difficult to handle safely, but they place innocent bystanders within the area at risk. In the event of accidental ignition, debris from a multiple-pound flash powder explosion can be thrown hundreds of feet with sufficient force to kill or injure. (Note: 25 grams of mixture is enough to explode in open air without constraint other than air pressure.)

No matter the quantity, care must always be taken to prevent any electrostatic discharge or friction during mixing or handling, as these may cause accidental ignition.

Magnesium and nitrate

Another flash composition common among amateurs consists of magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 powder and potassium nitrate
Potassium nitrate
Potassium nitrate is a chemical compound with the formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−.It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre , from medieval Latin sal petræ: "stone salt" or possibly "Salt...

. Other metal nitrates have been used, including Barium
Barium nitrate
Barium nitrate with chemical formula Ba2 is a salt of barium and the nitrate ion.Barium nitrate exists as a white solid at room temperature. It is soluble in water, and like other soluble barium compounds, is toxic and should be handled with care...

 and strontium
Strontium nitrate
Strontium nitrate is an inorganic compound with the formula Sr2. This colourless solid is used as an colorant in pyrotechnics.- Preparation:Strontium nitrate is typically generated by the reaction of nitric acid on strontium carbonate.....

 nitrates. Compositions using nitrate and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 metal have been used as photographic flash powders almost since the invention of photography.
2 KNO3 + 5 Mg → K2O + N2 + 5 MgO

Ba(NO3)2 + 5 Mg → BaO + N2 + 5 MgO


Mixtures designed to make reports are substantially different than mixtures designed for illumination. A stoichiometric ratio of three parts KNO3 to two parts Mg is close to ideal, and provides the most rapid burn. The magnesium powder should be smaller than 200 mesh, though up to 100 mesh will work. The potassium nitrate should be impalpable dust. This mixture is popular in amateur pyrotechnics because it is insensitive and relatively safe as such things go.

For photographic use, mixtures containing magnesium and nitrates are made much more fuel rich. 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. A formula from 1917 specifies 5 parts of magnesium to 6 parts of barium nitrate
Barium nitrate
Barium nitrate with chemical formula Ba2 is a salt of barium and the nitrate ion.Barium nitrate exists as a white solid at room temperature. It is soluble in water, and like other soluble barium compounds, is toxic and should be handled with care...

 for a stoichiometry of nine parts fuel to one part oxidizer. Modern recreations of photographic flash powders may avoid the use of barium salts because of their toxic nature. A mixture of five parts 80 mesh magnesium to one part of potassium nitrate provides a good white flash without being too violent. Fuel rich flash powders are also used in theatrical flash pots.

Magnesium based compositions degrade over long periods of time, as Magnesium does not form a passivating oxide coating, meaning the metallic Mg will slowly react with atmospheric oxygen and moisture. In military pyrotechnics involving magnesium fuels, external oxygen can be excluded by using hermetically sealed canisters. Commercial photographic flash powders are sold as two part mixtures, to be combined immediately before use.

Magnesium and PTFE

A flash composition designed specifically to generate flares that are exceptionally bright in the infrared portion of the spectrum use a mixture of pyro grade magnesium and powdered polytetrafluoroethylene
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....

. These flares are used as decoys from aircraft that might be subject to heat-seeking missile fire.
2n Mg + (C2F4))n → 2n MgF2 (s) + 2n C (s)

Antimony trisulfide and chlorate

This mixture, and similar mixtures sometimes containing pyro aluminum have been used since the early 1900s for small "Black Cat" style paper firecracker
Firecracker
A firecracker is a small explosive device primarily designed to produce a large amount of noise, especially in the form of a loud bang; any visual effect is incidental to this goal. They have fuses, and are wrapped in a heavy paper casing to contain the explosive compound...

s. Its extremely low cost makes it popular among manufacturers of low-grade fireworks in China. Like all mixtures containing Chlorates, it is extremely sensitive to friction, impact and ESD, and is considered unsafe in pyrotechnic devices that contain more than a few tens of milligrams of the mixture.
3 KClO3 + Sb2S3 → Sb2O3 + 3 SO2 + 3KCl


This mixture is not highly energetic, and in at least some parts of the United States, firecracker
Firecracker
A firecracker is a small explosive device primarily designed to produce a large amount of noise, especially in the form of a loud bang; any visual effect is incidental to this goal. They have fuses, and are wrapped in a heavy paper casing to contain the explosive compound...

s containing 50 mg or less of this mixture are legal as consumer fireworks.

See also

  • Pyrotechnic initiator
    Pyrotechnic initiator
    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...

  • Sprengel explosive
    Sprengel explosive
    Sprengel explosives are a generic class of materials invented by Hermann Sprengel in the 1870s. They consist of stoichiometric mixtures of strong oxidisers and reactive fuels, mixed just prior to use in order to enhance safety...

  • Thermite
    Thermite
    Thermite is a pyrotechnic composition of a metal powder and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction...

  • Black powder
  • Lycopodium powder
    Lycopodium powder
    Lycopodium powder is a yellow-tan dust-like powder historically used as a flash powder. It is composed of the dry spores of clubmoss plants, various fern relatives principally in the genera Lycopodium and Diphasiastrum...


External links

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