A pyrotechnic heat source, also called heat pellet, is a pyrotechnic device based on a

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

with a suitable

igniter In pyrotechnics, a pyrotechnic initiator (also initiator or igniter) is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, such as thermites, gas generators, and solid-fuel rockets. The ...

. Its role is to produce controlled amount of heat. Pyrotechnic heat sources are usually based on

thermite Thermite () is a pyrotechnic composition of metal powder and metal oxide. When ignited by heat or chemical reaction, thermite undergoes an exothermic reduction-oxidation (redox) reaction. Most varieties are not explosive, but can create br ...

-like (or sometimes

delay composition Delay composition, also called delay charge or delay train, is a pyrotechnic composition, a sort of pyrotechnic initiator, a mixture of oxidizer and fuel that burns in a slow, constant rate that should not be significantly dependent on temperatur ...

-like) fuel-

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

compositions with slow burn rate, high production of heat at desired temperature, and low to zero production of gases. Pyrotechnic heat sources can be activated by multiple means.

Electric match An electric match is a device that uses an externally applied electric current to ignite a combustible compound. Electric matches use a bridgewire consisting of a heating element to ignite a pyrogen, which is a quantity of readily ignited pyro ...

and

percussion cap The percussion cap or percussion primer, introduced in the early 1820s, is a type of single-use percussion ignition device for muzzle loader firearm locks enabling them to fire reliably in any weather condition. This crucial invention gave rise ...

are the most common ones. Pyrotechnic heat sources are often used for activation of

thermal batteries Molten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temp ...

, where they serve to melt the electrolyte. There are two main types of design. One uses a fuze strip (containing

barium chromate Barium chromate, named barium tetraoxochromate(VI) by the IUPAC, is a yellow sand like powder with the formula BaCrO4. It is a known oxidizing agent and produces a green flame when heated, a result of the barium ions. History The first naturally o ...

and powdered

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

metal in a ceramic paper) along the edge of the heat pellets to initiate burning. The fuze strip is typically fired by an electrical igniter or squib by application of electric current. The second design uses a center hole in the battery stack into which the high-energy electrical igniter fires a mixture of hot gases and

incandescent Incandescence is the emission of electromagnetic radiation (including visible light) from a hot body as a result of its high temperature. The term derives from the Latin verb ''incandescere,'' to glow white. A common use of incandescence is ...

particles. The center-hole design allows much faster activation times (tens of milliseconds) vs. hundreds of milliseconds for the edge-strip design. Battery activation can also be accomplished by a

percussion primer The percussion cap or percussion primer, introduced in the early 1820s, is a type of single-use percussion ignition device for muzzle loader firearm locks enabling them to fire reliably in any weather condition. This crucial invention gave rise t ...

, similar to a

shotgun shell A shotgun shell, shotshell or simply shell is a type of rimmed, cylindrical (straight-walled) cartridges used specifically in shotguns, and is typically loaded with numerous small, pellet-like spherical sub- projectiles called shot, fired th ...

. It is desired that the pyrotechnic source be gasless. The standard heat source typically consist of mixtures of iron powder and

potassium perchlorate Potassium perchlorate is the inorganic salt with the chemical formula K Cl O4. Like other perchlorates, this salt is a strong oxidizer although it usually reacts very slowly with organic substances. This, usually obtained as a colorless, crys ...

in weight ratios of typically 88/12, 86/14, and 84/16. The higher the potassium perchorate level, the higher the heat output (nominally 200, 259, and 297 calories/gram, respectively). The size and thickness of the iron-perchlorate pellets has little influence on their burn rate, however the effect of density, composition, and particle size have significant effect on the burn rate and can be used for its adjusting for desired heat output profile. Another composition in use is

with

. Another mixture is 46.67 wt.% of

titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...

, 23.33% of amorphous boron, and about 30%

. Yet another one is 45 wt.%

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

, 40.5%

, 14.5%

, and 1%

vinyl alcohol acetate Vinyl may refer to: Chemistry * Polyvinyl chloride (PVC), a particular vinyl polymer * Vinyl cation, a type of carbocation * Vinyl group, a broad class of organic molecules in chemistry * Vinyl polymer, a group of polymers derived from viny ...

resin binder. Reactions producing

intermetallic An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elem ...

components, e.g.

with boron, can be used when entirely gasless operation, non-

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...

behavior, and independence on environmental pressure are desired. SureChem
SureChem. Retrieved on 2010-02-08. Heat paper can be prepared by impregnating paper or a fiberglass tape with a

slurry A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal p ...

of the mixture of fuel and oxidizer. A pyrotechnic heat source can be a direct part of a pyrotechnic composition e.g. in

chemical oxygen generator A chemical oxygen generator is a device that releases oxygen via a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate; ozonides are a promising group of oxygen sources. The generators are usually igni ...

s a heat source composition with large surplus of oxidizer is used; the heat produced by burning the composition is used for

thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...

of the oxidizer. Relatively cold-burning compositions are used for production of

colored smoke Colored smoke is a kind of smoke created by an aerosol of small particles of a suitable pigment or dye. Colored smoke can be used for smoke signals, often in a military context. It can be produced by smoke grenades, or by various other pyrot ...

or for dispersion of aerosol of e.g. pesticides or

CS gas The compound 2-chlorobenzalmalononitrile (also called ''o''-chlorobenzylidene malononitrile; chemical formula: C10H5ClN2), a cyanocarbon, is the defining component of tear gas commonly referred to as CS gas, which is used as a riot control agen ...

, providing the heat of

sublimation Sublimation or sublimate may refer to: * ''Sublimation'' (album), by Canvas Solaris, 2004 * Sublimation (phase transition), directly from the solid to the gas phase * Sublimation (psychology), a mature type of defense mechanism * Sublimate of mer ...

of the desired compound. A phase moderating component of the composition, which forms together with the combustion products a mixture with at least one distinct temperature of

phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states ...

, may be used for stabilizing the burning temperature as a form of

phase change material A phase change material (PCM) is a substance which releases/absorbs sufficient energy at phase transition to provide useful heat or cooling. Generally the transition will be from one of the first two fundamental states of matter - solid and li ...

.(WO/2006/046245) HEAT SOURCES FOR THERMAL BATTERIES
Wipo.int. Retrieved on 2010-02-08.

References

{{reflist, 30em Pyrotechnic compositions