Pyrotechnic heat source
Encyclopedia
A pyrotechnic heat source, also called heat pellet, is a pyrotechnic device based on a pyrotechnic composition
with a suitable igniter. Its role is to produce controlled amount of heat. Pyrotechnic heat sources are usually based on thermite
-like (or sometimes delay composition
-like) fuel-oxidizer 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
and percussion cap
are the most common ones.
Pyrotechnic heat sources are often used for activation of thermal batteries, where they serve to melt the electrolyte. There are two main types of design. One uses a fuze strip (containing barium chromate
and powdered zirconium
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 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, similar to a shotgun shell
. It is desired that the pyrotechnic source be gasless. The standard heat source typically consist of mixtures of iron powder and potassium perchlorate
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 zirconium
with barium chromate
. Another mixture is 46.67 wt.% of titanium
, 23.33% of amorphous boron
, and about 30% barium chromate
. Yet another one is 45 wt.% tungsten
, 40.5% barium chromate
, 14.5% potassium perchlorate
, and 1% vinyl alcohol acetate resin binder.
Reactions producing intermetallic components, e.g. zirconium
with boron
, can be used when entirely gasless operation, non-hygroscopic behavior, and independence on environmental pressure are desired.
Heat paper can be prepared by impregnating paper or a fiberglass tape with a slurry
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
s a heat source composition with large surplus of oxidizer is used; the heat produced by burning the composition is used for thermal decomposition
of the oxidizer. Relatively cold-burning compositions are used for production of colored smoke
or for dispersion of aerosol of e.g. pesticide
s or CS gas
, providing the heat of sublimation
of the desired compound.
A phase moderating component of the composition, which forms together with the combustion products a mixture with at least one distincti temperature of phase transition
, may be used for stabilizing the burning tempeprature as a form of phase change material
.
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...
with a suitable igniter. Its role is to produce controlled amount of heat. Pyrotechnic heat sources are usually based on 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...
-like (or sometimes delay composition
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 temperature and pressure. Delay compositions are used to...
-like) fuel-oxidizer 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
Electric match
An electric match is a device that uses an externally applied electric current to ignite a combustible compound.-Use:Electric matches can be used in any application where source of heat is needed at a precisely controlled point in time, typically to ignite a propellant or explosive...
and percussion cap
Percussion cap
The percussion cap, introduced around 1830, was the crucial invention that enabled muzzleloading firearms to fire reliably in any weather.Before this development, firearms used flintlock ignition systems which produced flint-on-steel sparks to ignite a pan of priming powder and thereby fire the...
are the most common ones.
Pyrotechnic heat sources are often used for activation of thermal batteries, where they serve to melt the electrolyte. There are two main types of design. One uses a fuze strip (containing barium chromate
Barium chromate
Barium chromate is a fine light yellow powder with the formula BaCrO4. The chromium occurs in the +6 oxidation state. It is an oxidizing agent, and produces a green flame when heated, the result of barium ions.-Reactions:...
and powdered zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
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
Electric match
An electric match is a device that uses an externally applied electric current to ignite a combustible compound.-Use:Electric matches can be used in any application where source of heat is needed at a precisely controlled point in time, typically to ignite a propellant or explosive...
or squib
Squib
Squib may refer to:* Squib * Squib * Squib * Squib * Squib * Squib kick, a football play* Squib load, a firearm malfunction* Squib sailboat...
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 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, similar to a shotgun shell
Shotgun shell
A shotgun shell is a self-contained cartridge loaded with lead shot or shotgun slug designed to be fired from a shotgun....
. 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
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...
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 zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
with barium chromate
Barium chromate
Barium chromate is a fine light yellow powder with the formula BaCrO4. The chromium occurs in the +6 oxidation state. It is an oxidizing agent, and produces a green flame when heated, the result of barium ions.-Reactions:...
. Another mixture is 46.67 wt.% of titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
, 23.33% of amorphous boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
, and about 30% barium chromate
Barium chromate
Barium chromate is a fine light yellow powder with the formula BaCrO4. The chromium occurs in the +6 oxidation state. It is an oxidizing agent, and produces a green flame when heated, the result of barium ions.-Reactions:...
. Yet another one is 45 wt.% tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
, 40.5% barium chromate
Barium chromate
Barium chromate is a fine light yellow powder with the formula BaCrO4. The chromium occurs in the +6 oxidation state. It is an oxidizing agent, and produces a green flame when heated, the result of barium ions.-Reactions:...
, 14.5% 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 1% vinyl alcohol acetate resin binder.
Reactions producing intermetallic components, e.g. zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
with boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
, can be used when entirely gasless operation, non-hygroscopic behavior, and independence on environmental pressure are desired.
Heat paper can be prepared by impregnating paper or a fiberglass tape with a slurry
Slurry
A slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...
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
Chemical oxygen generator
A chemical oxygen generator is a device releasing oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
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
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....
of the oxidizer. Relatively cold-burning compositions are used for production of colored smoke
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 pyrotechnical devices...
or for dispersion of aerosol of e.g. pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s or CS gas
CS gas
2-chlorobenzalmalononitrile is the defining component of a "tear gas" commonly referred to as CS gas, which is used as a riot control agent...
, providing the heat of sublimation
Sublimation
Sublimation may refer to:* Sublimation , the change from solid to gas without entering liquid phase* Sublimation , the transformation of emotions* Sublimation , a music album by Canvas Solaris-See also:...
of the desired compound.
A phase moderating component of the composition, which forms together with the combustion products a mixture with at least one distincti temperature of phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....
, may be used for stabilizing the burning tempeprature as a form of phase change material
Phase Change Material
A phase-change material is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy...
.