Delay composition, also called delay charge or delay train, is 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 ...
, a sort of
pyrotechnic initiator
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. T ...
, a mixture of
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 ...
and
fuel that burns in a slow, constant rate that should not be significantly dependent on temperature and pressure. Delay compositions are used to introduce a delay into the
firing train
Dismissal (also called firing) is the termination of employment by an employer against the will of the employee. Though such a decision can be made by an employer for a variety of reasons, ranging from an economic downturn to performance-relat ...
, e.g. to properly sequence firing of
fireworks
Fireworks are a class of low explosive pyrotechnic devices used for aesthetic and entertainment purposes. They are most commonly used in fireworks displays (also called a fireworks show or pyrotechnics), combining a large number of devices ...
, to delay firing of
ejection charge
Ejection charge (commonly Black Powder), also called expelling charge, is a pyrotechnic composition, a type of a pyrotechnic gas generator designed to produce a small short-term amount of thrust to burst open a container and eject its content.
I ...
s in e.g. model rockets, or to introduce a few seconds of time between triggering a
hand grenade and its
explosion. Typical delay times range between several milliseconds and several seconds.
A popular delay charge is a tube of pressed
black powder. The mechanical assembly prevents the outright detonation of the charge.
While delay compositions are principally similar to other fuel-oxidizer compositions, larger grain sizes and less aggressively reacting chemicals are used. Many of the compositions generate little or no gas during burning. Typical materials used are:
* Fuels:
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
,
boron,
manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
,
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 ...
,
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient t ...
,
antimony trisulfide
Antimony trisulfide (Sb2S3) is found in nature as the crystalline mineral stibnite and the amorphous red mineral (actually a mineraloid) metastibnite. It is manufactured for use in safety matches, military ammunition, explosives and fireworks. It ...
,
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'' ...
,
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'' ...
–
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
alloy,
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, etc.
* Oxidizers:
lead dioxide
Lead(IV) oxide is the inorganic compound with the formula PbO2. It is an oxide where lead is in an oxidation state of +4. It is a dark-brown solid which is insoluble in water. It exists in two crystalline forms. It has several important applicatio ...
,
iron oxides,
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 ...
,
lead chromate
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
,
tin(IV) oxide
Tin(IV) oxide, also known as stannic oxide, is the inorganic compound with the formula SnO2. The mineral form of SnO2 is called cassiterite, and this is the main ore of tin. With many other names, this oxide of tin is an important material in tin ...
,
bismuth(III) oxide
Bismuth(III) oxide is perhaps the most industrially important compound of bismuth. It is also a common starting point for bismuth chemistry. It is found naturally as the mineral bismite (monoclinic) and sphaerobismoite (tetragonal, much more rare) ...
,
barium sulfate (for high-temperature compositions),
potassium perchlorate (usually used in small amount together with other oxidizers), etc.
* Additives to cool down the flame and slow down the reaction can be employed; inert materials or coolants like
titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolub ...
, ground glass,
chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...
,
sodium bicarbonate, etc. are common.
The burn rates are dependent on
* nature of fuel - fuels that release more heat burn faster
* nature of oxidizer - oxidizers that require less heat to decompose burn faster
* the composition ratio - stoichiometric mixtures burn the fastest, also slight excess of metallic fuel also increases burn rate, probably due to heat transfer
* particle sizes - smaller particles burn faster, but too small particles may lead to incomplete or interrupted burn due to too narrow heating zone
* mechanical assembly and housing - charge diameter and thermal conductivity of housing influence lateral heat losses
* ambient temperature - ideally this dependence is very low but extremely low or extremely high temperatures may have influence
Examples of some compositions are
*
black powder with addition of inert material, e.g.
chalk
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...
or
sodium bicarbonate
*
lead(II) oxide
Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula Pb O. PbO occurs in two polymorphs: litharge having a tetragonal crystal structure, and massicot having an orthorhombic crystal structure. Modern ap ...
with
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
, burning at 1.5–2 cm/s
*
red lead
Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...
with silicon, burning at intermediate rate
*
lead(IV) oxide with silicon, burning at 5–6 cm/s
*
potassium permanganate
Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution.
Potassium permanganate is widely used in the c ...
with
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient t ...
, very slow
* Manganese Delay Composition:
manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
with
lead chromate
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
and
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 ...
(lead chromate is the principal oxidizer, barium chromate acts as burning rate modifier, the more of it the slower the reaction
* Tungsten Delay Composition:
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 ...
with
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
potassium perchloratebr>
*Zirconium Nickel Alloy Delay Composition:
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'' ...
-
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
alloy with
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
potassium perchlorate.
*
boron with
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 ...
br>
h1>
References
Pyrotechnic compositions
Pyrotechnic initiators
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