A pyrotechnic composition is a substance or mixture of components designed to produce an effect in the form of heat, light, sound, gas, smoke, or a combination thereof, as a result of self-sustaining exothermic chemical reactions that take place without detonation. A similar process is independent of oxygen from external sources.
Classification of pyrotechnic compositions
They can be divided by action:
The first two groups can be divided into smaller species.
Flaming: lighting, signal night, tracing and some incendiary.
The smoke group includes compositions for daytime alarm and masking (fog).
The main types of pyrotechnics
The effect indicated above (light, sound, and so on) can be created using these components:
- A flash of powder - it burns very quickly, produces explosions or bright light emissions.
- Gunpowder - burns more slowly than powder, emits a large amount of gases.
- Solid fuel - produces many hot vapors used as sources of kinetic energy for missiles and shells.
- Pyrotechnic initiators - emit a large amount of heat, flame or hot sparks used to ignite other compositions.
- Discharge charges - quickly burn out, produce a lot of gas in a short time, and are used to release payloads from containers.
- Explosive charges - quickly burn out, produce a large amount of gas in a short time, are used to crush the container and dump its contents.
- Smoke compositions - burn slowly, produce fog (plain or color).
- Delay trains - blazes at a constant quiet speed, is used to introduce delays in the fire reserve.
- Pyrotechnic heat sources - emit a large amount of heat and practically do not spread gases, slow-burning, often termite-like.
- Sparklers - produce white or colored sparks.
- Flashes - burn slowly, create a large amount of light, are used for lighting or signaling.
- Color composition of fireworks - produce light, white or multi-colored sparks.
Application
Some technologies of pyrotechnic compositions and products are used in industry and aviation to generate large volumes of gas (for example, in airbags), as well as in various fixtures and in other similar situations. They are also used in the military industry when large amounts of noise, light or infrared radiation are required. For example, bait rockets, flares and stun grenades. A new class of reactive material compositions is being investigated by the military.
Many pyrotechnic compositions (especially those involving aluminum and perchlorates) are often very sensitive to friction, shock and static electricity. Even with only 0.1 to 10 millijoules, a spark can cause certain effects.
Powder
It is a black powder known to many. It is the earliest known chemical explosive, it consists of a mixture of sulfur (S), charcoal (C) and potassium nitrate (nitrate, KNO 3). The first two components act like fuel, and the third is an oxidizing agent. Due to its incendiary properties and the amount of heat and gas released, gunpowder is widely used in the production of propellant charges in firearms and artillery. In addition, it is used in the manufacture of rockets, fireworks and explosive devices in quarrying, mining and road construction.
Indicators
Gunpowder was invented in China in the 7th century and spread throughout most of Eurasia by the end of the 13th century. Originally developed by Taoists for medicinal purposes, the powder was used for war around 1000 AD.
Gunpowder is classified as a small explosive due to its relatively low decomposition rate and low brisance.
Explosive force
Ignition of gunpowder packed behind the projectile creates enough pressure to cause a shot from the muzzle at high speed, but not powerful enough to burst the gun barrel. Thus, gunpowder is a good fuel, but it is less suitable for destroying stone or fortifications due to its low explosive strength. By transferring enough energy (from the burning substance to the mass of the cannonball, and then from it to the target by means of shock ammunition), the bomber can ultimately crush the enemy’s fortified defense.
Gunpowder was widely used for filling shells and was used in mining and civil engineering projects until the second half of the 19th century, when the first explosives were tested. The powder is no longer used in modern weapons and for industrial purposes due to its relatively low efficiency (compared to newer alternatives such as dynamite and ammonium nitrate or fuel oil). Today, gunpowder firearms are limited mainly to hunting and target shooting.
Pyrotechnic heat source
Pyrotechnic compositions are a device based on combustible substances with a suitable igniter. Their role is to produce a controlled amount of heat. Pyrotechnic sources are usually based on termite-like (or composition retarding) oxidizing agents with a low burning rate, high heat production at the desired temperature, and low or zero gas formation.
They can be activated in several ways. Electric matches and shock caps are the most common.
Pyrotechnic heat sources are often used to activate batteries, where they serve to melt the electrolyte. There are two main types of design. One uses a fuse strip (containing barium chromate and metallic powdered zirconium in ceramic paper). Along its edge are thermal pyrotechnic granulation compositions to initiate combustion. The strip is usually triggered by an electric igniter or plug using current.
The second design uses a central hole in the battery pack, into which a high-energy electric igniter releases a mixture of flammable gases and incandescent lamps. The design with a central hole can significantly reduce the activation time (tens of milliseconds). For comparison, we note that in devices with an edge strip, this figure is hundreds of milliseconds.
Turning on the battery can also be done with a shotgun-like primer. It is desirable that the source of exposure be without gas. Typically, the standard composition of pyrotechnic mixtures consists of iron powder and potassium perchlorate. In weight ratios, these are 88/12, 86/14 and 84/16. The higher the level of perchlorate, the greater the heat release (nominally 200, 259 and 297 calories / gram). The size and thickness of iron-perchlorate tablets have little effect on the burning rate, however, they affect the density, composition, particle size and can be used to adjust the desired heat release profile.
Another composition used is zirconium with barium chromate. Another mixture contains 46.67% titanium, 23.33% amorphous boron, and about 30% barium chromate. There may also be such proportions: 45% tungsten, 40.5% barium chromate, 14.5% potassium perchlorate and 1% vinyl alcohol and binder acetate.
Reactions with the formation of intermetallic components of pyrotechnic compositions, for example, zirconium with boron, can be used when gas-free operation, non-hygroscopic behavior, and independence from ambient pressure are desired.
Heat source
It can be a direct part of the pyrotechnic composition, for example, such a component with a large excess of oxidizing agent is used in chemical oxygen generators. The heat generated during combustion is used for thermal decomposition. Relatively cold burning compositions are used to produce colored smoke or to spray aerosol, such as pesticides or CS gas, providing the heat of sublimation of the desired compound.
The phase retardation component of the composition, which together with the combustion products forms a mixture with one separate phase transition temperature, can be used to stabilize the height of combustion.
Materials
Pyrotechnic compositions are usually homogenized mixtures of small particles of fuel and oxidizing agents. The former may be grains or cereals. As a rule, the higher the surface area of the particles, the higher the rate of reaction and combustion. For some purposes, binders are used to turn the powder into a solid material.
Fuel
Typical species are based on metal or metalloid powders. The composition may indicate several different types of fuel. Some may also serve as binders.
Metals
Common fuels include these elements:
- Aluminum is the most common fuel in many classes of mixtures, as well as a regulator of combustion instability. A high-temperature flame with solid particles that interferes with the appearance of dyes reacts with nitrates (except ammonium) to form nitrogen oxides, ammonia, and heat (the reaction is slow at room temperature, but violent above 80 ° C, can ignite spontaneously).
- Magnesium is an aluminum-magnesium alloy, more stable and less expensive than a single metal. Less reactive than magnesium, but more easily ignited than aluminum.
- Iron - makes gold sparks, an often used element.
- Steel is an alloy of iron and carbon that makes branching yellow-orange sparks.
- Zirconium - produces hot particles useful for flammable mixtures, for example, NASA's standard initiator, as well as to suppress combustion instability.
- Titanium - produces hot pyrotechnic products and compositions, increases sensitivity to shock and friction. Sometimes Ti4Al6V alloy is used, which gives slightly brighter white sparks. Together with potassium perchlorate, it is used in some pyrotechnic igniters. Coarse powder produces beautiful branching blue and white sparks.
- Ferrotitanium is an iron-titanium alloy that creates bright sparks used in pyrotechnic stars, rockets, comets and fountains.
- Ferrosilicon is an iron-silicon substance used in some mixtures, sometimes replacing calcium silicide.
- Manganese - is used to control the burning rate, for example, in delayed compositions.
- Zinc - is used in some smoke compositions along with sulfur, which is used as amateur fuel for rockets, as well as in pyrotechnic stars. Sensitive to moisture. It can ignite spontaneously. It is rarely used as the main fuel (exception - smoke compositions), can be used as an additional component.
- Copper - used as a blue dye with other species.
- Brass is an alloy of zinc and copper used in some formulas for fireworks.
- Tungsten - is used to control and slow down the burning rate of compositions.
It is worth noting that it is dangerous to make pyrotechnic compositions with your own hands.