A pyrotechnic charge is a mixture of substances used to generate acoustic, optical, thermal or mechanical effects. They are the functional carriers of pyrotechnic objects and are used in a wide variety of products such as matches , fireworks and airbags . As a rule, they contain at least one oxidizing agent and a fuel . As explosive substances, they are subject to corresponding legal regulations ( explosives law , pyrotechnics law ).
A pyrotechnic charge is a substance or mixture of substances (pyrotechnic mixture) , the purpose of which is to produce an acoustic ( sound ), optical ( light , fog , smoke ), thermal (e.g. heat ), or mechanical ( pressure , movement ) effect to develop. The legislator does not classify substances and objects according to their chemical properties, but to what extent they cause such a pyrotechnic effect . Fuels in the general sense, for example, only count as pyrotechnics if they are explicitly used in an object in order to achieve an intended effect (the pyrotechnic effect ).
As with all energetic materials , the exothermic conversion (such as burn-off , deflagration ) is not linked to the presence of atmospheric oxygen in the pyrotechnic composition . This reaction, called reaction of a pyrotechnic sentence, takes place spontaneously and self-sustaining, but usually more slowly (less explosive ) than with explosives - the terms deflagration (slower than the speed of sound in the material) and detonation (faster) differentiate the terms pyrotechnic and explosives.
In contrast to the typical technical explosives (with the exception of the initial explosives used as detonators and the so-called firecrackers), the reaction takes place not only through an explosion, but usually through an open flame ( fire ), heat , friction , electrostatic charge , sparks , impact ( Vibration ) and with some sentences also moisture . Pyrotechnic sentences are therefore considered to be particularly dangerous to use, although their harmful effect is usually significantly less. Therefore, handling open pyrotechnic sentences is avoided. As a means of ignition for controlled release of the burn-up ( lighting ) serve electric igniter (electric ignition) or grater heads , Abreißanzünder , fuses (rovings), Anzündlitzen and other ( pyrotechnic ignition or grain enhancement ).
Building a pyrotechnic mixture
The most important component of a pyrotechnic charge is the oxidizing agent .
Typical oxidizing agents used in pyrotechnics are:
- Nitrates (NO 3 - ), chlorates (ClO 3 - ), perchlorates (ClO 4 - ), peroxides (O 2 2− ), dinitramides (N (NO 2 ) 2 - ), chromates (CrO 4 2− ) and permanganates ( MnO 4 - ) of the alkali and alkaline earth metals
- Oxides of the metals chromium (chromate), tungsten (WO 3 ), molybdenum (MoO 3 ), manganese (MnO 2 ), iron (Fe 3 O 4 ), copper (Cu 2 O), zinc (ZnO 2 ), bismuth (Bi 2 O 3 ), and tin (SnO 2 )
- Halogenated hydrocarbons such as B. hexachloroethane (C 2 Cl 6 ), hexachlorobenzene (C 6 Cl 6 ), polytetrafluoroethylene ((C 2 F 4 ) n ), graphite fluoride ((CF) n )
Other oxidizing agents are ammonium nitrate , ammonium perchlorate and ammonium dinitramide . However, even as pure substances, these count among the explosive or explosive substances.
While chlorates were often used as an oxidizing agent in light and whistle sets in the past, the more thermally stable and less reactive, but safer perchlorates are used today. Only with a few exceptions such as B. green luminous stars of high color purity you can not avoid the use of barium chlorate .
The only requirement for an electron acceptor is that the fuel in question, as a donor, has a lower electronegativity than the oxidizer available for selection. In addition to substances that split off oxygen, chlorine and fluorine, substances such as boron, carbon, sulfur or phosphorus in combination with more electropositive metals can also function as oxidizing agents, although they are all readily oxidized by the more electronegative oxygen even after thermal stimulation and with the appearance of flames.
In pyrotechnics, practically all combustible and highly inflammable solid substances are used as fuels (chemically referred to as reducing agents ), for example metals, their alloys and metal-containing compounds such as. B. hydrides , various non-metals and the extensive group of organic compounds.
- Classic black powder : charcoal powder and sulfur
- Binders such as B. natural resins , glue , sugar , gum arabic & c. and synthetic polymers such as. B. polyacrylates , polyolefins , polyurethanes , etc. have a double function: They act as fuel and hold the set together mechanically. Many pyrotechnic sets consist exclusively of binding agents, oxidizers and (color) additives, e.g. B. Ignition heads.
- Typical metallic fuels are: magnesium , aluminum , calcium silicide , titanium , zirconium , iron and silicon
- Nitrocellulose can be used both in polymerized form ( nitro lacquer , celluloid ) as a high-energy binding agent, as well as powdery gun cotton directly e.g. B. can be used as an independent propellant without additional oxidizing agent. The burning behavior depends on the degree of nitriding . For nitrocellulose, therefore, the nitrogen content is always given, which serves as a measure of the number of nitro groups. It burns with minimal smoke.
- Recently, other nitrogen-rich compounds have also been gaining importance as fuel in low-smoke and pure-color applications. Here the play hexamethylenetetramine , guanidine nitrate , nitroguanidine , dicyandiamide , and many tetrazolates an important role.
- Among the metal hydrides , magnesium dihydride and zirconium hydride are particularly used as fuel.
- Other fuels are z. B. Sulphides : Arsenic (III) sulphide (As 2 S 3 ), antimony (III) sulphide (Sb 2 S 3 ) and bismuth (III) sulphide (Bi 2 S 3 ).
- Among the organic compounds , the derivatives of aromatic carboxylic acids are of particular importance ( benzoates , phthalates , trihydroxybenzenes , picrates ).
- Resin-rich, fine bear moss spores are used less in pyrotechnic sentences than directly for fire effects, especially on stages. These effects are controlled dust explosions suitable for demonstration .
Furthermore, depending on their intended use, pyrotechnic sets can also contain one or more of the following components:
- Burndown moderators such as B. Oxides of transition metals
- Phlegmatizers such as. B. graphite , waxes , zinc stearate , etc.
- flame-coloring additives such as B. alkali and alkaline earth metal salts or copper and molybdenum salts
- Silicates such as B. Glass powder and sand serve a wide variety of purposes: In match detonators , a drop of molten glass helps to prevent the residues from splashing and to enclose them in slag . The glass serves as a spark arrester. Silicates are used as friction agents in friction surfaces and snap peas .
- Aerosol formers such as B. organic dyes, red phosphorus .
By varying the composition, adding catalysts and additives that moderate the burnup, the mixtures are optimized for the respective application. For example, special emphasis is placed on the development of heat ( pyrolant ), gas development, smoke development, a constant and stable burning rate, reliable flammability even at low temperatures, good storage stability, high temperature resistance or the toxicological properties of the combustion gases.
Black powder , black phrase :
- 75% KNO 3 + 10% S + 15% C
Saltpeter ( potassium nitrate ), sulfur (together nitric sulfur ) and coal - classic pyrotechnic mixture, is hardly used today.
- 75% KNO 3 + 10% S + 15% C
Fundamental set , fireworks black powder or gray set :
- is the most frequently used pyrotechnic charge in fireworks : a mixture of 75 parts of saltpeter, 18 parts of sulfur and 7 parts of coal or flour powder.
It is mainly used as an ejection charge and a decomposition charge.
- is the most frequently used pyrotechnic charge in fireworks : a mixture of 75 parts of saltpeter, 18 parts of sulfur and 7 parts of coal or flour powder.
According to the burn rate , i.e. the speed of implementation, and the resulting explosiveness, a distinction is made between lazy sentences and fast sentences .
Sentences can, however, also have an explosive character. The unpressed and cartridge-filled powder of an air howler explodes with a loud bang, for example; while in the heavily pressed original state it only burns down with a bright whistle. This effect does not occur through a whistle or the like. but is based on the fact that the mixture burns in layers - up to several thousand times per second, see section Howling .
Classification of sentences
Depending on the composition and application, a distinction is made accordingly:
- Standard rate : propellant, ejector, separator
- Encouragement phrase , delay phrase
- Effect set : bang set, flare set , whistle set, spray set, etc.
- Fog set , smoke set
- Gas set ( gas generator set ), heating set , pyrotechnic set for special effects .
Standard sentences are the basic pyrotechnic sentences. They provide the thermal and thus the mechanical energy .
Propellant charge and discharge charge
The propellant ( Propellant ) used for the continuous generation of thrust and burns evenly: it is as a propellant charge incorporated in missiles; see for example propellant (model rocket) .
The pyrotechnic charge in base bleed projectiles is similar to a propellant charge, but is weaker. It is not used to generate thrust, but is only supposed to "fill up" the negative pressure behind the flying projectile with its combustion gases in order to reduce air resistance and thus increase the range.
The ejector ( expellant ) drives the object out of a launch tube by suddenly generating pressure : as an ejector charge in a mortar (gun) , a bombette or bomb (fireworks) , or to catapult military missiles from their mounts so far into the air that the actual propellant can be ignited safely.
Separating set and dismantling set
Separation sets break the object down into individual parts in order to bring out the desired effects.
The separating charge splits a fireworks effect into several partial effects, for example, the splitting charge transports the effect charges to a desired distance, the effect radius . It causes the actual effect, commonly known as an “explosion” (for example the typical spherical shape of a fireworks rocket).
The decomposing charge can be significantly more explosive than an ejection charge, because it only conveys the compact stars (the effect spheres up to 1 cm in size) and similar effects; it also keeps the mass to be ejected lower and achieves better heights.
It is used to light the object, i.e. to set the reaction going. These are ignition devices such as the fuse cord , an electric igniter (detonator) or an initial ignition device for explosives.
Typical mixtures for ignition kits:
- 70% KNO 3 + 24% B + 6% PMMA
potassium nitrate , boron , polymethyl methacrylate - very reliable ignition mixture; also burns at 77 K (- 196 ° C)
- 43% KClO 4 + 57% Zr
potassium perchlorate and zirconium , short name: ZPP - pyrotechnic detonators for solid rockets (NASA), this detonator is ignited with a laser pulse
A retarder is used to either delay the start of a flying object, to create a time interval after the ignition has been triggered (e.g. in the case of explosions), or to bridge the rise time after the ignition of the ejection or propellant charge so that the effect rate has the desired effect level can ignite (as with high altitude fireworks ), or to couple several effects, i.e. to combine them with a common ignition (for example in fireworks batteries ).
- 74% Pb 3 O 4 + 25% Si + 1% PMMA
red lead , silicon , polymethyl methacrylate - delay set; burns slowly at a defined speed.
Typical delay times in fireworks are around 2 or 3 seconds, 1.5 to 4 seconds for hand grenades , and 25 milliseconds for detonators in explosive technology .
Luminous set, colored set
The characteristic luminous and color effects are created by adding various substances to the pyrotechnic sentences:
- Red: strontium salts (dark red), calcium (orange red), lithium (carmine red)
- Yellow: sodium salts
- Green: barium salts (yellow green), copper (emerald green), tellurium (grass green), thallium (meadow green), zinc (pale green)
- Blue: copper salts (azure blue), arsenic , lead , selenium (light blue), cobalt (deep blue)
- Violet: cesium , potassium
- Purple: rubidium
- White, silver colors: magnesium , aluminum , titanium , zirconium
- Gold colors: iron , coal
The colors are created by the excitation of atoms in the heat, which immediately fall back into a state of lower energy and radiate the previously absorbed energy as light. Since the possible energy differences are precisely determined by quantum mechanics , atoms of different elements - due to the structure of their electron shell - have different emission colors. Copper is the most difficult color because the color also depends on the compound present. Most copper compounds, however, color green, only a few, which, however, disintegrate easily at high temperatures, actually color blue.
Substances that burn very hot increase the luminosity and intensity of the flame. In order to increase the brilliance and the color intensity , various chlorine-containing substances (e.g. PVC ) are added to the sets .
There are other reactions that play a role in the glow. Bright sparks are created through reactions in which metals such as magnesium , aluminum , titanium and others burn at several thousand degrees Celsius. Golden sparks - mostly produced by charcoal or iron - burn at low temperatures of around 1500 degrees Celsius.
Typical lighting effect sets are (strobe), radio set, Brilliant fire set flame rate Flittersatz (firefly), glitter set, indicator set (for example in the tail effects), double - or hybrid set (spark and flame set combined), or Sprühsatz (for example in the sparkler ). Some of these reactions are extremely complex.
Lightning pack and pop pack
Bangs are used to generate noise.
- In Knallerbsen is silver fulminate , a salt of bang acid used. A cracked pea contains a maximum of 2.5 mg, which is wrapped in tissue paper with a small amount of quartz sand. The quartz sand gives the crackling pea the necessary weight on the one hand, and on the other hand it triggers the explosion when it hits a hard surface by crushing the fulminate crystals. However, since the substance can also explode by the weight of the crystals itself, a certain amount of substance must not be exceeded during its production. Even slight friction or shock can cause an explosion. In addition, wet silver fulminate is also explosive.
Pops, Knistersätze are used as blast charge , or Knatterladung , Knisterladung ( Crack replacement ) in corresponding effects use.
Mixtures of oxidizers and metal powders are called lightning charges (or possibly lightning bang charges (BKS) if they are primarily intended to generate a bang). A flash of lightning explodes with a bright flash of light - and a loud bang - with an enormous amount of energy, whereby some flashes can also detonate . Another essential property of these explosives is to explode without containment, which depends on the type and composition of the mixture. This property makes them very interesting for pyrotechnics, as you can generate a much louder bang with small amounts than is possible with black powder: A little damming of the powder is enough for a "full" bang, as the bang-generating overpressure does not come through Reaction resulting gases, but is essentially generated by heating the circulating air. For example, the cardboard tube of a bird or starch fright, which is open on one side, only contains 1.8 g of BKS. Even so, such a cartridge exploding in the hand can tear off several fingers.
Lightning bolt sentence
- 65.82% KClO 4 + 34.18% Al
fireworks bang set; Underwater explosives; explodes with a loud bang
The mixture used almost exclusively in pyrotechnics consists of potassium perchlorate and very finely divided aluminum powder. With this set, the aluminum must be available as dark aluminum ( aluminum pyro grinding , dark aluminum , dark pyro aluminum ), which is the finest of the available aluminum powders. The chemical reaction equation is
- Potassium perchlorate and aluminum react to form potassium chloride and aluminum oxide .
Alternatively, magnesium powder can also be used as fuel and various nitrates and chlorates as oxidizing agents.
It burns with an extremely high reaction speed and can go from deflagration to detonation from quantities of 100 to 200 g after ignition . It explodes even in small quantities, ignited openly with a deafening bang, even though the end products of the reaction (KCl and Al 2 O 3 ) are high-melting solids. This property makes the handling of lightning bolt compositions dangerous, especially since the mixture is sensitive to static charge . To find this mixture in firecrackers of alarms, Vogelschreck cartridges or salute bombs in the Großfeuerwerkerei and in some in Germany for the free acquisition as illegally classified soil firecrackers .
Further, Flash mixtures of barium nitrate , sulfur and highly fine aluminum powder in small Bombetten used as a bursting.
Over-the-counter floor blasters may not contain a bolt of lightning bolt in Germany, but in most other countries this is far more common than classic black powder. As a bang in rising fireworks effects, lightning bangs are almost exclusively used nowadays in Germany.
Whistle phrase (howling phrase)
Whistling sentences (crying sentences) usually contain chlorates or perchlorates as oxidizing agents, as well as salts of organic acids ( salicylic acid , benzoic acid , gallic acid , potassium picrate or potassium dinitrophenolate ). The noise development is not caused by the shape of the outlet opening, but by an oscillating, pulsating burn at around 3000–4000 Hz in an open cardboard tube. The sentence burns down with a series of small explosions. After every explosion, a pressure wave is created with an outflow of the combustion gases and a subsequent brief negative pressure with an inflow of outside air. Due to the many sound events occurring in quick succession, due to the opposing pressure waves, a high-pitched sound is created, which is characterized as a whistling. The whistle is determined by the length of the case and the external pressure.
In addition to rockets, whistle sets are used in air howlers .
Smoke sets are based on the fact that volatile hygroscopic salts are formed during the burn , which attract the water vapor in the air. Essential components of smoke sets are aluminum or zinc and halogenated hydrocarbons such as tetrachloromethane or hexachloroethane . This creates aluminum chloride or zinc chloride as hygroscopic salts.
Colored smoke can be achieved by adding organic dyes to pyrotechnic mixtures. The combustion temperature must be sufficient to sublime the fat without thermally decomposing it. Potassium chlorate is usually used as an oxygen carrier and powdered sugar as fuel , rarely lactose or carbohydrates such as dextrin , in very fuel-rich mixtures that burn relatively slowly at low temperatures. To protect the dyes from thermal decomposition, large quantities of sodium bicarbonate are added as a heat sink and coolant. Many of the dyes used in colored smoke are carcinogenic or contain carcinogenic contaminants. For this reason, such products are only approved in the civil sector as signaling and rescue equipment and not for entertainment purposes.
Dealing with pyrotechnic assemblies and pyrotechnic objects, including manufacturing, processing, processing, using, moving, transporting and leaving them within the business premises, as well as recovering and destroying them; traffic (trade) and import are strictly regulated by law due to the possible risk.
- For detailed information on legal regulations, see: Pyrotechnics (classification into hazard classes ), European Agreement on the International Carriage of Dangerous Goods by Road (Transport), Pyrotechnicians (job description).
- Herbert Ellern: Military and Civilian Pyrotechnics. Chemical Publishing Company, New York NY 1968.
- John A. Conkling: The Chemistry of Pyrotechnics. Basic Principles and Theory. Marcel Dekker, New York NY et al. 1985, ISBN 0-8247-7443-4 .
- Klaus Menke: The chemistry of fireworks In: Chemistry in our time . Vol. 12, No. 1, 1978, pp. 12-22, doi : 10.1002 / ciuz.19780120103 .
- Franz Sales Meyer (Hrsg.): Fireworks as a lover 's art (= Seemann's art handbooks . 12, ZDB -ID 53757-3 ). Seemann, Leipzig 1898, (Reprint. Survival Press, sl 2002, ISBN 3-8311-4012-X ).
- Takeo Shimizu: Fireworks. The Art, Science and Technique. 2nd edition. Pyrotechnica Publications, Austin TX 1988, ISBN 0-929388-04-6 .
- ↑ a b Alexander P. Hardt: Pyrotechnics , Pyrotechnica Publications, Post Falls Idaho USA 2001, ISBN 0-929388-06-2
- ↑ a b Pyrotechnics Lexicon
- ↑ Pyrotechnic FAQ
- ↑ § 20 1. SprengV - single standard. Retrieved August 26, 2017 .