EP2530065B1 - High performance active material for an infra-red decoy which emits spectral radiation upon combustion - Google Patents

Description

The invention relates to a high-performance active compound for a pyrotechnic infrared target that emits spectrally during combustion. A pyrotechnic infrared target, which radiates spectrally when burned, emits predominantly radiation with a wavelength of 3.5 to 4.6 µm when burned. H. radiation in the so-called B-band, and only to a lesser extent radiation in the range of a wavelength of 1.8 to 2.6 µm, the so-called A-band. The A-band and the B-band are the wavelengths that are detected by conventional seeker heads. Known spectrally emitting compositions for black body emitters contain nitrocellulose or ammonium perchlorate or potassium perchlorate and a binding agent such as hydroxyl-terminated polybutadiene.

Active compounds with ammonium perchlorate are mechanically and thermally very sensitive and therefore do not meet the criteria of insensitive ammunition. Splintering, fire and slow heating can trigger a violent explosion with these active ingredients. The practically achievable density of these active masses is a maximum of approx. 1500 kg / m ³ , so that relatively little of them can be accommodated in a decoy target of a given caliber. Another disadvantage of such active compounds is that ammonium perchlorate is only compatible with other chemicals and / or materials to a very limited extent. On the one hand, this leads to safety problems and, on the other hand, to the fact that a large number of effective firing sets, e.g. B. on the basis of black powder, magnesium or zirconium, cannot be used because they would be too sensitive in combination with ammonium perchlorate. Another disadvantage of active compounds containing ammonium perchlorate is that their radiant power is relatively low when burned and, moreover, a great deal of radiant power is lost as a function of the air speed. This means that for the simulation of one with more When the aircraft is flying at 150 m / s, a large amount of the effective mass can be used in order to generate sufficient radiation power. In practice, this means that such decoy targets must have a relatively large caliber and, as a result, the amount that can be transported in a given ammunition room is small due to the space required by the ammunition.

Active compositions containing nitrocellulose are also not insensitive and can easily explode. Furthermore, it is disadvantageous that such active masses only burn at low wind speeds and their radiant power is not high when burned off. To ensure that it burns up in the wind, complex devices are required which, because of their space requirements, reduce the effective mass to be effectively transported in a decoy target. The density of an active composition containing nitrocellulose is also a maximum of about 1500 kg / m ³ . A major disadvantage of such an active mass is that its ignition requires a strong ignition pulse, which causes a strong, often non-spectral flash. This lightning bolt can tell a seeker head that the burning active mass is only a decoy target.

the DE 26 14 196 A1 relates to an infrared heater made from incendiary devices that are in direct contact with a metal foil, the incendiary device consisting of an intimate mixture of potassium nitrate and metallic boron. According to Example 1, a mixture of potassium nitrate and boron is mixed with a nitrocellulose lacquer and the dispersion obtained in this way is drawn onto an aluminum foil. The nitrocellulose lacquer is produced by mixing butanone with a mixture of nitrocellulose and glycerine nitrate. According to Example 3, a black powder mixture is dispersed in the nitrocellulose lacquer and the resulting dispersion is applied to an aluminum foil.

From the EP 0 455 980 A2 a sea marker for emergency approach procedures for aircraft on board ships is known. This comprises a tube with a pyrotechnic charge arranged therein, the tube having a flare which can be overlaid by an intermediate charge. The intermediate set may include barium nitrate, sulfur, charcoal, flour black powder, methyl cellulose, silica, and a binder. An accentuation made of barium nitrate, potassium perchlorate and zirconium / nickel can be arranged on the intermediate set.

U.S. 5,834,680 A discloses a decoy active composition comprising 20-60% by weight magnesium, 5-50% by weight ammonium perchlorate, 8-30% by weight of a polymeric binder and 5-30% by weight anthracene or decacylene.

The object of the present invention is to provide an active composition which, when burned, radiates spectrally with high radiation power, ie radiation in the B-band emitted, which is far more intense than the radiation emitted when burning in the A-band. Furthermore, the active mass should be relatively insensitive, but should nonetheless be able to ignite quickly and easily, and should have a relatively low loss of radiant power when the surrounding air burns up as the speed of the surrounding air increases.

The object is achieved by the features of claim 1. Appropriate refinements of the invention result from the features of claims 2 to 8.

According to the invention, a high-performance active compound is provided for a pyrotechnic infrared target which is spectrally radiating when it is burned off. The high-performance active material comprises a fuel, an oxidizing agent, a binding agent and a substance containing carbon. The fuel and the oxidizing agent are selected in such a way that the oxidizing agent can oxidize the fuel in an exothermic primary reaction with the development of a temperature of at least 1000 K after it has been ignited. Combustion temperatures are known for a large number of known combinations of a fuel and an oxidizer. If the resulting temperature is not known, it can be estimated from known combustion temperatures and / or determined without great effort by measuring during the combustion. Furthermore, the substance is chosen so that the substance is endothermic pyrolysed by the heat released in the primary reaction and in the process releases flammable gas in air, in particular with a non-sooting flame. A large number of suitable substances are known to the skilled person. In particular, natural substances such as wood or lignite come into consideration for this. The specialist knowledge of the person skilled in the art is sufficient for the selection of such a substance. If there is any doubt about a substance that is highly likely to be considered, it is sufficient to carry out a single experiment to determine whether the substance is pyrolysed with the release of a gas that is combustible in air when the heat is released. The fuel is not so strongly reducing that the resulting CO ₂ can be reduced to carbon. The substance and its proportion in the high-performance active compound are selected so that the temperature of the high-performance active compound does not exceed 2000 K after it has been ignited because of the heat extraction due to the endothermic pyrolysis. The selection of a substance from the substances in question according to the above conditions and its proportion in the active mass only requires the implementation of a very limited number of routine experiments. The results of the routine experiments, such as, for example, the measured temperature of the high-performance active substance after its ignition, can be estimated before carrying out the experiments on the basis of known parameters of the substance, such as the specific heat requirement for its pyrolysis. A more precise specification of the features according to the invention is not possible without unduly restricting the invention. For the average person skilled in the art, however, the selection specified by the features does not pose a problem.

The carbon can be contained in the substance in elemental form or in the form of at least one carbon atom in a molecule comprised by the substance. The redox potential of the fuel is at least as high as the redox potential of carbon, ie the fuel is at most as strongly reducing as carbon. However, the redox potential may also be slightly lower, so that CO _{2 is} reduced to CO, as CO in the air _{burns immediately to CO 2} , creating a large flame that increases the power and the spatial effect. This means that the free enthalpy of a reaction of the fuel with CO at the resulting temperature is greater than or equal to 0, i.e. a reaction of the fuel with CO under the given conditions does not take place voluntarily. The resulting CO ₂ , which generates strong radiation in the desired B-band, cannot be reduced to carbon.

By avoiding the formation of elemental carbon, there is no soot and therefore little black body radiation, i.e. H. Radiation with a high proportion of radiation in the A-band and a low proportion of radiation in the B-band. This results in a strong emission of radiation in the B-band from the carbon-containing substance.

The radiation power of the burning high-performance active composition according to the invention exceeds the radiation power of conventional ammonium perchlorate-containing active compositions in some cases by more than three times and can, under operating conditions, i. H. at high speed of the surrounding air, even exceed the radiation power of the blackbody radiator MTV in the B-band.

The fuel can also contain carbon. At least the material properties of the substance and the fuel can be identical. If the material composition is identical, however, the material can be in a different form, for example as a compressed material in a loose fill of the fuel. Even if the fuel and the substance are identical in nature, part of them can serve as fuel and the remainder as substance, if only the amount of the oxidizing agent sufficient for the oxidation of the part serving as fuel. The rest is pyrolysed as a substance. The substance and the fuel can also have a different material composition.

The oxygen balance of a high-performance active composition according to the invention is generally negative, and yet the avoidance of the formation of soot avoids intense radiation in the A-band, which is otherwise common with active compositions that are not balanced with oxygen. A feature of the high-performance active composition according to the invention is that the primary reaction generates a temperature which is reduced by the endothermic pyrolysis. There is a spatial separation of the primary reaction and the reaction of the gas with the oxygen in the air.

The gas produced during pyrolysis enlarges a flame that is produced, which can consist of a primary flame formed by the primary reaction and a secondary flame formed by the reaction of the gas with atmospheric oxygen. A primary flame is understood to mean a flame in which there is no reaction with the oxygen in the air, i.e. H. an anaerobic flame. A secondary flame is understood to mean a flame in which a reaction with oxygen takes place, i.e. H. an aerobic flame. The released flammable gas ignites immediately when it comes into contact with the air, as the primary reaction causes it to be heated to a temperature above the ignition temperature. This creates a secondary flame with properties similar to a flame from a jet engine, which is also formed by combustible gases that burn in the air. The spectrum of the secondary flame is similar to the spectrum of a kerosene flame. Due to the spatial separation of the secondary flame from the surface of the high-performance active compound, this surface is not or at least not significantly heated by the secondary flame, thereby avoiding a shift in the wavelength of the radiation emitted by the high-performance active compound from the B-band to the A-band.

When the resulting gas is burned in the air, the oxygen in the air serves as a further oxidizing agent. As a result, less oxidizing agent is required and the performance of the high-performance active compound according to the invention and the gas volume that can be generated therefrom are considerably increased in relation to their mass compared to the previously known pyrotechnic active compounds which emit spectrally during combustion. Previous attempts to increase the radiant power of such active materials have always been based on changing the fuel contained therein and the oxidizing agent contained therein or on a change in the quantitative ratio of Fuel to oxidizer. The experiments always resulted in the generation of a higher temperature and thus in a shift in the wavelength of the emitted radiation towards the A-band.

Because the high-performance active compound according to the invention does not have to contain ammonium perchlorate, the high-performance active compound can be made so insensitive that it can be classified as insensitive ammunition. Another advantage of the high-performance active compound according to the invention is that it can be composed of very cost-effective components. The high-performance active material can be bound with almost any binding agent. When pressing the high-performance active compound, neither hardening resins such as HTPB (hydroxyl-terminated polybutadiene) nor solvents, for example to dissolve nitrocellulose, have to be used. The production and processing of the high-performance active compound is thereby significantly simplified and helps to keep its costs low.

A larger gas volume can be generated per unit mass with the high-performance active mass according to the invention than with known spectrally radiating active masses, because the high-performance active mass according to the invention contains less oxidizing agent and uses the atmospheric oxygen for oxidation. The essential advantage of the high-performance active compound according to the invention is that the radiation spectrum of the burning and moving high-performance active compound very precisely reproduces the spectrum of a moving jet engine.

The fuel contains either elemental carbon, e.g. B. in the form of graphite, or comprises boron, silicon, antimony, iron, manganese, cobalt or nickel or a mixture, e.g. B. from powders of these substances, or an alloys of these substances. The reaction products of the fuel with the oxidizing agent should not be volatile, since volatile reaction products cause a very hot flame and thus the emission of black body radiation.

The fuel is preferably selected so that after the primary reaction it leaves behind a solid, ie neither volatile nor liquid, reaction product. This can be ash, for example. The release of this reaction product when the high-performance active compound burns off creates a spectral spatial effect. After the primary reaction, a solid residue, ie a solid reaction product, is left behind Fuels are known in large numbers to the person skilled in the art. The oxidizing agent comprises a perchlorate, chlorate, oxide, sulfate, nitrate, dinitramine, nitrite, peroxide, dinitromethanate, in particular sodium, potassium or ammonium dinitromethanate, a nitro compound, a nitrate ester, hexogen, octogen, nitrocellulose or nitropenta.

The substance pyrolyzed by the heat released in the primary reaction includes sugar, wood, in particular in the form of wood flour or sawdust, grain flour, in particular wheat flour, lignite, peat, cellulose, starch, tobacco, an oxalate, in particular calcium oxalate, a formate, in particular magnesium formate, an acetate, in particular calcium acetate, a propionate, in particular calcium propionate, polyethylene glycol, polyoxymethylene, polyamide, in particular nylon®, urea, hexamethylenetetramine, trioxane or paraformaldehyde. The fuel, the oxidizing agent and the substance can, depending on how the respective other constituents of the high-performance active compound are selected, be selected from groups which comprise identical organic compounds. So z. B. Hexogen in combination with a perchlorate can be a fuel, on the other hand it is an oxidizing agent if a metal is used as fuel.

The fuel is not sulfur, although sulfur is contained in the high-performance active compound. The sulfur can prevent a primary flame generated in the primary reaction from being blown out at high wind speeds.

The fuel, the oxidizing agent and the substance and the amount of the fuel, the oxidizing agent and the substance are preferably selected in such a way that when the high-performance active substance burns off in the air, the ratio between the specific power of the emitted radiation in the wavelength range from 1.8 to 2 .6 µm for the specific power of the emitted radiation in the wavelength range from 3.5 to 4.6 µm is at most 1: 3, in particular at most 1: 5, in particular at most 1:10. The said ratio is smaller, the lower the temperature that the high-performance active compound reaches after it has been ignited. The selection and the determination of the quantity only requires the implementation of routine experiments. Since only two parameters have to be measured here, namely the power of the radiation in the two wavelength ranges, a person skilled in the art can quickly determine in which direction he has to change a quantity ratio in order to get into the correct range of the ratio between the two powers specified here. Preferred are the fuel, oxidizer, and substance and amounts of the fuel, the oxidizing agent and the substance selected so that the temperature of the high-performance active compound does not exceed 1770 K, in particular 1270 K, in particular 970 K, after it has been ignited. If the temperature does not exceed 970 K, the wavelength of the emitted radiation is almost exclusively in the B-band and only to a very small extent in the A-band. For intense radiation in the B-band and little radiation in the A-band, it is also advantageous if the substance is chosen so that the gas that can be released therefrom by pyrolysis is a gas which in the air with a maximum flame temperature below 2000 K burns. Apart from the fact that the flame temperatures for a large number of gases that can be released by pyrolysis are known from the literature, the temperature can also be easily determined by measurement. The selection of substances whose gases released by pyrolysis have a maximum flame temperature below 2000 K does not exceed the reasonable effort of routine experiments that is usual in this field.

The binder is preferably selected so that it does not cause any soot to form when the high-performance active compound burns off. Such binders are known to the person skilled in the art. If it is not known for a binding agent in question whether it produces soot when it burns, a simple experiment is sufficient to answer this question. Soot formation would lead to stronger radiation in the area of the A-band, which is not desired here. The binder can be, for. B. be polychloroprene.

The invention is explained in more detail below on the basis of exemplary embodiments.

From all of the compositions given below, 5 tablets each with a diameter of about 21 mm and a weight of 10 g were pressed at a pressure of 1500 bar. The tablets were burned and their performance in the form of radiant power measured with a radiometer and corrected for atmospheric attenuation. The specific performance was determined in relation to the performance of tablets made of MTV (Magnesium-Teflon-Viton) as a standard. The energy was measured in joules / (g / sr) in the B-band in the standing test, ie without wind. In addition, the performance of the burning active masses, designed as decoy targets with a caliber of 36 mm, was measured dynamically on a sled at a speed of 75 m / s and 150 m / s. Between 120 and 170 g of active material were used in each case.

Unless otherwise stated, all data have been measured in five parallel series of measurements, each compared to MTV with the radiometer at a distance of 1 m.

MTV standard:

material Type Weight percent Others Magnesium powder LNR 61 60.0 TMD = 1893 Teflon powder Hoechst TF 9202 23.0 Viton 3M Fluorel FC-2175 12.0 Graphite (as a lubricant) Merck 5.0

Reference example 1

State-of-the-art active substance based on ammonium perchlorate: material Type Weight percent Others Ammonium perchlorate Grain size <200 µm 86.98 TMD = 1702 HTPB Sartomer R45HT-M M = 2800 12.10 IPDI Sleeve 0.91 Iron acetonylacetate 0.02 "IPDI" stands for isophorone diisocyanate

Reference example 2

Other state-of-the-art active ingredients based on ammonium perchlorate: material Type Weight percent Others Ammonium perchlorate Grain size <50 µm 85.50 TMD = 1678 HTPB Sartomer R45HT-M M = 2800 13.47 IPDI Sleeve 1.01 Iron acetonylacetate 0.02

example 1

High-performance active compound according to the invention with boron as fuel, potassium nitrate as oxidizing agent and lignite as substance to be pyrolyzed:
The sulfur supports the primary reaction at high wind speeds by preventing the primary flame from being blown out. The high-performance active mass generates an approx. 30 m long spectral spatial effect when burned at speeds of 75 m / s and 150 m / s. material Type Weight percent Others Brown coal Heating professional, finely ground, 32.0 TMD = 1712 Grain size <100 µm Potassium nitrate finely ground, 53.0 Grain size <10 µm boron Grain size <1 µm 4.0 sulfur finely powdered 8.0 Chloroprene Macroplast 3.0

Example 2

Further high-performance active compound according to the invention with silicon as fuel and otherwise the same components as the high-performance active compound according to Example 3:
The high-performance active compound creates an approx. 30 m long spatial effect when burned at speeds of 75 m / s and 150 m / s. material Type Weight percent Others Brown coal Heating professional, finely ground, 30.0 TMD = 1735 Grain size <100 µm Potassium nitrate finely ground, 51.0 Grain size <10 µm silicon fine, grain size <30 µm 8.0 sulfur finely powdered 8.0 Chloroprene Macroplast 3.0

Example 3

Further high-performance active compounds according to the invention:
The primary reaction takes place between sodium nitrate as an oxidizing agent and lignite as a fuel. Lignite that has not been converted serves as the substance to be pyrolyzed. material Type Weight percent Others Brown coal Heating professional, finely ground, 33.0 TMD = 1750 Grain size <100 µm Sodium nitrate finely ground, 56.0 Grain size <10 µm sulfur finely powdered 8.0 Chloroprene Macroplast 3.0

Example 4

Further active mass according to the invention:
At 0 m / s wind, this active mass reaches 86% of the MTV performance in the B-channel and has a higher spectral ratio than the lignite active masses. material Type Weight percent Others Wood flour Oak dust from fine sanding of the floor with a drum sander, 100 grit 30.0 TMD = 1406 Potassium nitrate finely ground, 51.0 Grain size (d ₅₀ ) <10 µm silicon fine, grain size <30 µm 8.0 sulfur finely powdered 8.0 Polychloroprene Macroplast 3.0 “TMD” stands for the theoretical mean density of the total active mass in kg / m ³ .

The relative performance data achieved with the above active masses during combustion are given below. "% MTV" indicates the measured power as a percentage of the power measured for the MTV standard.
1. Radiation measurements in the laboratory without wind: sentence % MTV (B-channel) Standard MTV 100 Reference example 1 19th Reference example 2 29 example 1 84 Example 2 82 Example 3 87
2. Radiation measurement under dynamic conditions at an air speed of 75 m / s: sentence % MTV (B-channel) Standard MTV 100 Reference example 1 49 Reference example 2 75 example 1 137 Example 2 166
3. Radiation measurements under dynamic conditions at 150 m / s air speed: sentence % MTV (B-channel) Standard MTV 100 Reference example 1 17th Reference example 2 57 example 1 149 Example 2 131

All results of the measurement under dynamic conditions are in each case an average of 3 parallel tests, which were carried out with decoy targets made of the respective specified effective masses with a caliber of 36 mm.

Claims (8)

1. High-intensity active composition for a pyrotechnic infra-red decoy which irradiates spectrally on burning, comprising a fuel, an oxidizer, a binder and a carbon-containing substance, the fuel and the oxidizer being selected such that the oxidizer is able to oxidize the fuel after ignition thereof in an exothermic primary reaction, with development of a temperature of at least 1000 K, the substance being selected such that the substance is endothermically pyrolysed by the heat given off in the primary reaction, and in this procedure releases gas which is combustible in air, the fuel not being so strongly reducing that resultant CO₂ can be reduced to carbon, and the substance and its proportion in the high-intensity active composition being selected such that the temperature of the high-intensity active composition after ignition thereof does not exceed 2000 K owing to the removal of heat by the endothermic pyrolysis, where the fuel comprises carbon or comprises boron, silicon, antimony, iron, manganese, cobalt or nickel or a mixture or alloy of these substances, where the oxidizer comprises a perchlorate, chlorate, oxide, sulphate, nitrate, dinitramine, nitrite, peroxide, dinitromethanate, a nitro compound, a nitrate ester, hexogen, octogen, nitrocellulose or nitropenta, where the substance comprises sugar, wood, cereal flour, lignite coal, peat, cellulose, starch, tobacco, an oxalate, a formate, an acetate, a propionate, polyethylene glycol, polyoxymethylene, polyamide, urea, hexamethylenetetramine, trioxane or paraformaldehyde, where the fuel is not sulphur, but sulphur is present in the high-intensity active composition.
2. High-intensity active composition according to Claim 1,
   where the fuel comprises elemental carbon.
3. High-intensity active composition according to either of the preceding claims,
   where the fuel is selected such that after the primary reaction it leaves behind a solid reaction product.
4. High-intensity active composition according to any of the preceding claims,
   where the oxidizer dinitromethanate is sodium, potassium or ammonium dinitromethanate.
5. High-intensity active composition according to any of the preceding claims,
   where the substance comprises wood in the form of sawdust or wood shavings, the substance cereal flour is wheat flour, the substance oxalate is calcium oxalate, the substance formate is magnesium formate, the substance acetate is calcium acetate, the substance propionate is calcium propionate and the substance dinitromethanate is sodium, potassium or ammonium dinitromethanate.
6. High-intensity active composition according to any of the preceding claims,
   where the fuel, the oxidizer and the substance, and the amounts of the fuel, the oxidizer and the substance, are selected such that the temperature of the high-intensity active composition after ignition thereof does not exceed 1770 K, more particularly 1270 K, more particularly 970 K.
7. High-intensity active composition according to any of the preceding claims,
   where the binder is selected such that burning of the high-intensity active composition does not cause any soot formation.
8. High-intensity active composition according to Claim 7,
   where the binder is polychloroprene.