EP2695871B1 - High performance material for a pyrotechnic decoy flare with a fluorinated carbon compound - Google Patents

Description

The invention relates to a high-performance active compound for a pyrotechnic decoy with a fuel, an oxidizing agent for the fuel and optionally a binding agent, the oxidizing agent being a partially fluorinated pyrene or a partially fluorinated carbon compound.

From the DE 20 54 210 A1 For example, polytrifluorochloroethylene or polyvinylidene fluoride is known as an oxidizing agent for a metal. From the U.S. 4,445,947 A For example, poly (chlorotrifluoroethylene) is known as a binder in a fuel containing magnesium, aluminum or a mixture thereof. From the U.S. 5,472,533 A and from the EP 1 348 683 A2 poly (ethylene tetrafluoroethylene) is known in each case in a magnesium-containing fuel composition.

The task of an active mass for decoy targets is to simulate the infrared radiation of an exhaust plume of a jet aircraft for a seeker head, for example a guided weapon, when it burns. The wavelength range detected by conventional seeker heads is between 2 and 5 µm. So far, this has been achieved, for example, with the well-known black body active substance Magnesium-Teflon-Viton (MTV), in which polytetrafluoroethylene (PTFE, Teflon®) serves as the oxidizing agent. Up to 250% of MTV's performance can be achieved when graphite fluoride is used as an oxidizing agent. However, graphite fluoride is relatively expensive and can be difficult to obtain. To achieve the same performance without graphite fluoride, more active mass can be used in a decoy of a larger caliber. However, this has the disadvantage that with limited loading capacity, as is generally the case in aircraft, fewer dummy target charges can be accepted.

Furthermore, it is then necessary to provide launching devices for a larger caliber.

The object of the invention is therefore to provide an active mass for decoy targets which, when burned, in particular also at high air speeds, has a higher radiation power than MTV and does not have to contain any graphite fluoride. The object is achieved by the features of claim 1. Appropriate configurations result from the features of claims 2 to 5.

In an example based on the invention (not part of the invention), a high-performance active compound for a pyrotechnic decoy, comprising a fuel, an oxidizing agent for the fuel and optionally a binder, is provided, the oxidizing agent being a fluorinated carbon compound with a carbon chain at least 100 carbon atoms long or repeating units containing carbon atoms, forming a polymer, wherein in the carbon chain or per unit at least one of the carbon atoms has at least one binding site occupied by a molecular residue or an atom other than fluorine or carbon. The oxidizing agent is not graphite fluoride. The binder can be omitted if another component of the high-performance active compound has a binding property.

The oxidizing agent contained in the high-performance active composition according to the invention is therefore not completely fluorinated, like PTFE, but only partially fluorinated. So far it has been assumed that those fluorocarbons are best suited for black body active masses, which contain the maximum possible amount of fluorine and thus act as efficiently as possible as an oxidizing agent and deliver the highest enthalpy of combustion.

However, the inventor of the present invention has recognized that not only the enthalpy of combustion is decisive, but that the heat released during combustion must also be radiated efficiently and therefore a high emissivity of the combustion products is just as important. He has also recognized that the carbon black generated from completely fluorinated fluorocarbon compounds is too fine-grained to emit radiation in the desired wavelength range of 2 to 5 µm. With these active substances, the released energy is emitted in shorter wavelength ranges or dissipated convectively. Furthermore, the inventor has recognized that fine soot also burns off very quickly and is therefore quickly lost as an emitter of radiation.

The oxidizing agent Teflon is therefore unfavorable for decoy effective masses. The oxidizing agent graphite fluoride has a significantly higher emissivity in the desired wavelength range of 2 to 5 μm than Teflon when burned, but has the above-mentioned disadvantages of high price and limited availability.

The oxidizing agent contained in the high-performance active compound is a fluorinated carbon compound with a carbon chain at least 100 carbon atoms long or units containing repeating carbon atoms that form a polymer. In this case, in the carbon chain or in each of the units, at least one of the carbon atoms has at least one binding site not occupied by another carbon atom, this binding site being occupied by a molecular residue or an atom other than fluorine. Such an oxidizing agent produces soot particles with aromatic rings or double bonds and an average grain size of at least 1 µm when the active material is burned off. These soot particles efficiently generate radiation in the desired wavelength range of 2 to 5 µm. It is assumed that this is due to the fact that the remainder of the molecule or the atom other than fluorine or carbon provides sites in the carbon chain or the units at which double bonds or aromatic structures can arise during combustion, which stabilize the molecules that are formed in such a way that no soot particles that are too small are formed during further burn-off. The coarse soot produced with the active composition according to the invention also burns longer than fine soot and therefore emits longer. It has been shown that the emissivity of the combustion products and the proportion of the energy converted into radiation of the total energy released and thus also the specific radiation power in the high-performance active compound according to the invention is increased compared to active compounds with the fully fluorinated oxidizing agent PTFE. The amount of carbon compound in the high-performance active compound can be relatively high, although this reduces the temperature of the flame of the high-performance active compound that is created during the combustion by reducing the enthalpy of combustion. This is compensated by the increased emissivity due to the carbon compound and the better utilization of the available energy.

Furthermore, the burning rate of the high-performance active composition according to the invention is increased by the oxidizing agent, because the increase in the radiation output brought about by the oxidizing agent also means that more heat is applied to the burning surface is reflected back. The burn-up is further accelerated by the fact that a flame that arises during the burn-up is optically relatively dense and heat is therefore retained within the flame for a relatively long time. Compared to the fine-grained soot resulting from the use of Teflon as the oxidizing agent, the soot resulting from the oxidizing agent contained in the high-performance active compound according to the invention burns off more slowly. This allows it to radiate the released energy longer. As a result, the chemical energy contained in the high-performance active compound is converted into radiation with a higher degree of efficiency. In addition, the slowly burning soot creates an even and dense spatial effect. Due to the spatial effect, an exhaust gas plume of a jet aircraft can be imitated very well using the high-performance active compound according to the invention.

The soot or the carbon contained therein can also form carbides with titanium, zirconium, hafnium, niobium, tantalum, molybdenum and vanadium, which can be contained in the high-performance active compound as fuel. The carbon serves as a further oxidizing agent for the metals mentioned. The resulting carbides do not melt in the flame produced during the burn-up and emit radiation to the environment as carbide particles.

The reflection on the burning surface also makes it possible to provide a relatively high proportion of fuel in the high-performance active compound in relation to the oxidizing agent. As a result, the active substance can have a higher energy content than with an oxidizing agent other than the one contained therein.

In one embodiment of the invention, the ratio of the number of fluorine atoms to the number of other atoms in the oxidizing agent is less than 3 when all other atoms are hydrogen atoms.

The other atom can be a hydrogen, oxygen, nitrogen, sulfur, chlorine, bromine, or iodine atom. If the other atom is a hydrogen atom and a fluorine atom is bonded to an adjacent carbon atom, HF can be split off when the high-performance active compound burns, forming a double bond between the adjacent carbon atoms. In a further embodiment of the high-performance active material, more than one binding site of the carbon atom or a plurality of the carbon atoms are through a molecular residue or several molecular residues and / or another atom or atoms other than fluorine and carbon occupied, these binding sites each being occupied differently. The differently occupied binding sites can each be localized on adjacent carbon atoms. The other atoms can comprise at least one halogen atom, in particular a chlorine, bromine or iodine atom, and at least one hydrogen atom at points of attachment of adjacent carbon atoms. As a result, a hydrogen halogen can be split off with the formation of a double bond.

If a chlorine, bromine or iodine atom is bonded to a carbon atom and hydrogen is bonded to an adjacent carbon atom, HCl, HBr or HI can be split off when the high-performance active substance is burned off, forming a double bond between the adjacent carbon atoms. When HCl, HBr or HI are split off, the fuel can be magnesium, for example. The formation of double bonds through elimination reactions in halogenated polymers can occur as follows when a high-performance active compound is burned off:

The elimination reactions can take place thermally or by means of a base. As a base, e.g. B. function a metal oxide from the fuel in the mixture or a base can be added to the active material.

The oxidizing agent can be poly (ethylene tetrafluoroethylene) (ETFE), poly (chlorotrifluoroethylene) (PCTFE), poly (ethylene chlorotrifluoroethylene) (ECTFE), perfluoroalkoxy polymer (PFA), polyvinylidene fluoride (PVDF) or a partially fluorinated pyrene (according to the invention) .

The structures of PTFE, PVDF, ETFE, PFA, PCTFE and ECTFE are as follows:

According to the invention, the oxidizing agent can comprise at least one aromatic structure or polyaromatic structure.

The fuel can comprise a metal, a semimetal or a mixture or alloy of metals and / or semimetals or a mixture or alloy of at least one metal and at least one semimetal. The fuel can be aluminum, magnesium, titanium, zirconium, hafnium, calcium, lithium, niobium, tungsten, manganese, iron, nickel, cobalt, zinc, tin, lead, bismuth, tantalum, molybdenum, vanadium, boron, silicon, or an alloy Mixture of at least two of these metals or semi-metals, a zirconium-nickel alloy or mixture, an aluminum-magnesium alloy or mixture, a lithium-aluminum alloy or mixture, a calcium-aluminum alloy or mixture, an iron-titanium alloy or mixture, a zirconium-titanium alloy or mixture or a lithium-silicon alloy or mixture.

Titanium, zirconium, hafnium, niobium, tantalum, molybdenum and vanadium can form carbides with the carbon particles or the resulting soot particles. The carbon serves as a further oxidizing agent for the metals mentioned. The resulting carbides are present as solids at the temperatures that arise when the high-performance active compound burns and emit radiation as carbide particles.

The binder can be a fluoroelastomer, in particular a fluororubber, such as Viton® from "DuPont Performance Elastomers". Furthermore, the active composition can contain a burn-off catalyst, in particular ferrocene, iron acetonylacetate or copper phthalocyanine, to accelerate the burn-off.

The following examples are not according to the invention.

All of the compositions given below were prepared as follows:
The dry components and 5 conductive rubber cubes were mixed in a 250 ml mixing container for one hour using a tumble mixer at 120 revolutions / minute. The resulting mixture was emptied into a stainless steel bowl, the rubber cubes removed, and 3M Fluorel FC-2175 fluororubber as a 10% solution in acetone was added as a binder. In the case of active compositions containing carbon nanotubes, the carbon nanotubes were not mixed directly with the other constituents, but rather dispersed beforehand in the 10% solution of the binding agent in acetone by means of ultrasound in order to ensure the most uniform possible distribution in the active composition. The mass was stirred into a homogeneous dough and mixed until the acetone had evaporated to such an extent that the mass became granular. The resulting granules were dried at 50 ° C.

10 g of the granules were each compressed into tablets. The press tool had an inside diameter of 16.8 mm. The pressing pressure was 1500 bar. The

Densities of the tablets were between 86 and 94% of the theoretical maximum density (TMD). All tablets were coated on their cylindrical surfaces with polychloroprene (Macroplast) and glued with polychloroprene to 80 × 80 × 5 mm steel plates in order to limit their burning to a free end face. The tablets were allowed to dry overnight at room temperature.

The finished tablets were burned off and their radiation output was determined using a radiometer. In the following, the performance is expressed as a percentage of a corresponding base active mass, e.g. B. MTV indicated.

In the case of active masses with a spatial effect, the corresponding active masses without the additive in the form of carbon particles were used as a reference. In Table 1, this corresponds in each case to the reference value given as 100% before the value given below for the active composition according to the invention.

Example 1:

Standard-MTV (Magnesium-Teflon-Viton) active material according to the state of the art (burn rate 3.0 mm / s): material Type Wt% Others magnesium LNR 61 60.0 Teflon powder Dyneon TF 9205 35.0 Viton 3M Fluorel FC-2175 5.0 TMD = 1881 TMD = Theoretical Maximum Density

Example 2:

Standard MTV active material with graphite (charring rate 3.0 mm / s): material Type Wt% Others Magnesium powder LNR 61 60.0 Teflon powder Hoechst TF 9205 25.0 Viton 3M Fluorel FC-2175 10.0 graphite Merck 5.0 lubricant

Example 3:

Black body active material based on PVDF with combustion distributed in zones (burn rate 4.1 mm / s; very dense and even spatial effect):. material Type Wt% Others magnesium LNR 61 41.0 Hard coal finely ground 3.0 PVDF Solvay 80 µm 14.4 TMD = 2041 boron 1 µm 8.0 titanium Svenska kemi <100 µm 10.0 zirconium Chemetall type GH 8.6 Viton 3M Fluorel FC-2175 15.0

Example 4:

Black body active material based on PVDF with combustion distributed in zones (burn rate: 3.3 mm / s): material Type Wt% Others magnesium LNR 61 50 Hard coal finely ground 5.0 PVDF Solvay 20.0 TMD = 1882 boron 1 µm 7.0 titanium Chemetall type E 6.0 zirconium Chemetall type FA 1.0 Ferrocene Arapahoe Chemicals 1.0 Viton 3M Fluorel FC-2175 10.0

Example 5:

Black body active material based on PVDF (creates a dense and even spatial effect; burn rate: 9.6 mm / s): material Type Wt% Others magnesium LNR 61 60.0 PVDF Hylar 301 F 35.0 Viton 3M Fluorel FC-2175 5.0 TMD = 1745

Example 6:

Black body active material based on ECTFE (creates a dense and long spatial effect; burn rate: 4.1 mm / s): material Type Wt% Others magnesium LNR 61 60.0 ECTFE Solvay Halar 6014 35.0 Viton 3M Fluorel FC-2175 5.0 TMD = 1721

Example 7:

Black body active material based on ECTFE with combustion distributed in zones (very powerful set with a large and dense spatial effect; burn rate: 3.8 mm / s): material Type Wt% Others magnesium LNR 61 42.0 Expanded graphite NGS fine 4.0 ECTFE Solvay Halar 6014 33.0 titanium Svenska kemi <100 µm 10.0 boron 1 µm 5.0 Ferrocene Arapahoe Chemicals 1.0 Viton 3M Fluorel FC-2175 5.0 TMD = 1885 Table 1: Measurement results of the radiation measurements. All results are an average of 5 parallel tests. sentence E _KW [J / (g sr)] E _MW [J / (g sr)] (E _KW + E _MW ) [J / (g sr)] E _{MW /} E _KW % MTV KW % MTV MW % MTV KW + MW example 1 175 54 229 0.309 105 66 92 Example 2 166 82 248 0.496 100 100 100 Example 3 168 112 280 0.667 101 137 113 Example 4 174 161 335 0.925 105 196 135 Example 5 188 85 273 0.452 113 104 110 Example 6 189 189 378 1,000 114 230 152 Example 7 202 208 410 1,030 122 254 165 E _KW = specific power in the short wave range (approx. 1.8 = 2.6 µm) in J / (g sr);
E _MW = specific power in the medium wave range (approx. 3.5 - 4.6 µm) in J / (g sr);
(E _KW + E _MW ) in J / (g sr) = sums of the specific outputs in the KW and MW range;
E _MW / E _KW = the ratio of the specific power in the MW to the specific power in the KW range;
% MTV = performance as a percentage of the performance of the reference rate MTV (in example 2).

Claims (5)

1. High-intensity active composition for a pyrotechnic decoy, comprising a fuel, an oxidizer for the fuel and optionally a binder, the oxidizer being a partially fluorinated pyrene or a partially fluorinated carbon compound having a carbon chain at least 100 carbon atoms long or having repeating units that comprise carbon atoms and form a polymer, the unit comprising at least one aromatic structure or polyaromatic structure, or
   at least one of the carbon atoms in the carbon chain or in each of the units having at least one bonding site not occupied by a different carbon atom, with more than one bonding site of a plurality of the carbon atoms being occupied by atoms other than fluorine and than carbon, these bonding sites each being differently occupied, the other atoms comprising at least one bromine or iodine atom, and at least one hydrogen atom at bonding sites of adjacent carbon atoms.
2. High-intensity active composition according to Claim 1,
   the fuel comprising a metal, a semi-metal or a mixture or alloy of metals and/or semi-metals or a mixture or alloy of at least one metal and at least one semi-metal.
3. High-intensity active composition according to any of the preceding claims,
   the fuel comprising aluminium, magnesium, titanium, zirconium, hafnium, calcium, lithium, niobium, tungsten, manganese, iron, nickel, cobalt, zinc, tin, lead, bismuth, tantalum, molybdenum, vanadium, boron, silicon, an alloy or mixture of at least two of these metals or semi-metals, a zirconium-nickel alloy or mixture, an aluminium-magnesium alloy or mixture, a lithium-aluminium alloy or mixture, a calcium-aluminium alloy or mixture, an iron-titanium alloy or mixture, a zirconium-titanium alloy or mixture or a lithium-silicon alloy or mixture.
4. High-intensity active composition according to any of the preceding claims,
   the binder being a fluoroelastomer, more particularly a fluorinated rubber.
5. High-intensity active composition according to any of the preceding claims,
   further comprising a burn-up catalyst, more particularly ferrocene, iron acetonylacetate or copper phthalocyanine.