AU2013206584A1 - High-intensity active composition for a pyrotechnic decoy with a fluorinated carbon compound - Google Patents

Abstract

Abstract The invention relates to a high-intensity active composition for a pyrotechnic decoy, comprising a fuel, an oxidizer for the fuel and optionally a binder, the oxidizer being a 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, at least one of the carbon atoms in the carbon chain or in each of the units having at least one bonding site occupied by a molecular radical or by an atom other than fluorine or carbon, the oxidizer not being graphite fluoride.

Description

High-intensity active composition for a pyrotechnic decoy with a fluorinated carbon compound The invention relates to a high-intensity active 5 composition for a pyrotechnic decoy, comprising a fuel, an oxidizer for the fuel and optionally a binder, the oxidizer being a fluorinated carbon compound. The purpose of an active composition for decoys is to 10 mimic the infra-red radiation of a jet aircraft exhaust trail, on burn-up, to a seeker head, of a guided weapon, for example. The wavelength range detected by conventional seeker heads lies between 2 and 5 pm. This has to date been achieved, for example, using the known 15 blackbody active composition magnesium-Teflon-Viton (MTV), in which polytetrafluoroethylene (PTFE, Teflon@) serves as oxidizer. Up to 250% of the intensity of MTV can be achieved by using graphite fluoride as oxidizer. Graphite fluoride, however, is relatively expensive and 20 in some cases difficult to obtain. To achieve the same intensity without graphite fluoride, it is possible to use more active composition in a larger-calibre decoy. That, however, has the disadvantage that with a limited loading capacity, as is the case, generally, in 25 aircraft, fewer decoy charges can be accommodated. Furthermore, it is then necessary to provide launch devices for a larger calibre. It is an object of the invention, therefore, to provide 30 an active composition for decoys that has a higher radiant intensity than MTV on burn-up, in particular also at high air velocity, while requiring no graphite fluoride content to achieve this. The object is achieved through the features of Claim 1. Useful 35 embodiments are apparent from the features of Claims 2 to 11.

- 2 Provided in accordance with the invention is a high intensity active composition for a pyrotechnic decoy, comprising a fuel, an oxidizer for the fuel and optionally a binder, the oxidizer being a fluorinated 5 carbon compound having a carbon chain at least 100 carbon atoms long or having repeating units which comprise carbon atoms and form a polymer, at least one of the carbon atoms in the carbon chain or per unit having at least one bonding site occupied by a 10 molecular radical or by an atom other than fluorine or carbon. The oxidizer in this case is not graphite fluoride. The binder can be omitted if another component in the high-intensity active composition has a binding quality. 15 The oxidizer present in the high-intensity active composition of the invention, therefore, is not fully fluorinated, like PTFE, but instead only partly fluorinated. To date it has been assumed that for 20 blackbody active compositions the most suitable fluorocarbons are those which include the maximum possible amount of fluorine and thus act the most efficiently as oxidizers and yield the highest combustion enthalpy. 25 The inventor of the present invention, however, has recognized that it is not solely the combustion enthalpy that is critical, but that, instead, the heat released in the course of combustion must also be 30 efficiently irradiated and hence high emissivity on the part of the burn-up products is also important. Moreover, he has recognized that the soot generated from fully fluorinated fluorocarbon compounds is too fine to irradiate in the desired wavelength range from 35 2 to 5 pm. With these active compositions, the energy released is irradiated in shorter wavelength ranges or is dissipated convectively. Furthermore, the inventor has recognized that fine soot also burns up very - 3 rapidly and hence is also rapidly lost as an emitter of radiation. Teflon is therefore unfavourable as an oxidizer for 5 active decoy compositions. The graphite fluoride oxidizer has a much higher emissivity on burn-up in the desired wavelength range from 2 to 5 pm than Teflon, but has the abovementioned disadvantages of the high price and the limited availability in certain 10 circumstances. The oxidizer present in the high-intensity active composition of the invention is a fluorinated carbon compound having a carbon chain at least 100 carbon 15 atoms long or having repeating units which contain carbon atoms and which 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 bonding site which is occupied not by another carbon atom, this bonding 20 site being occupied by a molecular radical or by an atom other than fluorine. As the active composition burns up, an oxidizer of this kind generates soot particles with aromatic rings or double bonds and with an average particle size of at least 1 pm. These soot 25 particles efficiently generate radiation in the desired wavelength range from 2 to 5 pm. The reason for this is thought to be that the molecular radical or the atom other than fluorine or carbon results in the provision of sites, in the carbon chain or in the units, at 30 which, during burn-up, double bonds or aromatic structures are able to form, these bonds or structures stabilizing the resultant molecules in such a way that further burn-up does not produce excessively small soot particles. The coarse soot formed with the active 35 composition of the invention also burns for longer than fine soot and therefore radiates for longer as well. It has emerged that the emissivity of the burn-up products and the fraction of the total energy released accounted for by the energy converted into radiation, and hence - 4 also the specific radiant intensity, is increased with the high-intensity active composition of the invention by comparison with active compositions containing the fully fluorinated oxidizer PTFE. The amount of the 5 carbon compound in the high-intensity active composition can be relatively high, although this reduces the temperature of the flame produced on burn up of the high-intensity active composition, as a result of a reduction in the combustion enthalpy. This 10 reduction is compensated by the increased emissivity from the carbon compound and by the improved utilization of the available energy. Furthermore, the burn rate of the high-intensity active 15 composition of the invention is increased by the oxidizer, since the increase in radiant intensity brought about by the oxidizer also radiates more heat back onto the burning surface. Burn-up is further accelerated by the fact that a flame produced during 20 burn-up is relatively dense in optical terms and, as a result, heat is retained for a relatively long time within the flame. As compared with the fine soot formed when using Teflon as oxidizer, the soot formed from the oxidizer present in the high-intensity active 25 composition of the invention burns up more slowly. It is able, as a result, to irradiate the energy released for a longer time. Consequently, the chemical energy present in the high-intensity active composition is converted into radiation with a higher efficiency. 30 Furthermore, the slowly burning soot generates a uniform and dense space effect. The space effect allows very effective mimicking of a jet aircraft exhaust trail by means of the high-intensity active composition of the invention. 35 The soot or the carbon present therein may also form carbides with titanium, zirconium, hafnium, niobium, tantalum, molybdenum and vanadium, which may be present as fuel in the high-intensity active composition. In - 5 this case the carbon serves as a further oxidizer for the stated metals. The resultant carbides do not melt in the flame that is produced on burn-up, and, in the form of carbide particles, emit radiation to their 5 surroundings. The return radiation impinging on the burning surface makes it possible, furthermore, to provide a relatively high fraction of fuel, in relation to the oxidizer, in 10 the high-intensity active composition. As a result, the active composition can have a higher energy content than with an oxidizer different from the one it comprises. 15 In one embodiment of the invention, the ratio of the number of fluorine atoms to the number of the other atoms in the oxidizer is less than 3 if all of the other atoms are hydrogen atoms. 20 The other atom may be a hydrogen, oxygen, nitrogen, sulphur, chlorine, bromine or iodine atom. If the other atom is a hydrogen atom and if a fluorine atom is bonded to an adjacent carbon atom, the burn-up of the high-intensity active composition may be accompanied by 25 elimination of HF, with formation of a double bond between the adjacent C atoms. In another embodiment of the high-intensity active composition of the invention, more than one bonding site of the carbon atom or plurality of carbon atoms are occupied by a molecular 30 radical or plurality of molecular radicals and/or by an atom or atoms other than fluorine and than carbon, these bonding sites each being occupied differently. The differently occupied bonding sites may each be located on adjacent carbon atoms. The other atoms may 35 comprise at least one halogen atom, more particularly a chlorine, bromine or iodine atom, and at least one hydrogen atom at bonding sites of adjacent carbon atoms. As a result, a hydrogen halide can be eliminated, with formation of a double bond.

- 6 If a chlorine, bromine or iodine atom is bonded to a carbon atom and if hydrogen is bonded to an adjacent carbon atom, the burn-up of the high-intensity active 5 composition may be accompanied by elimination of HCl, HBr or HI, with formation of a double bond between the adjacent carbon atoms. In the case of the elimination of HCl, HBr or HI, the fuel may be magnesium, for example. The formation of double bonds as a result of 10 elimination reactions with halogenated polymers may take place, during the burn-up of a high-intensity active composition of the invention, as follows: H C1 H F

B:

H---- F ^+BH+Cl H F H C H F A ---- + HC1 H F H F H F H F H FHF - + H.F H F 15 The elimination reactions may take place thermally or by means of a base. A metal oxide from the fuel in the mixture may function as a base, for example, or a base may be admixed to the active composition. 20 The oxidizer may be poly(ethylenetetrafluoroethylene) (EFTE), poly(chlorotrifluoroethylene) (PCTFE), - 7 poly(ethylenechlorotrifluoroethylene) (ECTFE), perfluoroalkoxy polymer (PFA) , polyvinylidene fluoride (PVDF) or a partially fluorinated pyrene. 5 The structures of PTFE, PVDF, ETFE, PFA, PCTFE and ECTFE are as follows: F F F F F F 0 F PTFE PFA F F F H F F F H F Cl F PVDF PCTFE H F H F H F H F H F H CI H F H F ETFE ECTE 10 In one embodiment of the high-intensity active composition, the unit comprises at least one aromatic structure or polyaromatic structure. The fuel may comprise a metal, a semi-metal or a 15 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. The fuel may comprise aluminium, magnesium, titanium, zirconium, hafnium, calcium, lithium, - 8 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 5 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. 10 Titanium, zirconium, hafnium, niobium, tantalum, molybdenum and vanadium are able to form carbides with the carbon particles or resultant soot particles. The carbon in this case serves as a further oxidizer for 15 the stated metals. At the temperatures which prevail during burn-up of the high-intensity active composition, the resulting carbides are in the form of solids and, as carbide particles, they emit radiation. 20 The binder may be a fluoroelastomer, more particularly a fluorinated rubber, such as Viton@ from the company "DuPont Performance Elastomers", for example. Furthermore, in order to accelerate the burn-up, the active composition may comprise a burn-up catalyst, more particularly 25 ferrocene, iron acetonylacetate or copper phthalocyanine. The invention is elucidated in more detail below by means of working examples. 30 All of the compositions indicated below were produced as follows: The dry components and 5 conductive rubber cubes were mixed in a 250 ml mixing drum for one hour, using a 35 tumble mixer at 120 revolutions/minute. The resulting mixture was discharged into a stainless steel bowl, the rubber cubes were removed, and 3M Fluorel FC-2175 fluorinated rubber was added as binder, as a 10% strength solution in acetone. In the case of active - 9 compositions comprising carbon nanotubes, the carbon nanotubes were not mixed directly with the other ingredients, but were instead first dispersed in the 10% strength solution of the binder in acetone, using 5 ultrasound, in order to ensure maximum uniformity of distribution in the active composition. The composition was stirred to a uniform dough and mixed until the acetone had evaporated to an extent such that the composition became granular. The resulting granules 10 were dried at 50-C. 10 g of the granules were pressed in each case to form tablets. The pressing tool had an internal diameter of 16.8 mm. The pressing pressure was 1500 bar. The 15 densities of the tablets were between 86% and 94% of the theoretical maximum density (TMD) . On their cylinder faces, all of the tablets were coated with polychloroprene (Macroplast) and were adhered using polychloroprene to steel plates 80 x 80 x 5 mm, in 20 order to limit their burn-up to one free end face. The tablets were left to dry overnight at room temperature. The finished tablets were burnt, in the course of which their radiant intensity was determined using a radiometer. 25 The intensity is reported below as a percentage of a corresponding base active composition, e.g. MTV. In the case of active compositions with a space effect, the corresponding active compositions without the additive 30 in the form of carbon particles were used as reference. In Table 1 this corresponds in each case to the reference value indicated by 100%, before the subsequently reported value for the active composition of the invention. 35 Example 1: Standard MTV (magnesium-Teflon-Viton) active composition according to the prior art (burn rate 3.0 mm/s): - 10 Substance Type % by Other weight 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 5 Example 2: Standard MTV active composition with graphite (burn rate 3.0 mm/s): Substance Type % by Other weight 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 10 Example 3: Blackbody active composition based on PVDF with zonally distributed combustion (burn rate 4.1 mm/s; very dense 15 and uniform space effect): Substance Type % by Other weight Magnesium LNR 61 41.0 Bituminous coal finely ground 3.0 PVDF Solvay 80 pm 14.4 TMD = Boron 1 pm 8.0 2041 Titanium Svenska kemi < 100 pm 10.0 Zirconium Chemetall type GH 8.6 Viton 3M Fluorel FC-2175 15.0 Example 4: - 11 Inventive blackbody active composition based on PVDF with zonally distributed combustion (burn rate: 3.3 mm/s): Substance Type % by Other weight Magnesium LNR 61 50 Bituminous coal finely ground 5.0 PVDF Solvay 20.0 TMD = Boron 1 pm 7.0 1882 Titanium Chemetall type E 6.0 Zirconium Chemetall type FA 1.0 Ferrocene Arapahoe Chemicals 1.0 Viton 3M Fluorel FC-2175 10.0 5 Example 5: Inventive blackbody active composition based on PVDF (generates a dense and uniform space effect; burn rate: 10 9. 6 mm/s): Substance Type % by Other weight Magnesium LNR 61 60.0 PVDF Hylar 301F 35.0 Viton 3M Fluorel FC-2175 5.0 TMD = 1745 Example 6: 15 Inventive blackbody active composition based on ECTFE (generates a dense and long space effect; burn rate: 4.1 mm/s): Substance Type % by Other weight Magnesium LNR 61 60.0 ECTFE Solvay Halar 6014 35.0 Viton 3M Fluorel FC-2175 5.0 TMD = 1721 - 12 Example 7: Inventive blackbody active composition based on ECTFE with zonally distributed combustion (very high 5 intensity charge with a large and dense space effect; burn rate: 3.8 mm/s): Substance Type % by Other weight Magnesium LNR 61 42.0 Expanded graphite NGS fine 4.0 ECTFE Solvay Halar 6014 33.0 Titanium Svenska kemi < 100 pm 10.0 Boron 1 pm 5.0 Ferrocene Arapahoe Chemicals 1.0 TMD Viton 3M Fluorel FC-2175 5.0 1885 Table 1 10 Results of the radiation measurements. All results are an average from 5 parallel tests. Charge Es,[J/ EMw[J/ (Esw + Emw) EMW/Esw % MTV % MTV % MTV (g sr)] (g sr)] [J/(g sr) ] SW MW SW + MW Ex. 1 175 54 229 0.309 105 66 92 Ex. 2 166 82 248 0.496 100 100 100 Ex. 3 168 112 280 0.667 101 137 113 Ex. 4 174 161 335 0.925 105 196 135 Ex. 5 188 85 273 0.452 113 104 110 Ex. 6 189 189 378 1.000 114 230 152 Ex. 7 202 208 410 1.030 122 254 165 15 Esw = specific intensity in the short-wave range (about 1.8-2.6 pm) in J/(g sr); EMW = specific intensity in the medium-wave range (about 3.5-4.6 pm) in J/(g sr); 20 - 13 (Esw + EMW) in J/ (g sr) sums of the specific intensities in the SW and MW ranges; EMW/Esw = the ratio of the specific intensity in the MW 5 range to the specific intensity in the SW range; % MTV = intensity as a percentage of the intensity of the reference charge MTV (in Example 2).

Claims (11)

1. High-intensity active composition for a pyrotechnic decoy, comprising a fuel, an oxidizer 5 for the fuel and optionally a binder, the oxidizer being a 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, 10 at least one of the carbon atoms in the carbon chain or in each of the units having at least one bonding site occupied by a molecular radical or by an atom other than fluorine or carbon, the oxidizer not being graphite fluoride. 15

2. High-intensity active composition according to Claim 1, the ratio of the number of fluorine atoms to the number of the other atoms in the oxidizer being 20 less than 3 if all of the other atoms are hydrogen atoms.

3. High-intensity active composition according to either of the preceding claims, 25 the other atom being a hydrogen, oxygen, nitrogen, sulphur, chlorine, bromine or iodine atom.

4. High-intensity active composition according to any of the preceding claims, 30 where more than one bonding site of the carbon atom or of a plurality of the carbon atoms are occupied by a molecular radical or plurality of molecular radicals and/or by an atom or atoms other than fluorine and than carbon, each of these 35 bonding sites being differently occupied.

5. High-intensity active composition according to Claim 4, - 15 the other atoms comprising at least one halogen atom, more particularly a chlorine, bromine or iodine atom, and at least one hydrogen atom at bonding sites of adjacent carbon atoms. 5

6. High-intensity active composition according to any of the preceding claims, the oxidizer comprising poly(ethylenetetrafluoro ethylene) (EFTE), poly(chlorotrifluoroethylene) 10 (PCTFE), poly(ethylenechlorotrifluoroethylene) (ECTFE), perfluoroalkoxy polymer (PFA), polyvinylidene fluoride (PVDF) or a partially fluorinated pyrene. 15

7. High-intensity active composition according to any of the preceding claims, the unit comprising at least one aromatic structure or polyaromatic structure. 20

8. High-intensity active composition according to any of the preceding claims, 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 25 least one semi-metal.

9. High-intensity active composition according to any of the preceding claims, the fuel comprising aluminium, magnesium, 30 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 35 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 - 16 mixture, a zirconium-titanium alloy or mixture or a lithium-silicon alloy or mixture.

10. High-intensity active composition according to any 5 of the preceding claims, the binder being a fluoroelastomer, more particularly a fluorinated rubber.

11. High-intensity active composition according to any 10 of the preceding claims, further comprising a burn-up catalyst, more particularly ferrocene, iron acetonylacetate or copper phthalocyanine.