IL138858A

IL138858A - Pyrotechnic composition for producing ir-radiation

Info

Publication number: IL138858A
Application number: IL13885800A
Authority: IL
Original assignee: Diehl Munitionssysteme Gmbh
Priority date: 1999-10-09
Filing date: 2000-10-04
Publication date: 2004-06-01
Also published as: DE19964172B4; DE50001847D1; EP1090895B1; EP1090895A1; IL138858A0; DE19964172A1

Abstract

A pyrotechnic composition for producing IR-radiation characterised in that as an oxidation agent it contains between 15-85% poly-(carbon monofluoride), as a fuel it contains between 15-90% of a halophilic metallic fuel from the group of metals comprising magnesium, aluminum, titanium, zirconium, hafnium, calcium, beryllium, boron or mixtures or alloys of said metals, it contains an organic fluorine-bearing binding agent with proportions by mass of between 2.5 and 7.5%, and it contains graphite with a proportion by mass of 0.1-5%. 1109 י" ב בסיון התשס" ד - June 1, 20

Description

138858/2 PYROTECHNIC COMPOSITION FOR PRODUCING IR-RADIATION flttHN HW>X W)p *)13»ί7 >tt\?11>fi W S) Eitan, Pearl, Latzer & Cohen-Zedek P-3450-IL CO 25 ΡΕΆ1 WB/sp Comet GmbH Pyrotechnik-Apparatebau, 27574 Bremerhaven Pyrotechnic composition for producing IR-radiation The invention concerns a pyrotechnic composition for producing infrared radiation.

Hot bodies such as for example pyrotechnic flames emit preferably visible light as well as infrared radiation. The radiation emission from bodies, that is to say also pyrotechnic combustion products, is described by Planck's radiation law (equation 1). In accordance therewith the total energy irradiated from a body per unit of surface area is proportional to the absolute temperature of the body. In addition, the emission maximum is also a function of temperature. The functional relationship is described by Wien's displacement law (equation 2). (1) c e 1 AkT T = 0.289779 cnrrK"1 (2) The military sector, for combating aerial targets such as for example jet aircraft, helicopters and transport machines, involves the use of missiles which target on and track the IR-radiation emitted by the propulsion unit of the target, primarily in the range of between 0.8 and 5 pm, by means of an infrared radiation-sensitive seeker head.

To provide a defence against such missiles therefore decoy bodies are used, being pyrotechnic IR-radiating devices, which imitate the IR-signature of the target.

In order now to produce radiation in that wave length range, the requirement is for a flame of at least > 1700 K so that a sufficient level of 138858/3 IR-radiation density can be generated (lo.e-spm > 0.2 kW sr 1 S"1 cm"2). It will be appreciated however that pyrotechnic flames at that temperature generally provide only very little IR-radiation. That deviation from Planck's law is to be attributed to the emissivity ε of the combustion products. Emissivity is a factor which describes the deviation of real radiating bodies from the ideal of the Planck's or black body. By definition ε =1 applies in respect of a black body. All real radiating bodies have values of < 1 and in many cases < 0.5. With the exception of hot compressed gases which have ε -values > 0.9, typical reaction products of pyrotechnic reactions (MgO, KCI, Al203 etc.) have £-values 0.05 - 0.2. For that reason, in the development of IR-active materials, attention was already paid at a very early stage to affording as far as possible products which have a high level of emissivity. Those substances with a high ε -value include for example carbon black (ε = 0.85). Thus conventional active materials for producing black body radiation in the IR-range comprise Magnesium/Teflon/Viton-mixtures (MTV). Those compositions upon combustion in accordance with equation 3 predominantly give rise to magnesium fluoride and carbon black. 2Mg+(C2F,)n →2MgF2 + {C2}n + h v (3) The effectiveness of the MTV-containing decoy bodies (flares) in relation to IR-guidance heads is based on the one hand on the high level of heat of formation of the magnesium fluoride and on the high level of emissivity of the carbon black produced (ε * 0.85) which, due to thermal excitation, has an almost black body-like emission.

On a number of occasions, attempts have been made to increase the radiation density or radiance of such MTV-flares. For that purpose, conventional MTV-compositions are provided with additives for increasing the mass flow rate such as titanium, zirconium and/or boron [1 ,2]. The increase in the mass flow rate rrij means that it is possible to increase the radiance Ιλ (see equation 4). 138858/3 3 in which: Ελ = specific intensity [kJ g 1 sr"1] mi = mass flow rate [g s"1 cm"2] IA = radiance [kW sr 1 cm"2] It will be appreciated however that these substances weaken the spectral intensity distribution to the detriment of the black body level insofar as selectively emitting oxidation products are formed.

The object of the invention is to propose a pyrotechnic composition which, while retaining the known spectral characteristic of MTV-dummy or decoy targets, has a substantially higher level of specific power.

The invention attains that object by using a pyrotechnic composition for producing IR-radiation characterized in that as an oxidation agent it contains between 10-85% poly-(carbon monofluoride), as a fuel it contains between 15-90% of a halophilic metallic fuel from the group of metals comprising magnesium, aluminium, titanium, zirconium, hafnium, calcium, beryllium, boron or mixtures or alloys of these metals, it contains an organic fluorine-bearing bonding agent with proportions by mass of between 2.7 and 7.5%, and it contains graphite with a proportion by mass of 0.1 -5%. Advantageous developments of the invention are set forth in the appendant claims.

The increase in power in accordance with the invention serves to simplify the manufacture of the munition. Now, the same level of power can be achieved with smaller amounts of pyrotechnics, whereby the risk of fire and explosion in manufacture is reduced. In spite of a reduction in the ingredients of the mixture by about 50%, the same amount of decoy or dummy targets of the same power can still be produced.

In addition, by virtue of the reduction in the mass of the pyrotechnic active charge, the munition becomes lighter, thereby also affording logistical advantages. 138858/2 3A The invention further prevents the formation of polyaromatic hydrocarbons (PAHC) which are objectionable from the points of view of environment and human toxicology, as are produced in the combustion of MTV-flares.

The invention is based on the consideration of deliberately and specifically producing upon combustion graphite, the substance with the highest level of emissivity (ελ<5μπι = 0.95), which can be excited by the heat of the pyrotechnic reaction to afford thermal radiation. Furthermore, 4 in accordance with the invention the reaction heat was to be markedly increased in comparison with the established systems. This can be effected by the use of substances with a lower level of molar enthalpy of formation, in comparison with Teflon.

Various approaches for the pyrotechnic production of graphite make use either of incomplete combustion of aromatic compounds (anthracene, naphthalene or their derivatives or homologues) or the thermal decomposition of intercalation compounds of graphite (these are intercalation compounds in which the spaces between the individual graphite lattices can be occupied by foreign or impurity atoms or molecules, for example anions or cations). Incomplete combustion of aromatic hydrocarbons has already found its way into the production of pyrotechnic black body radiators [3]. It will be appreciated however that in the case of US patent No 5 834 680, only graphite-like pyrolysis products are formed, which suffer from surface contamination by low-molecular PAHCs, for which reason their emissivity is markedly below that of graphite; in addition the PAHC adhesions represent a toxicological potential which is not to be underestimated. The thermal disintegration of intercalation compounds of graphite [4] has hitherto only been proposed for producing dipole aerosols for damping electromagnetic radiation.

In both the described protection rights, the graphite precursor, that is to say the aromatic (anthracene or decacyclene respectively) or the intercalation compound of graphite does not contribute to the reaction heat, but rather acts as an endergonic additive which lowers the flame temperature (see US patent No 5 834 680, column 3, lines 23-25 and column 5, lines 18-21).

It has now been found that graphite can be produced by the reduction of poly-(carbon monofluoride) (PMF) by means of high-energy halophilic fuels (for example beryllium, magnesium, calcium). PMF is a tertiary polycyclic alkyl fluoride and already has a quasi-infinite two-dimensional stratified structure. Unlike the intercalation compounds of 5 graphite, which are described and claimed in DE 43 37 9071 CI, in the case of PMF there are true covalent bonds between the carbon and the fluorine atoms. Therefore the formation of graphite by reductive elimination of the fluorine atoms is already favoured just in relation to entropy, in comparison with the formation from condensed aromatics. In addition the conversion of a formerly saturated system into an aromatic system ("graphen") should represent a thermodynamic advantage.

In accordance with the invention compositions are produced from poly-(carbon monof!uoride) ((-CFx-)n) with a proportion by mass of 10 -85% of halophilic energetic fuels (beryllium, magnesium, calcium, titanium, zirconium, zirconium/nickel alloy, zirconium/iron alloy, hafnium, aluminium, boron, magnesium/aluminium alloy), with a proportion by weight of 15 - 90% with a preferably fluorine-bearing binding agent such as for example Fluorel FC 2175™ with a proportion by mass of 2.5 - 7.5%, and graphite with a proportion by mass of 0.1 - 5%.

The preferred fuel is magnesium as this has very highly advantageous thermochemical properties (low levels of fusion and evaporation enthalpy, high melting point of the corresponding fluoride), it is easy to ignite, it is cheap and it is not toxic (compare beryllium). Compositions according to the invention contain magnesium in proportions by mass of between 30 and 70%, preferably between 40 and 70%.

In accordance with the invention poly-(carbon monofluoride) ((-CFx-)ri) with a molar proportion of fluorine of x * 1.0 with particle sizes of < 50 μητι, is used in proportions by mass of between 90 and 15%, preferably however in proportions by mass of between 70 and 30%.

In accordance with the invention the binding agent used is combustion-supporting fluorine-bearing elastomers based on hexafluoropropylene-vinylidene difluoride copolymer, for example Fluorel FC 2175™, in proportions by mass of between 2.5 and 7.5%. 6 To reduce the electrostatic sensitivity of the compositions, in accordance with the invention graphite powder is used, with a specific resistance < 7 10-5 Ωττϊ1, in proportions by mass of from 0.5 to 5%.

The advantages of the magnesium/PMF/Viton (MPV) system will become apparent upon comparison with the magnesium/polytetrafluoroethylene/Viton (MTV) system : In the reaction of PMF with magnesium, magnesium fluoride and graphite are formed in accordance with equation 3: Mg + 2(-C -)„ → MgF2 + {C}graphite + h - v (3) By virtue of the fluorine content of PMF, which is lower in comparison with PTFE, the ideal stoichiometry (see equation 3) occurs with a proportion of magnesium ξ(Mg) of 0.29, in comparison with Teflon in which the ideal stoichiometry (see equation 1) is reached with a proportion ξ^) of 0.32. As the heat of formation of the PMF(-175 kJ mol"1) is just one fifth as great as that of Teflon (-854 kJ mol"1), the reaction heat of the reaction of magnesium with PMF is consequently also considerably higher than the reaction heat for the magnesium/Teflon system.

The specific power (E2-3 Vm and E3-5 Pm) of the Mg/PMF/Viton compositions is correspondingly high. Admittedly the specific power, in the region of ξ(Mg) > 45, approaches the values for Mg/PTFE/Viton, but Mg/PMF/Viton exhibits drastically higher values for the mass flow rate compared with Mg/PTFE/Viton compositions. The radiance Ιλ is therefore always higher by the factor of 10 in the case of Mg/PMF/Viton compositions, than in the case of Mg/PTFE/Viton compositions of comparable composition.

Therefore, in relation to the proportion of magnesium, compositions produced in accordance with the invention afford a level of radiance which is higher by a factor of 10 than the previously known Mg/PTFE/Viton compositions. "-· The Example set out hereinafter is intended to illustrate the invention without limiting it.

Example 1 55g of PMF is stirred into a suspension comprising 40g of magnesium, 5g of Viton and lg of graphite powder and 200 ml of acetone. The suspension is stirred in a flow of air until a crumbly material is produced. The solvent-moist granular material is passed through a sieve (2.5 mm mesh size) and dried at 40°C in a flow of air for 5 hours. The granular material is processed with a 6 s holding time with 12 tonnes pressing pressure to give cylindrical pressings of a mass of 40 g of a 25 mm calibre.

The results of radiometric measurement are set out in Table 1 with the measurement values for the Mg/PTFE/Viton system which is of a similar composition: Table 1 8 State of the art [1] T. Kuwahara, T. Ochiai, Burning Rate of Mq& TF Pyrolants. 18th International Pyrotechnics Seminar, 1992, 539. [2] T. Kuwahara, S. Matsuo, N. Shinozaki, Combustion and Sensitivity Characteristics of Mg TF Pyrolans, Propellants, Explosives, Pyrotechnics, 22 (1997), 198-202. [3] US patent No 5 834 680, D.B. Nielson, D.M. Lester, Blackbodv Decoy Flare for thrusted applications and methods of use, 1998. [4] DE 43 37 9071 CI, U. Krone, E. Schuiz, K. Moller, Pyrotechnischer Nebelsatz fur Tarnzwecke und dessen Verwenduno in einem Nebelkorper, 1995. 138858/3 9

Claims

1. A pyrotechnic composition for producing IR-radiation characterised in that as an oxidation agent it contains between 10 - 85% poly- (carbon monofluoride), as a fuel it contains between 15 - 90% of a halophilic metallic fuel from the group of metals comprising magnesium, aluminum, titanium, zirconium, hafnium, calcium, beryllium, boron or mixtures or alloys of said metals, it contains an organic fluorine-bearing binding agent with proportions by mass of between 2.5 and 7.5%, and it contains graphite with a proportion by mass of 0.1 - 5%.

2. A composition according to claim 1 characterised in that the metallic fuel is magnesium and is contained in proportions by mass of between 40-70%.

3. A composition according to any one of the preceding claims characterised in that poly- (carbon monofluoride) with a molar fluorine proportion of 1 .0 is used in proportions by mass of between 80 and 20%.

4. A composition according to any one of the preceding claims characterised in that as a binding agent it contains fluorine-bearing elastomers based on hexafluoropropylene-vinylidene difluoride copolymer by mass of between 2.5 and 7.5%.

5. A composition according to any one of the preceding claims characterised in that graphite powder with a specific resistance of < 7 10- 5 Ω m"1 is used in proportions by mass of 0.5 to 5%. 138858/3 10

6. A composition according to any one of claims 1 -5 substantially as described hereinabove.

7. A composition according to any of claims 1 - 6 substantially as described hereinabove. Eitan, Pearl, liatzer & Cohen-Zedek Lawyers, Patent Attorneys & Notaries P-3450-IL