US20080178757A1

US20080178757A1 - Pyrotechnic charge

Info

Publication number: US20080178757A1
Application number: US11/770,811
Authority: US
Inventors: Ernst-Christian Koch
Original assignee: Diehl BGT Defence GmbH and Co KG
Current assignee: Diehl BGT Defence GmbH and Co KG
Priority date: 2006-07-04
Filing date: 2007-06-29
Publication date: 2008-07-31
Also published as: EP1876161A1; DE102006030679A1

Abstract

A pyrotechnic charge for production of IR radiation, which is characterized in that a brominated compound is included as a fuel and/or as an oxidant and/or as a binder. A pyrotechnic charge such as this can be used, for example, to produce an IR decoy with β-band spectral matching.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a pyrotechnic charge for production of infrared (IR) radiation, and in particular to a pyrotechnic charge such as this for use in spectrally matched IR decoys.
In the military field, missiles such as air-to-air and surface-to-air guided missiles are used to attack airborne targets, such as jet aircraft, helicopters and transport aircraft, which find the direction of and track the infrared (IR) radiation which originates from the target engine, primarily in the band between 0.8 and 5 μm, by means of a search head which is sensitive to IR radiation. Decoys (also referred to as flares) are therefore used as defence against these missiles, and imitate the IR signature of the target in order to deflect approaching guided missiles. Decoys such as these can also be used preventively, in order to exacerbate or even to prevent the detection of targets, by reducing the contrast in the scene.
One typical effective substance for production of black-body radiation in the IR band is a pyrotechnic charge composed of magnesium, polytetrafluoroethylene (Teflon®) and vinylidenefluoride hexafluoroisoprene copolymer (Viton®), also referred to as MTV, whose spectral intensity distribution is similar to that of a black body during combustion. The actual signature of, for example, aircraft engines differs from the signature of a black-body radiator, however, since the hot exhaust gases from propeller or jet propulsion systems emit strong selective components in the wavelength band between 3 and 5 μm (so-called β band). This selective radiated emission is caused by the combustion products CO and CO₂, which emit at 4.61 μm and 4.17 mm, respectively.
In order to distinguish between decoys with a black-body signature and real airborne targets, modern search heads therefore additionally carry out a spectral assessment of the radiation source. In particular, this takes account of the fact that the integrated intensity of the signature of an aircraft or of its engine is greater by a factor of 2 in the wavelength band between 3 and 5 μm (β band) than the integrated intensity in the wavelength band between 2 and 3 μm (so-called α band). In contrast, this ratio is always less than 1 for decoys with a black-body signature.
2. Discussion of the Prior Art
In order to overcome the capability of search heads to spectrally distinguish decoys on this basis, matched decoys have been proposed in the past, which have a spectral intensity distribution similar to an aircraft. Conventional pyrotechnic effect charges such as these for spectrally matched IR decoys typically contain carbon-rich compounds together with powerful oxidants, such as perchlorates. Typical formulations for apparent targets such as these are composed of potassium perchlorate (KClO₄), potassium nitrate (KNO₃) and mellitic trianhydride (C₆(C₂O₃)₃)—see for example U.S. Pat. No. 6,427,599 B1, composed of potassium perchlorate and potassium benzoate (KC₇H₅O₂)—see for example US 2004/0011235 A1, or composed of potassium perchlorate and hexacyanobenzene (C₆(CN)₆)—as described, for example, in subsequently published DE 10 2004 024 857 A1 by the same applicant.
Table 1, below, shows typical compositions of the spectrally matched effective substances disclosed in the patent documents cited above:

TABLE 1

US	US
6,427,599 B1	2004/0011235 A1	DE 10 2004 024 857

KClO₄	60	65	65
KC₇H₅O₂		35
C₆(C₂O₃)₃	35
KNO₃	5
C₆(CN)₆			35

The above numerical details are in each case in the form of proportions by mass as % by weight, in which case a binder is in each case added to the substances formed in this way, in a proportion by weight of 5:100.
Furthermore, the applicant recently proposed the use of deuterized compounds as oxidants and/or as fuels for spectrally matched apparent targets—as in the above-referenced published DE 10 2004 024 857 A1.

SUMMARY OF THE INVENTION

The present invention is based on the object of providing a pyrotechnic charge for production of IR radiation, which produces a spectral intensity distribution similar to that of an aircraft during combustion of the fuels. One particular aim is for the integrated radiation intensity in the long-wave β band during combustion of the fuels in the pyrotechnic charge to be better matched to that of the signature of an aircraft.
The inventive pyrotechnic charge for production of IR radiation according to a first aspect of the invention is characterized in that a brominated compound is included as a fuel and/or as an oxidant. According to a second aspect of the invention, a brominated compound is included as a fuel and/or as an oxidant and/or as a binder.
The use of brominated compounds, or compounds containing bromine, as a fuel, oxidant and/or binder leads to increased selective radiated emission in the □ band and at the same time to reduced selective radiated emission in the α band, so that the quotient of the integrated radiation intensities in the □ band and the α band during combustion of the fuels in the pyrotechnic charge according to the invention is better matched to that of the signature of an aircraft.
In one refinement of the invention, the molar ratio of Br/H in the brominated compound or compounds is ≧0.5; and the molar ratio of Br/Mⁿ⁺ in the brominated compound or compounds is ≧n, where M is an alkali or alkaline-earth metal.
By way of example, one or more compounds from the group comprising brominated hydrocarbons with a melting point of >100° C., brominated aromatic compounds, brominated aromatic carbonyl compounds, brominated aromatic carboxylic acids and lactones may be included as a fuel.
One or more compounds from the group of alkali and alkaline-earth metal bromates and perbromates, and/or one or more compounds from the group of alkali and alkaline-earth metal nitrates, dinitramides and peroxides may be included as oxidants.
In one preferred embodiment of the invention, the fuel is included in a proportion by mass of approximately 10% to approximately 55%, the oxidant in a proportion by mass of approximately 40% to approximately 85%, and the binder in a proportion by mass of 0% to approximately 5%.

DETAILED DESCRIPTION OF THE INVENTION

The invention as explained above is in this case based on the considerations described in the following text.
According to the invention, the aim is to provide a pyrotechnic charge which concentrates to a greater extent selective radiated emission components in the desired long-wave β band, that is to say the wavelength band from approximately 3.5 to 4.8 μm, during combustion of the fuels, in order to better imitate the signature of an aircraft engine.
The previous development by the same applicant, as cited above, to use deuterized compounds as oxidants and/or as fuels for spectrally matched apparent targets is based on the idea of bathochromic shifting of the molecular bands of H₂O and HCl created during the combustion of substances containing hydrogen. While H₂O and HCl have resonant wavelengths of 2.73 μm and 3.43 μm, respectively, and are therefore disadvantageous in terms of the spectral ratio, and/or are outside the suitable long-wave spectral band, the resonant frequencies of the deuterated compounds HDO, D₂O and DCl appear at 3.67 μm, 3.74 μm and 4.66 μm, respectively, and therefore in each case within the advantageous long-wave β band between approximately 3.5 and 4.8 μm.
Until now, there have been no reports on other options for spectral matching by bathochromic or hypsochromic (long-wave or short-wave) shifting in the past. No other option has been previously known either for influencing the H₂O/CO₂ratio advantageously than by the choice of fuels with a suitable C/H ratio.
The present invention solves the problem of spectral matching and matching of the C/H ratio by the use of compounds containing bromine.
The advantageous characteristics of pyrotechnic compositions containing bromine are in this case a result of the following circumstances:

- the replacement of hydrogen in organic fuels by bromine leads to an increase in the C/H ratio and thus to suppression of the H₂O emission in the short-wave spectral range of the α band between 2 and 3 μm;
- the bromine that is introduced produces hydrogen bromide (HBr) during combustion, whose band centre is located at 3.91 μm, in the long-wave spectral range within the β band;
- together with oxidants such as nitrates and peroxides based on alkali and alkaline-earth metals, bromine introduced via the fuel results in volatile bromides and thus reduces the tendency for condensation in the flame zone, which in turn reduces the proportion of disturbing continuum radiation in the flame, which would have a disadvantageous influence on the band ratio;
- in the case of replacement of perchlorates by chlorine-free or brominated oxidants, the radiated emission of the HCl band at 3.34 μm can be prevented or shifted.

Suitable bromine compounds for modification of the C/H ratio for the purposes of the invention are brominated organic compounds, such as perbrominated aromatic compounds which, in addition to bromine, can also carry oxygen in the form of carbonyl and ether groups.
Suitable compounds including their [CAS No.] for the purposes of the invention are listed in the following text, without any intention of the present invention being restricted only to these specific compounds: perbromo (diphenyl ether) ((C₆Br₅)₂O) [1163-19-5], available, for example, under the trade mark Saytex 102; hexabromobenzene (C₆Br₆) [87-82-1]; tetrabromo-p-benzoquinone (C₆Br₄(═O)₂) [488-48-2]; tetrabromo-o-benzoquinone (C₆Br₄(═O)₂) [2435-54-3]; tetrabromophthalic anhydride (C₆Br₄C₂O₃) [632-79-1]; tetrabromophenolphthalein (C₂₀H₁₀Br₄O₄) [1301-20-8]; tetrabromohydroquinone (C₆Br₄(OH)₂) [2641-89-6]; tetrabromocyclohexadienone (C₆H₂Br₄O) [20244-61-5]; tetrabromocatechol (C₆Br₄(OH)₂) [488-47-1]; dibromobiphenyl (C₆H₄Br) [92-86-4]; dibromofluoresceine (C₂₀H₁₀Br₂O₅) [596-03-2]; dibromonaphthoquinone (C₁₀H₄Br₂O₂) [13243-65-7]; dibromohydroxynaphthalene (C₁₀H₆Br₂O) [16239-18-2]; dibromo-4-nitroaniline (C₆H₂(NO₂)NH₂Br₂) [827-94-1]; dibromonitrophenol (C₆H₂NO₂Br₂OH) [99-28-5]; and dibromonitrobenzene (C₆H₃NO₂Br₂) [3460-18-2].
When using bromocarbon compounds as fuels, additional fuels containing hydrogen can also be used up to a molar ratio Br/H of 1/1 depending on the proportion of bromine and the Br/H ratio, so that all of the hydrogen can be converted to HBr. For example, when using decabromo(diphenyl ether) as a carbon source, an equimolar amount of anthracene can be used as a carbon source, if all of the protons are intended to be converted into HBr as shown by the following example of the reaction of 1 mol of decabromo(diphenyl ether) with 1 mol of anthracene:
1 (C₆Br₅)₂O+1C₁₄H₁₀43 26 {C}+10HBr+1O
The temperature-dependent, integrated band intensity α_jfor the HBr molecule was determined recently by S. P. Fuβ, A. Hamins in “Determination of Planck Mean Absorption Coefficient for HBr, HCl and HF” in Journal of Heat Transfer, 124, 2002, pages 26-29. Table 2, below, shows the comparison of the band intensity at 300 K for the molecules CO₂, CO, HCl and HBr.

TABLE 2

		Band
	Spectral range of	centre [cm⁻¹,	Integrated band intensity
Molecule	the band [cm⁻¹]	μm]	at 296 K [atm⁻¹cm⁻²]

CO₂	2325-2410	2325, 4.30	2700
CO	1795-2317	2143, 4.67	250
HCl	2399-3161	2885, 3.47	155
HBr	2123-2791	2559, 3.91	35

The low band intensity of HBr in comparison to HCl and CO₂indicates that HBr is not in fact a suitable spectral emitter, but can be used for modification of conventional effect charges owing to the position of its band centre and the low intensity.
Conventional spectrally matched effect charges based on perchlorates and peroxides produce condensed reaction products during combustion, such as carbonates (K₂CO₃) and oxides (BaO), which increase the continuum radiation and thus cause the spectral ratio to deteriorate. In the presence of bromine or hydrogen bromide from the flame, the formation of condensed products can be prevented in-situ since appropriate bromides are created. Within the flame, these are gaseous up to temperatures of approximately 1200° C. or 1000° C., and do not condense until outside the flame zone.
According to the invention, the proportion of bromine is thus preferably set such that any alkali or alkaline-earth metal ions, such as K⁺ or Ba²⁺, can be converted by means of Br₂or HBr to KBr or BaBr₂, respectively.
The bromates and perbromates of the following general compositions are preferably used as oxidants
MBrO₃where M=NH₄, Li, Na, K, Rb, Cs,
M(BrO₃)₂where M=Mg, Ca, Sr, Ba,
MBrO₄where M=NH₄, Li, Na, K, Rb, Cs, and
M(BrO₄)₂where M=Mg, Ca, Sr, Ba.
Further suitable oxidants for the purposes of the invention are the nitrates and dinitramides of the alkali and alkaline-earth metals with the following general compositions:
MNO₃where M=NH₄, Li, Na, K, Rb, Cs,
M(NO₃)₂where M=Mg, Ca, Sr, Ba,
MN₂O₄where M=NH₄, Li, Na, K, Rb, Cs, and
M(N₂O₄)₂where M=Mg, Ca, Sr, Ba,
as well as the peroxides of lithium and of the alkaline-earth metals
M₂O₂where M=Li, Na, and
MO₂where M=Mg, Ca, Sr, Ba.
In all of the fuels and oxidants mentioned above, the proportion by mass of the fuel in a pyrotechnic charge for production of IR radiation according to the invention is preferably approximately 10% to approximately 55%, the proportion by mass of the oxidant is approximately 40% to approximately 85%, and the proportion by mass of the binder is from 0% to approximately 5%.
The pyrotechnic charges with the compounds stated above can advantageously be used for IR decoys since the integrated radiation intensity in the long-wave β band during combustion of the fuels in the pyrotechnic charge is better matched to that of the signature of an aircraft.

Claims

1. Pyrotechnic charge for production of IR radiation, wherein a brominated compound is included as a fuel and/or as an oxidant.

2. Pyrotechnic charge for production of IR radiation, wherein a brominated compound is included as a fuel and/or as an oxidant and/or as a binder.

3. Pyrotechnic charge according to claim 1 or 2, wherein the molar ratio of Br/H in the brominated compound or compounds is ≧0.5.

4. Pyrotechnic charge according to one of claims 1 or 2, wherein the molar ratio of Br/Mⁿ⁺ in the brominated compound or compounds is ≧n, where M is an alkali or alkaline-earth metal.

5. Pyrotechnic charge according to claim 1 or 2, wherein one or more compounds from the group comprising brominated hydrocarbons with a melting point of >100° C., brominated aromatic compounds, brominated aromatic carbonyl compounds, brominated aromatic carboxylic acids and lactones are included as a fuel.

6. Pyrotechnic charge according to claim 1 or 2, wherein one or more compounds from the group of alkali and alkaline-earth metal bromates and perbromates are included as oxidants.

7. Pyrotechnic charge according to claim 1 or 2, wherein one or more compounds from the group of alkali and alkaline-earth metal nitrates, dinitramides and peroxides are included as oxidants.

8. Pyrotechnic charge according claim 1 or 2, wherein the fuel is included in a proportion by mass of approximately 10% to approximately 55%.

9. Pyrotechnic charge according to claim 1 or 2, wherein the oxidant is included in a proportion by mass of approximately 40% to approximately 85%.

10. Pyrotechnic charge according to claim 2, wherein the binder is included in a proportion by mass of 0% to approximately 5%.