Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
2003-01-10
2003-10-21
Miller, Edward A. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S087000, C149S108200, C149S116000
Reexamination Certificate
active
06635130
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pyrotechnic active material for producing infrared (IR) radiation.
BACKGROUND OF THE INVENTION
Hot bodies such as, for example, pyrotechnic flames emit visible light as well as infrared radiation. The radiation emission from hot bodies, such as pyrotechnic combustion products, is described by Planck's radiation law, which is shown in equation 1 hereinbelow. In accordance therewith, the total energy irradiated from a hot body per unit of surface area is proportional to the absolute temperature of the hot body. In addition, the emission maximum is also a function of temperature. The functional relationship is described by Wien's displacement law, which is shown in equation 2.
E
(
v
)
=
8
π
v
3
c
3
e
(
h
-
v
/
λ
kT
)
-
1
(
1
)
&lgr;
max
T=
0.289779 cm.K
−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 aerial target, primarily in the range of between 0.8 and 5 &mgr;m, by means of an infrared radiation-sensitive seeker head.
To provide a defense against missiles from such aerial targets, decoy bodies are used, which are pyrotechnic IR-radiating devices that imitate the IR-signature of the target.
In order to produce radiation in the wavelength range which imitates the IR-signature of the target, the requirement is for a flame having a temperature of at least greater than 1700 K so that a sufficient level of IR-radiation density can be generated (I
0.8-5 &mgr;m
>0.2 kW.sr
−1
.s
−1
.cm
2
). It will be appreciated, however, that pyrotechnic flames at that temperature generally provide very little IR-radiation. The deviation from Planck's law is to be attributed to the emissivity &egr; of the combustion products. Emissivity is a factor that describes the deviation of real radiating bodies from the ideal of the Planck's or black body. By definition, &egr;=1 applies to a black body. All real radiating bodies always have emissivity values of less than 1 and, in many cases, less than 0.5. With the exception of hot compressed gases which have &egr;-values greater than 0.9, typical reaction products of pyrotechnic reactions (MgO, KCI, Al
2
O
3
, etc.) have &egr;-values of between 0.05-0.2. For that reason, in the development of IR-active materials, attention has been already paid, at a very early stage, to providing products which have a high level of emissivity. Those substances with a high &egr;-value include, for example, carbon black (&egr;=0.85). Thus, conventional active materials for producing black body radiation in the IR-range comprise Magnesium/TEFLON®/VITON®-mixtures (MTV). TEFLONS is a material that comprises polytetrafluoroethylene; while VITON® is a fluoroelastomeric material. Those prior art compositions upon combustion in accordance with equation 3 predominantly yield magnesium fluoride and carbon black.
2
n
Mg+(C
2
F
4
)
n
→2
n
MgF
2
+2
n
C+
h.v
(3)
The effectiveness of the MTV-containing decoy (i.e., flare) against IR-seeker heads is based on the high level of heat of formation of magnesium fluoride as well as on the high level of emissivity of carbon black produced (&egr;≈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 pointance of such MTV-flares. For that purpose, conventional MTV-compositions are provided with additives, such as titanium, zirconium and/or boron for increasing the mass consumption rate. The use of such additives in conventional MTV-flares is described, for example, in T. Kuwahara, T. Ochiai,
Burning Rate of Mg&/TF Pyrolants,
18
th
International Pyrotechnics Seminar,
1992, 539; and T. Kuwahara, S. Matsuo, N. Shinozaki,
Combustion and Sensitivity Characteristics of Mg/TF Pyrolans, Propellants, Explosives Pyrotechnics,
22 (1997); 198-202.
The increase in the mass consumption rate m
1
means that it is possible to increase the radiance I
&lgr;
(see equation 4).
I
&lgr;
=E
&lgr;
·m
i
(4)
in which:
E
&lgr;
=specific intensity [kJ.g
−1
.sr
−1
]
m
i
=mass consumption rate [g.s
−1
.cm
−2
]
I
&lgr;
=pointance [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.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a pyrotechnic composition which, while retaining the known spectral characteristic of MTV decoys, has a substantially higher level of specific power.
Accordingly, pursuant to the present invention there is provided a pyrotechnic composition for producing IR-radiation which comprises, by weight, 10-72.5% of a poly-(carbon monofluoride) oxidation agent; 15-90% of a halophilic metallic fuel comprising a metal selected from the group consisting of magnesium, aluminum, titanium, zirconium, hafnium, calcium, beryllium boron and mixtures or alloys of said metals; 2.5 and 7.5% of an organic fluorine-bearing agent; and 0.1-5% of graphite. Note that the various components present in the pyrotechnic composition of the present invention add up to 100%.
The increase in power of the pyrotechnic composition of the present 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 decoys of the same power can still be produced.
In addition by virtue of the reduction in the mass of the pyrotechnic payload, the munition becomes lighter, thereby also affording logistical advantages.
The present invention further prevents the formation of polyaromatic hydrocarbons (PAH) which are objectionable from the points of view of environment and human toxicology, as are produced in the combustion of MTV-flares.
The present invention is based on the consideration of deliberately and specifically producing upon combustion graphite, the substance with the highest level of emissivity (&egr;
&lgr;<5 &mgr;m
=0.95), which can be excited by the heat of the pyrotechnic reaction to afford thermal radiation. Furthermore, in accordance with the present invention, the reaction heat is markedly increased in comparison with the prior art systems. This can be affected by the use of substances with a lower level of molar enthalpy of formation, in comparison with TEFLON®.
DETAILED DESCRIPTION OF THE INVENTION
Various prior art approaches for the pyrotechnic production of graphite make use either of incomplete combustion of aromatic compounds (anthracene, naphthalene or their derivatives or homologues thereof) 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 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 radiator, see, for example, U.S. Pat. No. 5,834,680. It will be appreciated, however, that in the case of U.S. Pat. No. 5,834,680, only graphite-like pyrolysis products are formed, which suffer from surface contamination by low-molecular PAHs, for which reason their emissivity is markedly below that of graphite; in addition the PAH adhesions represent a toxicological potential which is not to be underestimated. The thermal decomposition of intercalation compounds of graphite has only been proposed for producing dipole aerosols for attenuating electromagnetic radiation
Diehl Munitionssysteme GmbH & Co. KG
Miller Edward A.
Scully Scott Murphy & Presser
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