AU2013206583B2

AU2013206583B2 - Effective material for a pyrotechnic phantom target with high emissivity

Info

Publication number: AU2013206583B2
Application number: AU2013206583A
Authority: AU
Inventors: Arno Hahma
Original assignee: Diehl Defence GmbH and Co KG
Current assignee: Diehl Defence GmbH and Co KG
Priority date: 2012-08-09
Filing date: 2013-06-28
Publication date: 2017-12-07
Anticipated expiration: 2033-06-28
Also published as: EP2695872A2; DE102012015761A1; AU2013206583A1; ZA201305930B; EP2695872A3; IL226718A0; EP2695872B1

Abstract

- 14 Abstract The invention relates to an effective material for a pyrotechnic phantom target with high emissivity, comprising a fuel, an additive consisting essentially of carbon, an oxidation means for the fuel and optionally a bonding means, wherein the additive is present in the form of particles, wherein a predominant number of the particles has a maximum extent in the range from 1 pm to 200 pm, wherein the particles do not consist of graphite.

Description

Effective Material for a Pyrotechnic Phantom target with High Emissivity

The invention relates to an effective material for a pyrotechnic phantom target with high emissivity with a fuel, an additive consisting essentially of carbon, an oxidation means for the fuel and optionally a bonding means . A pyrotechnic phantom target material for infrared phantom targets is known from DE 10 2010 053 694 A1 and comprises first particles comprising a first fuel, second particles comprising the first or a second fuel, an oxidation means for the first fuel and a bonding means. When said phantom target material is burnt the second particles are ignited by the reaction of the first fuel and the oxidation means and are released from the phantom target material. The nature of the first particles here is such that following ignition of the phantom target material they burn more rapidly in air than the second particles. The nature of the second particles is such that they burn for at least 10 ms in air. By means of the two types of particles it is achieved that the first particles react rapidly with the oxidation means and burn inside a primary flame, whereas the second particles are ignited in the primary flame but do not burn within the primary flame. Hot burning second particles are ejected from the flame and continue to burn in air without thereby reacting significantly with the oxidation means. By means of said phantom target material a very good simulation of the infrared radiation of an exhaust plume of a rapidly flying aircraft can be made. The second particles can have an average diameter of 0.5 to 3 mm for this phantom target material.

The object of an effective material for a pyrotechnic phantom target is to appear to be a rapidly flying vehicle to an image resolving infrared search head.

Besides the spatial extent of the flame, the wavelength of the emitted radiation is also important here.

Conventional search heads detect the radiation in the so-called A band, i.e. for a wavelength of approx. 1.8 to 2.6 pm, and in the so-called B band, i.e. for a wavelength of approx. 3.5 to 4.6 pm.

The object of the present invention is to provide an active mass for a pyrotechnic phantom target whose emissivity is particularly high and in particular higher than the emissivity of known phantom target effective materials.

The object is achieved by means of the features of

Claim 1. Advantageous embodiments arise from the features of claims 2 to 11.

According to the invention, an effective material for a pyrotechnic phantom target with high emissivity is provided. The effective material according to the invention comprises a fuel, an additive consisting essentially of carbon, an oxidation means for the fuel and optionally a bonding means, wherein the additive is present in the form of particles, wherein a predominant number of the particles has a maximum extent in the range from 1 pm to 200 pm, wherein the particles do not consist of graphite. The bonding means can be omitted if another component of the effective material has a bonding property. A maximum extent of a particle is understood to mean the length of the longest distance that can be covered by the particle. For nanotubes present in the form of a cylinder the maximum extent is thus a diagonal through the cylinder and not the cylinder diameter within the nanometer range. The inventor of the present invention has recognized that for a high emissivity in the desired wavelength range for a particle consisting essentially of carbon, the size of the radiation emitting soot particles that arise during combustion of the effective material is decisive. It has proved to be especially favourable if the soot particles are not smaller than 0.5 pm and not larger than 1.25 pm. This is achieved for the effective material according to the invention by means of the particles essentially consisting of carbon with a maximum extent in the range from 1 pm to 200 pm. The result of this is that the largest part of the emitted radiation lies in the wavelength range from 2 to 5 pm.

By the provision of the particulate additive a spatial effect is achieved when burning the effective material according to the invention, with which the radiation emission of the exhaust plume of a jet engine can be simulated very well.

Another advantage of the effective material according to the invention is that it exhibits very high radiation power during combustion, because a very large portion of the energy released during combustion of the effective material is released in the form of radiation in the wavelength range from 2 to 5 pm.

Furthermore, the effective material according to the invention enables graphite fluoride to be omitted as an oxidation means for increasing power. Graphite fluoride is relatively expensive and is sometimes difficult to obtain.

The particles provided in the effective material according to the invention accelerate the combustion, i.e. increase the rate of combustion, because the radiation power is increased by the particles and thus more heat is radiated back to the burning surface. Furthermore, the primary flame is thereby also optically denser. In this way heat is retained within the flame and the combustion is further accelerated. The effective material according to the invention has higher emissivity during combustion than the usually used mixture of magnesium, Teflon® and fluorine rubber Viton (MTV). A further increase in the rate of combustion can be achieved because the particles have porosity or there is porous material essentially consisting of carbon during combustion of the effective material. The porosity can e.g. be provided by an additive comprising charcoal, active carbon or porous graphite.

Furthermore, the back radiation at the burning surface boosted by the additive enables a relatively high portion of fuel to be provided in the effective material in comparison to the oxidation means. This enables the effective material to have a higher energy content than without the additive.

With one embodiment of the invention a predominant number of the particles have a maximum extent in the range from 1 pm to 100 pm, especially in the range from 5 pm to 80 pm, especially in the range from 10 pm to 70 pm, especially in the range from 30 to 60 pm. In order to prevent radiation in an unwanted wavelength range, the effective material can be designed so that essentially no particles of the additive are contained therein, whose maximum extent is smaller than 1 pm and/or greater than 200 pm. This can for example be achieved by means of suitable filtering out of particles of the additive.

The additive can comprise carbon fibres, carbon nanotubes, especially multi-wall carbon nanotubes, charcoal, activated carbon or porous graphite. Carbon fibres and carbon nanotubes are particularly efficient because they function as dipole antennas in the flame and as a result can radiate the combustion energy particularly efficiently. It is especially advantageous if the oxidation means is selected so that it cannot oxidize the carbon, so that the carbon particles are only oxidized by the atmospheric oxygen in the outer area of the flame occurring during combustion. Multiwall carbon nanotubes are advantageous, because with these the carbon structure of the nanotubes is maintained for longer during oxidation by atmospheric oxygen than for single-wall carbon nanotubes. For a proportion of 5 to 10% of carbon fibres or 5% carbon nanotubes, the radiation power of the effective material according to the invention can be increased by approximately 30%.

For a proportion of 5 to 15% of porous graphite, the power of the effective material is increased by approximately 15% relative to an effective material without the additive. Because porous graphite is relatively favourable compared to carbon nanotubes or carbon fibres, however, the higher number required for an increase in power can be provided without great additional costs. The additive can be contained in the effective material with a proportion of 1 to 20 % by weight, especially 2 to 15 % by weight, especially 3 to 10 % by weight. The quantity should be selected that the energy balance of the effective material is not affected by more than 20%.

The fuel can comprise a metal, a metalloid or a mixture or alloy of metals and/or metalloids or a mixture or alloy of at least one metal and at least one metalloid. The fuel can comprise 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 said metals or metalloids, 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.

Titanium, zirconium, hafnium, niobium, tantalum, molybdenum and vanadium can form a carbide with the carbon particles or soot particles arising therefrom. The carbon is used here as a further oxidation means for said metals. The resulting carbides are in the form of solids at the temperatures existing for combustion of the effective material and emit radiation as carbide particles .

The bonding means can be a fluoroelastomer, especially a fluorine rubber, such as e.g. Viton® by the "DuPont Performance Elastomers" company. The oxidation means can be a halogen-containing polymer, especially polytetrafluoroethylene (PTFE) or polychloroprene. Furthermore, the effective material can contain a combustion catalyst, especially ferrocene, iron acetonyl acetate or copper phthalocyanine for acceleration of the combustion.

With one embodiment of the effective material according to the invention, the oxidation means is selected so that as a result carbon is not oxidized at a temperature that exists for a reaction of the oxidation means with the fuel. In this way the carbon can form a carbide, e.g. with titanium, zirconium, hafnium, niobium, tantalum, molybdenum or vanadium.

The invention is explained in detail below using example embodiments.

All compounds specified below were produced as follows:

The dried 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 dish, the rubber cubes were removed and as a bonding means 3M Fluorel FC-2175 fluorine rubber was added as a 10% solution in acetone. For effective materials containing carbon nanotubes the carbon nanotubes were not directly-mixed with the other components, but previously dispersed in the 10% solution of the bonding means in acetone by means of ultrasound in order to ensure a highly uniform distribution in the effective material. The material was stirred to a homogenous paste and mixed until the acetone was evaporated sufficiently that the material was granular. The resulting granulate was dried at 50 °C. 10 g of the granulate was pressed into tablets in each case. The pressing tool had an internal diameter of 16.8 mm. The pressing pressure was 1500 bar. The density of the tablets lay between 86 and 94% of the theoretical maximum density (TMD). All tablets were coated on their cylinder surfaces with polychloroprene (Macroplast) and stuck using polychloroprene onto 80 x 80 x 5 mm steel plates in order to restrict their combustion to a free end face. The tablets were allowed to dry overnight at room temperature.

The prepared tablets were burned and thereby their radiation power was determined by means of a radiometer. The power is given below as a percentage of a corresponding basic effective material, e.g. MTV.

For effective materials with a spatial effect the corresponding effective materials without the additive in the form of carbon particles were used as reference.

In Table 1 this corresponds respectively to the 100% specified reference value before the subsequently given value of the effective material according to the invention.

Example: 1

Standard MTV(Magnesium-Teflon-Viton) effective material according to the prior art. (rate of combustion 3.0 mm/s):

Example: 2

Active material according to the invention with carbon nanotubes (rate of combustion 3.0 mm/s):

Example: 3

Active material according to the invention with porous graphite (rate of combustion 3.0 mm/s):

Example: 4

Black body effective material based on Poly(ethylenechlortrifluorethylene) (ECTFE) with combustion distributed in zones (very powerful composition with a great and dense spatial effect; rate of combustion 3.8 mm/s):

Example 5:

Black body effective material according to the invention based on ECTFE with combustion distributed in zones (very powerful composition with a great and dense spatial effect; rate of combustion 3.1 mm/s):

Table 1:

Measurement results of the radiation measurements. All results are an average of 5 parallel tests.

Ekw = specific power in the short wave range (approx. 1.8 = 2.6 pm) in J/(g sr) ;

Emw = specific power in medium wave range (approx. 3.5-4.6 pm) in J/(g sr); (EKW + Emw) in J/ (g sr) = sum of specific powers in short wave and medium wave ranges;

Emw/Ekw = the ratio of the specific power in the medium wave range to the specific power in the short wave range;

% Ref = power as a percentage of the power of the reference composition MTV

Claims

Claims

1. An active material for a pyrotechnic phantom target with high emissivity, comprising a fuel, an additive consisting essentially of carbon, and an oxidation means for the fuel, wherein the additive is present in the form of particles, wherein a predominant number of the particles has a maximum extent in the range from 30 pm to 60 pm, wherein the particles do not consist of graphite.
2. Active material according to Claim 1, wherein the active material further comprises a bonding means.
3. The active material according to any one of the preceding claims, wherein essentially no particles of the additive are contained therein whose maximum extent is less than 1 pm and/or greater than 200 pm.
4. The active material according to any one of the preceding claims, wherein the additive comprises carbon fibres, carbon nanotubes, especially multi-wall carbon nanotubes, charcoal or active carbon.
5. The active material according to any one of the preceding claims, wherein the additive is contained in the effective material as a proportion of 1 to 20 % by weight, especially 2 to 15 % by weight, especially 3 to 10 % by weight.
6. The active material according to any one of the preceding claims, wherein the fuel comprises a metal, a metalloid or a mixture or alloy of metals and/or metalloids or a mixture or alloy of at least one metal and at least one metalloid.
7. The active material according to any one of the preceding claims, wherein the fuel comprises 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 said metals or metalloids, 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.
8. The active material according to any one of the preceding claims, wherein the bonding means is a fluoroelastomer, especially a fluorine rubber.
9. The active material according to any one of the preceding claims, wherein the oxidation means is a halogen-containing polymer, especially polytetrafluoroethylene (PTFE) or polychloroprene.
10. The active material according to any one of the preceding claims, wherein furthermore a combustion catalyst, especially ferrocene, iron acetonyl acetate or copper phthalocyanine is contained therein.
11. The active material according to any one of the preceding claims, wherein the oxidation means is selected such that as a result carbon is not oxidized at a temperature that occurs for a reaction of the oxidation means with the fuel.