DESC:FIELD OF INVENTION
The present invention relates to spectrally balanced pyrotechnic compositions useful for advanced infrared decoy flares. In particular, the present invention relates to pyrotechnic compositions which include magnesium fuel, sodium nitrate oxidizer and partially oxidized organic fuels like carboxylic anhydrides. The pyrotechnic compositions of the present invention on combustion emits high infrared radiation in middle infrared wave band (ß - Band) and relatively less infrared radiation in lower infrared wave band (a - Band).

BACKGROUND OF THE INVENTION
In order to be effective, the decoy flares must exhibit approximately the same infrared spectral characteristics as are exhibited by the aircraft. The new generation infrared guided missiles are equipped with one or more electronic counter - countermeasures that can discriminate and reject current decoy flares used as aircraft protective countermeasures. Current infrared guided missiles have detection systems that can distinguish and analyze two bands in the spectral emission of the aircrafts. Therefore, any detected signal in which the band intensities and ratios do not conform to the target aircraft spectral signature would be recognized and ignored. Countermeasure flares have to produce a spectral signature similar to those of aircrafts in order to be effective.
Generally an aircraft emits more energy in the ß - band as compared to a - band and conventional infrared decoy flare emits more radiation in a - band as compared to ß - band. A ratio of the spectral response i.e. infrared spectral ratio (ß - band/ a - band) to the same radiator in different bands, at the same point in the seeker’s FOV is taken to determine whether the radiating object is decoy or an aircraft. When decoy flare is released, a sudden jump in the a – band energy is observed as compared to ß – band indicates a flare in the seeker’s FOV. The seeker could use two different detectors to monitor the energy levels in two bands or use a single detector with different band filters on the reticle spokes.
Although minimum required dynamic spectral efficiency is > 3.5 J g-1 sr-1 at air speed of 250 kts, minimum static spectral efficiency of > 35 J g-1 sr-1 is required because carbon type of payloads undergo degradation in IR efficiencies by a factor of about 10 at such air speed. Static IR spectral ratio of 3.0 is necessary to achieve an appropriate required IR spectral ratio under dynamic conditions due to its degradation to 66 % under the dynamic condition.
A problem with many conventional Magnesium-Teflon-Viton (MTV) decoy flares is that, they produce mainly a - band infrared emissions, which differ from aircraft spectral infrared emissions. Efforts have therefore been made to develop decoy flares that generate infrared spectral ratios that are more similar to those of target aircrafts. Standard MTV composition on combustion even in aerobic condition does not meet the infrared spectral ratio requirement and the infrared spectral ratio of the MTV based decoy flare is 1-1.25.
US5834680 discusses Pyrotechnic compositions based on magnesium, ammonium perchlorate and partially oxidized carbonaceous fuels like trioxane, paraformaldehyde, cyanuric chloride etc.wherein it was found that partially oxidized carbonaceous fuels prevents soot formation and generate large amounts of carbon dioxide which shows strong emission in ß - band. Infrared spectral ratio reported for these compositions is in the range of 1.3 to 3.5. Thus these compositions discusses in US5834680 have the disadvantage of low IR spectral ratio and the fuels used are irritant in nature.
US5472533 discloses a combination of two pyrotechnic compositions providing an adjustable spectrally balanced infrared flare. The first composition includes boron, aluminum, ammonium perchlorate, potassium nitrate and Viton. The second composition includes magnesium, polytetrafluoroethylene and Viton. The ratio between the first and second formulations may be adjusted to vary the infrared spectral ratio of the decoy flare matching with the aircraft to be protected. The spectral ratio of the composition reported is ~1.8. These compositions known in art have the disadvantage of low IR spectral ratio.
US3432370 discloses an illuminating flare composition comprising an alkali metal nitrate as oxidizer, particulate light metal as fuel and crosslinked copolymer of an epoxy resin and a nitrate or perchlorate salt of an amine terminated polyglycol as binder.
US6427599 discloses Pyrotechnic compositions comprising of aromatic poly carboxylic anhydride fuel (8-60 %), potassium perchlorate (40 - 90 %) with binder (1 - 20 %) which have combustion reaction products that include a high percentage of carbon dioxide. These pyrotechnic compositions emit minimum infrared emissions in a - band as compared to ß - band emissions. The compositions generate combustion products with molar ratio of CO2:H2O > 4, where infrared spectral ratio is > 3.0. It is necessary to take care of a low H/C ratio in order to suppress unwanted emission in the a - band.
US20040011235A1 discloses an infra-red emitting decoy flare consisting of a primer flare, a spectral flare and a means for igniting the primer flare. The primer flare is formed from a fast burning pyrotechnic composition and is adapted to produce an intense infra-red source of short duration on ignition. The spectral flare formed from a mix of boron/silicon/viton (20/10/70) produces a slower burning composition having a fixed infrared spectral ratio.
US 20060011277A discloses a pyrotechnic charge for producing IR radiation based on a deuterated fuel, deuterated oxidizing agent and deuterated binder. The use of such a pyrotechnic charge leads infrared spectral ratio is >2.
US20090120545A discloses Infra-red decoy flares based on nitrocellulose (04 - 35%), oxidizer like KClO4, KCIO3 and NH4CIO4 (40 - 80 %), organic fuels like potassium dinitrobenzoate, terephthalic acid, sodium salicylate or sodium-D ascorbate (15-35 %) and carbon sources like lampblack, soot, graphite, charcoal or coal (10%). These compositions display an excellent burning rate and secondly their compositions can be easily adjusted to conform to the desired infrared spectral ratio.
Theoretical study of IR emission of flare compositions was carried out by R. Webb and M. van Rooijen and published in 31st International Pyrotechnics Seminar, Fort Collins, CO, July 10 – 16, 2004, p.575 – 583. This study revealed that highest infrared spectral ratio is obtained in cases where there is the high molecular CO and CO2 and without H2O. Increasing the soot volume fraction at increasing temperatures quickly deteriorates the infrared spectral ratio value where it is no longer useful from the perspective of infrared spectral ratio.
Koch in Experimental advanced infrared flare compositions, 33rd International Pyrotechnics Seminar, Fort Collins, CO, July 16-21, 2006, p.71-80 has studied spectrally balanced decoy flare compositions based on potassium perchlorate, KClO4, with tetra cyano ethylene, C2(CN)4 and s-tri cyano triazine, C3N3(CN)3. Due to high combustion temperatures (~2900 K) and virtually no water content higher specific energies are available in ß - band compared to compositions based on aromatic carboxylic anhydrides and KClO4. These compositions have a disadvantage of low IR spectral efficiency (max. 50 J g-1sr-1)
EC Koch in Pyrotechnic countermeasures III: The influence of oxygen balance of an aromatic fuel on the color ratio of spectral flare compositions, propellants, explosives, pyrotechnics 32, no. 5 (2007), 365-370 has studied the influence of the oxygen balance of aromatic fuels, on the infrared spectral ratio of pyrotechnic compositions based on potassium perchlorate, polychloroprene binder and an aromatic fuels and has found that higher the carbon dioxide higher is the infrared spectral ratio and with the introduction of oxygen into the anthracene framework the infrared spectral ratio starts to increase. These compositions have a disadvantage of low burn rate (Max. 1.6 mm s-1) and low IR spectral efficiency (max. 40 J g-1sr-1).

OBJECT OF INVENTION
One of the object of the present invention is to provide a spectrally balanced infrared decoy flare compositions capable to divert a spectral discriminator based infrared guided missile.
Another object of the present invention to provide a pyrotechnic composition which on combustion produces combustion products with molecular CO and CO2 without carbon content.
Yet another object of the present invention to provide a pyrotechnic composition which on combustion produces infrared emissions having infrared spectral ratio greater than 6.0.
Yet another object of the present invention to provide a pyrotechnic composition which yields infrared spectral efficiency >120 J g-1 sr-1 in 3-5 µm wave band.
Yet another object of the present invention to provide a pyrotechnic composition which utilizes less sensitive and commonly available sodium nitrate oxidizer.
Yet another object of the present invention to provide a pyrotechnic composition which uses magnesium metallic fuel for sustained combustion.
Yet another object of the present invention to provide a pyrotechnic composition which on combustion produces Infra-red decoy flares with an excellent burning rate.
Yet another object of the present invention to provide a pyrotechnic composition which can be easily adjusted to conform to the desired infrared spectral ratio.

SUMMARY OF INVENTION
According to one aspect of the present invention there is provided a pyrotechnic composition comprising of
a) magnesium content from 10 to 60 %;
b) Oxidizing agent in the range of 20-70 wt%;
c) Partially oxidized organic fuel
d) Binder
According to another aspect of the present invention there is provided a process for the preparation of pyrotechnic composition comprising the steps of:
a. Spreading pyrotechnic metallic fuel such as magnesium;
b. Adding binder solution to the magnesium powder;
c. Coating the entire mixture of magnesium powder thoroughly and uniformly with the binder solution and spread it uniformly onto the tray
d. Drying the coated magnesium –binder mixture at room temperature;
e. Adding the oxidizer and the partially oxidized fuel to the coated magnesium –binder mixture and mix it thoroughly;
f. Sieving the entire bulk of composition through a dry sieve;
g. Air drying the composition by forming a thin layer on the appropriate tray at room temperature for 5-6 hours
h. Sieving the dried composition through a dry sieve.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides pyrotechnic compositions usable in IR decoy flares which capable to decoy the IR guided missiles equipped with counter-countermeasure (CCM) system. The pyrotechnic compositions of the present invention comprises of metallic fuel, oxidizer, fuel and binder.
The pyrotechnic metallic fuel to be used in the present infra-red decoy flares is in an amount in the range of from 10 - 60 wt %, based on total pyrotechnic composition. Preferably, the pyrotechnic fuel is present in an amount in the range of from 20 - 40 wt %, more preferably in an amount in the range of from 30 - 40 wt %, based on total pyrotechnic composition.
The oxidizer is present in the pyrotechnic composition to be used in accordance with the present invention in an amount in the range of from 20 - 70 wt %, based on total pyrotechnic composition. Preferably, the oxidizer is present in an amount in the range of from 40 - 50 wt %.
The partially oxidized pyrotechnic fuel to be used in accordance with the present invention can suitably be selected from the group consisting of organic anhydrides. More preferably, the pyrotechnic fuel is succinic anhydride.
In the pyrotechnic composition to be used in accordance with the present invention the partially oxidized pyrotechnic fuel is present in an amount of 18 wt % and binder 2 wt %, based on total pyrotechnic composition.
Fluorinated organic binders are advantageous in that the binder, also being an oxidising agent, will join in the reaction. A preferred binder is a copolymer of vinylidene fluoride and hexafluoroethylene, for example VITON A (™), which coats and binds the constituents very well as well as adding heat out put to the reaction.

A process for the preparation of pyrotechnic composition comprising the steps of:
a. Spreading pyrotechnic metallic fuel such as magnesium onto a tray;
b. Adding binder solution to the magnesium powder;
c. Coating the entire mixture of magnesium powder thoroughly and uniformly with the binder solution and spread it uniformly onto the tray
d. Drying the coated magnesium –binder mixture at room temperature;
e. Adding the oxidizer and the partially oxidized fuel to the coated magnesium –binder mixture and mix it thoroughly;
f. Sieving the entire bulk of composition through a dry 14 BS sieve;
g. Air drying the composition by forming a thin layer on the appropriate tray at room temperature for 5-6 hours
h. Sieving the dried composition through a dry 8 BS sieve.

An embodiment for the preparation of pyrotechnic composition is as follows:
Transfer and spread magnesium powder, to an appropriate clean and dry aluminium / SS tray. Mix it thoroughly initially using an appropriate SS spatula and finally by hands taking due care to avoid spillage. Mix viton solution thoroughly without spillage using an appropriate aluminium / SS rod. Transfer viton solution at the centre of the spread magnesium powder. Coat entire mixture of magnesium powder thoroughly and uniformly by hand with viton solution and spread it uniformly without spillage. Allow the coated magnesium to air dry at room temperature for 15 minutes. Transfer weighed quantity of sodium nitrate (passing 240 BSS) and anhydride (passing 120 BSS) to viton coated mixture of magnesium powder. Mix it thoroughly by hand without spillage. Carefully sieve the entire bulk of composition using a clean dry 14 BS sieve by circular motion of hand using rubber hand gloves.
Finally the composition should be air dried in thin layer in an appropriate tray at room temperature for 5-6 hours with proper label. Pack the composition in dry condition in an antistatic bag and store it properly in hermetically sealed condition. Next day take out the composition and sieve it through a clean and dry 8 BS sieve to an appropriate clean and dry SS/aluminium tray so as to break the lumps / to make composition more intimate and composition is ready for further application.

Weigh 10 g of composition on an electronic balance. Set the press to apply 5 ton dead load. Apply fine graphite to the components of mould and steel tube and assemble it. Position mould assembly on the die table of press and insert steel tube into the mould. Transfer previously weighed composition to the mould slowly using appropriate brass funnel. Spread uniformly 1g booster composition (50:50 wt/wt mixture of composition & priming composition) over flare composition. Level the top of composition using appropriate wooden rod. Insert plunger, remove spillage of composition, if any.
Lift up the ram of press to a suitable height and centre the mould assembly below the ram. Bring down the ram and observe that set dead load (5 tons) is displayed on digital load indicator. Maintain the load for 15 seconds. Lift the ram upto a suitable height. Slide the mould assembly little away from the ram on the die table of the press and cautiously remove the base plate without disturbing plunger. Remove spillage of loose composition if any.
Position the extractor on die table of the press and cushion it adequately with a soft bed of dry white waste cotton / felt piece. Position securely mould-plunger assembly on extractor. Bring down the ram slowly to extract the filled IR Flare. Carefully observe the downward travel of the ram and lift it up immediately as soon as filled IR Flare gets extracted. Remove the filled IR Flare safely, plunger and mould body from extractor.
Weigh (on an electronic precision balance) 1g of priming composition on a clean moisture free ammunition paper and transfer it into on the surface of filled IR Flare and close with paper tape. Short the leads of the squib pack the filled IR Flares in antistatic bag for IR intensity measurement.
The Infra Red intensity measurements of the pyrotechnic compositions were carried out using a computerized Spectro radiometer (SR 5000). The IR Spectro radiometer detects and analyses IR intensity in the different wave bands and in spectral mode.

Examples
The present invention has been described in detail hereinafter. In the given examples, the quantity of individual constituents is mentioned in weight percent. However, it must be taken into consideration that this invention is by no means restricted to such specific examples only.

Examples of pyrotechnic compositions which will meet infrared spectral ratio of the composition are as follows

Example 1
10g of magnesium powder is coated by 2g of viton, coated magnesium is sieved 3 - 4 times through 25 BS sieve. 70g of Sodium nitrate was added to coated magnesium and mixed thoroughly. Further, 18 g of succinic anhydride is added and mixed thoroughly. The composition is kept for 3 - 4 hour at room temperature and sieved again 3 - 4 times through 25 BS sieve. Finally the composition is dried at room temperature for 24 hours, sieved, packed and stored.
The results of radiometric measurement are depicted in table 1.

Table 1
Sr. No. Ingredients % wt IR Efficiency
a - band
(J g-1 sr-1) IR Efficiency
ß - band
(J g-1 sr-1) IR Spectral Ratio
ß - band/ a - band
1 Magnesium 10 22 73 3.3
2 Sodium nitrate 70
3 Succinic anhydride 18
4 Viton 2

Example 2
20g of magnesium powder is coated by 2g of viton, coated magnesium is sieved 3 - 4 times through 25 BS sieve. 60g of sodium nitrate was added to coated magnesium and mixed thoroughly. Further, 18 g of succinic anhydride is added and mixed thoroughly. The composition is kept for 3 - 4 hour at room temperature and sieved again 3-4 times through 25 BS sieve. Finally the composition is dried at room temperature for 24 hours, sieved, packed and stored.
The results of radiometric measurement are depicted in table 2.
Table2
Sr. No. Ingredients % wt IR Efficiency
a - band
(J g-1 sr-1) IR Efficiency
ß - band
(J g-1 sr-1) IR Spectral Ratio
ß - band/ a - band
1 Magnesium 20 14 76 5.4
2 Sodium nitrate 60
3 Succinic anhydride 18
4 Viton 2

Example 3
30 g of magnesium powder is coated by 2g of viton, coated magnesium is sieved 3 - 4 times through 25 BS sieve. 50 g of sodium nitrate was added to coated magnesium and mixed thoroughly. Further, 18 g of succinic anhydride is added and mixed thoroughly. The composition is kept for 3 - 4 hour at room temperature and sieved again 3-4 times through 25 BS sieve. Finally the composition is dried at room temperature for 24 hours, sieved, packed and stored.
The results of radiometric measurement are depicted in table 3.
Table 3
Sr. No. Ingredients % wt IR Efficiency
a - band
(J g-1 sr-1) IR Efficiency
ß - band
(J g-1 sr-1) IR Spectral Ratio
ß – band / a - band
1 Magnesium 30 16 93 5.8
2 Sodium nitrate 50
3 Succinic anhydride 18
4 Viton 2

Example 4
40 g of magnesium powder is coated by 2g of viton, coated magnesium is sieved 3 - 4 times through 25 BS sieve. 40 g of sodium nitrate was added to coated magnesium and mixed thoroughly. Further, 18 g of succinic anhydride is added and mixed thoroughly. The composition is kept for 3 - 4 hour at room temperature and sieved again 3-4 times through 25 BS sieve. Finally the composition is dried at room temperature for 24 hours, sieved, packed and stored.
The results of radiometric measurement are depicted in table 4.
Table 4
Sr. No. Ingredients % wt IR Efficiency
a - band
(J g-1 sr-1) IR Efficiency
ß - band
(J g-1 sr-1) IR Spectral Ratio
ß - band/ a - band
1 Magnesium 40 20 123 6.2
2 Sodium nitrate 40
3 Succinic anhydride 18
4 Viton 2

Example 5
50g of magnesium powder is coated by 2g of viton, coated magnesium is sieved 3 - 4 times through 25 BS sieve. 30g of sodium nitrate was added to coated magnesium and mixed thoroughly. Further, 18 g of succinic anhydride is added and mixed thoroughly. The composition is kept for 3 - 4 hour at room temperature and sieved again 3-4 times through 25 BS sieve. Finally the composition is dried at room temperature for 24 hours, sieved, packed and stored.
The results of radiometric measurement are depicted in table 5.
Table 5
Sr. No. Ingredients % wt IR Efficiency
a - band
(J g-1 sr-1) IR Efficiency
ß - band
(J g-1 sr-1) IR Spectral Ratio
ß - band/ a - band
1 Magnesium 50 28 153 5.5
2 Sodium nitrate 30
3 Succinic anhydride 18
4 Viton 2

Example 6
60g of magnesium powder is coated by 2g of viton, coated magnesium is sieved 3 - 4 times through 25 BS sieve. 20g of sodium nitrate was added to coated magnesium and mixed thoroughly. Further, 18 g of succinic anhydride is added and mixed thoroughly. The composition is kept for 3 - 4 hour at room temperature and sieved again 3-4 times through 25 BS sieve. Finally the composition is dried at room temperature for 24 hours, sieved, packed and stored.
The results of radiometric measurement are depicted in table 6.
Table 6
Sr. No. Ingredients % wt IR Efficiency
a - band
(J g-1 sr-1) IR Efficiency
ß - band
(J g-1 sr-1) IR Spectral Ratio
ß - band/ a - band
1 Magnesium 60 44 185 4.2
2 Sodium nitrate 20
3 Succinic anhydride 18
4 Viton 2

In embodiment of these examples, the pyrotechnic compositions have the property that combustion of the pyrotechnic composition produces infrared emissions having an infrared spectral output ratio in the range of 3 to 6. The IR intensity in ß - wave band ranges from 70 to 185 J g-1 sr-1. Burn rate and sensitivity data of spectrally balanced decoy flare compositions is presented in table 7.

Sr. No. Composition
Mg/NaNO3/succinic anhydride/Viton LBR
(mm/s) FOI Friction Insensitive
(kg)
1 10/70/18/2 1.00 61 36
2 20/60/18/2 2.50 58 36
3 30/50/18/2 3.30 69 36
4 40/40/18/2 3.90 69 36
5 50/30/18/2 3.80 73 36
6 60/20/18/2 3.40 90 36

Table 7: Burn Rate and Sensitivity Data of Compositions

Brief description of the drawings
A detailed description of the invention is hereafter described with specific reference being made to the drawing in which Fig.1, Fig.2 and Fig.3 shows IR Intensity of Magnesium/Sodium Nitrate/Succicnic anhydride/Viton (40/40/18/2) composition in a – band, ß -band and in spectral mode respectively.

CLAIMS:1. A pyrotechnic composition comprising of
a. magnesium content in the range of 10 to 60 %;
b. Oxidizing agent in the range of 20-70 wt%;
c. Partially oxidized organic fuel upto 18 wt%
d. Fluorinated organic Binder

2. The pyrotechnic composition as claimed in claim 1, wherein magnesium is present in the range of 20 to 40 wt%.

3. The pyrotechnic composition as claimed in claim 1, wherein the oxidizing agent is sodium nitrate.

4. The pyrotechnic composition as claimed in claim 1 and claim 3, wherein the oxidizing agent is present in the range of 40 to 50 wt%.

5. The pyrotechnic composition as claimed in claim 1, wherein the partially oxidized organic fuel is selected from the group consisting of anhydride.

6. The pyrotechnic composition as claimed in claim 1, wherein the partially oxidized organic fuel is succinic anhydride.

7. The pyrotechnic composition as claimed in claim 1, wherein the Fluorinated organic Binder is a copolymer of vinylidene fluoride and hexafluoroethylene.

8. A process for the preparation of pyrotechnic composition comprising the steps of:
a. Spreading pyrotechnic metallic fuel such as magnesium;
b. Adding binder solution to the magnesium powder;
c. Coating the entire mixture of magnesium powder thoroughly and uniformly with the binder solution and spread it uniformly onto the tray
d. Drying the coated magnesium –binder mixture at room temperature;
e. Adding the oxidizer and the partially oxidized fuel to the coated magnesium –binder mixture and mix it thoroughly;
f. Sieving the entire bulk of composition through a dry sieve;
g. Air drying the composition by forming a thin layer on the appropriate tray at room temperature;
h. Sieving the dried composition through a dry sieve.