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Home , Pyrotechnic composition, Smoke composition, Smoke screen

CHAPTER 1 INTRODUCTION INTRODUCTION

1.1 GENERAL

Pyrotechnics have been used since ancient times, as were employed to frighten the enemy and also for celebrations and entertainment. In the broader sense pyrotechnics cover a wide variety of explosives that are in use to produce effects different from those produced from high explosives or initiators or .

Pyrotechnics may be classified depending on their ultimate uses^; (i) to produce light for illumination, spotting, tracer, signalling, photography at night, decoys etc. (ii) to produce incendiary effects against targets as well as destruction of equipments and documents (iii) to measure intervals of time eg. delay composition (iv) to produce sound signals (v) as priming compositions for pyrotechnic fillings (vi) as an igniter for aircraft engines and fuel for missiles/rockets and (vii) to produce screens for screening, signalling, deceiving etc.

In the broad family of pyrotechnics, smoke compositions constitute an important class. The pyrotechnic smoke produced is basically an , a suspension of small solid particles in a gaseous medium. The small particles of smoke are formed due to the heat of chemical reaction between oxidizer and fuel to vaporise the volatile ingredients or the products from the pyrotechnic reaction and subsequently the volatile ingredients condense in air, creating smoke .

Smokes can be classified into the undermentioned types depending on their applications^

(i) Screening : These smokes are used to screen troops from visual observation. The burning type of screening smoke compositions utilise chlorinated hydrocarbons like to react with , , , , , dioxide etc to form metallic chlorides, which provide the screening action. Red based compositions are also used for visual screening. Large areas can be screened by oil smokes, wherein the pyrotechnic reaction is used to vaporise the oil. that has high boiling point and low volatility, which condenses creating . Smoke screen can also be produced by dispersing white phosphorus or plasticised white phosphorus or metallic flakes and powders using a central high explosive charge. Such type of smoke is called a bursting type of screening smoke.

(ii) Signalling Smokes: These are coloured smokes and may be formed by burning or bursting. In the burning type of , the coloured dyes are sublimed using heat of chemical reaction from the vaporiser (consisting of potassium and /) and the volatile dye condenses in air to form coloured solid particles. The bursting type of coloured smokes utilise a centrally placed high explosive charge to disperse dye particles.

2 (iii)Training Smokes: These are used for fire-fighting training or for military exercises. Ammonium choride, chloride, potassium chloride etc are the by-products produced from these pyrotechnic smoke compositions and are characterised by low toxicity.

(iv) Lachrymatory Smokes: The pyrotechnic reaction is used to volatilise lachrymatory or tear producing agent like chloroacetophenone. Such compositions are used in for , flushing out fugitives, etc.

(v) Marker Smokes: Phosphides of , and aluminium are used in the naval markers for marking the position on sea surface. The sea water reacts with the phosphide to produce gas which is spontaneously ignitable.

(vi) Tracking and Acquisition Smokes: These smokes are used for tracking the path of space vehicles, tracer projectiles etc at high altitudes.

(vii) Infra Red fIR) Screening Smokes: This smoke gives screening in the infra red region^ (2 um to 14 um) . The IR screening smoke provides screening from modern opto­ electronic equipments that utilise IR sensors.

1.2 BRIEF HISTORY OF DEVELOPMENT OF SMOKES

Smoke has been regarded as one of the signs of warfare from time immemorial. In 404 BC , during the Peloponnesian war between Spartans and Athens, pitch and sulphur were used to produce smoke. Our epics, the Ramayana and the Mahabharata mention about smoke produced in the battlefield and use of smoke along with incendiaries and noxious fumes to overcome the enemy. Records show that when

Alexander the Great invaded India (365-323BC), smoke along with other pyrotechnic compositions were used to fight against him. In first century AD, the English king Piets used smoke for signalling while fighting the Roman invaders and in 15th century, the American Red Indians used smoke puffs for communication amongst friendly tribes in their fight with the white settlers^. In 1701, the Swedish King

Charles XII produced screening smoke by burning damp straw, which helped to obscure his Army from the Polish-Saxon forces so that he could safely cross the Dvina river^. In 1906-

1909, the Germans used a mixture of Sulphur trioxide and

Chloro sulphonic acid to create smoke for screening and employed it with great success in screening ships in the battle of Jutland. The British and American Navies tried out screening of their ships by restricting air supply to the ship furnaces to produce 'funnel smoke'. Around the same time, the British, French, German and American armies utilised white phosphorus as well as liquids like SnCl^,

TiCl^, SiCl^, SO2CI2 , etc to produce smoke for protection of movements of reserves and river crossings. In 1915, the British developed "S" smoke mixture consisting of pitch,

4 tallow, black powder and sodium . They used smoke for

the first time to screen in the battle of Scarpe in

1917. During , the French produced a smoke

composition called Berger mixture consisting of zinc,

-tetrachloride, zinc oxide and Kieselguhr. Major advances

were made in the development of superior smoke stores at the

time of World War II. a solid mixture consisting of

Hexachloroethane-Zinc oxide was developed in U.K. along with

white phosphorus, and filled in bombs, grenades and smoke

pots. In 1941, mechanical smoke generators were developed in

U.K. for creating large smoke screens to prevent German

bombers from accurate aiming of ground targets. In these

generators, crude oil was vaporised to create smoke. Similar

type of smoke generators were used in USA in 1942 for

screening cities. At the time of World War II, the Americans created smoke screens using Venturi Thermal Generators and at the Anzio beach head 3500 tons of supplies could be landed everyday for six months under the cover of smoke. In 1944, a

Russian unit created smoke to hide the San river crossing^.

During 1952 Korean war, smoke was used to screen vital ports and combat areas along with troop movements.

The value of smoke was realised by the Israelies in the 1973

Arab-lsraeli War. After losing 130 tanks in two hours, the

Israeli gunners realised that they could overcome Egyptian Sagger anti-tank guided missiles by using smoke screens and ultimately won that war. This was the turning point in the realisation of the importance of smokes in warfare . Again, in the 1991 Iraq War, large smoke screens were created by

Iraq by burning oil wells for screening purposes.

Infra-red sensors are currently used in weapon systems for surveillance, guidance, night-vision and range finding^. A review of the fast development of infra red sensors^®”^^ reveals that before World War II, combat generally took place at daytime when binoculars or naked eye were used to detect targets and IR sensors were not used.

During the course of World War I I , active IR surveillance was first developed for night vision, wherein a target was illuminated by an infra-red search light and the reflected infra-red energy was observed using IR sensors. The disadvantages of the active IR sight (limited range, longer size, easy detectability by enemy etc) were removed when the passive IR sight was developed, which sensed black body radiations emitted by the target.

The first generation night vision devices (NVD) were image intensifiers that utilised the night sky radiation in visible and near IR (due to stars, moon and planets) for passive surveillance. These utilised caesium-gallium-arsenide or potassium-sodium-caesiurn-antirnony photocathode and phosphor screen (Cadmium activated zinc sulphide) and used by the American forces in the Vietnam War.

6 Around 1960, IR sensors were fitted on various types of missiles (Air to Surface, Surface to Air and Air to

Air) for homing onto the IR emissions of the target. The IR sensors used were lead sulphide, lead selenide and lead antimonide. These detectors had low resolution and were vulnerable to simple countermeasure techniques like flying into and then away from the sun. The second generation IR sensors used were indium antimonide and gallium silicide, which provided better discrimination of the target.

Currently, the IR sensor used is cadmium-mercury-telluride

(CMT) for guidance, detection, tracking and surveillance. A large number of CMT sensors are used in the thermal imager to get a video like image for the operator. The thermal imagers operate in two windows viz. 3-5 um and 8-14 um. In addition to night viewing, the thermal imager helps in detecting camouflage and gives better performance (as compared to optical systems and image intensifiers) in dusty and battlefield conditions.

1.3 APPLICATIONS OF SMOKES

Though smokes play an important role in defence, civil application of smokes outstrip their uses in defence. The current uses of smokes in civil sector and defence are as follows^^~^^.

1.3.1 Civil Uses

Testing leakages for boilers/pipes. Fire-fighting training.

As an (dispersing DDT, gammaxene using

KCIO3 , & anthracene).

Flushing out anti social elements.

Control and marking of rioters by invisible material

(visible in UV)

Optical tracking (and recovery) of space

craft/pilotless target aircraft.

Distress signal.

Indication for wind direction and landing aid for

helicopter/aircraft.

For theatre shows and movies scenes.

Putting off underground fires.

Protection of orchard from sudden temperature changes.

As a scavenger in dusty areas.

Rapid generation of gases for filling up of air bags in

cars automatically in case of accident, to cushion the

driver.

Protection of populated areas from nuclear radiation

Creation of rain by condensation of rain clouds using

Agl, Pbl for nuclei.

Removal of fog/cloud over airport for planes to resume

operation by seeding with Agl.

1 .3 .2 DEFENCE USES

Screening advancing and retreating troops and tactical

8 operations.

Blanket ground installation from aircraft or satellite

observation which helps against mapping and

reconnaissance techniques.

Use of dummy screen for deceiving.

Cause enemy to expend large ammunition against

unprofitable targets.

Create uncertainty and panic among enemy due to

isolation created in surroundings.

Surprise the enemy.

Disrupt enemy movements, operations and command.

For training and simulating battlefield atmosphere.

Mark a position on sea (rescue).

For signalling and in antisubmarine warfare.

As a spotting round in mountainous regions.

As a simulator

As a cheap countermeasure to high weapons

(Laser guided and Fire and Forget missiles) Night

Vision devices and top attack ammunition.

1.4 TYPES OF INFRA-RED COUNTERMEASURES

Various infra-red countermeasures (IRCMs) have been developed or are under development to IR sensors. Some of the IRCMs are as given below :

Decoys like and chaff are used in air for protection of aircrafts by distraction and seduction^®. The flares were very effective against first generation IR

seekers, but research is underway to provide a broader

spectral range of flares to deceive second generation and third generation IR seekers.

IR suppressant coatings that minimise the temperature

contrast between surface of vehicles and surroundings, and hence subdue IR radiations^^.

Heat suppression and dispersion techniques like burial of

hot components in the centre of a vehicle, use of jackets

over engines and exhaust pipes and masking exhaust by

blending with a high proportion of cold bypass air and by

dispersal along wide areas^^.

Thermal camouflage consisting of an inner thermal

blanket and outer thermal net. The thermal blanket consists

of a metallic film with plastic coating and fabric backing

incorporating a pattern of vent holes to allow controlled

escape of air. The thermal net consists of a foil

between at least two polymeric layers of different emissivity

for blending with the surroundings^^.

IR Jamming can be carried out by use of suitable IR

source whose output is modulated mechanically by shutters.

The modulated IR energy received in the missile's homing head renders its guidance system ineffective^®. It is thus an active IR jamming device.

Utilisation of 'stealth' techniques, whereby it is possible to reduce the signature of target by suitable design

10 and by chemical and electronic application^^.

Infra-red screening smoke dispersed from vehicle mounted dischargers, mortars, guns, or handgrenades^*^, and can reduce the effectiveness of conventional weapons by three to four times and blinding smoke by as much as fifteen times^^.

1.5 INFRA RED SCREENING SMOKE

Smoke composition which provide visible cover only is calledvisible screening smoke. The visible screeners are effective in visual and near infra red regions

(0.4 um to 1.1 um). The visual screening smoke is not effective in providing screening in the mid IR and far IR regions and smoke compositions which produce screening in the infra-red regions (2-2.4 um, 3-5 um and 8-14 um) are called infra-red screening smokes^.

Infra-red screening smoke can degrade the effectiveness of costly opto-electronic systems and target acquisition devices^^. It can increase the survivability of anti tank helicopter from shoulder fired IR guided missiles as the helicopter can manoeuvre to safety behind the smoke screen . It is cost effective since a smoke grenade worth a few thousand rupees can save the life of a tank worth crores of rupees^. It is also free from electronic jamming. Infra­ red screening smoke is most suited for fighting vehicles on the move as passive IRCMs like mats, umbrellas, jackets, paints films etc. are ineffective against moving targets 11 which are easily detected by visual means^^. Since Infra-red

sensors and guidance systems will play a major role in future

battlefield scenario^"^"^^, IRCM using infra-red screening

smoke has assumed great significance.

1-5.1 Infra-red screening smoke compositions

Pyrotechnic smokes in general contain an oxidiser,

cum fuel and other additives to impart required

properties. According to a French patent^^, a pyrotechnic

smoke formulation consists of hexachloroethane or

hexachlorobenzene (15-85%) (30%) and magnesium

powder (15-25%). This smoke produces 1-14 um carbon

particles at the combustion temperature (>1000°C) and can

camouflage targets from IR detectors. According to this

patent, anthracene may be used in place of naphthalene. Vega

al^^ have claimed that the castable smoke composition

containing chlorinated naphthalene (70%), magnesium powder

(17%) and polyvinylidene flouride (13%) produces IR screening smoke.

Potassium (40%), hexachloroethane

(30%), anthracene (30%) in combination with is described in a UK Patent to produce IR radiation absorption screen 2 8 . Carbonaceous smokes have been studied for IR and visible wave length obscuration. These are based on hexachlorobenzene (54%), magnesium powder (14%) and energetic binder glycidylazide polymer (GAP) or hydrocarbon binder

12 (32%) and have proved more effective than the smoke

formulation containing (70%), magnesium

(5%) and energetic binder (GAP) or hydrocarbon binder^^.

Carbon black (9%) was also used along with styrene-butadiene

rubber. The gel of the latter in red phosphorus (95%) on

detonation produced a smoke screen, which blocked the passage

of radiation from source to detector for more than 30 sec^°“ 31 • ^ s> According to a German patent"^ , carbon producing

aromatic hydrocarbon and their condensation product or

polymer were dispersed in a composition containing

hexachloroethane, zinc and zinc oxide to obtain radiation

blocking screen. A white smoke

consisting of hexachloroethane, zinc oxide, potassium

chlorate, iron containing silicocalcium, aluminium and

anthracene is described by Polish research workers^^, which absorbs in the IR range and also scatters in far IR region.

Smoke screen for visible, IR and microwave region has been produced by mixing conventional smoke with about 10% of 1-100 um long metal coated polymer or glass fibres as well as carbon, aluminium and, fibres^^. Active carbon with

80% of particles having size in the range 1-8 um and 10% above and 10% below this limit has been used in IR absorbing

aerosol^^.

Pyrotechnic compositions for absorption and reflection of IR and radiowaves are developed using components to produce primary and secondary fog. A primary

13 fog was produced using halogen donors, metal powder and

or red phosphorus, whereas a secondary fog was

generated using organic/inorganic acids or their

ammonium/alkali metal salts or alkaline earth metal salts or

organic ester of inorganic acids or micro bubbles/plastic

particles. a composition using chloroparaffin 75 %,

aluminium, 5%, calcium silicide 10% and powdered silicon lo%

has also been mentioned^^. Espagnacq & Sauvestre^^ have

claimed that use of two compositions (rapid and slow burning)

IS effective for obscuring visible and IR radiation. The

rapid burning composition consists of zinc powder 31%, zinc

oxide 12%, 16%, hexachloroethane 31% and

neoprene binder lo%, while the slow burning composition

consists of magnesium 2 0 , hexachlorobenzene 8 0 , naphthalene

10 and polyfluorovinyledene binder 10 parts by weight. A

smoke composition^^ effective on snow land for camouflaging

visible and infra-red range consists of hexachloroethane 65%,

powdered aluminium 7% and 28%. a

pyrotechnic smoke capable of absorbing in the visible and IR

radiation is generated by incorporating caesium chloride and

caesium nitate in hexachloroethane/phosphorus based smoke

composition. A smoke of high absorbance at 0.6 um, 3.5 um

and 10 um was generated by a charge of red phosphorus 4 3 . 75%,

33%, amorphous 6%, -70%

alloy 4.75% and butadiene binder 12.5%. Caesium salt is added to a charge containing hexachloroethane 5 0-7 0 %,

14 powdered silicon or aluminium 20-40% and other components or to a charge of red phosphorus 30-50%, nickel-70% zirconium O Q alloy 3-15%, amorphous boron 5-20% and other components-’^.

A self energizing and self sustaining unit for generating black smoke from diesel fuel has been described, which provides greater shielding from IR detection than previously obtained by white smoke generator^®. Compressed gas from aerosol containers has been used to atomise talc, kaolin, calcium or or sodium bicarbonate of particle size 3-60 urn. The particles generated are nontoxic, chemically neutral, cold and have a descent rate of <5 cm/sec and also optically and opto-electronically opaque at 3-5 um and 8-14 um. These unreactive powders are believed to be opaque to IR and other heat sensitive night vision devices^^.

Shukis et al*^^ have claimed that slurry filled obscuration payload for IR screening consists of mixture of iso and n-butane, trifluoro trichloroethane, tetrafluro dichloroethane and n-hexane along with conventional particulate material to give a slurry, which is detonated in suitable container using central burster tube. The volatile liquids of low surface tension and low density are used with the aim of filling up the particulate voids. As per another

US patent'^^, a composition consisting of fine metal flakes of copper, copper alloy (bronze or ) along with suitable volatile wetting liquid which helps to form compact mass of

15 flakes, produces an IR smoke screen aerosol on bursting. The metal flakes had a lateral dimension of 1.5 to 14 um and thickness 0.07 to 0.27 um. The weight ratio of compacted cohesive metal flakes massto high explosive charge was in the proportion of 40 : 1.

A composition consisting of an explosive charge of ammonium perchlorate (60%) and powdered magnesium-aluminium mixture (40%) was used for spraying copper particles of diameter 0.5 - 1.9 um together with red phosphorus to produce

IR smoke. Powder of ammonium phosphate, teflon or Si02 was used to prevent caking of copper particles. In addition, a mix based on red phosphorus or a mixture of PVC, zinc oxide, , thiourea, ammonium perchlorate, aluminium and a binder generates a visible light absorbing smoke when initiated by an explosive charge consisting of powdered magnesium, ferrous phosphate, chloroalkane, amorphous boron and black powder. It is claimed that this smoke can be made impermeable by addition of 2-30 um glass fibres to the copper powder^.

Adreev et al^^ studied the role of organic in the IR radiation attenuation by the atmosphere.

Burning type coloured smokes were formulated using various organic dyes like dye oil orange (42%) for orange colour smoke, mixture of dye rhodamine-B (20%) and dye oil orange

(30%) for red colour smoke, dye arlasol green (35%) and dye quinoline yellow (15%) for green colour smoke. Absorption of

16 IR radiation in wave length 1.5- 2.5 um region was measured using radiometer'^^. According to a recent European patent^^ on pyrotechnic composition useful for masking targets, the use of 25-70% of IR extinction particles ( or particles) together with an oxidation- reduction system consisting of an organic reducer and an organic oxidiser or mineral oxidiser (Guanidine nitrate < 10, azodicarbonamide < 1 0 , ammonium perchlorate < 1 2 , nitrocellulose < 10, calcium carbonate < 10, zinc oxide < 30, hexachloroethane < 30 and dicyandiamide < 10 wt%) has been recommended. Nitrocellulose/ were used as binder.

It has been claimed that the composition can produce smoke with controlled particle size. A Japanese patent describes a composition consisting of red phosphorus, ferric oxide, magnesium and linseed oil for IR light shielding smoke candles which produced smoke for 20 minutes, when packed in a

. d R container of 15 cm dia and 20 cm height . A pyrotechnic composition consisting of particulate material in metallic alloy or compound form of Ti/Si/Zr, Hf, Mn and V/Fe coated with fluorinated organic polymer or other material to retard combustion prior to expulsion, and a combustible having a substantial degree of radiation in the 3-14 um band

(Gun powder) together with minor constituents like PTFE or other fluorinated organic polymers which act as combustion A Q aid, has been claimed . A typical composition consists of powdered titanium 40%, 15% and mealed gun powder

17 45%. Radiance values for pyrotechnics consisting of Ti, Si,

Zr and A 1 , Ti and Zr s ilic id e s are given in 7 .5 - 8.4 um, 9 .8

- 11.5 um and 8.0 - 13.5 um regions, demonstrating the ability to tailor the spectral distribution of emitted radiation and to off set the resetting of detecting devices to contain the effect of the screen.

A recent German patent^*^ on generation of in fra ­ red and visible light obscuring smoke screen describes dispersal of mineral dust consisting of calcium and magnesium carbonates along with cations such as silicon, aluminium, iron, potassium and sodium using explosive charge. The mineral dust had particle size of 42-90 um consisting of dolomite 71.9% and calcite 25.2%. The dust was filled in a

PVC pot and 1.5 kg charge was dispersed using 2.5 g igniter and 65 gm explosive.

1. 5.2 PROCESSING OF IR SCREENING SMOKES

The method used to manufacture the conventional screening smoke composition can also be used for IR screening smoke formulations. The screening smoke composition is manufactured by first mixing various ingredients by hand, followed by sieving and in the end blending in the drum mixer. Mechanical mixing of screening smoke composition may also be adopted by observing the reguired precautions. The

4 ingredients are continuously ground, sieved, weighed, premixed and finally mixed in a drum mixer. Thereafter, the

18 smoke composition is filled either by direct filling into the hardware (smoke generators, bombs, smoke floats etc) at low tonnage or by pelleting method at high tonnage along with priming and/or delay composition in suitable containers, which are subseguently assembled in shells and bombs. The former method is used for stores, which do not have to withstand shock of projection and the latter is preferred for the stores, which have to withstand strong dynamic forces during flight^^. The castable method used for manufacturing conventional screening smoke composition has been described under references , Polymeric binders like polyester, polyamide, PVC, phenol-formaldehyde, etc are used as one of the constituents, which produce satisfactory mechanical stability to the pellets and incremental pressing and use of presses is avoided. Automatic and fast filling tried for pyrotechnic mixtures and ammunition could also be used for smokes to reduce the cost and risk.

1 .5 .3 TESTING OF IR SCREENING SMOKES

In Canada, laboratory evaluation of IR smoke and other screening systems are carried out in a large aerosol chamber (volume 326 Sources and detectors are installed to monitor entire visible and IR spectra. The discrete sources and detector used consists of Spectra-

Physics, helium-neon laser (0.632 um) coupled with Laser

Precision and General Photonics Nd-YAG Laser (1.06 um)

19 together with Molectron pyroelectric detector. In addition to these, there are broad band sources and detector consisting of a dual black body sources together with two

Molectron pyroelectric detectors to study 3-5 urn and 8-13 um wave bands and a Barnes Spectral Radiometer for measurements, both at discrete wavelength and broad band. Particle size measurements are made using Malvern 2600 D particle sizer.

Mass sampling is carried out using MSA glass fibres filters affixed to series of six large aperture (143 ram) downward facing filter holder. For field evaluation of IR smoke, a scanning LIDAR (Laser Induced Differential Absorption Radar) system was used alongwith various thermal imaging cameras.

The former is geared for evaluation of purely attenuating type smoke, while the latter is best suited for evaluating emissive type smoke. The thermal imaging cameras used are

Inframetrics 525 camera operating in the 3-5 um and 8-12 um wavebands, a Bass and Stroud IR-18 thermal imager operating in the 8-12 um region and a RDS-3 operating in the 8-14 um waveband. The IR-18 is roughly equivalent to the thermal imager common module field night sight whereas the RDS-3 is comparable to the AN/TAS-4.

As compared to large chamber used by Canadian research workers, the smoke chamber for IR 6e v i s i b l e screening smokes of capacity of 20 m^, has been also recommended . The temperature can be maintained between -5 and 40 °C and humidity range between 15 and 95% RH. The

20 inside of chamber is coated with a lacquer which gives

minimum background radiation. Four small axial fans are

placed in the chamber to ensure a uniform dispersion of

aerosol. After the test, the chamber is exhausted through a

filter. The extinction of electromagnetic radiation by the

aerosol is measured at the middle of the chamber over a path

of 2 m . For measurement in visible range, the chopped light

from a halogen lamp, powered by a regulated power supply, is

focussed on a pyroelectric detector after traversing the

chamber. The detector is a Molectron PR 200 which has a peak

sensitivity in range 0.4 - 1.3 um. The optical transmissometer systems display good stability with a resolution of about 2%. in the IR measuring system, the radiation is generated by a black body source at 900°C. The

IR light passes the chopper, traverses the chamber and hits at lithium tantalate pyroelectric crystal. By a system of mirrors it is possible to change quickly between the two radiation sources. The IR measurements are carried out in the wave length bands 0.7 - 1.3 um, 2-5 um and 7-14 um. For each band, a suitable filter is mounted in front of the detector. The IR transmissometer gives the same resolution as the one for visible light.

A cylindrical chamber with a diameter and height of 9.1 metres each, enclosing a volume of 590 m^ for IR smoke evaluation has been also used for smoke studies^®. The inner chamber surface is coated with fluoroepoxy type urethane 21 which has surface energy and reactivity properties comparable to those of FEP teflon. Extinction of electromagnetic radiation by pyrotechnic smokes in the v isible wavelength over a path length 2m was measured using incandescent bulb powered by regulated power supply and RCA 4440 photomultiplier detector, having peak sensitivity in the range 0.4 - 0.5 um wavelength. The IR transmissometer utilises 18.3 m path length, a 900°C black body source, a

HgCdTe detector at liquid N2 temperature. Continuous measurement of extinction as a function of wavelength are obtained via a variable wavelength filter wheel located in front of the detector. The spectral resolution of this filter is 2% over wavelength interval from 2.5 - 14 um.

Intensity measurements are obtained at approx. 0.02 m wavelength intervals with 2.5 - 14 um scan. This chamber was also used to measure the extinction characteristics of pyrotechnically generated alkalihalide smoke^^. Experimental facilities and procedures followed are also described by the same authors in other report^^. Work carried out by the Dow

Chemical Co., USA, in determination of total obscuration power (TOP) using visual target technique and light attenuation technique is described in another report^^.

A FTIR Spectrometer is also being used along with a reactor of 153 litres volume made of borosilicate glass. The IR source is a globar element and the detector is a DTGS pyroelectric bolometer^^. A smoke composition based 22 on hexachloroethane and zinc was ignited in an environmental simulation chamber and the spectral mass extinction coefficient (A ) was measured using a very stable cavity radiator at 773°K^^. The spectral intensity I ( X) in the 3-12 um range was determined with a rapid scanning

Michelson interferometer with subsequent Fourier analysis. A cascade impactor measured the size distribution of the droplets and the mass concentrations.

1 .6 OBJECT OF PRESENT STUDY

A review of work done so far as discussed and described in preceding paragraphs brings out that the applied research work carried out so far on infra-red screening smokes is by and large either patented or classified and scanty information on formulation, processing, and evaluation is available in the open literature. Hence, a systematic and exhaustive study on IR smoke formulations and their evaluation for anti-IR role and anti-laser role has been carried out, using 4 Watts continuous wave 10.6 um carbondioxide laser as well as determination of attenuation and emission characteristics of pyrotechnic smokes in different IR wavelength bands (2 -2.4 um, 3 - 5 um, 8-13 um) as well as specific wavelengths using IR

Spectroradiometer and various types of detectors. It was further the object of the present study to generate practical and useful information on the particle size distribution of

23 pyrotechnic smokes with a view to find out relationship g - ______^ between attenuation and particle size of aerosol.

Scanning electron microscopic study and energy

dispersive x-ray analysis were carried out for a few selected

smoke compositions to understand the morphology of aerosol particles as well as their elemental composition. The study also includes results on the thermal decomposition of smoke compositions. An attempt has been made to suggest the mechanism of action of infra-red screening smokes.

1.7 SCHEME OF THE THESTS

The present thesis is schematically divided into

FOUR chapters.

CHAPTER-1 : INTRODUCTION

This chapter deals with a brief introduction on pyrotechnics and pyrotechnic smokes, history of development of smokes, applications of smokes in civil and defence sectors along with various types of infra-red countermeasures including infra-red screening smoke. A brief resume on IR smoke compositions, their processing and testing is also included. This chapter closes with the object of the present study and plan of work.

CHAPTER-2 : EXPERIMENTAL

This chapter gives broad specification of the materials used. Also included are brief description of the operations involved in the preparation of pyrotechnic smoke

24 formulations by pressing technique and casting method, and details of the equipments employed. Methodology for determination of attenuation as well as emission characteristics of smoke produced from pyrotechnic smoke compositions using IR spectroradiometer are discussed.

Evaluation of a few smoke compositions for anti-laser role against carbondioxide laser is also described. Methodology adopted for determination of smoke particle size, scanning electron microscopy, energy dispersive spectrometry, mass concentration & extinction coefficient of few smoke aerosols and thermogravimetry of some smoke formulations are also d iscussed.

CHAPTER-3 : RESULTS AND DISCUSSION

This chapter contains the details of new technical information generated during the present study. The chapter has been divided into following sub-chapters.

3.1 Pyrotechnic screening smoke compositions.

3.2 Radiometric studies of pyrotechnic screening smoke

compositions.

3.3 Studies on IR emission of smoke clouds from pyrotechnic

screening smoke compositions.

3.4 Factors affecting the performance of IR Screening

smokes.

3.5 Evaluation of pyrotechnic screening smoke compositions

for anti-laser role.

25 3.6 Various other studies on size distribution, morphology,

elemental composition, mass concentration, spectral mass

extintion coefficient of smokes and thermal analysis of

pyrotechnic screening smoke compositions.

3.7 Mechanism of action of IR smokes.

3.8 Field evaluation of pyrotechnic IR screening smoke

compositions.

CHAPTER-4 : SUMMARY

This chapter summarizes the findings of present study and highlights important aspects observed.

References are included at the end and the thesis concludes with the list of publications of the author.

26