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CHAPTER 1

INTRODUCTION

Pyrotechnic mixtures are energetic compounds susceptible to

explosive degradation on ignition, impact and friction and are obtained by

mixing finely divided metal powders with inorganic oxidizing agents that are

capable of undergoing self-sustaining combustion.Firework products are a

type of pyrotechnic device used for entertainment. Firework products are of

two types, namely, light-producing and noise-producing (Shimizu, 1981). The

chemicals employed and their compositions vary depending on the type of

fireworks being produced.

Firework products are made of an oxidizer, fuel and optionally, a

colour enhancing chemical and a binder. The choice of fuels and oxidizers

can significantly affect activation energy, heat of reaction and the efficiency

of energy feedback. The selection of fuel and oxidizer has the potential for

having a major influence on the efficiency of the pyrotechnic mixture. There

is always an optimum fuel to oxidizer ratio, which produces the fastest

burning rate. During the process of manufacturing fire crackers, chemicals are

initially mixed to produce a reasonably homogeneous mixture. Chemicals

used as additives even in small quantities to improve their mechanical

properties can alter the combustion process by reducing the ignition

temperature.

The effectiveness of fire crackers depends not only on the

compositions of mixtures, but also on factors such as particle size and shape,

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choice of fuel and oxidizers, fuel to oxidizer ratio, degree of mixing, moisture

content, physical form, packing density, presence of additives, local pressure,

degree of confinement, degree of consolidation, crystal effects and purity of

the chemicals.

1.1 PREAMPLE

Flash powder is a pyrotechnic chemical. It contains a mixture of

oxidizer, ignitor and metallic fuel which burns quickly and if confined,

produces a loud noise. In fire crackers, flash powder consisting of potassium

nitrate (KNO3), sulphur (S) and aluminium (Al) particles have long been

employed as main ingredients(Conkling, 1985). At present, the different

particle sizes of the chemicals are used as per the requirement for each type of

products with micron level. It is difficult to estimate the degree to which

particle size of the fuel can affect burn rate (Ghosh, 1981). The explosivity

can be determined through mechanical and thermal sensitivity analysis.

Hence, an attempt is made specifically with nano powders of fuel under

different composition by considering metallurgical and safety aspect. Particle

size, particle morphology and metal content are the vital properties which

decide the explosivity of any explosive composition and the safety of

handling is decided by these properties.

The performance of the fire crackers is decided by the noise level it

produces. As per Govt. of India notification, crackers noise level should not

exceed 125 dB (AI) or 145 dB(C)pk at 4 meter distance from the point of

bursting. This has been framed in order to standardize the amount of

chemicals in authorized cake bomb manufacturing (Petroleum and Safety

Organization, Government of India, 2008 circular).

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The chemical reaction involved during the combustion of flash

powder is shown in equation (1.1)

2 KNO3+ 4Al + S K2S + N2 + 2Al2O3 (1.1)

In the manufacture of fire crackers, the chemicals of different ratio

were taken and sieved separately to remove the impurities and mixed

thoroughly in a non-conducting surface. The mixture was again sieved 4 or 5

times to make it homogeneous and free from grits. The shells were prepared

as the shape of cubic box from the card board for cake bomb. These shells

were taken and filled with the chemical mixtures. Then thin foil papers were

used to cover the shells and they were sealed. After some time, the gum

coated jute string was wound around it tightly for better confinement. Then

the fuse wire was inserted.

Most pyrotechnics and low explosives operated by combustion

processes are fuel combines with oxygen to release heat, light, smoke, gas and

a combination of above effects. A fuse is lit by a match and burns rapidly into

the core of the cracker where it ignites the flash powder walls of the interior

core. The three oxygen atoms in KNO3locked into this molecule provide the

"air" that the fuse and the cracker used to burn the other two ingredients,

aluminium and sulphur. Thus potassium nitrate oxidizes the chemical

reaction by easily releasing oxygen. The core is quickly filled with flames

and thus, the necessary heat to ignite, continue and spread the reaction

(Conkling, 1985). Meanwhile, the burning rate is also increased by the

homogeneity of the mixture.

However, in order to gain a better understanding of its combustion

properties, flash mixtures reacting in close contact area need further

investigation. When a pile of flash powder is ignited in the open atmosphere,

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a flame front spreads across the surface. Past flame spread studies of solid

fuels have provided a controlled manner to study the roles of fuel and oxidizer

properties during a combustion event.

Nano metallic particles are having lower ignition temperature,

faster burning rate and shorter burning time. This is because of high specific

surface area when compared to micron or larger-sized particles.

1.2 FIREWORKS PRODUCTS

means low hazard explosive comprising of any

composition or device manufactured with a view to produce coloured fire or

flame, light effect, noise effect, smoke effect (coloured or natural), or

combination of such effects and includes fog-signals, fuses, rockets, shells,

percussion caps etc.,

Fireworks are classified into the following categories depending

upon the desired pyrotechnic effect:

Noise emitting fireworks - Fireworks with noise level not

exceeding 125 dB (AI) or 145 dB (C)pk at 4 meters distance

from the point of bursting. For individual fire-cracker

constituting the series (joined fire-crackers), the above

mentioned limit may be reduced to 5 log 10(N) dB, where

N = number of crackers joined together. Figure 1.1(a) shows the

various noise emitting products available in the commercial

market.

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Cake bomb Chinese crackers Mini bullet

Figure 1.1(a) Noise emitting fireworks

Colour or light emitting fireworks - Such fireworks emit colour

or light and having noise level not exceeding 90 dB (AI) at 4 m

distance from the point of bursting. The varieties of colour /

light emitting fireworks are represented in Figure 1.1(b).

Sparklers

Flower pot

Ground chakra

Figure 1.1 (b) Colour / light emitting fireworks

Display Fireworks - Any product of fireworks assembled at the

site for the purpose of display including shell of diameter

exceeding 25 mm, multiple shots or cake products of any

diameter exceeding 25 nos., of shots in a product and lance

network. Figure 1.1 (c) describes the various display fireworks.

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Rockets

Display fireworks shell

Fire ball display

Figure 1.1 (c) Display fireworks

However, the different fireworks products are shown in Figure 1.2.

Figure 1.2Collection of fire products

1.3 FIREWORKSMANUFACTURING

Noise emitting fireworkproducts are discussed in this research. In a

fireworks industry, different chemicals like fuels, oxidisers, ignitors and

special effect chemicals are mixed manually. All the mixing operations are

done manually. Wooden trays with brass meshed bottoms are used to sieve

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the chemicals to attain homogeneous mixture. Here, the major causes of

accidents are due to friction, static electricity charges and human errors. The

well mixed chemicals are filled into the tubes or loading into the required

boxes. Charcoal, other chemicals and water are made into paste and is applied

on cotton wicks. After drying, the wicks are cut to the required size and fitted

suitably on the crackers and other fireworks. The fuses are inserted and

allowed to dry further. For drying the products, specially prepared platforms

are used. Fireworks after drying are packed in small boxes manually. Later,

are placed in large bundles. Push carts and trucks are used to transfer the

goods within the factory and to warehouses. Then daily wastes are collected

and burned the very same day itself in a proper manner. The flowchart for

fireworks manufacturing is shown in Figure 1.3.

Figure 1.3 Flowchart representing the manufacture of fireworks

Packing

Drying the products

Top side of the shell was plugged by the wet sand and fuse was inserted

Sieving and mixing of all the required chemicals to remove the grits and to

attain homogeneous mixture

Chemicals are filled into the shell (bottom side of the shell was plugged by

wet sand)

Fuse made from the gun powder coated threads and

cut into required size

Shells are prepared from paper rolls and cut into the

required size

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Some of the photographs for fireworks manufacturing are as

follows:

Connecting chinesecrackers with twine

Preparing long sticks for ground chakras

Flowerpots manufacturing

Filling explosive chemicals for aerial display fireworks

Making sparklers

Figure 1.4Photographs showing manufacture of fireworks

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1.4 CHEMISTRY AND MECHANISMOF REACTION

INFIRECRACKERS

The flash composition used in fire crackers consistsof an oxidizer,

potassium chlorate or barium nitratewith aluminium and sulphur. Sulphur acts

as afuel. The minimum energy required to initiate the ignition is called as the

activation energy (Ea). When a flash composition is ignited by itsfuse,

initially, the sulphur melts and the interactionbetween atoms increases. This

results in more atomswith energies exceeding Ea. The reaction rate

increaseswith the increasing rate of energy release that leads to thermal

runaway at a lower temperature and explosion occurs at a lower temperature.

Further, rise of reaction and liberating more heat, leads to an explosion.

Figure 1.5 Flow chart for the mechanism of firecracker bursting

Increase of temperature

Number of atoms with energy greater than Ea increases

Rate of reaction increases

Rate of energy increases

Temperature of materials rises

Cycle repeats again

Thermal run away = Ignition

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The minimum quantity ofthe material needed to produce an

noise.In fire crackers, a different mechanism takesplace as shown in the

flowchart (Figure 1.5).In a confined system, the hot gases, that are produced,

can build up substantial pressuredriving the gases into the high energy

mixturesand causing a violent reaction (Kosanke, 2004). High

explosivereactions produce high noise.

1.5 ROLE OF PARTICLE SIZE

The effect of noise level from different types offirecrackers mainly

depends on the particle size of the chemicals irrespective of the compositions.

It is clearthat as the particle size decreases, the pyrotechnicmixture is effective

in producing sound (Thanulingam, 2009). Variation of the particle-size of the

fuel in any mixture changes the burning rate. As particle size decreases, there

is a decrease in its melting enthalpy and melting temperature of chemicals.

The melting temperature depression is theorized to be an effect of the

increased fraction of surface atoms with decreased particle size (Brown,

2001). As the particle size decreases, the surface to volume ratio increases

dramatically and it increases the number of contact points with the oxidizer

and improves mixture homogeneity (Fathollahi, 2004). Inmissile applications,

different thrust timeprofiles are required. To predict the performance of solid

rocket motors during the design stage, the burnback steps of the solid

propellant must be known. If the properties of the propellant are fixed, the

main parameter affecting the thrust-time profile is the grain geometry. The

burning of the propellant changes the grain geometry during the operation of

the rocket motor, which in turn causes the thrust of the motor to change

(Puskulcu, 2008). Ignition temperature is earlier for fine size chemicals and

exhibits high thermal energy. If particle sizes are reduced, the

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sensitiveness to impact and friction is also increased and thus leads to hazards

in powder handling (Sivapirakasam, 2006). So, reducing the particle size of

the fuel, oxidiser and ignitor in flash powder composition of fireworks may

lead to increase the reactivity.

1.6 NANO TECHNOLOGY IN EXPLOSIVES

It is a well-known fact that in addition to its molecular structure,

the microstructure of a material is important in determining its properties.

Controlling structures at the micron and nanolevels are therefore essential to

new discoveries. Nanotechnology is emerging as one of the principal areas of

investigation that is integrating chemistry and materials science (QianQiu

Zhao, 2003). Nanosized aluminium powders can successfully replacing the

micron-sized Al powder in pyrotechnics is used to increase the combustion

efficiency and reduce agglomeration of the combustion products. Two stages

of oxidation are observed at temperatures in the range of 500 740°Cfor the

nano Al powder and precursor micron-Al powder. The mass gain for the first

oxidation stage of the nano powder is3.5 times which is higher than that of the

micron-sized powder. A decrease of the activation energy for Al oxidation has

been found for the nanoAl powder when compared to that of the precursor

aluminium powder. For the activated nano sized powder, the major part of

aluminium is oxidised below 740°C with the formation of -Al2O3, whereas

for the micron-size powder, the major part of aluminium is oxidized in the

range of 740 1000°C with predominant formation of -Al2O3(Pivkina, 2004).

Nano powders have more aluminium oxide content than micron

powders. This is because the surface area to volume ratio increases

dramatically as particle diameter decreases the oxide shell. As particle size is

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reduced, the active aluminium content is decreased such that a trade-off may

exist between the benefits of working on the nanoscale and the diminished

purity of the Al particle. Although the reactivity of the particle may not be

strongly influenced by the thickness of the oxide shell, the increased Al2O3

content of nanopowders may significantly influence the microstructure and

macroscopic properties of combustion synthesized alloys. Incorporating

nanoscale Al particles is also shown to promote a more complete reaction at

high reaction rates (Granier, 2004).

With nano sized aluminium (nAl) particles, the specific surface

area increases creating easier ignition and increased burn rates. When a pile of

nAl powder is ignited in the open atmosphere, a flame front spreads across the

surface. In contrast, ignition and flame spread cannot easily be obtained with

micron-sized aluminium powder. Increasing particle size decreases

propagation velocity and widens the fingers. Decreased propagation velocity

is due to the lower specific surface area of the particles. Because of this

decreased propagation velocity,the fingers have more time to diffuse laterally

creating wider fingers. Furthermore, the higher thermal conductivity of larger

particle beds likely aid in the lateral diffusion of the flame (Malchi, 2007).

Great attention is recently focused on solid propellant formulations containing

ultra-fine energetic particles, particularly Al nano particles, because of

advantages such as significant increase in propellant burning rates, shorter

ignition delays and shorter agglomerates burning times.

Nano particles can enhance the linear burning rate of aluminized solid

propellants by 100% or even more. The post-burning analysis shows the

better combustion efficiency of nano sized in comparison with micro-sized

aluminized propellants (Galfetti, 2007).

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1.7 CHEMICALS USED IN FIREWORKS

Explosives rapidly release large amount of energy. These mixtures

react violently, producing light, colour, smoke, heat, noise and motion. Most

of the compounds and mixtures of the fireworks are solids and are designed to

function in the absence of external oxygen.

The chemical reactions involved are of:

Electron transfer

Oxidation reduction type

The materials used in fireworks manufacture can be divided into

the following categories:

Oxidizing agents

Fuels

Colour producing agents

Reducing agents

Binders

Substances which improve particular effects

Substances which produce smoke, colour, light

Neutralisers which reduce the sensitivity of mixture

Stabilizers which help to prevent chemical reactions

Substances which accelerate or retard the combustion

Production aids such as solvents and lubricants

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1.7.1 Oxidizing agents

The major compositions of fireworks are oxidizing agents, fuels

and colour producing agents which include ammonium nitrate, potassium

nitrate, barium nitrate and sodium nitrate. These produce oxygen to burn the

mixture. Oxidizers are usually nitrates, chlorates or perchlorates. The

common oxidizers are nitrates. These are made up of a metal ion and the

nitrate ion. Nitrates only give up 1/3 of their oxygen. The resulting equation

(1.2) would look like this:

(1.2)

Other oxidizers are chlorates. Chlorates give up all of their oxygen

causing a more spectacular reaction. Unfortunately, this also makes the

chemicals extremely explosive. An example of a chlorate giving up its oxygen

by the reaction as below:

(1.3)

Perchlorates have more oxygen in them but are less likely to

explode if one drops them than chlorates. Again, these are made up of a metal

ion and perchlorate polyatomic ion.

1.7.2 Fuels

Fuels are classified as follows:

Metallic fuels

o Aluminium, Zinc, Magnesium, Iron and Titanium.

Organic fuels

o Stearic acid, Shellac, naphthalene etc.

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Inorganic fuels

o Sulphur, Charcoal etc.

Generally, aluminium is used as a fuel for fireworks industry. This

is because of easy availability and low cost.

1.7.3 Colour producing agents

Copper Sulphate - Blue

Strontium Nitrate - Red

Antimony Sulphide - White smoke

Copper Carbonate - Blue smoke

The above chemicals are sieved and mixed in the respective ratios

to produce varieties of colours in the fire crackers.

1.7.4 Reducing agents

The second elements of fireworks are the reducing agents. The

reducing agents burn the oxygen produced by the oxidizers to produce hot

gasses. Two examples of reducing agents are Sulphur and Charcoal (carbon).

These react with oxygen to form Sulphur Dioxide (SO2) and Carbon Dioxide

(CO2) respectively.

Usually, two reducing agents are combined. This results in

speeding or slowing the reaction. Therefore, the reducing agents are used to

control the speed of the reaction. Also, metals are often generally added to

speed up the reaction. However, finer the powder, faster the reaction.

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1.7.5 Binders

Binders hold the mixture in a lump like a star in aerial fireworks. In

order to form a star, two main elements are used. These two are dextrine

dampened by water, or a shellac compound dampened by alcohol. These are

rolled and then cut, or the mixture is forced into a paper tube, and pushed out

with a dowel. Then the stars are cut as they come out.

1.8 PROPERTIES OF FLASH POWDER CONSTITUENTS

1.8.1 Potassium nitrate

Potassium nitrate is a water-soluble mineral that occurs naturally

and is available in crystal or powder form. Potassium nitrate is also known as

saltpetre. Potassium nitrate is usually white or greyin colour but impurities

sometimes cause it to appear yellow or brown. Crystalline potassium nitrate is

typically translucent and tends to fracture unevenly. Potassium nitrate burns

with a violet flame when subjected to a flame test. This is due to the

potassium content of the mineral. Potassium nitrate has an orthorhombic

crystal structure at room temperature, which transforms to a trigonal system at

129°C. Upon heating to temperatures above 560°C, it decomposes into

potassium nitrite, generating oxygen. Potassium nitrate is typically used to

make explosives, fireworks, matches and fertilizer. Potassium nitrate is also

used in food preservatives and facilitates the manufacture of nitric acid and

glass. It is the safest oxidizing agent though it can be dangerous in some

situations when mixed with fine metal powder. This should be free from

carbonates, sodium, calcium and magnesium salts and nitrates. Figure 1.6(a)

shows the image of Potassium nitrate powder for fire crackers manufacturing.

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Figure 1.6 (a) Photo image of potassium nitrate powder

1.8.2 Sulphur

Sulphur is a multivalent non-metal, abundant, tasteless and

odourless material. In its native form, sulphur is a yellow crystalline solid.

The crystallography of sulphur is complex. Depending on the specific

conditions, sulphur allotropes form several distinct crystal structures. The

major derivative of sulphur is sulphuric acid which is the most important

chemical used as industrial raw material. Sulphur is also used in batteries,

detergents, fungicides, manufacture of fertilizers, gun power, matches and

fireworks. Other applications include corrosion-resistant concrete that has

great strength and is frost resistant, for solvents and in a host of other products

of the chemical and pharmaceutical industries. Sulphur burns with a blue

flame concomitant with formation of sulphur dioxide, notable for its peculiar

suffocating odour. Sulphur differs from most combustible dust by having a

relatively low ignition temperature. The ignition temperature of sulphur dust

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clouds varies upward from approximately 190ºC. Dilutions of sulphur with

inert solids are not effective in raising the ignition temperature. Whenever the

handling of sulphur creates a dust cloud, an explosion is possible. Besides its

low ignition temperature, a dust cloud can create a static electric charge

among the air-suspended sulphur particles. The static discharge can readily

cause ignition.Sulphur dust explosions occur with very rapid discharge of

flame and pressure waves. When confined or otherwise restricted in a

building, pressure waves can cause a great deal of damage.Sulphur reacts

violently with strong oxidizing agents, such as nitrates and chlorates. It also

undergo chemical changes moderately with alkalis.Figure1.6 (b) shows the

image of Sulphur powder.

Figure1.6 (b) Photo image of Sulphur powder

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1.8.3 Aluminium powder

Aluminium is a light, silvery-white to grey, odourless powder. It is

a fuel having ignition temperature of 700°C. It is a reactive flammable

material. Aluminium powder is a fine granular powder made from

aluminium. In form of powders, aluminium is used for several applications

such as manufacture of slurry, explosive and detonators, thermit process used

for manufacture of ferro alloys and for specialised welding applications such

as rails, pyrotechnic to manufacture crackers, sparkles and other pyrotechnic

products; manufacture of aluminium paste, paints and several powder

components used in automobiles. The most important property is that it

undergoes a vigorous exothermic reaction when in contact with water.

Aluminium powders are used in paints, pigments, protective coatings, printing

inks, rocket fuel, explosives, abrasives and ceramics; production of inorganic

and organic aluminium chemical are used as catalysts. Pyro powder is mixed

with carbon and is used in the manufacture of fireworks. The coarse powder is

used in alumina thermics (thermite reaction). Mixtures of aluminium powder

and air are ignitable over a wide range of concentrations and can cause violent

dust explosions. Highly flammable hydrogen can form a contact with water or

other chemicals and present an additional risk of explosion, and possibly be

responsible for causing a secondary dust explosion. The strong electrostatic

charge on aluminium powder can lead to electrical discharges, which can

possibly ignite a cloud of aluminium.

In the manufacture of fireworks, aluminium is added in large

amounts to give fireworks the required brilliance. This is used in finely

powdered or chip form in fireworks. The aluminium must be as free as

possible from oxide and from impurities which promote oxidation on storage.

Aluminium powders are prepared in hammer mills, in ball mills or by

atomization. Powders made by this method are mixed with stearic acid or

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other lubricants so that itforms tiny flat plates or irregular shape and large

surface area. Figure 1.6(c) is the photo image of aluminium powder in

micron size for fireworks manufacturing.

Figure1.6(c)Photo image of aluminium powder

1.9 MANUFACTURE OF QUICK MATCHES OR FUSES

Flash powder is mixed with dextrin in mixing room. The mixture is

moisturised with water. Then the mixture is taken to the dipping room. The

different number of plys of thread is dipped in the above solutions and the

dipped threads are dried in the same room by hanging. Then the threads are

Then, these threads are coated with flour gum and finally dried. Now, they are

ready for use as a quick match or fuse, to ignite the fire crackers.

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1.10 MANUFACTURE OF FLASH POWDER

Pyrotechnical grade aluminium powder, potassium nitrate and

sulphur are mixed in definite proportion in the white powder mixing room by

hand over rubber mat on the floor of the mixing shed. The mixture is sieved

for 5 to 6 times to make a homogeneous mixture. Now, the mixture is ready

for filling operation. The mixture is used for manufacturing Chinese crackers,

cake bombs and maroons etc.

1.11 EXPLOSION PRESSURE

The various gases that are formed during the combustion of

fireworks chemicals due to the reaction between the oxidiser, ignitor and fuel

as per the equation (1.1). Gases like nitrogen oxide, carbon dioxide and

potassium sulphide are emitted during the combustion. Expanding gases with

high thrust force will provide the propelling action. This is called ballistic

behaviour. In space applications, this behaviour is mainly utilised to lift the

space rockets. In fireworks industries, aerial display fireworks and rockets are

being lifted at elevated height by the burning of chemicals.

Flash powder is the mixture of aluminium, sulphur and potassium

nitrate, which is the main raw material for manufacturing the fire crackers.

The maximum pressure is developed during the confined burning which

decides the explosivity of the crackers. The explosivity and ballistic pressure

of the explosives can be recognized by finding the maximum pressure

developed during burning of air tight pressure vessel.

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1.12 ENVIRONMENTAL POLLUTION

During the manufacture of fireworks, many varieties of chemicals

like oxidising agents, fuels, colour producing agents, special effects creating

chemicals, substances to produce smoke, binders, neutralisers, stabilisers,

combustion accelerators / retardants are added (Ghosh, 1981). The chemicals

used for fireworks manufacturing are potassium nitrate, potassium chlorate,

potassium per chlorate, sodium oxalate, charcoal, sulphur, manganese,

aluminium, iron fillings, aluminium chips, strontium nitrate, barium nitrate,

sodium nitrate, calcium carbonate, pitch, dextrin, stearic acid, boric acid,

linseed oil, etc. Bursting of fireworks cracker results in the release of

pollutants like sulphur dioxide(SO2), carbon dioxide (CO2), carbon monoxide

(CO), nitrogen oxides (NOx), suspended particles and several metals like

aluminium, manganese and cadmium, etc., both as metals and oxides which

pose serious health hazards (Conkling, 1985). Nitrate was mainly formed

through homogeneous gas-phase reactions of NO2, while sulphate was largely

from heterogeneous catalytic transformations of SO2. Iron (Fe) could catalyze

the formation of nitrate through the reaction of Fe2O3 with HNO3, while in the

formation of sulphate (Ying Wang, 2007).

event recorded extremely high 24-h particulate matter of upto 10 microns

(PM10) levels shows 317.2 616.8, g/m3, which is 6 12 timesgreater than the

World Health Organisation standard(SayantanSarkar, 2010).

1.13 SAFETY

During the fireworks operations impact, friction, spark and heat

stimuli may occur under certain conditions, one or more stimuli may be

enough to cause ignition of the compositions. The sensitiveness of a

pyrotechnic mixture depends on, amongst other things, the type, compositions,

purity and moisture content of the chemicals used.

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The hazards associated with combustible dusts have been recognized

for the past 200 years. In powder handling industries, dust explosion can be

initiated by the rapid combustion of flammable particulates suspended in air.

Fireworks industries are mostly prone to fire and explosion. In fireworks

industry, different chemicals like fuels, oxidisers, ignitors and special effect

chemicals are mixed thoroughly by manual effort. All the chemicals used in

the industries are sensitive to friction, impact and static charge. Many fire and

explosion accidents were reported due to electro static discharge. A potential

hazard of nanopowders that appears to have received little attention to date is

their explosibility. Most organic materials, many metals and even some non-

metallic inorganic materials, if finely divided and dispersed in air, will

explode if ignited by a strong enough ignition source. During processing and

handling of powders, knowledge of how various powders react in the

presence of air is essential. Factors such as chemical composition, particle

size and size distribution, particle shape, chemical additives, surface coatings

and variations in gaseous environments have direct effect on the fire and

explosion sensitivity of a material. Dust clouds are usually generated during

processing, which produce flammable gases or vapours (for

example,hydrogen) in the presence of moisture, which compounds the danger

of explosion.

The upper size limit for the formation of an explosive dust cloud is

in the order of 500 µm. The violence of the dust explosion and the ease of

ignition isincreased as the particle size decreases, though for many dusts the

trend begins to plateau at particle sizes of the order of tens of microns. No

lower particle size limit has been established below which dust explosions

cannot occur. Ignition energies for dust clouds are usually higher than for

gases or vapours, typically of the order of a fraction ofmJ for gases and 1 to

10 mJfor dusts. The overpressures generated by a gas or dust explosion are

however, of comparable magnitude. There is therefore, the potential for

nanopowders to give rise to a significant explosion hazard.

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The primary factor influencing the ignition sensitivity and

explosion violence of a dust cloud is the particle size or specific surface area

(ie, the total surface area per unit volume or unit mass of the dust). As the

particle size decreases the specific surface area will increase. Electrostatic

charges can build-up on powders during transport, handling and processing.

The charging tendency has been found to drastically increase with increasing

specific surface area. Nanopowders, because of their large specific surface

areas, may well become highly charged in use and thus be their own ignition

source if the powder is dispersed to form an explosible cloud.

Dusts, like gases and vapours, can only form explosive clouds if the

dust concentration lies between certain limits, known as the Lower Explosion

Limit (LEL) and Upper Explosion Limit (UEL). For dusts the LEL is

sometimes referred to as the Minimum Explosive Concentration (MEC).

Actual values will depend on the dust composition, the particle size

distribution and the method of determination, but typical values are around

50-100 g/m3 for the lower limit (LEL) and 2000-3000 g/m3 for the upper limit

(UEL). If the dust is not combustible or reactive with the surrounding gaseous

atmosphere, there cannot be a dust explosion. The ignition energy must be

high enough to ignite the dust particles.

The parameter usually used as a measure of the ease of ignition of a

dust cloud is the Minimum Ignition Energy (MIE), which is defined as the

lowest electrical energy stored in a capacitor which upon discharge is

sufficient to ignite the most easily ignited dust cloud. Values for dusts are

typically in the range of 1 to 10 mJ. Dispersion and degree of agglomeration

affect the combustion as they change the effective local dust concentrations

and the effective particle size respectively. A more evenly dispersed dust will

burn more easily. The degree of dispersion is usually dependent upon the way

the dust is dispersed and the level of turbulence in the dust cloud. Increasing

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the initial temperature lowers the ignition energy and the LEL. Maximum

explosion pressure, however, decreases, as the air density is lower and thus

the mass of oxygen available for reaction is lower. Increasing the initial

pressure increases the explosion pressure, due to the increased air density and

lowers the ignition energy. Further increasing the turbulence of the dust cloud

will increase the rate of reaction and thus the rate of pressure rise.

Less oxygen in the air reduces the explosion severity, as it limits

the rate of combustion of the dust and increases the ignition energy. On

reducing the oxygen content of the air by diluting with an inert gas, such as

nitrogen or carbon dioxide, an oxygen concentration is reached below which

the explosion is completely suppressed. This oxygen concentration is known

as the Limiting Oxygen Concentration (LOC). The moisture content of the

dust will affect the ease of ignition and its ability to sustain an explosion.

Increasing the moisture content increases the ignition energy, for some dusts

and this increase can be exponential and reduces the explosion violence (the

water vapour produced acting as an inert heat sink). The presence of a

flammable solvent on the dust will have the opposite effect, lowering the

ignition energy and possibly increasing the explosion violence.

Electro Static Discharge (ESD) is the sudden and momentary

electric current that flows between two objects at different electrical

potentials. This can cause severe damage to equipment and fires and explode

if the air contains combustible gases or particles.

1.14 STATEMENT OF THE PROBLEM

At present, micron sized flash powders are used to prepare the fire

crackers. But due to this, enormous gases and smokes are being released when

they are fired. this is due to the increased amount of powders for the fireworks

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products. This creates a major environmental impact by polluting the air in

the atmosphere with various toxic gases and smokes. To reduce pollution,

lesser amount of chemicals inside the crackers should be used with high

reactivity. There are many methods to improve the reactivity of flash powders

like changing the composition, addition of chemicals, substitution and

reducing the particle size.

In case of nano flash powders, the quantity of the powder required

to perform the crackers has been reduced and thus the release of gas and

smoke to a lesser amount. Hence the environmental pollution will be greatly

compromised. In this research work, nanotechnology is applied in pyrotechnic

field to improve the reactivity of the flash powders as well as to reduce the

environmental impact due to existing firework products.

There is no research conducted to control the noise level with the

use of nano powders in this field. With nano size chemicals, the specific

surface area increases which will cause easier ignition and increased burn

rates.

1.15 AIM OF THE RESEARCH

The major aim of this research is to find the innovative properties

of nano chemicals that are being used in the fire crackers manufacturing. At

present, micron sized chemicals serves the purpose in fireworks to enlighten

the festivals in the form of noise, light, heat and amazing displays in aerial.

The performance can be further improved by many ways, but without

affecting the environment and human health. Without increasing the quantity

of the chemicals inside the fire crackers, the performance can be enhanced by

replacing the micron sized chemicals by nano sized chemicals.So, this

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research work focuses to attain the best and safe pyrotechnic materials with

environment friendly aspect. The aim of the research work is:

to study the effect of nano sized flash powder composition in

the noise emitting cake bombs.

to find out the combustion efficiency of the nano powders

through thermal analysis.

toanalyse the effect of nano flash powder crackers in the

environment by conducting gas emission analysis, suspended

particulate measurement and metal content analysis.

tomeasure the explosion pressure of micron and nano sized flash

powder in a confined space.

to measure the intensity of flame in open environment for

various trials of flash powder.

to evaluate the safe method for handling the flash powder by

studying the impact, friction and electro static discharge

properties.

to find out the optimum eco-friendly nano flash powder

composition for fire crackers.

1.16 NEED OF THE STUDY

Fireworks are the unique sources of atmospheric pollution that

generate massive quantities of pollutants within a short span of time. During

the festivals, like Deepavali, lantern and other celebrations like New Yearin

India and abroad, pollutants range in the atmosphere are with high ambient

concentrations. There are many varieties of crackers in global market by

various manufacturers that is giving priority to performance interms of noise

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level by adding various chemicals. However, there are limited products for

which the main focus is to envirofriendly with required performance.

Reduction of chemicals is the best way to reduce the pollution, but

if do so, the performance of fireworks cannot be achieved. To reduce the

pollution, lesser amount of chemicals in the crackers should be used with high

reactivity. There are many methods to improve the reactivity of flash powders

like changing the composition, addition of new chemicals, and reducing the

particle sizes. In case of nano flash powders, the quantity of the powder

required to perform the crackers has been reduced and thus the release of gas

and smoke will be reduced to a lesser amount, thereby the environmental

pollution greatly reduced.In view of this, it is necessary to develop nano

materials by introducing substances capable of imparting the most required

properties.

1.17 SCOPE OF THE STUDY

There are many fireworks products such as noise emitting, light

emitting and scintillating effects. The maximum limit for the performance for

the above products has not been fixed except noise. The chemicals used for

fireworks products are different in nature according to the requirements. All

the chemicals and compositions cannot be taken for the study. Generally,

many products having aluminium as a fuel, potassium nitrate as an oxidiser

and sulphur as an ignitor are used to make noise. In market, different fire

crackers are availablebut varying in their shell size, shell thickness, degree of

compactness and period of bursting. To ease the study, cake bomb one of the

noise emitting fireworks products has been taken as a reference to ascertain

the influence of the nano powder. So, this research work concentrates only on

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noise emitting fire cracker named cake bomb made up of nanoflash powder

composition.

1.18 OBJECTIVES OF THE STUDY

The objective of this work is

to study the effect of nano sized flash powder composition in

the noise emitting fireworks by manufacturing cake bomb and

conducting noise level analysis. The results are to be compared

with existing micron sized powders.

to study the combustion efficiency, flame parameters,

environmental impact, explosivity of the nano powders through

thermal analysis, open bed burning analysis and maximum

explosion pressure development in a closed vessel ignition.

to find out the effect in environment by crackers made up of

nano chemicals by conducting gas analysis, suspended

particulate measurement and metal content analysis.

to develop new approach to safe handling of nano powders for

fireworks product manufacturing by finding the nature of

sensitivity of the chemicals for impact, friction and electro static

discharge.

to derive the best nano flash powder composition for fireworks

with safety and envirofriendly.

1.19 METHODOLOGY

The methodology of the thesis is as below

Synthesis and characterization of nano Pottasium nitrate,

Sulphur & Aluminium

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Thermal analysis using DSC/DTA to find the peak temperature

& evolved heat.

Flame analysis to measure the flame height & width

To find the maximum explosion pressure

Safety analysis by finding the impact, friction & electrostatic

discharge sensitivity

Manufacture the cake bomb using the nano chemicals.

Performance analysis by measuring the noise level

Analysis of post blasting for metal content in the residue, gas

emission analysis

1.20 OPERATIONAL DEFINITION AND CONCEPT

Aluminium powder: Most widely used fuel in modern

pyrotechnics; produces a brilliant, bright flame and silvery-white sparkling

effects in sparklers, gerbs, fountains, waterfalls, etc., The particles are

available in several of different shapes, such as flakes and grains.

Cake bomb: Cake bomb, one of the noise emitting crackers is

being manufactured in the fireworks industry.

Charcoal: Charcoal is used widely in pyrotechnics. Charcoal is

the by-product of the burning of organic substances. It contains impurities

which make it more reactive, and therefore it is used more often than pure

carbon in fireworks. It can be made from any types of wood. Charcoal from

soft woods, such as grape vine or willow, is good for fast-burning

compositions like black powder, whereas charcoal from hard woods like pine

are used to create long-lasting spark effects.

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Exothermic:A term used to describe the generation of heat from a

chemical reaction.

Explosives: Explosives always mean chemical materials to create

an explosion, and are not generally referred to as pyrotechnics. It is a material

synthesized or mixed deliberately to allow the very rapid release of chemical

energy. Also, a chemical substance that is intrinsically unstable and liable to

detonate under conditions may reasonably be encountered.

Fire crackers: Noise emitting fireworks

Fireworks: Fireworks can be categorized as a specialized class of

pyrotechnic and explosive devices to create visual and noise effects for their

entertainment value. Fireworks include fire crackers, skyrockets, smoke pots,

whistlers, shells, and Roman candles.

Flash powder: Flash powder is the mixture of potassium

nitrate,sulphur and aluminium which is the main raw material for

manufacturing the fire crackers.

Gun powder: Gun powder is a mixture of potassium nitrate,

sulphur and charcoal with definite ratios.

Heat of combustion:The heat generated when a substance is

completely oxidized to produce gases such as sulphur dioxide, carbon

dioxide, and nitrogen dioxide.

Lower explosive limit (LEL): The lowest concentration of a

flammable vapour in air at which explosion or combustion can occur.

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Oxidizing agent:A material capable of bringing about oxidation

(the loss of electrons) in other materials, while is itself reduced (gains

electrons).

Potassium Nitrate: Potassium compounds are used as oxidizers.

Pyrotechnics: Pyrotechnics generally refers to chemical materials

to create fire, light, heat, noise, or gas emission, but not explosions. The

manufacture of fireworks, signal flares, and so on, involves the mixture of

different chemicals to achieve various visual and auditory effects. Chemicals

used in pyrotechnics include many explosive inorganic compounds such as

potassium nitrate, metal perchlorates, dichromate, powdered metals, and

phosphorus.

Safety:Safety is the proper planning of work, proper usage of tools,

an exercise of good judgement and intelligent supervision. Experience proves

that majority of the accidents are preventable.

Sulphur: Sulphur is one of the basic ingredients for many

fireworks. Having the low melting temperature initially melts and releases the

energy and thus induces the chemical reaction.

Upper Explosive Limit (UEL): The highest concentration of a

flammable vapour in air at which explosion or combustion can occur. Above

this concentration, the vapour-air mixture is too rich to combust.

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1.21 OVERVIEW OF THE THESIS

This thesis is organized into nine chapters. A brief chapter wise

outline of the thesis is given below:

The present chapter presents an introductory survey of fireworks

products, fireworks manufacturing, chemicals used and their properties,

explosivity of the fire crackers, safety during the handling of flash powder

and environmental issue of the fireworks.

Chapter 2 gives a literature survey of nano powders in explosives,

propellants, synthesis of nano aluminium powder, nano flash powder,

combustion analysis of micro / nano sized propellants, sensitiveness study for

the chemicals and measurement of explosivity / explosion pressure during the

combustion of explosives and environmental pollution due to the fireworks

products.

Chapter 3 of this thesis reports the experiment on nano aluminium

powder in flash powder. Aluminium powder is synthesized to nano size and

the other two chemicals are taken in micron size. Various compositions are

prepared by using the chemicals of micron sized KNO3 and S with various

nAl powders. Then the fire crackers are manufactured using these chemicals

and tested for their noise level.

Chapter 4 explains theexperiments conducted using flash powder

constituents like potassium nitrate, sulphur and aluminium in nano size. Then

the nano flash powders are mixed with micron powders and conducted

thermal and safety analysis. Cake bombs were manufactured and their noise

level is studied.

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Chapter 5 deals with burning of flash powder chemicals in the open

bed atmosphere. The flame height and width are measured by using high

speed camera still technique. Then cake bombs were manufactured and their

noise level was checked. Then the noise level data were checked for

correlation with flame parameters.

In chapter 6, measurement of explosion pressure of flash powder in

a closed vessel is elaborated. Also, explosivity of the nano flash powder cake

bomb is measured.

Chapter 7 describes the post blasting analysis of nano flash powder

cake bombs, in order to find the pollution. Here, analysis of emission gases

and metal content in the ash are carried out.

In chapter 8, measurement of minimum ignition energy to assess

the sensitivity to electro static discharge for the nano flash powder is analysed

using the Hartmann apparatus.

Chapter 9 is the concluding chapter in which the major

contributions of the research study are highlighted. Guideline for future work

is also included in this chapter. A bibliography of the literature relevant to the

research study is listed at the end of this thesis.