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Unit I
High energy materials
Introduction, classification (explosives, propellants and pyrotechnics), historical overview.

Short introduction to detonation, density, deflagration, combustion, heat of formation, heat of

detonation, stability and sensitivity, thermodynamics (detonation parameters, combustion
parameters), new developments,

Polymer Bonded Explosives (PBXs), secondary explosives and newly developed materials,
new primary explosives, Oxidizers, experimental characterization of energetic materials
(sensitivities, long-term stabilities, Gap test, etc.),

Significance of high nitrogen content, heterocycles, explosophoric groups, energetic salts,

nitration reactions, energetic materials of the future.

The History of Explosives

All explosives have three features:

1) Explosions are exothermic!

2) Explosions produce large volumes of gases!
3) Explosions must occur extremely rapidly!

If an explosion is not rapid then there wouldn’t be any damaging output.

Oxygen often has to come from within the molecule.

Nitro groups are almost always found in explosives.

Both are C7H7NO2!

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Gunpowder was the first known explosive, and it was used initially for
fireworks and firecrackers.

These explosives were used in China, India, and the Middle East, but
its ingredients were not recorded until about 1000 A.D.

Gunpowder is a physical mixture of saltpeter (potassium nitrate), charcoal, and sulphur.

It burns very rapidly, by producing large amounts of hot solids

and gases

2KNO3 + S + 3C  K2S + N2 + 3CO2

The first documented use of gunpowder as a weapon was in the form of bombs
used by the army of the Kingdom of Spain in the 13th century. Since
then, gunpowder has been used in firearms, artillery, and even as rocket
propellant.

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NITROGLYCERIN
Ascanio Sobrero (Italian chemist) first synthesized nitroglycerin in 1847.
He mixed HNO3 with glycerin and got an oil.
HNO3
He tasted the oil...

“Putting a trace on the tongue but not swallowing it causes a very painful, pulsing headache
and makes the limbs very weak.”

In later years, it was shown that nitroglycerin

releases nitric oxide (NO) in the body, which dilates
blood vessels.

4C3H5N3O9(l)  12CO2(g) + 6N2(g) + 10H2O(g) + O2 (g)

NOBEL’S DYNAMITE IDEA

Dynamite - from Dynamis, meaning power

Alfred Nobel’s family owned an explosives factory

that started to sell nitroglycerin in 1864 in
Stockholm, Sweden.

An accidental explosion killed his brother, Emil Nobel, but the Nobel company expanded to
have factories in 11 countries, even the US.

Eventually he found that mixing nitroglycerin with diatomaceous

earth (naturally occurring, soft, Siliceous sedimentary rock that can
be crumbled into a fine white to off-white powder.), a stable putty
could be made.

Nobel was a pacifist and he believed the The problem was that nitroglycerin is
destructive power of dynamite would be a unpredictable and will explode on shock or
deterrent to war. heating.

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DYNAMITES…..

 Dynamite is one of the most widely used high explosives in

blasting operations.

 Dynamite usually will be found in sticks or cylindrical form and

wrapped in buff, white, or colored waxed paper.

 It comes in a variety of diameters and lengths.

DYNAMITES…..
There are basically three types of dynamites: straight, ammonia, and gelatin.
 Straight dynamite (light tan to reddish-brown in color) has a
pungent, sweet odor because of its nitroglycerin content.
 A loose, slightly moist, oily mixture.
 Inhalation of the nitroglycerin fumes will usually cause a severe
and persistent headache. Straight dynamite
 It is highly sensitive to shock and friction and produces toxic
fumes when it is detonated.

 Ammonia dynamite (light tan to light brown in color) has a

pungent, sweet odor because it also contains some
nitroglycerin and the fumes will cause a severe headache.
 Have a pulpy, granular, slightly moist, oily texture.
 It is less sensitive to shock and friction than straight dynamite
because a part of the nitroglycerin content has been replaced
Ammonia dynamite with ammonium nitrate and nitroglycol.

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DYNAMITES…..

 Gelatin dynamite is insoluble in water and varies from

a thick liquid to a tough rubbery gelatinous substance.
 It contains nitrocellulose.
 It is used in wet blasting operations and for blasting
hard rock.
If crystals appear on the outside of a
cartridge of dynamite, it means that
nitrate salts have leached out and
solidified, making the dynamite
extremely unstable.

If it appears to be leaking any oily

substance, extreme caution should
be taken. This may indicate the
presence of nitroglycerin.

Ammonium Nitrate
 Synthesized in 1659 by J. R. Glauber.
 It is one of the least sensitive and most readily
available main charge high explosives.
 It is widely used as a blasting agent, an ingredient in
certain dynamites, and as a fertilizer.

Various other reactions

Pure ammonium nitrate does When ammonium nitrate occur during decomposes.
not explode easily and can be decomposes, it primarily These makes other gases
handled safely. breaks down in to Nitrogen, like Ammonia, and
The risk of explosion water vapour and oxygen Nitrogendioxide.
increases if it is contaminated gases.
with impurities
It decomposes at high temp.
and if confined can explode
Nitrogendioxide causes the
This rapid release of gases orange-red color sometimes
causes an explosion. seen in smoke from these
explosions.

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Ammonium Nitrate….
 Depending on its purity, it will range in color from white to buff-
brown and will have a saline or salty taste.

 To facilitate identification, colored dyes may be also added to

the product.
Ammonium Nitrate Prills
 It is usually found in the form of small compressed pellets,
commonly known as prills.
 In order to detonate ammonium nitrate, the use of a booster is required.
Commercially, Pentolite (Pentaerythriol tetranitrate phlegmatized with TNT) and
RDX are used as a booster, while the military will often use TNT as the booster
Pentolite
1,3,5-Trinitro-1,3,5-triazinane

OR

Trinitrotoluene (TNT) Cyclotrimethylenetrinitramine

Pentaerythriol tetranitrate (PETN)

ANFO (Ammonium Nitrate and Fuel Oil)

When fuel oil is added to the prills,

the mixture then becomes ANFO
(ammonium nitrate and fuel oil).

It is insensitive, and a detonator

alone will not cause ANFO to
detonate.

In order to initiate ANFO, it will require an initiating system and a booster.

ANFO is a commonly used explosive for

commercial blasting.
It has a slow rate of detonation that makes it
ideal to use in quarry and other blasting
applications.

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Water Gels
 Water gel is an explosive material containing substantial
portions of water, oxidizers (ammonium nitrate, sodium
nitrate and/or calcium nitrate) and fuel (aluminum), plus a
cross-linking agent which may be a high explosive or
blasting agent.

 The addition of aluminum to the water gel gives it a silver

Slurry Water gel explosive appearance.

 It is most likely packaged in a plastic “sausage tube”

and has metal ties on the ends.

 In recent years, water gels and emulsions have almost

completely replaced dynamite.
Water gel plastic explosive

Water Gels…. Developed in 1940s

Composition: Gelling agents- Methylamine
Polyvinyl alcohol, guar gum, dextran nitrate
gums, and urea-
formaldehyde resins. Methylamine Polyvinyl Alcohol Guar gum
nitrate, ammonium nitrate, calcium (galactomannan polysaccharide)
nitrate, aluminum, ethylene glycol
and TNT.
Ethylene Glycol
The proportions of these
components vary depending on the
Dextran gum
desired explosiveness of the water (Branched poly-α-d-glucosides)
gel.
Gelling agents
• Pros: economic, loading density, low sensitivity, water resistance, less toxic and less
hazardous than dynamite
• The majority of the blasting agents used in the commercial market and have almost
completely displaced dynamite

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Binary/Two Component Explosives

• Usually consist of Ammonium Nitrate

(sensitizer) and Nitromethane (fuel)
• Advantages include:
– not a Class A explosive until mixed
– no danger of fire while in storage
– available in correct type and size
– can deactivate after mixing
– will detonate at minus 14oF (-10 oC)
• Disadvantages include:
– cost
– time required to mix

Classification of Explosive

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Explosives

High
Propellants Pyrotechnics
Explosives

Primary Secondary Gun Rocket

Flashes
Explosives Explosives Propellants Propellants

Fireworks
Explosives

Primary Heat
Explosives generating

Low
Smoke
Explosives Generating
High
Explosives Noise
Generating

High
Explosives PRIMARY EXPLOSIVES OR DETONATORS
These are highly sensitive explosives which can explode under slightest shock or blow, by
ignition, and have to be very carefully handled. They are used in comparative small
quantities in blasting caps and cartridges.

Lead Azide (PbN6) It is low cost, excellent

initiating action and stable in storage. It Diazodinitro phenol
Tetrazine (DDNP) – it is
reacts with brass and caps loaded with it
(C2H7N7O) – it quite sensitive and
are made of aluminum.
is low initiating has high brisance
primary value. It is used in
explosive. It is blasting caps.
mainly used as
Mercury Fulminate (Hg(CNO)2) – More detonator.
sensitive as well as more expensive lead
azide but it is slightly toxic.

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High
Explosives SECONDARY EXPLOSIVES

This type is quite insensitive to mechanical shock as well as to flame

i.e. they do not explode on ignition. They explode with great violence
when initiated with an aid of detonators. They possess higher energy
contents then primary explosives and are stable.

 Secondary high explosives are mainly Nitro compounds, Nitrate and

Nitramines used as such or with an initiators or as mixtures.

 Trinitrotoluene (TNT), Ammonium nitrate (AN), RDX, Picric acid,

Dinitrotoluene, Pentaerythritotetranitrate (PETN), ethylene
dinitramine etc. come under this category of explosives which are
generally used in the main body of projectiles.

Secondary explosives are generally referred to as high explosives.

Trinitrotoluene (TNT)
 TNT is most commonly used in boosters and
demolition charges. TNT is yellowish crystalline
compound that comes in cast or flake form.
 When TNT is exposed to sunlight for prolonged
periods of time, it will turn brown.
 It is a moderately toxic explosive that is relatively insensitive, stable, and compatible
with other explosives.
 When stored properly, TNT has a shelf life of at least 40 years.
 TNT is the most common military explosive.
 It is used as a demolition charge, as part of a composition, and as main charge in
filler for hand grenades, mines, bombs, projectiles, rockets, and depth charges.
1910 - military use of TNT for artillery shells and armour-piercing shells

1939-1945 - World War II - Research on explosives intensified (nitration

chemistry) Development of cyclotrimethylenetrinitramine (RDX) and
cyclotetramethylenetetranitramine (HMX).

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Cyclotrimethylenetrinitramine (RDX)

 Cyclotrimethylenetrinitramine (RDX) is a stable white

crystalline. RDX is also known as cyclonite.
 The abbreviation of RDX stands for “Research and
Development Explosive.”

 RDX is one of the most widely used in composite and plastic explosives.

 RDX is extremely stable and has a shell life comparable to TNT.

 It is found in composite and plastic explosives such as C-4 (RDX,

PETN, TNT and Nitroglycerin) and Semtex (RDX and PETN).
RDX

PETN
Semtex

Cyclotrimethylenetrinitramine (RDX)

 It can also be found as a base charge in

detonators, the explosive core of some
types of detonating cord, as a component in
main charge explosive mixtures, and as a
booster explosive.

 RDX used by the military is a white

crystalline solid that has a shelf life
comparable to TNT. It is extremely stable
and non-toxic unless ingested.

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Pentaerythritotetranitrate (PETN)

It is prepared by reacting pentaerythritol (C5H12O4), an

alcohal traditionally used in paints and varnishes,
with HNO3.

It is a major ingredient of the

Semtex plastic explosive.

It can be used either as a powder or mixed

with phlegmatizing materials to form
shaped charges, such as the plastic
explosive Semtex

Dropping or igniting it will typically not cause an explosion (at standard

atmospheric pressure it is difficult to ignite and burns vigorously), but is
more sensitive to shock and friction than other secondary explosives such
as TNT

 Picric acid was accepted all over the world as the basic explosive
for military uses.
 Picric acid did have its problems: in the presence of water it
caused corrosion of the shells, its salts were quite sensitive and
prone to accidental initiation
Picric acid

 Tetryl was also being developed at the same time as picric

acid. It was first prepared in 1877 by Mertens and its
structure established by Romburgh in 1883.
 It is frequently used as the base charge of blasting caps.
(2,4,6-trinitrophenyl-n-methylnitramine)

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Explosives

High
Propellants Pyrotechnics
Explosives

Primary Secondary Gun Rocket

Flashes
Explosives Explosives Propellants Propellants

Fireworks
Explosives

Primary Heat
Explosives generating

Low
Smoke
Explosives Generating
High
Explosives Noise
Generating

PROPELLANTS (LOW EXPLOSIVES)

They do not explode suddenly but only burn and, their rate of combustion rarely
exceed 0.25 ms-1. the chemical reaction taking place in such explosives are fairly slow.
Colloidal cellulose nitrate(prepared by treating cellulose with nitric acid and sulphuric
acid) and gun powder (mixture of 75% potassium nitrate, 15% charcoal, 10% sulphur)
are examples of this category.

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Gun Propellants

 Gun propellants are also called “smokeless powders,” a

term that originated in the nineteenth century to
distinguish the newly developed nitrocellulose (NC)
propellants from the traditional gunpowder.
 They are indeed largely smokeless on firing. Solid gun
propellants mostly contain NC.
 Conventional gun propellants consist of
mixtures of one or more explosives with various
additives, formulated and carefully processed to
burn smoothly without detonating, under the
conditions in which they are normally used.

Gun propellants rapidly generate gas causing a pressure

difference accelerating a bullet through the barrel of a
firearm

Gun Propellants

The essential required properties of gun propellants are as follows:

 Minimal smoke or flash

 Less toxic fumes

 Long shelf life under all environmental conditions

 Easy and rapid ignition

 Low sensitivities to all other possible cause of initiation

 Low flame temperature

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Rocket Propellant
 Rocket propellant is the reaction mass of a rocket.

 It provide a simple and effective way of creating propulsion for

flight.
The first true military use was by
British troops in the eighteenth century
against Indians.
By the start of World War I, such rockets, all powered by gunpowder, had become obsolete.
Since then, the vital importance of rocket-powered weapons to attack on land, sea, and in the
air has tremendously increased.

Rocket Propellant
Important characteristics of Rocket Propellants:
1. It should have high specific impulse.

2. Density of propellant should be maximum so that rocket can carry maximum quantity
of propellant in a given storage space.

3. It should burn slowly, uniformly at required steady state.

4. It should be safe to handle, store and stable under the storing conditions.

5. Combustion products of propellant should be nontoxic, noncorrosive and non-

hygroscopic.

6. Combustion products should be of low molecular weight.

7. It should produce high temperature on burning and no residue remains after burning.

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Pyrotechnics (“Pyro” in Greek means “fire.”)

 The name “pyrotechnic” is derived from the Greek words ‘pyr’ (fire) and ‘techne’ (an art),
which describes the effect observed from a burning pyrotechnic composition.
 These effects include the production of coloured smoke, noise, and the emission of
bright coloured light.
 Most pyrotechnic compositions are based on reducing agents, oxidizer, binder and
ingredients to generate certain effects.

Explosives perform at the highest speed of reaction producing gaseous products,

propellants are gas generators and perform at a slower speed than explosives, and
pyrotechnics react at visibly observable rates with the formation of solid residues.

Pyrotechnics…

 Pyrotechnic compositions contain a fuel

and an oxidizer which is specifically
formulated to produce a lot of energy.

 This energy is then used to produce a

flame or glow, or combined with other
volatile substances to produce smoke
and light (i.e. fireworks), or to produce
large quantities of gas (firework rockets
and bangers)

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Some of the applications of pyrotechnics for

military use are as follows:
The main feature of most of the  Producing color signals (e.g., by use of the
pyrotechnic reactions are: salts of Ba, Sr, and Na for producing green,
red, and yellow colors, respectively).
(1)They are basically solid - solid
reactions (in which the particle size  Introducing a controlled or predetermined
of the reacting chemicals plays a time delay in certain operations (e.g., a few
vital role). milliseconds or even a few seconds delay in
the operation of a fuse or explosive mixture
(2)They evolve a large amount of heat of gases).
in many cases.  Producing flares attached to an antiaircraft
missile. The flares help the missile to home
(3)Most of them hardly evolve any gas. on to the target.
 Creating smoke for the purpose of
obscuration.

On the basis of the special effects produced by pyrotechnics, they can be categorized into four groups

Flashes and fireworks

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Light (Flashes and Firework):

 Emission of bright light is the primary function of many

pyrotechnic compositions.

 Aluminum or magnesium fuels are found in most white-light

pyrotechnic compositions. These metals evolve substantial
heat during oxidation and the magnesium oxide (MgO) and
aluminum oxide (Al2O3) reaction products are good light
emitters at the high reaction temperatures.

 Potassium used to produce Purple colour

 Strontium compounds are used to produce

red lights

 Barium salts used to produce green light

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Smoke:
 Smokes are used for military signaling and screening.

 These are usually prepared by mixing certain dye

stuffs with the fireworks.

 Military smokes were evolved from the mixtures of

metal powders with halogenated organic compounds
patented in 1920 by Captain Henri Berger of the
French army.
A colored pyrotechnic smoke-producing composition has an oxidizer, a fuel, a
flame retardant, a dye, a coolant, and a binder.

In modern warfare, special chemicals are being

developed to produce smokes that stop the penetration
of infrared radiation used by the enemy for detection
purposes.

Sound:

 The acoustic sound wave produced by pyrotechnics is by a

sudden release of high-pressure gas. Such pyrotechnics are
used in various simulation devices.

 Gun fire also produces sound that is also caused by

pyrotechnics.

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Heat:

 Heat is often considered as one of the byproducts of

pyrotechnics, and in some pyrotechnic applications heat or
flame is the desired product.

 This effect can be used for either constructive or destructive

purposes.

 Military pyrotechnic compositions as heat producers are

mainly used in igniters, incendiaries, and delays.

Accidental initiation of pyrotechnics during a large-scale

manufacture may result in the evolution of enormous
heat/fire followed by disastrous detonations.

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Explosives can be classified according to the functionality they contain and in particularly, the
functional groups that impart explosive properties to a compound.

There are eight classes of explosives depending on the groups they contained, each group is
known as an “explosophore”.
 -OClO2 and -OClO3 in inorganic and
organic chlorates and perchlorates
 -NO2 and -ONO2 in both inorganic
respectively
and organic substances
 -O-O- and -O-O-O- in inorganic
 -N=N- and -N=N=N- in inorganic
and organic peroxides and ozonides
and organic azides and diazo
respectively
compounds
 -C≡C- in acetylene and metal
 -NX2, where X=halogen
acetylides
 -N=C in fulminates
 M-C metal bonded with carbon in
some organometallic compounds

Most organic explosives contain -ONO2, -NNO2, or aliphatic or aromatic C-NO2

functionality.

Explosives containing azide, peroxide, azo functionality etc. are a minor class and
amount to less than 4-5% of the total number of known explosives.

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 Thermally stable explosives

Explosives with improved high temperature properties (safe working limit 2250C)

• Introduction of amino group

• Incorporation of triazole ring

• Salt formation

• Introduction of conjugation

Introduction of amino group

O
+ -
N O
-
O
+ N
N
N
O
NH2

-
O + O
N
H2N NH2

-
O + + O
N N
-
O NH2 O

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Incorporation of triazole ring

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Salt formation

Introduction of conjugation

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High performance explosives

Density is referred as primary parameter, detonation velocity and pressure of

the explosive proportionally with the packing density and square of it.

• Insertion of pentafluorosulfonyl (SF5) group

• Introduction of nitrogen-rich heterocycles

• Presence of strained and cage rings

• Poly-nitrogen compounds and guanidine derivatives

 Melt-castable explosives
Melt-cast explosives are loaded in the munition in melt state to avoid compression
by inertia.
• Improves safety in processing, handling, transportation and storage

• Imparts mechanical strength to the explosive charge

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 Insensitive high explosives

An ideal explosive is one, having high performance, insensitive enough to handle during
its use, storage and transport.

• Insertion of heterocyclic rings and their N-oxides

• Nitro and amino groups in the ring ortho to each other

• Introduction of picryl group

Classification of explosives based on chemical groups present

• Nitro compounds (-NO2)

• Nitric esters (-ONO2)
• Nitramines (-NHNO2 or NNO2)
• Derivatives of chloric and perchloric acids (OClO2, OClO3)
• Azides (-N3)
• Nitrogen-rich compounds
• Inorganic and organic peroxides and ozonides (-O-O- or –O-O-O-)
• Caged and strained compounds

Classifying explosives by the presence of certain molecular groups - does not give any
information on the performance of the explosive.

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Nitro group containing explosives

Nitro group containing explosives

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Nitro group containing explosives

Nitramines and Nitrate ester

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Nitrate ester

Nitramines

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Peroxide group containing compounds

Azide containing explosives

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Cl-O containing explosives

Nitrogen-rich compounds

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Caged & Strained explosives

Cyclopropane and cyclobutane derivatives

ONC
Cubane derivatives Adamantane

Caged & Strained explosives

Cubane & Prismane derivatives

Norbornanes Bicyclo[3.3.1]nonane
Diamantane

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Plastic Explosives
High-brisance crystalline explosives, such as RDX or HMX
+
polyadditive plastics such as polysulfides, polybutadiene, acrylic
acid, polyurethane, etc.
Other components such as aluminum powder can also be incorporated

Above mixture is then cured into the desired shape.

Plastic also means mixtures of RDX with vaseline or gelatinized

liquid nitro compounds of plastiline-like consistency.

Also propellant charges for rockets and guns have also been
developed by compounding solid explosives such as nitramines
with plastics.

Explosive properties
Short introduction to

 Detonation

 Density
 Stability
 Deflagration
 Sensitivity
 Combustion
 Thermodynamics (detonation
parameters, combustion parameters),
 Heat of formation
new developments,
 Heat of detonation

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Detonation
Detonate – burning at a supersonic rate producing a pressure wave
Detonation is a chemical reaction given by an explosive substance in
which produces a shock wave.
It is best defined as a reactive shock wave
A shock wave is a high intensity pressure pulse which
moves super- sonically, with respect to the sound
speed, in the uncompressed medium.
The speed of sound in water is around 1,500 m/s, a
shock wave would move faster than this e.g. 1,600 m/s

• A Good Secondary Explosive Has Good Detonation Performance

• Work is done by an explosion through a sharp increase in pressure
• Detonation performance is mostly judged by detonation pressure and
detonation velocity

Velocity of detonation (VOD) or Detonation

Detonation pressure velocity
 Detonation pressure is the
 It is the rate at which the detonation
pressure in the reaction zone as an
wave travels along an explosive column.
explosive detonates.
 The greater the VOD the greater the
 It is a significant indicator of the
power of an explosive.
ability of an explosive to produce
good fragmentation.  High VOD explosives are more suitable
in hard rock and low VOD in softer rock.
 A high detonation pressure is one
 Generally, explosives with a lower VOD
of the desirable characteristics for
tend to release gas over a longer period
high performance.
and consequently have more ‘heave’.
 The VOD range in commercial
explosives is 2500-7500 m/s.

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Density It is the measurement of how tightly a material is packed together.

Density is a substance's mass per unit of volume

 The density of an explosive may be expressed in

terms of specific gravity.

 Specific gravity is the ratio of the density of the

explosive to the density of water under standard
conditions.

 The specific gravity of commercial explosives ranges from 0.6 to 1.7 g/cc.

 With few exceptions, denser explosives give higher detonation velocities and
pressures.

Density

Density is an important consideration when choosing an explosive.

 For difficult blasting conditions or where fine fragmentation is required, a

dense explosive is usually necessary.

 In easily fragmented rock or where fine fragmentation is not needed, a

low-density explosive will often suffice.

 The density of an explosive is also important when working under wet

conditions.

 An explosive with a specific gravity of less than 1.0 will not sink in water.

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How density, detonation velocity and detonation pressure are related???

Deflagration

Deflagrate combines the Latin verb flagrare, meaning "to burn," with the
Latin prefix de-, meaning "down" or "away."

In the field of explosives, deflagrate is used to describe the burning of fuel

accelerated by the expansion of gasses under the pressure of containment,
which causes the containing vessel to break apart.

Propagating reactions in which the energy transfer from the reaction zone to the
unreacted zone is accomplished through ordinary transport processes such as heat and
mass transfer.

A deflagration occurs when a flame front propagates by transferring heat and mass to
the unburned air–vapor mixture ahead of the front.

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Deflagration

Explosives are those substances that have their own supply of oxygen in
their molecules. When they are initiated, they may either burn violently
(deflagrate) or explode disastrously generating shock waves (detonate).

Let us take a stick of a rocket propellant, say,

made of nitrocellulose and nitroglycerine (a
“double-base” propellant). When it is ignited at
one of its ends, it burns rather vigorously,
layer by layer.

Combustion
 The heat of combustion represents
 Combustion is a chemical process in which a the caloric equivalent of the total
substance reacts rapidly with oxygen and combustion energy of the given
gives off heat. substance.
 The original substance is called the fuel, and  It is determined in a calorimetric
the source of oxygen is called the oxidizer. bomb under excess oxygen
pressure.
 The fuel can be a solid, liquid, or gas,
although for airplane propulsion the fuel is  The heat of combustion is usually
usually a liquid. employed to find the heat of
formation.
 The heat of combustion depends
only on the composition of the
material and not on any other
factor, such as loading density or
other factors.

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Combustion of Explosives and Propellants

 The combustion process of propellant and explosive substances can be

defined as a self-sustaining, exothermic, rapid-oxidizing reaction.

 Propellant and explosive substances will liberate a large amount of gas at

high temperatures during combustion and will self-sustain the process
without the presence of oxygen in the surrounding atmosphere.

 Propellants and explosives contain both oxidizer and fuel in their

compositions and they are both classed as combustible materials.

 In general, propellants generate combustion gases by the deflagration

process, whereas explosives generate these gases by detonation.

 The combustion process of propellants is usually subsonic, whereas the

combustion process of explosives during detonation is supersonic.

Heat of Formation

Heat of formation is the heat of reaction or enthalpy change involved in making a

particular compound, or a molecule, from its elements where both the elements and final
compound are at standard state conditions.

It can be described as the total heat evolved when a given quantity of a substance is
completely oxidized in an excess amount of oxygen, resulting in the formation of carbon
dioxide, water and sulfur dioxide.

For explosive substances which do not contain sufficient

oxygen in its molecule for complete oxidation, (e.g. TNT)
products such as carbon monoxide, carbon and
hydrogen gas are formed.

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Heat of Formation

• Standard heat of formation of a compound is the change of enthalpy during

the formation of 1 mole of the substance from its constituent elements

• It is an important parameter for determining the energy content and

detonating power of an explosive.

Calculating gas phase heat of formation

 The value for the heat of formation can

be negative or positive.

 If the value is negative, heat is

liberated during the reaction and the
reaction is exothermic; whereas, if the
value is positive, heat is absorbed
during the reaction and the reaction is
endothermic.

 For reactions involving explosive components the reaction is always exothermic.

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Isodesmic reaction approach

An isodesmic reaction is a hypothetical (not existing in reality) chemical process in which
the number of bonds of each formal type remains the same on each side of the equation
but with changes occurring in their mutual relationships.
- -
O CH3 O O CH3 O
CH3 + + +
N
+
N
N N -
-
O O O O
+ CH3CH3 + 3 CH3NO 2 + 4 CH4
+ 3 CH3NO2 + 3 CH4
+
+ - N
- N O O
O O
Case study: e.g. TNT

Write the possible isodesmic reactions for TATB, Picric acid, ANTA, MTNI, TNAZ
- - -
O NH2 O O OH O - O
O O 2N NO2
+ +
+ + + + N
N N N N N O
- - O
O O O O N
N -
O O N
+ +
H2N NH2 N N N
NH2 N
N - NO2
+ + O O
- N - N H CH3
O O O O
TATB Picric Acid ANTA MTNI TNAZ

-
O CH3 O
CH3 + +
N N -
O O
+ 3 CH3NO2 + 3 CH4
+
- N
O O

Reactants Products

STEP-I: Find Hreaction using E0 (au)

Hreaction = E0 (Products) – E0 (Reactants)

Hreaction = [E0 (TNT) + 3 E0 (CH4) ] – [E0 (Toluene) + 3 E0 (CH3NO2)]

= [(-884.894983) + 3x(-40.469311)] – [(-271.431175) + 3x(-244.953849)]
= [(-1006.302916)] – [(-1006.292722)]
= -0.010194 au or hartree
= -0.010194 x 2625.5
= -26.7643 kJ/mol

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STEP-II: Find heat of formation (in gas phase) for TNT using Hreaction and Expt.
HOFs of compounds involved in isodesmic reaction

Hreaction = [E0 (TNT) + 3 E0 (CH4) ] – [E0 (Toluene) + 3 E0 (CH3NO2)]

Exp. HOF
𝐻𝑂𝐹 𝐶𝐻4 = −74.87
HOFTNT = Hreaction – 3 HOF(CH4) + HOF(Toluene) + 3 HOF(CH3NO2)
𝐻𝑂𝐹 𝑇𝑜𝑙𝑢𝑒𝑛𝑒 = 50.1
= -26.7643 – [3 x (-74.87)] + 50.1 + [3 x (-81.0)] 𝐻𝑂𝐹 𝐶𝐻3𝑁𝑂2 = −81.0

= -26.7643 – [-224.61] + 50.1 + [-243]

= -26.7643 – [-224.61] + 50.1 + [-243]

= 4.94 kJ/mol

Heat of detonation

The energy liberated by detonating explosives is called the heat of detonation in kJ/mol or
the heat of explosion in kJ/kg.

The heat of detonation for RDX can Δ𝐻𝑓 𝐶𝑂 = −110.525

be illustrated using Hess's law Δ𝐻1 𝑅𝐷𝑋 = 70.29
O 2N
N N
NO2 Δ𝐻𝑓 𝐻2𝑂 = −241.830
Δ𝐻𝑑 = 𝐻𝑒𝑎𝑡 𝑜𝑓 𝑑𝑒𝑡𝑜𝑛𝑎𝑡𝑖𝑜𝑛
N
NO2

The heat of detonation for RDX is −1127.355 kJ/mol

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The heat of detonation for PETN

Δ𝐻𝑑
𝐶5𝐻8𝑂12𝑁4 −−−−−→ 2CO + 3CO2 + 4H2O + 2N2

Δ𝐻1 Δ𝐻2

5𝐶 + 4𝐻2 + 6𝑂2 + 2𝑁2

The heat of detonation for PETN is −5815.078 kJ/mol

Calculations detonation velocity (D) and the detonation pressure (P)

 The driving force behind the development of any new materials for the defence use is
performance.

 For secondary explosives, the power of an explosive is often described by the

detonation velocity (D) and the detonation pressure (P).

 Velocity of detonation of explosives can reach over 10 km/s and detonation pressures
can surpass 40 GPa.

 Detonation performance depends on the energy release that accompanies the

decomposition and combustion processes occurring.

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The detonation velocity (D in km/s) and detonation pressure (P in GPa), computed using
the empirical Kamlet−Jacobs equations

C(a)H(b)N(c)O(d)
N represents the moles of detonation gases
per gram explosive.

M is the average molecular weight of these

gases(g/mol).

Q denotes the heat of detonation (cal/g).

D is detonation velocity (km/s)

P is detonation Pressure (GPa)

[ρ is the predicted density of salts (g/cm3)].

Detonation velocity (D) and Detonation Pressure (P) for RDX

O 2N NO2 MF: C3H6N6O6

N N (2𝑋6) + (2𝑋6) + 6
𝑁=
MW: 222.1 g/mol (48𝑋3) + (4𝑋6) + (56𝑋6) + (64𝑋6)
N
HOF: 60 kJ/mol or 14.34 kcal/mol
NO2 12 + 12 + 6
Density: 1.811 g/cc 𝑁=
RDX 144 + 24 + 336 + 384

First calculate the N i.e. number of moles of gaseous

detonation products per gram of explosive 𝑁= = 0.0338

For RDX, (C) a=3, (H) b=6, (N) c=6, (O) d=6

For RDX, N is 0.0338

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Now calculate M i.e. average molecular Calculate Q i.e. the chemical energy of the
weight of gaseous detonation products detonation reaction (Heat of Detonation)

For RDX, (C) a=3, (H) b=6, (N) c=6, (O) d=6

HOF of RDX= 14.34 kcal/mol

56𝑋6 + 88𝑋6 − (8𝑋6) 6

𝑀= 28.9𝑋6 + 47 6 − 2 + 14.34
(2𝑋6) + (2𝑋6) + 6 𝑄=
12𝑋3 + 6 + (14𝑋6) + (16𝑋6)
336 + 528 − 48 864 − 48
𝑀= = 173.4 + 141 + 14.34
12 + 12 + 6 30
𝑄=
36 + 6 + 84 + 96
816 328
𝑀= = 27.2 𝑄= = 1.480.8 𝑘𝑐𝑎𝑙/𝑔
30 222
For RDX, Q = 1480.8 cal/g
For RDX, M = 27.2

Calculation of detonation velocity D (km/s)

𝑭𝒐𝒓 𝑹𝑫𝑿 ⍴ = 1.811 g/cc

𝐷 = 1.01 0.0338 5.215 38.48 0.5 (1 + (1.30𝑋1.811))

For RDX,
N is 0.0338 .
𝐷 = 1.01[6.783]0 5 (3.3543)
M = 27.2 (Square root =5.215)
Q = 1480.8 (Square root =38.48) 𝐷 = 1.01[2.604] (3.3543)

𝑫 = 𝟖. 𝟖𝟐𝟑 𝒌𝒎/𝒔

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Calculation of detonation pressure P (GPa)

For RDX,
N is 0.0338
M = 27.2 (Square root =5.215) 2
𝑃 = 1.55 1.811 (0.0338)(5.215)(38.48)
Q = 1408.8 (Square root =38.48)
⍴ = 1.811 g/cc
𝑃 = 1.55 3.279 (0.0338)(5.215)(38.48)

𝑃 = 34.473

𝑷 = 𝟑𝟒. 𝟒𝟕𝟑 𝑮𝑷𝒂

RDX HMX
C3H6N6O6 C4H8N8O8
Density: 1.811 g/cc Density: 1.90 g/cc
HOF: 63 kJ/mol HOF: 76 kJ/mol
(60/4.184 = 14.34 kcal/mol) (76/4.184 = 18.16 kcal/mol)

N: 0.0338 N: 0.0338
M: 27.20 M: 27.20
Q: 1480.8 Q: 1476

D: 8.823 km/s D: 9.117 km/s

P: 34.473 GPa P: 384.7 kilobar or 38.47 GPa

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Stability

Stability is the ability of an explosive to be stored without any

deterioration
Stability of an explosive affected by mainly four factors;
1. Temperature of storage
2. Chemical constitution
3. Exposure to sunlight
4. Electrostatic discharge
Temperature of storage:
 Decomposition reactions are of considerable importance in determining stability of
explosives and it can be determined by measuring their rate of decomposition at
elevated temperatures.
 All military explosives are considered to possess stability of a high order at
temperatures ≈ − 40°C to +60°C but each has a higher temperature at which
decomposition rate becomes rapidly accelerated and stability is reduced.
 As a rule of thumb, most explosives become dangerously unstable at temperatures
above +70 ° C.

Chemical constitution : Electrostatic discharge :

 Some common chemical  Static or electrostatic

compounds which contain discharge may be sufficient
Exposure to sunlight : to initiate detonation in a
groups like nitro ( – NO2 ),
nitrate ( – ONO2 ) and number of explosives under
 Many explosives which some circumstances. As a
azide ( – N3 ) etc. undergo
contain nitrogen groups result, the handling of
explosion when heated
(primary explosives such explosives and pyrotechnics,
means that these are
as Lead azide, mercury most of the time, is unsafe
intrinsically in a condition
fulminate, etc.) and requires electrical
of internal strain and on
decompose rapidly on grounding of working tables
heating, this strain
exposure to the and operators.
increases leading to a
ultraviolet ( UV ) rays of
sudden disruption of
the sun, and thus affect
molecules and consequent
their stability.
explosion.

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Sensitivity
‘Sensitivity’ represent ease of initiation

‘Sensitiveness’ denotes propagating capability

 Sensitivity is a measure of the ease with which an explosive can be detonated by heat,
friction or shock and of its ability to propagate that detonation.

 Sensitivity represent amount of energy that material needs to attain probability of

developing explosive reaction.

 Some explosives with very high sensitivity, such as pure nitroglycerin or dynamite, can
be detonated by mechanical impact or friction.

 Sensitivity tests are required and applied for safety characterization of all classes of
explosive materials in different stages of their life cycle.

 During production, handling, storage, transport,

and similar activities, explosives are frequently
exposed to various external stimuli such as heat,
impact, friction etc. which might result in
combustion or detonation.

 This particular property of explosives is

considered a key factor in determining practical
applications of a given explosive.

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 From perspective of sensitivity, primary explosives are more sensitive than the
secondary explosives.

 Sometimes, to increase the sensitivity of material, glass dust is added.

 The sensitivity of well-established energetic materials can be reduced through various

material improvements, such as better crystal quality, reducing crystal or molecular
defects, eliminating voids, chemical impurities or the existence of multiple phases.

 Common explosives like TNT, RDX and HMX were considered adequate for all weapon
applications, but these explosives have now become less attractive due to a number
of accidents involving initiation of munitions by impact or shock aboard ships, aircraft
carriers and ammunition trains.

There are mainly five types of sensitivity

Sensitivity to Impact: distance through which a standard weight is allowed to drop to

cause an explosive to explode.
Sensitivity to Friction: what occurs when pendulum of known weight scrapes across an
explosive (ignites or explodes or crackles).
Sensitivity to Shock / Gap Sensitivity: ease with which an explosive can be set off by a
blow shock from another explosive charge.
Sensitivity to Spark: ease with which an explosive can be set off by an electrostatic
spark.
Sensitivity to Heat: ease with which an explosive can be set off by heat. It explained in
terms of temperature at which ignition or explosion of an explosive occurs.
Quantity of heat liberated by an explosive during decomposition also plays an important
role in raising the rate of decomposition.

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Influence of crystal size of Lead azide on sensitivity

Above figure shows that Fine particles are less sensitive

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Fall Hammer Impact Sensitivity Test

• Used for measuring impact sensitivity of solid high explosives,

propellants, pyrotechnics and also primary explosives.

• Defining their safety in handling.

• Its determination is a necessary part of characterization of new BAM fall hammer

explosives, modified formulations or manufacturing conditions, as

well as defining influences of impurities or ageing.

• Weight falling from a variable height and causing sample initiation.

Flash, flame or explosion are observed upon sample initiation.

Consists of
Two stainless steel guide rails (1);
A release device (2);
A column (3);
Three middle cross-piece (4);
A drop weight (5);
A tooth rack (6);
A ruler (7);
A main anvil (8);
A pedestal (9, 10)

BAM Fall Hammer is equipped with the automated lifting mechanism which allows to remotely operate the
positioning, dropping and collection of a drop weight via a touch screen of a remote control unit.
The equipment is fitted with a drop-down weight change window for a quick, easy and safe weight change

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Results obtained in tests on the explosive ANFO

Friction Sensitivity Test

• The friction sensitivity testing is the second most used mechanical
sensitivity test

BAM Friction test apparatus

• Used for determination of friction sensitivity
• Friction of explosives between hard surfaces is one of the most frequent causes of
accidental explosions.
• Friction force between a moving porcelain plate and a static porcelain peg causing
sample initiation is determined.

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The BAM apparatus consists of a fixed porcelain peg and a moving porcelain plate. The
plate is moved one centimeter forth and then returns to the starting position.
The peg is part of a one-sided lever and the force is generated by nine different weights that
can be fixed in six notches on the lever. Thus 0.5 to 360 N (Newton) force can act on the
specimen

Porcelain pestle and plate assembly (BAM friction apparatus)

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Friction sensitivity test of wetted PETN

The dry sample shows a friction

sensitivity of 50 ± 4 N.

Wetting causes the sensitivity to

drop linear to 87 ± 8 N at 15 %
water (same as up to 25%).

Up to 35 %,a decrease is

observed with a sensitivity of 105
± 8 N.

Gap Sensitivity or Shock Sensitivity Test

The explosive can be set off by a blow shock from another explosive charge

It is a shock test to measure the sensitivity

of a composition to a detonation shock

Shock loading is the main factor that

induces the violent reaction of an explosive,
and the reaction threshold can be used to
evaluate the sensitivity

The molecules reacted under shock loading

and released enough energy absorbed by
nearby molecules to rapidly reach a critical Schematics of the gap-test
high temperature. This was key to
triggering further reactions between
neighboring molecules.

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Oxygen Balance

The amount of oxygen, expressed in weight percent, liberated as a result of complete

conversion of the explosive material to CO2, H2O, SO2, Al2O3, etc.

If the amount of oxygen bound in the explosive is insuffient for the complete oxidation
reaction denoted as negative oxygen balance, while the explosive is said to have a positive
oxygen balance if it contains more oxygen than is needed.

CH4 + 2 O2  CO2 + 2 H20

Oxidation (combustion) of methane: 1 methane molecule : 2 oxygen

molecules (4 oxygen atoms).

• Imagine an explosive detonating.

– Reactant CHNO molecule is completely
broken down into individual component
• Many explosives and propellants atoms.
are composed of: • For Nitroglycol (C2H4N2O6):
– Carbon 2N  N2
– Hydrogen 2H + O  H20
– Nitrogen CO + O  CO2
– Oxygen
• First, all nitrogen forms N2
• Then, all the hydrogen is burned to H2O
• General Formula: CaHbNcOd • Any oxygen left after H20 formation burns carbon
to CO.
• CaHbNcOd  a C + b H + c N + d O • Any oxygen left after CO formation burns CO to CO
2
• Any oxygen left after CO2 formation forms O2
• Traces of NOx (mixed oxides of nitrogen) are
always formed.

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𝑏
𝑑− 𝑎+ 𝑋1600 • Oxygen balance for Nitroglycol C2H4N2O6
2
𝑂𝐵% = – a = 2, b = 4, c = 2, d = 6
𝑀. 𝑊𝑡
– M.Wt. = 152.068 g/mol
If the product is with CO
4
6 − 2𝑋2 − 2 𝑋1600
𝑂𝐵% =
152.068

12 − 8 − 4
2 𝑋1600 = 0 𝑋1600
𝑂𝐵% = 152.068
152.068
𝑶𝑩% = Zero
If the product is with CO2
The explosive molecule contains just
• In the case of nitroglycol enough oxygen to form carbon
O2N—O—CH2—CH2—O—NO2  N2 + 2H2O + 2 CO2 dioxide from carbon, water from
Exactly enough oxygen to burn all carbon to CO2 hydrogen molecules (Zero oxygen balance)
(C2H4N2O6 → 2 CO2 + 2 H2O + N2)

• Oxygen balance for Nitroglycerine C3H5N3O9 Calculate the oxygen balance for:
TNT (M.Wt. = 227.13 g/mol)
– a = 3, b = 5, c = 3, d = 9
C7H5N3O6 a=7, b=5, c=3, d=6
– Mwexp= 227.094 g/mol
5
5 6 − 2𝑋7 − 𝑋1600
9 − 2𝑋3 − 𝑋1600 𝑂𝐵% = 2
𝑂𝐵% = 2 227.13
227.094
12 − 28 − 5 −21
18 − 12 − 5 𝑋1600 𝑋1600
𝑋1600 𝑂𝐵% = 2 = 2
𝑂𝐵% = 2
227.13 227.13
227.094
1 𝑶𝑩% = -73.97
𝑋1600
𝑂𝐵% = 2 𝑶𝑩% = 3.52 The explosive molecule contains less oxygen
227.094
than is needed, the combustion will then be
The explosive molecule contains more oxygen incomplete, and large amount of toxic gases
than is needed to fully oxidize its components like carbon monoxide will be present.
(Positive oxygen balance) (Positive oxygen balance)
(4C3H5N3O9 → 12CO2+ 10H2O+ 6N2+ O2) (C7H5N3O6→CO2+2H2O+2CO+4C+1/2H2+3/2 N2)

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• Calculate the oxygen balance for

Picric acid RDX Triacetone triperoxide (TATP) TNA

M.Wt. = 229.10 g/mol 222.12 g/mol 222.24 g/mol 228.12 g/mol

1,1-diamino-2,2-dinitroethylene (DADNE)
3,4-diaminofurazan
(FOX-7)

148.08 g/mol 100.08 g/mol 119.07 g/mol

Polymer Bonded Explosives (PBX)

 Polymer-bonded explosive (PBX) also known as Plastic-bonded explosive - is an

explosive material in which explosive powder is bound together using small quantities
(typically 5–10% by weight) of a synthetic polymer (plastic).

 PBX was first developed in 1952 in Los Alamos National

Laboratory (LANL), as RDX embedded in polystyrene with
dioctyl phthalate plasticizer. polystyrene

 PBXs do not possess malleability after they have undergone

the curing process.
 PBXs are normally used for explosive materials that are not easily
dioctyl phthalate
melted into a casting, or are otherwise difficult to form.

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Advantages:

• If the polymer matrix is an elastomer (rubbery material), it tends to absorb shocks,

making the PBX very insensitive to accidental detonation

• Hard polymers can produce PBX that is very rigid and maintains a precise
engineering shape even under severe stress

• PBX powders can be pressed into a particular shape at room temperature, when
casting normally requires hazardous melting of the explosive

Examples of PBXs
EDC-29: HMX 95% + 5% HTPB

(HTPB)
Viton A- type fluoro elastomers
HMX (Octogen) Hydroxyl-terminated polybutadiene
LX-04-1: HMX 85% + Viton-A 15%:
High-velocity; nuclear weapons

Kel-F 3700
PBX 9010: RDX 90% + Kel-F 3700 10%: High-velocity; nuclear weapons

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Binders in PBXs

Fluoropolymers
 They are advantageous as binders due to their
high density (yielding high detonation velocity)
and inert chemical behavior (yielding long shelf
stability).

 They are however somewhat brittle, as their glass

transition temperature is at room temperature or
Polyvinylidene Polytetrafluoro Polyvinylidene difluoride-
above; this limits their use to insensitive difluoride ethylene Hexafluoropropylene
explosives
(e.g. Triaminotrinitrobenzene, (TATB)).

Binders in PBXs
Elastomers
 They are used with more mechanically sensitive explosives,
e.g. HMX.
hydroxyl-terminated polybutadiene

 The elasticity of the polymers lowers sensitivity of the bulk

material to shock and friction.

 Crosslinked rubber polymers are however sensitive to aging

(less shelf life), mostly by action of free radicals and by
hydrolysis of the bonds by traces of water vapor.

 Rubbers like Estane (Thermoplastic elastomers) or hydroxyl-

terminated polybutadiene (HTPB) are used for these
applications extensively. Silicone rubbers and thermoplastic
polyurethanes are also in use.

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Binders in PBXs
Energetic polymers

Energetic polymers (e.g. nitro or

azido derivates of polymers) can be
used as a binder to increase the
explosive power in comparison with
inert binders.

New Developments in PBXs

RDX based PBXs: HMX based PBXs:
 RDX or reduced sensitivity RDX (RS-  HMX is an explosive polynitramine.
RDX), which is also known as cyclonite
or hexogen, is currently the most  HMX compositions with teflon-based
important military high explosive in the binders were developed in the 1960s
world. and 1970s for gun shells and for lunar
seismic experiments.
 RDX is used as an explosive, usually in
mixtures with other explosives, including e.g. LX-04-1 85% HMX with 15% Viton-A
High-velocity Nuclear weapons
PETN, oils, or waxes.
PBXN-5 95% HMX and 5%
e.g. PBXN-106 RDX + polyurethane rubber fluoroelastomer Naval shells
Naval shells

PBXN-3 RDX 85% + nylon

Sidewinder Missile

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New Developments in PBXs

1,3,3-Trinitroazetidine
CL-20 based PBXs: TNAZ based PBXs: (TNAZ)
 CL-20 is a relatively new  TNAZ is a high performance, melt castable
nitramine explosive that is explosive that has been proposed as a potential
20% more powerful that replacement for RDX, and also for TNT, in PBXs.
HMX.
 As a material it is more powerful but less sensitive
 It was soon realized that CL- than HMX.
20 had greater energy output  Similar to CL-20, it presents the possibility of a high
than existing (in-use) explosive with increased performance but with
energetic ingredients (TNT, reduced sensitivity due to its special molecular
RDX, HMX). structure.
 As a nitrogen-rich compound, TNAZ can itself be
melted and molded, and is one of the few new
energetic materials found to be thermally stable
above its melting point.
Hexanitrohexaazaisowurtzitane (CL-20)

TATB based PBXs:

 TATB is considered a reference explosive for invulnerable explosives.

 TATB's high level of stability favors its use in military and civil applications when
insensitive high explosives are required.

 TATB is also used to produce the important intermediate, benzenehexamine which

has been used in the preparation of new heterocyclic explosives.

e.g.
• LX-17-0 92.5% TATB with 7.5% Kel-F 800 High-velocity and insensitive used in
Nuclear weapons (B83, W84, W87, W89 in USA)

• XTX 8003 PETN 80% with 20% Sylgard 182 (silicone rubber) High-velocity and
extrudable used in Nuclear weapons (W68, W76 in USA)

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Nitration

The explosive properties of any substance depend upon the presence of definite structural
groupings, called explosophores.

A plosophore has been defined as a group of atoms which is capable of forming an explosive
compound on introduction into a hydrocarbon.

There are two classes of plosophores differing sharply in effectiveness and consistency in
producing power.
Primary plosophores: nitrate esters, aromatic and aliphatic nitro groups and the nitramine
group.

Secondary plosophores: azo, azide, nitroso, peroxide, ozonide, perchlorate, etc.

NITRATION is one of the earliest known organic chemical reactions and one of the most
widely applied direct substitution reactions.

Why???
• nitration usually proceeds easily
• its products can readily be separated from the spent acid
• there is a wide range of possibilities in the practical use of nitro compounds, both as
intermediates and end products.

Highly nitrated nitro compounds and nitric acid esters have explosive properties and are of
practical importance.

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Frequently used nitrating agents

Direct methods of introducing nitro groups
• concentrated nitric acid
• mixtures of concentrated nitric acid and concentrated sulphuric
acid (or oleum) in different proportions - these are usually known
as nitrating mixtures
• alkali nitrates in the presence of sulphuric acid
• dilute nitric acid
• nitrogen dioxide
• a solution of nitrogen dioxide in sulphuric acid
• nitrogen dioxide in the presence of catalysts.

Based on chemical structure of compounds resulting from nitration processes,

three types of nitration reactions are possible:
C-nitration: the nitro group attached to a carbon atom

O-nitration: the formation of nitric acid esters

N-nitration: the formation of nitramines

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Nitrogen-Rich Heterocycles
High Energy materials store relatively large amounts of available energy that is readily
deliverable.

Employed when very rapid rates of energy application and high pressures are essential

Classical explosives (e.g. TNT, RDX, etc.) derive most their energy from oxidation of the
carbon backbone.

High-nitrogen compounds derive high heat of formation due to the large number of energetic
N – N and C – N bonds.

Heterocyclic compounds often been utilized in energetic roles due to higher heats of
formation, density, and oxygen balance than those of their carbocyclic analogues.

 Significant progress toward enhanced performance and increased stability is

being made in the synthesis of high-nitrogen-content heterocyclic molecules.

 Theoretical calculations predict that many of the nitrogen compounds will have
higher positive heats of formation (the calculated heat formation of the unknown
compound, N4, is 753 kJ/mol, whereas the heat formation of HMX is 75 kJ/mol,
higher densities (the calculated density of N4 is 2.76 g/cm3, whereas the density of
HMX is 1.90 g/cm3) lower combustion signatures, good calculated propellant
characteristics, and perhaps lower sensitivities

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HOF
Sr. No Compound Structure OB (%)
(kJ/mol)

1 Benzene 82.9 -307.7

2 Pyridine 140.2 -253.2

N

N N
3 1,3,5-Triazine 225.8 -148.1
N

N N
1,2,4,5-
4 487.2 -97.6
Tetrazine N N

Oxidizers

• Oxidizers want to gain electrons to be more stable

• Reducers want to lose electrons to be more stable
• The stronger the oxidizer, the more it wants to gain electrons
• The stronger the reducer, the more it wants to lose electrons

Oxidizer, Solid or Liquid: Any solid or liquid material that spontaneously

evolves oxygen either at room temperature or when under slight heat.

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The Fire Triangle

• Oxidizers • Fuels:
– Liquids – Liquids
– Gases • gasoline, acetone, ether,
• Oxygen, fluorine, chlorine pentane
• hydrogen peroxide, nitric – Solids
acid, perchloric acid
• plastics, wood dust, fibers,
– Solids
metal particles
• Metal peroxides,
ammonium nitrate – Gases
• acetylene, propane, carbon
 Ignition sources monoxide, hydrogen
 Sparks, flames, static
electricity, heat

Although most oxidizing substances do not burn themselves, they can form flammable
or explosive mixtures when in contact with the following materials.

Organic materials: Carbon containing materials such as paper, wood, flammable and
combustible liquids, greases, waxes, and some plastics or textiles.

Inorganic metals: Finely divided metals or biological media in the form of powders.

Other Oxidizable substances: Hydrogen, Hydrazine, Hydrides, Sulfur or Sulfur

containing compounds, Phosphorus, silicon, and ammonia or ammonium compounds.

Chemical Incompatibility: Oxidizers that come in contact with reducing agents, other
oxidizers, inorganic acids and water can result in violent explosions and or fires.

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Classes of Oxidizers Class 3 Severe increase in the burning rate of

combustible materials.
Class 1 Slightly increase in the burning rate of Will cause sustained & vigorous
combustible materials. decomposition if contaminated with
Does not cause spontaneous combustion when combustible material or exposed to sufficient
in contact with combustible materials heat
e.g. Aluminium Nitrate, Barium Peroxide, e.g. Ammonium Dichromate, Potassium
Potassium Nitrate, Silver Nitrate, Sodium Bromate, Sodium Chlorate, etc.
Nitrate, Sodium Nitrite, Strontium Nitrate,
Zinc Peroxide, etc. Class 4 Can explode when in contact with
certain contaminates.
Class 2 Moderate increase in the burning rate Can explode if exposed to slight heat, shock,
of combustible materials. or friction.
May cause spontaneous combustion when in Will increase the burn rate of combustible
contact with combustible materials materials.
e.g. Calcium Chlorate, Hydrogen Peroxide, Can cause spontaneous ignition of
Magnesium Perchlorate, Potassium combustible materials
Permanganate, Sodium Permanganate, Sodium e.g. Ammonium Perchlorate, Ammonium
Chlorite, Sodium Perchlorate, Sodium Permanganate, Tetranitromethane,
Peroxide, etc. Hydrogen Peroxide (Concentration > 91 % by weight)

Strong Oxidizers
• Fluorine • Nitrates
• Chlorine • Nitrites
• Ozone • Liquid oxygen
• Persulfates • Chlorates
• Peroxides
• Perchlorates
• Dichromates
• Chromates
• Permanganates
• Hypochlorites

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Examples of Oxidizers
Ammonium nitrate (AN)
Environment - friendly alternative to Ammonium perchlorate (AP)

Imparts slower burn rates but is a high gas producer and accordingly is used for gas
generator propellants.
Oxygen balance : 20%

It decomposes endothermically with heat energy of -365.04 kJ/mol, leading to low burn rate.

The most important drawback of AN is phase transition occurs at room temperature with
volume change.
AN crystal is thermally sensitive and undergoes five stable polymorphic transformations
with volume change in the temperature range of -200 °C to 125 °C.

Ammonium dinitramide (ADN)

[NH4 N(NO2)2- newly discovered inorganic solid salt, mainly intended as an

oxidizer for composite propellants.

Oxygen balance: 25.8%

Negative heat of formation: −150.60 kJ/mol, higher than that of AP and AN.

ADN is more hygroscopic than AN

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Hydrazinium Nitroformate HNF

High energy and environment friendly oxidizer

The m.p. of HNF lies in the range of 115 – 124 °C depending on its purity and it is
suitable for processing of propellant formulations.

Non - toxic, non - corrosive and non - irritating to skin and eyes and no indication of
danger exists with respect to inhalation

It is non-hygroscopic.

The ignition temperature HNF: between 115 °C and 120 °C

Potassium Nitrate (KNO3)

The oldest solid oxidizer used in high-energy mixtures, potassium nitrate (saltpeter)
remains a widely-used ingredient well into the 20th century.

Its advantages are ready availability at reasonable cost, low hygroscopicity, and the
relative ease of ignition of many mixtures prepared using it.

It has a high (39.6%) active oxygen content, decomposing at high temperature according
to the equation
2KNO3 K2O + N2 + 2.5 O2

Potassium nitrate has the additional property of not undergoing an explosion by itself,
even when very strong initiating modes are used

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Potassium Chlorate (KCIO3)

One of the very best, and certainly the most controversial, of the common oxidizers is
potassium chlorate.

It is a white, crystalline material of low hygroscopicity, with 39.2% oxygen by weight.

It remains in wide use today in coloured smoke, firecrackers, toy pistol caps, matches,
and colour-producing fireworks. However, potassium chlorate has been involved in a
large percentage of the serious accidents at fireworks manufacturing.
2 KClO3 2 KCl + 3 O2
Potassium chlorate compositions are quite prone to accidental ignition, especially if
sulphur is also present.

Chlorate /phosphorus mixtures are so reactive that they can only be worked with when
quite wet.

Potassium Perchlorate (KCIO4)

This material has gradually replaced potassium chlorate (KClO3) as the principal
oxidizer in civilian pyrotechnics. Its safety record is far superior to that of potassium
chlorate.
KClO4 KCl + 2O2

Potassium perchlorate is a white, non-hygroscopic crystalline material with a melting

point of 525 °C, considerably higher than the 356 °C melting point of KClO3.

Because of its higher melting point and less-exothermic decomposition, potassium

perchlorate produces mixtures that are less sensitive to heat, friction, and impact than
those made with KClO3.

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Ammonium Perchlorate (AP or NH4CIO4)

AP has found considerable use in modern solid-fuel rocket propellants and in the
fireworks industry.

The space shuttle alone uses approximately two million pounds of solid fuel per
launch; the mixture is 70% ammonium perchlorate, 16% aluminium metal, and
14% organic polymer.

2 NH4ClO4 N2 + 3H2O + 2HCl + 2.5O2

Ammonium perchlorate is more hygroscopic than potassium nitrate or potassium

chlorate

Strontium Nitrate [Sr(NO3)2]

This material is rarely used as the only oxidizer in a composition, but is commonly
combined with potassium perchlorate in red flame mixtures.

It is a white crystalline solid with a melting point of apprx. 570 °C. It is somewhat
hygroscopic.

At low decomposition temperatures,

Sr(NO3)2 SrO + NO + NO2 + O2

At high decomposition temperatures,

Sr(NO3)2 SrO + N2 + 2.5 O2

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Barium Nitrate [Ba(NO3)2]

Barium nitrate is a white, crystalline, non-hygroscopic material

with a melting point of approximately 592°C.

It is commonly used as the principal oxidizer in green flame

compositions, gold sparklers, and in photoflash mixtures in
combination with potassium perchlorate .

Ba(NO3)2 BaO + N2 + 2.5 O2

Mixtures containing barium nitrate as the sole oxidizer are

typically characterized by high ignition temperatures, due to its
higher melting point.

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