MATRUSRI ENGINEERING COLLEGE�DEPARTMENT OF SCIENCES AND HUMANITIES

SUBJECT NAME: CHEMISTRY

FACULTY NAME: K.ARUNA KUMARI

MATRUSRI

ENGINEERING COLLEGE

TOPIC: EXPLOSIVES

CHEMISTRY

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COURSE OBJECTIVES:

• Correlate the properties of materials with their internal structure and use the for Engineering applications
• Apply the principles of electrochemistry in storage of electrical energy in batteries.
• Gains knowledge in causes of corrosion and its prevention.
• Attains knowledge about the disadvantages of hard water for domestic and industrial purposes.
• Also learns the techniques of softening of hard water and treatment of water for drinking purpose.
• Exposed to qualitative and quantitative parameters of chemical fuels.
• Aware eco-friendly materials and processes.

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ENGINEERING COLLEGE

CHEMISTRY

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COURSE OUTCOMES:

• Basic knowledge about Explosives,Types of applications in industry.
• Discuss different types of polymers based on their end on use and the need to replace the conventional polymers with polymers of engineering applications.
• Identify and analyze different types of chemical fuels for domestic and automobile applications.
• Outline the principles of green chemistry for sustainable environment and preparation of biodiesel from renewable sources.

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ENGINEERING COLLEGE

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COURSE OUTCOMES: After completion of course students will be able to discuss different types Explosives,precautions in the storage of explosive ,blasting,Rocketpropellents

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ENGINEERING COLLEGE

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Unit-V: Explosives

An Explosive is a substance or mixture which when subjected to thermal or mechanical shock gets very rapidly oxidised exothermally into products of greatly increased volume, with a sudden release of potential energy.

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Classification of Explosive:

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1.) Primary or Initiating explosive(detonators):

They are highly sensitive explosives which explode on receiving a slight shock or by fire. They should be handled with utmost care. They are mainly used in small quantities in shells and cartridges to start or initiate the explosion.

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• Lead azide (PbN₆): It is very popular for military purposes due to its

I) low cost ii) Excellent initiating action iii) stability in storage.

However, it cannot initiate explosion in the comparatively less sensitive secondary explosives like cast TNT. Lead azide reacts with Brass. The caps loaded with it are made of aluminium.

• Mercury Fulminate [ Hg (CNO)₂]: It is more sensitive as well as more expensive than lead azide. However, it is slightly toxic and consequently used to a less extent than a Lead Azide.
• Tetracene[C ₂H₇N₇O): It is a low initiating primary explosive. It ignites easily, has high heat of explosion and produces a large volume of gases. However, it is not used in the military but used as detonator.
• Diazo dinitro phenol (DDNT): It is quite sensitive and has high brisance and can consequently initiate explosion even in less sensitive high explosives. It is widely used commercial blasting caps.

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2.) Low Explosives:

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Black powder (Gun powder): It is a mixture of 75% potassium nitrate ,15 % charcoal and 20% sulphur. It contains sufficient oxygen to combine with other elements present, when its ignited. The Decomposition reaction is:

10 KNO₃+3S+8C →3K₂SO₄ +2K₂CO₃ +6CO₂ ↑+ 5N₂↑

The excess of Carbon and sulphur take part in the slower reduction process, leading to the evolution of more gases:The excess of carbon and sulphur take part in the slower reduction process, leading to the evolution of more gases.

4K₂CO₃ + 7S →K₂SO₄ +3 K₂S₂ +4CO₂↑

4K₂SO₄+7C→2K₂CO₃+2K₂S₂+5CO₂↑

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2.) Smokeless powder (Nitrocellulose): It is prepared by treating cellulose with nitric and sulphuric acid. The Nitrocellulose so formed is dissolved in a mixture of ether and alcohol and the, the solvent is evaporated, when a jelly like solid is left behind. The stabilizer like diphenylamine is added since the product is likely to react with traces of acid. Finally, it is pressed into cylindrical rods. It is called as smokeless powder because it produces carbon dioxide and carbon monoxide, water vapour and almost no smoke.

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3.)High explosives:

Single compound Explosive

Ammonium Nitrate: It is very stable, Nontoxic, cheap, and has low brisance value. It is as powerful as TNT and is usually employed in the making binary explosive. It is dangerous to store near any inflammable material and also it it cannot be used in contact with alloys of copper since it forms Tetrammino cupric nitrate which detonates easily.

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2:4:6 -Trinitrotoluene: It is a high explosive made by nitrating toluene. It is widely used in shell firing and under -water explosions and well suited for loading in containers because of its low melting points (81⁰C.Its importance for military use comes from its comparative excellence in the following respects:

• It’s safe explosive in manufacture, transportation and storage.

It is a violent disruptive explosive and it does not react with metals to form unstable compounds

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iii.)Penta aerythritol Tetranitrate (PETN): It is an extremely powerful, sensitive and standard military explosive.

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Cylonite (RDX or Cyclotrimethylene Cylonite: (RDX or Cyclotrimethylene Trinitro amine: It is a powerful high explosive. It is more sensitive but less toxic than TNT. RDX came into prominence in military as well as industrial explosive in world War II

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Picric acid (Trinitrophenol) : It is ah high explosive ,largely replaced by TNT ,because it attacks metals to form Shock sensitive picrates.

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2.) Binary Explosives: It consists of mixture of TNT with other explosives. They are more convenient to make more superior when compared to single compound explosives in certain applications. TNT is an important ingredient in binary explosive. They are heated to liquid state and poured into containers and allowed to solidify.

i.)Amatol: It is an explosive mixture of TNT with ammonium nitrate (50 to 80%. It is a white smoke giving explosive with strength equal to TNT. It is used as blasting charges in large caliber shells.

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ii.) Pentolite is a mixture of TNT and PETN,50%each.

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iii.) Tetrytol is a (a mixture of 40% tetryl and 30% TNT.

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iv.) Tropex is a(a mixture of 40%RDX,40% TNT and 20% Al powder.

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v.) Tritonal is a (a mixture of 80% TNT and 20 % of Al Flakes.

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3.) Plastic Explosives: They are the combination of explosives, which are in plastic state and can be hand moulded and made into various shapes without any serious risk. They are mainly used for industrial and military purposes. High explosive is mixed with wax or oil which makes it more plastic and less sensitive. They can be moulded into sheet or putty like a mass. They are available in flexible sheet explosives containing high explosive (PETN). These sheets are cut into desired shaped and can be fixed by metal part by an adhesive

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4.) Dynamite: they are explosives containing Nitro-glycerine as the principal ingredient. It is an oily liquid which detonates by pressure, shock or spontaneously above 50⁰C

4C₃H₅(NO₃)₂→10 H₂0 ↑+N₂↑+ 12 CO₂↑ +O₂↑

The explosion is so sudden that Nitro-glycerine (NG) would shatter the breech of the rifle before the bullet had time to move. it also pulverizes rock, instead of breaking into fragments of usable size. On account of the danger in handling and impossibility of safety transporting the substance. it is usually mixed with an inert absorbent such as wood pulp, starch meals, saw dust , etc

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i.) Straight -dynamites: They contain 15 to 60% Nitro-glycerine in wood meal with sodium Nitrate. Sodium Nitrate is used as an oxidising agent for providing oxygen,so that good fume properties and good execution can be obtained. is used for blasting of hard rocks,coaland other minerals and demolitions

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ii.) Blasting gelatin -dynamite: They are those in which the NG has been partially gelatinised by Nitro-collon. The composition of blasting gelatin is 91.5%, NG:8%, Nitro cotton ,0.5%CaCO3.They are jelly like substance, powerful, water proof which can be used under wet conditions, where high density is desired. It can be used in submarine blasting, tunnel driving, deep well shooting etc.

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Gelatin sticks

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iii.) Guncotton (Cellulose Nitrate): It is obtained when cotton is steeped for half an hour in a cooled mixture of concnitric andconc sulphuric acid

C₆H₇O₂(OH)₃+ 3HNO₃→C₆H₇O₂(NO₃)₃+3H₂O

Dry gun cotton explodes very rapidly when set on fire, but when wet it is set off by a small amount of another explosive. Fulminate of mercury, Hg (CNO)₃ is commonly employed. It is ignited by shock.

It is used in torpedoes and submarine mines, used as propellant in rifles or artillery shells.

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iv.) Cordite: It is made by dissolving gun-cotton (65parts,)Nitro-glycerine (30 parts)and petroleum jelly (5 parts).The resultant paste is rolled and cut into pieces of different dimensions. The Vaseline acts as stabilizer and cooling agent on the powder. The gun cotton slows down the explosive reaction of NG and makes cordite an excellent propellant for large caliber naval guns.

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v.) Gelignite: It is a powerful explosive which can be used under water.

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Precautions during storage of Explosives:

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• Different Explosives must be stored in different box

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• Detonators and explosives must be stored totally separate.

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• All the Electric fittings and wirings must be properly insulated and frequently checked.

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• Jerks or drops of explosives must not be allowed.

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• Smoking /fire should be strictly prohibited with the radius of 50m from the explosive stores.

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• The Magazine should not be constructed with 500m from any working kiln or furnace

• Different Explosives must be stored in different box

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• Detonators and explosives must be stored totally separate.

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• All the Electric fittings and wirings must be properly insulated and frequently checked.

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• Jerks or drops of explosives must not be allowed.

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• Smoking /fire should be strictly prohibited with the radius of 50m from the explosive stores.

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• The Magazine should not be constructed with 500m from any working kiln or furnace

• Flame lantern should not be used in any case. Only torches should be used for lightening purposes.\

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Lightening conductors should be provided to safeguard the magazine

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• Only authorized persons should be allowed to the explosive store.

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• Magazine should not be opened during thunderstorm and no person should be in vicinity of the magazine during such storm.

Blasting fuse

A blasting fuse is a thin water proof canvas length of tube containing gun powder arranged to burn at a given speed for setting of charges of explosives

Blasting fuses are of two types

Characterisitics of Propellant

• Propellant is a material that is used to propel or

move an object.

• The material is usually expelled by gas pressure

through a nozzle.

• The pressure may be from a compressed gas or a

gas produced by a chemical reaction.

• The exhaust material may be a gas, liquid or

Plasma.

• The propellant supplies the necessary pressure

within an aerosol system to expel.

• Material from the container and in combination with

other components to covert the material into

desired physical form.

• Propellant is the chemical mixture burned to produce

thrust in rockets and consists of a fuel and an oxidizer.

• Fuel is a substance that burns when combined with oxygen

producing gas for Propulsion.

• An oxidizer is an agent that releases oxygen for combination

with a fuel.

• The ration of oxidizer to fuel is called the mixture ratio.

Rocket fuels

Rocket propellant is either a high oxygen containing fuel or a mixture of fuel plus oxidant. Its combustion takes place in definite and controlled manner with the evolution of a huge volume of gas.

Principle of rocket propulsion: A propellant burns quickly producing a very large volume of hot gases at a temperature of 3000⁰C and pressure of 300kg/cm² which escape through a nozzle at very high velocity i.e. supersonic velocity. This propulsion of rocket is based on Newton’s third law of motion, where the act of pushing the gases backwards produces an equal and opposite reaction which moves the rocket forward. The performance of the rocket engine depends on the exhaust velocity.

Rocket propellant

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The main parameter for the functioning of a rocket is the specific thrust or specific impulse (I_sp).

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It is the thrust delivered per unit mass of fuel consumed per sec.

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Isp ∝ √T/M

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Where, T = Temperature at which fuel burns.

M = Mean molecular weight of gaseous products of combustion.

Characterisitics of a good propellant

• It should have high impulse.
• It should produce high temperature on combustion.
• It should produce low molecular weight products during combustion.
• It should burn at a slow and steady rate.
• It should possess low ignition delay.
• It should possess high density to minimize container space.
• It should be stable at a wide range of temperatures.
• It should be safe for handling and storage.
• It should be readily ignitable at predictable rate of combustion.
• It should be non-corrosive and non-hygroscopic.
• It should not leave any solid residue after ignition.
• It should not produce toxic or corrosive products.

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Classification of rocket propellants: They are classified as solid and liquid propellants.

Solid propellants: They are further two types, homogeneous and heterogeneous.

• Homogeneous: These are mixture of propellants in colloidal state. Ex: Cellulose nitrate.
• Heterogeneous/Composite: When an oxidizing agent is dispersed in a fuel mass, the solid propellant is said to be heterogeneous. Ex: Gun powder, 3:1 mixture of KClO₄ and asphalt oil

Advantages of solid propellants: They can be easily and safely stored, handled and transported. They can be stored in combustion chamber itself. They are more economical in use.

Liquid propellants: They may be either monopropellants or bipropellants.

• Monopropellant: The have fuel as well as oxidizer in the same molecule itself. They can be directly injected to combustion chamber. Ex: Methanol(22%) + H₂O₂(78%)
• Bipropellant: The fuel and oxidizer are kept separately. They are injected separately into the combustion chamber. Ex: Fuels – Ammonia, aniline, hydrazine; Oxidant: liquid oxygen, fuming HNO₃. Advantages of liquid propellants: More versatile i.e. large number of combinations of fuel, oxidants is possible. They also have high specific impulse. Engines using them can be checked and calibrated more easily.

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