CHEMISTRY: EXPLOSIVES

CHEMISTRY: EXPLOSIVES

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Overview

• An explosive is a substance that contains a great deal of stored energy that can produce an explosion, usually accompanied by the production of light, heat and pressure
• The energy stored in an explosive material may be
  • Chemical energy such as nitroglycerine
  • Pressurised compressed gas such as a gas cylinder or aerosol can
  • Nuclear energy such as Uranium and plutonium

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CHEMICAL REACTIONS IN EXPLOSIVES

1. Deflagration
   1. Deflagration is a term that describes subsonic combustion that propagates through thermal conductivity
   2. Deflagration is easier to control and so is used when the goal is to move an object with the force of expanding gas
   3. Examples of deflagration include gas stove, internal combustion engine, gunpowder, pyrotechnics etc
2. Detonation
   1. Detonation is a combustion process in which a supersonic shock wave through the body of a material
   2. In detonation, a supersonic shock wave originating at the point of ignition compresses the surrounding material, thus increasing its temperature to the point of ignition
   3. Because detonations generate high pressures, they are much more destructive than deflagrations
   4. Detonations are difficult to control and are used primarily for demolition and in warfare.
   5. Examples of detonation includes high explosives, oxygen-methane mixture

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CLASSIFICATION OF EXPLOSIVES

1. High explosives

• Materials that explode faster than the speed of sound are called high explosives
• This type of explosion is known as detonation
• Used in mining, demolition and military applications

1. Low explosives
   1. Materials that explode slower than the speed of sound are called low explosives.
   2. This type of explosion is known as deflagration
   3. Used as propellants, gun powder, pyrotechnics (such as flares and fireworks)
2. Primary explosives
   1. A primary explosive is an explosive that is extremely sensitive to stimuli. These stimuli include impact, friction, heat, static electricity and electromagnetic radiation
   2. For primary explosives, a relatively small amount of energy is required for initiation of explosion
   3. In general, primary explosives are considered to be those explosives that are more sensitive than PETN
   4. Used in detonators to trigger larger charges of more stable secondary explosives
   5. E.g.: Mercury fulminate, Nitrogen trichloride, acetone peroxide, ammonium permanganate
3. Secondary explosives
   1. Secondary explosives are less sensitive than primary explosives and require more energy to be initiated
   2. They are safer to handle and store
   3. In general, secondary explosives are considered to be those explosives that are less sensitive than PETN
   4. Secondary explosives are usually used in large quantities and are initiated by small amounts of primary explosives
   5. E.g.: TNT, RDX

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SOME COMMON EXPLOSIVES

1. Trinitrotoluene (TNT)
   1. TNT is a useful explosive material with convenient handling properties. TNT is sometimes also used as a reagent in chemical synthesis
   2. TNT was first prepared by Joseph Wilbrand (GermanY) in 1863
   3. The explosive yield of TNT is considered to be the standard measure of strength of bombs and other explosives
   4. Sulphitation is a process used in the manufacture of TNT, specifically to stabilize the explosive
   5. TNT is one of the most commonly used explosives for industrial and military applications
   6. It is insensitive to shock and friction, reducing the occurrence of accidental detonation. TNT melts without exploding (allowing it to be combined with other explosives), does not absorb or dissolve in water (allowing use in wet environments) and is stable compared to other explosive
   7. TNT contains energy of 4.6 Mega Joules per kilogram (MJ/kg). By comparison gun powder contains 3 MJ/kg, dynamite contains 7.5 MJ/kg and gasoline contains 47.2 MJ/kg
      
   8. TNT is used as a reference for other explosives. Nuclear weapons have energy content measured in kilotonnes (kT) or megatonnes (MT) of TNT equivalent. 
      
   9. TNT is usually used in mixture with other substances. E.g.: Amatol (TNT + ammonium nitrate)
      
2. RDX
   1. RDX, chemically cyclotrimethylnetrinitramine, is also known as cyclonite and T4
   2. RDX is usually used in mixture with other explosives and plasticizers
   3. RDX is stable in storage and is considered one of the most powerful of military explosives
   4. RDX was discovered in 1898 by Goerg Friedrich Henning (Germany)
3. Pentaerythritol tetranitrate (PETN)
   1. PETN is one of the most powerful high explosives known
   2. It is more difficult to detonate than primary explosives, but less stable than secondary explosives
   3. It is more sensitive than other high explosives, and is rarely used alone
   4. Usually used in small calibre ammunition, detonators of land mines
   5. PETN is an effective underwater explosive
   6. PETN is a major ingredient of Semtex (plastic explosive)
   7. PETN was first synthesised by Bernhard Tollens (Germany) in 1891
4. Dynamite
   1. Dynamite is based on nitroglycerine
   2. It was invented by Alfred Nobel (Sweden) in 1867
   3. Used mainly for mining, quarrying, construction
   4. Dynamite was the first safely manageable explosive stronger than black powder
5. Plastic explosive
   1. Plastic explosives are explosives that are soft and can be moulded by hand
   2. Common plastic explosives include Semtex (Czech Republic) and C-4 (USA)
   3. Used mainly for demolition, also used by terrorists
   4. The first plastic explosive was Gelignite, invented by Alfred Nobel (Sweden) in 1875
   5. C-4 (composition 4) is made of RDX while Semtex is made from RDX and PETN
   6. Semtex became notoriously popular with terrorists because it is difficult to detect. Semtex was invented by Stanislav Berbera (Czech R.) in the 1950s

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