ChemicalExplosivesExplosives arechemical compounds or mixtures of them, inclined under the influence ofexternal action to a very rapid chemical transformation with the release of alarge amount of energy and a large volume of gases with a high temperature.Compressed gaseous products, instantly expanding, are capable of producingmechanical work to move or destroy the environment and form shock waves in the environment. It is estimated that the number ofexplosives prepared and known at the present time is over thousands. In appearance, they come in avariety of colours and have a variety of forms. Currently, explosives arewidely used in military affairs and various sectors of the economy; they arewidely used in the mining industry, construction, irrigation and reclamation,agriculture and in the fight against fires; they find application in cutting,stamping, welding, hardening metals and other fields of technology. In recenttimes, the incidence of terrorism has increased, so to combat them, you alsoneed a thorough knowledge of explosives, their operation principle and basiccharacteristics.There are two types of chemicalexplosives: detonating and deflagrating explosives.
Deflagrating explosive is anexothermic reaction that occurs when energy is released fast and at relatively lowpressure. It accelerates through the substance at subsonic speed, creating ashock wave. Deflagrations range from flames to small-scale explosions. Forexample, gunfire, fireworks, black and smoking powders, even ordinary flamefrom a candle can be considered as a deflagration.
However, under a certaincondition, such as using a large quantity of substance or sudden short-durationexplosive, the deflagration can be caused to detonate, because of a massiveamount of energy releases during a short time.2 Detonating explosives release energy very quickly, meaning it ishigh explosive. The chemical transformation of an explosive, is accompanied bythe release of energy and the propagation of the exothermic reaction throughthe substance at supersonic speed (6-7 thousand meters per second). The chemical reaction is excitedby an intense shock wave forming the leading edge of the detonation wave. Thepressure in the front of the shock wave is tens of thousands of megapascal(hundreds of thousands of atmospheres), which explains the tremendousdestructive effect of such processes.
The energy released in the chemicalreaction zone continuously maintains high pressure in the shock wave. Detonationoccurs in many compounds and mixtures. For example, tetranitromethane C(NO2)4,is a heavy colourless liquid with a sharp smell, that is not explosive when itis pure. However, mixing it with organic compounds can cause a detonatedexplosion. An unfortunate event happened at the lecture in one of the Germanuniversities in 1919 when many students were killed during demonstration ofburning a mixture of tetranitromethane and toluene. It turned out that the labtechnician, when preparing the mixture, mixed up the mass and volume fractionsof the components and at the reagent densities of 1.64 and 0.87 g / cm3which caused an almost twofold change in the composition of the mixture and ledto the tragedy.
Another characteristic examples of this explosion areTNT, hexogen, ammonite, etc.Detonation explosive split intoprimary and secondary high explosives.Primary high explosives easilyexplode under the action of a simple initial impulse (impact, friction, a beamof fire, sparks) with the release of sufficient energy to ignite or detonateblasting explosives (secondary explosives). Primary high explosives can alsoexist as individual compounds or mixtures. They usually contain a metal atom inthe molecule that acts as a catalyst for combustion, or a group of atoms, inthe decomposition of which a large amount of heat is released.
For example:mercury fulminate, lead(II) azide (Pb(N3)2), cyanuric triazide (C3N12), lead styphnate (C6HN3O8Pb), tetrazene (H4N4) and DDNP (C6H2N4O5).As stated above, secondary high explosives are usually initiated by primary highexplosives. They are relatively insensitive to a simple impulse such as shock,heat or friction. The major example of secondary explosives is nitroglycerin asmost important component of explosives material.
Other examples are dynamite,ammonium nitrate (NH3NO2), ANFO (Ammonium Nitrate andFuel Oil), pentolite, booster etc.China was the first country thatstarted using chemical explosives. An unknown inventor from China created gunpowder in the ninthcentury.
For a long period of time gunpowder was used only for fireworks, andonly in the beginning of the 13th century it was used as a a weapon. From the14th century gunpowder was used as a propellant in a firearm and in the 17thcentury this chemical explosive was used for blasting operations in mining, aswell as for equipping artillery grenades (explosive nuclei). In 1884 the Frenchengineer P. Vielle proposed smoke-free gunpowder. For 300 years there were noother explosives other than gunpowder. 4 In 1874, nitroglycerin was synthesized for thefirst time, but this explosive was too unstable and dangerous forproduction and storage as small friction can cause it to spontaneous explosion.It consists of oxygen, carbon and nitrogen atoms and when it explodes itreleases a lot of energy and new, strong gases such as nitrogen, oxygen andcarbon dioxide are formed. Thus, rapid expansion of this gases causes the fluidto burn and explode very vigorously.
This is chemical equation represent decomposition of nitroglycerin: 4C3H5(ONO2)3–> 12CO2+10H20+6N2+O2. Therefore,nitroglycerin was mixed with clay and stabilizers. It would rendering itsafe to use while retaining its powerful explosive properties. This mixedcompounds well known this days as a dynamite. Nowadays, dynamiteused for mining, constructionsand it iscomposed of nitroglycerin, ammonium nitrate, sodium nitrate calciumcarbonate, and wood to neutralise acids that could form during reaction and make it safer to use and store.
7TNT (trinitrotoluene), the most powerful explosive in theworld, was produced and replaced dynamite.It wasvery popular in big countries due to several properties: safety, security andproduction technologies. It is made by mixing nitric and sulfuric acids withtoluene forming (three NO2 groups) mononitroluenes. WhenTNT explode the three substances produces: carbon dioxide, carbon monoxide andnitrogen.These substances are highly stable and have strong bonds that allows explosionto be so powerful.
TNT also has interesting properties: it is chemically veryinert, does not react with metals in any way; has low sensitivity that it does not explode even from the detonators, thus it must befist detonated by using a pressure wave from another detonator. Moreover, it can be stored in water or ammunitionhulls for about 60-70 years, without changing the explosive properties. 8 After high success, TNT was used with other compounds in order to createother explosives such as RDX and PETN that considered one of the most powerful highexplosives. RDX is highly explosives, moreexplosive than TNT because it contains nitrogen-nitrogen bonds that makes itextremely unstable and sensitive, but it usually mixed with other chemicals tomake it more controlled. PETN is more similar to TNT as it contains nitro group,although, it contains more nitro groups means it explode with more power. 9Another powerful explosiveis TATP, triacetone triperoxide.
It is known to be about 80% as strong as TNT,whereas their structures are completely different. TATP is a primary highexplosive produced by mixture of acetone and hydrogen peroxide, it containsweak and unstable oxygen-oxygen bonds. This means, the structure is harder tocontrol as it is less stable and more capable to spontaneously exploding. Additionally,TATP cannot be detected as it doesn’t contain nitrogen, thus it is used a lotby terrorists. 10 In conclusion, there are more than a thousand types ofchemical explosives.
These can be deflagrating, high explosive that splitinto primary and secondary high explosives or detonating explosives. They alsoused for different purposes such as: for military, terrorist, mining, buildingdeconstruction, firework, fire candle and so on. However, chemical explosivesconsider as one of the dangerous weapons in the world as it can destroy thewhole nation with a few minutes.