Chemical the propagation of the exothermic reaction through the

Chemical
Explosives

Explosives are
chemical compounds or mixtures of them, inclined under the influence of
external action to a very rapid chemical transformation with the release of a
large amount of energy and a large volume of gases with a high temperature.
Compressed gaseous products, instantly expanding, are capable of producing
mechanical work to move or destroy the environment      and form shock waves in the environment.

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It is estimated that the number of
explosives prepared and known at the present time is over thousands. In appearance, they come in a
variety of colours and have a variety of forms. Currently, explosives are
widely used in military affairs and various sectors of the economy; they are
widely 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 recent
times, the incidence of terrorism has increased, so to combat them, you also
need a thorough knowledge of explosives, their operation principle and basic
characteristics.

There are two types of chemical
explosives: detonating and deflagrating explosives.

Deflagrating explosive occurs when energy
is released fast and at
relatively low pressure. It accelerates through the substance at subsonic
speed, creating a shock wave. Deflagrations range from flames to small-scale
explosions. For example, gunfire, fireworks, black and smoking powders, even
ordinary flame from a candle can be considered as a deflagration. However,
under a certain condition, such as using a large quantity of substance or
sudden short-duration explosive, the deflagration can be caused to detonate,
because of a massive amount of energy releases during a short time.2

 Detonating explosives release energy very quickly, meaning it is
high explosive. The chemical transformation of an explosive, is accompanied by
the release of energy and the propagation of the exothermic reaction through
the substance at supersonic speed (6-7 thousand meters per second). The chemical reaction is excited
by an intense shock wave forming the leading edge of the detonation wave. The
pressure in the front of the shock wave is tens of thousands of megapascal
(hundreds of thousands of atmospheres), which explains the tremendous
destructive effect of such processes. The energy released in the chemical
reaction zone continuously maintains high pressure in the shock wave. Detonation
occurs 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 it
is pure. However, mixing it with organic compounds can cause a detonated
explosion. An unfortunate event happened at the lecture in one of the German
universities in 1919 when many students were killed during demonstration of
burning a mixture of tetranitromethane and toluene. It turned out that the lab
technician, when preparing the mixture, mixed up the mass and volume fractions
of the components and at the reagent densities of 1.64 and 0.87 g / cm3
which caused an almost twofold change in the composition of the mixture and led
to the tragedy. Another characteristic examples of this

explosion are
TNT, hexogen, ammonite, etc.

Detonation explosive split into
primary and secondary high explosives.

Primary high explosives easily
explode under the action of a simple initial impulse (impact, friction, a beam
of fire, sparks) with the release of sufficient energy to ignite or detonate
blasting explosives (secondary explosives). Primary high explosives can also
exist as individual compounds or mixtures. They usually contain a metal atom in
the molecule that acts as a catalyst for combustion, or a group of atoms, in
the 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 high
explosives. They are relatively insensitive to a simple impulse such as shock,
heat or friction. The major example of secondary explosives is nitroglycerin as
most important component of explosives material. Other examples are dynamite,
ammonium nitrate (NH3NO2), ANFO (Ammonium Nitrate and
Fuel Oil), pentolite, booster etc.

China was the first country that
started using chemical explosives. An unknown inventor from China created gunpowder in the ninth
century. For a long period of time gunpowder was used only for fireworks, and
only in the beginning of the 13th century it was used as a a weapon. From the
14th century gunpowder was used as a propellant in a firearm and in the 17th
century this chemical explosive was used for blasting operations in mining, as
well as for equipping artillery grenades (explosive nuclei). In 1884 the French
engineer P. Vielle proposed smoke-free gunpowder. For 300 years there were no
other explosives other than gunpowder. 4

In 1874, nitroglycerin was synthesized for the
first time, but this explosive was too unstable and dangerous for
production and storage as small friction can cause it to spontaneous explosion.
It consists of oxygen, carbon and nitrogen atoms and when it explodes it
releases a lot of energy and new, strong gases such as nitrogen, oxygen and
carbon dioxide are formed. Thus, rapid expansion of this gases causes the fluid
to 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. It would rendering it safe to use while
retaining its powerful explosive properties. This mixed compounds
well known this days as a dynamite. Nowadays, dynamite used for mining,
constructions; it is composed of
nitroglycerin, ammonium nitrate, sodium nitrate calcium carbonate,
and wood to neutralise acids that could form during reaction  and make it safer to use and store. 7

TNT (trinitrotoluene), the most powerful explosive in the
world, was produced and replaced dynamite.
It was
very popular in big countries due to several properties: safety, security and
production technologies. It is made by mixing nitric and sulfuric acids with
toluene forming (three NO2 groups) mononitroluenes. When
TNT explode the three substances produces: carbon dioxide, carbon monoxide and
nitrogen.
These substances are highly stable and have strong bonds that allows explosion
to be so powerful. TNT also has interesting properties: it is chemically very
inert, does not react with metals in any way; has low sensitivity that it does not explode even from the detonators, thus it must be
fist detonated by using a pressure wave from another detonator. Moreover, it can be stored in water or ammunition
hulls for about 60-70 years, without changing the explosive properties. 8

 After high success, TNT was used with other compounds in order to create
other explosives such as RDX and PETN that considered one of the most powerful high
explosives. RDX is highly explosives, more
explosive than TNT because it contains nitrogen-nitrogen bonds that makes it
extremely unstable and sensitive, but it usually mixed with other chemicals to
make 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. 9

Another powerful explosive
is TATP, triacetone triperoxide. It is known to be about 80% as strong as TNT,
whereas their structures are completely different. TATP is a primary high
explosive produced by mixture of acetone and hydrogen peroxide, it contains
weak and unstable oxygen-oxygen bonds. This means, the structure is harder to
control 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 lot
by terrorists. 10

In conclusion, there are more than a thousand types of
chemical explosives. These can be deflagrating, high explosive that split
into primary and secondary high explosives or detonating explosives. They also
used for different purposes such as: for military, terrorist, mining, building
deconstruction, firework, fire candle and so on. However, chemical explosives
consider as one of the dangerous weapons in the world as it can destroy the
whole nation with a few minutes.