Engineering Chemistry S Datta

340 ENGINEERING CHEMISTRY
This excess carbon and sulphur undergo slower reduction leading to more gaseous
products
4K 2
CO 3
+7S ⎯⎯→ K 2
SO 4
+ 2K 2
S 2
+ 4CO 2
↑
4K 2
SO 4
+7C ⎯⎯→ 2K 2
CO 3
+ 2K 2
S 2
+ 5CO 2
↑
This large volume of gaseous products is responsible for its explosive action. It is used
for blasting of coal. Other uses include blasting in shells, igniters and primer assemblies for
propellants etc.
2. Nitrocellulose or smokeless powder: It is prepared by treating purified cellulose with
mixed acid, having an approximate composition of 63% H 2
SO 4
, 22% HNO 3
and 15% H 2
O. When
nitration is complete, the nitrocellulose and the spent acid are centrifuged. The acid is sent to
mixing tanks for fortification and subsequent re-utilisation. The nitrocellulose so formed is
dissolved in alcohol and ether and the solvent evaporated when it forms a jelly-like mass. It is
stabilized by adding a stabilizer like diphenyl amine which can react with the liberated acid.
This product is stored as pressed cylindrical rods. It produces CO, CO 2
, N 2
, water vapour and
no smoke. So, it is known as smokeless powder.
(C) High explosives: This group consists of six types of compounds.
1. Single compound explosives. Consist of only one chemical compound such as:
(i) Ammonium nitrate: It is a powerful explosive compound when once initiated by an
external detonation impulse of sufficient magnitude and in sufficient amount. It is
very safe to handle under ordinary condition, stable and cheap. It is readily prepared
by the neutralisation of HNO 3
with NH 3
, two universally available cheap raw
materials. It is used to prepare binary explosives. It is also used as an explosive salt
to replace a portion of the nitroglycerine used previously. It cannot be stored near
inflammable materials and contact with alloys of copper is to be avoided as it
detonates.
(ii) Picric acid: Chemically picric acid is trinitrophenol. It is a high explosive and used as
self-filling explosives. It is largely replaced by TNT, because of its objectionable
character as it reacts with metals to form picrates which are dangerously sensitive.
(iii) Pentaerythritol tetranitrate (PETN): It is obtained by the nitration of the irregular
tetrahydric alcohol pentareythritol, which in turn is made by condensation of formaldehyde
with acetaldehyde.
CH2OH
CH2OH
C
CH2OH
CH2OH
CH ONO 2 2
CH ONO 2 2
+ 4HNO 3 C
+4H 2 O
CH2ONO2
CH ONO 2 2
This explosive compound has become important since the First World War as powerful
military explosive.
(iv) 2, 4, 6, Trinitrotoluene (TNT): This high explosive is prepared by nitration of toluene.
The raw material toluene is derived from coal tar or synthetically from petroleum
products. TNT is widely used as shell-firing explosive and under-water explosions.
Because of its low melting point (80.8°C) it is suited for loading in containers. Its
comparative excellence has made it useful for military consumption, in the aspects
like (a) being safe explosive for manufacture, storage and transportation, (b) nonhygroscopic,
(c) violent-disruptive explosive, and (d) non-reactive towards metals to
form unstable compounds.