EXPLOSIVES
Names
and Formulae:
The
two main sets of rules cover all organic
and inorganic compounds. The former are
compounds associated with living matter , contain, mainly, carbon,
hydrogen , nitrogen, and oxygen atoms.
The latter, not generally linked with
living matter , are made up of
all other atoms. They include, for example , the many minerals which contain metallic atoms.
The
different states of a substance are represented by (s) for solid, (l) for liquid or (g) for gas or vapor after its name. Thus ice is H2O(s),
water H2O(l) and steam H2O(g) .
CHEMICAL
REACTIONS
A
chemical reaction involves
rearrangement of atoms. The
bonds in the molecules of the reagents split and the free atoms released , which exist
only momentarily , recombine to give the different molecules of the products . The reaction is commonly
summarized in the form of a chemical equation.
There
are three main requirements for the reaction
to be explosive . First , it must take place very quickly . Secondly ,
it must be an exothermic reaction ; that is heat must be evolved. Thirdly, as
many of the products as possible must be gases. As they will be hot , this
ensures a big rise in pressure which is the main cause of the explosion.
GUN
POWDER AND ITS MODIFICATIONS
Gunpowder
is made from carbon © , sulfur (S) and potassium nitrate ( KNO3) . No single chemical equation can fully represent the nature
of the complex chemical reaction
that occurs when it explodes but an over-simplification commonly used is as follows
4KNO3(s)+
7C(s) + S(s) à
3CO2(g)+ 3CO(g)+ 2N2(g)+K2CO3(s)+K2S(s)
Less
than half the gun powder is converted into gaseous products and much of the heat produced in the explosion is retained
in the solid products. Both of these factors limit the efficiency of gunpowder as an explosive.
ANFOs
, made from ammonium nitrate and fuel oils , are more efficient . The equation for the reaction of a typical example,
25NH4NO3(s)+C8H18(l)à
8 CO2(g)+ 59 H2O(g) + 25N2(g)
shows
that all the explosive mixture is converted into gases.
Other
chemicals used in making gunpowder
substitutes include
NaNO3 NH4NO3 KClO3
Sodium
nitrate Ammonium
nitrate Potassium chlorate (V)
NaClO3 KClO4 NH4ClO4
Sodium
chlorate (V) Potassium perchlorate Ammonium perchlorate
(chlorate
(VII)) ( chlorate
(VII))
EXPLOSIVES
CONTAINING THE NITRO-NO2 GROUP:
A
number of explosives are made by replacing the hydrogen atoms within the C-H or
N-H bonds in organic compounds by nitro-NO2 groups by treatment with a mixture
of nitric ( HNO3) and sulfuric (H2SO4) acids.
The process is known as nitration and is summarized as
If
only one hydrogen atom in a molecule , X, is replaced by a nitro group the
product is called nitro-X or mononitro-X; if two hydrogen atoms are replaced ,
it is dinitro-X, if three, tri-nitro-X. The precise position of the nitrogroup
within a molecule is shown by the use of numbers.
TRINITROTOLUENE,
TNT. Toluene got its name made in 1841,
by distilling Tolu balsam and because it
was like benzene . Its modern name methyl
benzene and it is converted into TNT by nitration.
When
TNT explodes , its molecules split up , partially , because te C-N bond is
weak; the equation is
C7H5N3O6(s)
--à3.5
CO2(g)+2.5H2O(g) + 1.5 N2(g) + 3.5C(s)
Because
there are too few atoms of oxygen within the molecule some of the carbon remains as a solid and is
not oxidized into gases . That is why black smoke is produced in a TNT
explosion and why ammonium nitrate is added in the amatols to provide more oxygen.
LYDDITE.
Lyddite is made by nitrating phenol .
Its old chemical name was picric acid( from the Greek pikros=bitter).
The
simple equation that best represents its explosion is
C6H3N3O7(s)--à5.5CO(g)
+1.5H2O(g)+1.5 N2(g)+0.5C(s)
RDX.
RDX or cyclotrimethylenetrinitramine is made by the nitration of hexamine or
hexamethylene tetramine.
The
equation for its explosion is
C3H6N6O6(s)à
3CO(g) + 3H2O(g) + 3N2(g)
HMX
and HNIW.
EXPLOSIVES
CONTAINING THE NITRATE –O—NO2 GROUP
Nitrates
are formed by reaction between a mixture between a mixture of nitric acid and
sulfuric acids and organic compounds
containing hydroxyl,--OH groups. In summary ,
Many
of the products have been and still are wrongly regarded as nitro—compounds.
They do contain an - NO2 group but it is linked to an oxygen atom so
that it is , really, just a part of a
nitrate group.
DYNAMITE.
The main component of dynamite is still commonly called nitroglycerine or
nitroglcerol but the more correct name is glycerol trinitrate , or better still
,propane –1,2,3---triyl trinitrate.
The
equation for its explosion is
C3H5N3O9(l)à3CO2(g)+2.5
H2O(g) +1.5 N2(g)+0.25O2(g)
GUNCOTTON.
When cellulose is treated with a mixture
of nitric acid and sulfuric acids, various products are formed. Prolonged
treatment with hot, concentrated acids gives a product which contains about
13.3 per cent of nitrogen and is called
guncotton; its main component is cellulose trinitrate. Weaker acids at a lower
temperature for a shorter time give a mixture containing between 8 and 12
percent of nitrogen. It is known as
pyroxylin or collodion and is a mixture of cellulose mono—and di-nitrates.
PETN.
PETN or pentaerylthritol tetranitrate is made by treating pentaerythritol with
a mixture of nitric and sulfuric acids.
INITIATING
EXPLOSIVES
Initiating
explosives are particularly sensitive . Some typical examples are given below:
Hg(CNO)2 Pb(N3)2 (NO2)3C6HO2Pb
Mercury
fulminate Lead
azide Lead styphnate
Lead
2,4,6-trinitro
Resorcinate
POSSIBLE
NEW PRODUCTS
APPENDIX
II
ENERGY
and POWER!!
Explosions
occur when there is a rapid release of energy which produces a large volume of
hot gases and build up of pressure. In a chemical explosion , the energy is
released in a chemical reaction; in a nuclear explosion , it is nuclear energy
that is released. The SI unit of the energy is the joule, with 1J being the
work required to move a force of 1 newton over a distance of 1 meter. That is
equivalent to lifting a small apple of mass 102 g , by 1 meter . 1kilojoule
(1kJ) is 1000J and 1 Megajoule (1MJ) is 106J.
In
both chemical and nuclear explosions the release of energy arises from the
conversion of a small amount of mass into energy in the course of the
explosion. As a consequence of his theory of relativity , Albert Einstein put forward the idea , in 1907, that mass and
energy were related according to the equation.
E = m * c2
Energy
= Mass * (Velocity
of light)2
(
in joules) (in
kilograms) ( in meters per
second)
Because
the velocity of light is a very large number ( 2.997924580*108 m per
sec) it follows that small amounts of mass can provide large amounts of energy
. 1kg of mass is indeed equivalent to 8.988*1016 joules.
Sir
James Jeans referred to mass as ‘ bottled energy’ but it is not easy to get
complete or efficient conversion of mass into energy . The energy liberated in
any ordinary chemical reaction requires a conversion of only about 100*10-12
kg of mass and this cannot be detected on any balance.
POWER
Energy
is a measure of the capacity to do work
whereas power is a measure of the rate at which the work is done. Thus a
man uses energy and does work when he lifts a suitcase . If he lifts it twice
as quickly he uses the same energy but needs twice the power. The unit of power
is the watt with 1 watt equivalent to 1 joule per second. The older unit of
horse power , based by James Watt on an estimate that an energy horse could
lift a weight of 51 kg to a height of 60 m in 1 minute and could go on doing it
for a whole shift , is now taken as 745.70watt.
EXOTHERMIC
REACTIONS.
A
chemical reaction which releases energy is called an exothermic reaction. The
burning of hydrogen in air is typical ; it is represent by the following
equations,
2H2(g)+O2(g)
à 2H2O(g) + 484kJ
2H2(g)+O2(g)
à
2H2O(g) ▲H=-484kJ
The
first equation indicates that 484kJ of energy are released when 2mol, 4 gram,
or 12.044273*1023 molecules of hydrogen are completely burnt. The
second equation provides the same information in a slightly different way by
giving what is known as the enthalpy change, ▲H , for the reaction. It is the
change in the energy that has taken place. Because energy has been released , the products of
the reaction have a lower enthalpy than the initial reagents. That is why the▲
H value is negative.
In
an endothermic reaction , energy is absorbed and the ▲H value is positive. For example,
N2(g)
+O2(g) à
2NO(g) – 90.4kJ
N2(g)+O2(g)à
2NO(g) ▲H =90.4kJ
In a simple way , an exothermic reaction can be
regarded as a ‘downhill’ reaction ; an endothermic one as an ‘uphill’.
HEATS
OF EXPLOSION: The amount of heat released by an explosive is commonly known as
the heat of explosion. It is usually expressed in joules per gram. Some typical
, calculated values , are listed below;
Nitroglycerine
6275 PETN 5940
RDX 5130 TNT 4080
The
experimentally measured values may be slightly different depending on the way the
explosion is brought about.
The
heat of explosion is calculated from bond energy values which give a measure of the amount of
energy involved in breaking or forming a particular bond . The values are
generally expressed in kilojoules (kJ) per mole of the bond , i.e. for
6.06*1023 individual bonds. Some typical values are
H-H 436 C-H 412 C-C 348
O=O 496 O-H 463 C=C 743
N≡
N 944 N-H 388 C≡C 305
The
burning or explosion of hydrogen and oxygen , according to the equation given
above , requires (2*436)kJ to split H-H bonds and 496 kJ to split one O=O bond ; that is 1368kJ.
Forming four O-H bonds releases (4*463),
i.e. 1852 kJ. The amount of energy released is, therefore , (1852-1368), i.e.
484kJ.
One
of the reasons , why chemicals containing
C-N bonds are likely to be explosive is that there is a large release of
energy when the weak C-N bond is converted into the much stronger N≡N bond.
THE
RATE OF REACTION
An
explosive depends more on the rate at which its energy is released than on the
total amount of energy . 1 kg of TNT, for example will release 4080kJ of energy when it is
detonated. 1 kg of petrol will release more than 30 MJ when it is fully burnt
in air, but because that burning is a relatively slow process, the petrol will
not normally explode. It can, however , be made to explode if it is well mixed
with a lot of air before ignition so
that the burning takes place much more rapidly.
Similarly,
natural gas or methane will normally burn steadily in a gas cooker on fire. A
mixture of a lot of air with only a little natural gas can, however, be
explosive. It is the build up of such mixtures( fire damp) in coal mines that
is the cause of many disasters.
NUCLEAR
EXPLOSIONS:
The
energy release in a nuclear explosion comes about because different atoms have
different bonding energies within their nuclei . As with a chemical explosion,
it is the associated very slight loss of mass which produces the energy.
A
possible way in which the nucleus of U might be split by a neutron ( 01n
) is summarized in the following equation
92235U + 01n-----------------à52144Ba
+3690Kr +201n
235.0439 1.0087 143.881 89.947
2.0147
236.0526 235.8454
The
masses of the particles involved are given in atomic mass units ( amu) with 1
amu being equal to 1.6605402*10-27kg.
The equation shows a loss of (236.0526-235.8454), i.e. 0.2072 amu or
3.440639*10-26kg. That means the liberation of
3.0924463*10-11J for the fission of 1 atom of 92235U. The fission of 1 gram (
25.6261*1020 atoms) would, therefore , release 7.9247338*1010J.
The scanned pages will be provided later !!
Dr. IR Durrani
EXPLOSIVES!!