EXPLOSIVES:

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EXPLOSIVES

• Effects of an Explosion
• Classification of Explosives
• Low Explosives
• High Explosives
• Primary
• Secondary
• Conclusion

• When an explosive is detonated, the material is
  instantly converted from a solid into a mass of
  rapidly expanding gases.
• Causes 3 primary effects
• Blast pressure
• Fragmentation
• Thermal effects

Taken in part from a seminar by Jim Kahoe and
Greg Brown
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Effects of an Explosion Blast Pressure

• At the time of detonation, the gases can rush out
  at velocities of up to 7,000 mph and can exert
  pressure of up to 700 tons per square inch.
• This gas travels in a outward circular pattern
  like a giant wave, smashing and shattering
  everything in its path.

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Order of Priorities
Priority Composition of Products of Decomposition
1 A metal and chlorine Metallic
chloride(solid) 2 Hydrogen and chlorine HCl
(gaseous) 3 A metal and oxygen Metallic oxide
(solid) 4 Carbon and oxygen CO (gaseous)
5 Hydrogen and oxygen H2O (gaseous) 6 CO and
oxygen CO2 (gaseous) 7 Nitrogen N2 (elemental)
8 Excess oxygen O2 (elemental) 9 Excess
hydrogen H2 (elemental)
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Order of Priorities
Priority Composition of Products of Decomposition
A Carbon and oxygen CO (gaseous) B Hydrogen
and oxygen H2O (gaseous) C CO and oxygen CO2
(gaseous) D Nitrogen N2 (elemental) E Excess
oxygen O2 (elemental) F Excess hydrogen H2
(elemental)
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Balancing Chemical Explosion Equations
The progression is from top to bottom you may
skip steps that are not applicable, but you never
back up. At each separate step there are never
more than two compositions and two products.
At the conclusion of the balancing, elemental
forms, nitrogen, oxygen, and hydrogen, are always
found in diatomic form. Example, TNT
C6H2(NO2)3CH3 constituents 7C 5H 3N 6O
Using the order of priorities priority 4 gives
the first reaction products 7C 6O -gt 6CO with
one mol of carbon remaining Next, since all the
oxygen has been combined with the carbon to form
CO, priority 7 results in 3N -gt 1.5N2
Finally, priority 9 results in 5H gt 2.5H2
The balanced equation, showing the products of
reaction resulting from the detonation of TNT is
C6H2(NO2)3CH3 -gt 6CO 2.5H2 1.5N2 C The
number of moles of gas formed is 10. The product,
carbon, is a solid.
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Volume of Products of Explosion
The molecular volume of any gas at 0 C and under
normal atmospheric pressure is very nearly 22.4
liters or 22.4 cubic decimeters. Thus,
considering the nitroglycerin reaction.
C3H5(NO3)3 -gt 3CO2 2.5H2O 1.5N2 .25O2
One mole of nitroglycerin produces 3 2.5
1.5 .25 7.25 molecular volumes of gas and
these molecular volumes at 0 C and atmospheric
pressure form an actual volume of 7.25 X 22.4
162.4 liters of gas. (Note that the products H2O
and CO2 are in their gaseous form.) Further, by
employing Charles' Law for perfect gases, the
volume of the products of explosion may also be
calculated for any given temperature. This law
states that at a constant pressure a perfect gas
expands 1/273 of its volume at 0 C, for each
degree of rise in temperature. Therefore, at 15
C the molecular volume of any gas is, V15
22.4 (1 15/273) 23.63 liters per mol Thus,
at 15 C the volume of gas produced by the
explosive decomposition of one gram molecule of
nitroglycerin becomes V 23.63 l (7.25 mol)
171.3 liters/mo
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The potential of an explosive is the total work
that can be performed by the gas resulting from
its explosion, when expanded adiabatically from
its original volume, until its pressure is
reduced to atmospheric pressure and its
temperature to 15 C. The potential is therefore
the total quantity of heat given off at constant
volume when expressed in equivalent work units
and is a measure of the strength of the
explosive. An explosion may occur under two
general conditions the first, unconfined, as in
the open air where the pressure (atmospheric) is
constant the second, confined, as in a closed
chamber where the volume is constant. The same
amount of heat energy is liberated in each case,
but in the unconfined explosion, a certain amount
is used as work energy in pushing back the
surrounding air, and therefore is lost as heat.
In a confined explosion, where the explosive
volume is small (such as occurs in the powder
chamber of a firearm), practically all the heat
of explosion is conserved as useful energy. If
the quantity of heat liberated at constant volume
under adiabatic conditions is calculated and
converted from heat units to equivalent work
units, the potential or capacity for work
results.
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Qmp represents the total quantity of heat given
off by a gram molecule of explosive of 15 C and
constant pressure (atmospheric) Qmv represents
the total heat given off by a gram molecule of
explosive at 15 C and constant volume and W
represents the work energy expended in pushing
back the surrounding air in an unconfined
explosion and thus is not available as net
theoretical heat Then, because of the
conversion of energy to work in the constant
pressure case, Qmv Qmp W Qmp ( viQfi
- vkQfk ) where Qfi heat of formation of
product i at constant pressure Qfk heat of
formation of reactant k at constant pressure v
number of mols of each product/reactants (m is
the number of products and n the number of
reactants) The work energy expended by the
gaseous products of detonation is expressed by
W Pdv W (10.132 x 104 N)(23.63
l)(Nmol)(10-3m3) W (0.572)(Nmol) kcal mol
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For TNT C6H2(NO2)3CH3 -gt with Nmol
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For TNT C6H2(NO2)3CH3 -gt 6CO 2.5H2 1.5N2
C with Nmol 10 mol Then Qmp 6(26.43)
-16.5 142.08 kca /l mol Note Elements in
their natural state (H2, O2, N2, C, et,.) are
used as the basis for heat of formation tables
and are assigned a value of zero. Qmv 142.08
0.572(10) 147.8 kcal / mol
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MW for TNT 227.1 g / mol Explosive Potential
is defined as heat per kg of explosive Qkv
147.8 (kcal/mol) x 1000 (g/kg) / 227.1 (g/mol)
651 kcal/kg Rather than tabulate such large
numbers, in the field of explosives, TNT is taken
as the standard explosive, and others are
assigned strengths relative to that of TNT. The
potential of TNT has been calculated above to be
651 kcal/kg (2.72 x 106 J/kg since 1kcal4185 J
). Relative strength (RS) may be expressed as
R.S. Potential of Explosive/ 2.72 x 106
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Example The PETN reaction will be examined as an
example of thermo-chemical calculations. PETN
C(CH2ONO2)4 MW 316.15 Heat of Formation
119.4 kcal/mol (1) Balance the chemical
reaction equation. Using priorities in order
decide reaction products 5C 12O -gt 5CO 7O
Next, the hydrogen combines with remaining
oxygen 8H 7O -gt 4H2O 3O Then the
remaining oxygen will combine with the CO to form
CO and CO2. 5CO 3O -gt 2CO 3CO2 Finally
the remaining nitrogen forms in its natural state
(N2). 4N -gt 2N2 The balanced reaction
equation is C(CH2ONO2)4 -gt 2CO 4H2O 3CO2
2N2
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(2) Determine the number of molecular volumes of
gas per gram molecule. Since the molecular volume
of one gas is equal to the molecular volume of
any other gas, and since all the products of the
PETN reaction are gaseous, the re-sulting number
of molecular volumes of gas (Nmol) is Nmol 2
4 3 2 11 mol-volume/mol (3) Determine
the potential (capacity for doing work). If the
total heat liberated by an explosive under
constant volume conditions (Qm) is converted to
the equivalent work units, the result is the
potential of that explosive. The heat liberated
at constant volume (Qmv) is equivalent to the
liberated at constant pressure (Qmp) plus that
heat converted to work in expanding the
surrounding medium. Hence, Qmv Qmp Work
(converted). a. Qmp Qfi (products) - Qfk
(reactants) where Qf Heat of Formation For
the PETN reaction Qmp 2(26.43) 4(57.81)
3(94.39) - (119.4) 447.87 kcal/mol (If the
compound produced a metallic oxide, that heat of
formation would be included in Qmp.
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b. Work 0.572(Nm) 0.572(11) 6.292 kcal/mol
As previously stated, Qmv converted to
equivalent work units is taken as the potential
of the explosive. c. Qmv 447.87 0.572(11)
454.16 kcal / mol Explosive Potential is
defined as heat per kg of explosive Qkv 454.16
(kcal/mol) x 1000 (g/kg) / 316.1 (g/mol) 1,436.8
kcal/kg 1,436.8 x 4185 6.01 x 106 J / kg
This product may then be used to find the
relative strength of PETN, which is e. RS Pot
(PETN 6.01 x 106 / (2.72 x 106 ) 2.21 Pot
(TNT)