Chemistry of Explosives

Report
Explosive Properties
Explosives 189
Dr. Van Romero
26 Jan 2012
Some Definitions
• Explosion – rapid expansion of matter into a
volume much greater than the original volume
Some Definitions
• Explosion – rapid expansion of matter into a
volume much greater than the original volume
• Burn & Detonate – Both involve oxidation
– Burn – relatively slow
– Detonate – burning at a supersonic rate producing
a pressure Wave
Some Definitions
• Explosion – rapid expansion of matter into a
volume much greater than the original volume
• Burn & Detonate – Both involve oxidation
– Burn – relatively slow
– Detonate – burning at a supersonic rate producing
a pressure Wave
• Deflagration – Burning to detonation (DDT)
Some Definitions
• Explosion – rapid expansion of matter into a
volume much greater than the original volume
• Burn & Detonate – Both involve oxidation
– Burn – relatively slow
– Detonate – burning at a supersonic rate producing
a pressure Wave
• Deflagration – Burning to detonation (DDT)
• Shock wave – High pressure wave that travels
faster then the speed of sound
Explosives Vs. Propellants
• The difference between an explosive and a
propellant is functional as apposed to
fundamental.
Explosives Vs. Propellants
• The difference between an explosive and a
propellant is functional as apposed to
fundamental.
• Explosives are intended to function by
detonation from shock initiation (High
Explosives)
Explosives Vs. Propellants
• Propellants are initiated by burning and then
burn at a steady rate determined by the
devise, i.e. gun (Low Explosives)
• Single molecule explosives are categorized by
the required initiation strength
Primary Explosives
• Primary Explosives – Transit from surface
burning to detonation within a very small
distance.
– Lead Azide (PbN6 )
Secondary Explosives
• Secondary Explosives – Can burn to
detonation, but only in relatively large
quantities. Secondary explosives are usually
initiated from the shock from a primary
explosive (cap sensitive)
• TNT
Tertiary Explosives
• Tertiary Explosives – Extremely difficult to
initiate. It takes a significant shock (i.e.
secondary explosive) to initiate. Tertiary
explosives are often classified as nonexplosives.
• Ammonium Nitrate (NH4NO3)
Exothermic and
Endothermic Reactions
• Chemical reaction
– Reactants  Products.
– Internal energy of reactants ≠ internal energy of
products.
– Internal energy: contained in bonds between
atoms.
– Reactants contain more energy than products—
energy is released as heat.
– EXOTHERMIC Reaction.
Exothermic and
Endothermic Reactions
• Products contain more internal energy than
reactants
• ENDOTHERMIC Reaction
• Energy must be added for the reaction to
occur.
• Burning and detonation are
Exothermic and
Endothermic Reactions
• Products contain more internal energy than
reactants
• ENDOTHERMIC Reaction
• Energy must be added for the reaction to
occur.
• Burning and detonation are Exothermic
Oxidation: Combustion
• Fuel + Oxidizer  Products (propellant)
Oxidation: Combustion
• Fuel + Oxidizer  Products (propellant)
• CH4 + 2 O2  CO2 + 2 H20
Methane Oxygen
Carbon
Dioxide
Water
Oxidation: Combustion
• Fuel + Oxidizer  Products (propellant)
• CH4 + 2 O2  CO2 + 2 H20
Methane Oxygen
Carbon
Dioxide
Water
• Oxidation (combustion) of methane
• 1 methane molecule : 2 oxygen molecules
(4 oxygen atoms).
Oxidation: Decomposition
• Oxidizer + Fuel  decomposition to products
(Explosive)
Oxidation: Decomposition
• Oxidizer + Fuel  decomposition to products
(Explosive)
• Example: Nitroglycol
• O2N—O—CH2—CH2—O—NO2 
Fuel (Hydrocarbon) + Oxidizer (Nitrate Esters)
Oxidation: Decomposition
• Oxidizer + Fuel  decomposition to products
(Explosive)
• Example: Nitroglycol
• O2N—O—CH2—CH2—O—NO2 
Fuel (Hydrocarbon) + Oxidizer (Nitrate Esters)
• Undergoes Decomposition to:
2 CO2 + 2 H2O + N2
Carbon
Dioxide
Water
Nitrogen
CHNO Explosives
• Many explosives and propellants are composed
of:
–
–
–
–
Carbon
Hydrogen
Nitrogen
Oxygen
• General Formula: CcHhNnOo
• c, h, n, o are # of carbon, hydrogen, nitrogen and
oxygen atoms.
• For Nitroglycol: C2H4N2O6
CHNO Explosive
Decomposition
• CcHhNnOo  c C + h H + n N + o O
• Imagine an explosive detonating.
– Reactant CHNO molecule is completely broken
down into individual component atoms.
CHNO Explosive
Decomposition
• CcHhNnOo  c C + h H + n N + o O
• Imagine an explosive detonating.
– Reactant CHNO molecule is completely broken
down into individual component atoms.
• For Nitroglycol:
– 2N  N2
– 2H + O  H20
– C + O  CO
– CO + O  CO2
Overoxidation vs
Underoxidation
• In the case of nitroglycol
• O2N—O—CH2—CH2—O—NO2 
2 CO2 + 2 H2O + N2
• Exactly enough oxygen to burn all carbon to CO2
• Some have more than enough oxygen to burn all
the carbon into CO2
– OVEROXIDIZED OR FUEL LEAN
• Most explosives do not have enough oxygen to
burn all the carbon to CO2
– UNDEROXIDIZED OR FUEL RICH
Simple Product Hierarchy
for CHNO Explosives
• First, all nitrogen forms N2
Simple Product Hierarchy
for CHNO Explosives
• First, all nitrogen forms N2
• Then, all the hydrogen is burned to H2O
Simple Product Hierarchy
for CHNO Explosives
• First, all nitrogen forms N2
• Then, all the hydrogen is burned to H2O
• Any oxygen left after H20 formation burns carbon
to CO.
Simple Product Hierarchy
for CHNO Explosives
• First, all nitrogen forms N2
• Then, all the hydrogen is burned to H2O
• Any oxygen left after H20 formation burns carbon
to CO.
• Any oxygen left after CO formation burns CO to
CO2
Simple Product Hierarchy
for CHNO Explosives
• First, all nitrogen forms N2
• Then, all the hydrogen is burned to H2O
• Any oxygen left after H20 formation burns carbon
to CO.
• Any oxygen left after CO formation burns CO to
CO2
• Any oxygen left after CO2 formation forms O2
Simple Product Hierarchy
for CHNO Explosives
• First, all nitrogen forms N2
• Then, all the hydrogen is burned to H2O
• Any oxygen left after H20 formation burns carbon
to CO.
• Any oxygen left after CO formation burns CO to
CO2
• Any oxygen left after CO2 formation forms O2
• Traces of NOx (mixed oxides of nitrogen) are
always formed.
Decomposition of
Nitroglycerine
• C3H5N3O9  3C + 5H + 3N + 9O
–
–
–
–
3N  1.5 N2
5H + 2.5O  2.5 H2O (6.5 O remaining)
3C + 3O 3 CO (3.5 O remaining)
3 CO 3O  3 CO2 (0.5 O remaining)
• 8.5 of 9 oxygen atoms consumed
– 0.5 O  0.25 O2
Decomposition of
Nitroglycerine
• C3H5N3O9  3C + 5H + 3N + 9O
–
–
–
–
3N  1.5 N2
5H + 2.5O  2.5 H2O (6.5 O remaining)
3C + 3O 3 CO (3.5 O remaining)
3 CO + 3O  3 CO2 (0.5 O remaining)
• 8.5 of 9 oxygen atoms consumed
– 0.5 O  0.25 O2
• Overall Reaction:
– C3H5N3O9  1.5 N2 + 2.5 H2O + 3 CO2 + 0.25 O2
• Oxygen Remaining = Nitroglycerine is
– OVEROXIDIZED
Decomposition of RDX
H2
• C3H6N6O6  3C + 6H +6N +6O
–
–
–
–
6N  3N2
6H + 3O  3H2O (3 O remaining)
3C + 3O  3CO (All O is consumed)
No CO2 formed.
H2
H2
Decomposition of RDX
H2
• C3H6N6O6  3C + 6H +6N +6O
–
–
–
–
6N  3N2
6H + 3O  3H2O (3 O remaining)
3C + 3O  3CO (All O is consumed)
No CO2 formed.
• Overall Reaction:
– C3H6N6O6  3 N2 + 3 H2O + 3 CO
• Not enough oxygen to completely burn
all of the fuel
– UNDEROXIDIZED
H2
H2
Oxygen Balance
• OB (%)
– 1600/MWexp[oxygen-(2 carbon+ hydrogen/2)]
• Oxygen balance for Nitroglycol C2H4N2O6
– c = 2, h = 4, n = 2, o = 6
– Mwexp=12.01 (2) + 1.008 (4) + 14.008 (2) + 16.000
( 6) = 152.068 g/mol
– OB = 1600
= 0%
6 – 2 (2) – 4
152.068
2
Perfectly Balanced
Oxygen Balance
• Oxygen balance for Nitroglycerine C3H5N3O9
– C = 3, h = 5, n = 3, o = 9
– Mwexp=12.01 (3) + 1.008 (5) + 14.008 (3) + 16.000
( 9) = 227.094 g/mol
1600
5
– OB =
9 – 2 ( 3) –
227.094
2
= 3.52%
Slightly overoxidized
Oxygen Balance
• Oxygen balance for RDX: C3H6N6O6
– C = 3, h = 6, n = 6, o = 6
– Mwexp=12.01 (3) + 1.008 (6) + 14.008 (6) + 16.000
( 6) = 222.126 g/mol
1600
6
– OB =
6 – 2 ( 3) –
222.126
2
= -21.61%
Underoxidized
Homework
• Calculate the oxygen balance for:
– TNT
– Picric Acid

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