Explosives and Explosions

Report
Explosives and Explosions
The Chemistry of High
Energy Organic Compounds
What is an Explosion?
Rapid burning of a material
resulting in a sudden build-up
and release of heat and gas
pressure.
Explosions Which Rely
on Oxygen from the Air
• Combustion of gasoline in the
engine of your car.
• How easy is it to make gasoline
explode?
Hexanes: Among the many hydrocarbons
found in gasoline, they are representative of
the volatility and explosivity of gasoline.
Hexanes burn rapidly in air to
form carbon dioxide and water.
2 C6H14
+
19 O2
12 CO2
+
14 H2O
Hexanes will not explode in a closed container
and neither will gasoline.
•Too much fuel
•Not enough oxygen
The gas tank on your car is not an explosion
hazard.
•Vapor phase concentration of hydrocarbons is
above upper explosive limit (UEL) of 8%.
Ethanol also burns in air.
CH3CH2OH
+
3 O2
2 CO2
+
14 H2O
Ethanol is highly explosive in a closed
container
• optimum balance of fuel and oxygen in the vapor
•Vapor phase concentration of ethanol at room
temperature falls between the LEL and UEL.
What about other types of
hydrocarbon fuels and fuel tanks?
• Diesel and Jet fuel tanks have a
higher risk of explosion than
automobile fuel tanks.
• TWA Flight 800 exploded in mid air in
1996, probably due to a vapor phase
fuel tank explosion.
Surprisingly, explosivity of jet
airplane fuel tanks is not well
studied or understood.
“The July 17, 1996, crash of TWA flight 800, a Boeing 747 airplane, was
blamed on a fuel-air explosion within the center wing tank, with the
ignition source still unidentified. As a consequence of the accident, the
Federal Aviation Administration (FAA) is evaluating improved safety
requirements for the fuel tanks on commercial aircraft. One technique,
recommended by the National Transportation Safety Board (NTSB), is to
maintain sufficient fuel in the center wing tanks of transport aircraft to
limit the liquid fuel temperature rise and evaporation, thus keeping the
vapor fuel/air ratio below the explosive limit. Initial attempts to determine
the benefit of additional fuel in the center tank were frustrated by the
lack of an acceptable method for determining the explosive hazard in the
tank under varying conditions.”
- FAA final report, TWA Flight 800 crash investigation.
How can we make explosives
without the limitation of needing
oxygen from the air?
• Make the “oxygen” (oxidizing agent)
part of the chemical structure.
• Example: Nitrocellulose used in gun
powder.
Cellulose (cotton) burns
slowly in air.
H OH
H
H OH
O
O
O
HO
H
OH
H
H
O
HO
H
H OH
H
H
OH
H
O
H
HO
O
H
Cellulose
major component of cotton
H
OH
H
O
Nitrocellulose (gun cotton)
burns very rapidly even
without air.
NO2
H
O
NO2
H
H
O
O
O
O
O
O2N
H
H
O
O
H
O2 N
H
O2N
O
H
H
O2N
Nitrocellulose
"gun cotton"
NO2
O
O
H
O
H
H
O
O
O2N
H
H
O
O2N
major component of modern gun powder and fireworks
O
H
High Explosives Burn at
Supersonic Speeds
Conflagration: rapid burning with a flame
front traveling through the material at
1 m/sec to 300 m/sec.
Detonation: “instantaneous” burning with
flame front traveling through the material
at 1000 m/sec to 3000 m/sec resulting in a
supersonic shock wave.
Primary and Secondary
High Explosives
• Primary High Explosives
- detonate very easily
- minimal activation energy.
• Secondary High Explosives
- do not detonate easily
- high activation energy
Early Examples of Primary
High Explosives
CH2OH
CH2ONO2
HNO3
CHOH
CHONO2
H2SO4
CH2OH
CH2ONO2
Nitroglycerine
Glycerine
CH2OH
CH2ONO2
HNO3
HOH2C
C
CH2OH
O2NOH2C
C
CH2ONO2
H2SO4
CH2OH
Pentaerythritol
CH2ONO2
Pentaerythritoltetranitrate
(PETN)
Nitroglycerine
• Nitroglycerine detonates by rapidly rearranging to a
collection of small stable gas molecules releasing a huge
quantity of heat and pressure.
CH2ONO2
4
CHONO2
CH2ONO2
•
Detonation
12 CO2 +
6 N2
+
10 H2O
+
O2
Pure Nitroglycerine is way too “sensitive” to be a useful
explosive. It was the invention of dynamite by Alfred Nobel
that converted nitroglycerine into a useful commercial and
military explosive by mixing nitroglycerine with clay
(diatomaceous earth) and forming the mixture into dynamite
sticks.
Nitrogen triiodide
• NI3 also detonates by rearrangement to a
collection of small stable gas molecules.
2 NI3
N2
+
3 I2
Secondary High Explosives
• Compounds which are not easily
(accidentally) detonated but which
can be detonated intentionally to
cause very high energy explosions.
• Secondary explosives require a
small amount of a primary explosive
to set them off.
Examples of Secondary
High Explosives
CH3
OH
O2N
NO2
O2N
NO2
NO2
NO2
TNT
Picric Acid
NO2
O2N
NO2
N
N
N
O2 N
N
N
N
N
NO2
RDX
O2N
HMX
NO2
Predicting the Products of
Organic High Explosive Reactions
• Carbon combines with oxygen to form CO to maximum
extent possible.
•
Hydrogen combines with any additional oxygen to form
H2O to maximum extent possible.
•
CO combines with any additional oxygen to form CO2.
•
Nitrogen forms N2.
•
Excess oxygen forms O2.
•
Excess hydrogen forms H2.
Oxygen Balance: A useful
concept for evaluating high
explosives.
Oavail - Oneeded
%OB = --------------------------- (100)
mass of comp.
Oxygen Balance of Some
Representative High Explosives
Explosive
%OB
TNT
-74
RDX
-43
Nitroglycerine
+7.0
Ammonium Nitrate
+20
Mixing Explosives to Achieve
Optimum %OB
Amatols =
mixtures of ammonium
nitrate and TNT
ANFO
mixtures of ammonium
nitrate and fuel oil
=
ANFO – A crude “low tech” high
explosive that has been used by
terrorists with devastating results.
Sterling Hall Bombing Here at UW:
“…. In the early morning hours of August 24, 1970, the New
Years Gang loaded about 2,000 pounds of ammonium nitrate
soaked in aviation fuel into a stolen Ford. The group parked the
van below the Army Mathematics Research Center, in a driveway
of Sterling Hall. At 3:42 A.M. the bomb exploded. It was powerful
enough to knock out windows six blocks away, and police found
pieces of the Ford van on top of an eight-story building
nearby….”
- www.sit.wisc.edu/~psohandbook
Organic Peroxides – A very different
and less predictable class of
potentially explosive compounds.
O
O
O
O
H3C
O
H
H
Perxyacetic Acid
O
H
Peroxyformic Acid
O
O
O
O
O
O
Diethylperoxide
Dibenzoylperoxide
O
O
O
n-octyldiperoxysuccinic acid
O
O
O
H
H
Acetone Peroxide
• Formed from acid catalyzed reaction of acetone
with hydrogen peroxide.
• Formed as a mixture of dimer and trimer
structures.
H3C
H3C
CH3
CH3
O
O
O
O
O
O
O
O
CH3
H3C
O
H3C
CH3
Dimer
O
H3C
Trimer
CH3
Acetone Peroxide
• Extremely dangerous and unpredictable in
it’s detonation behavior.
• Has been used by terrorists.
- easily prepared from common chemicals
which are not regulated.
- not detected by bomb-sniffing dogs.

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