Explosives and Explosions

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Explosives and Explosions

• The Chemistry of High Energy Organic Compounds

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What is an Explosion?

• Rapid burning of a material resulting in a
  sudden build-up and release of heat and gas
  pressure.

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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?

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Hexanes Among the many hydrocarbons found in
gasoline, they are representative of the
volatility and explosivity of gasoline.
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Hexanes burn rapidly in air to form carbon
dioxide and water.

• 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.

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Ethanol also burns in air.

• 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.

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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.

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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.

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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.

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Cellulose (cotton) burns slowly in air.
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Nitrocellulose (gun cotton) burns very rapidly
even without air.
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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.

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Primary and Secondary High Explosives

• Primary High Explosives
• - detonate very easily
• - minimal activation energy.
• Secondary High Explosives
• - do not detonate easily
• - high activation energy

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Early Examples of Primary High Explosives
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Nitroglycerine

• Nitroglycerine detonates by rapidly rearranging
  to a collection of small stable gas molecules
  releasing a huge quantity of heat and pressure.
• 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.

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Nitrogen triiodide

• NI3 also detonates by rearrangement to a
  collection of small stable gas molecules.

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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.

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Examples of SecondaryHigh Explosives
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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.

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Oxygen Balance A useful concept for evaluating
high explosives.

• Oavail - Oneeded
• OB --------------------------- (100)
• mass of comp.

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Oxygen Balance of Some Representative High
Explosives

• Explosive OB

TNT -74
RDX -43
Nitroglycerine 7.0
Ammonium Nitrate 20
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Mixing Explosives to Achieve Optimum OB

• Amatols mixtures of ammonium nitrate and
  TNT
• ANFO mixtures of ammonium nitrate and fuel
  oil

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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 342 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

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Organic Peroxides A very different and less
predictable class of potentially explosive
compounds.
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Acetone Peroxide

• Formed from acid catalyzed reaction of acetone
  with hydrogen peroxide.
• Formed as a mixture of dimer and trimer
  structures.

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Acetone Peroxide

• Extremely dangerous and unpredictable in its
  detonation behavior.
• Has been used by terrorists.
• - easily prepared from common chemicals
• which are not regulated.
• - not detected by bomb-sniffing dogs.