explosives and explosions revised

8/6/2019 Explosives and Explosions Revised

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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 thanautomobile fuel tanks.

� TW

A 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 thelack of an acceptable method for determining the explosive hazard in the

tank under varying conditions.µ

- FAA final report, TWA Flight 800 crash investigation.



How can we make explosives

without the limitation of needing

oxygen from the air?

� Make the ´oxygenµ (oxidizing agent)

part of the chemical structure.

� Example: Nitrocellulose used in gunpowder.



Cellulose (cotton) burns

slowly in air.

O

H

O

H

HO

H

H

OHH

O

OH

O

H

H

HO

H

H

OH

H

O

OH

O

H

H

HOH

H

OH

H

O

OH

Cellulose

major component of cotton



Nitrocellulose (gun cotton)

burns very rapidly even

without air.

O

H

O

H

O

H

H

O

H

O

O

O

H

H

O

H

H

O

H

O

O

O

H

H

OH

H

O

H

O

O

NO2

O2N

O2N

NO2

O 2N

O2N

O 2N

NO 2

O2N

N itrocellulose

"gun co tton"

major component of modern gun powder and f ireworks



High Explosives Burn at

Supersonic Speeds

Conflagration: rapid burning with a flame

front traveling through the material at1 m/sec to 300 m/sec.

Detonation: ´instantaneousµ burning with

flame front traveling through the materialat 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 ExplosivesCH2OH

CHOH

CH2OH

CH2ONO2

CHONO2

CH2ONO2

H NO 3

H2SO4

Glycer ine Nitroglycer ine

HOH2C C

CH2OH

CH2OH

CH2OH

H NO 3

H2SO4

O2NOH2C C

CH2ONO2

CH2ONO2

CH2ONO2

Pentaerythr itol Pentaerythr itoltetranitrate

(PETN)



Nitroglycerine

� Nitroglycerine detonates by rapidly rearranging to acollection of small stable gas molecules releasing a hugequantity of heat and pressure.

� Pure Nitroglycerine is way too ´sensitiveµ to be a useful

explosive. It was the invention of dynamite by Alfred Nobelthat converted nitroglycerine into a useful commercial andmilitary explosive by mixing nitroglycerine with clay(diatomaceous earth) and forming the mixture into dynamitesticks.

CH2ONO2

CHONO2

CH2ONO2

12 CO2 + 10 H2O +

6 N2 + O2

Detonation4



Secondary High Explosives

� Compounds which are not easily

(accidentally) detonated but whichcan be detonated intentionally tocause very high energy explosions.

� Secondary explosives require asmall amount of a primary explosiveto set them off.



Examples of Secondary

High ExplosivesCH3

NO 2

NO 2

O2N

N

N

N

NO 2

NO 2

O2N

T T

R DX

OH

NO2

NO 2

O2N

Picr ic Acid

N

N

N

N

NO 2

NO 2

O2N

O2N

HMX



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 formH2O 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 ammoniumnitrate and TNT

ANFO = mixtures of ammoniumnitrate and fuel oil



ANFO ² A crude ´low techµ high

explosive that has been used byterrorists 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-storybuilding nearby«.µ

- www.sit.wisc.edu/~psohandbook



Organic Peroxides ² A very different

and less predictable class of

potentially explosive compounds.

H3C O

O

O

H H O

O

O

H

O

O

O

O

O

O

O

O

O

H

O

O

O

H

Perxyacetic cid P eroxyformic cid

D ib enzoylperoxide

D iethylperox ide

n-octyld i peroxysucc in ic ac id



Acetone Peroxide

� Formed from acid catalyzed reaction of acetone

with hydrogen peroxide.

� Formed as a mixture of dimer and trimer structures.

OO

O

OO

O

CH3H3C

CH3

CH3H3C

H3C

Tr imer

O

O O

O

CH3H3C

CH3H3C

Dimer



Acetone Peroxide

� Extremely dangerous and unpredictable init·s detonation behavior.

� Has been used by terrorists.

- easily prepared from common chemicals

which are not regulated.

- not detected by bomb-sniffing dogs.

explosives and explosions revised

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