Explosive Properties

Explosives 189Dr. 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 non-explosives.

• 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 WaterCarbonDioxide

• Fuel + Oxidizer Products (propellant)• CH4 + 2 O2 CO2 + 2 H20

• Oxidation (combustion) of methane• 1 methane molecule : 2 oxygen molecules

(4 oxygen atoms).

Methane Oxygen WaterCarbonDioxide

Oxidation: Combustion

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

• Undergoes Decomposition to:2 CO2 + 2 H2O + N2

Fuel (Hydrocarbon) + Oxidizer (Nitrate Esters)

CarbonDioxide

NitrogenWater

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

• 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

H2

Decomposition of RDX

• 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

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 = = 0% 1600

152.0686 – 2 (2) – 4

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

– OB = = 3.52% 1600

227.094 259 – 2 ( 3) –

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

– OB = = -21.61% 1600

222.126 266 – 2 ( 3) –

Underoxidized

Homework

• Calculate the oxygen balance for:– TNT– Picric Acid