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 (PbN 6 )

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 (NH 4 NO 3 )

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) • CH 4 + 2 O 2 Methane Oxygen  CO 2 Carbon Dioxide + 2 H 2 0 Water

Oxidation: Combustion

• Fuel + Oxidizer  Products (propellant) • • CH 4 + 2 O 2 Methane Oxygen  CO 2 Carbon Dioxide + 2 H 2 Water 0 Oxidation (combustion) of methane • 1 methane molecule : 2 oxygen molecules (4 oxygen atoms).

Oxidation: Decomposition

• Oxidizer + Fuel  (Explosive) decomposition to products

Oxidation: Decomposition

• • • Oxidizer + Fuel  decomposition to products (Explosive) Example: Nitroglycol O 2 N — O — CH 2 — CH 2 — O — NO 2  Fuel (Hydrocarbon) + Oxidizer (Nitrate Esters)

Oxidation: Decomposition

• • • • Oxidizer + Fuel  decomposition to products (Explosive) Example: Nitroglycol O 2 N — O — CH 2 — CH 2 — O — NO 2  Fuel (Hydrocarbon) + Oxidizer (Nitrate Esters) Undergoes Decomposition to: 2 CO 2 + 2 H 2 O + N 2 Carbon Dioxide Water Nitrogen

CHNO Explosives

• • • • Many explosives and propellants are composed of: – Carbon – Hydrogen – – Nitrogen Oxygen General Formula: C c H h N n O o c, h, n, o are # of carbon, hydrogen, nitrogen and oxygen atoms.

For Nitroglycol: C 2 H 4 N 2 O 6

CHNO Explosive Decomposition

• • C c H h N n O o  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

C c H h N n O o  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  N 2 2H + O  C + O  H 2 0 CO CO + O  CO 2

• • • • •

Overoxidation vs Underoxidation

In the case of nitroglycol O 2 N—O—CH 2 —CH 2 —O—NO 2 2 CO 2 + 2 H 2 O + N 2  Exactly enough oxygen to burn all carbon to CO 2 Some have more than enough oxygen to burn all the carbon into CO 2 – OVEROXIDIZED OR FUEL LEAN Most explosives do not have enough oxygen to burn all the carbon to CO 2 – UNDEROXIDIZED OR FUEL RICH

Simple Product Hierarchy for CHNO Explosives

• First, all nitrogen forms N 2

Simple Product Hierarchy for CHNO Explosives

• • First, all nitrogen forms N 2 Then, all the hydrogen is burned to H 2 O

Simple Product Hierarchy for CHNO Explosives

• • • First, all nitrogen forms N 2 Then, all the hydrogen is burned to H 2 O Any oxygen left after H 2 0 formation burns carbon to CO.

Simple Product Hierarchy for CHNO Explosives

• • • • First, all nitrogen forms N 2 Then, all the hydrogen is burned to H 2 O Any oxygen left after H 2 0 formation burns carbon to CO.

Any oxygen left after CO formation burns CO to CO 2

Simple Product Hierarchy for CHNO Explosives

• • • • • First, all nitrogen forms N 2 Then, all the hydrogen is burned to H 2 O Any oxygen left after H 2 0 formation burns carbon to CO.

Any oxygen left after CO formation burns CO to CO 2 Any oxygen left after CO 2 formation forms O 2

Simple Product Hierarchy for CHNO Explosives

• • • • • • First, all nitrogen forms N 2 Then, all the hydrogen is burned to H 2 O Any oxygen left after H 2 0 formation burns carbon to CO.

Any oxygen left after CO formation burns CO to CO 2 Any oxygen left after CO 2 formation forms O 2 Traces of NO x (mixed oxides of nitrogen) are always formed.

Decomposition of Nitroglycerine

• • C 3 H 5 N 3 O 9  – 3N  1.5 N 2 3C + 5H + 3N + 9O – – 5H + 2.5O  2.5 H 2 O (6.5 O remaining) 3C + 3O  3 CO (3.5 O remaining) – 3 CO 3O  3 CO 2 (0.5 O remaining) 8.5 of 9 oxygen atoms consumed – 0.5 O  0.25 O 2

Decomposition of Nitroglycerine

• • • • C 3 H 5 N 3 O 9  – 3N  1.5 N 2 3C + 5H + 3N + 9O – – 5H + 2.5O  2.5 H 2 O (6.5 O remaining) 3C + 3O  3 CO (3.5 O remaining) – 3 CO + 3O  3 CO 2 (0.5 O remaining) 8.5 of 9 oxygen atoms consumed – 0.5 O  0.25 O 2 Overall Reaction: – C 3 H 5 N 3 O 9  1.5 N 2 + 2.5 H 2 O + 3 CO 2 + 0.25 O 2 Oxygen Remaining = Nitroglycerine is – OVEROXIDIZED

Decomposition of RDX

H 2 • C 3 H 6 N 6 O 6 – 6N   3N 2 – 6H + 3O  3C + 6H +6N +6O 3H 2 O (3 O remaining) – 3C + 3O  3CO (All O is consumed) – No CO 2 formed.

H 2 H 2

Decomposition of RDX

H 2 • • • C 3 H 6 N 6 O 6 – –  6N  3N 2 6H + 3O  – 3C + 3O  3C + 6H +6N +6O 3H 2 O (3 O remaining) 3CO (All O is consumed) – No CO 2 formed.

Overall Reaction: – C 3 H 6 N 6 O 6  3 N 2 + 3 H 2 O + 3 CO Not enough oxygen to completely burn all of the fuel – UNDEROXIDIZED H 2 H 2

Oxygen Balance

• • OB (%) – 1600/MW exp [oxygen-(2 carbon+ hydrogen/2)] Oxygen balance for Nitroglycol C 2 H 4 N 2 O 6 – c = 2, h = 4, n = 2, o = 6 – Mw exp =12.01 (2) + 1.008 (4) + 14.008 (2) + 16.000 ( 6) = 152.068 g/mol – 152.068

6 – 2 (2) – 4 2

Perfectly Balanced

Oxygen Balance

• Oxygen balance for Nitroglycerine C 3 H 5 N 3 O 9 – C = 3, h = 5, n = 3, o = 9 – Mw exp =12.01 (3) + 1.008 (5) + 14.008 (3) + 16.000 ( 9) = 227.094 g/mol – 9 – 2 ( 3) – 5 2

Slightly overoxidized

Oxygen Balance

• Oxygen balance for RDX: C 3 H 6 N 6 O 6 – C = 3, h = 6, n = 6, o = 6 – Mw exp =12.01 (3) + 1.008 (6) + 14.008 (6) + 16.000 ( 6) = 222.126 g/mol – 6 – 2 ( 3) – 6 2

Underoxidized

Homework

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