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 O 2  CO H 2 0 MethaneOxygenWaterCarbon Dioxide

Fuel + Oxidizer  Products (propellant) CH O 2  CO H 2 0 Oxidation (combustion) of methane 1 methane molecule : 2 oxygen molecules (4 oxygen atoms). MethaneOxygenWaterCarbon Dioxide Oxidation: Combustion

Oxidation: Decomposition Oxidizer + Fuel  decomposition to products (Explosive)

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  Undergoes Decomposition to: 2 CO H 2 O + N 2 Fuel (Hydrocarbon) + Oxidizer (Nitrate Esters) Carbon Dioxide NitrogenWater

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  H 2 0 – C + O  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 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  3C + 5H + 3N + 9O – 3N  1.5 N 2 – 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  3C + 5H + 3N + 9O – 3N  1.5 N 2 – 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 H 2 O + 3 CO O 2 Oxygen Remaining = Nitroglycerine is – OVEROXIDIZED

Decomposition of RDX C 3 H 6 N 6 O 6  3C + 6H +6N +6O – 6N  3N 2 – 6H + 3O  3H 2 O (3 O remaining) – 3C + 3O  3CO (All O is consumed) – No CO 2 formed. H2H2 H2H2 H2H2

Decomposition of RDX C 3 H 6 N 6 O 6  3C + 6H +6N +6O – 6N  3N 2 – 6H + 3O  3H 2 O (3 O remaining) – 3C + 3O  3CO (All O is consumed) – No CO 2 formed. Overall Reaction: – C 3 H 6 N 6 O 6  3 N H 2 O + 3 CO Not enough oxygen to completely burn all of the fuel – UNDEROXIDIZED H2H2 H2H2 H2H2

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) (4) (2) ( 6) = g/mol – OB = = 0% – 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) (5) (3) ( 9) = g/mol – OB = = 3.52% – 2 ( 3) – 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) (6) (6) ( 6) = g/mol – OB = = % – 2 ( 3) – Underoxidized

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