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 (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 nonexplosives. • 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 Carbon Dioxide Water Oxidation: Combustion • Fuel + Oxidizer Products (propellant) • CH4 + 2 O2 CO2 + 2 H20 Methane Oxygen Carbon Dioxide Water • Oxidation (combustion) of methane • 1 methane molecule : 2 oxygen molecules (4 oxygen atoms). 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 Fuel (Hydrocarbon) + Oxidizer (Nitrate Esters) • Undergoes Decomposition to: 2 CO2 + 2 H2O + N2 Carbon Dioxide Water Nitrogen 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 H2 • 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 Decomposition of RDX H2 • 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 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 = 1600 = 0% 6 – 2 (2) – 4 152.068 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 1600 5 – OB = 9 – 2 ( 3) – 227.094 2 = 3.52% 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 1600 6 – OB = 6 – 2 ( 3) – 222.126 2 = -21.61% Underoxidized Homework • Calculate the oxygen balance for: – TNT – Picric Acid