Explosives: Fundamentals, Classification, Composition, and Properties

Explosion Definition: A sudden, rapid combustion from chemical or physical action, resulting in violent air expansion, high heat, pressure waves, and sound.
Primary Criteria: The rapid generation and violent escape of gases.
Explosive Definition: An energetic material (compound or mixture) capable of a self-sustaining chemical reaction that releases energy rapidly.
Three Requirements for Explosion: - Evolution of heat (energy release). - Formation of gas. - Rapidity of reaction (must be instantaneous).
Stability Requirements: Must not be spontaneously explosive; must withstand temperature extremes and handling; must be capable of being molded or retaining shape.

Constituents: - Fuel: Reacts with oxygen (e.g., Carbon, Sulphur, Al, Mg, Nitromethane). - Oxidizer: Supplies oxygen (e.g., $NO_3$ , $NO_2$ , $ClO_3$ , $HClO_3$ , $KMnO_4$ ). - Sensitizer: Provides sensitivity (e.g., air bubbles, glass microballoons, Nitrobenzene).
Chemical Structure: Most contain $C$ , $H$ , $N$ , and $O$ . Oxygen is typically linked to atoms other than $C$ or $H$ (e.g., Nitro $-NO_2$ , Nitramine $-NNO_2$ , Chlorate $-ClO_3$ ).
Reaction Examples: - Black Powder: $8C + 3S + 10KNO_3 \rightarrow 3K_2SO_4 + 2K_2CO_3 + 6CO_2 + 5N_2$ - TNT: $2[CH_3C_6H_2(NO_2)] \rightarrow 12CO_2 + 5H_2 + 3N_2 + 2C$ - Nitroglycerin: $4[C_3H_5(NO_3)_3] \rightarrow 12CO_2 + 10H_2O + 6N_2 + O_2$

Low Explosives (Deflagrating): - Reaction: Deflagration (subsonic surface phenomenon, < 1,000\,m/s). - Confinement: Requires airtight confinement to explode; otherwise burns intensely. - Examples: Black Powder ( $75\%$ Potassium Nitrate, $15\%$ Charcoal, $10\%$ Sulphur), Smokeless Powder (Single-base: $NC$ ; Double-base: $NC + NG$ ; Triple-base: $NC + NG + Nitroguanidine$ ), Flash Powder ( $Al$ and $Mg$ ).
High Explosives (Detonating): - Reaction: Detonation (supersonic shockwave, $1,000 - 8,500\,m/s$ ). - Confinement: Does not require a container to detonate. - Characteristics: Creates craters; used for shattering (brisance) in demolition and military shells.

Primary Explosives: - Sensitivity: Extremely sensitive to heat, friction, impact, and sparks. - Usage: Used in small quantities (milligrams) in detonators to initiate less sensitive explosives. - Examples: Mercury fulminate $Hg(CNO)_2$ , Lead azide $Pb(N_3)_2$ , Lead styphnate, and Diazodinitrophenol (DDNP).
Secondary Explosives: - Sensitivity: Relatively insensitive; safe to handle. - Usage: Used in bulk; requires a booster or primary explosive for initiation. - Examples: TNT, RDX, PETN, HMX, Tetryl, and Ammonium Nitrate.

Industrial Explosives: - Dynamite: Nitroglycerin ( $NG$ ) absorbed in diatomaceous earth ( $VOD: 5,000 - 6,000\,m/s$ ). - ANFO: Ammonium Nitrate ( $94\%$ ) mixed with Fuel Oil ( $6\%$ ). Least sensitive, requires booster ( $VOD: 2,000 - 3,000\,m/s$ ). - Water-gels/Emulsions: Water-based Ammonium Nitrate solutions; safe and water-resistant.
Military Explosives: - TNT (Trinitrotoluene): The standard military high explosive ( $VOD: 6,900\,m/s$ ). - RDX (Cyclonite): High brisance; used in plastic explosives like C-4 and Semtex ( $VOD: 8,750\,m/s$ ). - PETN: Highly powerful; used in detonating cords ( $VOD: 8,400\,m/s$ ). - Plastic Explosives: RDX or PETN held in a plasticizer matrix (e.g., C-4 is $91\%$ RDX + $9\%$ plasticizer).

Accessories: - Safety Fuse: Carries flame at a uniform rate ( $35 - 45\,s/ft$ ). - Detonating Cord: Core of powdered PETN or RDX for simultaneous initiation. - Detonator: Contains ignition (Lead azide), intermediate (Tetryl), and base charges (RDX/PETN).
Explosive Trains: - Two-step: Blasting Cap $\rightarrow$ Secondary High Explosive (e.g., Dynamite). - Three-step: Safety Fuse $\rightarrow$ Blasting Cap $\rightarrow$ Secondary High Explosive. - Four-step: Safety Fuse $\rightarrow$ Blasting Cap $\rightarrow$ Dynamite Booster $\rightarrow$ Main Charge.