Explosive
Any explosive material has the following characteristics:
- It is chemically or otherwise energetically unstable.
- The initiation produces a sudden expansion of the material accompanied by large changes in pressure (and typically also a flash or loud noise) which is called the explosion.
Explosives be classified by their sensitivity, which is the amount of energy to initiate the reaction. This energy can be anything, from a shock, an impact, a friction, an electrical discharge, or the detonation of another explosive. There are two basic divisions on sensitivity:
- Low Explosives (Cannot support a detonation wave, are a mixture, are initiated by heat and require confinment to create an explosion) and
- High Explosives (will explode without confinement, are compounds, initiated by shock or heat, supersonic reaction, high brisance).
Classification by composition of the material
Mixtures of an oxidizer and a fuel
- gunpowder: potassium nitrate, charcoal and sulfur
- ammonal : ammonium nitrate and aluminium powder.
- cheddites : chlorates or perchlorates and oil
Chemically pure compounds, often mixed with stabilizers
- dynamite : nitroglycerin with flour, used as a stabilizer.
- RDX, PETN : very strong explosives which can be used pure.
Classification by sensitivity of the material
Primary Explosives
They are extremely sensitive and require a small quantity of energy to be initiated. They are mainly used in detonators to initiate secondary explosives (Examples: tetryl, Lead azide, Mercury fulminate, lead styphnate, tetrazene, hexanitromannitol).
Secondary Explosives
They are relatively insensitive and need a great amount of energy to initiate decomposition. They have much more power than primary explosives and are used in demolition. The require a detonator to explode. (Examples: Dynamite, TNT, RDX, PETN, HMX, tetryl, picric acid, nitrocellulose)
Detonation
Also called an initiation sequence or a firing train, this is the sequence of events which cascade from relatively low levels of energy to cause a chain reaction to initiate the final explosive material or main charge. They can be either low or high explosive trains. Low explosive trains are something like a bullet - Primer and a propellant charge. High explosives trains can be more complex, either Two-Step (e.g. Detonator and Dynamite) or Three-Step (e.g. Detonator, Booster and ANFO). Detonators are often made from tetryl.
Characteristics of Explosions
Explosive force is released at 90 degree angles from the surface of an explosive. If the surface is cut or shaped the explosive forces can be focused directionally, and will produce a greater effect. This is known as a shaped charge.
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