Chemistry Of Powder And Explosives
An explosive can be defined as a chemical compound that can be ignited by friction, heat, shock or impact when detonated to release rapid heat and pressurised gas. The energy released by the gases causes rock displacement, rock fragmentation, ground vibration and massive air blast. Thexplosivs theory states that detonation usually produces a high-velocity vibration and shock waves which in turn causes cracks in rocks. The common properties of explosives include: they are exothermic, spontaneous, produces heat and once initiated, they sustain the process on their own. Explosives are referred as energetic materials used to be known as black ...view middle of the document...
Examples o substances used as absorbents include; rice, shells, sawdust, hulls, wood and nut shells (Burtsell, 1943).
Antifreezes – Antifreeze are typically used in reducing the explosive point.
Air gap sensitivity – This is referred to as the degree of an explosive’s sensitivity from cartridges to cartridge under test conditions. The measurements are conveyed as the air distance through which a donor half –catridge can detonate a prime receptor half-cartridge (Burtsell, 1943).
Cap Sensitivity - This the minimum amount of pressure, power or energy that is needed to detonate an explosive.
Strength – in commercial dynamites, there are two ratings of strength, Weight strength and bulk/cartridge strength. According to Burtsell (1943), the weight strength relates products with same weight basis whereas the cartridge strength is compared on an equal volume basis. Both strengths are measured in percentages by use of straight nitroglycerin dynamite as the standard (Thompson, 1940). However, with the introduction of new explosives for instance he ANFO and slurries, the technique of receiving relevant data on strength using dynamite method failed. A contemporary blaster has to consider the detonation pressure and gas pressure (Burtsell, 1943).
Classification of Explosives
Propellants/low explosives. These are explosives made of combustible materials that contain oxygen in them that undergo combustion without exploding. The combustion, however, produces gases that yield an explosion that deliver different energy levels. An example of propellants is smokeless powder and black powder. Energy levels produced depend on the type of powder, slow or fast (Davis, 1941).
Primary explosives. These explosives are the initiators or detonators upon subjection to heat or shock. The primary explosives differ in their level of sensitivity to heat and shock a trait that reflects the amount of heat or shock released (Thompson, 1940).Examples of this explosives include mercury fulminate, lead salts of picric acid, lead azide, tetracene and mixtures of potassium chlorate with red phosphorus(Davis, 1941).
High explosives. The high explosives are usually detonated by the shock produced by the primary explosives. The do not operate by burning though they are combustible.The difference between the primary and the high explosives is that high explosives are more powerful and exert mechanical pressure and shock to any object around it. A high explosive is a compound that has a detonation reaction velocity of over 5000 ft/s. The reaction can be commenced by a No. 8 strength blasting cap. The high explosives comprise of:
Straight Dynamite – This is a Nitroglycerin in a porous state with velocity ranges of 10,000 and 20,000 ft/second (Glasshead Television and Web, 2010). The dynamite is the most sensitive among all commercial explosives. The weight strength is the actual percentage of nitroglycerin in the cartridge. This explosive has excellent water resistance, poor...