Explosives
From Encyclopædia
An explosive is a stable material that, upon proper stimulation, rapidly changes from a solid or liquid into a hot, expanding gas. The
pressure exerted on the surrounding materials by the expanding gas constitutes an explosion.Confining an explosive greatly increases its propensity to detonate by increasing the speed of the reaction. For example, GUNPOWDER, or black powder, confined within the paper wrapping of a firecracker explodes when ignited, but the same powder sprinkled in the open simply burns when ignited. During the relatively slow reaction of burning, the
pressure of the hot gases does not increase fast enough to have an explosive effect.Although many substances in various forms can be exploded (gasoline vapors, hydrogen, and finely dispersed coal or grain dust are all explosive substances, for example), only those substances specifically intended to produce an explosion are generally called explosives. They can be divided into two types: propellant explosives, such as gunpowder, and detonating explosives, such as TNT and
dynamite.Propellant ExplosivesGunpowder, which was developed by the Chinese in the 10th century and by the
Arabs, independently, soon afterwards, was the first explosive to be used in
firearms. In 1845 a nitrocellulose explosive called GUNCOTTON was introduced, but it proved too potent for its intended use as a
firearms propellant.Breakthroughs in the 1880s, however, resulted in satisfactory smokeless powders that, within 20 years, virtually supplanted black powder as a propellant. With the
Advent of the space age, many specialized explosives were developed for use as rocket propellants.Detonating ExplosivesDetonating explosives may be subdivided into initiating explosives and high explosives. Initiating explosives, which must be handled with extreme care, are the more sensitive of the two. Materials such as fulminate of mercury explode instantly when burned or ignited, which makes them desirable for use in blasting caps.High explosives are less sensitive and can burn without producing an explosion. They can only be detonated by a severe shock, which is delivered by another explosive (usually a blasting cap) placed in or near the high explosive. Since they are relatively stable, large amounts of high explosives can be moved and handled safely.In 1846 the Italian Ascanio Soberro invented NITROGLYCERIN, an explosive so sensitive that it was virtually unusable. It became important later, however, when in 1867 the Swedish inventor Alfred NOBEL combined it first with siliceous earth and later with wood pulp to produce
dynamite.TNT (trinitrotoluene), which was first used in the early 1900s, has become the standard by which all other explosives are measured. It is used either by itself or mixed with other ingredients and explosives to produce many subtypes with differing performance characteristics.Modern ExplosivesModern detonating explosives include PETN (pentaerythrite tetranitrate), which is used in blasting caps and detonating cord; RDX (also known as cyclonite), which is combined with other explosives and waxes to produce what are popularly known as plastic explosives; ammonium nitrate, an explosive of low detonating velocity that is used when a slow push or heave is more desirable than a shattering effect; and amatol, a mixture of ammonium nitrite and TNT that is used as a bursting charge.Explosives are used in a wide variety of civilian and military tasks. Tunnel construction, obstacle clearing, and open pit and underground mining employ large quantities of explosives. They are also used as propellants for
firearms and ROCKETs; as bursting charges for
bombs,
mines, ARTILLERY projectiles, TORPEDOs, and
hand GRENADEs; and for general engineering and DEMOLITION work. Small explosive charges have wide uses in industry, as well. In
metallurgy,
metals can be pressed into dies, extruded, or welded together by means of such explosions, and new
metal alloys have been created by such means. Explosives are also used in the production of diamond dust from graphite.David N. BucknerBibliography: Bahrani,
Aladdin, "Engineering with a Bang," New Scientist, July 10, 1986; DeBarry Burnett, Edward, Explosives (1980); Glackin, James, Elements of Explosives Production (1986); Haines, Gail K., Explosives (1976); Marshall, Arthur, Explosives, 3 vols. (1980); Meyer, Rudolph, Explosives, 2d ed. (1981).
