Explosives
Explosives are substances that produce violent chemical or nuclear reactions. These reactions generate large amounts of heat and gas in a fraction of a second. Shock waves produced by rapidly expanded gases are responsible for much of the destruction seen following an explosion.
The power of most chemical explosives comes from the reaction of oxygen with other atoms such as nitrogen and carbon or in the decomposition of solid or liquid compounds to form gases. This split-second chemical reaction results in a small volume of material being transformed into a large amount heat and rapidly expanding gas. The heat released in an explosion can incinerate nearby objects. The expanding gas can smash large objects like boulders and buildings to pieces. Chemical explosives can be set off, or detonated, by heat, electricity, physical shock, or another explosive.
The power of nuclear explosives comes from energy released when the nuclei of particular heavy atoms are split apart, or when the nuclei of certain light elements are forced together. These nuclear processes, called fission and fusion, release thousands or even millions of times more energy than chemical explosions. A single nuclear explosive can destroy an entire city and rapidly kill thousands of its inhabitants with lethal radiation, intense heat, and blast effects.
Chemical explosives are used in peacetime and in wartime. In peacetime they are used to blast rock and stone for mining and quarrying, project rockets into space, and fireworks into the sky. In wartime, they project missiles carrying warheads toward enemy targets, propel bullets from guns, artillery shells from cannon, and provide the destructive force in warheads, mines, artillery shells, torpedoes, bombs, and hand grenades. So far, nuclear explosives have been used only for tests to demonstrate their force and at the end of World War II in Japan.
The first chemical explosive was gunpowder, or black powder, a mixture of charcoal, sulfur, and potassium nitrate (or saltpeter). The Chinese invented it approximately 1,000 years ago. For hundreds of years, gunpowder was used mainly to create fireworks. Remarkably, the Chinese did not use gunpowder as a weapon of war until long after Europeans began using it to shoot stones and spear-like projectiles from tubes and, later, metal balls from cannon and guns.
Europeans probably learned about gunpowder from travelers from the Middle East. Clearly by the beginning in the thirteenth century gunpowder was used more often in the West to make war than to make fireworks. The English and the Germans manufactured gunpowder in the early 1300s. It remained the only explosive for 300 hundred years, until 1628, when another explosive called fulminating gold was discovered.
Gunpowder changed the lives of both civilians and soldiers in every Western country that experienced its use. (Asian countries like China and Japan rejected the widespread use of gunpowder in warfare until the nineteenth century.) Armies and navies who learned to use it first-the rebellious Czech Taborites fighting the Germans in 1420 and the English Navy fighting the Spanish in 1587, for example-scored influential early victories. These victories quickly forced their opponents to learn to use gunpowder as effectively. This changed the way wars were fought, and won, and so changed the relationship between peoples and their rulers. Royalty could no longer hide behind stone walls in castles. Gunpowder blasted the walls away and helped, in part, to end the loyalty and servitude of peasants to local lords and masters. Countries with national armies became more important than local rulers as war became more deadly due, in large part, to the use of gunpowder. It was not until the seventeenth century that Europeans began using explosives in peacetime to loosen rocks in mines and clear fields of boulders and trees.
Other chemical explosives have been discovered since the invention of gunpowder and fulminating gold. The most common of these are chemical compounds that contain nitrogen such as azides, nitrates, and other nitrocompounds.
In 1846, Italian chemist Ascanio Sobrero invented the first modern explosive, nitroglycerin, by treating glycerin with nitric and sulfuric acids. Sobrero's discovery was, unfortunately for many early users, too unstable to be used safely. Nitroglycerin readily explodes if bumped or shocked. This inspired Swedish inventor Alfred Nobel in 1862 to seek a safe way to package nitroglycerin. In the mid-1860s, he succeeded in mixing it with an inert absorbent material. His invention was called dynamite.
Dynamite replaced gunpowder as the most widely used explosive (aside from military uses of gunpowder). But Nobel continued experimenting with explosives and in 1875, invented a gelatinous dynamite, an explosive jelly. It was more powerful and even a little safer than the dynamite he had invented nine years earlier. The addition of ammonium nitrate to dynamite further decreased the chances of accidental explosions. It also made it cheaper to manufacture.
These and other inventions made Nobel very wealthy. Although the explosives he developed and manufactured were used for peaceful purposes, they also greatly increased the destructiveness of warfare. When he died, Nobel used the fortune he made from dynamite and other inventions to establish the Nobel Prizes, which were originally awarded for significant accomplishment in the areas of medicine, physics, and peace.
Continued research has produced many more types of chemical explosives than those known in Nobel's time: percholates, chlorates, ammonium nitrate-fuel oil mixtures (ANFO) and liquid oxygen explosives are examples.
Explosives are not only useless but dangerous unless the exact time and place they explode can be precisely controlled. Explosives would not have had the influence they have had on world history if two other devices had not been invented. The first device was invented in 1831 by William Bickford, an Englishman. He enclosed gunpowder in a tight fabric wrapping to create the first safety fuse. Lit at one end, the small amount of gunpowder in the core of the fuse burned slowly along the length of the cord that surrounded it. When the thin, burning core of gunpowder reached the end of the cord, it detonated whatever stockpile of explosive was attached. Only when the burning gunpowder in the fuse reached the stockpile did an explosion happen. This enabled users of explosives to set off explosions from a safe distance at a fairly predictable time.
In 1865, Nobel invented the blasting cap, a device that increased the ease and safety of handling nitroglycerin. Blasting caps, or detonators, send a shock wave into high explosives causing them to explode. It is itself a low explosive that is easily ignited. Detonators are ignited by primers. Primers burst into flame when heated by a burning fuse or electrical wire, or when mechanically shocked. A blasting cap may contain both a primer and a detonator, or just a primer. Another technique for setting off explosives is to send an electric charge into them, a technique first used before 1900. All these control devices helped increase the use of explosives for peaceful purposes.
In 1905, nine years after Nobel died, the military found a favorite explosive in TNT (trinitrotoluene). Like nitroglycerin, TNT is highly explosive but unlike nitroglycerin, it does not explode when it is bumped or shocked under normal conditions. It requires a detonator to explode. Many of the wars in this century were fought with TNT as the main explosive and with gunpowder as the main propellant of bullets and artillery shells. Explosives based on ammonium picrate and picric acid were also used by the military.
A completely different type of explosive, a nuclear explosive, was first tested on 16 July 1945, in New Mexico. Instead of generating an explosion from rapid chemical reactions, like nitroglycerin or TNT, the atomic bomb releases extraordinary amounts of energy when nuclei of plutonium or uranium are split apart in a process called nuclear fission. This new type of explosive was so powerful that the first atomicbomb exploded with the force of 20,000 tons of TNT.
Beginning in the early 1950s, atomic bombs were used as detonators for the most powerful explosives of all, thermonuclear hydrogen bombs, or H-bombs. Instead of tapping the energy released when atoms are split apart, hydrogen bombs deliver the energy released when types of hydrogen atoms are forced together in a process called nuclear fusion. Hydrogen bombs have exploded with as much force as 15 million tons of TNT.
All chemical explosives, whether solid, liquid, or gas, consist of a fuel, a substance that burns, and an oxidizer, a substance that provides oxygen for the fuel. The burning and the resulting release and expansion of gases during explosions can occur in a few thousandths or a few millionths of a second. The rapid expansion of gases produces a destructive shockwave. The greater the pressure of the shockwave, the more powerful the blast.
Fire or combustion results when a substance combines with oxygen gas. Many substances that are not explosive by themselves can explode if oxygen is nearby. Turpentine, gasoline, hydrogen, and alcohol are not explosives. In the presence of oxygen in the air, however, they can explode if ignited by a flame or spark. This is why drivers are asked to turn off their automobile engines, and not smoke, when filling fuel tanks with gasoline. In the automobile engine, the gasoline fuel is mixed with oxygen in the cylinders and ignited by spark plugs. The result is a controlled explosion. The force of the expanding gases drives the piston down and provides power to the wheels.
This type of explosion is not useful for most military and industrial purposes. The amount of oxygen in the air deep in a cannon barrel or a mine shaft may not be enough ensure a dependably powerful blast. For this reason, demolition experts prefer to use explosive chemicals that contain molecules that readily decompose to form gases.
Many chemical explosives contain nitrogen because it readily combines to form nitrogen gas (N2). Nitrogen is usually introduced through the action of nitric acid, which is often mixed with sulfuric acid. Nitrogen is an important component of common chemical explosives like TNT, nitroglycerin, gunpowder, guncotton, nitrocellulose, picric acid, and ammonium nitrate.
Another type of explosion can happen when very fine powders or dust mixes with air in an enclosed space. Anytime a room or building is filled with dust of flammable substances such as wood, coal, or even flour, a spark can start a fire that will spread so fast through the dust cloud that an explosion will result. Dust explosions such as these have occurred in silos where grain is stored.
There are four general categories of chemical explosives: blasting agents, primary, low, and high explosives. Blasting agents such as dynamite are relatively safe and inexpensive. Construction workers and miners use them to clear rock and other unwanted objects from work sites. Another blasting agent, a mixture of ammonium nitrate and fuel oil, ANFO, has been used by terrorists around the world because the components are readily available and unregulated. Ammonium nitrate, for instance, is found in fertilizers. One thousand pounds of it, packed into a truck or van, can devastate a large building.
Primary explosives are used in detonators, small explosive devices used to set off larger amounts of explosives.Mercury fulminate and lead azide are used as primary explosives. They are very sensitive to heat and electricity.
Low, or deflagrating, explosives such as gunpowder do not produce as much pressure as high explosives but they do burn very rapidly. The burning starts at one end of the explosive and burns all the way to the other end in just a few thousandths of a second. This is rapid enough, however, that when it takes place in a sealed cylinder like a rifle cartridge or an artillery shell, the gases released are still powerful enough to propel a bullet or cannon shell from its casing, though the barrel of the rifle or cannon toward a target hundreds or thousands of feet away. In fact this relatively slow burning explosive is preferred in guns and artillery because too rapid an explosion could blow up the weapon itself. The slower explosive has the effects of building up pressure to smoothly force the bullet or shell out of the weapon. Fireworks are also low explosives.
High, or detonating, explosives are much more powerful than primary explosives. When they are detonated, all parts of the explosive explode within a few millionths of a second. Some are also less likely than primary explosives to explode by accident. TNT, PETN (pentaerythritol tetranitrate), and nitroglycerin are all high explosives. They provide the explosive force delivered by hand grenades, bombs, and artillery shells. High explosives that are set off by heat are called primary explosives. High explosives that can only be set off by a detonator are called secondary explosives. When mixed with oil or wax, high explosives become like clay. These plastic explosives can be molded into various shapes to hide them or to direct explosions. In the 1970s and 1980s, plastic explosives became a favorite weapon of terrorists. Plastic explosive can even be pressed flat to fit into an ordinary mailing envelope for use as a "letter bomb."
The power of chemical explosives comes from the rapid release of heat and the formation of gases when atoms in the chemicals break their bonds to other atoms. The power of nuclear explosives comes not from breaking chemical bonds but from the core of the atom itself. When unstable nuclei of heavy elements, such are uranium or plutonium, are split apart, or when the nuclei of light elements, such as the isotopes of hydrogen, deuterium or tritium, are forced together, in nuclear explosives they release tremendous amounts of uncontrolled energy. These nuclear reactions are called fission and fusion. Fission creates the explosive power of the atomic bomb. Fusion creates the power of the thermonuclear or hydrogen bomb. Like chemical explosives, nuclear weapons create heat and a shock wave generated by expanding gases. The power of nuclear explosive, however, is far greater than any chemical explosive. A ball of uranium-239 small enough to fit into your hand can explode with the force equal to 20,000 tons of TNT. The heat or thermal radiation released during the explosion travels with the speed of light and the shock wave destroys objects in its path with hurricane-like winds. Nuclear explosives are so much more powerful than chemical explosives that their force is measured in terms of thousands of tons (kilotons) of TNT. Unlike chemical explosives, nuclear explosives also generate radioactive fallout.
Explosives continue to have many important peacetime uses in fields like engineering, construction, mining, and quarrying. They propel rockets and space shuttles into orbit. Explosives are also used to bond different metals, like those in U.S. coins, together in a tight sandwich. Explosives carefully applied to carbon produce industrial diamonds for as cutting, grinding and polishing tools.
Today, dynamite is not used as often as it once was. Since 1955 different chemical explosives have been developed. A relatively new type of explosive, "slurry explosives," are liquid and can be poured into place. One popular explosive for industrial use is made from fertilizers like ammonium nitrate or urea, fuel oil, and nitric or sulfuric acid. This "ammonium nitrate-fuel oil" or ANFO explosive has replaced dynamite as the explosive of choice for many peacetime uses. An ANFO explosion, although potentially powerful and even devastating, detonates more slowly than an explosion of nitroglycerin or TNT. This creates more of an explosive "push" than a high velocity TNT blast. ANFO ingredients are less expensive than other explosives and approximately 25% more powerful than TNT. As of 1995, sale of ANFO components were not regulated as TNT and dynamite were. Unfortunately, terrorists also began using bombs made from fertilizer and fuel oil. Two hundred and forty-one marines were killed when a truck loaded with such an ANFO mixture exploded in their barracks in Beirut Lebanon in 1983. Six people were killed and more than 1,000 injured by a similar bombing in the World Trade Center in New York in 1993. In 1995, terrorists used the same type of explosive to kill more than 167 people in Oklahoma City.
Other popular explosives in use today include PETN (pentaerythrite tetranitrate), Cyclonite or RDX, a component of plastic explosives and Amatol, a mixture of TNT and ammonium nitrite.
Nuclear explosives have evolved too. They are more compact than they were in the mid-part of the century. Today, they fit into artillery shells and missiles launched from land vehicles. Weapons designers also have created "clean" bombs that generate little radioactive fallout and "dirty" bombs that generate more radioactive fallout than older versions. Explosions of "neutron" bombs have been designed to kill humans with neutron radiation but cause little damage to buildings compared to other nuclear explosives.
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