explosive
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What is an explosive?
An explosive is any substance or device that can produce a rapidly expanding gas volume in an extremely brief period. There are three types: mechanical, nuclear, and chemical, with chemical explosives accounting for virtually all explosive applications in engineering.
Chemical explosives are divided into detonating (high) and deflagrating (low) explosives. Detonating explosives, such as TNT and dynamite, have rapid decomposition and high pressure development. Deflagrating explosives, such as black and smokeless powders, burn fast and produce relatively low pressures.
Nitroglycerin is another chemical explosive, and Nobel's 1865 invention of the blasting cap, a device for detonating explosives, is considered the greatest advance in explosives science since black powder's discovery.
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How do chemical explosives work?
Chemical explosives produce a rapidly expanding gas volume in a brief period through a chemical reaction. These explosives are of two types: detonating (high) and deflagrating (low). High explosives, such as TNT and dynamite, rapidly decompose and create high pressure. Low explosives, like black and smokeless powders, burn quickly and produce relatively low pressures.
The transition from combustion to explosion occurs when the reaction accelerates due to a temperature rise or increasing reaction chains.
Detonating explosives are divided into primary and secondary categories. Primary explosives detonate upon ignition from a flame, spark, or impact. Secondary explosives need a detonator and sometimes a booster.
The combustion and detonation of explosives are widely used for mechanical action, with practical applications based on their combustion theory. For instance, rockets use explosive chemical reactions, burning fuel to produce hot, expanding gas, which generates thrust.
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What is the difference between low explosives and high explosives?
Chemical explosives fall into two primary categories: detonating (high) explosives and deflagrating (low) explosives. High explosives, such as TNT and dynamite, rapidly decompose and generate high pressure. Low explosives, like black and smokeless powders, burn quickly and produce relatively low pressure. Under specific conditions, such as high confinement, some deflagrating explosives can be forced to detonate.
Detonating explosives are divided into primary and secondary categories. Primary explosives can be ignited by flame, spark, impact, or heat. Secondary explosives require a detonator and sometimes a booster.
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How are explosives made to be safe for storage and transport?
Military explosives are made to be insensitive to shock and friction, unlikely to detonate from small-arms fire, and have excellent shattering power. They must be able to withstand long periods of adverse storage without deterioration and must be able to be fired in projectiles or dropped in aerial time bombs without premature explosion. Some must have complex fuses for detonation and possess almost unlimited water resistance.
To improve safety, nonexplosive sensitizers can replace TNT in water gels. Water gels also have good safety characteristics, ease of handling and loading, and plasticity that permits them to displace air or water and completely fill the borehole.
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What are some uses of chemical explosives in everyday life and industry?
Chemical explosives are substances that produce rapidly expanding gas in a short time and are used in various applications in engineering. There are two types: detonating (high) explosives and deflagrating (low) explosives.
Everyday and industrial uses of chemical explosives:
* Mining Chemical explosives are used to create drifts, which are tunnels made in the rock for haulage, ventilation, or exploration.
* Tunneling Drilling and blasting methods are used for harder rock.
* Military Military explosives must be unlikely to detonate from small-arms fire and have excellent shattering power.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
explosive, any substance or device that can be made to produce a volume of rapidly expanding gas in an extremely brief period. There are three fundamental types: mechanical, nuclear, and chemical. A mechanical explosive is one that depends on a physical reaction, such as overloading a container with compressed air. Such a device has some application in mining, where the release of gas from chemical explosives may be undesirable, but otherwise is very little used. A nuclear explosive is one in which a sustained nuclear reaction can be made to take place with almost instant rapidity, releasing large amounts of energy. Experimentation has been carried on with nuclear explosives for possible petroleum extraction purposes. This article is concerned with chemical explosives, which account for virtually all explosive applications in engineering.
Types of chemical explosives
Basically, chemical explosives are of two types: (1) detonating, or high, explosives and (2) deflagrating, or low, explosives. Detonating explosives, such as TNT and dynamite, are characterized by extremely rapid decomposition and development of high pressure, whereas deflagrating explosives, such as black and smokeless powders, involve merely fast burning and produce relatively low pressures. Under certain conditions, such as the use of large quantities and a high degree of confinement, some normally deflagrating explosives can be caused to detonate.
Detonating explosives are usually subdivided into two categories, primary and secondary. Primary explosives detonate by ignition from some source such as flame, spark, impact, or other means that will produce heat of sufficient magnitude. Secondary explosives require a detonator and, in some cases, a supplementary booster. A few explosives can be both primary and secondary depending on the conditions of use.
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Black powder
History of black powder
It may never be known with certainty who invented the first explosive, black powder, which is a mixture of saltpetre (potassium nitrate), sulfur, and charcoal (carbon). The consensus is that it originated in China in the 10th century, but that its use there was almost exclusively in fireworks and signals. It is possible that the Chinese also used black powder in bombs for military purposes, and there is written record that in the mid-13th century they put it in bamboo tubes to propel stone projectiles.
There is, however, some evidence that the Arabs invented black powder. By about 1300, certainly, they had developed the first real gun, a bamboo tube reinforced with iron, which used a charge of black powder to fire an arrow.
A strong case can also be made that black powder was discovered by the English medieval scholar Roger Bacon, who wrote explicit instructions for its preparation in 1242, in the strange form of a Latin anagram, difficult to decipher. But Bacon read Arabic, and it is possible that he got his knowledge from Arabic sources.
Some scholars attribute the invention of firearms to an early 14th-century German monk named Berthold Schwarz. In any case they are frequently mentioned in 14th-century manuscripts from many countries, and there is a record of the shipment of guns and powder from Ghent to England in 1314.
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Not until the 17th century was black powder used for peaceful purposes. There is a doubtful claim that it was used in mining operations in Germany in 1613 and fairly authentic evidence that it was employed in the mines of Schemnitz, Hungary (modern Banská Štiavnica, Czechoslovakia), in 1627. For various reasons, such as high cost, lack of suitable boring implements, and fear of roof collapse, the use of black powder in mining did not spread rapidly, though it was widely accepted by 1700. The first application in civil engineering was in the Malpas Tunnel of the Canal du Midi in France in 1679.
For 300 years the unvarying composition of black powder has been approximately 75 percent saltpetre (potassium nitrate), 15 percent charcoal, and 10 percent sulfur. The saltpetre was originally extracted from compost piles and animal wastes. Deposits found in India provided a source for many years. During the 1850s tremendous quantities of sodium nitrate were discovered in Chile, and saltpetre was formed by reaction with potassium chloride, of which there was a plentiful supply.
Chilean nitrate was not at first considered satisfactory for the manufacture of black powder because it too readily absorbed moisture. Lammot du Pont, an American industrialist, solved this problem and started making sodium nitrate powder in 1858. It became popular in a short time because, although it did not produce as high a quality explosive as potassium nitrate, it was suitable for most mining and construction applications and was much less expensive. To distinguish between them, the potassium nitrate and sodium nitrate versions came to be known as A and B blasting powder respectively. The A powder continued in use for special purposes that required its higher quality, principally for firearms, military devices, and safety fuses.