Energetic Materials, Part I: Black Powder, Nitroglycerin, and Dynamite
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Energetic Materials, Part I: Black Powder, Nitroglycerin, and Dynamite An explosive, according to the dictionary, is "any substance that can be made to produce a volume of rapidly expanding gas in an extremely brief period." This Historical Note and the next one will look at the development of energetic materials used as industrial and military explosives. This first part will focus on black powder, used thousands of years ago, through the création of nitroglycerin, to the discovery of dynamite. Next month's Historical Note will describe the development of nitrocellulosic explosives such as gun-cotton, as well as TNT and other explosives used in World Warsl and E. Dynamite, discovered by Alfred B. Nobel in 1866, was one of the first detonating, or "high" explosives, which are characterized by extremely rapid décomposition and the development of high-pressure shocks. Earlier materials used deflagrating or "low" explosives, which were simply fast-burning powders that produced relatively low pressures. The most familiar low explosive had been used for many centuries—black powder. For perhaps 2000 years the Chinese used black powder in their fireworks and to send smoke signais. Called "Greek fire," black powder (or some similar low explosive) was also used for pyrotechnies in eastern Europe in the 700s A.D. By the late 13th cenrury, the Arabs were using black powder in a "gun"—a bamboo tube reinforced with iron, which used an explosive charge to fire an arrow. About this same time, on another continent, English médiéval scholar Roger Bacon at Oxford University included thorough instructions for preparing black powder in a published volume—but he encoded the détails in a difficult Latin anagram to conceal the instructions. Black powder, a mixture of 75% saltpeter (potassium nitrate), 10% sulfur, and 15% charcoal (carbon), is relatively insensitive to shôck and friction, but is easily ig-
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nited by flame or heat. In the early days, torches, hot iron rods or glowing tinder were used to set off black powder, usually by igniting a trail of powder leading to the main charge, giving people time to take cover before the explosion. Since the déflagration of black powder is a surface phenomenon, coarse granulations burn more slowly thàn fine grains. Grain sizes are designated with a complicated System of letters and numerals.
Italian chemist Ascania Sobrero discovered "blasting-oil" —nitroglycerin— in 1846. The saltpeter for black powder was originally extracted from compost piles and animal dung; later, large deposits in India supplied manufacturing needs. During the 1850s, enormous quantifies of sodium nitrate, which could be converted to saltpeter through reaction with readily available potassium chloride, were discovered in Chile. Chilean sodium nitrate absorbed a great deal of moisture, fhough, and manufacturers did not initially consider it good enough for use in black powder. In 1858, American industrialist Lammot du Pont began to make sodium nitrate, from which he made his own blasting powder. Du Pont's sodium nitra
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