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An explosive material, also called an explosive, is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material. This potential energy stored in an explosive material may be * chemical energy, such as nitroglycerin or grain dust * pressurized gas, such as a gas cylinder or aerosol can. * nuclear energy, such as in the fissile isotopes uranium-235 and plutonium-239 Explosive materials may be categorized by the speed at which they expand. Materials that detonate (the front of the chemical reaction moves faster through the material than the speed of sound) are said to be "high explosives" and materials that deflagrate are said to be "low explosives". Explosives may also be categorized by their sensitivity. Sensitive materials that can be initiated by a relatively small amount of heat or pressure are primary explosives and materials that are relatively insensitive are secondary or tertiary explosives. A wide variety of chemicals can explode; a smaller number are manufactured specifically for the purpose of being used as explosives. The remainder are too dangerous, sensitive, toxic, expensive, unstable, or decompose too quickly for common usage. In contrast, some materials are merely combustible or flammable if they burn without exploding. ==History== Though early thermal weapons, such as Greek fire, have existed since ancient times, the first widely used explosive in warfare and mining was black powder, invented in 9th century China. This material was sensitive to water, and it produced dark smoke. The first useful explosive stronger than black powder was nitroglycerin, developed in 1847. Since nitroglycerin is a liquid and highly unstable, it was replaced by nitrocellulose, smokeless powder, dynamite and gelignite (the two latter invented by Alfred Nobel). World War I saw the introduction of TNT trinitrotoluene in artillery shells. World War II saw an extensive use of new explosives (see explosives used during World War II). In turn, these have largely been replaced by more powerful explosives such as C-4 and PETN. However, C-4 and PETN react with metal and catch fire easily, yet unlike TNT, C-4 and PETN are waterproof and malleable.〔Ankony, Robert C., ''Lurps: A Ranger's Diary of Tet, Khe Sanh, A Shau, and Quang Tri,'' revised ed., Rowman & Littlefield Publishing Group, Lanham, MD (2009), p.73.〕 The increased availability of chemicals has allowed the construction of improvised explosive devices. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Explosive material」の詳細全文を読む スポンサード リンク
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