Gunpowder, also known as Black Powder to distinguish it from modern gunpowder, it is the earliest known chemical explosive. It consists of a mixture of sulfur, charcoal, and potassium nitrate (saltpeter). The sulfur and charcoal act as fuels while the saltpeter is an oxidizer.
Regular Black Powder with sulfur is:
- 6 KNO3 + C7H4O + 2 S → K2CO3 + K2SO4 + K2S + 4 CO2 + 2 CO + 2 H2O + 3 N2
Black Powder without sulfur gives:
- 10 KNO3 + 2 C7H4O → 5 K2CO3 + 4 CO2 + 5 CO + 4 H2O + 5 N2
Gunpowder contains 3 megajoules per kilogram and contains its own oxidant. For comparison, the specific energy of TNT is 4.7 megajoules per kilogram, and the specific energy of is 47.2 megajoules per kilogram (though gasoline requires an oxidant, so an optimized gasoline and O2 mixture contains 10.4 megajoules per kilogram). Gunpowder is a low explosive, so it does not detonate but rather deflagrates. Since it contains its own oxidizer and additionally burns faster under pressure, its combustion is capable of bursting barrels.
Because of its incendiary properties and the amount of heat and gas volume that it generates, gunpowder has been widely used as a propellant in firearms, rockets, fireworks, and as a blasting powder for quarrying, mining, and road building.
Gunpowder was invented in China during the 9th Century and spread throughout most parts of Europe and Asia by the end of the 13th Century. Most arguments on early gunpowder developments now revolve around how much Chinese advancements in gunpowder influenced warfare in the Middle East and Europe, but controversy over gunpowder's precise origins continue to be debated even today.
Gunpowder is classified as a low explosive because of its relatively slow decomposition rate and consequently low brisance. Low explosives deflagrate (i.e., burn) at subsonic speeds, whereas high explosives detonate, producing a supersonic wave. Ignition of powder packed behind a bullet must generate enough pressure to force it from the muzzle at high speed, but not enough to rupture the gun barrel. Gunpowder thus makes a good propellant, but is less suitable for shattering rock or fortifications. Gunpowder was widely used to fill artillery shells and in mining and civil engineering to blast rock until the second half of the 19th century, when the first high explosives were put into use.
Gunpowder is no longer used in modern weapons nor is it used for industrial purposes due to its relatively inefficient cost compared to newer alternatives. Today gunpowder firearms are limited primarily to hunting, shooting, and bulletless historical reenactments.