lighthorseman
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<h3 class="post-content">Black Powder</h3>
Black powder was the sole propellant, explosive and pyrotechnic agent for 500 years, from 1300 to 1800, and is still in use for certain applications. It is a unique and fascinating compound chemically, technologically and socially. It was invented as a pyrotechnic substance, then applied as a propellant in firearms, and finally used in engineering and mining. The history of black powder and firearms is treated in Cannon. Some authors make assertions about the history of black powder that are not supported by good evidence, and should not be accepted without better proof. An egregious assertion is that Chinese alchemists experienced a black powder explosion in 220 BCE. There is no evidence of "black powder" in China, and this is about 1200 years before nitrates were first discovered and used, according to more reliable sources. The great Chinese invention was pure nitrates, which they used in pyrotechnic devices, arrow throwers and rockets. The invention of black powder is shrouded in mystery; neither Roger Bacon nor Berthold Schwartz invented it, but high-nitrate powder is probably a European invention. Black powder is not a simple mixture of nitrate, charcoal and sulphur.
The composition of ordinary black powder is 65-75 KNO<sub>3</sub>, 15-20 C, 10-15 S, which is close to the "stoichiometric" ratio of 84:8:8 that gives the ideal reaction 10KNO<sub>3</sub> + 8C + 3S → 2K<sub>2</sub>CO<sub>3</sub> + 3K<sub>2</sub>SO<sub>4</sub> + 6CO<sub>2</sub> + 5N<sub>2</sub>. The heat released is 685 kcal/kg, and the volume expansion factor is 5100. The solid products make the characteristic white smoke. The actual reaction depends on the exact constitution of the powder, how it is prepared, and how it is detonated. The density of gunpowder is about 1.04 g/cc. Black powder is the safest of all explosives. It is insensitive to shock and friction or to electric spark. It must be initiated by heat or flame. Moisture renders black powder useless, and drying does not restore its properties.
The nitrogen in KNO<sub>3</sub> has a formal charge of +5, which is reduced to 0 in N<sub>2</sub> (in such molecules the formal charge is taken as zero, its average value). The carbon is oxidized from 0 to +4 in CO<sub>2</sub> and the carbonate, and the sulphur from 0 to +6. KNO<sub>3</sub> is a stable and safe oxidizing agent, not capable of explosion on its own. Black powder is a very stable explosive, insensitive to shock or friction, but sensitive to heat and flame. Like all explosives, it supplies its own oxygen and does not rely on the atmosphere. Note that it is much less efficient as a heat source than carbon and oxygen, which gives 2140 kcal/kg. Its utility lies in its ability to furnish its energy in a very short time, while the carbon will take a good while to burn.
How the powder burns is affected by the grain size. The larger the grain, the slower the powder burns. Fine powder is used for blasting, small grain for firearms, and large grain for cannon. A large variety of black powders are manufactured, and each type has a special designation and use. Black powder is essentially a propellant that burns at a rapid but finite rate determined mainly by its temperature. It is often said that gunpowder will only burn in the open, but explodes when confined. This is much too simple a statement. When in the open, the unburnt powder never becomes hot enough to burn rapidly. When confined, as in a firecracker, the powder quickly becomes hot enough to burn very rapidly, releasing all the energy in a very short time, quickly enough to make a loud report. Pressure does raise the rate of burning, but gunpowder has the least pressure effect of any common explosive, and for this reason is gentle to guns. A thread of gunpowder, wrapped in paper or other covering, burns at a slow and reliable rate, making a delay element or fuse.
Because of its safety and reliability, pressed black powder is used as the propellant in small rockets. A powder for this service has less KNO<sub>3</sub> and S, and more C. Its rate of burning can be slowed with chalk, wax or talc. A typical mix is 91 black powder, 9 chalk. No more than 3% of the powder can be stopped by a <a href='/tags/20' rel='nofollow' title='See all tagged subjects with: #20'>#20</a> sieve (0.84 mm) and no less than 60% must be stopped on a <a href='/tags/40' rel='nofollow' title='See all tagged subjects with: #40'>#40</a> sieve (0.42 mm). It is compressed to 1.82-1.89 g/cc, and contains 1.8%-2.5% moisture. This propellant grain is burned in a chamber with a ceramic choke in army signal rockets, which reach 700 ft. altitude. A bursting charge expels 5 white stars that free-fall, or else a red star with parachute, that burns for about 50 sec. and falls at 10-15 ft/s. A model rocket has a pressed black powder propellent grain, and a granular black powder ejection charge. There is a delay element between the two charges, so that the rocket coasts to its maximum altitude before releasing the payload. The fuel for solid-fuel rockets, though called the "powder grain," is a cast plastic cylinder of the fuel material. The word "grain" does, in fact, seem to come from the grains of black powder that are used in a pressed charge, and has been transferred to the whole fuel assembly of any type.
Black powder is an oxidizer--fuel mixture of the type we shall discuss at more length under pyrotechnics. The sulphur and charcoal are first ground together, so that the thixotropic sulphur coats the colloidal charcoal intimately. Then the nitrate is mixed in by wet grinding. The nitrate produces oxygen to oxidize the sulphur and carbon, catalyzed by the large active surface of the charcoal, while releasing the nitrogen with the evolution of heat. The reaction begins at a temperature where there is a change in the crystal structure of the nitrate, which creates lattice defects that encourage the solid-state reaction.
War rockets were not extensively developed in China, and were used only incidentally in the West. Rockets for pleasure pyrotechnics did, however, become widely used, and were the basis for later war rockets. William Congreve developed his war rockets in the late 18th century, but they were only successfully used first in 1807 at Copenhagen. They were difficult to control, and not very effective. However, they could be fired with a light launcher instead of a heavy cannon, a principle later extensively applied. The last major use of Congreve rockets was in the Zulu war of 1879. Rockets appeared again in the Second World War for use in mass flights from landing ships and to support infantry. They also were used in the recoilless rifles and antitank rocket launchers that are still valuable, providing powerful artillery without the weight and recoil.
Black powder was the sole propellant, explosive and pyrotechnic agent for 500 years, from 1300 to 1800, and is still in use for certain applications. It is a unique and fascinating compound chemically, technologically and socially. It was invented as a pyrotechnic substance, then applied as a propellant in firearms, and finally used in engineering and mining. The history of black powder and firearms is treated in Cannon. Some authors make assertions about the history of black powder that are not supported by good evidence, and should not be accepted without better proof. An egregious assertion is that Chinese alchemists experienced a black powder explosion in 220 BCE. There is no evidence of "black powder" in China, and this is about 1200 years before nitrates were first discovered and used, according to more reliable sources. The great Chinese invention was pure nitrates, which they used in pyrotechnic devices, arrow throwers and rockets. The invention of black powder is shrouded in mystery; neither Roger Bacon nor Berthold Schwartz invented it, but high-nitrate powder is probably a European invention. Black powder is not a simple mixture of nitrate, charcoal and sulphur.
The composition of ordinary black powder is 65-75 KNO<sub>3</sub>, 15-20 C, 10-15 S, which is close to the "stoichiometric" ratio of 84:8:8 that gives the ideal reaction 10KNO<sub>3</sub> + 8C + 3S → 2K<sub>2</sub>CO<sub>3</sub> + 3K<sub>2</sub>SO<sub>4</sub> + 6CO<sub>2</sub> + 5N<sub>2</sub>. The heat released is 685 kcal/kg, and the volume expansion factor is 5100. The solid products make the characteristic white smoke. The actual reaction depends on the exact constitution of the powder, how it is prepared, and how it is detonated. The density of gunpowder is about 1.04 g/cc. Black powder is the safest of all explosives. It is insensitive to shock and friction or to electric spark. It must be initiated by heat or flame. Moisture renders black powder useless, and drying does not restore its properties.
The nitrogen in KNO<sub>3</sub> has a formal charge of +5, which is reduced to 0 in N<sub>2</sub> (in such molecules the formal charge is taken as zero, its average value). The carbon is oxidized from 0 to +4 in CO<sub>2</sub> and the carbonate, and the sulphur from 0 to +6. KNO<sub>3</sub> is a stable and safe oxidizing agent, not capable of explosion on its own. Black powder is a very stable explosive, insensitive to shock or friction, but sensitive to heat and flame. Like all explosives, it supplies its own oxygen and does not rely on the atmosphere. Note that it is much less efficient as a heat source than carbon and oxygen, which gives 2140 kcal/kg. Its utility lies in its ability to furnish its energy in a very short time, while the carbon will take a good while to burn.
How the powder burns is affected by the grain size. The larger the grain, the slower the powder burns. Fine powder is used for blasting, small grain for firearms, and large grain for cannon. A large variety of black powders are manufactured, and each type has a special designation and use. Black powder is essentially a propellant that burns at a rapid but finite rate determined mainly by its temperature. It is often said that gunpowder will only burn in the open, but explodes when confined. This is much too simple a statement. When in the open, the unburnt powder never becomes hot enough to burn rapidly. When confined, as in a firecracker, the powder quickly becomes hot enough to burn very rapidly, releasing all the energy in a very short time, quickly enough to make a loud report. Pressure does raise the rate of burning, but gunpowder has the least pressure effect of any common explosive, and for this reason is gentle to guns. A thread of gunpowder, wrapped in paper or other covering, burns at a slow and reliable rate, making a delay element or fuse.
Because of its safety and reliability, pressed black powder is used as the propellant in small rockets. A powder for this service has less KNO<sub>3</sub> and S, and more C. Its rate of burning can be slowed with chalk, wax or talc. A typical mix is 91 black powder, 9 chalk. No more than 3% of the powder can be stopped by a <a href='/tags/20' rel='nofollow' title='See all tagged subjects with: #20'>#20</a> sieve (0.84 mm) and no less than 60% must be stopped on a <a href='/tags/40' rel='nofollow' title='See all tagged subjects with: #40'>#40</a> sieve (0.42 mm). It is compressed to 1.82-1.89 g/cc, and contains 1.8%-2.5% moisture. This propellant grain is burned in a chamber with a ceramic choke in army signal rockets, which reach 700 ft. altitude. A bursting charge expels 5 white stars that free-fall, or else a red star with parachute, that burns for about 50 sec. and falls at 10-15 ft/s. A model rocket has a pressed black powder propellent grain, and a granular black powder ejection charge. There is a delay element between the two charges, so that the rocket coasts to its maximum altitude before releasing the payload. The fuel for solid-fuel rockets, though called the "powder grain," is a cast plastic cylinder of the fuel material. The word "grain" does, in fact, seem to come from the grains of black powder that are used in a pressed charge, and has been transferred to the whole fuel assembly of any type.
Black powder is an oxidizer--fuel mixture of the type we shall discuss at more length under pyrotechnics. The sulphur and charcoal are first ground together, so that the thixotropic sulphur coats the colloidal charcoal intimately. Then the nitrate is mixed in by wet grinding. The nitrate produces oxygen to oxidize the sulphur and carbon, catalyzed by the large active surface of the charcoal, while releasing the nitrogen with the evolution of heat. The reaction begins at a temperature where there is a change in the crystal structure of the nitrate, which creates lattice defects that encourage the solid-state reaction.
War rockets were not extensively developed in China, and were used only incidentally in the West. Rockets for pleasure pyrotechnics did, however, become widely used, and were the basis for later war rockets. William Congreve developed his war rockets in the late 18th century, but they were only successfully used first in 1807 at Copenhagen. They were difficult to control, and not very effective. However, they could be fired with a light launcher instead of a heavy cannon, a principle later extensively applied. The last major use of Congreve rockets was in the Zulu war of 1879. Rockets appeared again in the Second World War for use in mass flights from landing ships and to support infantry. They also were used in the recoilless rifles and antitank rocket launchers that are still valuable, providing powerful artillery without the weight and recoil.
