thumb|Finnish smokeless powder

Smokeless powder is a type of propellant used in firearms and artillery that produces less smoke and less fouling when fired compared to black powder. Because of their similar use, both the original black powder formulation and the smokeless propellant which replaced it are commonly described as gunpowder. The combustion products of smokeless powder are mainly gaseous, compared to around 55% solid products (mostly potassium carbonate, potassium sulfate, and potassium sulfide) for black powder.

Despite its name, smokeless powder is not completely free of smoke; Sharpshooters firing from concealed positions risked revealing their locations with a cloud of smoke.

Black powder burns in a relatively inefficient process that produces lower pressures, making it about one-third as powerful as the same amount of smokeless powder.

To prevent buildup of the deterioration products, stabilizers are added. Diphenylamine is one of the most common stabilizers used. Nitrated analogs of diphenylamine formed in the process of stabilizing decomposing powder are sometimes used as stabilizers themselves. Propellants in storage should be periodically tested for the amount of stabilizer remaining,

Composition

Propellants using nitrocellulose (detonation velocity , RE factor 1.10) (typically an ether-alcohol colloid of nitrocellulose) as the sole explosive propellant ingredient are described as single-base powder. These "cold propellant" mixtures have reduced flash and flame temperature without sacrificing chamber pressure compared to single- and double-base propellants, albeit at the cost of more smoke. In practice, triple-base propellants are, due to their higher price, reserved mainly for high-velocity large caliber ammunition such as used in (naval) artillery and tank guns, which suffer from bore erosion the most. During WWII they had some use by British and German artillery, and after the war they became the standard propellants in all British large-caliber ammunition designs except small arms. Most Western nations, except the United States, followed a similar path.

In the late 20th century new propellant formulations started to appear. These are based on nitroguanidine and high explosives of the RDX type (detonation velocity , RE factor 1.60).

Detonation velocities are of limited value in assessing the reaction rates of nitrocellulose propellants formulated to avoid detonation. Although the slower reaction is often described as burning because of similar gaseous end products at elevated temperatures, the decomposition differs from combustion in an oxygen atmosphere. Conversion of nitrocellulose propellants to high-pressure gas proceeds from the exposed surface to the interior of each solid particle in accordance with Piobert's law. Studies of solid single- and double-base propellant reactions suggest reaction rate is controlled by heat transfer through the temperature gradient across a series of zones or phases as the reaction proceeds from the surface into the solid. The deepest portion of the solid experiencing heat transfer melts and begins phase transition from solid to gas in a foam zone. The gaseous propellant decomposes into simpler molecules in a surrounding fizz zone. Energy is released in a luminous outer flame zone where the simpler gas molecules react to form conventional combustion products like steam and carbon monoxide.

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Bibliography

  • The Manufacture of Smokeless Powders and their Forensic Analysis: A Brief Review. Robert M. Heramb, Bruce R. McCord
  • Hudson Maxim papers (1851–1925) at Hagley Museum and Library. Collection includes material relating to Maxim's patent on the process of making smokeless powder.