Smokeless powder
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Smokeless powder is the name given to a number of gunpowder-like propellants used in firearms which produce negligible smoke when fired, unlike the older black powder which it replaced.
Types of smokeless powder include cordite, ballistite and, historically, Poudre B. They are classified as single-base, double-base or triple-base powders.
Description
Smokeless powder consists of nitrocellulose (single-base powders), frequently combined with up to 50 percent nitroglycerin (double-base powders), and sometimes nitroglycerin and nitroguanidine (triple-base), corned into small spherical balls or extruded into cylinders or flakes using solvents such as ether. Other minor ingredients, such as stabilizers and ballistic modifiers, are also added.The reason that they are smokeless is that the combustion products are mainly gaseous, compared to around 60% solid products for black powder (potassium carbonate, potassium sulfate etc).
Smokeless powder burns only on the surfaces of the granules, flakes or cylinders - described as granules for short. Larger granules burn more slowly, and the burn rate is further controlled by flame-deterrent coatings which retard burning slightly. The intent is to regulate the burn rate so that a more or less constant pressure is exerted on the propelled projectile as long as it is in the barrel so as to obtain the highest velocity. Cannon powder has the largest granules, up to thumb-sized cylinders with seven perforations (one central and the other six in a circle halfway to the outside of the cylinder's end faces). The perforations stabilize the burn rate because as the outside burns inward (thus shrinking the burning surface area) the inside is burning outward (thus increasing the burning surface area, but faster, so as to fill up the increasing volume of barrel presented by the departing projectile). Fast-burning pistol powders are made by extruding shapes with more area such as flakes or by flattening the spherical granules. Drying is usually performed under a vacuum. The solvents are condensed and recycled. The granules are also coated with graphite to prevent static electricity sparks from causing undesired ignitions.
History
Military commanders had been complaining since the Napoleonic Wars about the problems of giving orders on a battlefield that was covered in thick smoke from the gunpowder used by the guns. A major step forward was introduced when guncotton, a nitrocellulose-based propellant, was first introduced by Christian Friedrich Schönbein in 1846. He also promoted its use as a blasting explosive.Guncotton was more powerful than gunpowder, but at the same time was somewhat more unstable. This made it unsuitable as a propellant for small firearms: not only was it dangerous under field conditions, but guns that could fire thousands of rounds using gunpowder would be "used up" after only a few hundred with the more powerful guncotton. It did find wide use with artillery however. However, within a short time there were a number of massive explosions and fatalities in guncotton factories due to lack of appreciation of its sensitivity and the means of stabilization. Guncotton then went out of use for some twenty years or more until it could be tamed; however, it was not until the 1880s that it became a viable propellant.
In 1886 Paul Vieille invented a smokeless gunpowder called Poudre B, made from gelatinized guncotton mixed with ether and alcohol. It was passed through rollers to form thin sheets, which were cut into flakes of the desired size. The resulting propellant, today known as pyrocellulose, contains somewhat less nitrogen than guncotton and is less volatile. A particularly nice feature of the propellant is that it would not burn unless it was compressed, making it very safe to handle under normal conditions.
Vieille's powder revolutionized the effectiveness of small guns, for the following reasons:
- It gave off almost no smoke. After a few shots, a soldier with black powder ammunition would have his view obscured by a huge pall of smoke unless there was a strong wind.
- It was three times more powerful than black powder. This gave two advantages:
- * The higher muzzle velocity meant a flatter trajectory and therefore more accurate long range fire, out to perhaps 1000 metres in the first smokeless powder rifles.
- * Less powder was needed to propel a bullet, so the cartridge could be made smaller and lighter. This allowed troops to carry more ammunition for the same weight.
- It would burn even when wet. Black powder ammunition had to be kept dry and was almost always stored and transported in watertight cartridges.
Meanwhile, in 1887 Alfred Nobel developed a smokeless gunpowder called ballistite. A modified form of this was devised by Sir Frederick Abel and James Dewar which eventually became known as cordite, leading to a lengthy court battle between Nobel and the other two inventors over patent infringement. Both explosives were more stable and thus safer to handle than Poudre B, and also more powerful. Today propellants based on nitrocellulose alone are known as single-base, whereas cordite-like mixtures are known as double-base. A triple-base flashless cordite was also developed, primarily for large naval guns, but also used in battle tank ammunition.
Smokeless powder allowed the development of modern semi- and fully automatic firearms. Burned blackpowder leaves a thick, heavy fouling which is both hygroscopic and corrosive. Smokeless powder fouling exhibits none of these properties. This makes an autoloading firearm with many moving parts feasible (which would jam or seize under heavy blackpowder fouling).
Single and double-base smokeless powders now make up the vast majority of propellants used in firearms. They are so common that most modern references to "gunpowder" refer to a smokeless powder, particularly when referring to small arms ammunition.
Instability and stabilization
Nitrocellulose deteriorates with time, yielding acidic byproducts. Those byproducts catalyze the further deterioration, increasing its rate. The released heat, in case of bulk storage of the powder, or too large blocks of solid propellant, can cause self-ignition of the material. Single-base nitrocellulose propellants are most susceptible to degradation, double-base and triple-base propellants tend to deteriorate slower. To neutralize the decomposition products, which could otherwise cause corrosion of metals of the cartridges and gun barrels, calcium carbonate is added to some formulations.To prevent buildup of the deterioration products, stabilizers are added. 2-nitrodiphenylamine is one of the most common stabilizers used, with others being eg. 4-nitrodiphenylamine, N-nitrosodiphenylamine, N-methyl-p-nitroaniline, and diphenylamine. The stabilizers are added in the amount of 0.5-2% of the total amount of the formulation; higher amounts tend to degrade its ballistic properties. The amount of the stabilizer is depleted with time. Propellants in storage should be periodically tested on the remaining amount of stabilizer, as its depletion may lead to autoignition of the propellant.
Smokeless propellant components
The propellant formulations may contain various energetic and auxiliary components:- Propellants:
- * Nitrocellulose, an energetic component of most smokeless propellants
- * Nitroglycerin, an energetic component of double-base and triple-base formulations
- * Nitroguanidine, a component of triple-base formulations
- Plasticizers, to make the grains less brittle
- * Dibutyl phthalate
- * Polyester adipate
- Binders, to hold the grain shape
- * Rosin
- * Ethyl acetate
- Stabilizers, to prevent or slow down self-decomposition
- * Diphenylamine
- * 2-nitrodiphenylamine
- * 4-nitrodiphenylamine
- * N-nitrosodiphenylamine
- * N-methyl-p-nitroaniline
- Decoppering additives, to hinder the buildup of copper residues from the gun barrel rifling
- * Tin metal and compounds, eg. tin dioxide
- * Bismuth metal and compounds, eg. bismuth trioxide, bismuth subcarbonate, bismuth nitrate, bismuth antimonide; the bismuth compounds are favored as copper dissolves in molten bismuth, forming brittle and easily removable alloy
- * Lead foil and lead compounds, phased out due to toxicity
- Flash reducers, to reduce the brightness of the muzzle flash
- * Potassium nitrate
- * Potassium sulfate (both have a disadvantage - production of smoke)
- Wear reduction additives, to lower the wear of the gun barrel liners [link]
- * Wax
- * Talc
- * Titanium dioxide
- * Polyurethane jackets over the powder bags, in large guns
- Other additives
- * Graphite, a lubricant to cover the grains and prevent them from sticking together, and to dissipate static electricity
- * Calcium carbonate, to neutralize acidic decomposition products
Faster-burning propellants generate higher temperatures and higher pressures, however they also increase the wear of the gun barrels.
A Primex powder contains 0-40% nitroglycerin, 0-10% dibutyl phthalate, 0-10% polyester adipate, 0-5% rosin, 0-5% ethyl acetate, 0.3-1.5% diphenylamine, 0-1.5% N-nitrosodiphenylamine, 0-1.5% 2-nitrodiphenylamine, 0-1.5% potassium nitrate, 0-1.5% potassium sulfate, 0-1.5% tin dioxide, 0.02-1% graphite, 0-1% calcium carbonate, and nitrocellulose as the remainder to 100%. [link]
External link
- [U.S. Patent 430212] - Manufacture of explosive -- H. S. Maxim
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