Low-smoke powders (often called NC powders with nitrocellulose as a component) are a group of explosives whose main component is cellulose nitrate ; often also nitrocellulose (NC), gun cotton or engl. called guncotton . A distinction is made between single-base, two-base and three-base blowing agents. Paul Vieille 1882 developed the propellant charge of gun cotton , smokeless Poudre B , turning them with a mixture of alcohol and ether treated. But it was only Alfred Nobel who managed to produce a progressively burning powder. He left with saltpeter treated cotton with nitroglycerin gel. These components form the basis of all modern smokeless fuels.
The low-smoke gunpowder was developed at the end of the 19th century, when black powder , which up until then was mainly used as a propellant, no longer met the requirements of modern artillery weapons .
The problem arose as follows: Black powder was unsuitable for use in large-caliber guns because it was too offensive: the propellant charge had already burned down before the projectile had reached the end of the barrel, thus causing a rapidly increasing pressure curve. Attempts to reduce the burning rate first by using a coarser grain size of the black powder and then by increasing the density of the raw powder mass have shown only limited success. Further disadvantages were the heavy smoke development and the heavy soiling of the pipes by salts, which are produced when black powder is burned. When burned, one kilogram of black powder yields around 560 grams of a salt mixture, mainly potassium sulfite and potassium carbonate . The salt pollution caused problems in particular with rifles (in which the aggressiveness of the black powder did not interfere) and was a hindrance to the transition to smaller calibers.
After unsuccessful experiments on the basis of potassium picrate and a mixture of potassium chlorate , blood liquor salt and sugar, experiments with nitrated cellulose began . This developed hardly any smoke and left no residue, but was too aggressive with rifles.
A remedy for the unwanted aggressiveness was found by gelatinizing with various solvents and phlegmatizing . The gelatinization process used, the variation of the additives and the size and shape of the powder particles could now largely influence the burning behavior, but the smoke development increased due to the additives used and the powder no longer burned completely residue-free. However, this was accepted due to the other advantages.
As early as 1882, the French chemist Paul Vieille had been developing Poudre B , perfected in 1884 , which today is considered the first low-smoke powder to be used in rifles in the form of the 8 × 50 mm R Lebel cartridge . Another nitrocellulose powder was invented by Max Duttenhofer in the Rottweil powder factory in 1884 and produced on a large scale. Alfred Nobel marketed nitrocellulose powder as ballistite from 1887 and is also named as the inventor. In this context, there were patent disputes over a British parallel invention , the cordite by Frederick Augustus Abel and James Dewar . The low-smoke powders have almost completely replaced black powder as a propellant , as they have the advantage over black powder that the barrel hardly gets dirty and that they are safer to use.
In 1802 , Eleuthère Irénée du Pont founded the DuPont company in the USA , which initially specialized in the manufacture of black powder. With the advent of the low-smoke powder, she took over their introduction.
NC powders are the standard powder for firearms today. Only smokeless powder is used for military purposes , since, in addition to being less polluted, it has the advantage that the position of the shooter is not revealed by clouds of smoke. The powders used in firearms need an initial spark . This is taken over by the primer in firearms . However, the powder only burns off relatively slowly if you light it with a lighter, for example, and only unfolds its full effect from a certain ignition temperature.
Exceptions to this standard can be found in historical black powder shooters.
NC powder classes - composition
According to the composition, the NC gunpowders are divided into three classes:
- Monobasic gunpowder (cellulose nitrate powder): Mixtures of 80% gun cotton and 20% collodion wool , which are gelatinized with alcohol- ether (ether) mixtures and, after molding and drying, are phlegmatized with plasticizers such as centralites, camphor, dibutyl phthalate and the like.
- Two-base gunpowder: Mixtures of nitroglycerin and cellulose nitrate, which are gelatinized with acetone / alcohol, then formed into cords and then the solvent is removed. A typical example is British cordite , which owes its name to the shape of the cord.
- Tri-base gunpowder: mixtures of diethylene glycol dinitrate or triethylene glycol dinitrate and cellulose nitrate to which nitroguanidine is added as a third component; these powders have a low energy content with a large gas volume. They protect the pipes due to the lower combustion temperature and are used especially for field artillery (continuous fire) and anti-aircraft guns (high cadence ).
- Polybasic gunpowder: These include mixtures of three or more components; Mixtures with more than three components are rarely made. For example, during the Second World War the Germans used mixtures of diethylene glycol dinitrate or triethylene glycol dinitrate, cellulose nitrate (nitrated cellulose), hydrocellulose (hydrogenated cellulose) and nitroguanidine - sometimes picric acid (TNP) or benzene trinitrate (TNB) were also added to increase the explosiveness.
Because of the lack of nitric acid / saltpeter and low-smoke powders (especially made of cellulose), the Germans stretched gunpowder during World War II. B. also with ammonium acid (ammonium salts).
To reduce the muzzle flash, additives are often added, such as salts such as B. Sulphates (Potassium Sulphate).
The pipe life can be increased by adding nitrogen, such as nitrides or azides.
Pyroxilin powder and nitroglycerin powder
The low-smoke (smokeless) powders are divided into pyroxilin and nitroglycerin powder. Chemists call them colloidal powders and differentiate between
- Powder based on volatile solvents,
- Powder based on poorly volatile solvents.
The pyroxilin powder are mainly used in the cartridges of firearms, the nitroglycerin powder with the greater explosive power z. B. in mines and projectiles. The modern pyroxilin powder consists of gelatinous pyroxilin. Pyroxilin is obtained by treating the cell tissue (e.g. wood, cotton wool, flax, hemp and the like) with a mixture of nitric and sulfuric acid, and nitroglycerin after processing the glycerin with a mixture of nitric and sulfuric acid . The nitroglycerin powder is made from the mixture of pyroxilin and nitroglycerin. Pyroxiline is one of the explosives , the characteristic of which is the very high burning rate and the shattering splinter effect caused by the rapidly expanding hot gases. Pyroxilin is treated with solvents to reduce its explosiveness and convert it into powder. The pyroxiline swells under the action of the solvent and partially mixes with it. Its fibrous structure breaks down to a certain extent and it turns into a dough-like plastic mass that can take any shape. This property makes pyroxilin particularly valuable. After removing the volatile solvent, the mass solidifies.
As POL powder (powder without [organic] solvents) di- or tribasic propellant charge powder of artillery or rocket propellants as well be referred to. Gelatinization and homogenization are carried out with water using roller, extrusion or screw press processes, with diethylene glycol dinitrate or glycerol trinitrate acting as “solvents and swelling agents” for cellulose nitrate. The water is then evaporated to about 1% and the powder is then shaped by machine.
In Germany, triethylene glycol dinitrate was used instead of diethylene glycol dinitrate for the so-called tropical powder because of its lower volatility. Glycerin trinitrate was only available to a limited extent as a raw material during both world wars due to the shortage of fats and oils.
To reduce smoke development and increase storage stability, 0.5% to 2% diphenylamine can be added.
The addition of 1% sodium oxalate or 2% potassium sulfate prevents the flue gases from igniting and thus the muzzle flash.
Dinitrotoluene can be used as a substitute for glycerol trinitrate or diethylene glycol dinitrate, but it is significantly more toxic. Ethylene glycol dinitrate can also be used for the same purpose, but due to its much lower boiling point, evaporation and recondensation slowly separate. Therefore this powder cannot be stored for a long time.
Up to 50% ammonium nitrate can be added to replace cellulose nitrate, but the gunpowder is then sensitive to moisture. Pellets made from coal dust and ammonium nitrate were used as propellants for artillery in Germany during the First and Second World Wars.
The finished powders are graphitized to avoid static charging when pouring and thus avoid sparks.
Depending on the shape, a distinction is made between tube powder (in different lengths), multi-hole powder (tubes, perforated several times), flake powder, strip powder, ball powder, cube powder, ring powder, noodle powder (short-cut sticks) and other shapes. The shape and size of the powder particles is largely determined by the size and shape of the propellant charge and the desired combustion profile. In large-caliber cannons, tube powder is mostly used, in steep-fire guns plate powder, and in handguns mainly fine-grained powder. Propellant charges for rockets are produced in the form of cylindrical pellets, which are additionally provided with bores and grooves to increase the burn-off surface.
In order to prevent an artillery propellant charge from detonating instead of deflagrating , it is not ignited directly by the initial charge, but via an intermediate charge of black powder. This also ensures that the entire charge is ignited evenly.
- John Baptiste Bernadou, Smokeless Powder, Nitro-cellulose: And Theory Of The Cellulose Molecule ISBN 978-1-103-12711-5 .
- BG Chemie (editor), M 037 - Nitrocellulose ISBN 978-3-86825-039-8 .