Science Fair Project Encyclopedia
Cordite is a smokeless propellent explosive made by combining two high explosives: nitrocellulose and nitroglycerin. It is commonly used in firearms since the early 20th Century. It has also been used in solid fuel rockets .
In 1886, a French chemist called Paul Vieille invented the first smokeless powder, called Poudre B (Poudre Blanche = white powder). It was made out of two forms of nitrocellulose (collodion and guncotton) softened with ethanol and ether and kneaded together. Three times more powerful than black powder, and not generating vast quantities of smoke, Poudre B was a great improvement on black powder (or Poudre Noire = black powder). The reason that it was smokeless is that the combustion products were mainly gaseous, compared to around 60% solid products for black powder (potassium carbonate, potassium sulphate etc). It was immediately adopted by the French military but tended to become unstable over time and led to many accidents, for example two battleships, the Jena and the Liberte blew up in Toulon harbour in 1907 and 1911 respectively.
Alfred Nobel invented a similar propellant explosive called ballistite in 1887, which was composed of 10% camphor and 45% nitroglycerin and 45% collodion. His patent specified that the nitrocellulose should be "of the well-known soluble kind". Over time, the camphor tended to evaporate leaving an unstable explosive.
A government committee in Great Britain, called the "Explosives Committee", chaired by Sir Frederick Abel monitored foreign developments in explosives. Abel and Sir James Dewar, who was also on the committee, jointly patented a new mixture, consisting of 58% nitroglycerin by weight, 37% guncotton and 5% vaseline in 1889. Using acetone as a solvent, it was extruded as spaghetti-like rods initially called "cord powder" or "the Committee's modification of ballistite", but this was swiftly abbreviated to cordite. It was quickly discovered that the rate of burning could be varied by altering the surface area of the cordite. Narrow rods were used in small-arms and gave relatively fast burning, whilst thicker rods would burn more slowly and were used for longer barrels such as those used in artillery.
Nobel sued Abel and Dewer over patent infringement, eventually getting to the House of Lords in 1895 but lost, because of the words "of the well-known soluble kind" in his patent was taken to mean the soluble collodion and hence specifically excluded the insoluble guncotton.
Cordite, ballistite and Poudre B continued to be used in different armed forces for many years, but cordite gradually became predominant. One problem was that early versions of cordite quickly corroded gun barrels. To combat this, the British changed the mixture to 65% guncotton, 30% nitroglycerine (and keeping 5% vaseline) in their version shortly after the end of the Second Boer War. This was known as cordite MD (=MoDified).
During the First World War, acetone was in short supply for the British and so a new form was developed. This was Cordite RDB (Research Department formula B), which was 52% collodion, 42% nitroglycerin and 6% vaseline. It tended to become unstable if stored too long, once acetone production increased the older form replaced it. Research on solvent-free Cordite RDB continued primarily in the addition of stabilizers which led to the type commonly used today.
An important development during the Second World War was the addition of another explosive, nitroguanidine to the mixture to form triple-base cordites, or Cordite N. This solved two particular problems with the large naval guns of the day as fitted to capital ships. Nitroguanidine produces large amounts of nitrogen when heated which had the benefit of reducing the muzzle flash, and its lower burning temperature greatly reduced the erosion of the gun barrel.
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