Stabilization smokeless powder

Figure 45. Marius Marqueyrol, Inspecteur-General des Poudres, France. 1919. Author of many researches on aromatic nitro compounds, nitrocellulose, smokeless powder, stabilizers and stability, chlorate explosives, etc.—published for the most part in the Memorial des poudres and in the Bulletin de la societe chimique de France.

Stabilization of smokeless powder Stabilization with diphenylaminc Inorganic stabilizers Organic stabilizers Apparent stabilizers Literature... 

DuPont in the U.S. developed about 1909, a smokeless powder from cotton of relatively low nitrogen that was quite soluble in ether alcohol. A small amount of diphenylamine was used as a stabilizer. After forming the grains and removing the liquid, a coating of graphite was added to make the smokeless powder that was used in the U.S. Other double-base types contain about 25% nitroglycerin. Cotton lint for nitration has been replaced by purified wood cellulose. 

The presence of N02 and other nitrogen oxides and/or acids in explosives (especially in smokeless powders and dynamites)is very undesirable because they act as catalyzers and promote further, more rapid decomposition. Most of the stabilizers used in smokeless powder, such as diphenylamine, centralites, urethanes etc are really inhibitors because they react with N02 and other nitrogen oxides to form nitroso- and nitrocompounds. 

Since black powder is relatively low in energy, it leaves a large proportion of corrosive solids after explosion and absorbs moisture readily, it was succeeded in late 1800s by smokeless gunpowder and picric acid. The first smokeless powder, known as cordite, was invented by tbe English chemists Sir James Dewar and Sir Frederick Augustus Abel in 1889. It was made in two forms a gelatinized nitrocellulose and a mixture of NC and NG with a small quantity of petroleum jelly added to act as a stabilizer. Smokeless powder soon became tbe primary ammunition for use in pistols. 

The advantage of the majority of the mixtures concerned lies in the cheapness and stability of their ingredients, which do not decompose during storage and the uncomplicated and relatively safe method of manufacture. Periodic chemical stability testing for smokeless powders, which necessitates a suitable organization and entails a high expenditure, is unnecessary. 

Soon after the manufacture of nitrocellulose smokeless powder began it was established that the powder obtained by the partial dissolution of nitrocellulose in a mixture of alcohol and ether (partly colloidal powder) has a chemical stability inferior to that of the nitrocellulose from which it derived. Thus Vieille [11] reports that on heating to a temperature of 110°C CPj guncotton undergoes denitration with the evolution of 0.04 cm3 NO/hr/gramme whereas the powder obtained from these substances without a stabilizer undergoes denitration at more than twice the rate, namely 0.10-0.15 cm3 NO/hr/gramme of substance. 

Originally, the cause of this phenomenon was unknown. In all the countries producing smokeless powder methods for improving the stability of the powder were sought. Similar research was also initiated by Vieille but in spite of systematic... 

The lower stability of smokeless powder in comparison with that of nitrocellulose is accounted for by its content of residual solvent and of the oxidation products of this solvent. Since in a finer powder the ratio of the surface to weight is high, the oxidation processes are more intense. A larger amount of decomposition products of residual solvent is formed by oxidation, and their destructive effect... 

If a powder which decomposes and forms acid products is mixed with a healthy" powder it causes the latter to decompose. The products of decompostion of smokeless powder were found to contain formic add, hydroxypyruvie acid CH2OH- CO COOH, hydroxyisobutyric acid (CH3)2C(OH)COOH and oxalic acid. All these acids except oxalic acid are hygroscopic, hence by increasing the moisture content in the powder, they hasten its decomposition. Acid products react with alkaline stabilizing components. 

Strong bases have an adverse effect on the stability of smokeless powder as described above. Moreover, Angeli [59] found that pyridine and its homologues cause decomposition of nitrocellulose. (On the action of pyridine on other nitric esters see Yol. II.) At an elevated temperature (e.g. 110°C) pyridine can produce an intense denitration of esters which may even lead to an explosion. 

After World War I the influence of sea water on the stability of smokeless powder was examined. It was found that nitrocellulose powder submerged in the sea during military activities did not suffer any perceptible deterioration as a result of immersion in sea water for several years, neither in its colloidal properties nor in its stability. 

Sunlight is a factor which hastens the decomposition of smokeless powder. Experiments carried out by D. Berthelot and Gaudechon [60] showed that powders containing various types of stabilizers behave in different ways towards light. E.g. powder stabilized with amyl alcohol proved to be more resistant to sunlight than that containing diphenylamine. The latter darkens very rapidly under the influence of light, which no doubt accelerates the decomposition of diphenylamine. 

The majority of the stability tests for smokeless powder are much the same as the methods used to determine the stability of nitric esters, in particular nitrocellulose (Vol. II). They are based on heating samples of the powder, thus starting decomposition processes or hastening processes already initiated within the powder. The value of such methods is comparative, since at an elevated temperature different reactions occur than those which would arise under normal conditions of storage. Nevertheless experiments over many years have shown that certain interrelations may be established for the stability of powder at various temperatures. Vieille [61] reports that the heating of a sample of powder for 1 hr at a temperature of 110°C involves approximately the same decomposition as ... 

In addition to the testing methods common to nitric esters (nitrocellulose, nitroglycerine) and smokeless powder there are also methods used exclusively for testing the stability of smokeless powders. 

The method was very useful for research but. was difficult to apply as an everyday control of stability (Ref 3). Besides, the fact that nitrogen oxides are removed from the sample by the stream of C02 creates conditions which differ from those existing during storage of NC or smokeless powder, when all the decompn products remain in contact with the parent substance Refs 1) Barnett (1919), 225 2) Reilly... 

Silvered Vessel test. The so-called Silvered Vessel test is a stability test that consists in determining the period of heating necessary to cause exothermic decomposition of the substance. It is usually limited to determining the stability of smokeless powder and is described in Vol. III. 

Finally the purified, stabilized and filtered nitroglycerine is transported from the store to the departments where it is required for further manufacturing processes (to make dynamite or smokeless powder). When required for smokeless powder manufacture, nitroglycerine can be transported as an aqueous emulsion by means... 

Brunswig s Test(Loss in Weight at 110°). A heat or stability test applicable to gelatinized smokeless powder... 

Figure 65. Fred Olsen. Has done important work on cellulose and has made many improvements in detonating explosives, high explosives, and smokeless powder in particular, has invented processes for the quick stabilization of nitrocellulose and for the production of ball-grain powder. Chief of Chemical Research, Aetna Explosives Company, 1917-1919 Chemical Adviser, Picatinny Arsenal, 1919-1928 Technical Director, Western Cartridge Company, 1929—.

Calcium carbonate, either powdered limestone or precipitated chalk, is used as an anti-acid in dynamite where it serves as a satisfactory stabilizer. Urea is used in dynamite and in celluloid. It reacts with nitrous acid to produce nitrogen and carbon dioxide, and is unsuitable for use in smokeless powder because the gas bubbles destroy the homogeneity of the colloid and affect the rate of burning. The small gas bubbles however commend it for use in celluloid, for they produce an appearance of whiteness and counteract the yellowing of age. 

Diphenylnitrosamine, which is always present in powders made from diphenylamine, is decomposed at 110°, and that temperature therefore is not a suitable one for a study of the stability of smokeless powder. At 75° diphenylnitrosamine attacks nitrocellulose less rapidly than diphenylamine itself, but this is not true at lower temperatures (40° and 60°) at which there is no appreciable difference between the two substances. Carbazol at 110° is an excellent stabilizer but at 60° and 75° is so poor as to... 

Nitrocellulose, pulped and given a preliminary or sour boiling, may be used directly without poaching. Deteriorated smokeless powder, containing nitro derivatives of diphenylamine and acidic decomposition products, may be reduced to a coarse powder under water in a hammer mill, and may then be used. Whichever is used, the first necessity is to stabilize it by complete removal of the acid. For this purpose, the material in the presence of water (which may contain a little chalk in suspension or urea in solution) is introduced into a still where it is dissolved with agitation in ethyl acetate to form a heavy syrup or lacquer, and is treated with some substance which is adsorbed by nitrocellulose more readily than acid is adsorbed. It is a curious fact that nitrocellulose is dissolved or dispersed by ethyl acetate much more readily... 

For many years guanidine thiocyanate was the most easily prepared and the most commonly used of the salts of guanidine. Other salts were made from it by metathetical reactions. Nitro-guanidine, prepared from the thiocyanate by direct nitration with mixed acids, was found to contain traces of sulfur compounds which attacked nitrocellulose and affected the stability of smokeless powder, and this is one of the reasons why nitroguanidine powders did not come into early use. Guanidine thiocyanate is deliquescent. Strong solutions of it dissolve filter paper. 

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