Stability nitrocellulose powder

Many methods have been proposed and are used to study the thermal stability of propellants and to ensure the absence of possible autocatalysed decompositions during storage. None are sufficiently reliable to merit individual description. In practice, stabilisers are added, the usual being diphenylamine for nitrocellulose powders and symmetrical diethyl diphenyl urea (carbamate or centralite) for double base propellants. Provided a reasonable proportion of stabiliser remains, the propellant can be assumed to be free from the possibility of autocatalytic decomposition. The best test of stability is therefore a chemical determination of the stabiliser present. 

The following findings point to the harmful effect of air on the stability of green nitrocellulose powder, i.e. freshly pressed and containing a considerable quantity of solvent (alcohol and ether) (Table 171). 

Fig. 193. Stability of tubular nitrocellulose powder at 75-80°C as a function of the web thickness of the tubes, according to Brunswig [17],...

Atmospheric humidity has a deleterious effect on the stability of powder. Storm [54] reports that a good nitrocellulose powder, which withstood heating at a temperature of 65.5°C for 400 days without marked decomposition, showed evident decomposition in 175 days when stored at the same temperature in an atmosphere saturated with water vapour. Powder which passed the first test subsequently withstood heating for 5 hr at a temperature of 135°C without explosion, whereas powder from the second test exploded at the same temperature after 10 min. 

Fig. 194. Stability of nitrocellulose powder at 110°C (measured as a reduction of weight)...

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. 

The stability test for nitrocellulose powder at a temperature of 134.5°C the sample will not be considered serviceable unless the time necessary to produce the evolution of nitrogen oxides is at least 45 min and the powder withstands this temperature without exploding for 5 hr. The test can be combined with methyl violet test decoloration of the test paper should not occur before 30 min or longer according to particular specifications. 

Fig. 196. Effect of the addition of amyl alcohol and diphenylamine on the stability of nitrocellulose powder, according to Berger [66],...

More recently Demougin and Landon [67] examined the stability of nitrocellulose powder containing 1.02-7.8% diphenylamine at a temperature of 110°C. After 160 hr of heating they determined the nitrogen content in nitrocellulose isolated from powder (Table 174.). The initial content of diphenylamine in the sample was 7.8% on heating for 180 hr at a temperature of 110°C it was reduced to 1%. 

The systematic studies of T. Urbanski, Kwiatkowski and Miladowski [76] proved that the addition of an aromatic nitro compound distinctly enhances the stability of nitrocellulose and nitrocellulose powder. Thus, nitrocellulose containing 13.4% N which on heating for 5 hr at 120°C had pH=2.28 showed pH=2.89 on addition of 9 1% p-nitrotoluene, pH=3.17 on addition of 9.1 % 2,4-dinitrotoluene and pH=3.34 on addition of the same amount of a-trinitrotoluene. The same samples when heated in a constant volume (Tagliani test) gave at 134.5°C a pressure of decomposition... 

The alcohol (usually refined to 95-96%) must not be acid. To make a 100 cm3 sample of alcohol neutral towards phenolphthalein no more than 1.6 cm3 of 0.1 N NaOH is required. A larger quantity of acid is detrimental since it may adversely influence its stability and gives a dark powder. The alcohol should not contain nitrites. A nitrocellulose powder plant should be equipped with a plant for the distillation of alcohol. 

Powder produced with a volatile solvent should be freed from it as thoroughly as possible since too large a content of residual solvent is detrimental to the ballistic stability of the powder. In nitrocellulose powders the content of residual solvent should be lower than 1% in coarser powders (thicker flakes, strips or tubes) its content may be relatively higher, while it is relatively lower in finer ones. Powders... 

Nitroglycerine is a very powerful secondary explosive with a high brisance, i.e. shattering effect, and it is one of the most important and frequently-used components for gelatinous commercial explosives. Nitroglycerine also provides a source of high energy in propellant compositions, and in combination with nitrocellulose and stabilizers it is the principal component of explosive powders and solid rocket propellants. 

Loss of weight. One of the oldest and simplest quantitative methods is the determination of the loss of weight of a sample heated at a constant temperature. The original Sy-test [90] used in the U.S.A. for determining the stability of nitrocellulose and nitrocellulose powder ( U.S. Ordnance Department 115° Test ) consisted in heating a sample of the substance on a watch-glass at 115+0.5°C. 

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.

Trinitronaphthalene appears to be a genuine stabilizer for nitrocellulose, a true inhibitor of its spontaneous decomposition. Marqueyrol found that a nitrocellulose powder containing 10 per cent of trinitronaphthalene is as stable as one which contains 2 per cent of diphenylamine. The trinitronaphthalene has the further effect of reducing both the hygroscopicity and the temperature of combustion of the powder. 

Olsen patented simplified process for stabilizing and gelatinizing nitrocellulose powder and for producing it in spherical form, with or without deterrents, coatings, and other modifying agents. 

Nitrocellulose powder is heated gradually from icx> upwards as in the deflagration test. A strip of iodide p ier is suspended over the powder and the temperature at which the test-paper gives a coloration is taken as an indication of the stability of the powder. 

Nitroglycerine is one of the most important and most frequently used components of explosive materials together with nitroglycol, it is the major component of gelatinous industrial explosives. In combination with nitrocellulose and stabilizers, it is the principal component of powders, gun propellants and smokeless solid rocket propellants (- double base propellants). 

Single-base casting powder the casting powder consists of nitrocellulose, stabilizer, solid additives for ballistic modification, and a small amount of plasticizer. The normal ratio of casting powder to casting solvent, 2 1 by volume, yields a final composition of approximately 60% nitrocellulose. 

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. 

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. 

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