Powders, test methods storage stability

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 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. 

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 ... 

Stability during storage may be tested by chromatographic analysis of a powder subjected to accelerated ageing in an oven. The most practical method remains taste evaluation of the atomized product by a panel (Table II). 

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