Powders, test methods chemical stability

A method, developed by Bergmann and Junk in 1904, for testing the chemical stability of nitrocellulose it was also subsequently employed for testing single-base powders. The test tube, which contains the specimen being tested, and which is equipped with a cup attachment, is heated at 132 °C= 270.4°F for two hours (nitrocellulose) or five hours (single base powders). At the end of the heating period the sample is extracted with water, and the test tube filled to the 50-ml mark with the water in the cup. The solution is filtered, and the content of nitrous oxides is determined by the Schulze-Tiemann method on an aliquot of the filtrate. 

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. 

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. 

Using a portable beam stability-controlled XRF spectrometer, Romano et al. (2005) have determined the concentrations of Rb, Sr, Y, Zr, and Nb in 50 fine potsherds from the votive deposit of San Francesco in Catania (Italy) by using a multilinear regression method in their bid for quantitative nondestructive determination of trace elements in archaeological pottery. A small portion of a few potsherds was even powdered in order to test the homogeneity of the material composing the fine pottery samples and the XRF data were compared with those obtained by chemical analysis of the powdered samples. 

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