On the decomposition of metallic azides

Abstract

The purpose of this paper is to attempt a theoretical explanation of some of the phenomena observed during the decomposition of metallic azides by heat or by irradiation with ultra-violet or β -rays, and in particular of the new results on barium azide Ba(N 3 ) 2 obtained in the two preceding papers (Garner and Maggs 1939; Wischin 1939). This salt is stable at room temperature in the absence of radiation. If heated to a temperature of the order of 100° C, it decomposes slowly, nitrogen being given off. A similar effect may be obtained at room temperature through prolonged irradiation with ultra-violet light. In both cases metallic nuclei are formed on the surface of the crystals, and also inside it (at internal cracks?). We shall consider first some of the phenomena observed on heating. The number N of nuclei formed on a given surface of a crystal after heating for a time t is (Wischin 1939) given approximately by the law N = At 3 . (1) Formula (1) is satisfied best for the lower temperatures at which decomposition is observed; for higher temperatures a rather higher exponent than 3 fits the facts better. The constant A is “structure-sensitive”; in other words it varies from one crystal to another. Also rows of nuclei are observed, probably along cracks, showing that there exist on the crystal surface favoured places where a nucleus can form easily.