Undesired Formation of Copper Azides

Lead azide, otherwise a very good primary explosive, has one major drawback, apart from its toxicity. It reacts with water and forms volatile azoimide (b.p. 35 °C) which may react with copper forming sensitive copper azides. This process is accelerated by the presence of acidic substances such as carbon dioxide (from the air) or even lead styphnate, which is often used together with LA [3, 5, 8,40]. 

The liberated azoimide attacks copper or its alloys (brass) and copper azides form on the metal surface. The concurrent use of LA and copper (or brass) in fuses or blasting caps therefore represents an inherent safety hazard. Although the LA-copper (copper alloys) reaction has been known since 1913, it has been a cause of many incidents decades later [49]. These incidents have been sometimes erroneously reported as spontaneous explosions. The reality, however, is that, in all known cases, they have been linked to some type of movement and therefore should not be considered spontaneous [70]. 

The chemical processes involved in the formation of copper azides may be summarized by the following set of equations  

The azoimide is the first substance formed from LA in presence of moisture. It reacts with copper giving cuprous azide—CuNa— which appears as a white film on the copper surface. The cuprous azide is then oxidized to yellow-brown 

While corrosion of the copper surface is usually concentrated in the vicinity of the source of the LA, diffusion of the azoimide vapor can occur and result in the formation of the sensitive products at some distance from the LA (for example in moving parts of fuses). 

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