Silver azide melting temperature

Bowden and Singh placed single crystals in a furnace under a vacuum and at a controlled temperature. Experiments with cadmium azide, a-lead azide, and silver azide showed that crystals having a thickness greater than a critical value exploded when kept at a fixed temperature and that smaller crystals decomposed slowly at that temperature. At 600°K the measured value for cadmium azide was 27 fjm and for lead azide 46 jum. Silver azide melted before explosion, but estimated thicknesses of the droplets were of a similar order. The results were taken to support earlier conclusions, arrived at from friction and impact experiments [1,2], that hot spots must be lO" -10 jm diam for explosions to occur. 

It has been noted that silver azide explodes at a lower temperature when tested in copper blasting caps than when tested in aluminum blasting caps. It has been observed that the thermocouple catalyzes a strong exothermic reaction just above the azide melting point, whereas when the thermocouple is encapsulated the exothermic reaction is milder [27]. 

Bowden and Singh [37, 38] achieved explosion of lead and silver azides when crystals were irradiated with an electron beam of 75 kV and 200 pA. Explosion was partly due to heating of the crystals by the electron beam. To substantiate this, crystals of potassium chlorate with a melting point of 334°C readily melted in the beam, showing a temperature rise close to the explosion temperature of the azides. Sawkill [97] investigated with an electron microscope the effect of an electron beam on lead and silver azides. If explosion did not take place, color changes and nucleation occurred cracks developed within the crystals which broke up into blocks about 10 cm across and were believed to be associated with a substructure in the crystals. In silver azide the progression to silver was pronounced but did not follow the thermal decomposition route. 

The sensitivity of azides to heat is one of their properties which can be most precisely determined. The more practically useful substances, such as lead and silver azides, do not detonate until temperatures close to or at their melting points are attained. Among technologically important sohd explosives such as TNT, tetryl, and RDX, the relatively high melting points of lead and silver azides (<300°C) and the good vacuum stability in standard tests are perhaps not representative of their overall sensitivity. Once a threshold temperature has been attained in the azides, the transition from slow decomposition to detonation is... 

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