Silver Azide, AgN3, is a white crystalline solid which is photosensitive and has the property of explosion. The technical product is often gray. The
azide is practically insoluble in water and organic solvents. Aqueous ammonia [ l ] or anhydrous hydrogen fluoride [196] dissolve it as a complex;
upon evaporation, the azide is recovered unchanged. Colorless needles more than 10 mm long are easily obtained from the ammonia solution [197]. In
nitric acid it dissolves with chemical destruction, evolving HN3 gas. On exposure to light, silver azide turns first violet and finally black, as
colloidal silver is formed and nitrogen evolves [175,176]. As photographic emulsion, the azide is found to be 200 times less photosensitive than
silver bromide, but more easily reducible by developers. The emulsions are not explosive [198]. A suspension of silver azide in boiling water
decomposes with a discoloration similar to that of the photodecomposition [176]. When heated dry, the azide turns violet at 1 50'C and melts at 25 1OC
to a blackish liquid. Starting at 253'C the melt evolves nitrogen gas at a rate which simulates boiling. The mass then shrinks to a brown solid and
finally, at the end of decomposing, appears white. Under the microscope the particles appear as silver metal (21. When heated rapidly, silver azide
explodes at 3W°C with high brisance, emitting a green light flash [1,2,176]. A partially (50%) decomposed, gray sample explodes with the same
brisance at 305'~ [176]. The degree of decomposition has evidently little influence on the explosive behavior. The same was found for mechanical
explosion; white and gray samples are equally highly sensitive to friction and impact
(1991. However, the particle size has a distinct influence on impact sensitivity; coarser samples are more sensitive [l92,200]. Long needles of silver
azide frequently explode when broken with a metal wire [197]. The AgN3/N3- half cell assumes a standard potential of +0.384 V at 21 "C; the solubility
of silver azide in water was electrochemically determined as 8.4 X g/liter at 18OC [201].
Of historic interest is a reaction in which the azide group was synthesized from hydrazine and nitrite in the presence of silver ions [19,98] (see p.
24). Most commonly, silver azide is prepared by mixing aqueous solutions of hydrazoic acid or sodium azide with silver nitrate. The product is
precipitated in fine crystalline form; larger crystallites are obtained from more dilute reagents [200]. One author recommended the use of an excess
of sliver nitrate; another believed this would enhance the photodecomposition of the product [202]. Of more significance is the recommendation to make
the azide in the dark, or at least under red light, [203.204] and to wash the product completely ion free.
To prepare 3-g batches, a solution of 3.42 g silver nitrate (slight excess) in 100 ml water is placed in a 500-rnl beaker and heated to 60-70'~. The
solution is stirred with a rubber-clad glass rod, and a solution of 1.3 g sodium azide in 100 ml water (60-70'~) is added within 3-4 min. The
precipitate is stirred until well coagulated and then transferred to a Buchner funnel. To avoid contact with the hard funnel material, both the bottom
and walls are covered with filter paper. The product is washed with water until nitrate free, thed h alcohol and ether, followed by drying at
70-90°C.
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