Silver azide, decomposition

As a heavy metal azide, it is considerably endothermic (A// +279.5 kJ/mol, 1.86 kJ/g). While pine silver azide explodes at 340°C [1], the presence of impurities may cause explosion at 270° C. It is also impact-sensitive and explosions are usually violent [2], Its use as a detonator has been proposed. Application of an electric field to crystals of the azide will detonate them, at down to — 100°C [3], and it may be initiated by irradiation with electron pulses of nanosecond duration [4], See other catalytic impurity incidents, irradiation decomposition... 

Bowden and Singh [94] and later Bowden and McAuslan [95] using the electron microscope, observed that on heating at a temperature above 120°C the separate crystals of lead azide (like those of cadmium or silver azides), break down into fine particles, approximately 10 5 cm in dia. and decomposition reaction takes place chiefly on the newly-formed surfaces. This makes it evident that the thermal decomposition of azides cannot be regarded as a surface reaction or a process occurring within large crystals only the whole mass is involved, due to crystal breakdown. 

The researches of Wischin [113] and those of Garner and Maggs [84] have shown that metallic nuclei are formed during the slow thermal decomposition of silver azide. These researches were carried out by means of an optical microscope. 

Eggert and Courtney-Pratt and Rogers state that the decomposition of silver azide under the influence of irradiation has a thermal character, i.e. that light absorbed by a thin surface layer of the crystal is degraded into heat in a very short time interval (less than 1/50 fisec), whereupon explosion occurs by the normal thermal mechanism. 

Gray and Waddington [57,120] examined the physico-chemical properties of silver azide and state that its melting point is 300°C. On the basis of the latest opinion that the explosive decomposition of azides results from processes involving ions and electrons caused by imperfection and deficiencies in the crystal lattice (Jacobs and Tompkins [22]), the authors incorporated silver cyanide, Ag2(CN)2,... 

Other authors quote the following values for the activation energy of the thermal decomposition of silver azide ... 

Thus it is similar to the decomposition of azides. There have been several papers on silver oxalate — Ag2C204. Macdonald and Hinshelwood [76] confirmed the Berthelot equation, according to which the only products of decomposition of silver oxalate are metallic silver and C02. 

This substance forms salts with acids, and was first isolated in the form of its nitrate. The nitrate is not detonated by shock but undergoes a rapid decomposition with the production of light when it is heated. The picrate and the perchlorate explode violently from heat and from shock. Guanyl azide is not decomposed by boiling water. On hydrolysis with strong alkali, it yields the alkali metal salt of hydrazoic acid. It is hydrolyzed by am-moniacal silver nitrate in the cold with the formation of silver azide which remains in solution and of silver cyanamide which appears as a yellow precipitate. By treatment with acids or weak bases it is converted into 5-aminotetrazole. 

AgN3 (c). Wohler and Martin1 measured the heat of decomposition of silver azide to be 67.3. 

The undiluted material is extremely unstable, usually exploding violently without cause at any temperature, even as solid at —100°C [1], Explosion is likely to be triggered by pressure fluctuations of around 10 Pa [4], It gives an explosive yellow liquid with liquid ammonia when condensed on to yellow phophorus at —78°C an extremely violent explosion soon occurs. Addition of phosphorus to a solution of the azide in carbon tetrachloride at 0°C causes a series of mild explosions if the mixture is stirred, or a violent explosion without stirring. Contact of the liquid or gaseous azide with silver azide at —78°C gave a blue colour, soon followed by explosion, and sodium reacted similarly under the same conditions [1], When chlorine azide (25 mol %) is used as a thermally activated explosive initiator in a chemical gas laser tube, the partial pressure of azide should never exceed 16 mbar [2], The explosive decomposition has been studied in detail [3]. 

SYN NITROGEN CHLORIDE DOT CLASSIFICATION Forbidden SAFETY PROFILE Strong irritant by inhalation. An extremely unstable explosive. Reacts with liquid ammonia to form an explosive liquid. Explosive reaction with 1,3-butadiene, C2H6, C2H4, CH4, CsHs, phopshorus, silver azide, sodium. Reacts with water or steam to produce toxic and corrosive fumes of HCl. Has been used as an initiator in chemical gas lasers. When heated to decomposition it emits toxic fumes of Cr and NOx- See also CHLORINE and AZIDES. 

OSHA PEL TW A 0.01 mg(A /m3 ACGIH TLV WA 0.01 mg(Ag)/m3 DOT CLASSIFICATION Forbidden SAFETY PROFILE Explodes when heated above 270°C or on impact. Pure silver azide explodes at 340°. An electric field or irradiation by electron pulses can explode the crystals. Shock-sensitive when dry and has detonated 250°C. Solutions in aqueous ammonia explode above 100°C. Reacts to form more explosive products with iodine (forms iodine azide) bromine and other halogens. The presence of metal oxides or metal sulfides increases the azide s sensitivity to explosion. Mixtures with sulfur dioxide are explosive. When heated to decomposition it emits toxic fumes of NO,. See also AZIDES and SILVER COMPOUNDS. 

Slow thermal decomposition was examined by Garner [Vol. Ill, p. 171). It was shown 1112 that when silver azide is heated, silver is formed in an oriented way througli the a/idc lattice. The rapid growth of nuclei by the surface migra- tion of metal in lead azide seems to be demonstrated 113]. Oioi and Boutin [1141 showed the existence of azide radicals in the course of the decomposition. 

Kabanov and Skrobot have shown [67] that magnetic fields (200 to 500 oersteds) caused a slight diminution in the rate of KMn04 decomposition. Relatively few studies of this type have been made but these workers mention that magnetic fields increase the rate of barium azide decomposition, decrease the rate of decomposition of silver oxalate and do not change the rate of decomposition of silver azide. 

Decomposition of silver azide in vacuum [52], induced by an electron beam, yields ultrafine particles of silver, predominantly less than 100 nm in diameter, and in the form of well-defined hexagonal or trigonal crystals and polygonized spheres. This technique of nanoparticle synthesis is recommended as having advantages over other methods. 

Minute amounts (0.01% to 2%) of impurities significantly affect the rate of thermal decomposition of lead and silver azides (Chapter 6, Volume 1). For example, the ionic impurities Ag, Fe IFeNs], and [BiN,] increase [59-61] and Cif decreases [100] the rate of thermal decomposition of lead azide Cu increases the rate for silver azide. In contrast to ionic unpurities incorporated in the azide lattice, semiconductors [62,63] in contact with the surface and proton- or electron-donor vapor adsorbed on the surface of azide (Chapter 4. Volume 2) affect its decomposition properties. 

Irradiation increased the rate of tliermal decomposition of lead azide, but the effect was not as pronounced as with lithium azide, for which the induction period was reduced to about one half and the rate increased considerably. Cadmium azide produced pressure-time curves similar to lead azide. Irradiated silver azide was unaffected, but the experiment was conducted at 315°C, which caused the silver azide to be molten. 

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. 

UV irradiation of other azides was conducted by Muller and Brous on sodium azide [99], by Garner and Maggs on barium and strontium azides [113], by Mott on metal azides [114], and by Boldyrev and Skorik on silver and barium azides [115]. Sodium, strontium, and barium azides are decomposed by UV light at room temperature, and their thermal decomposition is accelerated by preirradiation. Boldyrev et al. found that irradiating silver azide with UV light or X-rays at the instant of decomposition had no effect on the rate of its thermal decomposition. 

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... 

O. Sandus, N. Slagg, D. Wiegand, W. Garrett, Studies of the Fast and Slow Decomposition of Azides, presented at the DEA-AF-F/G-7304 Technical Meeting Physics ofExplosives, Naval Ordnance Laboratory, Silver Springs, Md., April-May, 1974. 

Of various complexes of silver azide known to exist in solution, [1,196, 200], only the MeL(N3) type has been isolated [164,182] e.g., the compound [P(C6H5)3Ag(N3)] is a white, crystalline solid which melts with decomposition at 170°C. It is made from a suspension of silver azide in benzene, which is treated with triphenylphosphine until soluble. The complex is then precipitated by adding pentane. 

In practice, it proves to be very difficult to obtain unambiguously reproducible values of either j3 or despite great care in collecting a vs. t data. Moreover, it is rare for any one power law to apply over the whole measured curve, unless, as in the case of silver azide studied by Bartlett et al. [22], a decay-type curve applies from 10-95% decomposition. 

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