Barium azide, 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. 

Fig. 15. Isothermal a—time curves for the decomposition of barium azide [696]. (Reproduced, with permission, from Monatshefte fur Chemie.)...

Dining the preparation of cellular rubber by thermal decomposition of calcium, strontium or barium azides, various additives were necessary to prevent explosive decomposition of the azide in the blended mixture. 

The explosive properties of sodium, calcium, strontium and barium azides have been investigated at the Chemisch-Technische Reichsanstalt [135]. These azides differ markedly from lead, silver and cupric azides in that they show none of the properties of primary explosives. All three may be ignited by a spark, a glowing wire or the flame of blackpowder. Calcium azide bums most rapidly and has distinctly marked explosive properties. Larger quantities of it may explode when ignited in a closed tin, while strontium and barium merely bum violently. Calcium azide detonates under the influence of a detonating cap. The sodium azide does not decompose in these conditions. The other azides show weak decomposition under the influence of a standard (No. 3) detonator. Their most important properties are tabulated below. 

Tompkins et al. [22, 85] studied the photochemical decomposition of potassium and barium azide. Originally they found that the rate of photolysis was proportional to the square of the intensity of the radiation. 

Tompkins [80] investigated the thermal decomposition of silver oxalate at 110— 130°C. Its decomposition, in his opinion, is similar to that of barium azide. 

Lepin K. Andreev, Decomposition of Solid Barium Azide Under the Action of X-rays , KhimReferatZh No 10-11, 120-21 (1940) CA 37, 1271 (1943) 19) R.C. Grass, Tests... 

D.J. Moore, Thermal Decomposition of Barium Azide , Nature 203, 860—61 (1964) 132) J. Roth, Initiation of Lead Azide by High Intensity Light , JChemPhys 41, 1929—36 (1964) 133) G. Odian et al, Radiation-... 

The problem of the action of radiation on azides, particularly lead and barium azide has been review cd [116]. Irradiation prior to thermal decom-Jposition often effects a reduction or elimination of the induction period, a de-ICrcasc in activation energy and an increase in the rate of decomposition. Zak-rov and co-workers [117] have found that the application of a moderate electric field can affect the rate of thermal decomposition of azides. 

Coalesence of neighbouring nuclei decreases the acceleratory contribution, leading to the deceleratory behaviour characteristic of the later stages of reaction. Hemispherical nuclei, indicative of equal rates of growth in all directions, are found, for example, in the decomposition of barium azide [17] and in the dehydration of chrome alum [10,19,20]. Other reactions develop nuclei of different shapes characteristic of preferred advance in certain ciysteillographic directions. 

The relatively stable azides of the strongly electropositive metals undergo controlled (i.e. non-explosive or "slow") decomposition. For this reason, sodium and barium azides are probably the most completely studied salts in the azide group [12], Their decompositions are characterized by relatively large apparent activation energies and well-defined induction periods to onset of reaction [10], Mechanistic aspects of azide decompositions have been reviewed by Tompkins [17], The radiation stabilities of the Group lA metal azides do not correspond to the sequence of thermal stabilities [10]. The catalytic decomposition of HNj has also been investigated [12]. 

The sigmoid or-time ciuves observed for the decomposition of barium azide are often characteristic of nucleation and growth processes and such a mechanism was here confirmed by microscopic observations [21]. This early study by Wischin (1939) has been described [11] as "one of the most important experimental papers on solid decompositions". Kinetic observations reported include the following ... 

Both the photolytic and thermal decompositions of barium azide were studied by Thomas and Tompkins [23], When allowance was made for an initial period of slow growth of nuclei, the reaction obeyed the power law a=k t- and the value... 

Torkar, Spath et al. [24-26] confirmed the main features of the above behaviour but also noted a few points of difference. They found a fourth power dependence ( = 4) of nr upon time rather than = 6, as reported previously [23]. Nucleation according to an exponential law occurred on (100) and (001) planes, generating randomly distributed growth particles of the product. The rates of reactions of powdered samples were directly proportional to the surface area of the salt. A fluther difference from other reports was that yields of up to 73% of the nitride BajNj (possibly arising through intermediate formation of BajNj) were found, whereas other workers mention only barium metal as the product. Salot and Warf [27] have described the preparation of barium pemitride from thermal decomposition of barium azide. 

Many kinetic studies of the thermal decomposition of silver oxalate have been reported. Some ar-time data have been satisfactorily described by the cube law during the acceleratory period ascribed to the three-dimensional growth of nuclei. Other results were fitted by the exponential law which was taken as evidence of a chain-branching reaction. Results of both types are mentioned in a report [64] which attempted to resolve some of the differences through consideration of the ionic and photoconductivities of silver oxalate. Conductivity measurements ruled out the growth of discrete silver nuclei by a cationic transport mechanism and this was accepted as evidence that the interface reaction is the more probable. A mobile exciton in the crystal is trapped at an anion vacancy (see barium azide. Chapter 11) and if this is further excited by light absorption before decay, then decomposition yields two molecules of carbon dioxide ... 

Many studies have been intentionally concerned with relatively simple rate processes to minimize stoichiometric problems. However, even relatively simple reactions do not always give a single product, for example barium azide has been reported to give about 70% BajNj together with the metal [26]. The extensively studied decompositions of oxalates require that the identity of the residual solid be identified, for each constituent cation, as either carbonate, oxide or metal, together with any change of cation valency. The chemistry of oxalate breakdown can, however, be much more complicate as has been shown for the Y, Eu and Yb salts [27]. 

Gamer and Moon [34] reported effects of radiation other than color changes the effects produced by the emission from radium on barium azide were dependent on temperature and led to the acceleration in the thermal decomposition. On the other hand the thermal decomposition of mercury ftilmi-nate was not affected in the same environment. 

Thermal decompositions of barium and strontium azides, preirradiated with 1 MeV gamma rays, were conducted by Prout and Moore [78,79]. With dehydrated barium azide a total gamma dose of 20 Mrad (2.24 X 10 R) eliminated the induction period and increased the acceleration of the decomposition. A somewhat greater effect was evidenced with strontium azide. Avrami et al. [80] subjected barium azide to Co gamma radiation to exposure levels up to 1 XIO R (Table XIII). Differential thermal analyses (Figure 16) showed a steady decomposition of the sample, and after 1 X 10 R exposure (W hr at room temperature), infrared analysis indicated that the residue was in the form of barium carbonate. 

Most of the studies conducted on azides irradiated with X-rays have involved the changes caused in the subsequent thermal decomposition of the samples. Erofeev and Sviridov [90] studied the effects of moisture and aging on barium azide. An increased decomposition rate was noted with strontium azide preirradiated with X-rays and decomposed at 126°C [91]. Zakharov and coworkers... 

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. 

Barium azide has a structure related to that of PbFCl [167] the azide ions afford regular 9-coordination for the barium ions (see Fig. 19). The decomposition of BalN,), results in mixtures of Ba, , and Ba,N4 [168]. however, the reported tetragonal cell of Ba,N4 does not match the observed powder pattern [134, 135], The supernitride BaN2 reported to be formed at high pressure is amorphous [169],... 

BARIUM AZIDE (18810-58-7) Highly unstable in dry form. Dust forms explosive mixture with air. Heat, shock, or friction can cause spontaneous decomposition and explosion. Forms shock-sensitive mixtures with lead and other heavy metals. Contact with barium, iron, or sodium will increase its sensitivity to explosion. Contact with acids forms corrosive hydrogen azide. Reacts violently with oxidizers, carbon disulfide. Commercially available in ethyl alcohol. Keeping the chemical wet greatly reduces its explosion hazard. 

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