Explosive properties metal azides

Azides, metal, physico-chemical and explosive properties 475 Azides, organic 472.473,505 (III, 191-196)... 

J.N. May cock et al, Electronic Absorption Spectra of Metallic Azides, Perchlorates, Nitrates and their Related Explosive Properties , SpectrochimicaActa 23A (1957), 2849—53... 

The material is impact-sensitive when dry and is supplied and stored damp with ethanol. It is used as a saturated solution and it is important to prevent total evaporation, or the slow growth of large crystals which may become dried and shock-sensitive. Lead drains must not be used, to avoid formation of the detonator, lead azide. Exposure to acid conditions may generate explosive hydrazoic acid [1], It has been stated that barium azide is relatively insensitive to impact but highly sensitive to friction [2], Strontium, and particularly calcium azides show much more marked explosive properties than barium azide. The explosive properties appear to be closely associated with the method of formation of the azide [3], Factors which affect the sensitivity of the azide include surface area, solvent used and ageing. Presence of barium metal, sodium or iron ions as impurities increases the sensitivity [4], Though not an endothermic compound (AH°f —22.17 kJ/mol, 0.1 kj/g), it may thermally decompose to barium nitride, rather than to the elements, when a considerable exotherm is produced (98.74 kJ/mol, 0.45 kJ/g of azide) [5]. 

Narang, K. K. et al., Synth. React, lnorg. Met.-Org. Chem., 1996, 26(4), 573 The explosive properties of a series of 5 amminecobalt(III) azides were examined in detail. Compounds were hexaamminecobalt triazide, pentaammineazidocobalt diazide, cis- and fram-tetraamminediazidocobalt azide, triamminecobalt triazide [1], A variety of hydrazine complexed azides and chloroazides of divalent metals have been prepared. Those of iron, manganese and copper could not be isolated cobalt, nickel, cadmium and zinc gave products stable at room temperature but more or less explosive on heating [2],... 

The infra-red spectra of the heavy metal azides, which are the most interesting because of their explosive properties, were investigated by Gamer and Gomm [37], Lecomte et al. [38], and the Raman spectra have been studied by Kohlrausch and Wagner [36], and by Deb and Yoffe [26]. The results are given in Table 29. 

Martin carried out extensive research into the explosive properties of the azides of various metals (Table 33). The high sensitiveness of cuprous azide to impact is noteworthy. 

Physico-chemical and explosive properties of metal azides Opt ical properties Sli>w decomposition of a/ides Fast decomposition and explosion Lead azide... 

PHYSICO-CHEMICAL AND EXPLOSIVE PROPERTIES OF METAL AZIDES... 

Impurities may have a profound effect on the chemical and physical properties of primary explosives. Of particular importance are metals, such as copper, that sensitize lead azide. An increased knowledge of the effect of impurities on explosive properties emphasizes the need for accurate determinations of these impurities. 

Materials such as propellants and explosives contain tightly bonded groups of atoms which retain their molecular character until a sufficient stimulus is applied to cause exothermic dissociation. This, in turn, triggers further dissociation leading to initiation or ignition. The macroscopic behavior or equation of state is ultimately controlled by microscopic properties such as the interatomic forces. Only when it is possible to quantitatively describe these forces will it be possible to predict whether a given molecular structure will support an explosive reaction. It is toward advances in this area relative to metal azides that this chapter is devoted. 

Recent research with the II-VI semiconductor material ZnO (band gap = 3.8 eV, similar to those of the heavy-metal azides) has revealed that the ability of the specimen to retain stable ions formed by electrostatic charging is a critical function of the degree of surface order A highly disordered surface allows the formation of stable adsorbed ions a highly ordered surface does not [43]. A semiquantitative theory to account for this has been proposed [44]. Further, with disordered surfaces, the location of the electronic state of the adsorbed ions relative to the band structure of the specimen can be probed by an optical discharge technique to yield information about the electronic properties of the surface [43]. These potentialities, coupled with the field-assisted initiation capabilities of an azide specimen, argue that the electrostatic charging technique should be applied quantitatively to explosive azides. 

Apart from being able to better compare observed with theoretical detonation properties, it would appear profitable to carry out refined C-J calculations on heavy-metal azides and other detonator compounds to determine whether the correlations noted earlier indeed exist. (They relate computed explosion temperatures to sensitivity, and C-J pressures to detonator effectiveness.) If the correlations can be substantiated, there appears to be merit in performing C-J calculations on multicomponent detonator mixes in order to predict the optimum composition for minimum sensitiveness and maximum effectiveness. Thus hazardous empirical testing would be held to a minimum. 

Azides react explosively or form other explosive azides when they come in contact with a number of substances. With acids, almost all metal azides react to form hydrazoic acid, which is dangerously sensitive to heat, friction or impact. Azides can react with salt solutions of many metals forming azides of those metals, some of which—especially, the heavy metal azides—are highly sensitive to friction and impact. The rates and yields of such reaction products would depend on the equilibrium constants and solubility products. For example, soluble alkali-metal azides can readily form lead or cadmium azide when mixed with a salt solution of lead or cadmium. The hazardous properties of some of the compounds of this class are discussed below. 

The decreasiug pattern above is of little practical iuterest, however, as all the heavy metal azides detouate violeutly upou heatiug aud mechauical impact. Table 33.1 lists the heat of formatiou AHf(s) for some azides. It may be seeu that explosivity decreases with a decrease of AH° and at a low value of +16.8 kcal/mol, sodium azide is nonexplosive. Discussed below are individual compounds of commercial interest or those presenting severe explosion hazard. The explosive properties of additional compounds are highlighted in Table 33.2. 

All heavy metal azides run very quickly into detonation. This spedlic property has estabhshed the use of silver azide and lead azide as primary explosives in detonators. 

Exothermic Decompositions These decompositions are nearly always irreversible. Sohds with such behavior include oxygen-containing salts and such nitrogen compounds as azides and metal styphnates. When several gaseous products are formed, reversal would require an unlikely complex of reactions. Commercial interest in such materials is more in their storage properties than as a source of desirable products, although ammonium nitrate is an important explosive. A few typical exampes will be cited to indicate the ranges of reaction conditions. They are taken from the review by Brown et al. ( Reactions in the Solid State, in Bamford and Tipper, Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980). 

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