Properties of the Azides

Among the most important functional parameters of the azides are the detonation velocity and pressure, and these depend on the material parameters (density, azide content, particle size, etc.) and the confinement (its material, density, dimensions, etc.). Even with the most modem techniques the functional quantities are not easy to measure with reliability and precision. In this section 

Because of the difficulty of setting up a streak camera and of inaccuracies in reading velocities from the records, a faster, more accurate method for measuring equilibrium velocities is to use switches and electronic time-interval meters. 

The manganin gauge may be calibrated by using a gas gun with known output characteristics, and a typical gauge coefficient foruid by the method is 0.0024 Q/Q/kbar. If only peak pressure is of interest, this may be determined by using an aquarium apparatus to determine the shock velocity produced in a material whose shock Hugoniot is known (in this case water) [21]. Because ofextrapola- 

It has been indicated in previous discussion that the initiation of detonation in the azides is structure and confinement sensitive, and the variation in the behavior is reflected in differing detonation velocities (Table III). Notwithstanding the question whether steady detonations are achieved in some instances, available theories confirm that the detonation velocities depend on dimensions and confinement for small-diameter samples and on the density and azide content of a given mixture. 

The critical diameter of lead azide for Unconfined powders or crystals has not been established and cannot be until one determines the pressure or absence of detonations in the small dimensions cited above. In the case of heavily confined charges, work on swaged-lead detonating cord lead to the expression [24] 

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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. 

Discussion. The limited amount of work concerning the effects of ionic impurities on the explosiA e properties of the azides is more tantalizing than conclusive. It appears that small amounts of impurities can increase or decrease both the sensitivity and the detonation velocity of the azides. The degree to which the effects will hold up under military loading conditions remains to be seen. 

Determination of the crystal structures is, moreover, but a foundation upon which to build both more comprehensive characterizations and an understanding of the fundamental properties of the azides. In Chapters 4, 5, and 7, in particular, these topics are interwoven, but in other chapters structural data is also used extensively to derive explanations of stability and mechanisms of decomposition. 

Information on the inorganic azides is voluminous and is widely spread through the increasing scientific literature. Particularly, in older publications, the availability of data is often camouflaged by confusing nomenclature, as discussed in the next section. Table I summarizes a count of the number of articles dealing with the preparation, behavior, and chemical and physical properties of the azides, as listed in reference [3]. 

Optical properties of the azides which have been studied include optical absorption, luminescence, photoconductivity, and photoemission. As the latter... 

Alkali Azides. The photoconductivity and photoemission properties of the azides of Na, K, Cs, and Rb were studied by Deb [142] in the spectral range of... 

The properties of chlorine azide resemble those of bromine azide. Pon-sold has taken advantage of the stronger carbon-chlorine bond, i.e., the resistance to elimination, in the chloro azide adducts and thus synthesized several steroidal aziridines. 5a-Chloro-6 -azidocholestan-3 -ol (101) can be converted into 5, 6 -iminocholestan-3l -ol (102) in almost quantitative yield with lithium aluminum hydride. It is noteworthy that this aziridine cannot be synthesized by the more general mesyloxyazide route. Addition of chlorine azide to testosterone followed by acetylation gives both a cis- and a trans-2iddMct from which 4/S-chloro-17/S-hydroxy-5a-azidoandrostan-3-one acetate (104) is obtained by fractional crystallization. In this case, sodium borohydride is used for the stereoselective reduction of the 3-ketone... 

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]. 

Macroscopic n-type materials in contact with metals normally develop a Schottky barrier (depletion layer) at the junction of the two materials, which reduces the kinetics of electron injection from semiconductor conduction band to the metal. However, when nanoparticles are significantly smaller than the depletion layer, there is no significant barrier layer within the semiconductor nanoparticle to obstruct electron transfer [62]. An accumulation layer may in fact be created, with a consequent increase in the electron transfer from the nanoparticle to the metal island [63], It is not clear if and what type of electronic barrier exists between semiconductor nanoparticles and metal islands, as well as the role played by the properties of the metal. A direct correlation between the work function of the metal and the photocatalytic activity for the generation of NH3 from azide ions has been made for metallized Ti02 systems [64]. 

The phosphorus heterocycle (13) has been characterized23 by a reaction with trimethylsilyl azide. Other aminophosphines have been used as precursors of phosphazenes because of interest in the physiological properties of the latter compounds.24... 

Even if a same azide is used as the sensitizer, such properties of the photoresist as photosensitivity, photocurability and adhesion to base surfaces differ depending on the property of the base polymer. That is, degree of cyclization, content of the unsaturated groups and molecular weight of the polymer affect the photoresist properties mentioned above. H.L.Hunter et al. have discussed the dependence of the sensitivity of polybutadiene photoresist on the polymer structure, and have concluded that a higher sensitivity was obtained when 1,2- and 3, -isomers were used( 7.) ... 

The method of preparation and physical properties of the alkyl azides used in the study are also presented in Table 2.1. The alkyl bromide and sodium azide in aq MeOH is denoted as A and aq EtOH and sodium azide is denoted as B. 1,2-Diazidobenzene and 1,4-diazidobenzene were synthesized using the process shown in Fig. 2.10. 1-Azidonorborniane was synthesized according to a modified literature procedure shown in Fig. 2.11. 

As described in Sections 4.2.4.1 and 5.2.2, GAP is a unique energetic material that burns very rapidly without any oxidation reaction. When the azide bond is cleaved to produce nitrogen gas, a significant amount of heat is released by the thermal decomposition. Glycidyl azide prepolymer is polymerized with HMDI to form GAP copolymer, which is crosslinked with TMP. The physicochemical properties of the GAP pyrolants used in VFDR are shown in Table 15.3.PI The major fuel components are H2, GO, and G(g), which are combustible fragments when mixed with air in the ramburner. The remaining products consist mainly of Nj with minor amounts of GOj and HjO. 

Are properties of the molecule of interest inhibited by components of the buffers (e.g., inhibition of hem proteins by sodium azide or enzyme activity by SDS) ... 

The earlier opinion that the / -form is the more sensitive to impact appears to be incorrect. This problem will be discussed more fully in the section on the explosive properties of lead azide. 

When exposed to light lead azide soon turns yellow on the irradiated side. The layer of changed substance protects the deeper layers from further decomposition and thus irradiation does not entail changes in the explosive properties of the substance. However, as Wohler and Krupko [80] have shown, if the lead azide is subjected to stirring during irradiation, decomposition may proceed too far. 

Other data concerning the initiating properties of lead azide, as compared with the other primary explosives, are given in Table 32. 

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,... 

Thus migration of the cation is possible, and the authors presume that this is the cause of the initiating property of silver azide. 

The physical properties of mercurous azide — Hg2(N3)2 — were examined by Evans and Yoffe [33] and its photochemical decomposition by Deb and Yoffe [26], The activation energy was found to be 8.4 kcal/mole. 

The properties of thallous azide have been examined in detail by Gray and Waddington [120]. 

Lead azide can exist in two allotropic forms the more stable a-form which is orthorhombic, and the /1-form which is monoclinic. The a-form is prepared by rapidly stirring a solution of sodium azide with a solution of lead acetate or lead nitrate, whereas the /1-form is prepared by slow diffusion of sodium azide in lead nitrate solutions. The /1-form has a tendency to revert to the a-form when its crystals are added to a solution containing either the a-form crystals or a lead salt. If the /1-form crystals are left at a temperature of 160 °C they will also convert to the a-form. Some of the properties of lead azide are presented in Table 2.3. 

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