Sensitivity of the Azides

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]. 

In spite of these restrictions, the relative effects of impurities appear real and offer intriguing possibilities Based on Figure 20 lead azide containing a very small amount of silver has essentially the same detonation velocity and impact sensitivity as pure silver azide. Could silver-doped lead azide be produced and used in place of the more expensive silver azide The lead-doped silver azide appears to have a higher detonation velocity than pure silver azide and, therefore, could be very useful in small detonator applications. The results indicate that small amounts of ionic impurities can increase or decrease sensitivity of the azides to impact. This observation is most important from safety and quality-control viewpoints. 

Studies of slow thermal decomposition, when combined with the hot-spot theory, proved to have particularly interesting consequences for understanding the sensitivity of the azides and their troublesome and seemingly temperamental response to some stimuli. 

Impact sensitivity is further influenced to a very large extent by the thickness of the layer of explosive tested. The sensitivity of the azides of silver, lead, and mercury increases with the layer thickness, that of cadmium is almost constant. 

Similar products are obtained from the photosensitized decomposition of the tertiary azides, suggesting that decomposition may result from the triplet azides under both direct and sensitized photolysis/461 Additional evidence for a discrete nitrene intermediate comes from the observation that this intermediate can be trapped by decomposition of the azides in the presence of good hydrogen donors such as tri- -butyItin hydride and jec-butyl mercaptan. Triarylamines result ... 

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... 

Dining the preparation of 2-azidoethanol from a stirred mixture of 2-bromoethanol (14.6 mol) and sodium azide (15.4 mol) heated on a steam bath, a violent explosion occurred after 100 min. The preparation had been carried out previously without mishap. The need for care in handling azides of low MW is stressed [1], Later detailed studies showed that the most probable cause of the explosion was the extraordinarily high mechanical and thermal sensitivity of the compound, with initiation by vibration from the agitator [2],... 

The azide is very explosive, even when moist. Loosening the solid from filter paper caused frictional initiation. Explosion initiated by impact is very violent, and spontaneous explosion has also been recorded [1], It is also an exceptionally powerful initiator [2]. Detonation of the azide when dry has been confirmed [3], Good crystals are considerably more sensitive to shock, friction and electric discharge than is powder [4],... 

We have found the combination of the azide compound and the styrene resin is well suited for achieving high resolution and high aspect ratio patterns using KrF excimer laser stepper system, because of the absence of swelling-induced pattern deformation during alkaline development and the suitable optical density at 248 nm in terms of sensitivity. 

Figure 2 shows the exposure characteristics for azide-styrene resin resist film with an azide concentration from 10 to 40 wt% (based on the styrene resin weight) and Figure 3 shows the contrast of the resist films as a function of the azide concentration. Development was done with a 60s immersion in 0.83% TMAH solution. The styrene resin matrix alone has been found to be a negative deep UV resist. However, rather low contrast (1.48) and low sensitivity (2.5 J/cm2) are observed. The contrast and the sensitivity of the styrene resin is remarkedly increased by adding the azide, as shown in Figures 2 and 3. 

When the concentration of the azide exceeds 30 wt%, sensitivity decreases (Figure 2) and the contrast becomes worse (Figure 3). This is due to the increase of the optical density of the resist. Large optical density prevents the light from penetrating into the resist (3,11). Also, the resist thickness remainig after development is maximum at the 30 wt% azide concentration (Figure 2). From these results, it was concluded that the azide-styrene resin resist which contains 30 wt%... 

In general, C-nitro compounds are more stable than /V-nitro compounds because of the higher bonding energies in the former type. Evidence is offered [1] that decomposition and explosion of many nitro-derivatives proceeds through the aci-form, and that sensitivity corresponds to the proportion of that present. In terms of this work, sensitisation by very small proportions of soluble organic bases is most important this is not limited to nitroalkanes. TNT can apparently be brought to the sensitivity of lead azide by this means. For a physicist s view of this sensitisation,... 

The transition states for the stepwise (fej, Fig. 2.3) and concerted (fecon) reactions of (4-MeO,X)-3-Y lie at distinct well-separated positions on the More O Ferrall diagram and show different sensitivities to changes in solvent polarity, meta substituents X at the aromatic ring, and the leaving group Y. For example, in 50 50 (v/v) water/trifluoroethanol (4-MeO,H)-3-Cl reacts with azide ion exclusively by a stepwise mechanism through the primary carbocation intermediate (4-MeO,H)-3" with a selectivity for reaction with azide ion and solvent of feaz/ s = 25 However, two-thirds of the azide ion substitution product obtained from the reaction of (4-MeO,H)-3-Cl in the less polar solvent 80 20 acetone/water forms by concerted bimolecular substitution and only one-third forms by trapping of the carbocation intermediate (4-MeO,H)-3 with a selectivity of k z/h = 8 The preferred... 

Shortly after Anderson and Falvey reported the first observation of a shortlived nitrenium ion in CH3CN by UV spectroscopy, Novak and McClelland and co-workers demonstrated that the nitrenium ions 75h and 75o could be observed in aqueous solution after LFP of the pivalic acid ester 76h, the sulfuric acid ester 76o, and its N-chloro analogue N-chloro-4-phenylacetanilide. The transients with A ax of ca. 450 nm were identified as singlet nitrenium ions, based on the kinetics of their decomposition in the presence of NJ, the equivalence of kaz/ks determined by the azide clock method and by direct observation, the lack of sensitivity of the transients to O2, product studies that showed similar products from solvolytic and photolytic decomposition of N-chloro-4-phenylacetanilide, and identical transient UV spectra for 75o derived either from 76o or its N-chloro analogue. A comparison of azide/solvent selectivity data obtained by azide clock and direct observation of 7Sh and 75o is presented in Table 1. 

Yuill [81] investigated the sensitiveness of lead azide to impact at room temperature and at — 190°C. He found that 10-15% more energy is required for the initiation of explosion by impact at a low temperature than that at room temperature (Table 31). 

It is assumed that the presence of silver cyanide increases the sensitiveness of silver azide at elevated temperatures sensitized AgN3 explodes at a lower temperature than the ordinary compound and the induction period is shorter. 

The ignition temperature is 273°C and is thus much lower than that of lead azide, although the sensitiveness of silver azide to impact is also lower than that of lead azide. Taylor and Rinkenbach [124] report that with a 0.5 kg weight a 77.7 cm drop is necessary to cause detonation of silver azide, whereas for mercury fulminate a 12.7 cm drop is sufficient. 

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. 

Gyunter et al, decompd approx 6% of Ba(Ns)a with more than half of the decompn product appearing as nitride. This fact was connected with the impact sensitivity of Ba azide. Groocock Tompkins (Ref 24) described a technique for studying the effects of pre-irradiation and of prolonged bombardment with 100 and 200 V electrons on Ba azide at RT... 

According to Curtius and Rissom (Ref 1), the(ahyd)Cu(Ns )j was considered to be very sensitive to shock or heat, even when water wet. Based on more recent data, Cirulis (Ref 11 13) states that the product is sensitive only when dry or wet with ether the moist product wet with ale is rather insensitive to friction or shock. The sensitivity of-the dry azide to friction is so great that it explodes while being removed from filter paper (Refs 7,18 21)... 

According to Stettbacher, mercuric azide develops the same vol of gas on deton as MF but it is 20 times more brisant. Wohler Krupko (Ref 3) observed that its sensitivity depended on the cryst size of the azide. Mercuric azide is considered to be more sensitive to impact and friction than MF and is so unstable that it frequently undergoes spontaneous deton at the slightest touch even under w (Refs 5 7). Hitch (Ref 4) noted this sensitivity expecially when the azide was prepd from mercuric nitrate and Na or K azide solns but by careful thermal studies he decompd it quanty into its elements without expln below 300°. Miles (Ref 8) reported that in every case when /3-crysts of Hg(N3)2 were present the material was likely to expl, and in w or more rapidly in mercuric nitrate soln, the /3-type was unstable being transformed to the o-type, as in the parallel case of LA,... 

Thermolysis or sensitized photolysis of the azide (272) leads to the nitrene-inserted product (273). Here electrophilic attack at C-3 by singlet nitrene is prevented by the presence of a substituent. Apparently attack at sulfur is either unfavourable or reversible. 

Lead azide is produced as a white precipitate by mixing a solution of sodium azide with a solution of lead acetate or lead nitrate. It is absolutely essential that the process should be carried out in such manner that the precipitate consists of very small particles. The sensitivity of lead azide to shock and to friction increases rapidly as the size of the particles increases. Crystals 1 mm. in length are liable to explode spontaneously because of the internal stresses within them. The U. S. Ordnance Department specifications require that the lead azide shall contain no needle-shaped crystals more than 0.1 mm. in length. Lead azide is about as sensitive to impact when it is wet as when it is dry. Dextrinated lead azide can apparently be stored safely under water for long periods of time. The belief exists, however, that crystalline service azide becomes more sensitive when stored under water because of an increase in the size of the crystals. 

It is as efficient as fulminate only if it is externally initiated. It is used in detonators either initiated by another primary explosive and functioning as an intermediate booster or mixed with another primary explosive to increase the sensitivity of the latter to flame or heat. A recent patent62 recommends the use of a mixture of tetracene and lead azide in explosive rivets. Tetracene is used in primer caps where as little as 2 °/o in the composition results in an improved uniformity of percussion sensitivity. 

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