Pressures of Lead Azide

On the basis of hydrodynamic theory, detonation velocity can be related approximately to the detonation pressure by the equation  

It is only recently that measurements have been made of the detonation pressure of lead azide, and similar data are not known for other azides. The values in Table VI were obtained using the manganin gauges described earlier, and the detonation velocities were obtained by streak photography [11]. 

The differences between the calculated and measured values may in part be explained by the small diameter, confinement, and the assumptions made in the derivation of the formula for pressure which applies to CHNO explosives, not necessarily azides. 

Density (g/ml) Detonation velocity (kni Msec) Peak pressure (kbar)  

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Table VL Experimental and Theoretical Detonation Pressures of Lead Azide...

Scanning electron microscopic examination of pure, dextrinated and RD 1333 LA) 10) L. Avrami N. Palmer, Impact Sensitivity of Lead Azide in Various Liquids with Different Degrees of Confinement , PATR 3965 (1969) 11) M.F. Zimmer L.D. Lyston, Dynamic Pressure Measurements on Small Amounts of Detonating Lead Azide , Explosivst 18, No 1, 12-15 (Jan 1970) 12) R.W. Hutchinson,... 

It is characteristic of lead azide that even under a pressure as high as 2000 kg/cm2 it cannot be dead pressed . This is a great advantage. In practice a pressure of 500-600 kg/cm2 is used. 

Resorcinol nitrates readily to the trinitro compound, yellow prisms from water or alcohol, m.p. 175.5°. Styphnic acid is more expensive and less powerful than picric acid. Liouville67 found that styphnic acid exploded in a manometric bomb, at a density of loading of 0.2, gave a pressure of 2260 kilos per sq. cm., whereas picric acid under the same conditions gave a pressure of 2350 kilos per sq. cm. It did not agglomerate to satisfactory pellets under a pressure of 3600 kilos per sq. cm. It is a fairly strong dibasic acid, and its salts are notably more violent explosives than the picrates. Lead styphnate has been used to facilitate the ignition of lead azide in detonators. 

Iti vacuo no critical size of crystals was observed [128]. The previously mentioned behaviour of primary explosives at high vaato [39-45] may explain the failure to find the critical size of lead azide under very low pressure. 

It should be borne in mind that the reactions of lead azide and water-carbon dioxide are reversible, and the extent of lead azide deterioration will be influenced by a number of factors which include temperature, the partial pressure of reactants, diffusion rates, container dead space, and leakage from the container. 

Forsyth et al. [39] described corrosion of some drums in long-term storage, observing dark blue and brown residues inside the containers. Laboratory studies [48] of lead azide in alcohol-water were conducted in sealed glass capsules which were outgassed and pressurized to one atmosphere with carbon dioxide. Iron, sawdust, and polyethylene were added individually, and the capsules were analyzed at intervals to determine the decomposition rate of lead azide. For iron it was found that the overall reaction is... 

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. 

Tests on dextrinated and RD 1333 lead azide (Table XVII) showed that ambient pressure, sample thickness, and the type of lead azide are important factors in determining the sensitivity to pulsed electron beams [107]. 

Type of lead azide density (g/ml) Sample Thickness (in.) Gas pressure Responses produced Average dose to lead azide (J/g) ... 

A study of the initiation of lead azide by the impact of flyer plates (Section F) showed that stress excursions behind the shock front produce pressure waves which travel through the shock-compressed azide at a velocity at least equal to the sonic velocity. The sonic velocity in the precompressed explosive is higher than in the uncompressed explosive, so the amplitude of the initial shock increases rapidly until steady-state detonation is achieved in less than 1 mm, as indicated by the data in Table IV. For an initial stress over 4 kbar, instantaneous detonation occurred however, pressures this high are not normally present at the input to the azide in an explosive train. 

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]... 

Figure 17 shows the effect of pressure on the density and effectiveness of lead azide in the above detonators. Streak-camera and contact-pin measurements of sectioned detonators showed that high-order detonation develops in the center of the 0.060-in. (0.152-cm) -thick layer oflead azide. 

A plot of P vs. Up has the slope poDs and passes through the origin. If the Hugoniot curve for the detonation products of lead azide at the C-J point were known (the curve for unreacted RDX is known [40]), it would be possible to determine the strength of the shock wave generated in RDX by the detonation wave from lead azide. It is to be recalled that the Chapman-Jouget model as modified calls for a reaction zone at the end of which the reactants have been completely converted to products in equilibrium and travel at the local sonic velocity. The end of the reaction zone is often called the C-J plane, and the associated pressure and temperature called the C-J pressure and temperature. 

Figure 19. Pressure vs. time for initiation of lead azide.

Shock initiation of lead azide by an electron beam has been compared with that of potassium dinitrobenzofuroxan (KDNBF), lead styphnate, and lead mononitroresorcinate (LMNR) [49], An aluminum slab was heated rapidly by electron deposition, generating a pressure pulse that propagated through the slab and was transmitted to a specimen bonded to its rear. The mean energy of the electrons was in the range of 900 keV and produced a stress pulse in the aluminum with a duration of approximately 0.2 psec. 

Although the output of primer is known to consist of hot particles, a pressure pulse (in some cases a shock wave), and thermal radiation, no general quantitative requirement for initiation of lead azide is known to designers. Failures occur in igniting the primer, but once the primer bums, it always ignites the azide. Primer mixtures are complex, empirically determined compositions for which no general quantitative relationships are known. This situation makes it difficult to optimize them for a particular requirement, or to determine the cause of failures, except by trial and error. 

The atmosphere in which azides decompose significantly influences decomposition kinetics. Reitzner [88] investigated the effect of water vapor on the decomposition of lead azide and concluded that the induction period was the result of the reaction of water vapor with lead nuclei. Not until all the water was consumed by the reaction did the azide decomposition accelerate. The length of the induction period was, thus, proportional to the vapor pressure of water in the system. However, in the presence of large amounts of water the azide reacted to produce a basic material which decomposed in a complex manner. Slow decomposition of lead azide in air also produced various oxides, hydroxides, and carbonates of lead [2,4]. 

Groocock [16] made an experimental and theoretical study of the thermal explosion of lead azide but found no crystal size effect. However, he used batches of l0,000 crystals in vacuum so it was a different experiment from that of Bowden and Singh. The critical temperature for a batch of crystals will be reached when any one crystal reaches critical conditions, and this will be influenced by the heat transfer from neighboring crystals. Unfortunately, neither Bowden and Singh nor Groocock specify their vacuum conditions, although one can infer that Groocock s work was at lower pressures his analysis also assumes... 

Recently Afanas ev and Bobolev [9] studied the effects of the thickness of lead azide pellets and pelleting pressure on sensitivity. In particular they measured the pressures generated during the impact and found that, as the thickness of the charge was reduced, the average impact pressure at which explosion occurred increased (Figure 11). The results fitted the hyperbolic relation given by... 

The silver salt is a powerful primary explosive with a performance similar to that of lead azide [42]. Unlike Hg(NT)2, the silver salt can be dead-pressed even at relatively low pressures ( 20 MPa) [2, 4]. 

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