Lead azide crystal density

M lead acetate and 2 M sodium azide solutions to the reactor which contains a quantity of sodium carbonate solution. The lead acetate is started a little ahead of the sodium azide so that some lead carbonate is formed which serves as a seeding agent for lead azide crystals. It contains 98.1% Pb(N )j, crystals are large (cb. 55 jjin), density under 15,000 kg/cm is 3.31. Its temperature of explosion is 350 C with an induction period of 5 sec. It is non-hydroscopic, contrary to the dextrinated lead azide which is slightly hygroscopic due to the presence of dextrin. 

Two crystallographic forms of lead azide are important, the ordinary alpha form which is orthorhombic and the beta form which is monoclinic. The densities of these forms are 4-71 and 4-93 respectively. It was for many years believed that the beta form is the more sensitive to friction and impact and accounted for detonations which have occurred in the manufacture and handling of the substance. It is now known that the beta form is in fact no more sensitive than the alpha. Even the alpha form, when present as large crystals, is very sensitive and conditions can arise (particularly when the formation of the lead azide is controlled by diffusion effects) where spontaneous detonation occurs. Although with modern knowledge these hazards can be avoided, pure lead azide is nevertheless a dangerous compound and is now made only for military purposes. 

The heat capacity (C ) and heat conductivity (A) of crystals depend respectively on the vibrational density of states weighted by a Boltzmann s distribution factor and the anharmonic terms in the vibrational potential energy. C has been found to be in the range 0.100 to 0,117 cal./g./°C between 100—250 °C for crystals as widely varying in lattice geometry as mercuric fulminate, silver azide and lead azide 62). This is... 

Pressed lead azide is a two-phase dielectric system consisting of azide crystals of various dimensions and air in the pores at ambient pressure. Its dielectric strength varies with the density, crystal dimensions, thickness, etc. 

Extensive measurements have been made on lead azide in the U.S.S.R. in recent years, but no description is provided of the lead azide. Sten gach [33] carried out a study on the sensitivity of lead azide to spark discharge in relation to density, size of crystals, interelectrode distance, temperature, and presence of inert impurities. The lead azide was pressed into a chamber containing a spark gap formed by two pointed electrodes. The mean density of the azide was varied from 1.1 to 2.7 g/ml and the interelectrode gap was varied from 0.020 to 0.50 mm (0.0008-0.020 in.). The 50% firing point was used as a measure of sensitivity. 

The effect of crystal size on the critical hght energy and ignition delay was studied by Rogers and reported by Bowden and Yofle [32] for silver azide and by Roth [125] for lead azide. Each found that crystal size had no effect. Roth further reported that the density range 1.6-3.2 g/ml and the particle size range... 

It has been noted (Chapter 8) that propagation velocities of lead azide, extrapolated to crystal density from observations on infinite diameter packed powders, are appreciably higher than most values reported for single crystals. A notable exception is the experimental 8 km/sec value reported by Chaudhri for single crystals whose minimum dimension exceeds 2 mm. 

It is a primary explosive. It explodes violently upon thermal and mechanical shock. It requires lesser energy for initiation than lead azide and also fires with a shorter time delay. The heats of combustion and detonation are 1037 and 454 cal/g, respectively (i.e., 156 and 68 kcal/mol, respectively). The detonation velocity is 6.8 km/sec (at the crystal density 5.1 g/cm ). The pure compound explodes at 340°C (644°F) (Mellor 1967). The detonation can occur at much lower temperatures in an electric field when initiated by irradiation. Also, the presence of impurities can lower down the temperamre of detonation. Such impurities include oxides, sulfides, and selenides of copper and other metals. 

Lead azide forms white or yellowish crystals. It is known to form four allotropic modificatimis a, p, y, and 8 (older literature refers only to the first two of them). The orthorhombic a-form with crystal density reported from 4.68 to 4.716 g cm [12-14] is the main product of precipitation, with traces of other forms present, and is the only form acceptable for technical applications [15]. A variety of crystal... 

Melting point (decomposes), 120 Relative density (water-1) 2.9 Solubility in vrater, g/100 ml at 17 0 17.3 Relative molecular mass 221.4 WHITE CRYSTALS Finely dispersed in air can cause dust explosion. Can decompose explosively if subjected to shock. Reacts with lead compounds and other heavy metals, to form exbemely slk sensitive compounds. Can produce explosion wmen heated. Decomposes when heated above 120 C, giving off nitro and -> nitrous KSpors. Reacts with acids to form toxic and corrosive hydrogen azide. Reacts violently with oxidants. ... 

A method of preparing a reduced sensitivity SA introduced in USA is called the Costain process after Thomas Costain who improved the original procedure for RD 1336 developed in England in the ERDE laboratories shortly after World War 11 [96]. In the Costain process, aqueous solutions of silver nitrate and sodium azide are added to the dilute aqueous ammonia (or an aqueous solution of sodium azide is added to an aqueous solution of silver nitrate and ammonia). The reaction mixture is then heated and part of the ammonia is distilled from the solution. When the first silver azide precipitate appears, a small amount of acid (e.g., acetic acid) is added to induce crystal seeding and results in profuse nucleation ( shock crystallization ). The distillation of ammonia then continues and the precipitation of silver azide is total. Costain reported several improvements for his product, first of all bulk density 1.4 g cm [96]. Hirlinger and Bichay later reported a further improvement leading to a product with density 1.6 g cm [97] (vs. 1.0 g cm for original ERDE silver azide). Further, concentration and addition parameters are not as critical as for the ERDE process [96]. Not much has been published about the Costain process but some details have been published in [98]. 

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