Lead azide decomposition temperature

Lead azide is insoluble in an aqueous solution of ammonia. Acetic acid causes its decomposition but it is soluble in water and concentrated solutions of sodium nitrate, sodium acetate or ammonium acetate. There are fairly big differences of solubility, depending on temperature. 

Bowden and Singh [94] and later Bowden and McAuslan [95] using the electron microscope, observed that on heating at a temperature above 120°C the separate crystals of lead azide (like those of cadmium or silver azides), break down into fine particles, approximately 10 5 cm in dia. and decomposition reaction takes place chiefly on the newly-formed surfaces. This makes it evident that the thermal decomposition of azides cannot be regarded as a surface reaction or a process occurring within large crystals only the whole mass is involved, due to crystal breakdown. 

Azide Ignition temperature °C Lead block expansion cm3 Heat of decomposition kcal/mole... 

Some substances, including impurities, enhance the decomposition of azides. The impurities can be present in the course of preparation of azides or formed during their storage. It is known that the presence of carbon dioxide in air may produce a decomposition of lead azide. Also water vapour in air even at rcoin temperature may accelerate (he decompr>sition. fhis problent was tackled by. Reitzner (115]. He found that the induction period was the result of the re-laction of water vapour with lead. 

To test the theory that metal deposited on the surface of lead azide would act as an electron trap, Reitzner et al. [6] deposited silver on the surface of lead azide. A sensitization was found for both slow and explosive decomposition. Lead nuclei are produced on the surface of lead azide by the action of ultraviolet light with the concomitant production of nitrogen. It has been postulated that the lead nuclei behave at elevated temperatures as electron sinks during the induction period and account for the observed shortened ignition delays [4,7]. 

The time to explosion was significantly prolonged when lead azide was preheated in the presence of water and Freon before testing [18]. In this case the retardation may be due to the scavenging of lead nuclei over a period of time at an elevated temperature by the water and Freon. The presence of water for shorter periods of time at ambient temperature did not influence the induction time. It is of interest to note that the induction period of lead azide was lengthened during thermal decomposition in the presence of adsorbed water [19], but... 

However, when lead azide, lead styphnate, mercury fulminate, RDX, TNT, and PETN were subjected to bombardment with a negative pion beam, no explosions or decompositions were observed for any of the explosives. The analysis had predicted initiation only for RDX. Also it had indicated that nuclear fission events would produce higher energy densities and greater temperature increases than were actually observed. 

Lead azide is a white, crystalline solid which is sparingly soluble in water [276] its solubility may be enhanced by complexation [157,276]. Hydrolysis at room temperature is negligible [197]. The compound is somewhat photosensitive and, unless handled under yellow light, appears buff or gray [175,176]. It is highly sensitive to impact, heat shock, and friction and explodes with high brisance [197]. Thermal decomposition leads to explosion above 345 C [2,176]. 

Early measurements of the rates of photodecomposition of lead azide powders were conducted at a single wavelength, 254 nm, under varying conditions of light intensity and temperature [231,119]. From the data, reaction paths and decomposition models were suggested. The general conclusions were ... 

It has long been assumed that since lead azide, for example, is more sensitive than sodium azide when impacted, the reactivity of the former is greater than that of the latter. That this is not so was demonstrated by Walker [58] and Fox [59], who compared the rates of slow thermal decomposition under identical experimental conditions for the azides of sodium, thallium, and lead. The results, summarized in Figure 7, show that over most of the temperature range studied lead azide is the least reactive, and that above about 560°K sodium azide reacts more rapidly than either lead or thallium azides. Moreover, above 590 K the rate of evolution of heat is greater in sodium than in lead azide. Alternatively, the application of data for the energetics of decomposition derived from slow reactions is not applicable to fast reactions, since in the latter thermodynamic equilibrium is not attained and the mechanism for slow decomposition discussed in Chapter 6 may not apply. There is some evidence that this is so [60]. 

Some comments on the calculations should be noted. The molar enthalpies of decomposition of sodium, potassium, barium, and lead azides that were calculated by the third-law method are given in Table 16.20. The initial data for these calculations were the absolute decomposition rates J of these azides, measured in [49-51]. The results obtained for NaNs and Pb(N3)2 at different temperatures and in different studies show good agreement. In Table 16.21, these results are compared with the averaged molar enthalpies measured for these and some other azides by the second-law method (the initial values of... 

Silver azide is slightly hygroscopic and is a very vigorous initiator, almost as cllicient as lead azide, Like lead azide, silver azide decomposes under the influence of ultra-violet irradiation. If the intensity of radiation is suflicicntly high the crystals may explode by photochemical decomposition. The ignition temperature and sensitiveness to impact of silver azide are lower than that of lead azide. Some of its properties are presented in Table 2.5. 

Heavy metal azides are notoriously explosive and should be handled by trained personnel. Silver azide (and also fulminate) can be generated from ToUens reagent, which is often found in undergraduate laboratories. Sodium azide is explosive only when heated to near its decomposition temperature (300 C), but heating it should be avoided. Sodium azide should never be flushed down the drain. This practice has caused serious accidents because the azide can react with lead or copper in the drain lines to produce an azide that may explode. It can be destroyed by reaction with nitrous acid ... 

C min (LA type RD 1333) [35] 357-384 C at a heating rate of 40 °C min [43]. The 5-s explosion temperature of LA is 340 °C [49]. LA has been found not to have changed after being stored for 4 years at 80 °C. The thermal stability threshold is, according to Danilov, 200 °C at which temperature it keeps its explosive properties for 6 h. It is therefore used in thermostable detonators TED-200 with maximum application temperature 200 °C [3]. We have tested various types of lead azides at our laboratory and found that standard industrial dextrinated LA (product of Austin Detonator) is surprisingly even more thermally stable than pure crystalline product. The decomposition of both types (pure and dextrinated) of LA under the same conditions is shown in Fig. 4.2. 

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