Lead azide dioxide

Lead azide, like hydrazoic acid, is liable to undergo oxidation and reduction reactions. It is partially decomposed by atmospheric oxygen to form free hydrazoic acid, nitrogen and ammonia. This reaction is promoted by the presence of carbon dioxide in the air. When boiled in water, lead azide undergoes slow decomposition with the evolution of hydrazoic acid. 

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. 

In the presence of carbon dioxide, moist lead azide did not react with aluminium. 

In the presence of carbon dioxide or other acidic compounds, moist lead azide can react with copper casing. Hydrazoic acid was evolved which reacted with copper or copper oxides to yield copper azides. 

As recently discovered moisture without carbon dioxide can also promote reactions of lead azide. 

Comparative analyses of the various methods are presented in Table 11. From the data available the gas-evolution method is generally the most precise and least subject to error once the operator has developed the manipulative skill and experience. It tends to yield the highest azide contents, particularly for lead azide. Loss of hydrazoic acid is minimal, and provisions are made for collecting any carbon dioxide generated by oxidation of the phlegmatizing agent. The 2-g... 

In these experiments, carried out statically under one atmosphere of carbon dioxide, only basic lead carbonate was detected. Basic lead azide and normal lead carbonate were not obscncd by X-ray diffraction [48]. This is probably due to a "cocoon effect," with basic lead azide surrounding the kernel center, basic lead carbonate as an intermediate layer, and a thin outer skin of the normal carbonate. It seems likely that in preparation of the sample for X-ray diffraction analysis the basic lead carbonate masked the normal lead carbonate below the X-ray diffraction detection threshold, as noted by Todd [49]. 

The formation of the normal carbonate was reported by Todd when the carbon dioxide content was in excess of 4%. At ambient temperatures, water in equilibrium with air has a pH of about 5.9, which drops to 3.9 as the carbon dioxide is enriched to 100%. Neglecting the bicarbonate ion, the pH figures mean that water in contact with CO2 contains 10 -10" g ions of carbonate per liter. A saturated solution of lead azide with a solubility of 0.02% (w/v) contains 6.9 X 10" g ions of lead per liter. Since the solubility product of lead carbonate is 3.5 X 10 ", it follows that the carbonate ion concentration has only to rise about 10 g ions/liter for lead carbonate to precipitate. 

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... 

The iron from the capsule experiments was brittle and fell apart when rubbed. In this investigation iron azide (ferric or ferrous azide) and hydrazine could not be detected, contrary to the work of Franklin [51] and Curtius and Risson [52]. Polyethylene becomes brittle, opaque, and porous when exposed to hydrazoic acid, and hydrazoic acid diffused through 0.008 in polyethylene bags within 90 days. Blay and Dunstan [53] reported little azide interaction with polyethylene, but noted a marked drop in azide value when Service lead azide was in contact with various rubbers, plastics, and other synthetic packaging materials. A reduction in azide content as high as 70% was shown (Figure 4). This was attributed to the slow release of carbon dioxide from the test material, followed by further hydrolysis of the lead azide. 

G. M. Thornley, The Reactions of Lead. Azide with Carbon Dioxide and Water Vapor, University of Utah Report, 1963. 

The hydrolysis of lead azide has been studied by Todd et al [138], who found it to be a complex process involving a sequence of hydroxyazides in which the hydroxyl-to-azide ratio gradually increases. If carbon dioxide is also present, basic lead carbonate and normal lead carbonate can be formed. This difference in final product is important since basic lead azide is explosive whereas basic lead carbonate is not. 

Chemical weapons Chemical gas weapons, explosives, etc. Chlorine, chloropicrin, hydrogen cyanide, arsines, psychotomimetic agents, toxins, carbon monoxide, carbon dioxide phosgene, mustard gas, tear gas, lewisite, G-series nerve agents, V-series nerve agents, mercury fulminate, lead styphnate, lead azide, dynamite, TNT, RDX, PETN, HMX, ammonium nitrate, etc. 

Lead azide is stable in air under normal conditions when dry. However, it slowly decomposes in presence of moist air containing carbon dioxide. Detailed analysis of the reactions of LA with water and carbon dioxide has been presented by Lamnevik [31]. According to this author, basic lead azide forms and gaseous azoimide is liberated by reaction of LA with moisture ... 

If the partial pressure of carbon dioxide is lower than 1.2 kPa azoimide, basic lead azide forms in a similar way as with water (see above). At higher carlxMi dioxide partial pressures, dibasic lead carbonate and also azoimide form according to the following equation ... 

It was originally assumed that the deterioration of LA in a detonator, because of its decomposition by carbon dioxide and the formation of basic lead azide or basic lead carbonate, would decrease its initiation efficiency and hence decrease overall ability of the detonator to perform with the desired strength. Danilov et al., however, published that the lead carbonate that forms during the reaction of LA with carbrni dioxide creates a surface layer which protects LA from further decomposition [3]. The mechanism of deterioration of LA depends upon hydrolysis cmiditions. According to Blay and Rapley, if the hydrolysis is not accelerated by abnormal conditions, the deterioration does not proceed beyond an acceptable level in service detonators [36]. The same thinking was reported in 1975 by Lamnevik who did not notice any loss of function in an LA detonator due to LA degradation [3, 31]. 

Lead azide is used in many applications accompanied by other substances that compensate for its drawbacks, particularly its low sensitivity to flame and stab. The most common additive in detonators is lead styphnate which improves the inflammability of resulting mixture. A typical composition of this binary mixture is 30 % LS and 70 % LA. It is sometimes presented that lead st3q)hnate can serve as a protective layer against access of water and carbon dioxide to LA surface [3, 4]. However, lead styphnate increases the level of acidity and accelerates the rate of hydrolysis of LA in presence of moisture [35, 49]. Regardless of this fact a combination of LA/LS is still used in detonators. 

Bubbling of carbon dioxide-free air through a boUing suspension of lead azide in water until the calculated amount of azoimide is evolved [24]... 

I Inlike lead azide S A does not react with water in presence of carbon dioxide [6,69] or, more precisely, it yields very low partial pressure of azoimide, too low for formation of copper azides in applications with copper or brass [70]. 

Some of the copper azides are extremely sensitive and may form wherever copper comes into contact with lead azide in presence of weak acids. Even carbonic acid forming from moisture and carbon dioxide has the ability to decompose lead azide liberating azoimide. Copper and its alloys react with liberated azoimide and, depending on conditions, form various copper azides. 

Lead azide, otherwise a very good primary explosive, has one major drawback, apart from its toxicity. It reacts with water and forms volatile azoimide (b.p. 35 °C) which may react with copper forming sensitive copper azides. This process is accelerated by the presence of acidic substances such as carbon dioxide (from the air) or even lead styphnate, which is often used together with LA [3, 5, 8,40]. 

The nucleophilic attack of nitrogen bases leads to a variety of products as the result of addition or addition-elimination reactions The regioselectivity resembles that of attack by alcohols and alkoxides an intermediate carbanion is believed to be involved In the absence of protic reagents, the fluorocarbanion generated by the addition of sodium azide to polyfluonnated olefins can be captured by carbon dioxide or esters of fluonnated acids [J 2, 3] (equation I)... 

The ring-opening process leading to 164 (route a) is analogous to that which has been demonstrated to follow the cycloadditions of tosyl azide to certain enamines176. Similar results have been reported for the reaction of 2,3-diphenylcyclopropenone with 2-diazopropane177. Other 1,3-dipolar cycloadditions with thiirene dioxides could also be affected (see below). 

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