The s alt of hydrazoic acid is Pb(N3)2, a chemical compound otherwise called lead azide. This crystalline substance can have one of at least two crystalline forms: the first form α with a density of 4.71 grams per cubic centimeter, the second form β - 4.93. It dissolves poorly in water, but it is good in monoethanolamine. Please do not follow the recommendations given in this article at home! Lead azide is not a joke, but a highly sensitive explosive (explosive).
Properties
Lead azide initiates an explosion, because its sensitivity is very high, and the critical diameter is very small. It is used in blasting caps. It cannot be handled without special technical techniques and special care skills. Otherwise, an explosion occurs, the heat of which approaches 1.536 megajoules per kilogram, or 7.572 megajoules per cubic decimeter.
Lead azide has a gas volume of 308 liters per kilogram or 1518 liters per squaredecimeter. Its detonation speed is approximately 4800 meters per second. Azides, whose properties look very intimidating, are synthesized during the exchange reaction between soluble alkali metal azides and solutions of lead s alts. The result is a white crystalline precipitate. This is lead azide.
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The reaction is usually carried out with the addition of glycerin, dextrin, gelatin, or the like, which prevent the formation of too large crystals and reduce the risk of detonation. It is not recommended to synthesize lead azide at home, even for the purpose of making festive fireworks. To obtain it, special conditions are required, knowledge and understanding of the danger, as well as sufficient experience as a chemist.
However, there is quite a lot of information on the net regarding the manufacture of this dangerous explosive. Many Internet users share their experience on how to get lead azide at home, including a detailed description of the process and its step-by-step illustrations. Sometimes the texts contain warnings about the dangers of making these colorless crystals or white powder, but they are unlikely to stop everyone. However, you need to remember what lead azide is. Mercury fulminate is less dangerous than its use.
Modifications
Crystalline modifications of lead azide are described in total four, but in practice one of the two is most often obtained. Either it is a technical white-gray powder, or colorless crystals obtained by mergingsolutions of sodium azide and lead acetate or nitrate. In practice, precipitation must be carried out with water-soluble polymers in order to obtain a product that is relatively safe to handle. If organic solvents, such as ether, are added, and also if diffusion interaction of solutions occurs, a new form is formed, which crystallizes acicularly and coarsely.
Acidic medium gives less stable forms. During long-term storage, exposure to light and heating, the crystals are destroyed. It is insoluble in water, slightly soluble in an aqueous solution of ammonium acetate, sodium and lead. But 146 grams of azide are perfectly dissolved in one hundred grams of ethanolamine. In boiling water, it decomposes, gradually releasing nitric acid. With moisture and carbon dioxide, it also decomposes, spreading over the surface. This is when carbonate and basic lead azide are formed.
Interactions and susceptibility
Light decomposes it into nitrogen and lead - also on the surface, and if you apply intense irradiation, you can get an explosion of newly minted and immediately decomposing azide. Dry lead azide does not react to metals and is chemically stable.
However, there is a danger of a humid environment, then almost all metal azides become dangerous in their reactions. Keep the resulting substance away from copper and its alloys, since a mixture of azides and copper has even more unpredictable explosive properties. All azide reactions are toxic and the substance itself is toxic.
Sensitivity
Azides prettyheat-resistant, decompose only at temperatures above 245 degrees Celsius, and the flash occurs at about 330 degrees. Impact sensitivity is very high, and any production of azides is fraught with bad consequences, regardless of whether the azide is dry or wet, it does not lose its explosive properties, even if moisture accumulates up to thirty percent in it.
Especially sensitive to friction, even more than mercury fulminate. If you grind azide in a mortar, it detonates almost immediately. Different modifications of lead azides react differently to impact (but everyone reacts!). Since the crystals are covered with a film of lead s alts, it may not react to a beam of fire and a spark. But this applies only to those samples that have been stored for some time and exposed to moist carbon dioxide. Freshly produced and chemically pure azide is highly susceptible to flame attack.
Explosion
Lead azide is extremely dangerous precisely because of its sensitivity to friction and mechanical stress. This is especially dependent on the size of the crystals and on the method of crystallization. Crystal sizes larger than half a millimeter are absolutely explosive. An explosion can follow at every stage of the synthesis process: explosive decomposition can also be expected at the stage of saturation of the solution, both during crystallization and during drying. Many cases of spontaneous explosions have been described even with a simple pouring of the product.
Professional chemists are sure that the azide obtained from lead acetate is much more dangerous than that synthesized from nitrate. He is able to detonatehigh explosives are much better than mercury fulminate, since the pre-detonation region of azide is narrower. For example, the initiating charge in a detonator cap made of pure lead azide is 0.025 grams, hexogen needs 0.02, and TNT is 0.09 grams.
Use of azides
The use of this initiator of explosions has been practiced by mankind not so long ago. Lead azide was first obtained in 1891 by the chemist Curtius, when he added a solution of lead acetate to a solution of ammonium azide (or sodium - now it’s not clear). Since then, lead azide has been pressed into detonator caps (pressure is applied up to seven hundred kilograms per square centimeter). Moreover, very little time passed from discovery to obtaining patents - already in 1907 the first patent was received. Before 1920, however, lead azide caused too much trouble for manufacturers to be of little practical use.
The sensitivity of this substance is too high, and the pure crystalline finished product is even more dangerous. But ten years later, methods for handling azides were developed, precipitation with organic colloids began to be used, and then the industrial mass production of lead azide began, which turned out to be less dangerous and nevertheless suitable for equipping detonators. Dextrin lead azide has been produced in the USA since 1931. He especially strongly pressed the explosive mercury in detonators during the Second World War. Mercury fulminate fell into disuse at the end of the twentieth century.
Featuresapplications
Lead azide is used in shock, electric and fire blasting caps. It usually comes with the addition of THRS - lead trinitroresorcinate, which increases susceptibility to flame, as well as tetrazene, which increases susceptibility to prick and impact. For lead azide, steel cases are preferred, but aluminum cases are also used, much less often tinned and copper.
A stable detonation velocity where dextrin lead azide is used is guaranteed by a charge of 2.5 millimeters or more in length, as well as a long charge of moistened lead azide. That is why dextrin lead azide does not work with small-sized products. There is, for example, in England the so-called English service azide, where the crystals are surrounded by lead carbonate, this substance contains 98% Pb(N3)2 and unlike dextrin, heat-resistant and proactively explosive. However, in many operations it is much more dangerous.
Industrial production
Lead azide on an industrial scale is obtained in the same way as at home: dilute solutions of sodium azide and lead acetate (but more often lead nitrate) are merged, then mixed (with the presence of water-soluble polymers, dextrin for example). This method has advantages and disadvantages. Dextrin assists in obtaining particles of a controlled size (less than 0.1 millimeters) that have good flowability and are not as susceptible to friction. These are all pluses. The disadvantages include the fact that the substance obtained in this way has increased hygroscopicity, andinitiative is reduced. There are methods in which, after the formation of dextrin azide crystals, calcium stearate in an amount of 0.25% is added to the solution to reduce hygroscopicity and sensitivity.
Extra care is taken here and exact doses are applied. If solutions of lead nitrate (acetate) with sodium azide have a concentration of more than ten percent, a spontaneous explosion is very possible during crystallization. And if the mixing stops, the explosion occurs absolutely always. Previously, chemists assumed that the formed crystals of the β form exploded, detonating from internal stress. However, now, after many and careful studies, it has become clear that the form β can also be obtained in its pure form, and its sensitivity is similar to the form α.
What causes the explosion
In the eighties of the last century it was authoritatively confirmed that the causes of explosions are electrical in nature: the electric charge is redistributed in the layers of the solution and provokes such a reaction of the substance. That is why water-soluble polymers are added and constant mixing is carried out. This prevents electrical charges from being localized, and therefore a spontaneous explosion is prevented.
In order for lead azide to precipitate, instead of dextrin, gelatin is most often used in a solution of 0.4-0.5%, adding a little Rochel s alt to it. After rounded agglomerates are formed, a one percent suspension of zinc stearate, or aluminum, or (more often) molybdenum sulfide, must be introduced into this solution. Adsorption occurs on the surface of the crystals, which serves as a good solid lubricant. This method makes lead azide less sensitive to friction.
Military purpose
In order for lead azide to improve its susceptibility to flame, surface treatment of crystals with solutions of lead nitrate and magnesium styphnate is used to form a film. Caps for military purposes are produced differently. Dextrin and gelatin are canceled, and instead of them the additive of sodium s alt of carboxymethyl cellulose or polyvinyl alcohol is used. As a result, the final product is obtained with a greater amount of lead azide than with the dextrin precipitation method, 96-98% versus 92%. In addition, the product has less hygroscopicity, and the initiating ability is greatly increased.
If the solutions are drained quickly and water-soluble polymers are not added, the so-called colloidal lead azide is formed, which has a maximum explosion-initiating ability, but is not technologically advanced enough - the flowability is poor. It is sometimes used in electric detonators as a mixture of an ethyl acetate solution of nitrocellulose with colloidal lead azide.
