The salt of nitric acid is Pb (N 3 ) 2 , a chemical compound, otherwise called lead azide. This crystalline substance can have one of at least two crystalline forms: the first form is α with a density of 4.71 grams per cubic centimeter, the second form is β - 4.93. It is poorly soluble in water, but good in monoethanolamine. An urgent request at home for the data in this article does not comply with the recommendations! Lead azide is not a joke, but a highly sensitive explosive (explosive).
The properties
Lead azide initiates an explosion because its sensitivity is very high and its critical diameter is very small. Apply it in detonator capsules. It is impossible to handle it without special technical techniques and special care skills. Otherwise, an explosion occurs whose heat 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 1,518 liters per square decimeter. Its detonation speed is approximately 4800 meters per second. Azides, whose properties look very frightening, are synthesized during the exchange reaction between soluble azides of alkali metals and solutions of lead salts. The result is a white crystalline precipitate. This is lead azide.
Getting
The reaction is usually carried out with the addition of glycerol, dextrin, gelatin or the like, which interfere with the formation of too large crystals and reduce the risk of detonation. It is extremely not recommended to synthesize lead azide at home, even for the purpose of making holiday fireworks. To obtain it, special conditions, knowledge and understanding of the danger, as well as sufficient experience of the chemist are necessary.
Nevertheless, quite a lot of information is contained on the network regarding the manufacture of this dangerous explosive. Many Internet users share their experience on how to get lead azide at home, attaching a detailed description of the process and its step-by-step illustrations. Sometimes texts contain warnings about the dangers of making these colorless crystals or white powder, but they are unlikely to stop everyone. Nevertheless, one must remember what lead azide is. Explosive mercury is less dangerous than its use.
Modifications
Four crystalline modifications of lead azide have been described; however, in practice one of the two is most often obtained. Either it is a technical white-gray powder, or colorless crystals obtained by merging solutions of sodium azide and acetate or lead nitrate. In practice, precipitation must be carried out with water-soluble polymers in order to obtain a relatively safe product to handle. If organic solvents, for example ether, are added, and also if diffusion interaction of solutions occurs, a new form forms, crystallizing needle-like and coarse.
An acidic environment gives less stable forms. During prolonged storage, when exposed to light and when heated, the crystals are destroyed. It does not dissolve in water, it is 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. It decomposes in boiling water, gradually releasing nitric acid. It also decomposes with moisture and carbon dioxide, spreading over the surface. It is then that carbonate and basic lead azide are formed.
Interactions and receptivity
Light decomposes it into nitrogen and lead - also on the surface, and if you use intensive radiation, you can get an explosion of a newly made 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 substance obtained away from copper and its alloys, since the mixture of azides and copper has even more unpredictable explosive properties. All azide reactions are toxic and the substance itself is toxic.
Sensitivity
Azides are quite heat-resistant, decompose only at temperatures above 245 degrees Celsius, and the flash occurs at about 330 degrees. Shock sensitivity is very high, and any production of azides is fraught with bad consequences, regardless of whether the azide is dry or moist, it does not lose explosive properties, even if moisture accumulates up to thirty percent in it.
Particularly susceptible to friction, even more than explosive mercury. If you rub the azide in the mortar, it detonates almost immediately. Different modifications of lead azides react differently to a shock (but everyone reacts!). Since the crystals are coated with a film of lead salts, the spark of fire and spark may not respond. But this applies only to those samples that have been stored for some time and they were exposed to moist carbon dioxide. Freshly prepared and chemically pure azide is very susceptible to flame effects.
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 crystallization method. Crystal sizes exceeding half a millimeter are absolutely explosive. An explosion can follow at each stage of the synthesis process: and at the saturation stage of the solution, explosive decomposition can be expected, both during crystallization and during drying. Many cases of spontaneous explosions are described even with a simple pouring of the product.
Professional chemists believe that lead azide derived from lead acetate is far more dangerous than that synthesized from nitrate. It is able to detonate blasting explosives much better than that obtained with explosive mercury, since the pre-detonation section of azide is narrower. For example, the initiating charge in the detonator capsule from pure lead azide is 0.025 grams, 0.02 for hexogen, 0.09 grams for TNT.
The use of azides
The use of this initiator of explosions, humanity has been practicing not so long ago. The chemist Kurtius first received lead azide in 1891, when he added a solution of lead acetate to a solution of ammonium azide (or sodium - now it is not clear). Since then, lead azide has been pressed into detonator capsules (the pressure is applied up to seven hundred kilograms per square centimeter). Moreover, from the opening to obtaining patents, very little time has passed - already in 1907 the first patent was received. However, until 1920, lead azide brought manufacturers too much trouble, and therefore the practical application was poor.
The substance is too sensitive, and a pure crystalline finished product is even more dangerous. But after ten years, the methods for handling azides were worked out, deposition with organic colloids began to be applied, and then industrial mass production of lead azide began, which turned out to be less dangerous and nevertheless suitable for equipping detonators. In the USA, dextrin lead azide has been produced since 1931. Especially strongly he squeezed explosive mercury in detonators during the Second World War. At the end of the twentieth century, explosive mercury was phased out.
Application features
Lead azide is used in shock, electric and fire detonator capsules. Usually it comes with additions of THRS - lead trinitroresorcinate, which increases the susceptibility to flame, as well as tetrazene, which increases susceptibility to pricking and shock. Steel lead is preferred for lead azide, but aluminum, much less often tinned and copper, is used.
A stable detonation speed where dextrin lead azide is used is guaranteed by a charge of 2.5 millimeters or more, as well as a long charge from 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 (N 3 ) 2 and, unlike dextrin, is heat-resistant and initiatively explosive. However, with many operations, it is much more dangerous.
Industrial production
Lead azide on an industrial scale is obtained in the same way as at home: diluted solutions of sodium azide and lead acetate (but more often lead nitrate) are merged, then mixed (with the presence of water-soluble polymers, for example, dextrin). This method has advantages and disadvantages. Dextrin promotes the production of particles of a controlled size (less than 0.1 mm), which have good flowability and not so high susceptibility to friction. These are all pluses. The disadvantage is that the substance obtained in this way has increased hygroscopicity, and initiative is reduced. There are methods in which, even after the formation of crystals of dextrin azide, calcium stearate in the amount of 0.25% is added to the solution to reduce the hygroscopicity and sensitivity.
Extra care is taken here and exact doses are applied. If solutions of lead nitrate (acetate) with sodium azide will have a concentration of more than ten percent, spontaneous explosion is very possible during crystallization. And if mixing stops, the explosion happens absolutely always. Chemists previously assumed that the crystals of form β explode, detonating from internal stress. However, now, after many and thorough 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.
Why is the explosion
In the eighties of the last century, it was authoritatively confirmed that the causes of the explosions are electric 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 continuous mixing is performed. This does not allow electric charges to be localized, and therefore spontaneous explosion is prevented.
So that lead azide precipitates, instead of dextrin, gelatin in a solution of 0.4-0.5% is most often used, adding a little Rochelle salt to it. After round 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 flame susceptibility, surface treatment of the crystals with solutions of lead nitrate and magnesium styphnate is used to form a film. Capsules for military use are made differently. Dextrin and gelatin are canceled, and instead they use the addition of sodium salt of carboxymethyl cellulose or polyvinyl alcohol. As a result, the final product is obtained with a larger amount of lead azide than with the precipitation method with dicstrin, 96-98% versus 92%. In addition, the product has less hygroscopicity, and the initiating ability is significantly increased.
If the solutions are drained quickly and water-soluble polymers are not added, the so-called colloidal lead azide is formed, which has the maximum explosive ability, but is not technologically advanced — poor flowability. Sometimes it is used in electric detonators in the form of a mixture of an ethyl acetate solution of nitrocellulose with colloidal lead azide.