Explosive substances azides

Sodium azide is a toxic as well as an explosive substance (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, 2nd e(j New York John Wdey Sons). Although inert to shock, violent decomposition can occur when heated at 275°C. Contact of solid or solution with lead and copper must be avoided. Reactions with halogens, carbon disulfide, or chromyl chloride can be explosive. Dissolution in water produces toxic vapors of hydrazoic acid. The salt is an acute poison causing headache, hypotension, hypothermia, and convulsion. 

Explosive, primary Explosive substance manufactured with a view to producing a practical effect by explosion which is very sensitive to heat, impact or friction and which, even in very small quantities, either detonates or bums very rapidly. It is able to transmit detonation (in the case of initiating explosive) or deflagration to secondary explosives close to it. The main primary explosives are mercury fulminate, lead azide and lead styphnate. UN App. B, ICAO A2, lATA App. A... 

Explosive Initiating. Explosive substances which, even in very small quantities, detonate on contact with a flame, on mild or low impact or as a result of friction they are able to transmit detonation to other explosives close to them. The main initiating explosives are mercury fulminate and lead azide. For transport purposes some explosives, such as lead styphnate, are considered as initiating explosives because of their great sensitivity to the contact of a flame, to impact or to friction. (Both these types of sensitive explosives are referred to as primary explosives.) lATA App. A... 

Fluorine azide is a greenish-yellow gas at normal conditions with an odor resembling that of CIO2. Like the other halogen azides, N3F is a very explosive substance. Only a few data concerning the chemical and physical properties are known. 

As opposed to alkaline azides which do not have properties of explosives, alkaline fulminates are mostly reported as highly sensitive and explosive substances [8,107, 108] even though one source mentioned sodium fulminate as not so sensitive (impact sensitivity for NaCNO to be 32 cm with 0.5 kg hammer compared to 7.5-10 cm MF under the same conditions) [27]. Sensitivity of these fulminates is reported as extreme and handling a hazardous operation [8, 107, 108]. Extreme sensitivity is further reported for the rubidium and cesium salts. Alkaline fulminates undergo explosion when initiated by flame, even in small amounts, whereas mercury fulminate only deflagrates. The exact sensitivity data are, however, not reported in this work [107]. Sensitivity of cadmium fulminate to impact is about the same as that of MF sensitivity of thallium fulminate is higher [15, 57]. 

Hydrogen azide, HN3, and its salts (metal azides) are unstable substances used in detonators for high explosives. Sodium azide, NaNs, is used in air-bag safety systems in automobiles (see page 212). A reference source lists the following data for HN3. (The subscripts a, b, and c distinguish the three N atoms from one another.) Bond lengths Ng—Nt, = 124 pm Nb—Nc = 113 pm. Bond angles H—Na—Nb = 112.7° N —Nb—Nc = 180°. 

Lead Azide. The azides belong to a class of very few useflil explosive compounds that do not contain oxygen. Lead azide is the primary explosive used in military detonators in the United States, and has been intensively studied (see also Lead compounds). However, lead azide is being phased out as an ignition compound in commercial detonators by substances such as diazodinitrophenol (DDNP) or PETN-based mixtures because of health concerns over the lead content in the fumes and the explosion risks and environmental impact of the manufacturing process. 

Mechanical treatment alone may be sufficient to induce significant decomposition such processes are termed mechanochemical or tribo-chemical reactions and the topic has been reviewed [385,386]. In some brittle crystalline solids, for example sodium and lead azides [387], fracture can result in some chemical change of the substance. An extreme case of such behaviour is detonation by impact [232,388]. Fox [389] has provided evidence of a fracture initiation mechanism in the explosions of lead and thallium azide crystals, rather than the participation of a liquid or gas phase intermediate. The processes occurring in solids during the action of powerful shock waves have been reviewed by Dremin and Breusov [390]. 

Explosions involving flammable gases, vapours and dusts are discussed in Chapter 5. In addition, certain chemicals may explode as a result of violent self-reaction or decomposition when subjected to mechanical shock, friction, heat, light or catalytic contaminants. Substances containing the atomic groupings listed in Table 6.7 are known from experience to be thermodynamically unstable, or explosive. They include acetylides and acetylenic compounds, particular nitrogen compounds, e.g. azides and fulminates, peroxy compounds and vinyl compounds. These unstable moieties can be classified further as in Table 6.8 for peroxides. Table 6.9 lists a selection of potentially explosive compounds. 

Explosion. Use shielding when working with explosive classes such as acetylides, azides, ozonides, and peroxides. Peroxidizable substances such as ethers and alkenes, when stored for a long time, should be tested for peroxides before use. Only sparkless flammable storage refrigerators should be used in laboratories. 

Carbon disulfide is an extremely flammable liquid, the closed cup flash point being -22°F (-30°C). Its autoignition temperature is 90°C (194°F). Its vapors form explosive mixtures with air, within a wide range of 1.3 to 50.0% by volume in air. Reactions with certain substances can progress to explosive violence. They include finely divided metals, alkali metals, azides, fulminates, and nitrogen dioxide. 

Lead azide explodes on heating at 350°C or on percussion. Its detonation velocity is 5.1 km/sec (Meyer, E. 1989. Chemistry of Hazardous Materials, 2nreaction with carbon disulfide and forms shock-sensitive copper and zinc azides when mixed with the solutions of copper and zinc salts (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, ed. New York John Wdey). 

It becomes a problem in semantics to set a time limit for "development within which a process can be considered "spontaneous or "instantaneous . These two words seem to apply well to such extremely sensitive compounds as Nitrogen Triodide and Cupric Azide, which explode at the slightest touch when dry and, in addition, explode at a fairly low temperature. Attempts to correlate initiation in such cases with the attainment of a certain temperature seem unrealistic, especially in view of differences between relative sensitivity of different compounds to mechanical and thermal influences. For example, Mercuric Azide is so sensitive to impact that it explodes even under water, hut its heat sensitiveness is about the same as that for Cadmium Azide, which has been reported not to explode by percussion (Ref 5) Information about susceptibility of different explosives to spontaneous detonation is highly important from the viewpoint of safety. In Refs which follow are listed examples of spontaneous detonations of substances, some of them previously considered safe in this respect... 

Cd azides, Ag acetylide and nitrogen iodide) by electrons, neutrons, fusion products and X-rays. All these substances were exploded by an intense electron stream but it was shown that this was due to a thermal effect. Fission products exploded nitrogen iodide but in the other substances some changes within the crystals took place but no explosions. The experiments showed that, in general, the activation of a small group of adjacent molecules was not enough to cause explosion... 

The substance (II) is converted by the action of nitrous acid into nitroguanyl azide (Ha) at 0°C or into nitraminotetrazole (lib) (Lieber et al. [53]) at 70°C. Both substances are explosive ... 

When exposed to light lead azide soon turns yellow on the irradiated side. The layer of changed substance protects the deeper layers from further decomposition and thus irradiation does not entail changes in the explosive properties of the substance. However, as Wohler and Krupko [80] have shown, if the lead azide is subjected to stirring during irradiation, decomposition may proceed too far. 

They also found that by adding small amounts of dextrin, polyvinyl alcohol or other hydrophilic polymers explosion could be prevented. It is known that these compounds are able to alter the crystal habit of several substances, including lead azide. 

Curtius [1] who prepared ammonium azide did not notice its explosive properties. They were reported by Berthelot [139] who found ammonium azide to be an endothermic substance with a heat of formation — AH( of —19.0 kcal. 

A low explosion temperature together with a great amount of gaseous products and a high specific pressure suggested the used of ammonium azide as a propellent explosive. In practice the use of the substance, however, is prevented by its high volatility. 

CAUTION Many organic and inorganic azides are unstable or explosive under appropriate conditions of I initiation. Appropriate safety precautions and procedures should be adopted when handling these substances... 

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