1.5. Brief information about the main explosives
Depending on their sensitivity to external influences and their ability to transition from combustion to detonation, explosives are divided into three main groups of explosives.
Initiating or primary explosives are used to initiate detonation or combustion of explosives of other groups. Combustion and detonation of initiating explosives occurs with an insignificant expenditure of external energy as a result of thermal or mechanical effects (heating, impact, friction).
High explosives, or secondary explosives, are used to make explosive rounds for ammunition and for blasting purposes. Their combustion turns into detonation only under certain conditions (for example, when burning a large mass of a substance with a large number of pores or when burning in a closed, durable vessel). When using high explosives, detonation is caused by the explosion of an auxiliary charge of the initiating (primary) explosive or by the explosion of a charge of another high explosive.
Gunpowder, or propellant explosives, are used as propellant charges for firearms and as fuel for jet engines. In composition they are close to high explosives, but their combustion is more stable. The combustion of gunpowder does not turn into detonation even at a pressure of several thousand atmospheres.
Under certain conditions (for example, when they are exposed to a sufficiently powerful initial impulse or if their diameter is larger than the critical one), gunpowder can detonate. Some of the gunpowders have a large critical diameter, and, in addition, the detonation of gunpowders is possible only with the explosion of a powerful detonator - for these reasons, the opinion arose that gunpowders cannot detonate.
Initiating explosives
Mercury fulminate [Hg(CNO)2] is a salt of fulminate acid HCNO, mercury fulminate is a white or gray crystalline powder with a density of 4.4 g/cm3. Flash point 175 – 1800C. Easily explodes from minor impact and friction. The decomposition of fulminate mercury occurs in accordance with the equation
[Hg(CNO)2]Hg+ 2CO+N2+ 494 kJ.
It can burn, but combustion easily and quickly turns into detonation. There are known cases of detonation as a result of a falling box of dry mercury fulminate, as a result of an object falling onto scattered mercury fulminate, etc. Sensitivity to the mechanical and thermal effects of mercury fulminate decreases in the presence of water (with a content of 30% water, it does not even ignite, but can be exploded by a detonator capsule). Mercury fulminate reacts vigorously with aluminum in the presence of moisture, so it should not be stored in aluminum containers, and mercury fulminate blasting caps are not made of aluminum. Aluminum fulminates are very sensitive compounds. A similar reaction is the formation of copper fulminate, a compound sensitive to shocks. Copper capsules are protected from moisture by varnishing inside and out.
Salts of explosive acid - fulminates - are extremely dangerous, because explode when wet and even under water (especially fulminates of mercury, gold and silver). When a splash of water containing mercury fulminate dries, the solid residue explodes under the influence of sunlight. Dust, as well as all wash water and water waste from the production of fulminates, are prone to spontaneous explosion and before removal must be neutralized by heating to 90 - 950C, which is also unsafe. Fulminates are used in pyrotechnics as fuses for other explosives, for gilding (explosive gold), for the manufacture of caps and fuses. All these drugs explode from impact, falling, friction, shock, heat, flame, acids and sunlight. Mercury fulminate is used to equip primers - igniters and primers - detonators. Due to the high sensitivity of dry mercury fulminate to mechanical stress, it can only be transported in equipped products. Long-term storage of mercury fulminate in front of equipment is permitted only under water.
Lead azide [Pb(N3)2] is a salt of hydronitric acid HN3, white powder with a density of 4.8 g/cm3 and a flash point of 330-3400C. Has high sensitivity. There are known cases where lead azide exploded as a result of pressing a fingernail on its crystals. To reduce sensitivity, it is phlegmatized with paraffin. When moistened, lead azide does not lose its sensitivity. When ignited by an external heat source, it instantly detonates. Interacts with copper, does not interact with aluminum. Lead azide is used to fill detonator caps. Hydronitric acid HN3 in anhydrous form can explode even by simply shaking the vessel. In a dilute aqueous solution during storage, it practically does not decompose. Its vapors are very poisonous, solutions cause inflammation of the skin.
The explosive decomposition of hydronitric acid follows the equation: HN3H2+ 3N2+ 590 kJ
Lead trinitroresorcinate (TNRS) [C6H(NO2)3(O2Pb)H2O] is a yellow-brown powder with a density of 3.1 g/cm3 and a flash point of 2750C. The impact sensitivity is lower than lead azide and the ignition sensitivity is higher. Used for equipping igniter primers.
Tetrazene or guanylnitrosoaminoguanyltetrazene [C2H8ON10] NH2 NH–NH-NO NH=C–NH–N=N–C=NH
Fine-crystalline yellowish powder with a density of 1.65 g/cm3 and a flash point of about 1400C. Slightly hygroscopic. It is close in sensitivity to mercury fulminate. Does not interact with metals.
Receipt
In the laboratory it is obtained by esterification of glycerin with a mixture of concentrated nitric and sulfuric acids. Acids and glycerin must be free of impurities. To ensure process safety and good glycerol yield, the acid mixture must have a low water content. The process begins by mixing oleum (or laboratory 98% sulfuric acid) and melange. Mixing of acids is carried out while cooling to prevent thermal decomposition of concentrated nitric acid. Glycerin is added from a dropping funnel with vigorous stirring and constant cooling of the flask with ice (with the addition of table salt). Temperature control is carried out with a mercury or electronic thermometer. The process of mixing acids can be expressed in a simplified form by the following reaction:
The reaction is equilibrium with a strong shift of equilibrium to the left. Sulfuric acid is necessary for binding water into strong solvates and for protonating nitric acid molecules to form nitrosonium cations NO2+. The positive charge is delocalized over all electron orbitals of the cation, which ensures its stability.
Then the reaction mixture of acids and glycerin is kept for a short time under ice cooling. The liquid separates into two layers. Nitroglycerin is lighter than the nitrating mixture and floats as a cloudy layer. The esterification process is carried out at temperatures around 0˚C. At lower temperatures the speed of the process is low; at higher temperatures the process becomes dangerous and the product yield sharply decreases. Exceeding the temperature above 25 ° C threatens an explosion, so the synthesis must be carried out under strict temperature control. The equation for the esterification of glycerol with nitric acid in the presence of sulfuric acid can be simplified as follows:
The top layer from the reaction glass (flask) is immediately poured into a large volume of cold water with stirring. The water temperature should be 6–15 °C, the volume should be no less than 100–110 times the volume of the obtained NGC. Acids dissolve in water, and nitroglycerin settles to the bottom of the container in the form of cloudy beige drops. The water is drained and replaced with a new portion of cold water with the addition of a small amount of soda (1-3% by weight). The final washing is carried out with a small amount of soda solution until the aqueous phase reacts neutrally. To obtain the purest possible nitroglycerin (for example, for research purposes), a final purification is carried out by washing with water, which makes it possible to separate the remaining soda and sodium nitrate. The disadvantages of laboratory production of NGC are largely associated with the need to use a large volume of washing water, which sharply reduces the yield of the product due to irreversible losses of NGC due to solubility in water; in practice, these losses can reach 30-50% of the total product obtained. A large volume of rinsing water, on the contrary, allows you to rinse the NGC as quickly and safely as possible. Insufficient washing of NGC from acidic impurities and products of incomplete esterification leads to very low stability of products (gunpowder, TRT, BVV, etc.) and makes NGC extremely dangerous.
In industry, it is obtained by continuous nitration of glycerin with a nitrating mixture in special injectors. The resulting mixture is immediately separated in separators (mainly Biazzi systems). After washing, nitroglycerin is used in the form of an aqueous emulsion, which simplifies and makes its transportation between workshops easier and safer. Due to the possible risk of explosion, NGC is not stored, but is immediately processed into smokeless powder or explosives.
Most of the production premises of the enterprise producing NGC are occupied by workshops for the cleaning and processing of liquid waste and other production waste. The most promising technologies in this area are based on closed cycles of using circulating media (wash water, spent acid mixture, etc.).
High explosives
High explosives can be homogeneous or heterogeneous (explosive mixtures).
I. Homogeneous high explosives
Based on their chemical structure, homogeneous high explosives are divided into 2 groups: nitro compounds and nitro esters.
NITROESTERS – nitrates of alcohols or carbohydrates.
1. Nitrate esters of carbohydrates: the main representative of these explosives are cellulose nitrates (nitrocellulose). Depending on the nitrogen content, they are divided into two varieties: pyroxylins (nitrogen content 12 - 13.5%) and colloxylins (nitrogen content 11.5 - 12%).
Nitrocellulose and pyroxylin were discovered in 1832 by Bracono. In 1846 - 1848 G.I. Hess and A.A. Fadeev investigated the properties of pyroxylin and showed that it is several times more powerful than black gunpowder.
The explosive decomposition of pyroxylin can be represented by the equation: 2C6H7O2(ONO2)33N2+ 9CO + 3CO2+ 7H2O.
When 1 kg of pyroxylin explodes, work is done equal to lifting 470 tons to a height of 1 meter.
Pyroxylin is used for the production of pyroxylin powders. In terms of sensitivity, pyroxylin is close to hexogen. Dry pyroxylin with a density of 1.3 g/cm3 has a detonation speed of about 6500 m/s.
Colloxylin is less sensitive than pyroxylin and is dangerous mainly in terms of fire. Store nitro fiber in a damp state (with a moisture content of up to 30%). Colloxylin is used to produce varnishes and celluloid.
2. Nitrate esters of alcohols.
Glycerol trinitrate (nitroglycerin) [C3H5(ONO2)3 – oily liquid with a density of 1.6 g/ml, with a flash point of 1800C. It was first obtained by the Italian chemist Sobrero in 1846. Pure nitroglycerin, free of acid impurities, is less explosive and more durable. Nitroglycerin is very sensitive to mechanical influences (shocks, blows, ignition with fulminate of mercury). The flame ignites with difficulty and burns without explosion. During an explosion, 1 g of nitroglycerin forms 467 cm3 of gases, and 1 liter – 750 liters of gases (gunpowder only 280 liters). Nitroglycerin freezes at +80C and becomes much more dangerous because its crystals become very hot when rubbed or broken. When turning into a liquid state, it cannot be heated above 11-120C, otherwise it will explode.
In 1854, the famous Russian chemist N.N. Zinin first raised the question of using nitroglycerin as an explosive. In 1867, nitroglycerin was used by the staff of artillery officer V.F. Petrushevsky for blasting at gold mines in Eastern Siberia.
In 1865, Zinin’s employee, Captain D.I. Andrievsky proposed an explosive detonator cap, the use of which sharply increased the blasting effect of explosives and led to the discovery of the phenomenon of detonation.
During the period of work of Zinin and Petrushevsky, the Swedish engineer A. Nobel lived in Russia. He is credited with further development and practical use of the works of Russian scientists. Nobel invented a number of dynamites and nitroglycerin gunpowder (ballistite), and improved the design of the detonator cap).
To make nitroglycerin less dangerous during storage, transportation and use, as well as to better use its explosive power, it is mixed with kieselguhr (ciliate shells, ciliate earth) and solid dynamite is obtained. 100 g of kieselguhr absorbs 75 g of nitroglycerin. Ready-made dynamite can withstand shocks, falls, and friction without exploding. However, sudden heating and explosion of mercury fulminate can lead to an explosion. Just like nitroglycerin, dynamite should not be allowed to freeze, which occurs at -40C. Thawing can only be done very slowly using damp, moderately warm sand. Frozen dynamite should not be subjected to sudden heating (flame, sparks, or even room temperature).
Explosive jelly (explosive gelatin) consists of 90% nitroglycerin and 10% pyroxylin. It is less dangerous than its components because it contains a little camphor. It burns like dynamite, when frozen it becomes somewhat more sensitive to shocks, but is not as dangerous as dynamite or nitroglycerin. It explodes violently underwater.
Nitroglycol (glycol dinitrate) [CH2ONO2 - CH2ONO2] is used to produce antifreeze dynamite. Has increased volatility.
Nitrodiglycol (diglycol dinitrate) [CH2ONO2–CH2–O – CH2–CH2ONO2] due to its low volatility and a number of properties similar to nitroglycerin, it is used for the preparation of gunpowders.
PETN – nitrate ester of pentaerythritol – pentaerythritol-tetranitrate [C(CH2ONO2)4 or
CH2ONO2 O2NOH2C – C – CH2ONO2 CH2ONO2
- white crystalline substance, density 1.77 g/cm3, non-hygroscopic. Melting point 1410C, flash point 2150C. Compared to other nitrate esters, PETN is stable. More sensitive to impact than TNT, tetryl and RDX. Detonation speed 7900 m/s. PETN is mostly phlegmatized by adding small amounts of paraffin (up to 5%) and wax. Pure PETN is used as secondary charges for equipping detonator caps, and phlegmatized PETN is used for equipping detonating cords, detonators, and some projectiles.
NITRO COMPOUNDS represent the most important class of high explosives. They are characterized by a significant high-explosive and blasting effect with low sensitivity to mechanical influences. These substances are especially suitable for loading artillery shells and other ammunition. The advantage of these compounds is their chemical resistance.
TNT or trinitrotoluene [C6H2CH3(NO2)3 – yellow crystalline powder or flakes. Density 1.66 g/cm3, flash point 3000C. The solidification temperature of pure TNT is 80.850C, so it is often used in fused form. Cast TNT does not detonate from a detonator capsule, but only as a result of the explosion of an intermediate detonator made of pressed high explosive. Detonation speed up to 6900 m/s. Bulk TNT is more sensitive to detonation than cast TNT.
TNT combustion usually does not lead to detonation, but if it occurs in a closed vessel with strong walls or in large masses of TNT, then detonation is possible.
TNT does not react with metals, but can react with alkalis to form TNT. TNTs are less dangerous than picrates, but their formation generates a significant amount of heat, which can lead to fire. A case of TNT ignition due to contact with soap emulsion has been reported.
Although the combustion of TNT, like other explosives, occurs due to the oxygen contained in the TNT itself, burning TNT can and should be extinguished with water . When water hits it, it evaporates; evaporation requires a lot of heat, so the temperature of the combustion products decreases. Due to lack of heat, the following layers do not heat up to the flash point, and combustion stops.
TNT is the main high explosive for ammunition filling. It is used in significant quantities in alloys with other nitro compounds: with hexogen for equipping small-caliber cumulative projectiles; with 20% dinitronaphthalene called K-2; with 5% xylyl called alloy L, etc. TNT is used to prepare cartridges and bombs for explosive work; in wartime they were used mixed with saltpeter.
Picric acid - trinitrophenol [C6H2OH(NO2)3] - yellow crystalline powder, soluble in hot water. Density 1.6 – 1.8 g/cm3, flash point 3000C, detonation speed about 7200 m/s. Little sensitive to impact and friction.
Obtained by P. Wulf in 1771. For a long time, picric acid was used as a yellow dye for wool, silk, leather and hair. And only by chance, at the end of the 19th century, it was discovered that it is an explosive.
In an open space, pure picric acid burns quietly with a highly smoky flame. When burning large masses (for example, warehouses), as well as when burning in closed metal vessels, combustion can lead to detonation.
The big disadvantage of picric acid is its ability to form salts when it comes into contact with metals (except tin) in the presence of even a small amount of water. In this case, salts are formed - picrates, whose properties are similar to the initiating explosives. The most dangerous are alkali metal picrates.
Picric acid should be stored only in plastic or wooden containers. Currently, picric acid is practically not used as an explosive.
In the first half of the 20th century, it was used as an explosive in various countries under the names melinite (Russia, France), lyddite (Great Britain), shimosa (Japan), s/88 (Germany).
Ammonium picrate, an ammonium salt of picric acid, was used in the USA to equip aerial bombs.
Tetrilyl trinitrophenylmethylnitramine - NO2 yellow-brown crystalline powder C6H(NO2)3N with a density of 1.71 g/cm3, flash point CH3 about 1900C. Tetryl is much more sensitive to shock than TNT or picric acid. Detonation speed 7470 m/s. Tetryl is particularly suitable for making blasting caps and detonators. A large number of accidents have been reported when working with tetryl.
Hexogen or cyclotrimethylenetrinitramine [C3H6O6N6] is a white crystalline substance with a flash point of 2300C and a melting point of 202.50C. Extremely sensitive to impact, NO2-NCH2 detonation speed 8500 m/s. Due to its high sensitivity, it is not used in its pure form to make charges, but phlegmatized hexogen is used. To distinguish phlegmatized RDX, an orange dye is added to the phlegmatizer. Non-phlegmatized hexogen is used to equip ammunition in alloys with TNT. In this case, TNT is a phlegmatizer. Such mixtures are less sensitive than RDX and more powerful than TNT.
HMX or cyclotetramethylenetetranitramine [C4H8O8N8] - O2N–NCH2N–NO2 / H2C CH2 / O2N – N CH2 N – NO2 Substance with a density of 1.95 g/cm3, melting point about 2800C. Thermal stability is higher than that of hexogen, detonation speed is 9100 m/s. HMX is used as a heat-resistant explosive when drilling deep wells and crushing hot ingots by explosive method when unloading and repairing blast furnaces. The blasting effect of HMX is greater than that of RDX.
Edna – ethyleneditramine, chemical formula CH2–NH–NO2 CH2–NH–NO2 Equal in strength and sensitivity to tetryl. Compared to the latter, it is less toxic and does not have coloring properties.
Dina – diethanolnitratenitramine [O2N – N(CH2CH2ONO2)2]. The shock sensitivity is the same as that of heating element. The explosion force is close to PETN and hexogen. It plasticizes nitrocellulose well.
Xylyl – trinitroxylene [C6 H(CH3)2(NO2)3]. Xylyl is a neutral substance that does not form salts with metals. Flash point 3300C. The shock sensitivity is greater and the detonation sensitivity is less than that of TNT. They are used to equip ammunition in the form of mixtures with ammonium nitrate and in the form of an alloy with TNT (alloy L).
Dinitronaphthalene [C10H8(NO2)2]. The sensitivity of naphthalene to detonation is very low, so it is used only in a mixture with ammonium nitrate (dinaphthalite).
Dinitrobenzene [C6H4(NO2)2] – a substance with a density of 1.57 g/cm3, detonation speed 6100 m/s. Has low sensitivity to detonation. Poisonous.
II. Heterogeneous high explosives.
Heterogeneous high explosives include mixtures of an oxidizer with an explosive or combustible substance.
1. Ammonium nitrate explosives ammonites as an oxidizing agent . Ammonites consisting of a mixture of TNT and saltpeter, containing more than 20% TNT, are called ammotols. In terms of sensitivity and danger during manufacture, these substances are more dangerous than TNT. Ammonals are ammonites containing aluminum powder. These mixtures may ignite on contact with water. Extinguishing fires with water is strictly prohibited. Dynamons are mixtures of ammonium nitrate with flammable non-explosive additives (dry peat, tree bark, etc.).
2. Chlorate and perchlorate explosives contain salts of chloric and perchloric acids.
The salts most commonly used are potassium chlorate KСlО3 (“Berthollet's salt”), potassium perchlorate KСlО4 and ammonium perchlorate NH4ClO4. When heated, KClO3 melts, and at about 4000C it begins to decompose, and decomposition can go in two directions: 4KClO3 → 4KCl + 6O2 or 4KClO3 → 3KClO4 + KCl
Berthollet's salt KСlО3 and perchlorate Pb(СlО3)2 lead when rubbed, pushed or heated with sugar, flour, wood (i.e. with organic substances), as well as with coal, sulfur, phosphorus, and metal powders explode very strongly. Even more powerful explosions occur when the chlorates of these metals interact with potassium cyanide KCN, potassium thiocyanate KNS, iron sulfide Fe2S3, and antimony sulfide. When working with chlorates, there should be no release of hydrogen sulfide nearby. Chlorates are extremely sensitive to fats and oils, so contact of these substances with oily rags is not allowed. Strong acids, when interacting with chlorates, release explosive chlorine dioxide from it, which boils at +90C and explodes at 600C. The greatest danger comes from drying chlorates and grinding the dry product. The explosive element in chlorates is the perchloric acid HClO3 that is part of it, which is known only in solution. Its concentrated solutions ignite organic substances such as paper, fabric, wood, etc. by simple contact. The possibility of using chlorate and perchlorate explosives for loading ammunition is greatly limited due to their high sensitivity to mechanical stress.
3. Oxyliquits – mixtures of liquid oxygen with porous flammable substances. Impregnation of oxyliquit cartridges, for example, with peat, is carried out immediately before use. Liquid oxygen evaporates vigorously, and depending on the size of the cartridge, in a time from several minutes to 1.5 hours, this type of ammunition loses its explosive properties. Liquid air can be used in a similar way (it turns into a liquid state at a pressure of 39 atmospheres and cooled to – 1400C). When liquid air evaporates, it loses more volatile nitrogen than oxygen, and therefore the remaining liquid is constantly enriched with oxygen. At this point, liquid air is like dynamite.
4. Explosive compounds of nitrogen with chlorine, bromine, iodine and sulfur. Nitrochloride – nitrogen chloride NCl3 (Dulong oil) is obtained by passing chlorine through a solution of ammonium chloride: NH4Cl+ 3Сl24HCl+NCl3. Nitrogen chloride is an oily yellow liquid with a pungent odor. When heated above 900C (or impact), it explodes with extreme force, while breaking down into elements (nitrogen and chlorine). Even wet, it explodes on contact with phosphorus, ammonia, arsenic, selenium, potassium, sodium, fatty and essential oils, grease, turpentine, rubber. When dry, it explodes when illuminated by the sun or artificial light. When nitrogen chloride explodes, no flame is formed, but if it comes into contact with flammable substances, they ignite due to the explosion, and a fire is possible. Nitrogen bromide NBr3 and nitrogen iodide NI3 are an oily liquid and black powder, respectively, with properties similar to nitrogen chloride. There are cases where a small amount of dry nitrogen iodide, located at one end of the bench, exploded if a person carefully sat down on the other end of the bench. Small amounts of these substances exploded even from the sounds of musical instruments. Nitrogen sulfide N2S3 is a yellow substance that explodes from friction, impact and at 1790C, but less energetically than the previous ones. In this case, an explosion occurs with the formation of a flame and can cause a fire.
Toxicity of nitroglycerin
Physiological effects
Nitroglycerin is highly toxic. The toxicity of nitroglycerin is explained by the fact that it is easily and quickly absorbed through the skin and mucous membranes (especially the mucous membranes of the oral cavity, respiratory tract and lungs) into the blood. A toxic dose for humans is considered to be 25-50 mg. A dose of 50-75 mg causes severe poisoning: a decrease in blood pressure occurs, severe headache, dizziness, redness of the face, severe burning in the throat and in the pit of the stomach, possible shortness of breath, fainting, nausea, vomiting, colic, photophobia, short-term symptoms are often observed. and transient visual disturbances, paralysis (especially of the eye muscles), tinnitus, beating of arteries, slow pulse, cyanosis, cold extremities. Chronic effects of nitroglycerin (chronic poisoning of the body with nitroglycerin was observed in workers producing dynamite), inhalation, as well as ingestion of large doses (100-150 mg/kg) can be fatal. LD100 for humans is about 112-210 mg/kg, death occurs within 2 minutes. Nitroglycerin can also cause severe skin irritation. Those who work with dynamite develop stubborn ulcers under the nails and on the ends of the fingers, rashes on the soles and between the fingers, dry skin and cracks. Rubbing 1 drop of nitroglycerin into the skin caused general poisoning that lasted 10 hours.
The maximum permissible concentration of nitroglycerin for the working area is 0.02 mg/dm³. Hazard class - 2.
