EXPLOSIVES (a. explosives, blasting agents; n. Sprengstoffe; f. explosifs; i. explosivos) - chemical compounds or mixtures of substances that, under certain conditions, are capable of extremely rapid (explosive) self-propagating chemical transformation with the release of heat and the formation of gaseous products.

Substances or mixtures of any state of aggregation can be explosive. So-called condensed explosives, which are characterized by a high volumetric concentration of thermal energy, are widely used. Unlike conventional fuels, which require gaseous input from outside for their combustion, such explosives release heat as a result of intramolecular decomposition processes or interaction reactions between the components of the mixture, the products of their decomposition or gasification. The specific nature of the release of thermal energy and its conversion into the kinetic energy of explosion products and shock wave energy determines the main area of ​​​​application of explosives as a means of crushing and destroying solid media (mainly) and structures and moving crushed mass (see).

Depending on the nature of the external influence, chemical transformations of explosives occur: when heated below the self-ignition (flash) temperature - relatively slow thermal decomposition; when ignited - combustion with movement of the reaction zone (flame) through the substance at a constant speed of the order of 0.1-10 cm/s; when exposed to shock waves, detonation of explosives occurs.

Classification of explosives. There are several signs of classification of explosives: according to the main forms of transformation, purpose and chemical composition. Depending on the nature of the transformation under operating conditions, explosives are divided into propellant (or) and. The former are used in combustion mode, for example, in firearms and rocket engines, the latter - in combustion mode, for example, in ammunition and on. High explosives used in industry are called. Typically, only high explosives are classified as actual explosives. Chemically, the listed classes may contain the same compounds and substances, but processed differently or mixed in different proportions.

Based on their susceptibility to external influences, high explosives are divided into primary and secondary. Primary explosives include explosives that can explode in a small mass when ignited (rapid transition from combustion to detonation). They are also much more sensitive to mechanical stress than secondary ones. The detonation of secondary explosives is most easily caused (initiated) by shock wave action, and the pressure in the initiating shock wave should be on the order of several thousand or tens of thousands of MPa. In practice, this is carried out with the help of small masses of primary explosives placed in detonation in which is excited by a beam of fire and transferred by contact to the secondary explosive. Therefore, primary explosives are also called . Other types of external influences (ignition, spark, impact, friction) lead to the detonation of secondary explosives only under special and difficult-to-control conditions. For this reason, the widespread and targeted use of high explosives in the detonation mode in civil and military explosives was begun only after the invention of the blasting cap as a means of initiating detonation in secondary explosives.

Based on their chemical composition, explosives are divided into individual compounds and explosive mixtures. In the first, chemical transformations during an explosion occur in the form of a monomolecular decomposition reaction. The final products are stable gaseous compounds, such as oxide and dioxide, and water vapor.

In explosive mixtures, the transformation process consists of two stages: the decomposition or gasification of the components of the mixture and the interaction of the decomposition products (gasification) with each other or with particles of non-decomposable substances (for example, metals). The most common secondary individual explosives are nitrogen-containing aromatic, aliphatic heterocyclic organic compounds, including nitro compounds (,), nitroamines (,), nitroesters (,). Among inorganic compounds, ammonium nitrate, for example, has weak explosive properties.

The variety of explosive mixtures can be reduced to two main types: those consisting of oxidizers and combustibles, and mixtures in which the combination of components determines the operational or technological qualities of the mixture. Oxidizer-fuel mixtures are designed to ensure that a significant portion of the thermal energy is released during the explosion as a result of secondary oxidation reactions. The components of these mixtures can include both explosive and non-explosive compounds. Oxidizing agents, as a rule, during decomposition release free oxygen, which is necessary for the oxidation (with the release of heat) of flammable substances or the products of their decomposition (gasification). In some mixtures (for example, metal powders contained as fuel), substances that emit not oxygen, but oxygen-containing compounds (water vapor, carbon dioxide) can also be used as oxidizing agents. These gases react with metals to release heat. An example of such a mixture is .

Various natural and synthetic organic substances are used as combustibles, which upon explosion release products of incomplete oxidation (carbon monoxide) or flammable gases (,) and solids (soot). The most common type of high explosive mixtures of the first type are explosives containing ammonium nitrate as an oxidizing agent. Depending on the type of fuel, they, in turn, are divided into ammotols and ammonals. Less common are chlorate and perchlorate explosives, which contain potassium chlorate and ammonium perchlorate as oxidizing agents, oxyliquits - mixtures of liquid oxygen with a porous organic absorber, and mixtures based on other liquid oxidizers. Explosive mixtures of the second type include mixtures of individual explosives, such as dynamites; mixtures of TNT with hexogen or PETN (pentolite), most suitable for manufacturing.

In a mixture of both types, in addition to the indicated components, depending on the purpose of the explosives, other substances can be introduced to give the explosive any operational properties, for example, increasing susceptibility to initiation means, or, conversely, reducing sensitivity to external influences; hydrophobic additives - to make the explosive water resistant; plasticizers, flame retardant salts - to impart safety properties (see Safety explosives). The main operational characteristics of explosives (detonation and energy characteristics and physico-chemical properties of explosives) depend on the recipe composition of the explosives and manufacturing technology.

The detonation characteristics of explosives include detonation ability and susceptibility to the detonation impulse. The reliability and reliability of explosions depend on them. For each explosive at a given density, there is a critical charge diameter at which detonation steadily propagates along the entire length of the charge. A measure of the susceptibility of explosives to a detonation pulse is the critical pressure of the initiating wave and the time of its action, i.e. the value of the minimum initiating pulse. It is often expressed in units of mass of some primer explosive or secondary explosive with known detonation parameters. Detonation is excited not only by contact detonation of the initiating charge. It can also be transmitted through inert media. This is of great importance for systems consisting of several cartridges, between which there are jumpers made of inert materials. Therefore, for cartridgeed explosives, the rate of detonation transmission over a distance through various media (usually air) is checked.

Energy characteristics of explosives. The ability of explosives to produce mechanical work during an explosion is determined by the amount of energy released in the form of heat during explosive transformation. Numerically, this value is equal to the difference between the heat of formation of explosion products and the heat of formation (enthalpy) of the explosive itself. Therefore, the coefficient of conversion of thermal energy into work for metal-containing and safety explosives, which during an explosion form solid products (metal oxides, flame retardant salts) with high heat capacity, is lower than for explosives that form only gaseous products. For the ability of explosives to produce local crushing or blasting effects, see Art. .

Changes in the properties of explosives can occur as a result of physical and chemical processes, the influence of temperature, humidity, under the influence of unstable impurities in the composition of explosives, etc. Depending on the type of closure, a guaranteed period of storage or use of explosives is established, during which the standardized indicators of explosives either should not change, or their change occurs within the established tolerance.

The main safety indicator in handling explosives is their sensitivity to mechanical and thermal influences. It is usually assessed experimentally in laboratory conditions using special methods. In connection with the massive introduction of mechanized methods of moving large masses of bulk explosives, they are subject to requirements for minimal electrification and low sensitivity to static electricity discharge.

Historical reference. The first explosive was black (smoky) gunpowder, invented in China (7th century). It has been known in Europe since the 13th century. From the 14th century Gunpowder was used as a propellant in firearms. In the 17th century (for the first time in one of the mines in Slovakia), gunpowder was used for blasting in mining, as well as for equipping artillery grenades (explosive cores). The explosive transformation of black powder was excited by ignition in the explosive combustion mode. In 1884, the French engineer P. Viel proposed smokeless gunpowder. In the 18th-19th centuries. a number of chemical compounds with explosive properties were synthesized, including picric acid, pyroxylin, nitroglycerin, TNT, etc., but their use as high explosives became possible only after the discovery by Russian engineer D. I. Andrievsky (1865) and Swedish inventor A. Nobel (1867) of the explosive fuse (detonator capsule). Before this, in Russia, at the suggestion of N.N. Zinin and V.F. Petrushevsky (1854), nitroglycerin was used in explosions instead of black powder in explosive combustion mode. Mercury fulminate itself was obtained at the end of the 17th century. and again by the English chemist E. Howard in 1799, but its ability to detonate was not known then. After the discovery of the phenomenon of detonation, high explosives were widely used in mining and military affairs. Among industrial explosives, initially according to A. Nobel's patents, gurdynamites were most widely used, then plastic dynamites, and powdered nitroglycerin mixed explosives. Ammonium nitrate explosives were patented back in 1867 by I. Norbin and I. Olsen (Sweden), but their practical use as industrial explosives and for filling ammunition began only during the First World War of 1914-18. Safer and more economical than dynamites, they began to be used on a larger scale in industry in the 30s of the 20th century.

After the Great Patriotic War of 1941-45, ammonium nitrate explosives, initially primarily in the form of finely dispersed ammonites, became the dominant type of industrial explosives in the CCCP. In other countries, the process of mass replacement of dynamites with ammonium nitrate explosives began somewhat later, approximately in the mid-50s. Since the 70s The main types of industrial explosives are granular and water-containing ammonium nitrate explosives of the simplest composition, not containing nitro compounds or other individual explosives, as well as mixtures containing nitro compounds. Fine-dispersed ammonium nitrate explosives have retained their importance mainly for the manufacture of combat cartridges, as well as for some special types of blasting work. Individual explosives, especially TNT, are widely used for the manufacture of detonator bombs, as well as for long-term loading of flooded wells, in pure form () and in highly water-resistant explosive mixtures, granular and suspension (water-containing). For deep use and.

An explosive is a chemical compound or a mixture thereof capable of exploding as a result of certain external influences or internal processes, releasing heat and forming highly heated gases.

The complex of processes that occurs in such a substance is called detonation.

Traditionally, explosives also include compounds and mixtures that do not detonate, but burn at a certain speed (propellant powders, pyrotechnic compositions).

There are also methods of influencing various substances that lead to an explosion (for example, a laser or an electric arc). Such substances are not usually called “explosives.”

The complexity and diversity of explosive chemistry and technology, political and military contradictions in the world, and the desire to classify any information in this area have led to unstable and varied formulations of terms.

An explosive substance (or mixture) is a solid or liquid substance (or mixture of substances) that is itself capable of a chemical reaction, releasing gases at such a temperature and such a pressure and at such a speed that it causes damage to surrounding objects. Pyrotechnic substances are included in this category even if they do not emit gases.

Pyrotechnic substance (or mixture) - a substance or mixture of substances that is intended to produce an effect in the form of heat, fire, sound or smoke or a combination thereof.

Explosives include both individual explosives and explosive compositions containing one or more individual explosives, metal additives and other components.

The most important characteristics of explosives are:

Explosive transformation speed (detonation speed or burning speed),

Detonation pressure

Heat of explosion

Composition and volume of gas products of explosive transformation,

Maximum temperature of explosion products,

Sensitivity to external influences,

Critical detonation diameter,

Critical detonation density.

During detonation, the decomposition of explosives occurs so quickly that gaseous decomposition products with a temperature of several thousand degrees are compressed in a volume close to the initial volume of the charge. Expanding sharply, they are the main primary factor in the destructive effect of the explosion.

There are 2 main types of action of explosives:

Blasting (local action),

High explosive (general action).

Brisance is the ability of an explosive to crush and destroy objects in contact with it (metal, rocks, etc.). The amount of brisance indicates how quickly gases are formed during an explosion. The higher the brisance of a particular explosive, the more suitable it is for loading shells, mines, and aerial bombs. During an explosion, such an explosive will better crush the shell of the projectile, give the fragments the greatest speed, and create a stronger shock wave. The characteristic directly related to brisance is the detonation speed, i.e. how quickly the explosion process spreads through the explosive substance. Brisance is measured in millimeters.

High explosiveness - in other words, the performance of an explosive, the ability to destroy and throw out surrounding materials (soil, concrete, brick, etc.) from the explosion area. This characteristic is determined by the amount of gases formed during the explosion. The more gases are formed, the more work a given explosive can perform. High explosiveness is measured in cubic centimeters.

From this it becomes quite clear that different explosives are suitable for different purposes. For example, for blasting work in the ground (in a mine, when constructing pits, destroying ice jams, etc.), an explosive with the highest explosiveness is more suitable, and any explosiveness is suitable. On the contrary, for equipping shells, high explosiveness is primarily valuable and high explosiveness is not so important.

Explosives are widely used in industry for various blasting operations.

The annual consumption of explosives in countries with developed industrial production, even in peacetime, amounts to hundreds of thousands of tons.

In wartime, the consumption of explosives increases sharply. Thus, during the 1st World War in the warring countries it amounted to about 5 million tons, and in the 2nd World War it exceeded 10 million tons. Annual use of explosives in the United States in the 1990s was about 2 million tons.

In the Russian Federation, the free sale of explosives, blasting agents, gunpowder, all types of rocket fuel, as well as special materials and special equipment for their production, regulatory documentation for their production and operation is prohibited.

Explosives have individual chemical compounds.

Most of these compounds are oxygen-containing substances that have the property of being completely or partially oxidized inside the molecule without access to air.

There are compounds that do not contain oxygen, but have the property of exploding. They, as a rule, have increased sensitivity to external influences (friction, impact, heat, fire, spark, transition between phase states, other chemicals) and are classified as substances with increased explosiveness.

There are explosive mixtures that consist of two or more chemically unrelated substances.

Many explosive mixtures consist of individual substances that do not have explosive properties (combustibles, oxidizers and regulating additives). Regulating additives are used for:

Reducing the sensitivity of explosives to external influences. To do this, add various substances - phlegmatizers (paraffin, ceresin, wax, diphenylamine, etc.)

To increase the heat of explosion. Metal powders are added, for example, aluminum, magnesium, zirconium, beryllium and other reducing agents.

To improve stability during storage and use.

To ensure the necessary physical condition.

Explosives are classified according to their physical state:

Gaseous,

Gel-like,

Suspension,

Emulsion,

Solid.

Depending on the type of explosion and sensitivity to external influences, all explosives are divided into 3 groups:

1.Initiating
2. Blasting
3. Throwing

Initiating (primary)

Initiating explosives are intended to initiate explosive transformations in the charges of other explosives. They are highly sensitive and easily explode from simple initial impulses (impact, friction, pricking with a sting, electric spark, etc.).

High explosive (secondary)

High explosives are less sensitive to external influences, and the initiation of explosive transformations in them is carried out mainly with the help of initiating explosives.

High explosives are used to equip warheads of missiles of various classes, rocket and cannon artillery shells, artillery and engineering mines, aircraft bombs, torpedoes, depth charges, hand grenades, etc.

A significant amount of high explosives is consumed in mining (stripping operations, mining), in construction (preparing pits, destruction of rocks, destruction of liquidated building structures), in industry (explosion welding, pulse processing of metals, etc.).

Propellant explosives (powder and rocket fuels) serve as sources of energy for throwing bodies (shells, mines, bullets, etc.) or propelling rockets. Their distinctive feature is the ability to undergo explosive transformation in the form of rapid combustion, but without detonation.

Pyrotechnic compositions are used to obtain pyrotechnic effects (light, smoke, incendiary, sound, etc.). The main type of explosive transformations of pyrotechnic compositions is combustion.

Propellant explosives (powder) are used mainly as propellant charges for various types of weapons and are intended to impart a certain initial speed to a projectile (torpedo, bullet, etc.). The predominant type of their chemical transformation is rapid combustion caused by a beam of fire from ignition means.

There is also a classification of explosives according to the direction of use: military and industrial for mining (mining), for construction (dams, canals, pits), for the destruction of building structures, anti-social use (terrorism, hooliganism), while low-quality handmade substances and mixtures.

Types of explosives

There are a huge number of explosives, such as ammonium nitrate explosives, plasticite, hexogen, melinite, TNT, dynamite, elastite and many other explosives.

1. Plastic- a very popular explosive in the media. Especially if it is necessary to emphasize the particular insidiousness of the adversary, the terrible possible consequences of a failed explosion, a clear trace of the special services, especially the severe suffering of the civilian population under bomb explosions. As soon as it is not called - plasticite, plastid, plastic explosive, plastic explosive, plastic explosive. One matchbox of plastid is enough to smash a truck to pieces; the plastic explosives in the case are enough to destroy a 200-apartment building to the ground.

Plastite is a high explosive of normal power. Plastite has approximately the same explosive characteristics as TNT, and its only difference is its ease of use in blasting operations. This convenience is especially noticeable when demolishing metal, reinforced concrete and concrete structures.

For example, metal resists explosion very well. To break a metal beam, it is necessary to line its cross-section with explosives, and so that it fits as tightly as possible to the metal. It is clear that it is much faster and easier to do this if you have explosives like plasticine on hand, rather than something like wooden blocks. Plastic is easy to place so that it fits tightly to the metal even where rivets, bolts, ledges, etc. interfere with the placement of TNT.

Main characteristics:

1. Sensitivity: Virtually insensitive to impact, bullet penetration, fire, spark, friction, chemical exposure. Reliably explodes from a standard detonator capsule immersed in the mass of explosives to a depth of at least 10 mm.

2. Energy of explosive transformation - 910 kcal/kg.

3. Detonation speed: 7000 m/sec.

4. Brisance: 21mm.

5. High explosiveness: 280 cc.

6. Chemical resistance: Does not react with solid materials (metal, wood, plastics, concrete, brick, etc.), does not dissolve in water, is not hygroscopic, does not change its explosive properties during prolonged heating or wetting with water. Under prolonged exposure to sunlight, it darkens and slightly increases its sensitivity. When exposed to an open flame, it ignites and burns with a bright, energetic flame. Combustion in a confined space of a large quantity can develop into detonation.

7. Duration and conditions of the working state. The duration is not limited. A long (20-30 years) stay in water, soil, or ammunition casings does not change the explosive properties.

8. Normal state of aggregation: Plastic clay-like substance. At subzero temperatures it significantly reduces ductility. At temperatures below -20 degrees it hardens. With increasing temperature, plasticity increases. At +30 degrees and above it loses mechanical strength. At +210 degrees it lights up.

9. Density: 1.44 g/cm.

Plastite is a mixture of hexogen and plasticizing substances (ceresin, paraffin, etc.).

The appearance and consistency are highly dependent on the plasticizers used. It can have a consistency ranging from paste to dense clay.

Plastic material is supplied to the troops in the form of briquettes weighing 1 kg, wrapped in brown waxed paper.

Some types of plasticite can be packaged in tubes or produced in the form of tapes. Such plastics have the consistency of rubber. Certain types of plasticity have adhesive additives. Such an explosive has the ability to stick to surfaces.

2. Hexogen- an explosive belonging to the group of high-power explosives. Density 1.8 g/cc, melting point 202 degrees, flash point 215-230 degrees, impact sensitivity 10 kg. load 25 cm, explosive transformation energy 1290 kcal/kg, detonation speed 8380 m/sec, brisance 24 mm, high explosive 490 cc

The normal state of aggregation is a fine-crystalline, white, tasteless and odorless substance. Insoluble in water, non-hygroscopic, non-aggressive. Does not react chemically with metals. It doesn't press well. When struck or shot by a bullet, it explodes. Lights up readily and burns with a white, bright hissing flame. Combustion turns into detonation (explosion).

In its pure form it is used only for equipping individual samples of detonator caps. It is not used in its pure form for blasting operations. Used for the industrial production of explosive mixtures. Typically, these mixtures are used to equip certain types of ammunition. For example, sea mines. For this purpose, pure RDX is mixed with paraffin, painted with Sudan orange and pressed to a density of 1.66 g/cc. Aluminum powder is added to the mixture. All this work is carried out in industrial conditions using special equipment.

The name “hexogen” became popular in the media after memorable acts of sabotage in Moscow and Volgodonsk, when several houses were blown up in a row.

Hexogen in its pure form is used extremely rarely; its use in this form is very dangerous for the blasters themselves; production requires a well-established industrial process.

3. TNT is an explosive of normal power.

Main characteristics:

1. Sensitivity: Not sensitive to impact, bullet penetration, fire, spark, friction, chemical exposure. Pressed and powdered TNT is highly sensitive to detonation and explodes reliably from standard detonator caps and fuses.

2. Energy of explosive transformation - 1010 kcal/kg.

3. Detonation speed: 6900 m/sec.

4. Brisance: 19mm.

5. High explosiveness: 285 cc.

6. Chemical resistance: Does not react with solid materials (metal, wood, plastics, concrete, brick, etc.), does not dissolve in water, is not hygroscopic, does not change its explosive properties during prolonged heating, wetting with water, and changing state of aggregation (in molten form). Under prolonged exposure to sunlight, it darkens and slightly increases its sensitivity. When exposed to an open flame, it ignites and burns with a yellow, highly smoky flame.

7. Duration and operating conditions: The duration is not limited (TNT manufactured in the early thirties works reliably). A long (60-70 years) stay in water, soil, or ammunition casings does not change the explosive properties.

8. Normal state of aggregation: Solid. It is used in powder, flake and solid form.

9. Density: 1.66 g/cm.

Under normal conditions, TNT is a solid substance. It melts at a temperature of +81 degrees, and lights up at a temperature of +310 degrees.

TNT is a product of the action of a mixture of nitric and sulfuric acids on toluene. The output is flaked TNT (individual small flakes). From flaked TNT, mechanical processing can produce powdered, pressed TNT, and fused TNT by heating.

TNT has found the widest application due to the simplicity and convenience of its mechanical processing (it is very easy to make charges of any weight, fill any cavities, cut, drill, etc.), high chemical resistance and inertness, and immunity to external influences. This means that it is very reliable and safe to use. At the same time, it has high explosive characteristics.

TNT is used both in pure form and in mixtures with other explosives, and TNT does not enter into chemical reactions with them. In a mixture with hexogen, tetryl, PETN, TNT reduces the sensitivity of the latter, and in a mixture with ammonium nitrate explosives, TNT increases their explosive properties, increases chemical resistance and reduces hygroscopicity.

TNT in Russia is the main explosive for filling shells, missiles, mortar mines, aerial bombs, engineering mines and landmines. TNT is used as the main explosive when carrying out blasting operations in the ground, blasting metal, concrete, brick and other structures.

In Russia, TNT is supplied for blasting operations:

1. Flaked in kraft paper bags weighing 50 kg.

2. In pressed form in wooden boxes (checkers 75, 200, 400 g.)

TNT blocks are available in three sizes:

Large - measuring 10x5x5 cm and weighing 400g.

Small - measuring 10x5x2.5 cm and weighing 200g.

Drilling - diameter 3 cm, length 7 cm. and weighing 75g.

All checkers are wrapped in waxed paper of red, yellow, gray or gray-green color. On the side there is the inscription "TNT block".

Demolition charges of the required mass are made from large and small TNT blocks. A box with TNT blocks can also be used as a demolition charge weighing 25 kg. To do this, there is a hole in the center of the top cover for the fuse, covered with an easily removable board. The checker under this hole is placed so that its ignition socket is located just under the hole in the lid of the box. The boxes are painted green and have wooden or rope handles for carrying. The boxes are marked accordingly.

The diameter of the drill bit corresponds to the diameter of a standard rock drill. These blocks are used to assemble drilling charges when breaking rocks.

TNT is also supplied to the engineering troops in the form of ready-made charges in a metal shell, which has sockets for various types of fuses and fuses, and devices for quickly securing the charge to a destructible object.

Explosives – improvised explosive device.

There is probably not a single state in the world that is not faced with the problem of using improvised explosive devices. Well, homemade explosive devices (at one time they were aptly called infernal machines) have long become a favorite weapon of both international terrorists and half-crazed youths who imagine that they are fighting for a bright future for all progressive humanity. And many innocent people have been killed or injured as a result of terrorist attacks.

Explosives are chemicals. Different components of explosives are produced by different chemical reactions and have different explosive forces and different stimuli for ignition, such as heat, impact or friction. Of course, it is possible to build an increasing rating of explosives based on the weight of the charge. But you should know that simply doubling the weight does not mean doubling the explosive effect.

Chemical explosives come in two categories - low and high power (we are talking about the speed of ignition).

The most common low yield explosives are black powder (opened at 1250g), gun cotton and nitro cotton. They were originally used in artillery, for loading muskets and the like, since in this capacity they best reveal their characteristics. When ignited in a confined space, they release gases that create pressure, which actually causes the explosive effect.

Explosives of high power differ from explosives of low power quite significantly. The former were used from the very beginning as detonating ones, because upon detonation they disintegrated, creating supersonic waves, which, passing through the substance, destroyed its molecular structure and released super-hot gases. As a result, an explosion occurred that was disproportionately stronger than when using low-power explosives. Another distinctive property of this type of explosives is safety in handling - to cause them to explode, a powerful detonator is required.

But in order for an explosion to occur in the circuit, a fire must first be lit. You can’t just make a piece of coal burn right away. You need a chain, consisting of a simple sheet of paper, to first make a fire, where you then need to put firewood, which, in turn, can light the coal.

The same circuit is also necessary for the detonation of high-power explosives. The initiator will be an explosive cartridge or detonator consisting of a small amount of initiating substance. Sometimes detonators are made two-part - with a more sensitive explosive and a catalyst. The explosive particles used in detonators are usually no larger than a pea in size. There are two types of detonators - flash and electric. Flash detonators operate as a result of chemical (the detonator consists of chemicals that ignite after detonation) or mechanical (the firing pin, as in a hand grenade or pistol, strikes the primer, and then an explosion occurs).

The electric fuse is connected to the explosive by electrical wires. The electrical discharge heats the connecting wires, and the detonator naturally fires. Terrorists mainly use electric detonators for their explosive devices, while the military prefers flash detonators.

There are simple, series and parallel electrical circuits for terrorist explosive devices. Simple circuits consist of an explosive charge, an electrical detonator (most often two, since terrorists usually hedge their bets out of fear that one detonator might not work), a battery or other source of electrical power, and a switch that prevents the device from going off.

By the way, terrorists often die by closing the circuits of explosive devices with jewelry (for example, their rings, watches, or something like that), and placing a second switch in series in the circuit as a fuse. If there is a high probability that the bomb could be defused on the street, terrorists may well add a parallel switch. However, the electrical switches used in terrorist bomb circuits have an infinite number of variations and differences. After all, in the end, they depend on the imagination and technical capabilities of the master. And also from the set goal. This means that there is simply no point in checking and studying all the options in detail.

EXPLOSIVES. 1.1 General information about explosives

1.1 General information about explosives

Explosives are individual compounds or mixtures capable of rapid, self-propagating chemical transformation (explosion) with the formation of large amounts of gases and heat. Explosives can be solid, liquid and gaseous.

An explosion is characterized by:

High speed of chemical transformation (up to 8–9 km/s);

Exothermicity of the reaction (about 4180–7520 kJ/kg);

Formation of a large amount of gaseous products (300-1000 l/kg);

Self-propagation of the reaction.

Failure to fulfill at least one of the specified conditions excludes the occurrence of an explosion.

The rapid formation of large volumes of gases and heating of the latter due to the heat of reactions to high temperatures causes the sudden development of high pressures at the site of the explosion. The energy of compressed gaseous explosion products is a source of mechanical work in various types of explosives applications. Unlike the combustion of conventional fuels, the explosion reaction of explosives occurs without the participation of atmospheric oxygen and, due to the high speed of the process, allows one to obtain enormous power in a small volume.

Thus, the combustion of 1 kg of coal requires about 11 m 3 of air, and approximately 33,440 kJ is released. The combustion (explosion) of 1 kg of hexogen, occupying a volume of 0.65 liters, occurs in 0.00001 s and is accompanied by the release of 5680 kJ, which corresponds to a power of 500 million kW.

This chemical transformation is called an explosive transformation (explosion). There are always two stages in it:

The first is the conversion of latent chemical energy into compressed gas energy;

The second is the expansion of the resulting gaseous products, which do the work.

Based on the mechanism of propagation and the speed of the chemical reaction, two types of explosive transformations are distinguished: combustion and explosion (detonation).

Combustion– a relatively slow process. Heat is transferred from a more heated layer in depth to a less heated layer by thermal conductivity. The burning rate depends on the conditions under which the chemical reaction occurs. For example, as pressure increases, the combustion rate increases. In some cases, combustion can turn into an explosion.

Explosion– a fleeting process occurring at a speed of up to
9 km/s. The energy during an explosion is transferred by the resulting shock wave - a region of highly compressed matter (compression wave).

The explosion mechanism can be represented as follows. An explosive transformation excited in the first layer of an explosive by a foreign agent sharply compresses the second (subsequent) layer, that is, it forms a shock wave in it. The latter causes an explosive transformation in this layer. Then the shock wave reaches the third layer and also excites explosive transformations in it, then the fourth, etc. During the propagation process, the energy of the shock wave decreases, this is expressed in a decrease in the compression force from layer to layer. When the compression is insufficient, the explosion will turn into combustion. However, another case is also possible. The energy released as a result of the explosive transformation in the next layer is sufficient to compensate for the energy loss in the shock wave when passing through this layer. In this case, the explosion turns into detonation.

Detonation– a special case of an explosion occurring at a constant speed (the speed of shock wave propagation) for a given substance. Detonation does not depend on external conditions, and its propagation speed is an important parameter of the explosive. The type of explosive transformation of a given explosive depends on the properties of the substance and on external conditions. For example, the explosive substance TNT burns under normal conditions, but if it is in a closed volume, then the combustion can turn into an explosion and detonation. Gunpowder burns in the open air, but if you ignite gunpowder dust, it can detonate. Therefore, regardless of the purpose of explosives and their sensitivity to various impulses, they should be handled with care, with mandatory compliance with safety requirements.

Terminology

The complexity and diversity of explosive chemistry and technology, political and military contradictions in the world, and the desire to classify any information in this area have led to unstable and varied formulations of terms.

Industrial Application

Explosives are also widely used in industry for various blasting operations. The annual consumption of explosives in countries with developed industrial production, even in peacetime, amounts to hundreds of thousands of tons. In wartime, the consumption of explosives increases sharply. Thus, during the 1st World War in the warring countries it amounted to about 5 million tons, and in the 2nd World War it exceeded 10 million tons. Annual use of explosives in the United States in the 1990s was about 2 million tons.

• throwing
  Propellant explosives (powder and rocket fuels) serve as sources of energy for throwing bodies (shells, mines, bullets, etc.) or propelling rockets. Their distinctive feature is the ability to undergo explosive transformation in the form of rapid combustion, but without detonation.
• pyrotechnic
  Pyrotechnic compositions are used to obtain pyrotechnic effects (light, smoke, incendiary, sound, etc.). The main type of explosive transformations of pyrotechnic compositions is combustion.

Propellant explosives (powder) are used mainly as propellant charges for various types of weapons and are intended to impart a certain initial speed to a projectile (torpedo, bullet, etc.). The predominant type of their chemical transformation is rapid combustion caused by a beam of fire from ignition means. Gunpowder is divided into two groups:

a) smoky;

b) smokeless.

Representatives of the first group can be black powder, which is a mixture of saltpeter, sulfur and coal, for example, artillery and gun powder, consisting of 75% potassium nitrate, 10% sulfur and 15% coal. The flash point of black powder is 290 - 310° C.

The second group includes pyroxylin, nitroglycerin, diglycol and other gunpowders. The flash point of smokeless powders is 180 - 210 ° C.

Pyrotechnic compositions (incendiary, lighting, signal and tracer), used to equip special ammunition, are mechanical mixtures of oxidizing agents and flammable substances. Under normal conditions of use, when they burn, they produce a corresponding pyrotechnic effect (incendiary, lighting, etc.). Many of these compounds also have explosive properties and can detonate under certain conditions.

According to the method of preparing charges

• pressed
• cast (explosive alloys)
• patronized

By application area

• military
• industrial

• for mining (mining, production of building materials, stripping operations)
  According to the conditions of safe use, industrial explosives for mining are divided into

• non-safety
• safety

• for construction (dams, canals, pits, road cuttings and embankments)
• for seismic exploration
• for destruction of building structures
• for processing materials (explosion welding, explosion hardening, explosion cutting)

• special purpose (for example, means for undocking spacecraft)
• antisocial use (terrorism, hooliganism), often using low-quality substances and homemade mixtures.
• experimental.

By degree of danger

There are various systems for classifying explosives according to the degree of danger. The most famous:

• A globally harmonized system of hazard classification and labeling of chemicals

• Classification according to the degree of danger in mining;

The energy of the explosive itself is small. The explosion of 1 kg of TNT releases 6-8 times less energy than the combustion of 1 kg of coal, but during the explosion this energy is released tens of millions of times faster than during conventional combustion processes. In addition, coal does not contain an oxidizing agent.

see also

Literature

1. Soviet military encyclopedia. M., 1978.
2. Pozdnyakov Z. G., Rossi B. D. Handbook of Industrial Explosives and Explosives. - M.: “Nedra”, 1977. - 253 p.
3. Fedoroff, Basil T. et al Encyclopedia of Explosives and Related Items, vol.1-7. - Dover, New Jersey: Picatinny Arsenal, 1960-1975.

Links

• // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional ones). - St. Petersburg. , 1890-1907.

Wikimedia Foundation.

Chapter 2

General information about explosives and

thermochemistry of explosive processes

In human economic activity, we often encounter explosive phenomena (explosions).

In the broadest sense of the word, “explosion” is the process of a very rapid physical and chemical transformation of a system, accompanied by the transition of its potential energy into mechanical work.

• 
  Examples of an explosion include:
• 
  explosion of a vessel operating under high pressure (steam boiler, chemical vessel, fuel tank);
• 
  explosion of a conductor when it short-circuits a powerful source of electricity;
• 
  collision of bodies moving at high speeds;
• 
  spark discharge (lightning during a thunderstorm);
• 
  eruption;
• 
  nuclear explosion;

In the examples given, various systems undergo very rapid transformations: superheated water (or other liquid), a metal conductor, a conductive layer of air, a molten mass of the bowels of the earth, a charge of radioactive substances, chemical substances. All these systems at the time of the explosion had a certain supply of energy of various types: thermal, electrical, chemical, nuclear, kinetic (collision of moving bodies). The release of energy or its transformation from one type to another leads to very rapid changes in the state of the system, as a result of which it does work.

In relation to explosives (in particular to explosive explosives), an explosion should be understood as a process of extremely rapid (instantaneous) chemical transformation of a substance, as a result of which its chemical energy is converted into the energy of highly compressed and heated gases that perform work during their expansion.

The above definition gives three characteristic features of an “explosion”:

• 
  high rate of chemical transformation;
• 
  the formation of gaseous products of chemical decomposition of a substance - highly compressed and heated gases that play the role of a “working fluid”;
• 
  exothermicity of the reaction.

Let's look at the factors that determine an explosion in more detail.

Exothermicity reaction is the most important condition for an explosion. This is explained by the fact that the explosive explosive explosion is excited by an external source that has a small amount of energy. This energy is only sufficient to cause an explosive transformation reaction of a small mass of explosive located at a point on the line or plane of initiation. Subsequently, the explosion process spreads spontaneously throughout the explosive mass from layer to layer (layer-by-layer) and is supported by the energy released in the previous layer. The amount of heat released ultimately determines not only the possibility of self-propagation of the explosion process, but also its beneficial effect, that is, the performance of the explosion products, since the initial energy of the working fluid (gases) is completely determined by the thermal effect of the chemical reaction of the “explosion”.

High speed of reaction propagation explosive transformation is its characteristic feature. The explosion process of some explosives occurs so quickly that it seems that the decomposition reaction occurs instantly. However, it is not. The speed of propagation of an explosive explosion, although large, has a finite value (the maximum speed of propagation of an explosive explosion does not exceed 9000 m/s).

The presence of highly compressed and heated gaseous products is also one of the main conditions for an explosion. Expanding sharply, compressed gases produce a shock to the environment, exciting a shock wave in it, which performs the planned work. Thus, the jump (difference) in pressure at the interface between the explosive and the environment, which occurs at the initial moment, is a very characteristic sign of an explosion. If no gaseous products are formed during a chemical transformation reaction (i.e. there is no working fluid), the reaction process is not explosive, although the reaction products may have a high temperature without having other properties, they cannot create a pressure jump and, therefore, cannot make work.

The necessity of the presence of all three factors considered in the explosion phenomenon will be illustrated with some examples.

Example 1 Coal burning:

C + O 2 = CO 2 + 420 (kJ).

During combustion, heat is released (there is exothermicity) and gases are formed (there is a working fluid). However, the combustion reaction is slow. Therefore, the process is not explosive (there is no higher rate of chemical transformation).

Example 2 Thermite burning:

2 Al + Fe 2 O 3 = Al 2 O 3 + 2 Fe +830 (kJ).

The reaction proceeds very intensely and is accompanied by a large amount of heat (energy) released. However, the resulting reaction products (slags) are not gaseous products, although they have a high temperature (about 3000 o C). The reaction is not an explosion (there is no working fluid).

Example 3 Explosive transformation of TNT:

C 6 H 2 (NO 2) 3 CH 3 = 2 CO + 1.2 CO 2 + 3.8 C + 0.6 H 2 + 1.6 H 2 O +

1.4N 2 +0.2 NH 3 +905 (kJ).

Example 4 Explosive decomposition of nitroglycerin:

C 3 H 5 (NO 3) 3 = 3CO 2 +5 H 2 O + 1.5N 2 + Q (kJ).

These reactions proceed very quickly, heat is released (the reactions are exothermic), and the gaseous products of the explosion, expanding, do work. The reactions are explosive.

It must be borne in mind that the above main factors determining the explosion should not be considered in isolation, but in close connection with each other and with the conditions of the process. Under some conditions, the chemical decomposition reaction can proceed calmly, while in others it can be explosive. An example is the combustion reaction of methane:

CH 4 + 2O 2 = CO 2 + 2H 2 O + 892 (kJ).

If methane combustion occurs in small portions and its interaction with atmospheric oxygen occurs along a fixed contact surface, the reaction has the character of stable combustion (there is exothermicity, there is gas formation, there is no high speed of the process - no explosion). If methane is pre-mixed with oxygen in a significant volume and combustion is initiated, the reaction rate will increase significantly and the process can become explosive.

It should be noted that the high speed and exothermic nature of the process gives the impression that explosives have an extremely large energy reserve. However, it is not. As follows from the data given in Table 2.1, in terms of heat content (the amount of heat released during the explosion of 1 kg of a substance), some flammable substances are much superior to explosives.

Table 2.1 - Heat content of some substances

The difference between the explosion process and conventional chemical reactions is the greater volumetric concentration of the released energy. For some explosives, the explosion process occurs so quickly that all the released energy at the first moment is concentrated almost in the initial volume occupied by the explosive. It is impossible to achieve such a concentration of energy in reactions of a different kind, for example, from the combustion of gasoline in car engines.

Large volumetric concentrations of energy created during an explosion lead to the formation of specific energy flows (specific energy flow is the amount of energy transmitted through a unit area per unit time, dimension in W / m 2) of high intensity, which predetermines the greater destructive ability of the explosion.

2.1. Classification of explosive processes

The following factors have a decisive influence on the nature of the explosion process and its final result:

• 
  the nature of the explosive, i.e. its physicochemical properties;
• 
  conditions for excitation of a chemical reaction;
• 
  conditions under which the reaction occurs.

What is common in both examples considered is that the chemical decomposition by mass (volume) of TNT occurs sequentially from one layer to another. However, the speed of propagation of the reacting layer and the mechanism of decomposition of TNT particles in the reacting layer will be completely different in each case. The nature of the processes occurring in the reacting explosive layer ultimately determines the rate of propagation of the reaction. However, the opposite statement is also true: the speed of propagation of a chemical reaction can also be used to judge its mechanism. This circumstance made it possible to place the reaction rate of explosive transformation as the basis for the classification of explosive processes. Based on the speed of reaction propagation and its dependence on conditions, explosive processes are divided into the following main types: combustion, explosion (actual explosion) and detonation .

Combustion processes proceed relatively slowly (from 10 -3 to 10 m/s), while the combustion rate significantly depends on external pressure. The greater the pressure in the environment, the greater the burning rate. In the open air, combustion proceeds calmly. In a limited volume, the combustion process accelerates and becomes more energetic, which leads to a rapid increase in the pressure of gaseous products. In this case, the gaseous combustion products acquire the ability to produce throwing work. Combustion is a characteristic type of explosive transformation of gunpowder and rocket fuels.

The actual explosion Compared to combustion, it is a qualitatively different form of process propagation. The distinctive features of the explosion are: a sharp jump in pressure at the site of the explosion, a variable speed of propagation of the process, measured in thousands of meters per second and relatively little dependent on external conditions. The nature of the explosion is a sharp impact of gases on the environment, causing crushing and severe deformation of objects located near the explosion site. The process of explosion differs significantly from combustion in the nature of its propagation. If during combustion the energy is transferred from the reacting layer to the adjacent unexcited explosive layer by thermal conductivity, diffusion and radiation, then during an explosion the energy is transferred by compressing the substance by a shock wave.

Detonation represents a stationary form of the explosion process. The speed of detonation during an explosion occurring under given conditions does not change and is the most important constant of a given explosive. Under conditions of detonation, the maximum “destructive” effect of the explosion is achieved. The mechanism for excitation of the explosive transformation reaction during detonation is the same as during the explosion itself, that is, the transfer of energy from layer to layer occurs in the form of a shock wave.

The explosion occupies an intermediate position between combustion and detonation. Although the mechanism of energy transfer during an explosion is the same as during detonation, the processes of energy transfer in the form of thermal conductivity, radiation, diffusion, and convention cannot be neglected. That is why an explosion is sometimes considered as non-stationary, combining the combination of the effects of combustion, detonation, expansion of gaseous products and other physical processes. For the same explosive, under the same conditions, the explosive transformation reaction can be classified as intense combustion (gunpowder in a gun barrel). Under other conditions, the process of explosive transformation of the same explosive occurs in the form of an explosion or even detonation (for example, an explosion of the same gunpowder in a hole). And although during an explosion or detonation processes characteristic of combustion are present, their influence on the general mechanism of explosive decomposition is insignificant.

2.2. Classification of explosives

Currently, a huge number of chemical substances are known that are capable of explosive decomposition reactions, their number is constantly increasing. In their composition, physical and chemical properties, in their ability to excite explosion reactions in them and in their distribution, these substances differ significantly from each other. For the convenience of studying explosives, they are combined into certain groups according to various characteristics. We will focus on three main classification features:

• 
  by composition;
• 
  by appointment;
• 
  by susceptibility to explosive transformation (explosiveness).

Explosive chemical compounds are unstable chemical systems that, under the influence of external influences, are capable of rapid exothermic transformations, resulting in complete rupture of intramolecular bonds and subsequent recombination of free atoms, ions, groups of atoms into thermodynamically stable products (gases). Most explosives in this group are oxygen-containing organic compounds, and their chemical decomposition reaction is a reaction of complete and partial intramolecular oxidation. Examples of such PVVs include TNT and nitroglycerin (as components of PVV). However, there are other explosive compounds (lead azide , Рb(N 3 ) 2 ), not containing oxygen, capable of exothermic reactions of chemical decomposition during an explosion.

Explosive mixtures are systems consisting of at least two components that are not chemically related to each other. Typically, one of the components of the mixture is a substance relatively rich in oxygen (oxidizer), and the second component is a flammable substance that does not contain oxygen at all, or contains it in quantities insufficient for complete intramolecular oxidation. The first ones include black powder, emulsion explosives, the second ones include ammotol, granulites, etc.

It should be noted that there is a so-called intermediate group of explosive mixtures:

• 
  substances of the same nature (explosive chemical compounds) with different contents of active oxygen (TNT, hexogen).
• 
  an explosive chemical compound in an inert filler (dynamite).

By purpose Explosives are divided into four main groups:

• 
  initiating explosives;
• 
  high explosives (including the class of industrial explosives);
• 
  propellant explosives (powder and fuel);
• 
  pyrotechnic compositions (including PVV, black powder and other igniters).

High explosives have a large reserve of energy and are less sensitive to the effects of initial impulses.

The main type of chemical decomposition of explosives and BrVVs is detonation.

A characteristic sign (type) of chemical decomposition of propellant explosives is combustion. For pyrotechnic compositions, the main type of explosive transformation reaction is also combustion, although some of them are capable of an explosion reaction. Most pyrotechnic compositions are mixtures (mechanical) of combustibles and oxidizers with various cementing and special additives that create a certain effect.

By susceptibility Explosives for explosive transformation are divided into:

• 
  primary;
• 
  secondary;
• 
  tertiary.

The tertiary category includes explosives with weakly expressed explosive properties. Typical representatives of tertiary explosives can be considered ammonium nitrate and an emulsion of an oxidizer in fuel (emulsion explosives). Tertiary explosives are practically safe to handle; it is very difficult to initiate a decomposition reaction in them. Often these substances are classified as non-explosive. However, complete disregard for their explosive properties can lead to tragic consequences. When tertiary explosives are mixed with flammable materials or when sensitizers are added, their explosiveness increases.

2.3. General information about detonation, features

detonation of industrial explosives

According to the hydrodynamic theory, detonation is considered to be the movement of a chemical transformation zone along an explosive, driven by a shock wave of constant amplitude. The amplitude and speed of movement of the shock wave are constant, since the dissipative losses accompanying the shock compression of the substance are compensated by the thermal reaction of the transformation of the explosive. This is one of the main differences between a detonation wave and a shock wave, the propagation of which in chemically inactive materials is accompanied by a decrease in the speed and parameters of the wave (attenuation).

Detonation of various solid explosives occurs at speeds from 1500 to 8500 m/s.

The main characteristic of explosive detonation is the detonation speed, i.e. the speed of propagation of the detonation wave along the explosive. Due to the very fast speed of propagation of the detonation wave along the explosive charge, changes in its parameters [pressure ( R), temperature ( T), volume ( V)] in the front, the waves occur abruptly, as in a shock wave.

Scheme for changing parameters ( P,T,V) during detonation of a solid explosive is shown in Figure 2.1.

Figure 2.1 - Scheme of changes in parameters during detonation of solid explosives

Pressure ( R) increases abruptly at the front of the shock wave, and then begins to gradually fall in the chemical reaction zone. Temperature T also increases abruptly. but to a lesser extent than R, and then, as the chemical transformation proceeds, the explosive increases slightly. Volume V occupied by the explosive, due to the high pressure, decreases and remains practically unchanged until the end of the transformation of the explosive into detonation products.

Hydrodynamic theory of detonation (Russian scientist V.A. Mikhalson (1890), English scientist physicist D. Chapman, French scientist physicist E. Jouguet), based on the shock wave theory (Yu.B. Khariton, Ya.B. Zeldovich, L.D. Landau), makes it possible, using data on the heat of transformation of explosives and on the properties of detonation products (average molecular weight, heat capacity, etc.), to establish a mathematical relationship between the speed of detonation, the speed of movement of explosion products, the volume and temperature of detonation products.

To establish these dependencies, generally accepted equations are used that express the laws of conservation of matter, momentum and energy during the transition from the initial explosive to its detonation products, as well as the so-called Jouguet equation and the equation of state of detonation products, expressing the relationship between the main characteristics of the explosion products. According to Jouguet's equation, in a steady process, the detonation speed D equal to the sum of the speed of movement of detonation products behind the front  and speed of sound With in detonation products:

D =  +s. (2.1)

For detonation products of “gases” that have a relatively low pressure, the well-known equation of state of ideal gases is used:

PV=RT (2.2)

Where P- pressure,

V – specific volume,

R– gas constant,

T- temperature.

For detonation products of condensed explosives L.D. Landau and K.P. Stanyukovich derived the equation of state:

PV n =const , (2.3)

Where P And V- pressure and volume of explosion products at the moment of their formation;

n= 3 - exponent in the equation of state for condensed explosives (polytropic index) at explosive density >1.

Detonation speed according to hydrodynamic theory

, (2.4)

Where - heat of explosive transformation.

However, the values ​​obtained from this expression
are always overestimated, even taking into account the variable, depending on the explosive density, value " n" Nevertheless, for a number of estimates it is useful to use such a dependence in general form:

D = ƒ(p O )
, (2.5)

Where p O– explosive density.

For approximate estimates of the detonation rate of a new substance (if it is not possible to determine it experimentally), the following relation can be used:

, (2.6)

Where is the index " X" refers to an unknown (new substance), and " THIS" - to the reference one with a known detonation velocity at equal densities and assumed close values ​​of the polytrope ( n).

Thus, the detonation speed depends on three main characteristics of an explosive: the heat of its explosion, the density and composition of the explosion products (via “ n" And " M * »).

The transformation of explosives in the form of detonation is the most desirable, since it provides a significant rate of chemical transformation and creates the highest pressure and density of explosion products. This provision can be observed under the condition formulated by Yu.B. Khariton:

   , (2.7)

Where  - duration of chemical transformation of explosives;

 - dispersion time of the initial explosive.

Yu.B. Khariton introduced the concept of critical diameter, the value of which is one of the most important characteristics of an explosive. The relationship between the reaction time and the dispersion time allows us to give a correct explanation of the presence of a critical or limiting diameter for each explosive.

If we take the speed of sound in the explosion products through “ With", and the charge diameter through "d", then the time of dispersal of the substance can be approximately determined from the expression

. (2.8)

Considering that the condition for the possibility of detonation  >, can be written down >, where does the critical diameter come from, i.e. the smallest diameter at which stable detonation of an explosive can still occur will be equal to:

d cr =с. (2.9)

From this expression it follows that any factor that increases the time of dispersal of a substance should contribute to detonation (shell, increase in diameter). There will also be factors that accelerate the process of chemical transformation of explosives in a detonation wave (the introduction of highly active explosives - powerful and susceptible).

Experimental measurements show the asymptotic nature of the increase in detonation velocity with increasing charge diameter. Starting from the maximum charge diameter d etc, with further increase, the speed practically does not increase (Figure 2.2).

Figure 2.2 - Detonation speed dependence D on charge diameter d h :

D AND-ideal detonation speed; d cr– critical diameter; d etc– maximum diameter.

The critical geometric characteristics of the charge also depend on the density of the explosive and its homogeneity. For individual explosives, the density decreases with increasing density. d cr, up to the region close to the density of a single crystal, where, as A.Ya. Apin showed, a slight increase can be observed d cr(for example for TNT).

If the diameter of the explosive charge is significantly higher than the critical one, then an increase in the explosive density leads to an increase in the detonation speed, reaching a limit at the maximum possible explosive density.

For ammonium nitrate explosives, the critical diameters are relatively large. In commonly used charges, the effect of density is dual: an increase in density initially leads to an increase in detonation speed ( D), and then with a further increase in density, the detonation speed begins to fall and detonation may decay. For each ammonium nitrine explosive, depending on the conditions of its use, there is its own “critical” density. Critical is the maximum density at which (under given conditions) stable detonation of an explosive is still possible. With a slight increase in the “charge” density above the critical value, detonation fades.

Critical density ( p cr) (maximum points on the curve D= ( O ) ) is not a constant of a particular industrial explosive, determined by its chemical composition. It changes with changes in the physical characteristics of the explosive (particle sizes, uniform distribution of component particles in the mass of the substance), the transverse dimensions of the charges, the presence and properties of the charge shell.

Based on these ideas, secondary explosives are divided into two large groups. For type 1 explosives, which include mainly powerful monomolecular explosives (TNT, hexogen, etc.), the critical diameter of stationary detonation decreases with increasing explosive density. For type 2 explosives, on the contrary, the critical diameter increases with decreasing porosity (increasing density) of the explosive. Representatives of this group are, for example, ammonium nitrate, ammonium perchlorate, and a number of mixed industrial explosives: ANFO (ammonium nitrate + diesel fuel); emulsion explosives, etc.

For type 1 explosives, the detonation speed D cylindrical charge with diameter d increases monotonically with increasing density  O explosive. For type 2 explosives, the detonation velocity first increases as the porosity of the explosive decreases, reaches a maximum, and then decreases until detonation stops at the so-called critical density. Non-monotonic dependency behavior D= ( O ) for mixed (industrial) explosives is associated with difficult filtration of explosive gases, absorption of detonation wave energy by inert additives, multi-stage explosive transformation of individual components, incomplete mixing of the explosion products of components and a number of other factors.

It is believed that as the porosity of an explosive decreases, the detonation velocity first increases due to an increase in the specific explosion energy Q V, because D~
, and then decreases for the reasons stated above.

2.4. Main characteristics of explosives.

Explosive sensitivity

Since the appearance of explosives, their high danger under mechanical and thermal influences (shock, friction, vibration, heating) has been established. The ability of explosives to explode under mechanical influences was defined as sensitivity to mechanical influences, and the ability of explosives to explode under thermal influences was defined as sensitivity to thermal influences (thermal impulse). The intensity of the impact, or, as they say, the magnitude of the minimum initial impulse required to initiate an explosive decomposition reaction, can be different for different explosives and depends on their sensitivity to a particular type of impulse.

To assess the safety of production, transportation and storage of industrial explosives, their sensitivity to external influences is of great importance.

There are various physical models of the occurrence and development of an explosion under local external influences (impact, friction). In the study of explosive sensitivity, two concepts about the causes of explosions under mechanical influences have become widespread: thermal and non-thermal. Everything about the causes of an explosion due to thermal influence (heating) is clear and unambiguous.

According to non-thermal theory– the excitation of an explosion is caused by the deformation of molecules and the destruction of intramolecular bonds due to the application of certain critical pressures of uniform compression or shear stresses to the substance. In accordance with thermal theory When an explosion occurs, the energy of the mechanical action dissipates (dissipates) in the form of heat, leading to heating and ignition of the explosive. In creating ideas about the thermal nature of the sensitivity of explosives, the ideas and methods of the theory of thermal explosion, developed by academicians N.N. Semenov, Yu.B. Khariton and Ya.B. Zeldovich, D.A. Frank-Kamenetsky, A.G. Merzhanov.

Since the rate of thermal decomposition of explosives, which determines the possibility of a reaction occurring via the thermal explosion mechanism, is an exponential function of temperature (Arrhenius law: k=k O e - E/RT), then it becomes clear why not the total amount of dissipated heat, but its distribution over the volume of the explosive should play a decisive role in the processes of initiation of an explosion. In this regard, it seems natural that the various paths through which mechanical energy is converted into heat are unequal to each other. These ideas were the starting point for the creation of a local-thermal (focal) theory of explosion initiation. (N.A. Kholevo, K.K. Andreev, F.A. Baum, etc.).

According to the focal theory of explosion excitation, the energy of mechanical action does not dissipate uniformly throughout the entire volume of the explosive, but is localized in individual areas, which, as a rule, are physical and mechanical inhomogeneities of the explosive. The temperature of such areas (“hot spots”) is much higher than the temperature of the surrounding homogeneous body (substance).

What are the reasons for the appearance of a hot spot during mechanical action on an explosive? It can be considered that internal friction is the main source of heating of viscoplastic bodies that have a homogeneous physical structure. High-temperature hot spots in liquid explosives under shock-mechanical influences are mainly associated with adiabatic compression and heating of gas or explosive vapors in small bubbles scattered throughout the volume of the liquid explosive.

What is the size of the hot spots? The maximum size of hot spots that can lead to an explosive explosion under mechanical stress is 10 -3 - 10 -5 cm, the required temperature increase in the hot spots reaches 400-600 K, and the heating duration ranges from 10 -4 to 10 -6 s.

L.G. Bolkhovitinov concluded that there is a minimum bubble size that is capable of collapsing adiabatically (without heat exchange with the environment). For typical conditions of mechanical shock, its value is about 10 -2 cm. Film footage of the collapse of the air cavity is presented in Figure 2.3

Figure 2.3 - Stages of bubble collapse during compression

What determines the sensitivity of explosives and what factors influence its value?

Such factors include the physical state, temperature and density of the substance, as well as the presence of impurities in the explosive. As the temperature of an explosive increases, its sensitivity to impact (friction) increases. However, such an obvious postulate is not always clear in practice. As proof of this, an example is always given when charges of ammonium nitrate with the addition of fuel oil (3%) and sand (5%), in the middle of which steel plates were placed, exploded when shot by a bullet at normal temperature, but did not explode under the same conditions with preliminary heating the charge to 60 0 S. S. M. Muratov pointed out that in this example the factor of change in the physical state of the charge when the temperature changes and, what is especially important, the conditions of inter-boundary friction between the moving object and the explosive charge are not taken into account. The effect of temperature is often offset by other temperature-related factors.

Increasing the density of an explosive usually reduces sensitivity to impact (friction).

The sensitivity of explosives can be specifically adjusted by introducing additives. To reduce the sensitivity of explosives, phlegmatizers are introduced, and to increase them, sensitizers are introduced.

In practice, you can often encounter such sensitizing additives - sand, small rock particles, metal shavings, glass particles.

TNT, which in its pure form produces 4-12% explosions when tested for impact sensitivity, gives 29% explosions when 0.25% sand is added to it, and 100% explosions when introduced with 5% sand. The sensitizing effect of impurities is explained by the fact that the inclusion of solid substances in explosives contributes to the concentration of energy on solid particles and their sharp edges upon impact and facilitates the conditions for the creation of local “hot spots”.

Substances with a hardness less than the hardness of explosive particles soften the impact, create the possibility of free movement of explosive particles and thereby reduce the likelihood of energy concentration in individual “points”. Low-melting substances, oily liquids with good enveloping ability and high heat capacities are usually used as phlegmatizers: paraffin, ceresin, petroleum jelly, various oils. Water is also a phlegmatizer for explosives.

2.5. Practical assessment of explosive sensitivity

For practical assessment (determination) of sensitivity parameters, there are various methods.

2.5.1. Explosive sensitivity to thermal

impact (impulse)

The minimum temperature at which, over a conventionally specified period of time, the heat input becomes greater than the heat removal and the chemical reaction, due to self-acceleration, takes on the character of an explosive transformation, is called the flash point.

The flash point depends on the explosive test conditions - sample size, device design and heating rate, therefore the test conditions must be strictly regulated.

The period of time from the start of heating at a given temperature until the outbreak occurs is called the flash delay period.

The flash delay is shorter, the higher the temperature to which the substance is exposed.

To determine the flash point, which characterizes the sensitivity of an explosive to heat, use a device “to determine the flash point” (a sample of the explosive is 0.05 g, the minimum temperature at which a flash occurs 5 minutes after placing the explosive in a heated bath).

The flash point is for

The sensitivity of explosives to heating is more fully characterized by a curve showing the dependence

T av = ƒ(τ ass).

and in

Figure 2.4 - Dependence of flash delay time (τ set) on heating temperature ( O WITH) - schedule " A", and also the dependence in logarithmic form (Arrhenius coordinates) lgτ ass - ƒ(1/T, K)- schedule " V».

2.5.2. Sensitivity to fire

(flammability)

Industrial explosives are tested for susceptibility to the fire ray of a fire cord. To do this, 1 g of PVV is placed in a test tube mounted on a stand. The end of the OSHA is inserted into the test tube so that it is at a distance of 1 cm from the explosive. When the cord burns, the flame beam, acting on the explosive, can cause it to ignite. In blasting operations, only those explosives are used that do not give a single flash or explosion in 6 parallel definitions. Explosives that do not withstand such a test, such as gunpowder, are used in blasting operations only in exceptional cases.

In another version of the test, the maximum distance at which the explosive still ignites is determined.