Explosive substances

EXPLOSIVE SUBSTANCES (EN: explosives, blasting agents; DE: Sprengstoffe; FR: explosifs; ES: explosivos; RU: взрывчатые вещества) are the chemical compounds, or the mixtures of the substances, which are able, under the certain conditions, to perform the extremely rapid (explosive) self-propagating chemical transformation, with the release of the heat, and with the forming of the gaseous products.

There may be explosive the substances or mixtures of any aggregate state. There have obtained the widespread usage within the mining craft the so-called condensed explosive substances, which are characterized with the high voluminous concentration of the thermal energy. Unlike the usual fuels, which require the inflow of the gaseous oxygen from the outside for their combustion, such explosive substances yield the heat as the result of the intramolecular processes of the decay, or of the reactions of the interaction between the constituent parts of the mixture, between the products of their decomposition or gasification. The specific character of the yield of the thermal energy, and of the conversion of this energy into the kinetic energy of the products of the explosion, and into the energy of the shock wave, determines the major field for the usage of the explosive substances, as the means for the crushing and destruction of the solid media (mainly of the rocks), and of the built structures, and for the moving of the crushed mass (see within the "Explosive technology" article).

Depending on the character of the external impact, the chemical transformations of the explosive substances proceed: in case of the heating below the temperature of the spontaneous ignition (of the flash), there proceeds the comparatively slow thermal decomposition; in case of the ignition, there proceeds the combustion with the movement of the zone of the reaction (of the flame) throughout the substance at the constant speed with the order of magnitude of 0.1-10 centimetres per second; in case of the shock-wave impact, there proceeds the detonation of the explosive substances.

The classification of the explosive substances. There exist several distinctive features for the classification of the explosive substances: according to the major forms of the transformation, according to the purpose, and according to the chemical composition. Depending on the character of the transformation under the conditions of the usage, they sub-divide the explosive substances into the propelling substances (or the gunpowders), and into the brisant substances. They use the substances of the first type in the mode of the combustion, for example, within the firearms and rocket engines, and they use the substances of the second type in the mode of the detonation, for example, within the munitions and at the blasting works. The brisant explosive substances, which are used within the industry, are called the industrial explosive substances. Usually, they categorize as the explosive proper only the brisant explosive substances. In the chemical sense, the classes, which have been listed, may be comprised of the same compounds and substances, but which have been differently processed, or which have been taken in the different proportion during the mixing.

According to the susceptibility to the external impacts, they sub-divide the brisant explosive substances into primary and secondary. They categorize as primary the explosive substances, which are able to explode within the small mass during the ignition (the rapid transition of the combustion into the detonation). These substances are also significantly more sensitive to the mechanical impacts, than the secondary substances. There is most easy to cause (initiate) the detonation of the secondary explosive substances using the shock-wave impact, while the pressure within the initiating shock wave must be with the order of magnitude of several thousands or tens of thousands megapascals. Practically, they perform this process with the help of the small masses of the primary explosive substances, which have been placed into the blasting cap, while the detonation within these masses is excited from the ray of the fire, and is transmitted through the contact into the secondary explosive substance. Because of this fact, the primary explosive substances are also called the initiating substances. Other types of the external impact (the ignition, spark, shock, friction) lead to the detonation of the secondary explosive substances only under the special and difficult to regulate conditions. According to this cause, the widespread and purposeful usage of the brisant explosive substances in the mode of the detonation within the civil and military explosive technology has been started only after the invention of the blasting cap as the device for the initiating of the detonation within the secondary explosive substances.

According to the chemical composition, they sub-divide the explosive substances into the individual compounds and explosive mixtures. Within the substances of the first type, the chemical transformations during the explosion proceed in the form of the reaction of the monomolecular decay. The end products are the stable gaseous compounds, such as the nitrogen, carbon monoxide and carbon dioxide, and the vapours of the water.

Within the explosive mixtures, the process of the transformation comprises the two stages: the decay or gasification of the components of the mixture, and the interaction of the products of the decay (of the gasification) among themselves or with the particles of the non-decomposing substances (for example, of the metals). The most widespread secondary individual explosive substances belong to the nitrogen-containing aromatic, aliphatic heterocyclic organic compounds, including the nitro compounds (TNT, tetryl, nitromethane), to the nitroamines (RDX, HMX), to the nitroesters (nitroglycerin, nitroglycols, nitrocellulose, PETN). Of the inorganic compounds, there possesses the weak explosive properties, for example, the ammonium nitrate.

The diversity of the explosive mixtures may be reduced to the two major types: the mixtures, which are consisting of the oxidants and fuels, and the mixtures, within which the combination of the components determines the operating or technological qualities of the mixture. The mixtures of the fuel with the oxidizer are calculated with such intention, that the significant portion of the thermal energy is released during the explosion as the result of the secondary reactions of the oxidation. As the components of these mixtures, there may be both the explosive and non-explosive compounds. The oxidants, as a rule, release during the decomposition the free oxygen, which is necessary for the oxidation (with the release of the heat) of the combustible substances, or of the products of their decomposition (of the gasification). Within the certain mixtures (for example, which contain the metallic powders as the fuel), there may be also used as the oxidizers the substances, which are relea sing not oxygen, but the oxygen-containing compounds (the vapours of the water, the carbon dioxide). These gases react with the metals with the release of the heat. The tritonal is the example of such mixture.

They use as the fuels the natural and synthetic organic substances of various types, which emit during the explosion the products of the incomplete oxidation (the carbon monoxide), or the combustible gases (hydrogen, methane), and the solid substances (soot). The explosive substances, which are containing the ammonium nitrate as the oxidant, are the most widespread type of the brisant explosive mixtures of the first type. Depending on the type of the fuel, they, in their turn, are sub-divided into the ammonites, amatols, and ammonals. There are less widespread the chlorate and perchlorate explosive substances, within the composition of which there belong as the oxidants the potassium chlorate, and the ammonium perchlorate, the oxyliquits, which are the mixtures of the liquid oxygen with the porous organic absorber, and the mixtures on the basis of other liquid oxidants. There belong to the explosive mixtures of the second type the mixtures of the individual explosive substances, for example the dynamites; the mixtures of the TNT with the RDX or PETN (pentolite), which are most suitable for the producing of the cartridges-detonators.

Within the mixtures of the both types, besides the components, which have been listed above, depending on the purpose of the explosive substances, there may also be introduced other substances for the imparting of the certain operating properties to the explosive substance, for example, the sensitizers, which are increasing the susceptibility to the means for the initiating, or otherwise, the phlegmatizers, which are decreasing the sensitivity to the external impacts; the hydrophobic additives may be introduced for the imparting of the water resistance to the explosive substance; the plasticizers and the flame-extinguishing salts may be introduced for the imparting of the safety properties (see within the "Safety explosive substances" article). The major operating characteristics of the explosive substances (the detonating and energetic characteristics, and the physical-chemical properties of the explosive substances) depend on the recipe composition of the explosive substances, and on the technology of the manufacturing.

The detonating characteristic of the explosive substances includes the detonating ability, and the susceptibility to the detonating impulse. There depend on them the infallibility and reliability of the detonation. For each explosive substance with the given density, there exists such critical diameter of the charge, in case of which the detonation stably propagates throughout the entire length of the charge. There serve as the measure for the susceptibility of the explosive substances to the detonating impulse the critical pressure of the initiating wave, and the time of the action of this impulse, that is the magnitude of the minimal initiating impulse. They often express this magnitude in the units of the mass of some initiating explosive substance, or of the secondary explosive substance with the known parameters of the detonation. The detonation is excited not only during the contact detonation of the initiating charge. The detonation can also be transmitted through the inert media. This fact has the great significance for the blasthole charges, which comprise several cartridges, between which there emerge the partitions of the inert materials. Because of this fact, there is verified for the cartridged explosive substances the indicator of the transmission of the detonation at the distance through various media (usually through the air).

The energetic characteristics of the explosive substances. The ability of the explosive substances to perform the mechanical work during the explosion is determined by the reserve of the energy, which is released in the form of the heat during the explosive transformation. Numerically, this value is equal to the difference between the heat of the forming of the products of the explosion, and the heat of the forming (enthalpy) of the explosive substance itself. Because of this fact, the coefficient of the conversion of the thermal energy into the work is lesser for the metal-containing and safety explosive substances, which are forming during the explosion the solid products (the oxides of the metals, the flame-extinguishing salts) with the high heat storing capacity, than for the explosive substances, which are forming only the gaseous products. About the ability of the explosive substances to the local crushing or brisant action of the explosion, see within the "Brisance of the explosive substances" article.

The change of the properties of the explosive substances may proceed as the result of the physical-chemical processes, of the influence of the temperature, and humidity, under the impact of the unstable impurities within the composition of the explosive substances, and so on. Depending on the type of the sealed packing, they establish the warranty time for the storage or usage of the explosive substances, during which the normalized indicators of the explosive substances either must not change, or their change proceeds within the limits of the established tolerance.

The major indicator of the safety during the handling of the explosive substances is their sensitivity to the mechanical and thermal impacts. This sensitivity is usually evaluated experimentally within the laboratory installations according to the special methodologies. In association with the massive introduction of the mechanized methods for the movement of the large masses of the loose explosive substances, there are presented to them the requirements of the minimal electrization, and of the low sensitivity to the discharge of the static electricity.

The historical reference. The gunpowder (black powder), which has been invented within China (the 7th century), was the first of the explosive substances. Within Europe, the gunpowder is known since the 13th century. Since the 14th century, they used the gunpowder as the propelling agent within the firearms. During the 17th century (for the first time at one of the ore mines within Slovakia), they used the gunpowder at the blasting works within the mining craft, and also for the charging of the artillery grenades (of the bursting cannon balls). The explosive transformation of the gunpowder was excited using the ignition in the mode of the explosive combustion. During the 1884, there has been proposed by the French engineer Paul Vieille the smokeless powder. During the 18-19 centuries, there has been synthesized the series of the chemical compounds, which are possessing the explosive properties, including the picric acid, guncotton, nitroglycerin, TNT, and others, however, t heir usage as the brisant detonating explosive substances has become possible only after the discovery of the fuse with the mercury fulminate (of the blasting cap) by the Russian engineer D. I. Andrievsky (1865), and by the Swedish inventor Alfred Nobel (1867). Before this invention, within Russia, according to the proposal by N. N. Zinin and V. F. Petrushevsky (1854), nitroglycerin was used during the blasting, instead of the gunpowder in the mode of the explosive combustion. The mercury fulminate itself has been obtained yet during the end of the 17th century, and again by the English chemist Edward Howard during the 1799, but the ability of this compound to detonate was not known then. After the discovery of the phenomenon of detonation, the brisant explosive substances have obtained the widespread usage within the mining craft and military service. Among the industrial explosive substances, initially, according to the patents of Alfred Nobel, there have obtained the greatest dis tribution the gurdynamites, later the plastic dynamites, and the powdered mixed explosive substances with nitroglycerin. The explosive substances with the ammonium nitrate have been patented yet during the 1867 by I. Norbin and I. Olsen (Sweden), but their practical usage as the industrial explosive substances, and for the charging of the munitions, has been started only during the years of the 1st World War during the 1914-18. More safe and economic than the dynamites, during the 30-ies of the 20th century, they have started to be used on the ever larger scale within the industry.

After the Great Patriotic War of the 1941-45, the explosive substances with the ammonium nitrate, initially prevalently in the form of the thinly dispersed ammonites, have become the dominant type of the industrial explosive substances within the USSR. Within the other countries, the process of the massive replacement of the dynamites with the explosive substances with the ammonium nitrate has been started somewhat later, approximately since the middle of the 50-ies. Since the 70-ies, the major types of the industrial explosive substances are the granulated and water-containing explosive substances with the ammonium nitrate of the simplest composition, which are not containing any nitro compounds or other individual explosive substances, and also the mixtures, which are containing the nitro compounds. The thinly dispersed explosive substances with the ammonium nitrate have retained their significance mainly for the producing of the live cartridges-detonators, and also for the cert ain special types of the blasting works. The individual explosive substances, especially TNT, are widely used for the producing of the cartridges-detonators, and also for the prolonged charging of the water-flooded boreholes, both in the pure form (the granulated TNT), and within the highly water-resistant explosive mixtures, both granulated and of the suspension type (water-containing). For the springing works within the deep petroleum boreholes, they use RDX and HMX.