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The combustion rate increases with increasing degree of unsaturation in the molecule: alkanes, alkenes, alkadienes, alkynes. As the chain length increases, this effect decreases, but the combustion rate of air mixtures for n-hexene is approximately 25% higher than for n-heisane.
The combustion rate is reduced by the value Lv - gasification heat. It tends to be low for liquids and relatively high for solids. Respectively, solids tend to burn much slower than liquids.
The burning rate depends on temperature and pressure. With increasing temperature or pressure, the burning rate increases greatly. If the combustion reaction proceeds at a very high speed, then a phenomenon called an explosion occurs. An explosion can occur from contact with a fire of heated petroleum product, the vapors of which are mixed with air. This mixture becomes explosive when it contains a certain amount of fuel.
The burning rate and costs associated with reducing flammability depend not only on the type of resin, but also on the presence and amount of fillers, the characteristics of the material structure (for example, a multi-layer structure using balsa) and the use of heat intumescent coatings.
The burning rate at constant pressure can be determined by burning a charge in a chamber with a nozzle. If the surface of the charge is constant, then the pressure remains almost unchanged during combustion. In this case linear speed combustion can be calculated as the ratio of the half-thickness of the wall (thickness of the roof) of the powder tube to the burning time. The advantage of the determination method is the proximity of combustion conditions to the conditions of real use, the disadvantage is the need to prepare relatively large samples of gunpowder. It is simpler to perform in a laboratory and does not require large quantities of gunpowder to determine the burning rate at constant pressure of a cylindrical charge armored from the side surface, ignited from the end, with recording the burning time of a section of a certain length or the movement of the combustion zone over time. The first device, developed for this purpose by Varga, was a glass tube with a diameter of about 30 mm, sealed at the bottom. The tube has two side outlets at the top. One of them connects the tube to a pressure gauge, the other to a large-volume container into which gases enter during combustion, due to which an almost constant pressure is maintained in the tube. The tube is closed at the top with a rubber stopper, through which passes a thin glass tube sealed at the bottom for a thermocouple and a second tube for current conductors, ending with an ignition spiral made of thin wire.
The burning rate of hydrazine increases approximately in proportion to the square root of the pressure. Above 10 atm, the data are reproduced worse and the average values tend to some constant value independent of pressure. Above a certain pressure, the liquid does not ignite from a hot wire.
The burning rate generally increases with increasing pressure. This is quite natural in the case when exothermic reactions during combustion occur in the gas phase. An increase in pressure, increasing the absolute rate of these reactions, brings the zone of their occurrence closer to the surface of the condensed phase, increases the temperature gradient near this surface and, accordingly, heat transfer to the latter.
The burning rate, if determined in tubes of the same diameter, increases with increasing pressure, not proportionally to it, but more slowly. It is assumed that this is due to heat exchange with the walls of the tube. If the burning rate at each pressure is measured using a tube diameter equal to five times the critical diameter, then the data obtained show (for 97 7% hydrazine) in the pressure range 0 5 - 1 ag that the burning rate is directly proportional to pressure. Comparing the dependence of the combustion rate on the combustion temperature, changed by dilution with inert gases (taking into account the effect of this dilution on thermal conductivity), we obtain an activation energy equal to 30 kcal/mol.
The burning rate of a fire, as these experiments have shown, increases with increasing combustible load.
Methods for determining the burning rate of pyrochemical compositions are based on recording the time of the beginning and end of combustion of a column of a composition of a certain length. This fixation is carried out visually (with atmospheric pressure), using thermocouples, a photographic recorder or a movie camera.
There are two ways to quantify the burning speed: linear speed in mm/s and mass speed it, expressed in the dimension g/cm2-s; the latter shows the amount of composition burned in 1 second of a unit of burning surface. The mass burning rate can be calculated using the formula Um = 0.1 u*d where d- composition density in g/cm3.
As already indicated, combustion proceeds evenly only if the composition is sufficiently compacted. To assess the degree of compaction, it is necessary to determine the compaction coefficient /C, which is the quotient of the practically achieved density d to the maximum density of the composition dmax the latter is found by calculation based on the density of the components of the composition:
dmax = ..............100...................
A/d1 + b/d2 + ... n/dn
where di, d1 d2, . . ., dn, - component density;
a, b, . .., p - content of these components in the composition in %.
For most compressed compounds, the compaction coefficient ranges from 0.7-0.9. Bulk Density powder formulations is 40-60% of dmax.
For different compositions, the linear burning rate varies quite significantly: from tenths of mm/s (for smoke compositions) to 20-30 mm/s (for fast-burning lighting compositions).
From What factors does the burning rate of cosgavas depend on?
The speed of the most difficult physical and chemical process- combustion - is determined by the speed of individual (elementary) chemical reactions and the processes of diffusion and heat transfer from one reaction zone to another.
The intensity of heat transfer is largely determined by the temperature difference in different reaction zones. Compositions that have the highest flame temperature are, as a rule, the fastest burning.
However, existing exceptions to this rule show that high flame temperature is only one of the factors determining the burning rate of compositions.
1 The porosity of the composition will be characterized by the value (-TO). Consequently, the porosity of the compressed compositions lies in the range of 0.3-0.1.
The burning rate largely depends on the presence of low-melting or highly volatile components in the composition. If they are present, the heat that under other conditions would cause a sharp increase in temperature in the reaction zone is spent on melting or evaporating these substances.
This largely explains the fact that low-melting organic substances (resins, paraffin, stearin, etc.) when introduced into binary mixtures (oxidizer - megall) sharply reduce the burning rate.
Leading in the combustion process are highly exothermic (flame) reactions.
However, the speed of a multi-stage combustion process as a whole is determined primarily by the speed at which the most difficult and slow-moving stage of the process occurs; These are endothermic chemical processes.
In many cases, the combustion rate of compositions is determined by the rate of decomposition of the oxidizer.
An objective indicator characterizing the ease of decomposition of an oxidizing agent can be the partial pressure of oxygen above it at different temperatures.
As is known, the rate constant chemical reaction TO, increases extremely strongly with increasing temperature according to the law
Where IN- preexponential factor;
E- activation energy in kcal/g-mol (kJ/g-mol);
R- gas constant.
But knowing the maximum temperature and activation energy of the process does not give us a real opportunity to calculate the combustion rate, since combustion is a set of chemical reactions occurring under non-isothermal conditions.
Of course, knowledge of the intermediate stages of the combustion process is very important. But to “clarify them, a very complex experiment is required; at present, these data for most pyrocompositions, unfortunately, are not available.
Moving on to the consideration of the actual material, it should be pointed out that the burning rate of the compositions is determined both by their recipe (chemical factors) and by the combustion conditions (physical factors).
Under chemical factors influence is understood:
1) individual properties of the components of the composition;
2) the quantitative relationship between them;
3) accelerating action of catalytic additives. From an examination of the data on the burning rate of highly compacted compositions at atmospheric pressure and 20 ° C, it follows that the fastest burning are double mixtures of alkali (or alkaline earth) metal nitrates with magnesium, containing 40-65% magnesium. Compositions containing zirconium burn even faster.
Compositions with aluminum, subject to the same grinding of the metal, burn much more slowly than compositions with magnesium 1. One of the reasons is the large difference in the boiling point of magnesium and aluminum: 1100 and ~2300°, respectively. Compositions containing beryllium, boron or cream as the main fuel burn slowly. The higher the ignition temperature of the fuel, the lower the other equal conditions burning rate of the composition. Perhaps there is also a relationship between the burning rate of the composition and the Pilling and Badworth numbers for the metal contained in the compositions (as well as B and Si). For fast-burning metals, Mg and Zr, these numbers are respectively 0.81 and 1.45; for Be, Si and B these numbers are greater and equal to 1.75, respectively; 2.04 and 4.08.
At practical use In mixtures containing aluminum, incomplete combustion occurs. The combustion of aluminum droplets in a gas flow has been studied by many authors. Much attention was paid to the combustion process of the ternary system:
МН4СlO4+ organic fuel+A1.
A.F. Belyaev draws the following conclusions:
1. Increasing the concentration of aluminum powder (in a ternary mixture, approx. auto of this book) leads to an increase in the burning time of its particles.
2. An increase in combustion time occurs due to deterioration of the gas composition of the oxidizing medium and as a result agglomerations(italics by the author), which leads to enlargement of burning aluminum particles.
3. Agglomerates, in addition to aluminum, contain a significant amount of products of partial decomposition of organic fuel. The burning time of agglomerates depends on the amount of aluminum they contain.”
The aluminum droplets located in the gas flow (in the smoke-gas zone of the flame) are covered with a layer of oxide film and access of the oxidizing gas to the not yet oxidized metal is difficult. Damage to the oxide film on a drop of metal can be caused by:
1) melting Al2O3 (at 2030° C);
2) by piercing it from the inside with metal steam at a temperature close to its boiling point (~2300°C). Consequently, the combustion of aluminum droplets occurs very intensely when the flame temperature exceeds 2200-2300° C.
* One of possible ways activating the combustion of aluminum particles - covering them with magnesium film.
ric double mixtures (NH4C104+ organic matter) at 20 atmospheres. 25 different organic solids were studied.
Mixtures with organic acids burned the slowest - 3.0 mm/s, mixtures with alcohols and hydrocarbons burned faster, 4.5-4.8 mm/s, mixtures with amines and nitro compounds burned even faster, 5.4-6.0 mm /s, then mixtures with nitramines - 7.0 mm/s; the mixture with ferrocene burned much faster than all others - 15 mm/s.
The authors of the work came to the conclusion that in in this case the burning rate does not depend on the calorie content of the mixtures, but is determined by the strength of the weakest bond in the fuel molecule; bond strength decreases to row C-C, C-NH2, C- NOz, N-NO2. The authors explain the high combustion rate of the mixture with ferrotsane (C5H5)2Fe by the catalytic effect of iron oxide formed as a result of combustion.
On the issue of the dependence of the maximum combustion rate on the ratio of components in the mixture, the following considerations are expressed.
The compositions are divided into two groups, in the first of which the maximum combustion rate lies near the stoichiometric ratio between the components (K = 0.7/0.9), and for the second group it is sharply shifted towards excess fuel (up to K1< O,1).
The first group includes compositions in which the main fuel is an organic binder, and the metal powder plays only the role of an additive.
The second group includes compositions where the main fuel is metal powder, and the organic binder is used only as an additive that improves the mechanical properties of the charge.
In accordance with this, the combustion rate of double oxidizer-metal mixtures increases rapidly with increasing content of metal fuel in the composition (of course, up to a certain limit; for magnesium this limit is 60-70%). This is to a certain extent due to the increase in the thermal conductivity of the composition with an increase in the metal content in it.
Zirconium compositions burn stably with a zirconium content of up to 80%.
According to A.F. Belyaev, double mixtures KS104-W burn stably with a tungsten content of up to 90-95%. One must think that the value of the limiting metal content at which the mixture is still capable of combustion is determined not only by the thermochemistry of the process or the ease of oxidation of the metal, but also by its density; it increases along the Mg- series >Zr->-W. When burning compositions containing the A1-Mg alloy, a peculiar phenomenon is observed: first, magnesium evaporates from the particles of the alloy and burns in vapors, and only later does aluminum burn.
*TO - provision of the composition with an oxidizing agent.
At the same metal content, double mixtures of NaNO3 with magnesium burn faster than mixtures of NaClO3 with magnesium. Perhaps the reason for this is the exothermic interaction of the nitrate melt with magnesium in the condensed phase. A significant role here is also played by the fact that gas
Table 8.1
the environment in the case of nitrates will consist of a mixture of nitrogen oxides and oxygen, and in the case of chlorates - only oxygen.
Of mixtures that do not contain metallic fuels, many chlorate mixtures and black powder burn quickly. The works of A.F. Belyaev examine the influence of sulfur on the burning rate of black powder;
There is also work by Bentur et al. on the effect of various organic additives on the burning rate of gunpowder.
Mixtures of potassium nitrate with charcoal or iditol have an average burning rate.
Burning rate data various types compositions are given in table. 8.1.
Compositions with nitrates that do not contain metal powders burn in most cases slowly and with low intensity.
The burning rates of some chlorate and nitrate mixtures are shown in Table. 8.2.
End of work -
This topic belongs to the section:
A. A. Shidlovsky: Development of chemistry and physics of combustion
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PYROTECHNICS BASICS
Fourth edition, revised and expanded Approved by the Ministry of Higher and Secondary special education USSR as a teaching aid
GENERAL CONCEPT OF PYROTECHNIC PRODUCTS AND COMPOSITIONS
The word “pyrotechnics” comes from the Greek words: pir - fire and techne - art, skill. Pyrotechnics is the science of the properties of pyrotechnic (fire) compositions and products made from them and methods
COMBUSTION OF COMPOSITIONS
Highly exothermic chemical reactions can occur during combustion. The formation of a flame (or glow) observed in most cases is not, however, an indispensable sign of
REQUIREMENTS FOR PYROTECHNIC PRODUCTS AND COMPOSITIONS
The main requirement is to obtain the maximum special effect from the action of the pyrotechnic means. For various means the special effect is determined by various factors. This one
PURPOSE OF COMPONENTS
Pyrotechnic compositions include the following components: a) flammable; b) oxidizing agents; c) binders (cementants) - organic polymers that provide mechanical strength
POSSIBLE HIGH EXOTHERMAL REACTIONS
Any chemical reaction occurs with the breaking of bonds between atoms and the formation of other new bonds. Obviously, heat will be released when the bonds being broken are weak,
ABILITY TO BURN VARIOUS SUBSTANCES AND MIXTURES
In accordance with Berthelot's principle (it is certainly valid for highly exothermic reactions occurring at room temperature) any chemical system for which exothermism is possible
OXIDIZERS
A mixture of fuel and oxidizer is the basis of any pyrotechnic composition. The combustion of flammable substances in air usually proceeds more slowly than their combustion due to oxygen as an oxidizing agent.
SELECTION OF OXIDIZING AGENTS
The oxidizing agent must be a solid with a melting point of at least 50-60 ° C and have the following properties: 1) contain maximum quantity oxygen; 2) giving it away easily
PROPERTIES OF OXIDIZING AGENTS
The most important properties of oxidizing agents for pyrotechnics are: 1) density; 2) melting point; 3) temperature of intensive decomposition; 4) heat
HYGROSCOPICITY
Magnesium, calcium and sodium salts, which are highly soluble in water, as well as many ammonium salts, are very hygroscopic. The amount of water absorbed by salts from the air depends on humidity and temperatures
TECHNICAL REQUIREMENTS
The following requirements are imposed on oxidizing agents: 1. Maximum content of the main substance (usually at least 98-99%). 2. Minimum moisture content (no more than 0.1-0.2%).
HIGH CALORIE FUEL
The greatest amount of heat during combustion (see Table 3.1) is released by the following 12 simple substances (elements): metals - lithium, beryllium, magnesium, calcium, aluminum, titanium and zirconium;
TECHNICAL REQUIREMENTS FOR METAL POWDERS
1. Maximum content of active (unoxidized) metal (for different varieties Mg and A1 powders from 90 to 98%). 2. The content of iron and silicon impurities is no more than tenths of a percent.
PRODUCTION OF METAL POWDERS
The production of metal powders is carried out by the following methods: 1) mechanical grinding; 2) spraying liquid metals; 3) reduction of oxides; 4) el
INORGANIC COMBUSTIBLE MEDIUM CALORIE RATINGS
In compositions that do not emit a large amount of heat, the following can be used as combustibles: manganese, tungsten, molybdenum, chromium, antimony, and in smoke compositions - zinc, iron and other simple substances
ORGANIC COMBUSTIBLE
Liquid hydrocarbons - gasoline, kerosene, fuel oil, oil and other petroleum products are used in incendiary mixtures that burn due to oxygen in the air. In table 3.6 describes some of them
ROLE OF LINKERS. SPROCK STRENGTH TEST
Achieve high strength compositions only by using high pressure when pressing, it is not always possible or appropriate. In order to increase the strength of the product, they add
FACTORS AFFECTING STRENGTH
The strength of the compressed product depends on: 1) the properties of the main oxidizer-fuel mixture; 2) on the properties of the binder and its quantity in the composition; 3) depending on the degree of grinding
Some properties of organic combustible substances
Name and formula of the substance Density, g/cm3 Conditional molecular weight Amount of substances a in g, burned due to 1 g of oxygen
PRINCIPLES OF CALCULATION OF PYROTECHNIC COMPOSITIONS
The basic principles for calculating double mixtures were given in late XIX century by Russian pyrotechnician P. S. Tsytovich. He proceeded from the assumption that fuel burns completely due to oxygen oxide
DOUBLE MIXTURES
Example 1. The combustion reaction of a mixture containing potassium perchlorate and magnesium can be expressed by the equation KC104+4Mg=KCl+4MgO. (5.1) For 139 g of potassium perchlorate there is
TRIPLE AND MULTICOMPONENT MIXTURES
Often, ternary mixtures can be considered as consisting of two double mixtures containing the same oxidizing agent. However, the presence of two different fuels sometimes dramatically changes the direction
COMPOSITIONS WITH NEGATIVE OXYGEN BALANCE
In many cases special pyrotechnic effect increases if not only an oxidizer, but also air oxygen takes part in the combustion process of fuel. This happens because
METAL CHLORIDE COMPOSITIONS
In such compositions, the role of an oxidizing agent is performed by an organochlorine compound, and the active metal powder is combustible. In this case, enough oxidizing agent should be taken so that the contained
COMPOSITIONS WITH FLUORIDE BALANCE
The calculation of compositions with a fluorine balance is similar in principle to the calculation of metal chloride compositions. The role of oxidizing agents is performed by fluorine compounds (fluorides of low-active metals or organofluorine
CALCULATION OF HEAT OF COMBUSTION
Calculations are carried out on the basis of Hess’s law, which is formulated as follows: the amount of heat released during a chemical reaction depends only on the initial and final state of the system and does not depend
EXPERIMENTAL DETERMINATION
To determine the heat of combustion, a certain portion of the composition is burned in a calorimetric bomb. The amount of heat released is determined as the product of the heat capacity of the system (water + equipment) n
RELATIONSHIP BETWEEN THE PURPOSE OF COMPOSITIONS AND THE HEAT OF THEIR COMBUSTION
Based on experimental data, it is possible to establish a connection between the purpose of the compositions and the amount of heat released during their combustion (in kcal/g): Photo mixtures. .........................
GASEOUS COMBUSTION PRODUCTS
Education gaseous substances combustion is observed for almost all types of pyro compositions. Of the actually used compositions, apparently only iron-aluminum t does not produce them at all during combustion.
DETERMINATION OF COMBUSTION TEMPERATURE
Determining the combustion temperature of pyrochemical compositions is of great importance, since it is a criterion for evaluating existing compositions and facilitates the creation of new, more advanced compositions. Them
EXPERIMENTAL DETERMINATION
The combustion temperature of most flame pyrocompositions lies in the range of 2000-3000 ° C. Measurement of the flame temperature of such compositions is most often carried out using optical methods.
Types of optical pyrometers
A vanishing filament pyrometer is a visual photometer in which the brightness of the light emitted by the body under test (flame) is measured by comparing it with the brightness of a standard filament
SENSITIVITY OF COMPOUNDS
The initial impulse is the amount of energy required to initiate a combustion reaction (explosion) in a pyrotechnic composition. The less this amount of energy is, the more sensitive
DETERMINATION OF SENSITIVITY TO THERMAL INFLUENCES
Determination of the auto-ignition temperature The auto-ignition temperature is the lowest temperature to which the composition must be heated in order for it to occur.
Additional tests
For difficult-to-flammable compositions, additional tests are carried out on their ability to ignite from various igniting compositions. At the same time, they gradually move from weaker to stronger
DETERMINATION OF SENSITIVITY TO MECHANICAL IMPACTS
In the process of manufacturing and compacting compounds, no matter how carefully these operations are carried out, friction inevitably arises, and the possibility of shocks and impacts cannot be ruled out. In artillery
Impact Sensitivity Determination
To determine sensitivity, the same equipment is used as when testing high explosives, i.e. vertical pile drivers and roller instruments (GOST 4545-48). The pyro composition is tested with a load of 10 kg
FACTORS AFFECTING THE SENSITIVITY OF COMPOSITIONS TO THE INITIAL PULSE
The amount of energy that needs to be imparted to the system for a rapid chemical reaction to occur in it is determined, on the one hand, by the possibilities of its own energy, and on the other hand, by the internal
COMBUSTION MECHANISM
The combustion process of compositions can be divided into three stages: initiation (ignition) ignition combustion. Initiation is usually carried out using those
Catalytic additives
Until now, the problem of catalysis during the combustion of pyrotechnic compositions has not been completely resolved. There are works on studying the influence of various catalytic additives on the combustion rate of model
Physical factors
1. Density. The effect of density on the combustion rate of the composition is determined by the fact that as it increases, the possibility of penetration of hot gases into the composition decreases and thereby slows down the burning process.
EXPLOSIVE PROPERTIES OF COMPOSITIONS
Most pyrochemicals are designed to burn evenly, and therefore it is desirable that they have minimal or no explosive properties. Production of compositions, and
Oxidizing agent + aluminum powder
Oxidizing agent and its content in the composition, % Expansion in the Trauzl block, cm8; quantity of mixture 10 g Detonation speed, m/s KS104-66 V
Expansion in the Trauzl block in cm3 depending on the initial impulse; amount of composition 20 g
Composition (unpressed), % Bifird cord Detonator cap No. 8 Potassium perchlorate - 85 Charcoal - 15
PHYSICAL AND CHEMICAL STABILITY OF COMPOSITIONS
When storing pyrotechnic products, physical and chemical changes occur in the compositions. In some cases, they are so significant that the products become unfit for use, but
PHYSICAL CHANGES
Physical changes in compositions are most often caused by their hydration. In this case, partial dissolution of the components of the composition occurs, a change in the density and shape of the compressed charge.
Compositions containing magnesium or aluminum powders and inorganic oxidizing agents
The decomposition of these compositions in the presence of moisture begins with corrosion of metal powders: Mg+2H20=Mg(OH)2+"H2; A1+ZH20=A1(OH)3+1.5H2.
Compositions that do not contain metal powders
When such compounds are moistened, in most cases no significant chemical changes occur. The exception is mixtures that contain two water-soluble salts that can react
METHODS FOR DETERMINING HYGROSCOPICITY AND CHEMICAL RESISTANCE
A preliminary assessment of the durability of newly created pyro-compositions is called a component compatibility test. In some cases, the previously described procedure can be used for this purpose.
PERMITTED STORAGE LIFE
Humidification of the compositions usually leads to a decrease in the special effect. When burning, wet compositions develop a lower temperature and emit less light. Reduced metal “activity”
LIGHTING COMPOSITIONS AND PRODUCTS
With the current state of military equipment, the importance of troop operations at night has increased immeasurably. Night darkness, although it makes it difficult to conduct offensive and defensive operations, nevertheless allows
Artillery means
A non-parachute lighting projectile is similar in design to an incendiary thermite-segment projectile (see Fig. 15.8), in which instead of incendiary elements there are up to 1.6 lighting elements
Combined arms assets
The most common of the combined arms weapons are illumination cartridges (non-parachute and parachute, fired from a rocket launcher, and jet). In Fig. 11.5 shows the device
LIGHT CHARACTERISTICS OF LIGHTING COMPOSITIONS AND MEANS
1. The unit of luminous intensity is a new candle (sv), equal to 1/600,000 of the luminous intensity obtained from 1 m2 of the surface of a black body in the normal direction at the solidification temperature of platinum (1 sv = 1.005 m
THERMAL AND LUMINESCENT RADIATION
The radiation of solid and liquid bodies obeys the laws of black body radiation (hereinafter referred to as the black body, see § 6 in Chapter VI). At high temperatures (500° C and above) it increases significantly. * This is a calculation
SPECIAL REQUIREMENTS FOR LIGHTING COMPOSITIONS; DOUBLE MIXTURES
When burning a weight unit of the composition, the maximum amount of light energy should be released, and it is desirable that the main part of it be released in the spectral region to which it is most sensitive
Thermochemical characteristics of binary mixtures
Oxidizing agent in the combustion mixture Heat of combustion of the mixture, kcal/g Ba (N03)2 BaSO4 Ba (N03)
Lighting characteristics of double mixtures of barium nitrate with aluminum powder
Composition No. Aluminum content, % Density, g/cm3 Burning speed, mm/s Luminous intensity, thousand ev (cd) Specific light sum
MULTI-COMPONENT LIGHTING COMPOSITIONS
The actual recipe for the composition is created based on a given linear burning rate, while trying to obtain a specific light sum value of at least 20-25 thousand light s/g. To the double oxide mixtures described above
Recipes for multi-component lighting compositions in black and white
Composition No. Oxidizing agent Metallic fuel Binder Other components Used in lighting products
Self-curing compounds
Recently, a number of compositions have been proposed that do not require pressing under high pressure in the manufacture of products. The solidity of the composition in the product is achieved as a result of its self-hardening, p
FACTORS AFFECTING THE EFFECTIVENESS OF LIGHTING COMPOSITIONS AND PRODUCTS
The intensity of light, the spectral composition of the radiation, the duration and uniformity of burning of torches (or stars) depend on numerous factors. Lighting performance indicators of the product
BRIEF INFORMATION ABOUT PYROTECHNIC IR EMMITTERS
Pyrotechnic infrared emitters found application in rocket and space technology on unmanned targets used for testing missiles with IR homing heads, in tracking systems
Characteristics of pyrotechnic IR emitters
Dimensions, mm Output by Index Quantity
Energy quantities and units
Term Definition Unit of measurement Healing energy (lu Energy transferred by radiation J
PHOTOMETERING AND RADIOMETERING OF FLAMES OF PYROTECHNIC COMPOSITIONS
The basis of practical photometry and radiometry of flames is the measurement of illumination or energy illumination (irradiance) E of the corresponding receivers. By OS
PHOTO LIGHTING COMPOSITIONS
These compositions are used to produce short-term flashes of light with a luminous intensity of several million to several billion candles and a duration of up to tenths of a second. In contrast
NIGHT AIR PHOTOGRAPHY
Work to create new highly effective reconnaissance means is very important. It is known that abroad they are creating complex systems reconnaissance, including various technical means: photo
PHOTO MATERIALS
Photographic materials (aerial films) used in aerial photography are varied: they differ in photosensitivity, contrast, spectral sensitivity, photographic latitude and time
PHOTO AIR BOMBS
The main requirement for a photo bomb is the maximum light intensity of the flash when it explodes. Subject to coordination with the operation of the camera and the high sensitivity of the film, this is up to
PHOTO CARTRIDGES
For shooting from medium and low altitudes (from 0.5 to 2.6 km), photo-lighting cartridges (photo cartridges) are used; they are transported in multi-barreled cassettes, from which they are fired at the moment of photographing.
Main characteristics of photo lighting cartridges
Cartridge type Length and diameter mm Total weight g Number of photostm g Maximum luminous intensity
PHOTOS. FACTORS AFFECTING THE LIGHTING CHARACTERISTICS OF FLASHES AND THE PROPERTIES OF PHOTOGRAPHIC COMPOSITIONS
Photo lighting compositions are divided into two groups: photo mixtures - mechanical mixtures of finely ground metal powders (aluminum, magnesium and their alloys) and oxygen-containing yuols (KS104, Ba(NO3) 2, etc.
METHODS FOR DETERMINING CHARACTERISTICS OF FLASHES
TO quantitative characteristics photo flashes refer to the maximum luminous intensity of the flash in candles; duration of the entire flash t in seconds; time from the beginning of the outbreak to the onset of max.
LIGHT SIMULATORS, PHOTOCHARGES-MARKERS
Light and smoke effects accompanying the explosion of small charges of black powder, pyrotechnic compositions, and sometimes weak explosives with smoke-enhancing additives have long been used
TRACERS
With the adoption of small-caliber rifled weapons by the armies of a number of countries, great difficulties arose in adjusting fire, since when shooting at long ranges it is extremely difficult to estimate distances
Purpose of tracers and requirements for them
During flight, tracers (tracers) leave a fire (or smoke) trail (path) and make the flight path of a projectile (bullet, aerial bomb) visible. A tracer is a piece of pyrotechnic
Tracer bullets
There are actually tracer bullets; armor-piercing-tracer (AP) and armor-piercing-incendiary-tracer (APT). A tracer bullet (Fig. 13.1) is a clad shell in which
Artillery shells
The designs of projectile tracers are very diverse. In Fig. Figure 13.3 shows a mechanical ignition tracer with a simplified Bofors fuse. At the moment of firing, the striker 8 settles under
Projectiles with self-destruction through a tracer
In order to prevent unexploded anti-aircraft shells from falling to the ground, they are usually equipped with devices for self-destruction in the air if the shell does not hit the target. Self-destruction
Tracers for guided missiles (PC) and aerial bombs. Special types of tracers
Tracers for guided missiles and bombs are subject to the additional requirement of minimum smoke generation so that the smoke plume does not impair visibility of the tracer or conditions
TRACE COMPOSITIONS
The following requirements apply to tracer compositions. First of all, they must: 1) release the maximum amount of light energy during combustion; 2) burn from a certain sky
Ignition compositions for tracers
In this case, mixtures that produce little gas phase and burning slags are used as igniting compositions, for example, a mixture of 80% BaO2, 18% Mg and 2% binder. Burning speed
FACTORS AFFECTING THE EFFECTIVENESS OF TRACE COMPOSITIONS AND TRACERS
The characteristics of tracer compositions and agents depend on the following main factors: composition recipe, particle size of components, degree of compaction, block diameter, shell material, temperature
ROUTE VISIBILITY AND CALCULATION OF THE REQUIRED FLAME LIGHT POWER
The eye's perception of a luminous point located at a great distance depends primarily on the general illumination of the area and the brightness of the background against which it (the point) is observed. Brightness background
TRACER TESTS
The quality of tracers is characterized by burning time, luminous intensity and flame color (dominant wavelength and saturation). To measure these characteristics, the same equipment is used as
ALARM SYSTEMS. REQUIREMENTS FOR COMPOSITIONS
Compositions of signal lights are intended to give signals at night, as well as during the day. The most common alarm system is three-color - with red, yellow and
CHARACTER OF FLAME RADIATION
The ideal would be to recognize the radiation of the flame, which would fall entirely on any one part of the spectrum. In this case, the radiation would be monochromatic and the flame color would be pure
DEVELOPMENT OF RECIPES FOR COMPOSITIONS AND BASIC REQUIREMENTS FOR THEIR COMPONENTS
1. The amount of energy released during torching of the composition must be sufficient to excite or ionize the atoms or molecules in the flame. Sufficiently powerful color radiation
COMPOSITIONS OF YELLOW FIRE
To produce a yellow flame in pyrotechnics, only atomic sodium radiation is used. The sodium salts included in the composition should easily dissociate at high temperatures and have
COMPOSITIONS OF RED FIRE
The red flame is created exclusively by the introduction of strontium compounds into the composition. The glow of atomic strontium cannot be used, since its emission occurs in the short-wavelength part of the speck
COMPOSITIONS OF GREEN FIRE
Green flames in pyrotechnics are most often obtained using barium compounds. Atomic barium produces a number of lines in different parts of the spectrum, and therefore its radiation cannot be used
COMPOSITIONS OF BLUE AND WHITE FIRE
Compositions of blue fire that, when burned, produce a flame of sufficient brightness and pronounced blue, are still unknown. Blue flames are obtained almost exclusively from radiation
TEST METHODS
Special tests of signal stars consist of determining the luminous intensity and color of their flame. Luminous intensity is determined using photoelectric lux meters using the same method as
INCENSIBLE PRODUCTS AND INSTANTIABLE COMPOSITIONS. BASIC REQUIREMENTS FOR COMPOSITIONS
Unlike other pyrotechnics, incendiary ammunition (shells, aerial bombs, etc.) belongs to the group of primary-purpose ammunition. Incendiary agents are used by all
Incendiaries
1. Aviation means: small-caliber projectiles (fragmentation-incendiary-tracer (FZT), armor-piercing incendiary (AP) and armor-piercing incendiary-tracer (APT) and bullets (BZ and BZT), as well as an air bomb
Incendiary compositions
According to their state of aggregation, they are divided into solid, liquid and liquid-viscous. In some cases, to enhance the incendiary effect of ammunition, solid and liquid (or liquid) are used simultaneously.
Ignition and combustion of liquid fuels
The combustion of gasoline, kerosene and other liquid hydrocarbons occurs in the gas phase. Combustion can only occur when the concentration of fuel vapor in the air is within certain limits.
THERMITE-IGNITER COMPOSITIONS
The basis of these compositions is iron-aluminum thermite, which is included in them in quantities from 40 to 80%. Thermite is a mechanical mixture of coarse aluminum powder and iron scale (Fe
ALLOY "ELECTRON" AND ITS APPLICATION
The “electron” alloy has found wide application for the manufacture of electron-thermite bomb casings (Fig. 15.9) and electron-thermite incendiary elements for artillery shells. Approximate composition
MIXTURES BASED ON PETROLEUM PRODUCTS NAPALM
These mixtures are divided into the following main groups: 1) liquid (unthickened) petroleum products; 2) cured flammables; 3) liquid-viscous (thickened) incendiary mixtures;
PHOSPHORUS AND ITS COMPOUNDS
Phosphorus, its solutions and compounds with sulfur (sulfides) are usually used to ignite flammable materials. The advantage of white phosphorus over other incendiary substances
FLUORINE HALOID COMPOUNDS
Free fluorine reacts extremely vigorously with organic substances; this releases a large amount of heat and ignites flammable materials. However, the use of free fluorine
OTHER FLAMRIABLE SUBSTANCES AND MIXTURES
Of the simple substances, in addition to magnesium and phosphorus, alkali metals - potassium and especially sodium - have found use in incendiary agents. The advantage of sodium metal over other igniters
METHODS FOR TESTING INCHANT COMPOSITIONS
Heat is transferred to the ignited object during combustion of the composition, either with the help of solid or liquid hot slag, or by direct exposure to flame. The total amount of heat,
COMPOSITIONS OF MASKING SMOKES
Smoke camouflage agents are used to camouflage the location of friendly troops, as well as to smoke (blind) enemy troops in order to hinder their combat operations. Smoke managers
GENERAL INFORMATION ABOUT AEROSOLS
Colloidal systems consist of a dispersion medium and a substance crushed in it - the dispersed phase; if the dispersion medium is air, the colloidal system is called an aerosol.
METHODS FOR OBTAINING AEROSOLS.
Smokes and mists are obtained using dispersion methods or condensation methods. The first method comes down to crushing the substance by grinding it, splashing it or spraying it with an explosion. Zatra
COMPOSITIONS OF MASKING SMOKES AND REQUIREMENTS FOR THEM
The following requirements are imposed on these compositions: 1) the smoke obtained from three combustions of pyrochemical compositions must have a high covering power and be sufficiently stable in the air; 2)
COLORED CLOUDS AND METHODS OF OBTAINING THEM
For signaling, smoke clouds of four colors are mainly used: red, yellow, green and blue (violet). There are indications of possible use for signaling
DYES
The following requirements are imposed on organic dyes: 1) they must sublimate quickly at 400-500 ° C; 2) their sublimation should be accompanied by minimal decomposition of the paint
COMPOSITIONS OF COLORED SMOKES
Sublimation of dyes is carried out due to the so-called thermal mixture, consisting of an oxidizing agent and a fuel. The thermal mixture must release heat in the amount necessary to transfer
OPERATING REQUIREMENTS
When developing a specific charge solid fuel In addition to energy characteristics, it is necessary to take into account other properties of the fuel. Usually for given dimensions, the law of change of rods
OXIDIZERS
The choice of oxidizer largely determines the properties of the fuel. Substances that, when mixed with combustible materials, produce high-calorie mixtures, the combustion of which produces gases, are used as oxidizing agents.
ORGANIC AND METAL FLAMMABLES
From the point of view of fuel energy, combustible binders must contain the maximum amount of hydrogen, have a low heat of formation and high density. Of particular interest are the mountains
GAS-FREE COMPOSITIONS
Gas-free (more precisely, low-gas) compositions are used to equip various pyrotechnic retardants, as well as in some special heating products. In addition, they are used in
FLAMMABLE COMPOSITIONS AND REQUIREMENTS FOR THEM
These compositions serve to ignite the main pyrotechnic compositions (lighting, smoke, solid rocket fuel, etc.). The action of the ignition composition is to heat the surface
IGNITION COMPOSITIONS FOR ROCKET ENGINES
The reliability of a rocket engine largely depends on the availability effective system ignition. Black powder based igniters proved unsuitable for ignition
GAS-GENERATOR COMPOSITIONS
The production of small quantities of gas should be classified as purely pyrotechnic operations. Gas-generating pyrotechnic products (cartridges) are used in many cases: for pressurizing fuel tanks,
High nitrogen gas generator compositions according to percentage data
Composition No. NHiNO, Nitroguanidine Ammonium bichromate Other substances
OTHER TYPES OF COMPOUNDS
Pyrotechnic compositions used for various special purposes are also known. Sometimes, in their recipes, they are quite close to incendiary, illuminating, or other types already described
APPLICATION OF PYROTECHNIC COMPOSITIONS IN THE NATIONAL ECONOMY
The use of pyrochemicals in industry, agriculture, in space, in scientific research, during filming, as well as when launching fireworks and fireworks, it becomes more and more every year
COMPOSITIONS FOR PRODUCING CHEMICALS
Thermite compounds are currently used in a wide range of applications. They are used to produce a number of carbon-free metals, including Ti, V, Cr, Mn, Co, Ni, Zr, Mo, W, etc.
USE OF ENERGY OF PYROTECHNIC COMPOSITIONS
The heat released when compounds burn is used for many different purposes. Thermite compounds as a source of energy. The use of thermite compounds for welding rails is well known. In on
MATCH COMPOSITIONS
Currently (l972) all over the world, mainly so-called safety matches are produced, which ignite only when rubbed against the grease of a matchbox. World production of joint ventures
FIREWORKS COMPOSITIONS
These compositions are very diverse. Great value when making fireworks, they have not only composition recipes, but also the design of the fireworks product. The main types of fireworks
BASICS OF TECHNOLOGY AND EQUIPMENT FOR PYROTECHNIC PRODUCTION
Modern pyrotechnic production is a complex complex of production departments and workshops, connected into a single technological flow, in which the specificity is clearly expressed
PREPARATION OF COMPONENTS
Components arrive at pyrotechnic plants in a wide variety of closures. Thus, M.g, A1, AM alloy powders are supplied in metal closure; zirconium - in metal closure or in
Technical characteristics of the cabinet
Loading surface in m2 ...... 2.5 Heating surface in m2 ....... 6.27 Residual pressure in kg/m2 ...... 2.63 (20 mm Hg) Slab dimensions in mm........ 730x610
PREPARATION OF COMPOSITIONS
Mixing pyrotechnic compositions is one of the most important operations. The composition must be homogeneous. Samples of compounds taken from different places in the mixer bowl, should not differ in chemical
COMPACTING COMPOSITIONS
Compaction and shaping of the compounds can be done by pressing, screwing, pouring, and in some cases, manual stuffing. In photobombs, the degree of compaction of the composition should be insignificant
EQUIPMENT AND ASSEMBLY OF PRODUCTS
When equipping and assembling products, the following operations are performed: a) preparing parts and assemblies for equipment; b) assembly of parts and assemblies; V) final finishing products (about
The main characteristic of combustion is the burning rate. There are normal (linear) and mass combustion rates.
Under normal speed understand U n. – linear speed of movement of the combustion front in the direction perpendicular to the combustion surface:
Un=ℓ/τ [cm/s]
Mass burning rateU m is the amount of the initial combustible system burned per unit time from a unit surface of the combustion front.
Um=Un × p0[g/cm2×s]
When talking about the burning rate, it is necessary to distinguish between combustion itself and the surface spread of combustion. When a powder column burns, the condensed phase usually takes the shape of a cone, and the combustion surface turns out to be significantly larger than the original one.
(Afterburning of flammable products of incomplete combustion due to oxygen in the air leads to an increase in temperature and, as a consequence, causes acceleration of the spread of combustion over the surface of the charge).
When powder elements burn in the barrel, ignition usually occurs over the entire free surface.
The weight amount of gases formed during combustion is equal to:
Q=Um × s
If the surface of a particle decreases as it burns, then this shape is called depressed(for example, a ball, a cube), if the surface increases – progressive(checker with channels).
IN
Rice. 3. Burning a stick of gunpowder
Combustion of condensed explosive systems
During the combustion of condensed BC charges, one should distinguish three main processes:
ignition from an ignition source at the end of the charge;
layered combustion;
ignition of the charge from the side surface (in the absence of armor on the side surface).
It is very difficult to theoretically describe such a complex heterogeneous process as combustion. But if we make a number of assumptions:
The reaction takes place entirely at the maximum combustion temperature,
The substance first completely evaporates, and then reactions occur in vapors, etc., then the process can be described.
According to normal combustion theory the speed of propagation of the chemical reaction zone is determined by a combination of two processes:
● transfer of heat from the chemical reaction zone to the heating zone due to thermal conductivity and
● mass transfer of a substance from the heating zone to the chemical reaction zone due to diffusion.
By jointly solving the equations of thermal conductivity and diffusion, we obtained the expression for the mass combustion rate:
U m =
λ – thermal conductivity coefficient;
–thermal effect of the oxidation reaction (per unit mass of gas);
m – reaction order;
T r – combustion temperature;
E – activation energy;
T 0 – initial temperature;
W T Г – reaction rate at combustion temperature.
W T Г =ρ о ·z·exp(-E/RT g).
WITH 
Diagram of temperature distribution and reaction during stationary combustion of volatile explosives according to Belyaev.
Dependence of burning rate on various factors
The linear and mass burning rate depends on:
geometric dimensions of the charge (diameter);
external conditions (temperature and pressure);
GS dispersion (particle size);
presence of impurities.
For mixed systems, they additionally influence:
chemical nature of the components, their thermophysical characteristics;
the ratio of components and the dispersion of each of them.
Combustion occurs in as a result of heat transfer to the adjacent layer, released in the reacting layer. Simultaneously with the release of heat, losses it into the environment.
Combustion is leaking stationary only if the amount of heat transferred to the adjacent layer and heat loss are balanced by heat gain due to the reaction.
If the total heat transfer becomes greater than the heat gain, then combustion is no longer possible.
As the diameter of the charge decreases, the amount of heat released per unit time decreases in proportion to the square of the diameter. Heat transfer also decreases, but more slowly; it is proportional to the surface of the heat sink, i.e. first degree of diameter. At a certain diameter value, heat gain cannot compensate for heat loss and combustion dies out.
Critical combustion diameter They call the minimum diameter at which combustion is still possible. The critical diameter is not constant, it depends not only on the nature of the explosive, but also on the combustion conditions, primarily on pressure, initial temperature, charge density and crystal dispersion.
● Increasing temperature and pressure reduce the critical combustion diameter, increase the combustion rate, and reduce losses to the environment.
The combustion of solid combustible substances in the initial stage of combustion is called combustion. This type of combustion is characterized by instability of combustion, a relatively low temperature in its zone, a small size of the flame and a small area of the source.
Temperature environment increased slightly, only directly at the source of combustion.
The initial stage of a fire (ignition) can be eliminated with primary fire extinguishing agents. If the fire is not extinguished immediately, the heat released during combustion will intensify the combustion process. In this case, the size of the flame will increase and combustion will become stable. At the same time, the ambient temperature increases and intensifies the effect of thermal energy emitted by the combustion center. And eliminating such a fire requires a large number of primary fire extinguishing agents, water and foam jets.
If the fire extinguishing agents used are insufficiently effective or if they are used late, the combustion continues to develop and its zone increases over a significant area. At the same time, the temperature increases, a significant amount of thermal energy is released, and convection air flows increase. Under these conditions, deformation and collapse of structures are possible.
To extinguish such a fire requires a lot of effort and powerful means.
The rate of combustion of materials during a fire is different and depends on the combustion conditions, the composition of the combustible substance and the intensity of the transfer of heat from the combustion zone.
There are two burning rates: weight and linear. Weight velocity is the weight (int, kg ) substance burned per unit time (inmin, h ). The linear speed of combustion of solid combustible substances is the speed of fire propagation (inm/min ) and the rate of growth of the fire area (inm 2 /min ).
Burning rate solids is unstable and depends on the ratio of their surface to volume, humidity, air access and other factors.
Based on the data obtained from studying a number of cases of fires on river vessels, the linear speed of fire spread is from 0.05 to 2.5 m/min, and the growth rate of the fire area is from 0.3 to 50.0 m 2 /min.
At the beginning of a fire, approximately during the first 2-3 minutes, there is an intensive increase in the area of its source on passenger ships up to 41-44 m 2 /miya. This is explained by the fact that during this period a lot of time is spent on gathering the ship’s crew and there is no active fire fighting yet. In the next 10 minutes, when stationary water and foam extinguishing agents are put into operation, the growth of the fire area slows down to approximately 6-7 m 2 /min.
Research has established that a passenger ship can be destroyed by fire within 20-30 minutes if the organization of its extinguishing is imperfect.
The linear speed of fire spread determines the area of the fire, and the degree of burning of everything that can burn in this area determines the duration of the fire.
The linear speed of burning of a liquid is the height of its layer (in mm, cm) burned out per unit of time (in min, h).
The speed of fire flame propagation when igniting flammable gases ranges from 0.35 to 1.0 m/sec.
Burnout rate is the amount of fuel burned per unit time per unit combustion area. It characterizes the intensity of combustion of a liquid during a fire. It must be known to determine the estimated duration of a fire in tanks, the intensity of heat release and temperature regime fire, etc.
The rate at which a liquid burns out is not constant and depends on its initial temperature, the diameter of the tank, the level of liquid in it, the content of non-flammable liquids in it, wind speed and other factors.
In tanks with a diameter of up to 2 m, the rate of liquid burnout increases with its increase. It is practically the same in tanks with a diameter greater than 2 m.
The burnout rate of liquid spilled on the surface is approximately the same as in tanks, if the thickness of its layer is significant
For example, the oil burnout rate is 25 cm/h , gasoline -40 cm/h, oil -20 cm/h.
During flaming combustion of an oil product in a cargo tank, the liquid is heated.
Heating of the liquid from the upper to the lower layers occurs in the mass of heavy oils at a speed of 30 cm/h, and in the mass of light oils - from 40 to 130 cm/h.
When burning, kerosene and diesel fuel warm up slowly, and a heated layer of the same temperature does not form.
Oil and fuel oil are heated deep down very intensively, the temperature of the layer is almost always above 100° C. The temperature of the heated layer of oil can reach 300° C and heat the bottom layer of water in the reservoir.
The temperature of the heated layer of gasoline is usually below 100 ° C, and therefore the bottom layer of water in the container does not warm up.
Heating liquid in tanks may cause it to boil or erupt. Boiling refers to the transition of a large number of small droplets of water contained in a petroleum product into steam. In this case, foam forms on the surface of the liquid, which can overflow over the side of the tank. By release we mean the instantaneous transition of water at the bottom of the tank into steam. In this case, increased pressure is created, under the influence of which the burning liquid is ejected from the reservoir.
The boiling of petroleum products in most cases is due to the presence of water in them and, less often, a cushion of water at the bottom of the tank. All petroleum products containing water, which heats up above 100° C during combustion, are capable of boiling.
Oil and fuel oil can boil only with a certain moisture content in them: for oil - 3.3% and for fuel oil - above 0.6%."
Engine oil and heavy gasoline can boil when you add a bottom layer of water.
Cooling the walls of the tank with water jets and periodically introducing a sprayed jet of water onto one third or a quarter of the combustion surface prevents boiling and overflow of heated gasoline or oil from it.
If (the height of the free side exceeds the thickness of the heated layer by more than 2 times, then when a sprayed jet of water is introduced into the combustion zone iB, boiling is observed, but liquid overflowing from the container does not occur.
Dark oil products are capable of release - oil containing 3.8% moisture, fuel oil containing up to 0.6% moisture.
The release of a burning liquid can occur if: there is water under the layer; When burning, the liquid heats up deep; the temperature of the heated layer is higher than the boiling point of water.
The release occurs at the moment when the oil product at the water-oil product interface heats up above 100 ° C (approximately 150-300 ° C). After the first release, the layer of oil product heated to a higher temperature comes into contact with water again and a powerful release occurs.
The release in height, range and affected area depends on the diameter of the tank. In a tank with a diameter of 1.387 m, the mass of burning oil thrown out ranges from 51 to 145 kg at a height of 10 to 20 times the height of the tank.
The duration of the ejection process from the container ranges from 3 to 60 seconds. The onset time of the release varies, ranging from 2 to 5 hours 30 minutes from the start of combustion for different petroleum products in different containers.
Typically, a release is accompanied by numerous releases of petroleum product. The release of all the petroleum product in one take-off is a rare occurrence and is observed when the remaining petroleum product layer is small and its viscosity is significant.
A characteristic sign of the onset of emission is the occurrence of vibrations in the walls of the container, accompanied by noise and an increase in the size of the flame.
Larger diameter containers release faster than small diameter containers. The size of the water cushion layer does not affect the emission.
The normal combustion rate of a gas and steam-air mixture is the speed at which the boundary surface between the burned and unburned gases moves relative to the unburned gas, which is at rest in close proximity to the combustion surface.
- this is a set of simultaneously occurring physical processes (melting, evaporation, ionization) and chemical reactions of oxidation of a flammable substance and material, accompanied, as a rule, by light and thermal radiation and the release of smoke. Combustion is based on the interaction of a combustible substance with an oxidizing agent, mainly air oxygen.
However, combustion can be carried out without access to air (oxygen), if the composition of the combustible mass (environment) includes an oxidizing agent in the form of an impurity or an integral part of the molecule. In industrial conditions or rocket technology, combustion can be carried out in an atmosphere of oxidizing gases such as fluorine, chlorine, nitrogen oxides and others.
Some substances (powdered titanium and zirconium) are capable of burning in an atmosphere of nitrogen and carbon dioxide, which are not traditional oxidizers.
Depending on the method of supplying the oxidizer, there are:
- diffusion combustion when the reagents (fuel and oxidizer) were not mixed before the start of combustion, and their mixing occurs during the combustion process due to diffusion;
- homogeneous combustion when the reagents were mixed without a phase interface before combustion began;
- heterogeneous combustion when the reactants are in different state aggregates (solid + gas, solid + liquid) or there is an interface between them (solid + solid, immiscible liquid + liquid). Heterogeneous combustion is often referred to as diffusion combustion.
- combustion, the rate of which is limited by the rate of a chemical reaction, is called kinetic combustion. Since the rate of chemical interaction is, as a rule, higher than the rate of diffusion, kinetic combustion proceeds at the maximum rate for a given system (deflagration, detonation).
In case of fire it is noted mixed type combustion. Depending on the speed, combustion can be slow (smoldering), normal (deflagration) and explosive (explosion), turning into detonation (detonation).
In appearance, combustion can be flaming or flameless.
Flameless burning can occur as a result of a deficiency of the oxidizer (smoldering) or at low pressure of saturated vapors of a combustible substance (combustion of refractory metals and coke).
According to the mechanism of development, combustion can be thermal, in which the cause of self-acceleration of oxidation reactions is an increase in temperature, and autocatalytic (chain), when acceleration of the process is achieved by the accumulation of intermediate catalytic products (active centers). Autocatalytic combustion occurs at relatively low temperatures. When certain concentrations of intermediate catalytic products are reached, autocatalytic combustion can transform into thermal combustion. In this case, the combustion temperature increases sharply.
Combustion can occur and develop spontaneously, spontaneously (fire), but it can be specially organized and expedient: energy combustion (for the purpose of obtaining thermal or electrical energy) And technological combustion (blast furnace process, metallothermy, synthesis of refractory inorganic compounds, etc.).
Combustion is characterized by such quantities as: temperature, speed, completeness, composition of products. Having data on the combustion mechanism and its characteristic features, it is possible to increase the combustion rate and temperature (combustion promotion) or reduce them until combustion stops (combustion inhibition).
Sources: Basic combustion characteristics. Maltsev V.M., Maltsev M.I., Kashporov L.Ya. -M., 1977; Combustion processes in chemical technology and metallurgy. Merzhanov A.G. -Chernogolovka, 1975; Physics of combustion and explosion. Khitrin L.N. -M., 1957.
