All labor protection measures were carried out in accordance with the system of labor safety standards and the rules for the safe operation of equipment.
Thermogravimetric and differential thermal analyzes were performed on a METTLER TOLEDO STARe TGA/SDTA 851e instrument.
The study of a number of characteristics and properties of powders was carried out in stages in accordance with standard methods:
The study of the physical-chemical and fire-hazardous properties of ultrafine powders according to the literature data;
Production of laboratory samples for all studies weighing 30g. ;
Carrying out a complex of necessary studies in accordance with the assignment.
Since some components are toxic and fire and explosion hazardous, most of the work was carried out under traction in compliance with all safety conditions: all equipment was grounded, tools made of fluoroplastic and porcelain, textolite or non-ferrous metal were used; substances were taken in minimal quantities; work with solvents near heating devices was not carried out. All work was carried out using personal protective equipment: cotton gown, cotton gloves, respirator "Petal". Fulfilled all safety requirements for protection against static electricity.
Characteristics of the used reagents and components in terms of toxicity and fire hazard
Aluminum powder ASD - 6
ALEX™ is a combustible metal powder and can form an open flame with a release of high energy, including when interacting with static electricity. Reactions can release hydrogen. Ways to extinguish the flame: use fire extinguishers designed to extinguish combustible metals. Avoid contact with water. Dangerous concentration - 5 mg/m3, MPC - 0.1 mg/m3. If it comes into contact with the mucous membrane of the eyes, it can cause necrosis. Use protective equipment as when working with flammable substances. Use respirators. Do not heat above 300°C.
Ammonium perchlorate
White powder. Hygroscopic. Density 1350 - 1430 kg/m3. It dissolves well in water. Practically insoluble in benzene, gasoline, dichloroethane, nitrobenzene, slightly soluble in acetone and ethyl alcohol. In terms of toxicity, the product is highly hazardous. MPC in indoor air is 1 mg/m3. With prolonged exposure to it on the body, changes are observed in the thyroid gland, lungs and kidneys. Ammonium perchlorate is resistant, and at temperatures up to 150 °C, at temperatures above 150 °C, decomposition of the product begins, at a temperature of 370 ± 30 °C, rapid decomposition occurs, which can end in a flash. Tvsp.= 550±50 °С, Qburn. = 18000-20700 kJ/kg. When wet, it is flammable; when dry, it is explosive. Tvos. = 390 °С; Ts-sun = 450°С; c = 250 g/m3. In case of fire, extinguish with sprayed water, air-mechanical foam.
The sensitivity of PCA to impact at H = 250 mm, P = 10 kg is 50% of explosions (on the K-44-I, headframe), the sensitivity to friction (on the I-6 device) at a load of 1535 kg/cm2 is 0% of explosions. Sensitivity to mechanical stress increases in the presence of impurities in it, and especially in mixtures with metal powder. By electrostatic properties, it belongs to the class of dielectrics. By sensitivity to an electric spark, it belongs to the fourth group of substances. Guaranteed shelf life for a fraction of more than 160 mm - three years, less than 160 mm - one and a half years.
Under laboratory conditions, ammonium perchlorate is stored in tightly closed glasses or in waxed paper bags at a temperature of 20 - 25 ° C with a relative humidity of 65%.
HMX product
White or grayish crystalline powder. Toxic. MPC in the air of working premises - 1.0 mg/m3, belongs to the second class in terms of toxicity, a highly hazardous substance.
Prolonged exposure to the human body leads to anemia and circulatory disorders, negatively affects the central nervous system.
The HMX product is a powerful explosive. Shock sensitivity with a load of 10 kg and a height of 250 mm is 84 - 100% of explosions; sensitivity to friction on the device K - 44 - III at the lower limit of 3115 kg s / cm3.
The NMX product is a combustible substance; if it catches fire, extinguish it with a carbon dioxide fire extinguisher and an asbestos blanket.
Product HMX - resistant, Tm. \u003d 272 - 280 ° C, decomposes at a temperature of 278 - 280 ° C, T vsp. = 291 °C.
The NMX product is not hygroscopic, it dissolves poorly in water, practically does not dissolve in benzene, toluene, in methyl and isobutyl alcohols, and is readily soluble in acetone. According to its electrostatic properties, it belongs to dielectrics, it is very strongly electrified. In terms of sensitivity to an electric spark, it belongs to the III group of substances. Under laboratory conditions, NMX should be stored in glass beakers with unground lids, the shelf life is ten years.
Rubber SKDM - 80
Rubber SKDM - 80 is a high-molecular, very viscous rubber with a density of 0.89 g/cm3, toxic properties of SKDM - 80 are due to the presence of butadiene.
The maximum permissible concentration of butadiene in the air is 100 mg/m3. Rubber SKDM - 80 belongs to the fourth class of danger. Rubber is stored in a polyethylene film at a temperature not exceeding 30 °C.
Shelf life is one year.
UDC 544.452
V.P. Sinditsky, A.N. Cherny, S.Kh. Zhuo, R.S. Bobylev
Russian University of Chemical Technology DI. Mendeleev, Moscow, Russia 125480, Moscow, st. Geroev Panfilovtsev, 20, bldg. one
COMBUSTION OF MIXTURES OF AMMONIUM PERCHLORATE WITH HIGH-CALORIE FUEL
The regularities of combustion of mixtures of ammonium perchlorate (APC) with high-calorie combustible aluminum, boron, and boron carbide have been studied. It has been shown that aluminum additions up to 40% do not increase the burning rate of PCA. In contrast to aluminum, boron additives at all studied contents (5-30%) significantly increase the burning rate of PCA, while boron carbide in small amounts (5%) reduces the combustion rate of PCA, and at a content of 13-30% behaves like boron, but with less efficiency. A mechanism for the combustion of mixtures is proposed.
Keywords: combustion, ammonium perchlorate, high-calorific fuel, aluminum, boron, boron carbide
Over the past 60 years, ammonium perchlorate (APC) has been used as the main oxidizer in composite solid propellants (SFRs). To improve the energy characteristics of TRT, various high-calorie fuels are introduced into their composition. The most effective among them are boron and aluminum. Fuels containing aluminum powders have been developed for a long time, which cannot be said about boron-containing compounds. The addition of boron to fuels based on ammonium perchlorate and polybutadiene polymer HTPB increases the burning rate significantly more than aluminum additions. In general, the literature presents rather scarce experimental data on the effect of boron on the ballistic characteristics of TPT; nothing is known about the combustion of compositions with boron derivatives, such as carbide and nitride. Meanwhile, these compounds can be formed intermediately during the combustion of fuels containing boron. The purpose of this work is to study the patterns of combustion of PCA binary mixtures with high-calorie combustible aluminum, boron and its compounds.
We used powdered aluminum grade ASD-6 with an average particle size of 4 µm, PCA fraction 7–11 µm, particle size of boron and boron carbide was 1–4 µm. Samples for combustion studies were prepared by pressing a crushed and well-mixed substance into plexiglass tubes with an inner diameter of 4 mm at a pressing pressure of 200 MPa. The charge density averaged 0.85 of the maximum theoretical density. Experiments on measuring the burning rate were carried out in a BPD-360 constant-pressure bomb with a volume of 1.5 liters in the pressure range of 0.115 MPa. The pressure was created with nitrogen. The charge placed in the bomb was ignited in a twisted spiral.
Thermodynamic calculations were carried out using the REAL program.
First of all, let us consider the influence of the ratio of fuel and oxidizer (excess ratio of oxidizer a) on the combustion temperature. According to calculations, the maximum combustion temperature of mixtures with boron (3690 K) is realized for the composition of 15% boron and 85% PCA, which is close to stoichiometry (13.3% B) (Fig. 1). Mixtures with boron carbide have lower
temperature. The maximum combustion temperature is also achieved for a mixture (15% B4C) close to stoichiometry (12.8% B4C). For mixtures with aluminum, the maximum combustion temperature (4500 K) is almost 1000 K higher than for mixtures with boron. It is noteworthy that this maximum is significantly shifted to the area of excess fuel: 40% A1 compared to 29% A1 for
Fig.1. Dependence of the adiabatic combustion temperature on the fuel content for mixtures of PCA^, PCA-B4C, and PCA-A1.
The addition of 10-30% aluminum to PCA increases the combustion temperature by 2 or more times, as evidenced by the brightness of the glow during combustion. However, at all studied pressures, fluctuations and pulsations of the gas flame are observed, indicating the presence of instability. The combustion process is an alternation of ignition and extinction of aluminum. Unlike pure PCA, mixtures with 10% A1 begin to burn already from 6 atm. However, a further increase in the aluminum content leads to a regular increase in the pressure of the lower combustion limit. Thus, a mixture with 40% Al burns steadily from 60 atm. It is striking that the addition of high-calorific fuel, significantly increasing the combustion temperature of the mixture, negatively affects the combustion rate (Fig. 2). The dependence of the burning rate of mixtures on pressure has two parts. mixtures,
containing 10-30% A1, in the region of low pressures (up to 50 atm) burn at close speeds with the index in the combustion law, similar to the index in the combustion law of pure PCA. The burning rate in this section is ~ 2 times less than the burning rate of PCA. In the next section, the combustion rate with pressure begins to grow faster (y>1), approaching the combustion rate of PCA at high pressures. A mixture with 40% Al burns stably only in the second section, and at rates comparable to those of pure PCA.
Pressure, atm
Fig.2. Pressure dependence of combustion rate for PHA-L1 (ASD-6) mixtures in comparison with PHA.
In contrast to aluminum, boron additions at all studied ratios are significantly
Pressure, atm
Fig.3. Combustion rate vs. pressure for PCA2 mixtures compared to PCA.
Compositions with boron stably burn in the entire studied pressure range. The flame is colored green. A mixture containing 5% boron starts burning at 6 atm. An increase in the boron content leads to a further decrease in the pressure of the lower combustion limit of mixtures. The dependences of the burning rate of mixtures also consist of several segments. At a low boron content (5 and 10%), the sections at low pressures demonstrate a transitional character and have an increased index in the combustion law.
Areas at high pressures have an index in the combustion law close to that of pure PCA, although the combustion rate increased by more than 2 times. In the case of a content of 20 and 30% boron, the upper section extends to a pressure of 5 atm.
The patterns of combustion of mixtures based on boron carbide are similar to the patterns of combustion of mixtures with boron, however, significant differences are also observed (Fig. 4). First of all, it should be noted that the addition of 5% B4C reduces the combustion rate of PCA in the entire studied pressure range, but at the same time significantly reduces the pressure of the lower combustion limit. Additives of 13-30% B4C increase the burning rate of mixtures similar to boron additives, although their efficiency is slightly lower. An important feature of the combustion of mixtures based on 13–30% boron carbide is that the main section of the dependence of the combustion rate on pressure with an index in the combustion law close to that of ammonium perchlorate has a break at pressures of 50–60 atm. The flame of mixtures with В4С is also colored green, however, at high pressures,
Pressure, at
Fig.4. Combustion Rate vs. Pressure for PCA-B4C Blends vs. PCA
The fact that mixtures with Al content up to 30% burn significantly more slowly than pure PCA indicates the absence of its interaction with PCA in the zone of influence. As is known, the combustion of PCA is controlled by the reaction of its decomposition at its surface temperature. If the metal does not react in this zone, since heat is required for its heating and melting, the combustion of such mixtures can be interpreted as the combustion of PCA with the addition of a "diluent". Indeed, the observed patterns of combustion are described using the k-phase model of Ya.B. Zel'dovich. The following values of the main thermophysical parameters of PCA (average = 0.365 cal/gK, DNpl = 60 cal/g) and aluminum (average = 0.245 cal/gK, DNpl = 96.3 cal/g) were taken for calculation. The surface temperature was taken equal to the PCA dissociation temperature according to the equation
the kinetic parameters of PCA decay were taken from .
Aluminum reacts with PCA decomposition/evaporation products in the gas zone away from the combustion surface. With an increase in pressure, the gas zone approaches the combustion surface and the heat flow begins to flow into the condensed phase. As a result, the combustion rate of the mixture begins to deviate from the k-phase combustion model. The combustion of such compositions is described by the Merzhanov-Dubovitsky model. At 40% aluminum content, the heat flow from the gas phase at high pressures compensates for the losses for heating and melting of the metal; as a result, the mixture burns at a rate close to that of PCA. The very high lower combustion limit of this mixture speaks in favor of the proposed combustion mechanism: at low pressures, the heat gain from the gas phase is small, and the losses for heating the inert additive are large.
Obviously, the main mechanism of the effect of boron in binary compositions with PCA is also an increase in heat gain from the gas phase. The calculation shows that the combustion of a stoichiometric composition is described by the Merzhanov-Dubovitsky model under the assumption that 200 cal/g of thermal energy is supplied from the gas phase, which is quite realistic.
Boron carbide is a heat-resistant substance; its oxidation in air begins at temperatures above 600°C. This leads to the fact that B4C begins to oxidize in the combustion wave at a greater distance from the surface than boron. As a result, the heat flux from the 5% B4C additive does not compensate for the heating losses of the additive in the condensed phase. However, at a higher content of the additive, the behavior of mixtures with B4C is similar to that of mixtures with boron. The difference lies only in the appearance of a break in the dependences of the combustion rate on pressure for mixtures with B4C in the region of 60 atm and a decrease in the rate of increase in the rate with pressure. Since B4C reacts in the gas phase, a change in the combustion law indicates a drop in the heat flux from the gas phase. The drop in the heat flux can be associated with a change in the chemistry of reactions in the combustion wave. Boron carbide decomposes endothermally at temperatures above 2450°C. Obviously, this reaction is slower than the B4C oxidation reaction. However, it can be assumed that at high pressures, when the diffusion coefficient decreases and the oxidizing zone around the PCA particle narrows, the B4C decomposition reaction proceeds along with the B4C oxidation reaction, reducing the heat flux to the c-phase.
Sinditsky Valery Petrovich Doctor of Chemical Sciences, Dean of the Faculty of Chemical Technology, Head of the Department of Chemistry and Technology of Organic Nitrogen Compounds of the Russian Chemical Technology Technical University named after. DI. Mendeleev, Moscow, Russia
Cherny Anton Nikolaevich Ph.D., Leading Engineer of the Department of Chemistry and Technology of Organic Nitrogen Compounds D. I. Mendeleev, Moscow, Russia
Bobylev Roman Sergeevich V-year student of the Department of Chemistry and Technology of Organic Nitrogen Compounds of the Russian Chemical Technical University named after D. I. Mendeleev, Moscow, Russia
Cho Swar Htet Master of the Department of Chemistry and Technology of Organic Nitrogen Compounds DI. Mendeleev, Moscow, Russia
Literature
1. Kubota N. Propellants and Explosives. Thermochemical Aspects of Combustion. - 2007. - WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim. -530P.
2. Liu L.-L., He G.-Q., Wang Y.-H. and Hu S.-Q. Chemical analysis of primary combustion products of boron-based fuel-rich propellants // RSC Adv.- 2015-Vol.5,- PP.101416-101426.
3. Belov G.B. Thermodynamic Analysis of Combustion Products at High Temperature and Pressure // Propellants, Explosives, Pyrotechnics. - 1998. - Vol.23. - P. 86 - 89.
4. A. P. Glazkova, Catalysis of combustion of explosives. M.: Science. - 1976. - 264p.
5. Sinditsky V.P., Egorshev V.Yu., Serushkin V.V., Filatov S.A. Combustion of energy materials with a leading reaction in the condensed phase // Physics of Combustion and Explosion. - 2011. - T. 48. - No. 1. - S.89-109.
6. Zeldovich Ya.B. Theory of combustion of gunpowder and explosives // Journal of Experimental and Theoretical Physics. - 1942. - T. 12. - No. 11-12. - S.498-524.
7. Inami S.E., Rosser W.A. and Wise B. Dissociation pressure of ammonium perchlorate // J. Phys. Chem. - 1963. - Vol. 67. - No. 5. - P. 1077-1079.
8. Merzhanov A.G., Dubovitsky F.I. On the theory of stationary combustion of gunpowder // Dokl. 129.-S. 153-156.
9. Frank-Kamenetsky D. A. Diffusion and heat transfer in chemical kinetics.- M.: Nauka, 1987 (3rd ed.).-502 p.
Sinditskii Valery Petrovich, Chernyi Anton Nikolaevich, Kyaw Swar Htet, Bobylev Roman Sergeevich.
D.I. Mendeleev University of Chemical Technology of Russia, Moscow, Russia.
COMBUSTION OF THE MIXTURE OF AMMONIUM PERCHLORATE WITH HIGH-CALORIFIC FUELS
abstract. The combustion behaviors of ammonium perchlorate (AP) mixtures with a high-calorific fuels aluminum, boron and boron carbide have been studied. It is shown that the additives of aluminum up to 40% content do not increase the burning rate of AP. In contrast to aluminum, boron, taking in amounts 5-30%, significantly increases the burning rate of AP. The boron carbide taking in small amounts (5%) reduces the AP burning rate, while 13-30% of B4C behaves like boron, but with less efficiency. The combustion mechanism of mixtures was proposed.
Key words: combustion, ammonium perchlorate, high-energy fuel, aluminum, boron, boron carbide.
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5. Persons working with oxidizing agents, at a minimum protection, must wear "heat resistant clothing". Contaminated clothing should be stored in metal cabinets. Frequent washing is necessary to reduce the risk.
6. Small amounts of oxidant splashes must be removed immediately. Such splashes cannot be collected. If large amounts of oxidant are spilled, the top layer can be collected, ensuring that it is not contaminated.
Perchlorates form somewhat less sensitive mixtures than chlorates and should be handled whenever possible. The advantage of using perchthorates is that they are less sensitive to impact and friction; they do not form a free acid in the presence of moisture and are less dangerous in case of accidental contact with weak acids, which are the main part of most resins, for example, catshfoly, which serves to bind pyrotechnic mixtures. 1 "¦
1. Ammonium perchlorate itself is an explosive, but it does not explode easily. At ordinary temperatures, NH4ClO4 is stable and will decompose if the temperature is maintained at 150 °C. It has the same degree of shock sensitivity as picric acid. Ammonium perchlorate becomes a strong explosive when mixed with combustibles and metal powders.
2. Containers for storage of perchlorates and chlorates are wooden boxes, barrels, barrels and sometimes iron drums. All damaged and broken containers should be removed from the warehouse, spilled material quickly removed and destroyed.
3. Fire, if only perchlorate burns, can be extinguished with water.
Perchlorates packed and stored in the packaging used for transportation, or similar, are considered flammable (class 1). In this case, no indication is given as to the distances at which certain quantities of perchlorates should be stored. If perchlorates are packaged and stored in a package other than those used for transport, they are Class 2 explosives. % oxidizing agent, refer to class 9 explosives. Storage requirements for certain quantities of BB of various
Perchlorates
241
classes at corresponding distances from each other are set out in special instructions109" 110.
Ammonium, barium, potassium, magnesium and similar perchlorates, referred to as "perchlorates not specified by cccs", are classified42 as oxidizing agents, i.e. substances which "easily give off oxygen, causing combustion of opianic substances". When transporting not more than 0.454 kg (net) of perchlorates of this, less dangerous group in the inner container and not more than 11.35 kg (net) in the outer container, unless otherwise specified, no special packaging, marking and label are required, with the exception of the indication the name of the contents on the outer container when shipping by water. The maximum quantities of perchlorates that can be transported in a single outer container by rail are 45.4 kg, by air 5-11.35 kg (passenger aircraft) and 45.4 kg (cargo aircraft).
Combustible solids and oxidizers4", with the exception of compounds for which there are special packaging requirements, must be packed in containers made of materials that do not react with the contents and do not decompose under the influence of the chemical substance stored therein.
1) metal barrels or drums;
2) metal drums (one latch); S) wooden barrels or kegs (barrels);
4) wooden barrels and casks with inner containers or suitable lining for bulk filling;
5) wooden drums and casks with inner containers or lined with metal for transport in bulk;
6) boxes made of sheet fiber with inner containers-metal boxes; wooden boxes with sliding lid; fiber boxes and boxes with a capacity not exceeding 2.27 kg or glass bottles with a capacity not exceeding 0.454 kg each; places with glass koteers should weigh no more than 29.5 kg each;
I) wooden boxes lined with metal; S) wooden crates with containers inside; 9) fiber drums;
10) plywood drums;
11) plywood drums with metal drums inside.
Potassium perchlorate also provides for the use of tight bags, the powder of which should not be sieved during transportation42.
The regulations for the transport of hazardous substances52 are similar to the above for the transport, storage and packaging of ammonium, barium, magnesium, potassium perchlorates and "perchlorates not specifically specified" that are equally dangerous42. On cargo ships, perchlorates must be stored "on a protected deck, on a deck under a roof, in an easily accessible cockpit or below deck, but without cargo on it." The first two
16-758
242
Chapter XI. Safety
of the listed methods of storage also apply to passenger ships.
It should be noted that the listed requirements apply only to a few of the above perchlorates, which are especially flammable when in contact with oxidizable substances. Therefore, the shipper must determine for himself the correct use of a particular container (with appropriate labels) for the packaging of other perchlorates or their mixtures that pose a great danger.
The invention relates to the field of mixed solid fuels. A method for obtaining ground ammonium perchlorate for mixed solid rocket fuel is proposed, including preparing a solution of lecithin in a dispersion liquid, preparing a suspension of ammonium perchlorate in this solution, grinding the suspension in a bead mill in the presence of glass beads. A solution of lecithin in a dispersion liquid is prepared by dissolving lecithin in 2.7÷15.0% of the dispersion liquid, filtering the resulting solution, introducing it to the rest of the dispersion liquid and stirring. Fluorodichloroethane is used as the dispersion liquid. Grinding the suspension in a bead mill is carried out at a temperature not exceeding 25°C. The invention is aimed at obtaining ammonium perchlorate with a particle size of two or less microns. 2 tab.
The invention relates to the field of grinding solid materials, including ammonium perchlorate, to obtain particles with a size of 2 microns or less, used in the manufacture of mixed solid rocket fuel. A known method for producing ammonium perchlorate with the specified particle sizes [RF Patent No. 2246472 IPC SW 21/00, 29/22, 45/30, SW 5/00, which the authors adopted as a prototype]. According to this patent, ammonium perchlorate is ground in a bead mill in the form of a suspension in the presence of glass beads, while trifluorotrichloroethane (HFC-113) or methylene chloride is used as a dispersion liquid, and the surfactant lecithin is introduced. Then the dispersion liquid is removed by temperature and vacuum distillation.
However, the method of obtaining ammonium perchlorate according to the prototype has certain disadvantages. In 1999-2000 production of trifluorotrichloroethane as an ozone-hazardous substance by domestic producers has been discontinued and its reserve has now been exhausted. No pretreatment of the lecithin surfactant is provided. The allowable temperature of the suspension during the grinding process is not set, which leads to the loss of a part of the dispersion liquid with a change in the concentration of ammonium perchlorate in the suspension and, thereby, to a violation of the established regimes in the process.
The technical objective of this invention is to obtain ammonium perchlorate with a particle size of two or less microns in a new dispersion liquid, the introduction of preparatory operations for lecithin and limiting the upper limit of the temperature of the suspension in the grinding process to reduce the loss of the dispersion liquid.
The technical result in the method for obtaining crushed ammonium perchlorate for mixed solid rocket fuel, including the preparation of a solution of lecithin in a dispersion liquid, the preparation of a suspension of ammonium perchlorate in this solution, the grinding of the suspension in a bead mill in the presence of glass beads, is achieved due to the fact that the solution of lecithin in a dispersion liquid liquids are prepared by dissolving lecithin in 2.7-15.0% of the dispersion liquid, filtering the resulting solution, introducing it to the rest of the dispersion liquid and mixing, while fluoro-dichloroethane is used as the dispersion liquid, grinding the suspension in a bead mill is carried out at a temperature no more than 25°С.
Of the currently produced dispersion liquids, the most suitable for ammonium perchlorate in terms of basic physicochemical, fire hazardous and toxic characteristics close to trifluorotrichloroethane is fluorodichloroethane (chladone-141b). The possibility of its use for obtaining ground ammonium perchlorate with a particle size of two or less microns was established by the manufacture of its samples in laboratory and semi-factory installations with a bead mill.
Table 1 shows the data obtained during the grinding of ammonium perchlorate in suspension with a dispersion liquid of freon-141b in a two-rotor bead mill.
From the data in Table 1, it can be seen that when freon-141b is used as a dispersion liquid, ammonium perchlorate is crushed to sizes of 2 microns or less. Used as a surfactant, lecithin is a pasty or waxy mass. To complete the surface-active role, lecithin must be dissolved in the dispersion liquid. When it is dissolved in the process of preparing the suspension and grinding in the first period, namely until the complete dissolution of lecithin, its activity will not be fully manifested and the technological cycle of grinding ammonium perchlorate will be extended. In addition, lecithin is a complex substance - an ester of the amino alcohol choline and diglyceride phosphoric (phosphatidic) acids. When lecithin is dissolved in freon-141b, an insignificant part of the insoluble substances floats to the surface, and some part precipitates. Therefore, it becomes necessary to separate them by filtration after the dissolution of lecithin in halon-141b. However, the implementation of these operations on a factory scale with a large volume of dispersion liquid will lead to an extension of the technological cycle with a decrease in productivity or require the installation of additional equipment. It seems possible to solve this problem by first dissolving a sample of lecithin in a small part of the dispersion liquid, followed by filtering from undissolved substances. Carrying out these operations for the preparation of a solution of lecithin and filtering for the next portion in the process of grinding the next portion will not lead to an extension of the technological cycle, that is, to a decrease in productivity. The calculation of the minimum required amount of dispersion liquid for the preparation of a lecithin solution is given. The minimum dosage of lecithin is 1.1% of the ammonium perchlorate sample. The dispersion liquid is taken in the ratio of ammonium perchlorate: dispersion medium = 1:(3-4). The minimum required amount of dispersion liquid for dissolution in relation to the total mass will be at a ratio of ammonium perchlorate and dispersion liquid of 1:4. With this ratio, the concentration of lecithin in the dispersion liquid will be 1.1:4=0.275%. With a sufficiently rapid dissolution of lecithin in the dispersion liquid to a concentration of 10%, its required amount will be 10:0.275=36.4 times less of the total amount. If we take the total amount of the dispersion liquid as 100%, then the minimum amount for preparing a lecithin solution will be only 100:36.4=2.7%. According to the experience in the manufacture of ammonium perchlorate in laboratory conditions and on a semi-factory installation, with a relatively small amount of ground product and, accordingly, a dispersion liquid for dissolving lecithin in freon-141b, it is advisable to take a portion of it up to 15% of the total amount. Thus, to dissolve lecithin, the amount of the dispersion liquid will be (2.7-15.0)% of its total volume.
For vessels operating without pressure, its maximum value should be no more than 0.7 kgf / cm 2 (0.07 MPa). This pressure level corresponds to the vapor pressure of freon-141b at a temperature of 25°C. In the process of intensive grinding, heat is released and the temperature of the suspension in the bead mill rises. To cool the suspension, a refrigerant is supplied to the bead mill jacket. In view of the foregoing, when grinding ammonium perchlorate in suspension, cooling is necessary to ensure its temperature is not higher than 25°C.
The preparation of crushed ammonium perchlorate, taking into account the proposed method of the invention is as follows. Take a sample of lecithin, which is dissolved in (2.7÷15.0)% dispersion liquid (chladone-141b). The proportion of the dispersion liquid within the specified limits is chosen depending on the amount of the crushed product and, accordingly, the dispersion liquid. The solution is filtered through a fabric filter. The solution after filtration is added to the bulk of the dispersion liquid and stirred. A weighed amount of ammonium perchlorate is added to the solution of lecithin in the dispersion liquid with continuous stirring, then the suspension is circulated through a centrifugal pump. The above-prepared suspension of ammonium perchlorate in halon-141b is circulated through a bead mill, into which glass beads are preliminarily loaded. As the suspension passes through the bead mill, ammonium perchlorate crystals are ground. The circulation of the suspension according to the scheme stirrer-pump-bead mill-mixer is continued until the required particle size is obtained, which is set by the grinding time. The crushed suspension is poured into a mobile container and sent to the drying phase. At this phase, the dispersion liquid is distilled off with the release of dry ground ammonium perchlorate, which is used for the manufacture of mixed solid rocket fuel.
The following are the distinguishing features of the invention in comparison with the prototype.
| table 2 | ||
| Distinctive features of the invention from the prototype | ||
| Name | Prototype | The proposed invention |
| dispersion liquid | Trifluorotrichloroethane | Fluorodichloroethane |
| Preparation of lecithin solution | ||
| a) dissolution | Full dispersion liquid | In 2.7-15.0% of the total volume of the dispersion liquid |
| b) filtering | Missing | Filtration |
| c) mixing | In the process of dissolving lecithin | Entering the lecithin solution to the bulk of the dispersion liquid and mixing |
| Suspension temperature during grinding | Not regulated | Not more than 25°С |
A method for obtaining crushed ammonium perchlorate for mixed solid rocket fuel, including preparing a solution of lecithin in a dispersion liquid, preparing a suspension of ammonium perchlorate in this solution, grinding the suspension in a bead mill in the presence of glass beads, characterized in that the solution of lecithin in the dispersion liquid is prepared by dissolving lecithin in 2.7 ÷ 15.0% of the dispersion liquid, filtering the resulting solution, introducing it to the rest of the dispersion liquid and mixing, while fluorodichloroethane is used as the dispersion liquid, grinding the suspension in a bead mill is carried out at a temperature of not more than 25 ° C.
Experimental studies show that the thermal decomposition of solid inorganic oxidants in the first approximation can be considered as a monomolecular reaction, the rate of which obeys the Arrhenius equation. The pre-exponential factor and the activation energy seem to depend on temperature. Therefore, extrapolation from lower temperatures, at which it is much more convenient to carry out measurements, to temperatures that occur during combustion, must be treated with caution. As an example, consider the process of thermal decomposition of ammonium perchlorate.
According to L. L. Birkemshaw and V. N. Newman, decomposition begins near the active centers of the surface, the number of which increases with time. Then the decomposition process spreads along the hemisphere from these centers inward and over the surface of the crystal until the reaction zones merge. After that, the reaction zone gradually moves towards the center of the crystal. The linear velocity of propagation of the contact reaction zone depends on the temperature according to an exponential law.
Obviously, the rate of decomposition of ammonium perchlorate will largely depend on the amount of contaminants and on the nature of the crystal surface, since these factors affect the rate of formation of active centers. In addition, the rate of decomposition will depend on the size of the crystalline particles and on the depth of the reaction, since these factors determine the area of the contact reaction zone. This complex nature of the decomposition process is typical for solids. Therefore, the results of kinetic calculations of processes in the solid phase based on the laws derived mainly for reactions occurring in the gas phase and solutions should be treated with great caution.
Thermal decomposition of ammonium perchlorate begins at a temperature of about 200°C. At temperatures below 300°C, the decomposition reaction occurs
and at temperatures above 300°C - the reaction
Nitric oxide reacts with chlorine to form nitrosyl chloride. According to the data of the gas analysis of the decomposition products, the equation for a reaction occurring at a temperature above 300°C has the form
At 240°C, the rhombic crystal structure of ammonium perchlorate turns into a cubic one, which affects the decomposition process. At temperatures below 240°C, the activation energy of the decomposition reaction is 124 kJ/mol, and at temperatures above 240°C it is 79 kJ/mol. In the temperature range 400-440°C, the activation energy is 307.3 kJ/mol. Since at these temperatures sublimation proceeds more actively than decomposition of the solid phase, the higher activation energies are to some extent due to decomposition in the vapor phase. In differential thermal analysis, exo-effects can be observed at 270-275°C (decomposition) and above 400°C, when the sublimation rate becomes greater than the decomposition rate in the solid phase.
Recently, studies have been carried out to clarify the process of the initial decomposition of ammonium perchlorate crystals and the composition of the resulting products. Many researchers believe that the low-temperature decomposition of ammonium perchlorate begins with the stage of salt dissociation into ammonia and perchloric acid. The decomposition rate of ammonium perchlorate is due to the decomposition of HClO4 in the salt lattice, which leads to the appearance of reaction centers containing perchloric acid and its decomposition products. In these centers, ammonium perchlorate is converted and an additional amount of HClO4 is formed. This acid causes the formation of new reaction centers on nearby defects.
Reaction centers appear at a depth of ~3 μm in places of the crystal with an increased density of dislocations, and the development of the decomposition process is accompanied by the multiplication of dislocations near the growing decomposition zone.
A number of works have been devoted to the study of the role of dislocations in the thermolysis of NH4ClO4. However, the question of why only one thousandth of the dislocations present in the crystal is active in the process of formation of reaction centers has not yet been clarified. This is probably due to the unfavorable stereochemical arrangement of dislocations. The development of reaction centers can be described as follows. The reaction proceeds both on stationary dislocations (induction period) and on moving ones (period of accelerated development of reaction centers). The growth of centers occurs where conditions are created that are favorable for the movement and multiplication of dislocations under the action of mechanical stresses due to the accumulation of reaction products. It can be assumed that one of the reasons for stopping the growth of nuclei is the inhibition of the reaction during the accumulation of products in the nucleus under high pressure (reaction in a closed volume). The movement of dislocations can facilitate the transfer of products from the reaction zone.
Features of the initial stages of low-temperature decomposition of ammonium perchlorate were also studied in the work of KR Kishi (1958). Using the method of potentiometric titration and spectrophotometry in the UV region, the authors determined the content of chlorine, chloride ions, the sum of oxychloranions, and perchloric acid. It was shown that at the early stages of decomposition in the condensed phase, there are no analytically determined amounts of chlorine oxides, and the main products of thermolysis are C12, HC1, and HClO4. Comparison of data on the kinetics of accumulation of thermolysis products in the condensed phase with the kinetics of weight loss shows that even at the degree of decomposition P= 0.25, the proportion of decomposition products in the condensed phase is -20%, and in the early stages it is even higher. At the beginning of the induction period (at 190°С for 6000 s), the process proceeds so slowly that thermolysis products cannot be detected, but then a rapid increase in the content of Cl2, HC1, and HClO4 in the condensed phase begins. According to the authors, it is especially important for understanding the decomposition mechanism that perchloric acid does not accumulate in the induction period, but its formation occurs simultaneously with the rest of the thermolysis products. The maximum concentration of perchloric acid in the condensed phase reaches 0.1-0.2% (relative to the initial NII4ClO4) and is observed at the stage of maximum acceleration of the thermolysis process ( P= 0.07-0.1); then (before P-0.15) it does not change, and then gradually falls. The ratio of the rate of formation of Cl2 + HC1 to the rate of formation of HClO4 at the initial stages is constant, from which it follows that C12 and HCl are not decomposition products of perchloric acid, but are formed from ammonium perchlorate in an independent way.
The researchers suggest that in the early stages of decomposition, the products of thermolysis of ammonium perchlorate can be formed according to the following scheme:
Moreover, the rate-limiting step in the thermolysis of ammonium perchlorate is reaction 1, not 2.
- Adapted from the 4th International Symposium on Combustion, Baltimore, 1953 ( Markstein G . N. Instability phenomena in combustion waves // Proceedings of the Fourth Symposium (International) on Combustion. Baltimore: Williams and Wilkins, 1953, pp. 44-59).
- Voevodsky V.V. Report to the All-Union. meeting according to chem. kinetics and reactions. abilities // In the book: Questions of chemical kinetics, catalysis and reactivity. M. : Publishing House of the Academy of Sciences of the USSR, 1955. S. 150-164; Cullis FROM . F., Minkoff L.J., Netleton M . A. Infra-red spectrometric study of the pyrolysis of acetylene. Part 1. The homogeneous reaction // Trans. farad. soc. 1962 Vol. 58. P. 1117-1127.
