RU2625981C1 - Method of producing nanopowder of cobalt ferrite and microreactor to this end - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method comprises supplying the primary components - a mixture of solutions of cobalt and iron salts in the ratio corresponding to stoichiometry CoFe₂O₄, and an alkali solution in proportion to the salts solutions providing acidity of the medium in the range from ₇ to 8, corresponding to the conditions of coprecipitation of the components, while the solutions of the primary components are supplied in the form of thin jets with a diameter of 50 to 1000 micron at the speed of 1.5 to 20 m/s colliding in the vertical plane at the angle of 30° to 160°, at the temperature in the range of 20°C to 30°C, and a pressure close to atmospheric pressure. The usage ratio of the primary components is set in such a way that when the jets collide, a liquid fog is formed in which the solutions of the primary components are mixed and engage. The microreactor for the method comprises a housing 1 and nozzles 2 with flow diffusers 3 for supplying primary components 10 and a nozzle 4 for products removal, the microreactor housing 1 is of a cylindrical shape with a conical bottom 5, a cover 6, the nozzles 2 with flow diffusers 3 for supplying primary components 10 are made with the possibility to provide fine adjustment of the jet direction, in the cover 6 coaxially to the housing 1 a nozzle 9 is provided for supplying purging gas, and an outlet nozzle 4 is installed in the bottom 5 to remove purge gas and reaction products. The area of the outlet nozzle 4 is 20-50 times bigger than the total area of all nozzles for supplying primary components. Two or more nozzles 17 may be installed in the cylindrical part of the housing to supply a surface-active substances solution in the form of thin jets with a diameter of 10 to 1000 micron, directed to the liquid fog of the primary components engaging solutions.

EFFECT: invention enables to reduce the temperature and pressure necessary to make a synthesis of oxide nanoscale cobalt ferrite particles, to reduce energy costs and ensure continuity of the process with the possibility of its implementation on an industrial scale, to reduce the cost of equipment, to increase yield and selectivity of the process, to provide optimal conditions for rapid reactions via maintenance of stable and effective hydrodynamic conditions for reagents contacting and rapid removal of reaction products.

3 cl, 5 dwg, 2 ex

Description

The invention relates to methods and devices for producing cobalt ferrite nanopowders, as well as to micro-scale reactors.

К.,

Т., Drofenika М., Makoveca D. Synthesis of aqueous suspensions of magnetic nanoparticles with the co-precipitation of iron ions in the presence of aspartic acid // Journal of Magnetism and Magnetic Materials. 2016. V. 413. Pages 65-75; Castellano M.,

E. Uniform Colloidal zinc compounds of various morphologies // Chemistry of Materials. 1989. V. 1. N. 1. P. 78-82). Однако, этим методом, варьируя параметры процесса осаждения, можно получать порошки стержневой, пластинчатой, неправильной формы (Цзан С., Авдеева А.В., Мурадова А.Г., Юртов Е.В. Получение наностержней оксида цинка химическими жидкофазными методами // Химическая технология. 2014. Т. 15. вып. 12. С. 715-722; V.S. Kumbhar, A.D. Jagadale, N.M. Shinde, C.D. Lokhande, Chemical synthesis of spinel cobalt ferrite (CoFe₂O₄) nano-flakes for supercapacitor application, Appl. Surf. Sci. 259 (2012) 39-43; Y.I. Kim, D. Kim, C.S. Lee, Synthesis and characterization of CoFe₂O₄ magnetic nanoparticles prepared by temperature-controlled coprecipitation method // Phys. В Condens. Matter 337 (2003) 42).Chemical methods for producing oxide nanoparticles, including CoFe ₂ O ₄ nanopowders, consist in the fact that nanoparticles are produced using a particular chemical reaction in which certain classes of substances are involved. The widely used method for producing nanoparticles is based on the deposition method, which consists in the implementation of the process of deposition of various metal compounds from solutions of their salts using precipitators. The precipitation product is usually metal hydroxides. By adjusting the pH and temperature of the salt solution, it is possible to create optimal deposition conditions under which the crystallization rate is increased, and a highly dispersed hydroxide is formed. Then the product is, if necessary, calcined to decompose the hydroxides to form the corresponding metal oxides. The resulting nanopowders typically have particle sizes of 10 to 100 nm. The shape of individual particles is usually close to spherical (

TO.,

T., Drofenika M., Makoveca D. Synthesis of aqueous suspensions of magnetic nanoparticles with the co-precipitation of iron ions in the presence of aspartic acid // Journal of Magnetism and Magnetic Materials. 2016. V. 413. Pages 65-75; Castellano M.,

E. Uniform Colloidal zinc compounds of various morphologies // Chemistry of Materials. 1989. V. 1. N. 1. P. 78-82). However, by this method, varying the parameters of the deposition process, it is possible to obtain powders of rod, plate, irregular shape (Zang S., Avdeeva A.V., Muradova A.G., Yurtov E.V. Preparation of zinc oxide nanorods by chemical liquid-phase methods // Chemical Technology. 2014.Vol. 15. Vol. 12. P. 715-722; VS Kumbhar, AD Jagadale, NM Shinde, CD Lokhande, Chemical synthesis of spinel cobalt ferrite (CoFe ₂ O ₄ ) nano-flakes for supercapacitor application, Appl. Surf. Sci. 259 (2012) 39-43; YI Kim, D. Kim, CS Lee, Synthesis and characterization of CoFe ₂ O ₄ magnetic nanoparticles prepared by temperature-controlled coprecipitation method // Phys. Condens. Matter 337 (2003) 42).

In recent years, for the production of nanocrystalline oxide materials, the hydrothermal method has been increasingly used, which allows one to control the morphology of the dispersed product by varying the parameters of the process (temperature, pressure, chemical composition and concentration of the hydrothermal solution, duration of the process, etc.) (LZ Pei, T. Wei, N. Lin, CG Fan, Zao Yang Aluminum bismuthate nanorods and the electrochemical performance for detection of tartaric acid // Journal of Alloys and Compounds. Volume 679, September 15, 2016, Pages 39-46).

Nanosized oxide particles are used in the manufacture of catalysts, functional and structural ceramics, and composite materials for various purposes.

The essence of the hydrothermal method is the treatment of metal salts, oxides or hydroxides in the form of a solution or suspension at elevated temperatures and pressures (usually up to 500 ° C and 100 MPa). In this case, chemical reactions occur in the solution or suspension, leading to the formation of the reaction product - a simple or complex oxide.

Hydrothermal synthesis is carried out in autoclaves, often lined with Teflon, ranging from tens of milliliters to hundreds of liters. The processing time can vary from several minutes to several days. For fast-flowing processes, flow-type autoclaves can be used, which have a significantly more complicated design than batch autoclaves. High pressure increases the boiling point, so the process can be carried out at a higher temperature than in aqueous solutions at atmospheric pressure. With increasing temperature, the solubility of substances increases, the precipitation of the reaction product is slower, the crystals of the product are less agglomerated than during precipitation under ordinary conditions.

After autoclaving, in the case of using batch autoclaves, the reaction vessel is cooled to room temperature. The hydrothermal synthesis product is separated from the mother liquor by filtration, for example, on a glass filter, or by centrifugation, after which it is washed several times with distilled water and dried, usually at 80-105 ° C.

The hydrothermal method has been widely developed in recent decades due to its comparative simplicity and low cost (only an autoclave is needed from the equipment) and the possibility of producing practically monodisperse nanopowders with particle sizes from units to tens of nanometers.

The disadvantages of the hydrothermal method of nanoparticle synthesis include: 1) the need to heat aqueous solutions or suspensions to high temperatures and pressures, which requires the use of autoclaves from expensive heat-resistant materials; 2) the operation mode of the apparatus, as a rule, is periodic, which reduces the average equipment productivity per cycle; 3) when heating and cooling reagents, it is also necessary to heat / cool the equipment itself - autoclaves having a large mass and, therefore, a large heat capacity, which leads to unproductive expenditure of energy and time; 4) in large-volume autoclaves, it is difficult to ensure uniform distribution of temperature and component concentration over the entire volume of the reaction space, which does not allow the synthesis of the product under optimal conditions for the course of the chemical reaction.

Known hydrothermal synthesis of oxide nanoparticles by high-temperature hydrolysis of salt solutions directly in an autoclave [Kolenko Yu.V., Maksimov VD, Garshev AV, Mukhanov VA, Oleynikov NN, Churagulov BR Physicochemical properties of nanocrystalline zirconium dioxide synthesized from aqueous solutions of zirconyl chloride and zirconyl nitrate by the hydrothermal method // Journal of Inorganic Chemistry, 2004. V. 49, No. 8, p. 1237-1242], or by dehydration under hydrothermal conditions of previously precipitated hydroxides [Almyasheva OA, Gusarov VV Hydrothermal synthesis of nanoparticles and nanocomposites in the ZrO ₂ -Al ₂ O ₃ -H ₂ O system // Alternative Energy and Ecology. 2007. No1. S. 113-115; Pozhidaeva O.V., Korytkova E.N., Romanov D.P., Gusarov V.V. The formation of zirconia nanocrystals in hydrothermal media of various chemical compositions // Zh. general chemistry. 2002.V. 72. No. 6. S. 910-914; Popkov VI, Almjasheva OV Formation mechanism of YFeO3 nanoparticles under the hydrothermal condition // Nanosystems: Physics, Chemistry, Mathematics. 2014, V. 5, No. 5, P. 703-708; Kolenko Yu.V., Meskin P.E., Mukhanov B.A., Churagulov B.R., Balakhonov SV. The effect of the nature of the cation on the phase composition of nanocrystalline dioxides of the titanium subgroup synthesized by hydrothermal treatment of amorphous hydroxide gels // Journal of Inorganic Chemistry, 2005. V. 50, No. 12, p. 1941-1946; Gavrilov A.I., Rodionov I.A., Gavrilova D.Yu., Zvereva I.A., Churagulov B.R., Tretyakov Yu.D. Hydrothermal synthesis of titanium dioxide-based nanostructures for photocatalytic decomposition of water // Doklady Akademii Nauk, 2012. V. 444, No. 5, p. 510-513]. The disadvantages of this method are also high temperatures and low productivity due to the use of autoclaves.

A known method of producing oxide nanosized particles and a device for its implementation, in which to intensify the process in order to lower the temperature of hydrothermal synthesis and to obtain a finer dispersed nanopowder before hydrothermal treatment or directly in the process of hydrothermal synthesis, ultrasonic treatment of the starting reagents is carried out [Pozhidaeva OV, Korytkova E.N., Drozdova I.A., Gusarov V.V. Effect of hydrothermal synthesis conditions on the phase state and particle size of ultrafine zirconium dioxide // Zh. general chemistry. 1999.V. 69. No. 8. S. 1265-1269; Kuznetsova V.A., Almyasheva O.V., Gusarov V.V. The effect of microwave and ultrasonic treatment on the formation of CoFe ₂ O ₄ under hydrothermal conditions // Physics and Chemistry of Glass. 2009.V. 35. No. 2. S. 266-272]. Ultrasonic processing has significant limitations on the volume being processed, and its use requires expensive equipment with low efficiency, which leads to an increase in energy consumption and limits the scope of this method to the laboratory level.

A known method of producing oxide nanosized particles and a device for its implementation, in which for the same purpose hydrothermal conditions in an autoclave are created using microwave heating of a hydrothermal medium [Almyasheva OV, Gusarov VV The role of prenatal formations in controlling the synthesis of nanocrystalline CoFe ₂ O ₄ powders // ZhPKh. 2016.V. 89. No. 6; R.F. Short, A.E. Baranchikov, O.V. Boytsova, A.E. Goldt, S.A. Kurzeev, V.K. Ivanov. Selective hydrothermal-microwave synthesis of various polymorphic modifications of manganese dioxide. Zhurn. nonorgan, chemistry. 2016.V.61. No. 2. S. 139-144; Kushnir S.E., Gavrilov A.I., Grigoryeva A.V., Zaitsev D.D., Churagulov B.R., Kazin P.E. Hydrothermal and hydrothermal-microwave synthesis of hard magnetic nanoparticles of strontium hexaferrite // Alternative Energy and Ecology, No. 11]. In addition, examples of the simultaneous use of both ultrasonic exposure and microwave heating are known to intensify hydrothermal synthesis and obtain the final product - oxide nanopowders of higher dispersion (Almyasheva O.V., Gusarov V.V. The role of prenatal formations in controlling the synthesis of nanocrystalline CoFe ₂ O powders ₄ // ZhPKh. 2016. T. 89. No. 6; Meskin P.E., Gavrilov A.I., Maksimov V.D., Ivanov V.K., Churagulov B.R. Hydrothermal-microwave and hydrothermal-ultrasonic synthesis of nanocrystalline wild plants rows of titanium, zirconium, hafnium Journal of Inorganic Chemistry, 2007, T. 52, №11, pp. 1755-1764). Ultrasonic and microwave processing require expensive equipment with limited productivity, which limits the transition from laboratory to industrial level and increases the cost of a unit of production.

There is a method - an analogue of the invention - the process of hydrothermal synthesis of nanosized particles of oxides, implemented in [Ivanov V.K., Ivanova OS, Scherbakov AB, Gil D.O., Baranchikov A.E., Tretyakov Yu. D., Zholobak N.M., Spivak N.Y .; A method of obtaining a stabilized aqueous sol of nanocrystalline cerium dioxide doped with gadolinium. RF patent No. 2503620, 2013]. In the known method for producing a stabilized aqueous sol of nanocrystalline cerium dioxide doped with gadolinium, characterized by high aggregate stability, which consists in preparing an aqueous solution of salts of cerium and gadolinium, in which the total concentration of rare-earth elements is 0.005 ÷ 0.02 mol per liter of water, and the molar ratio of Ce: Gd is from 19: 1 to 4: 1, an anion-exchange resin in the OH form is added to the resulting solution of cerium and gadolinium salts until a pH of 9.0–40.0 is reached, the formed colloidal the solution is separated from the anion-exchange resin by filtration and subjected to hydrothermal treatment at 120 ÷ 210 ° C for 1.5 ÷ 4 hours, then cooled to room temperature, characterized in that the obtained unstable sol of nanocrystalline cerium dioxide doped with gadolinium is further stabilized with a polybasic salt acid by adding a polybasic acid with a molar ratio of rare earths to acid equal to 1: 1 ÷ 4, and then slowly adding dropwise an aqueous solution of ammonia until reaching p H 7 ÷ 8.

The invention allows to obtain aggregate-stable aqueous sols of nanocrystalline cerium dioxide doped with gadolinium, with a characteristic average particle diameter of about 4 nm, with a hydrodynamic diameter of 25 ± 5 nm, with high morphological homogeneity, retaining their properties for a long time.

The disadvantages of the known invention include: 1) the need for the process at a relatively high temperature (up to 210 ° C), which leads to the following disadvantage; 2) the need to maintain a pressure in the apparatus of about 20 atm; 3) the excessive duration of the process (up to 4 hours) and the need for subsequent slow (dropwise) addition of an aqueous solution of ammonia significantly limits the performance of the equipment. These limitations reduce the known method to laboratory methods for producing nanosized particles. So, with the apparatus volume of the initial solution of 0.1 l (which is equal in this case to the volume of the final product) and the total processing time (taking into account the heating time, adding ammonia solution and cooling) 5 hours (300 min, or 18000 s) its productivity the final product will be 5.56⋅10 ^-6 l / s (5.56⋅10 ^-3 ml / s). At the maximum total concentration of rare earth elements of 0.02 mol per liter of water, the productivity of rare earth elements will be only 1.11⋅10 ^-7 mol / s. In addition, the need to use anion exchange resin increases the cost per unit mass of the product and complicates the process. All this significantly limits the possibility of transition from the laboratory scale of obtaining nanoparticles to industrial.

The closest in technical essence to our proposed method for producing oxide nanosized oxide particles is a method based on hydrothermal treatment of hydroxide salts precipitated from aqueous solutions in a continuous autoclave and a device for its implementation (prototype, patent of the Russian Federation No. 2528979, C01F 7/02 (2006.01 ), C01F 7/36 (2006.01)). In the specified method for producing the alpha phase of aluminum oxide, including the distillation purification of aluminum alcoholate, its hydrolysis and synthesis of the alpha phase of aluminum oxide, the distillation purification of aluminum alcoholate is carried out in an inert gas stream, and the hydrolysis of aluminum alcoholate and the synthesis of α-Al2O3 are carried out in a supercritical reactor. In this case, it is permissible: distillation purification to be carried out in a stream of nitrogen; the synthesis of finely crystalline α-Al ₂ O _{3 is} carried out on nanoscale seed precursors of the alpha phase of aluminum oxide of various sizes.

The disadvantages of the prototype include: 1) the need for supercritical conditions with a pressure of 22.5 MPa and a temperature of 410 ° C, which requires the use of a special thick-walled reactor and equipment to create high pressure; 2) the need to introduce into the reactor nanoscale seed granules of α-Al ₂ O ₃ . This greatly complicates the design of the installation, increases both the capital and current costs of obtaining products - nanoscale particles. In addition, the very method of obtaining the products is significantly complicated, since three processing steps have to be used: dissolution in the reactor, atmospheric distillation, and reaction in a supercritical batch reactor.

A device is known for producing nanosized particles by contacting solutions of the starting components, comprising a chamber with two side nozzles arranged coaxially to each other (J. Han, Z. Zhu, N. Qian, A.R. Wohl, C.J. Beaman, T. R. Noue, C.W. Macosko A Simple Confined Impingement Jets Mixer for Flash Nanoprecipitation // Journal of Pharmaceutical Sciences. DOI 10.1002 / jps.23259; K. Krupa, MA Sultan, CP Fonte, MI Nunes, MM Dias, J. C. B. Lopes, RJ Santos Characterization of mixing in T-jets mixers // Chemical Engineering Journal, 2012, http://dx.doi.Org/10.1016/j.cej.2012.07.062). In the collision of coaxial jets of fluid flowing out of the nozzles, self-oscillations occur in the chamber in a certain flow range, leading to intensification of mixing in the chamber. However, due to the presence of large-scale vortices in the device chamber, the residence time of the micro-scale fluid elements in it has a significant scatter. This leads to the occurrence of adverse reactions in the apparatus with the formation of undesirable products, to the formation of excessively large particles that are not related to the nanoscale scale (more than 100 nm). In addition, the known device does not provide for the adjustment of structural parameters, which allows to achieve optimal modes of its functioning. Finally, the known device does not provide for the possibility of expanding the range of operating costs of solutions of the starting components.

This significantly limits the capabilities of the known device, not allowing to achieve optimal conditions even on a laboratory scale, and even more so, go to the industrial level of production of nanoparticles.

The objective of the invention is to reduce the temperature and pressure necessary for the synthesis of oxide nanosized particles, in particular, cobalt ferrite nanoparticles, to reduce energy costs and ensure the continuity of the process with the possibility of its implementation on an industrial scale, reducing equipment costs, increasing output and process selectivity ensuring optimal conditions for fast reactions by maintaining stable and effective hydrodynamic conditions of contact Nia reagents and rapid removal of the reaction products.

The problem is achieved in that in the method for producing nanopowders of cobalt ferrite, which consists in supplying the starting components — a mixture of solutions of cobalt and iron salts in a ratio of components corresponding to stoichiometry of CoFe ₂ O ₄ and an alkali solution in a ratio with salt solutions providing an acidity in the range from 7 to 8, corresponding to the coprecipitation of the components according to the invention, the solutions of the starting components are supplied in the form of thin jets with a diameter of 50 to 1000 μm at a speed in the range of 1.5 to 20 m / s, colliding in the vertical plane at an angle from 30 ° to 160 °, at a temperature in the range from 20 ° C to 30 ° C, and a pressure close to atmospheric, while the ratio of the flow rates of the initial components is set in such a way that a liquid shroud is formed when the jets collide in which mixing and contact of solutions of the starting components occurs.

The task is also achieved by the fact that in a microreactor for producing nanopowders of cobalt ferrite, containing a housing and nozzles with nozzles for supplying the starting components and a nozzle for removal of products, according to the invention, the microreactor housing has a cylindrical shape with a conical bottom, a cover, nozzles with nozzles for feeding the initial components are made with the possibility of fine adjustment of the direction of the jet, a nozzle for supplying a purge gas is installed in the lid coaxially to the body, and an outlet nozzle is installed in the bottom for removal of purge gas and reaction products, moreover, the area of the exhaust pipe is 20-50 times greater than the total area of all pipes for supplying the starting components.

In addition, the task is achieved by the fact that in the microreactor for the production of cobalt ferrite nanopowders in the cylindrical part of the housing, two or more nozzles are installed for supplying a solution of surface-active substances in the form of thin jets with a diameter of 10 to 1000 microns directed to a liquid sheet of contacting solutions of the initial components.

The inventive method and device allows to exclude the heating of aqueous solutions or dispersions to high temperatures (specifically, to provide the product at room temperature in the range from 20 ° C to 30 ° C), to avoid the use of autoclaves from heat-resistant materials, the operation mode of the apparatus is continuous, t .e. access to the mode is carried out once - at the start-up of the apparatus, which leads to a reduction in unproductive energy and time costs.

The claimed technical solution is new, has an inventive step and is industrially applicable.

In FIG. 1 shows a diagram of a microreactor for implementing the proposed method, FIG. 2 is a diagram of the installation of a nozzle with a nozzle in an eccentric sealing assembly (cross section of the apparatus shown in FIG. 1), in FIG. 3 - diagram of the microreactor with peripheral equipment. In FIG. 4 presents an X-ray diffraction pattern of a sample obtained in the proposed device - a microreactor, in FIG. 5 - X-ray diffraction patterns of samples obtained by deposition (curve 1) and subsequent hydrothermal treatment (curve 2).

In FIG. 1 shows the proposed device comprising a housing 1, nozzles 2 with nozzles 3 for supplying the starting components and a nozzle 4 for removal of products, while the housing 1 of the microreactor has a cylindrical shape with a conical bottom 5 and a cover 6.

Preferred are the diameter D of the housing 1 in the range from 30 to 100 mm, the shape of the cover 6 is preferably spherical or elliptical. The height of the cylindrical part of the housing 1 should be sufficient to prevent the formation of secondary spatter, reflected from the walls of the apparatus and leading to the formation of large particles and assemblies. The design of the diameter of the housing 1 less than 30 mm also leads to the effect of secondary spray formation, and more than 100 mm - to increase the size and cost of the apparatus.

The nozzles 2 with nozzles 3 are hermetically mounted in the mounting sockets 7, for example, using conical sections 8. For the installation of nozzles 2 in the housing 1, other hermetic assemblies can also be used (for example, stuffing boxes or sleeve), allowing them to rotate the nozzles around their own axis .

The nozzles 2 with nozzles 3 for supplying the starting components have the ability to fine-tune the direction of the jets due to the eccentric (with eccentricity e , see Fig. 2) arrangement of the axes of the nozzles 3 with respect to the axes of the mounting sockets 7 of the nozzles 3 in the eccentric sealing assembly. This allows you to achieve exact coincidence of the jets even with a significant mismatch of the axes of the holes for the nozzles 2, made in the housing 1.

A nozzle 9 for supplying a purge gas is installed in the cover 6 coaxially to the housing 1, and an outlet nozzle 4 for removing the purge gas and reaction products is installed in the bottom 5, and the area of the outlet nozzle is 20-50 times the total area of all nozzles for supplying the initial components. The specific value of the area of the exhaust pipe 4 is determined from the Bernoulli equation from the condition of the removal of products from the housing 1 by gravity (or at a small pressure created above the liquid mirror in the conical part 5 of the apparatus).

The proposed device operates as follows.

In FIG. 3 presents a diagram of the microreactor with peripheral equipment. When feeding the solutions of the initial media (conventionally designated as solution 1 and solution 2) into the apparatus through nozzles 3 in the form of thin jets 10, they collide at an angle ϕ (Fig. 1) with the formation of a thin shroud 11, which in the lower part breaks up into jets and drops and flows down. A certain amount of liquid that can get on the walls of the conical bottom 5 also flows down. The supply of solutions of the source media is carried out by pumps 12 from the tanks 13 and 14, and the purge gas is supplied by a supercharger 15 (gas blower or fan). The reaction products are collected in tank 16.

When jets collide, a thin veil is formed in which quick and effective mixing occurs, which promotes the homogenization of solutions of contacting reagents and, as a result, nucleation (nucleation) of nanosized particles.

The thickness of the thin sheet 11, as well as the intensity of mixing in it, depends on the angle ϕ, the speed of the jets (and, therefore, on the flow rate of the supplied solutions), the viscosity and density of liquids (solutions and the resulting product). Typical values of the thickness of the shroud for aqueous solutions are from 5-7 to 20-30 microns. Specific values of the angle ϕ from 30 ° to 160 ° are selected depending on the calculated flow rates of the solutions: the lower the flow rate, the more the angle of collision of the jets in the vertical plane should be set. At high flow rates and angles of the order of 160 ° or more, the veil quickly falls into droplets. At angles less than 30 ° the thickness of the shroud is too great, the mixing conditions are worsened, which leads to an increase in the size of the resulting nanoparticles.

Studies have shown that the speed of the jets should be set in the range from 1.5 to 20 m / s; the larger the diameter of the apparatus, the higher the estimated speed of the jets. At a speed of less than 1.5 m / s, the thickness of the shroud also increases significantly, and mixing in it deteriorates. At a speed of more than 20 m / s, the veil quickly decomposes with the formation of sprays of a gel-like product, which fall on the walls of the apparatus and nozzles, partially clogging them.

Obtaining nanopowders of cobalt ferrite at a temperature in the range from 20 ° C to 30 ° C, on the one hand, provides a nanoscale composition of the product particles, on the other hand, allows the process to be carried out in “mild” conditions, at a pressure close to atmospheric, which, in in turn, it allows to reduce the cost of equipment for heating and creating high pressure, as well as repeatedly reduce operating costs.

The ratio of the costs of the starting components is set in such a way that when the jets collide, a liquid veil is formed, in which mixing and contact of the solutions of the starting components occurs. As a rule, the ratio of costs should not differ by more than 8-10 times, otherwise the formation of the shroud is disrupted, and the operation of the device is disrupted.

Two or more nozzles 17 for supplying a solution of surface-active substances (SAS) in the form of thin jets with a diameter of 10 to 1000 microns directed to a liquid sheet 11 of the contacting solutions of the starting components can also be installed in the cylindrical part of the housing. The introduction of surfactants in some cases helps to block the newly formed nanosized particles, and prevents the formation of aggregates. The thickness of the jets of the solution of surfactants and their speed depends on the thickness of the shroud and is determined by the conditions of its stable flow: the lower the consumption of the initial components (reagents), the thinner the surfactant jets should be, and their speed should be less. The number of nozzles 17 is two or more. Two nozzles 17 - for devices of small diameter and / or height, symmetrically, for uniformly introducing a solution of surfactants into the shroud, coaxial to each other or with a shift relative to the axis of the apparatus. A greater number of nozzles 17 - for devices of larger diameter and / or height.

Calculations based on experimental studies show that in the proposed device with two nozzles 3 with a diameter of about 0.5 mm and jet speeds of 6, 8 and 15 m / s, the productivity of the resulting gel-like suspension of the product, respectively, 2.36, 3, 14 and 5.89 ml / s, which exceeds the productivity of the analogue of the invention, respectively, 424, 565 and 1060 times. With an equal concentration of the starting reagents, the productivity of the finished product — particles of cobalt ferrite nanopowder — will increase by the same amount.

Thus, the use of the invention allows to increase productivity by hundreds and thousands of times in comparison with known analogues. This means that the invention can be used on an industrial scale for the production of nanosized powders.

The proposed method is illustrated by the following example.

Example 1. The synthesis of nanoparticles of cobalt orthoferrite (CoFe ₂ O ₄ )

10.3 g (COCl ₂ ⋅ 6H ₂ O) and 23.13 g (FeCl ₂ ⋅ 9H ₂ O) were dissolved in distilled water in a glass beaker. The resulting solution using a peristaltic pump 12 was fed into the housing 1 of the microreactor in the form of thin jets through the pipe 2 with the nozzle 3 at a speed of 8 m / s (Fig. 3). From the opposite nozzle 2 with nozzle 3, an aqueous NaOH solution with a concentration of 1.3 mol / L was supplied at the same rate, providing a pH of the medium that corresponded to the coprecipitation of the components, i.e. pH values of 7-8.

A liquid veil with a brown curdled sediment formed at the junction of jets. The resulting suspension was collected in a container under the reactor, the precipitate was washed by decantation from impurity ions to neutral pH (pH 7) and the absence of a high-quality reaction to chlorine ions (Cl ^- ), and then dried in an oven at a temperature of 50 ° C.

The resulting material was analyzed by a set of methods of physicochemical analysis.

The elemental composition of the samples was determined by the method of X-ray spectral microanalysis on a FEI Company Quanta 200 scanning electron microscope with an attachment of an EDAX X-ray microanalysis with nitrogen-free cooling.

X-ray diffraction patterns were obtained on a DRON-3M diffractometer (CoKα radiation). The size of crystallites (coherent scattering regions) was determined from the broadening of X-ray diffraction lines using the Scherrer formula (1):

where D is the crystallite size, nm; λ is the wavelength, nm; k is a constant (the value of k depends on the nature of the reacting substance, in this case k≈1); β is the width of the intensity distribution curve at half the height of the maximum of the reflex; θ is the Bragg angle.

The results of elemental analysis indicate that the Co: Fe ratio corresponded to the stoichiometric Co: Fe ratio = 1: 2.

The results of the analysis of the obtained powder by x-ray diffraction (Fig. 4) show that, during microreactor synthesis, nanocrystalline cobalt ferrite with an average crystallite size of 8 nm was obtained.

An analysis of the data obtained indicates that nanocrystalline cobalt orthoferrite particles were obtained without additional high-temperature or hydrothermal treatment, which is necessary in traditional hydrothermal methods for producing oxide nanoparticles.

The basic version is illustrated by the following example.

Example 2

In the work [Kuznetsova V.A., Almyasheva O.V., Gusarov V.V. The effect of microwave and ultrasonic treatment on the formation of CoFe ₂ O ₄ under hydrothermal conditions // Physics and Chemistry of Glass. 2009.V. 35. No. 2. C. 266-272] the deposition was carried out from a solution of CoCl ₂ and FeCl ₃ , a concentration of 0.7 mol / L and 1.4 mol / L, respectively, using a 2 M NaOH solution at pH 12. Then the precipitate was washed with distilled water until no reaction chloride ion and neutral pH and dried at a temperature of 70 ° C. The results of the x-ray phase analysis carried out using a DRON-3 diffractometer (CuK _α radiation) indicate that the obtained sample was an X-ray amorphous material (Fig. 5, curve 1). And only further hydrothermal treatment at a temperature of 130 ° C allowed us to obtain crystalline cobalt ferrite nanoparticles with a crystallite size of about 8 nm (Fig. 5, curve 2).

Thus, the use of the proposed method and device allows to obtain cobalt ferrite nanopowder at lower temperatures and pressures (in comparison with the known technical solutions), reduce energy costs and ensure the continuity of the process with the possibility of its implementation on an industrial scale. In addition, eliminating the need for autoclaves, furnaces, and supercritical reactors reduces the cost of equipment. Due to the almost instant contact of the reagents, fast and efficient mixing, an increase in the process selectivity and yield is achieved. By maintaining stable and effective hydrodynamic conditions for contacting the reagents and rapid removal of the reaction products, optimal conditions are provided for the occurrence of rapid precipitation reactions, in which the formation of large particles is practically excluded.

Claims (3)

1. A method of producing nanopowders of cobalt ferrite, which consists in supplying the starting components - a mixture of solutions of cobalt and iron salts in the ratio of components corresponding to stoichiometry of CoFe ₂ O ₄ and an alkali solution in relation to salt solutions providing an acidity in the range from 7 to 8, corresponding to the coprecipitation of the components, characterized in that the solutions of the starting components are supplied in the form of thin jets with a diameter of 50 to 1000 μm at a speed in the range of 1.5 to 20 m / s, colliding in a vertical plane at an angle from 30 ° to 160 °, at a temperature in the range from 20 ° C to 30 ° C, and a pressure close to atmospheric, while the ratio of the flow rates of the starting components is set so that when the jets collide, a liquid shroud is formed in which mixing and contact solutions of the starting components. 2. The microreactor for implementing the method according to claim 1, comprising a housing and nozzles with nozzles for supplying the initial components and a nozzle for withdrawing products, characterized in that the microreactor housing has a cylindrical shape with a conical bottom, a cover, nozzles with nozzles for feeding the initial components with the possibility of fine adjustment of the direction of the jet, a nozzle for supplying purge gas is installed in the lid coaxially to the housing, and an outlet nozzle for removing purge gas and reaction products is installed in the bottom, moreover, outlet is 20-50 times higher than the total area of all the nozzles for supplying the starting components. 3. The microreactor according to claim 2, characterized in that two or more nozzles are installed in the cylindrical part of the housing for supplying a solution of surfactants in the form of thin jets with a diameter of 10 to 1000 microns directed to a liquid sheet of contacting solutions of the starting components.

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