RU2770102C1 - Method for producing iron carbide nanopowder - Google Patents

Abstract

FIELD: powder metallurgy.

SUBSTANCE: invention relates to the production of iron carbide, in particular to the production of iron carbide nanopowders by gas-phase methods, which can be used in such fields as electrochemistry, catalysis, biomedicine. A method is proposed for producing iron carbide nanoparticles with a “core-shell” structure with a controlled content of metallic iron in the core of the nanoparticle and iron carbide in its shell, including evaporation of iron from a drop of molten iron suspended in a high-frequency field of a countercurrent inductor in a vertically oriented reactor, capture of iron vapor from a drop by a continuous downward flow of carrier gas, condensation of iron vapor into iron nanoparticles in the condensation zone, interaction of iron with carbon in the gas phase in iron nanoparticles in the reaction zone downstream, the transfer of the formed iron carbide nanoparticles by the carrier gas flow into the cooling zone and their capture by a filter, while the carbon source is a carbon-containing gas that is introduced into the carrier gas flow above the reaction zone through an annular gap in the reactor located at a distance of more than 7 mm and less than or equal to 30 mm from the lower coil of the countercurrent inductor, an inert gas is used as a carrier gas, and the mass loss of the evaporated drop of molten iron is replenished by continuous supply of iron wire into it. Acetylene is used as a carbon-containing gas.

EFFECT: proposed method is characterized by simplicity and manufacturability, which makes it possible to significantly expand the scope of its use.

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Description

The invention relates to the production of iron carbide, in particular, to methods for producing iron carbide nanopowders by gas-phase methods, and can be used in such areas as electrochemistry, catalysis, biomedicine.

From the prior art, technical solutions are known for producing iron carbide powder by gas-phase methods, which include the processes of reduction-carburization of iron oxides from iron ore and make it possible to obtain iron carbide with a particle size of 0.1-5.0 mm for use in the metallurgical industry in the production of iron and steel, but not allow to obtain nano-sized powders of iron carbide Fe ₃ C in a free-bulk state .

Known methods for producing nanoparticles of iron carbide, including the decomposition of vapor organometallic compounds of iron (precursor).

In the method (Jun Liu, Bowen Yu et al. Synthesis and magnetic properties of Fe3C-C core-shell nanoparticles. IOP Publishing Nanotechnology, 26, 2015, 085601), an organometallic compound iron acetylacetonate Fe(acac) ₃ is used as a precursor, which is placed in a quartz boat in the evaporation zone in a horizontal tube furnace, and in the deposition zone in the same furnace, a silicon dioxide plate is installed to collect the finished product. Then the furnace is sealed, a constant flow of hydrogen is arranged in it at a controlled pressure, the temperature is increased at a given rate to 180°C in the evaporation zone and to 700-800°C in the precipitation zone, kept for 2 hours until the end of the synthesis of nanoparticles and cooled to room temperature. temperature. The resulting product is a crystalline iron carbide encapsulated in carbon and deposited on a substrate, the particle size is less than 100 nm. The method does not allow to obtain iron carbide nanopowder in a free-bulk state.

The method (DW Lee, JH Yu, B.K. Kim, TS Jang. Fabrication of ferromagnetic iron carbide nanoparticles by a chemical vapor condensation process. Journal of Alloys and Compounds, 449, 2008, 60-64) uses liquid iron pentacarbonyl Fe(CO) ₅ vaporized in an insulated sparger at a temperature of 150°C. High purity CH ₄ methane stream transfers precursor vapor to a tubular reactor with a maintained temperature of 650-800°C and a pressure of 101 kPa, where the precursor vapor decomposes and interacts with methane to form iron carbide. The condensed iron carbide particles are then deposited on the walls and on the bottom of a collector chamber filled with pure argon and maintained at room temperature. The product obtained by a known method is a loose agglomerate consisting of long tangled chains of iron carbide nanoparticles firmly soldered together (with an average size of 30-50 nm). The known method allows to obtain precipitated agglomerates of iron carbide nanoparticles, but does not allow to obtain Fe ₃ C iron carbide nanopowder in a free-bulk state.

In the method (Vasilyeva E.S., Nasibulin A.G. et al. Synthesis of nanoparticles by the method of vapor phase decomposition of iron pentacarbonyl in an atmosphere of carbon monoxide. Physicochemical kinetics in gas dynamics, 2006, v. 4, http://chemphys.edu .ru/issues/2006-4/articles/96/) also use iron pentacarbonyl Fe(CO) ₅ , which is dosed into a thermostat, where it is evaporated at a temperature of 150°C at a controlled rate. Next, iron pentacarbonyl vapor is transferred to a flow reactor (tube furnace) with a controlled flow of carbon monoxide CO, which is used simultaneously as a carrier gas and a carbon source. In the reactor at temperatures above 250 ° C, the process of pyrolysis of iron pentacarbonyl occurs with the formation of iron atoms, and at temperatures of 400-1100 ° C, iron reacts with carbon monoxide in the reaction: 3Fe _(t) + 2CO _(g) \u003d Fe ₃ C _(t) + CO _{2 (g} ) or with atomic carbon: 3Fe _(t) + C _(t) \u003d Fe ₃ C _(t) to form iron carbide. Atomic carbon C _(t) is formed as a result of the disproportionation reaction of carbon monoxide: 2CO _(g) → C _(t) + CO _{2 (g)} at temperatures of 400-800°C. The resulting iron carbide nanoparticles (with a size of 50-170 nm) in the form of an aerosol enter the working chamber, where they are completely deposited. Due to coagulation at the points of contact, the nanoparticles form long continuous "threads", which leads to a high degree of agglomeration of the resulting product. The known method allows to obtain precipitated agglomerates of iron carbide nanoparticles, but does not allow to obtain Fe ₃ C iron carbide nanopowder in a free-bulk state.

A known method for obtaining microcrystalline powders of the Fe-C system in arc discharge plasma (V.I. Podgorny, B.Z. Belashev et al. Obtaining carbide samples in arc discharge plasma. Journal of technical physics, vol. 83 (7), 2013, 77 -81). In this method, iron and carbon atoms are introduced into the gap between graphite electrodes and their interaction is ensured under conditions of an arc discharge in an argon environment. The experimental setup includes a vacuum hood, inside which is installed a horizontally oriented discharge chamber of a cylindrical shape with a diameter of 80 mm with electrodes placed at the ends, a water cooling system for the walls of the discharge chamber, a plasma gas puffing system, and a rectified voltage source of 60 V. A graphite plate is used as a cathode, and The source of iron and carbon atoms are sputtered anodes - graphite rods with cylindrical cavities for inserts made of iron wire, which evaporates during the burning of an arc discharge. In the operating mode, the interelectrode gap is adjusted in the range of 0.1-1 mm, the arc current is in the range from 60 A to 75 A, and the argon pressure is maintained in the range of 1×10 ⁴ -4×10 ⁴ Pa, while the burning time of the arc discharge is 20 -30 minutes. Under such conditions, iron ions with different degrees of ionization - Fe ⁺¹ , Fe ⁺² , Fe ⁺³ - can exist in the plasma of an argon arc discharge, and the synthesis of iron carbide molecules occurs only at the periphery of the arc plasma at a lower temperature compared to its central region. . The formation of iron carbide molecules in this known method is limited by the entry into the arc plasma of carbon atoms from graphite, which has a much higher melting point (3700°C) compared to iron (1500°C). The final product obtained is agglomerates of microcrystals condensed on the water-cooled wall of the reactor, containing crystalline phases of iron carbide Fe ₃ C (23%), pure iron α-Fe (55%) and hexagonal graphite (22%). During the reaction, a brittle deposit of a quasi-cylindrical shape up to 30 mm high is formed on the cathode from the evaporated anode substance, which consists of microcrystals of α-Fe and graphite and does not contain iron carbide.

Known methods for producing iron carbide nanoparticles have a complex technological cycle and limited technological capabilities, narrowing the scope of their application - they do not allow to obtain iron carbide nanopowder in a free-bulk state. Precipitated iron carbide nanoparticles obtained by known methods are either encapsulated in carbon, or are in agglomerates mixed with microcrystals of iron and graphite, or form long continuous "threads", which leads to a high degree of agglomeration of the resulting product.

The proposed method for producing iron carbide nanopowder was created as a result of a long study by the authors of the possibilities of the Gene-Miller method for the synthesis of ultrafine powders of metals, alloys, metal compounds (A.N. Zhigach, M.L. Kuskov, I.O. Leipunsky, N.I. Stoenko, V. B. Storozhev Obtaining ultrafine powders of metals, alloys, metal compounds by the Gene-Miller method: history, state of the art, prospects // Russian Nanotechnologies, 2012, V. 7, No. 3-4, pp. 28-37 ). As a result of improvements and modifications of the levitation-jet Gene-Miller method and installations for its implementation (M.L. Kuskov, A.N. Zhigach, I.O. Leipunsky and others. by jet and crucible methods // Instruments and experimental technique. 2018, No. 5, pp. 157-158), methods were developed for obtaining submicron and nanoparticles of aluminum coated either with a layer of aluminum oxide (RU 2397045) or having a dense dielectric nitride-containing coating (RU 2397046 ), and methods for producing nanopowders of titanium hydride (RU 2616920) and titanium carbide (RU 2707596).

In the work of M.L. Kuskov, A.N. Zhigach, I.O. Leipunsky, E.S. Afanasenkova, O.A. Safronova, N.G. Berezkina et al. Synthesis of nanopowders of Fe-C system via Flow-Levitation method and study of their properties. IOP Conf. Ser.: Mater. sci. Eng. 558 (2019) 012021 using a modified Gen-Miller levitation-jet method, a study was made of the influence of the parameters of the gas-phase reaction of nascent iron nanoparticles with acetylene in an inert carrier gas flow on the morphology, structure, elemental and phase composition of the resulting nanoparticles of the Fe-C system. It can be noted here that the structural and phase state of nanoobjects with the "metal core-carbon shell" structure has been studied extremely insufficiently, taking into account the variety of synthesis methods, each of which introduces its own characteristics into the structure of such micro- and nanoparticles.

In the mentioned work of the authors, much attention is paid to the study of the influence on the size and structure of the synthesized nanoparticles of the flow rate of acetylene - its concentration in the argon flow carrying the nascent nanoparticles. The concentration of acetylene varied by more than 2 orders of magnitude: from 5.5 to 0.02 vol. %. The argon pressure and its flow rate were the same in all experiments. The effect of the point of introduction of acetylene relative to the drop of molten iron was also studied: the point of introduction of acetylene shifted below the drop within the range from 8–10 mm to 30 mm. The distance was estimated visually. Were obtained nanoparticles of the Fe-C system with an average size of 38-45 nm of complex internal structure. Depending on the acetylene flow rate, nanoparticles containing crystalline iron, iron carbides of various compositions (total content of iron carbides from 0 to 83.6 wt %), and elemental carbon were synthesized. The results obtained in this work made it possible to develop the proposed method for producing iron carbide nanopowder.

The objective of the invention is to develop a method for producing nanoparticles of iron carbide Fe ₃ C with a "core-shell" structure with a controlled content of metallic iron in the core and iron carbide Fe ₃ C in a shell in a free-bulk state.

The technical result of the invention is expressed in the simplification of the technological cycle and the provision of a continuous process for producing iron carbide nanopowder, which expands the technological capabilities of the method and its scope.

The technical result of the invention is also expressed in obtaining nanoparticles of iron carbide Fe ₃ C with a "core-shell" structure with a controlled content of metallic iron in the core and iron carbide Fe ₃ C in a shell with an average particle size of less than 50 nm in a free-bulk state and expansion the most technological possibilities of the method and its scope.

The solution of this problem is achieved by the proposed method for obtaining iron carbide nanoparticles with a "core-shell" structure with a controlled content of metallic iron in the core and iron carbide in the shell, including the evaporation of iron from a drop of molten iron suspended in the high-frequency field of a countercurrent inductor in a vertically oriented reactor, capture iron vapor from a drop by a continuous downward flow of carrier gas, condensation of iron vapor into iron nanoparticles in the condensation zone, interaction of iron with carbon in the gas phase in iron nanoparticles in the downstream reaction zone, transfer of the formed iron carbide nanoparticles by the carrier gas flow to the cooling zone and capturing them with a filter, while the source of carbon is a carbon-containing gas, which is introduced into the carrier gas stream above the reaction zone through the annular gap in the reactor, located at a distance of more than 7 mm and less than or equal to 30 mm from the lower turn of the countercurrent inductor, as ha For the carrier, an inert gas is used, and the mass loss of the evaporated drop of molten iron is replenished by the continuous supply of iron wire into it.

Acetylene can be used as the carbonaceous gas.

In FIG. 1. a diagram of a device for implementing the proposed method for producing iron carbide nanopowder is shown: 1 - reactor, 2 - argon flow, 3 - countercurrent high-frequency inductor, 4 - drop of molten iron, 5 - iron vapor condensation zone, 6 - reaction zone, 7 - input acetylene, 8 - leak, 9 - annular gap, 10 - cooling zone of iron carbide nanoparticles, L - distance from the lower turn of the countercurrent inductor 3 to the annular gap 9.

The proposed method for producing iron carbide nanopowder is carried out as follows. A continuous descending laminar flow of argon 2 is fed into the reactor 1, made of a transparent heat-resistant dielectric material, for example, quartz or Pyrex glass. at the end of a drop 4 of molten iron, the drop 4 is suspended contactlessly inside the reactor 1 in the area between the turns of the countercurrent inductor 3 and the evaporation of metallic iron from the surface of the drop 4 is ensured. condensation 5 below the drop 4. Downstream, a reaction zone 6 is organized by introducing a carbon-containing gas 7 from the leak 8 through the annular gap 9. An argon flow transfers iron nanoparticles from the condensation zone 5 to the reaction zone 6. In the reaction zone 6, the carbon-containing gas interacts with the metal iron m in iron nanoparticles and get iron carbide nanoparticles. The argon flow carries away the iron carbide nanoparticles from the reaction zone 6 downstream to the cooling zone 10. The argon flow carries away the cooled iron carbide nanoparticles from the cooling zone 10 downstream, is caught by the filter and a commercial product is obtained in the form of iron carbide nanopowder in a free-bulk state.

Replenishment of the metal in the evaporating drop is carried out by continuous supply of iron wire from above.

The uniformity of the supply of acetylene to the reaction zone is ensured by its leakage into the reactor from the leak through the annular gap. The position of the reaction zone is controlled by the position of the annular gap relative to the drop of molten iron, thereby regulating the temperature in the reaction zone.

As a result of the experiments carried out during the development of the proposed method, it was found that the place where acetylene is introduced into the inert gas flow carrying nascent nanoparticles has the greatest influence on the internal structure of the resulting nanoparticles, while the flow rate of acetylene entering the argon flow has little effect. The place of introduction of acetylene is determined by the position of the annular gap.

When implementing the proposed method for producing iron carbide nanopowder with a "core-shell" structure with a controlled content of metallic iron in the core of the nanoparticle and iron carbide Fe ₃ C in its shell, the annular gap is set at a distance L> 7 mm.

Displacement of the annular gap away from the molten iron drop by a distance L>7 mm allows not only to obtain iron carbide nanoparticles with a “core-shell” structure (α-Fe-Fe ₃ C), but also to control the content of metallic iron in the core and iron carbide Fe ₃ C in the shell by adjusting the distance L. Increasing the distance L over 30 mm will lead to a shift in the reaction zone (the place where acetylene leaks into the flow of iron nanoparticles) towards lower temperatures and thereby reduce the temperature interval for the effective interaction of acetylene with cooling nanoparticles, which in in turn will lead to a decrease in the content of iron carbide and an increase in the content of metallic iron.

Measuring the distance L from the lower turn of the countercurrent inductor significantly improves the manufacturability of the proposed method, which is important when using it.

The achievement of a technical result in the implementation of the proposed method is demonstrated by the examples below.

Example 1

When implementing the proposed method, an iron wire with a diameter of D=0.5 mm is continuously introduced into the reactor at a rate of 5.9 g/hour. A quartz tube with a nominal inner diameter of 14 mm is used as the reactor. The absolute pressure of argon inside the reactor is maintained equal to 0.2 atm., the flow rate of argon is maintained equal to 50 norms. cm ³ /sec, the flow rate of acetylene is maintained equal to 14.8 norms. cm ³ / sec. The annular gap is set at a distance L=12 mm from the lower turn of the countercurrent inductor. The continuous process of obtaining nanopowder of iron carbide is continued for 8 hours. The resulting product is a black nanopowder in a free-flowing state with an average particle size of less than 50 nm. Nanoparticles do not tend to coalesce, agglomerate, clump, or form strong aggregates.

In FIG. 2 shows the diffraction pattern of the obtained nanopowder

According to X-ray phase analysis, the obtained nanoparticles contain crystalline phases of iron carbide Fe ₃ C (67.6 wt %) and metallic iron α-Fe (32.4 wt %).

Example 2

The method is carried out under the conditions of example 1, but the annular gap is set at a distance L=8 mm from the lower turn of the countercurrent inductor.

The resulting product is a black nanopowder in a free-flowing state with an average particle size of less than 50 nm. Nanoparticles do not tend to coalesce, agglomerate, clump, or form strong aggregates.

In FIG. Figure 3 shows the characteristics of the obtained nanopowder: A - a typical image of nanoparticles in a transmission electron microscope; B - size distribution of nanoparticles. Transmission electron microscopy studies demonstrate nanoparticles isolated from each other with an average size <D>=38 nm.

According to X-ray phase analysis, the resulting nanoparticles contain crystalline phases of iron carbide Fe ₃ C (83.6 wt %) and metallic iron α-Fe (16.4 wt %).

Example 3

The method is carried out under the conditions of example 1, but the annular gap is set at a distance L=30 mm from the lower turn of the countercurrent inductor.

The resulting product is a black nanopowder in a free-flowing state with an average particle size of less than 50 nm. Nanoparticles do not tend to coalesce, agglomerate, clump, or form strong aggregates.

In FIG. Figure 4 shows the characteristics of the obtained nanopowder: A - a typical image of nanoparticles in a transmission electron microscope; B - size distribution of nanoparticles. Transmission electron microscopy studies demonstrate nanoparticles isolated from each other with an average size <D>=38 nm.

According to X-ray phase analysis, the resulting nanoparticles contain crystalline phases of iron carbide Fe ₃ C (55.6 wt %) and metallic iron α-Fe (44.4 wt %).

The above examples show that when the position of the annular gap in the reactor at a distance L of more than 7 mm, iron carbide nanoparticles with a core-shell structure are obtained, in which the core is α-iron (α-Fe), and the shell is iron carbide (Fe ₃ C). Adjusting the distance L makes it possible to control the content of metallic iron in the core of the nanoparticle and iron carbide Fe ₃ C in its shell.

The examples also show that the implementation of the proposed method is provided by a simple technological cycle, and thus demonstrate the solution of the problem and the achievement of the technical result. The examples confirm the expansion of the technological capabilities of the method in terms of ensuring the continuity of the process. The examples show the possibility of obtaining iron carbide nanopowder in a free-bulk state with an average particle size of less than 50 nm.

Thus, the proposed method is characterized by simplicity and high manufacturability, which will significantly expand the scope of its use.

Claims (2)

1. A method for producing iron carbide nanoparticles with a "core-shell" structure with a controlled content of metallic iron in the core of the nanoparticle and iron carbide in its shell, including the evaporation of iron from a drop of molten iron suspended in the high-frequency field of a countercurrent inductor in a vertically oriented reactor, vapor capture iron from a drop by a continuous downward flow of carrier gas, condensation of iron vapor into iron nanoparticles in the condensation zone, interaction of iron with carbon in the gas phase in iron nanoparticles in the downstream reaction zone, transfer of the formed iron carbide nanoparticles by the carrier gas flow to the cooling zone, and capturing them with a filter, while the source of carbon is a carbon-containing gas, which is introduced into the carrier gas stream above the reaction zone through the annular gap in the reactor, located at a distance of more than 7 mm and less than or equal to 30 mm from the lower turn of the countercurrent inductor, as a gas - carriers use an inert gas, and the mass loss of the evaporated drop of molten iron is compensated by the continuous supply of iron wire into it. 2. The method according to p. 1, characterized in that acetylene is used as a carbon-containing gas.

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