RU2371381C2 - Method and device for plasmochemical synthesis of nano-objects - Google Patents

Abstract

FIELD: nanotechnology.

SUBSTANCE: invention relates to synthesis of nano-objects of different chemical elements and its compounds, which can be used in electronic components, catalysts, in medicine, construction etc. Method of plasmochemical synthesis of nano-objects is in that it is created plasma jet by means of passage of orifice gas through the voltaic arc with following going out of formed plasma through parallel hole, in which it is introduced initial dispersed material in the form of powder and it is act to plasma and this material by high-frequency magnetic field, increasing volume of plasma jet and plasma temperature, and into area between reaction zone and water-cooled chamber it is fed flow of cooling inert gas, herewith into plasma it is introduced catalyst by means of evaporation of composition cathode, into content of which it is included catalyst, cathode is moved while its evaporation for providing of arc length constancy, and in low-temperature area of plasma by electrons excitation system it is additionally increased electron energy by means of feeding of direct voltage 25 V to emitter of resonance-tunnel structure of electrons excitation system, herewith into cooling flow of inert gas it is introduced dispersed liquid. Device for method implementation contains dielectric casing of plasmatron 22 with opening 24 for feeding of orifice gas, in which there are placed holder 19 with cathode 18 and anode 23, containing openings 25 for feeding of carrier gas and initial dispersed material, reaction chamber 26, waterproof connected to anode 23, around which it is located generator of high-frequency magnetic field 27, water-cooled chamber 29, connected to reaction chamber 26. Device is additionally outfitted by rollers 20, controlled device of autofeed of cathode with checking by current between cathode and anode, cathode 18 is located in opening of anode 23 at depth 1-2 mm with clearance in 2±1 mm, herewith cathode 18 is implemented as composition, into content of which it is included nano-object synthesis catalyst, herewith device contains excitation system of plasma electrones 28, including resonance-tunnel structure with system of heatproof electrodes, located in reaction chamber 26, placed into system of heatproof electrodes sprayer 36 for feeding by means of supercharger 35 of flow of inert gas mixture and dispersed liquid, gas distributor 33, inlet of which is connected to airlift pump 34, and outlets - with opening of dielectric casing of plasmatron 22, with opening in anode 23 for feeding of carrier gas and dispersed material and with first inlet of supercharger 35, herewith the second inlet of supercharger 35 is connected to water-cooled chamber 29, which is divided for two sections and for two thirds is filled by liquid, selected from row: distilled water, alcohol, solvent, and top part of the first section is connected to bottom part of the second section through mesh 31 with openings less than 0.2 mm, and reaction chamber 26 is connected to water-cooled chamber 29 pipe 32, bottom part of which is submerged into liquid of water-cooled chamber 29.

EFFECT: development of effective method of plasmochemical synthesis of nano-objects.

2 cl, 2 ex, 5 dwg

Description

The present invention relates to methods for the synthesis of nano-objects of various chemical elements and their compounds, which can be used in electronic components, catalysts, in medicine, construction, etc. to enhance the service properties.

There is a method of coupling an arc plasma reactor with a high-frequency magnetic field (US Patent 4386258 05/31/1983) to expand the plasma core and increase the residence time of the injected material in this core, where the plasma is first formed by the electric arc method, passing the plasma gas between the electrodes with a burning arc, and then introduce the reaction material and it is affected by a high-frequency magnetic field.

The disadvantage of this method is the lack of the ability to effectively control the process of the plasma-chemical reaction, which makes it difficult to obtain nanoscale objects.

There is a device for coupling an arc plasma reactor with a high-frequency magnetic field (U.S. Patent 4386258 05/31/1983) to expand the plasma core and increase the residence time of the injected material in this core, containing an electric arc plasma generator, a reaction chamber, and a high-frequency magnetic field generator.

The disadvantage of this device is the uncontrollability of the synthesis process of nano-objects, which does not allow to obtain nano-objects of a given shape and size.

The prototype adopted the method of production of carbon nano-objects (Bogdanov A.A., Dainiger D., Dyuzhev G.A. / Prospects for the development of industrial methods for the production of fullerenes // Journal of Technical Physics. - T 70, issue 5, 2000 C.1), where the technological environment is formed by passing argon through an arc direct current plasma torch and an area with an RF magnetic field. Soot with a particle size <10 μm with a soot feed rate of 0.05-0.5 g / min is injected into the plasmatron with an argon flow.

The disadvantage of this method is the ability to synthesize nano-objects of only one type, for example, fullerenes with a low content of <7% in the final product.

The prototype is a device for the production of carbon nanoobjects (Bogdanov A.A., Dainiger D., Dyuzhev G.A. / Prospects for the development of industrial methods for the production of fullerenes // Journal of Technical Physics. - T 70, issue 5, 2000 P.1), containing DC arc plasma torch, RF magnetic field generator, reaction chamber.

The disadvantage of this device is the lack of devices in it, which allow to synthesize nano-objects of a certain type, for example, nanotubes, fullerenes, graphenes, etc., as well as to increase their number in the final product.

The technical task of the invention is the synthesis of nanoscale objects of a certain type and structure, as well as increasing their number in the synthesized product.

The stated technical problem is achieved by the fact that in the method of plasma-chemical synthesis of nano-objects, which consists in creating a plasma jet by passing a plasma-forming gas through an electric arc with the subsequent exit of the resulting plasma through a cylindrical hole into which the initial dispersed material is introduced in the form of a powder and act on the plasma and this material with a high-frequency magnetic field that increases the volume of the plasma jet and the temperature of the plasma, while the region between the reaction zone and water-cooled the inert gas is supplied by the cooling chamber, in addition, the catalyst is introduced into the plasma by evaporation of the composite cathode, which includes this catalyst, while the cathode is moved as it evaporates to ensure a constant arc length, and in the low-temperature region of the plasma, the electron excitation system additionally increases energy electrons by applying a constant voltage of 25 V to the emitter of the resonant tunneling structure of the electron excitation system, while in the cooling stream of inert gas lead a dispersed liquid.

In the device for plasma-chemical synthesis of nano-objects, containing a dielectric plasmatron case with an opening for supplying a plasma-forming gas, in which there is a holder with a cathode and an anode containing holes for supplying a transporting gas and source dispersed material, a reaction chamber sealed to the anode around which a high-frequency generator is placed magnetic field, a water-cooled chamber connected to the reaction chamber is additionally equipped with rollers controlled automatically by the device cathode feed with current control between the cathode and the anode, the cathode is located in the anode hole at a depth of 1 - 2 mm with a gap of 2 ± 1 mm, and the cathode is made of composite, which includes a catalyst for the synthesis of nano-objects, while the device contains an excitation system plasma electrons, including a resonant tunneling structure with a system of heat-resistant electrodes placed in the reaction chamber, a nozzle placed in a system of heat-resistant electrodes to supply a mixture of an inert gas and a disperser with a supercharger bath fluid, a gas distributor, the inlet of which is connected to the pneumatic pump, and the outputs - with the hole of the dielectric housing of the plasma torch, with a hole in the anode for supplying transporting gas and dispersed material and with the first inlet of the supercharger, the second inlet of the supercharger connected to a water-cooled chamber, which is divided into two compartments and two-thirds filled with a liquid selected from the series: distilled water, alcohol, solvent, and the upper part of the first compartment is connected to the lower part of the second compartment through a mesh with Verstov less than 0.2 mm, and the reaction chamber is connected to a water cooling chamber tube, the lower part of which is immersed in the water-cooled chamber fluid.

The essence of the developed method (figure 1) is as follows. Plasma with a temperature of more than 10,000 K is formed in plasma generator 3. In this case, stable plasma combustion is supported by the cathode supply unit 1, the cathode supply rate control unit 4 and the gas distributor 5. During plasma formation, the cathode material performed by a composite with an experimentally selected composition according to the criteria for ensuring high the emission properties of the cathode and the good catalytic properties of the ionized vapors of the cathode material, evaporates and is delivered to the reaction zone by a plasma-forming gas stream, where it serves to an analyzer of the process of synthesis of nanoobjects. Next, a conveying gas and a powder of the starting material with a dispersion <0.1 mm are fed into the plasma jet through the feed unit 2; Part of the powder, passing through the nozzle, dissociates into atoms and ionizes. A more efficient dissociation of the powder of the starting material is carried out in the high-temperature region of the high-frequency plasma formed by the high-frequency plasma generator 6.

At the boundary of the high-frequency plasma region, the rates of dissociation and association processes become comparable, which shifts the process towards the formation of nanoscale associations. In this case, the introduction of a catalyst promotes the formation of a certain type of association and an increase in the rate of this process. Additionally, an increase in the number of nanoobjects in this area can be achieved by increasing the stability of already formed nanoobjects while maintaining the dissociation rate of other products (initial products, random associations, amorphized conglomerates, etc.).

In this case, an increase in the stability of the formed nano-objects is achieved by the action of an external field from the electron excitation system 7, due to which the electrons are excited in the plasma by applying a constant voltage of 25 V to the emitter of the resonant-tunnel structure of the electron excitation system 7. This reduces the dissociation of nano-objects in the low-temperature region plasma (~ 2500 K) due to the creation in the plasma of conditions for the stable existence of nanoscale formations.

It is known (Encyclopedia of Low-Temperature Plasma. Book 1: Introductory Volume / Ed. By V.E. Fortov. - M .: Nauka, 2000. - 585 p.) That more than 100 processes of ionization, recombination, dissociation, association occur in plasma etc. To achieve the stability of nanoobjects in a plasma, it is necessary to create conditions for dumping the excitation energy of nanoobjects. The analysis showed that of the entire variety of plasma processes for the formation of neutral nano-objects, the two processes are most acceptable. Firstly, this is the inelastic interaction of an electron with an ion with the transfer of released energy to a third electron:

e + A ⁺ + e → e + A.

Secondly, inelastic interaction of an electron with an ion by emission of excess energy in the form of a photon:

e + A ⁺ → A + ћv.

Here, the designation A ⁺ means an ionized molecule with a large number of atoms, by which we can mean ionized nano-objects, i.e. in which there is no electron.

As a result of these two processes, the recombination of nano-objects occurs, the energy from which is transferred to the circuit of the electron excitation system, and is also transferred to the external medium in the form of radiation.

The excitation of plasma electrons is carried out using an electron excitation system (Fig. 3), which is based on the resonant tunneling effect in quantum systems, which consists in the tunneling of charge carriers through a two-barrier quantum structure (V. Demikhovsky. Physics of quantum low-dimensional structures / V. Ya.Demikhovsky, G.A. Vugalter. - M .: Logos, 2000 .-- 248 p.). In contrast to the known bipolar resonant tunneling transistor in a resonant tunneling structure with nano-objects, the energy well 8 of the energy diagram (Fig. 4) is formed from synthesized nano-objects 9 (Fig. 3), and at the boundary between the dielectric 10 and the base region 11 from the side of the emitter 12 there is also a layer of synthesized nano-objects 13. The current passing through the resonant tunnel structure with nano-objects can be represented as follows:

,

,

where e is the electron charge, S is the cross-sectional area of the structure, m is the electron mass E _i is the energy of the quasistationary state in the quantum well, μ is the Fermi level, i is the number of the level of the excited state of nano objects, l is the number of excited states, V is the voltage at the emitter , τ _n is the relaxation time of the electron momentum at the nth level. As can be seen from this relation, a current I _Σ is observed on the collector of a resonant tunneling structure with nanoobjects, formed by electrons with the energy spectrum E _{i of the} quasistationary levels of the quantum well, which in our case is a layer of nanoobjects.

The collector of the resonant tunneling structure 14 (Fig. 3) is connected to the cathode of the plasma electron excitation system 15, through which electrons with the energy of the excited states of nano-objects are transferred to the plasma through field emission without energy loss (Physical Encyclopedia / Ch. Ed. A.M Prokhorov, Edited by D.M. Alekseev, A.M. Baldin, A.M. Bonch-Bruevich, A.S. Borovik-Romanov, etc. - M .: Sov. Encyclopedia. T. 1. Aronova -Boma effect - Long lines. 1988. 704 p.). Thus, electrons with the energy of the excited states of nano-objects are formed in the plasma, which are captured by ionized nano-objects, carrying out the recombination process, and, accordingly, the destruction of nano-objects is prevented.

The decrease in the activity of nanoobjects is carried out in the system of intensive cooling of the plasma stream 16 by passing a mixture of liquid dispersed in a gas (Ar, He, etc.).

Next, a mixture of gas with a dispersed liquid, nano-objects, a plasma-forming and transporting gas is supplied to the accumulation and purification system of nanomaterial 17, where nano-objects are uniformly distributed throughout the volume, and gas is pumped into the gas distributor 5 for reuse in plasma formation, transportation and dispersion of the liquid.

The proposed method is implemented by the device, a diagram of which is shown in figure 2. The device consists of a cathode 18, mounted in a cathode holder 19 and moved by rollers 20, which are controlled by a device for automatically moving the cathode 21, a dielectric housing 22, into which the cathode holder is placed, the anode 23 and which contains a plasma gas supply 24, the anode has transporting holes gas and source material 25, a reaction chamber 26, around which there is a generator of a high-frequency magnetic field 27, an electron excitation system 28, a water-cooled chamber 29, containing carrying liquid 30, a grid 31 and a tube 32 connected to the reaction chamber, a gas distributor 33 connected to an air pump 34 and a dispersed liquid supercharger 35 connected to the nozzle 36.

The device implements the proposed method as follows. A stream of plasma-forming gas (Ar, He, etc.) is supplied into the hole 24 of the dielectric housing 22. Then, an oscillating voltage is supplied to the cathode 18 and anode 23 to ignite the arc, after which a constant voltage is formed that maintains stable burning of the arc. The plasma-forming gas passing through the arc is ionized and a plasma with a core temperature of 10,000 K is formed in the anode nozzle. As the cathode is worn, the automatic transfer device 21 by means of rolls 20 moves the cathode toward the anode, and the movement speed is monitored by the arc current between the cathode and the anode. Next, a conveying gas and a powder of the starting material with a dispersion <0.1 mm are supplied to the opening 25 of the anode 23. Part of the powder of the starting material, passing through the nozzle, dissociates into atoms and ionizes. A more efficient dissociation of the powder of the starting material is carried out in the high-temperature region of the high-frequency plasma formed by the coil 27.

Next, the electron excitation unit 28 in the low-temperature region of the plasma increases the electron energy by applying a constant voltage of 25 V to the emitter of a resonant tunnel structure with nano-objects, which is the basis of the electron excitation block and is made using synthesized material placed between two energy barriers formed by two dielectric layers 10 (figure 3), and on the border between the dielectric and the base region 11 from the side of the emitter 12 is a layer of synthesized nano-volume such as are for 13.

To reduce the activity of nanoobjects through the nozzle 36, figure 2 under pressure injected liquid dispersed in a gas (Ar, He, etc.).

Next, through the tube 32, a mixture of technical fluid vapors, nano-objects, plasma-forming and transporting gas through the grid 31 enters the liquid tank 30, where the nano-objects are evenly distributed throughout the volume, and the gas is pumped through the filter into the gas distributor 33 through a filter 34 for reuse in plasma formation, transportation and dispersion of liquids.

The main advantage of the claimed method in comparison with the known ones is that it can be used to purposefully form various types of nano-objects, for example, nanotubes, nanospheres (carbon-fullerenes), and from various materials and with a high content in the final product, due to the formation of favorable synthesis conditions by introducing catalyst vapor into the reaction zone, as well as increasing the energy of the plasma electrons by applying a constant voltage of 25 V to the emitter of the resonant tunneling structure, to llektor which is connected to the excitation electrodes of the electron system.

A feature of the claimed method is that in it, in contrast to the known methods, a material containing a catalyst is used as a cathode, which promotes the synthesis of nano-objects of a given type, and in the reaction zone, electrons are excited by the electron excitation system, which increases the lifetime of nano-objects in the plasma. For example, on the one hand, the use of nickel, iron as catalysts promotes the bonding of carbon atoms in the form of nanotubes, the use of cobalt, nickel allows the formation of nano-objects in the form of nanobands, the use of titanium additives in the cathode allows the synthesis of sphere-like compounds of carbon atoms with titanium. On the other hand, the excitation by the electron excitation system increases the content of nano-objects in the final product.

The main advantage of the claimed device in comparison with the known is the ability to synthesize nano-objects of a given type with a high content of them in the final product. A device that implements the method allows you to evaporate and ionize the dispersed starting material, mix with the vapor of the catalyst and to influence the excited plasma electrons on the nano-objects formed during the synthesis.

Example 1

In the proposed device by electric arc method, a plasma with a power of 16 kW was formed. A composite material consisting of 8.2% cobalt and 91.8% tungsten was used as a cathode; argon was used for plasma formation. Manganese oxide powder was supplied to the plasma using a transport gas - argon. The dispersion of the powder is not more than 63 microns. The powder flow rate was set at 5 g / min. Then, a high-frequency (4 MHz) magnetic field with a power of 10 kW was applied to the high-temperature region of the plasma. Further, plasma components were additionally affected by the electron excitation system.

Plasma components were excited by forming a resonant tunneling structure on the emitter with the corresponding nano-objects of a constant voltage of 25 V. This voltage covers the energy series: E ₁ = 1.364 eV, E ₂ = 3.046 eV, E ₃ = 3.364 eV, E ₄ = 6.53 eV, E ₅ = 8.39 eV, E ₆ = 11.68 eV, E ₇ = 12.01 eV, E ₈ = 16.68 eV, E ₉ = 18.03 eV, which corresponds to the excited quasistationary levels of nano-objects based on manganese oxide and does not exceed the breakdown voltage of the resonant tunneling structure. During the synthesis, 50 g of the initial manganese oxide powder was introduced into the plasma. The synthesized material was collected in a water-cooled chamber. Then, during the day, they settled and poured into a container for further separation of the reaction products from the process fluid. As a result of separation, a friable substance was obtained, the study of which in an electron microscope with an increase of x 100,000 showed that the structure has the form of nano-objects, Fig. 5. With further extraction of nano-objects, the mass of the final product was 10.747 g.

In a similar experiment with a composite cathode, but without an electron excitation system, the mass of the obtained nanoobjects was 6.934 g. When using a tungsten cathode, nanoobjects were practically not observed.

Example 2

An electric arc method was used to form a plasma with a power of 16 kW. Tungsten with a sputtering of lanthanum was used as a cathode; argon was used for plasma formation. Carbon gas in the form of soot was supplied to the plasma using a conveying gas - argon, which was preliminarily prepared by dispersion in alcohol, drying, abrasion, and sifting through a 63 μm sieve. The powder flow rate was set at 0.5 g / min. Then, a high-frequency (4 MHz) magnetic field with a power of 10 kW was applied to the high-temperature region of the plasma. Further, the plasma components were additionally affected by the electron excitation system, increasing their energy to the level of fullerene ionization.

Electrons were excited to the ionization energies of fullerenes by forming a resonant tunnel structure with fullerenes of a constant voltage of 25 V. This voltage covers the energy series: E ₁ = 3.78 eV, E ₂ = 5.36 eV, E ₃ = 7.78 eV, E ₄ = 8.53 eV, E ₅ = 9.18 eV, E ₆ = 11.84 eV, E ₇ = 13.75 eV, E ₈ = 15.82 eV, E ₉ = 16.84 _E V , E ₁₀ = 19.26 eV, which is similar to the excited quasistationary fullerene levels and does not exceed the breakdown voltage of the resonant tunneling structure.

During the synthesis, 40 g of carbon black was passed through the plasma. It was then dissolved in toluene, separated from the soot residues by filtration and extracted. As a result of extraction, a black substance was formed, the analysis of which showed that it consists of fullerenes. The mass of the obtained material was 3.476 g.

In a similar experiment without an electron excitation system, the mass of the material obtained was 2.453 g.

An analysis of the obtained experimental data allows us to conclude that the use of an electron excitation system increases the content of necessary nano-objects in the final product by 40-55%, and this increase depends on the type and structure of the obtained nano-objects.

Claims (2)

1. The method of plasma-chemical synthesis of nano-objects, which consists in creating a plasma jet by passing a plasma-forming gas through an electric arc with the subsequent exit of the resulting plasma through a cylindrical hole, into which the original dispersed material is introduced in the form of a powder and exposed to the plasma and this material by a high-frequency magnetic field increasing the volume of the plasma jet and the temperature of the plasma, while in the region between the reaction zone and the water-cooled chamber serves a flow of cooling inert gas, characterized in that the catalyst is introduced into the plasma by evaporation of the composite cathode, which contains this catalyst, while the cathode is moved as it evaporates to ensure a constant arc length, and in the low-temperature region of the plasma, the electron excitation system additionally increases the electron energy by applying a constant voltage 25 V to the emitter of the resonant tunnel structure of the electron excitation system, while a dispersed liquid is introduced into the cooling stream of inert gas. 2. A device for plasma-chemical synthesis of nano-objects, containing a dielectric plasma torch housing with an opening for supplying a plasma-forming gas, in which a holder with a cathode and an anode are located, containing holes for supplying a transporting gas and source dispersed material, a reaction chamber sealed to the anode around which the generator is placed high-frequency magnetic field, a water-cooled chamber connected to the reaction chamber, characterized in that it is additionally equipped with rollers, controlled an automatic cathode feed device with current control between the cathode and the anode, the cathode is located in the anode hole at a depth of 1-2 mm with a gap of 2 ± 1 mm, the cathode being made composite, which includes a catalyst for the synthesis of nano-objects, while the device contains a plasma electron excitation system comprising a tunnel resonance structure with a system of heat-resistant electrodes placed in a reaction chamber, a nozzle placed in a system of heat-resistant electrodes to supply a mixture flow using a supercharger, and gas and dispersed liquid, a gas distributor, the inlet of which is connected to the pneumatic pump, and the outputs - with the hole of the dielectric housing of the plasma torch, with a hole in the anode for supplying conveying gas and dispersed material and with the first input of the supercharger, the second input of the supercharger connected to a water-cooled chamber , which is divided into two compartments and two-thirds filled with a liquid selected from the series: distilled water, alcohol, solvent, and the upper part of the first compartment is connected with the lower part of the second th compartment through a grid with openings of less than 0.2 mm, and the reaction chamber is connected to a water cooling chamber tube, the lower part of which is immersed in the water-cooled chamber fluid.

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