RU2797467C1 - System for obtaining nanoparticles of metal oxides by electric explosion of a wire - Google Patents

Abstract

FIELD: powder metallurgy.

SUBSTANCE: invention relates to the production of powder materials comprising nanoparticles. It can be used to produce metal oxides for use as an antimicrobial additive in paints and varnishes. The system for obtaining nanoparticles of metal oxides by electric explosion of wire comprises a reactor connected by a pipeline into a single gas-flow structure, adapted for feeding metal wire from the chamber of the wire feed mechanism, a high-voltage electrode and a grounded electrode placed in the reactor to provide electric explosion of metal wire, a separator with a hopper for collecting and unloading large particles of metal oxides, a cyclone with a hopper for collecting and unloading nanoparticles of metal oxides and a centrifugal fan that provides forced circulation of the operating gas according to the above design. A cylindrical structure is used as a separator, in which a cutter is additionally installed, having the shape of a truncated cone and installed at an angle of 45 degrees relative to the separator body, and the diameter of the cutter opening is 2 times smaller than the diameter of the inlet to the separator.

EFFECT: obtaining powders of stable chemical and disperse composition.

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Description

The invention relates to powder metallurgy, namely to the production of powder materials containing nanoparticles, in particular for the production of metal oxides for use as an antimicrobial additive in paints and varnishes. Known installation for the production of fine powders of inorganic materials by electric explosion and a reactor for the explosion of a metal workpiece (RF Patent 2048278, B22F 9/14, publ. a billet feed mechanism, while it is equipped with a switch connected to the accumulator and the reactor, a powder collector, a pipeline for returning gas to the reactor and a powder container, while one of the reactor electrodes is connected to the switch, and the other is grounded, and the reactor is connected to the powder collector . The energy of the accumulator is supplied to the workpiece, and it explodes with the formation of highly dispersed aluminum particles, which enter the powder collector, where they are captured and poured into the powder container. This design does not provide a unit (separator) for separating particles into fractions, i.e. in the process of buffer gas circulation, it is impossible to separate particles to obtain nanoparticles with a size of no more than 200 nm, which is necessary for the use of electroexplosive powders in paints and varnishes. All the particles formed in the EEW process enter the powder collector. Chang Kyu Kim, Gyoung-Ja Lee, Min Ku Lee, Chang Kyu Rhee "A novel method to prepare Cu@Ag core-shell nanoparticles for printed flexible electronics" (Powder Technology V. 263 (2014) pp. 1- 6) a plant is disclosed that contains a wire feed mechanism, a power source, a reactor with electrodes, an argon supply system, a fan, a closed gas circulation system inside the plant, a cyclone and a filter system, a powder collection container. The design of the installation allows for the separation of particles into two fractions: with a distribution of particles less than 1 μm, and a distribution of particles larger than 1 μm. In the filtering system (Filtering system) particles with sizes less than 1 micron are collected, which follows from the particle size distribution curves given in the article. The impossibility of obtaining particles no larger than 200 nm follows from the design features of the setup described in the article. The use of a cyclone (Cyclone) at the first stage of particle separation does not provide separation into fractions smaller than 200 nm and large particles larger than 200 nm. Known installation, disclosed in the article (Research into nanoparticles obtained by electric explosion of conductive materials, V. Jankauskas, J. Padgurskas, Electronic processing of materials, 2011, 47(2), 79-85), containing a source of high voltage pulses; current input bus (+); power supply, current-carrying tires, camera; current input bus; wire segment feeding mechanism; explosive wire; a separation system comprising a separator and three cyclones: a large particle cyclone, a medium particle cyclone; cyclone of fine particles and fan. The disadvantage of this device is the use of three cyclones in the design. In this design, particles smaller than 200 nm in the form of large agglomerates are separated and deposited in the hoppers of three cyclones. This leads to a significant reduction in the yield of the main product and a decrease in the utilization rate of raw materials in the preparation of nanoparticles.

A known installation for obtaining ultrafine powders of metals, alloys and chemical compounds by the method of electric explosion of a wire, containing a power source with a capacitive storage, a switching system, a reactor for blasting a wire with high-voltage and grounded electrodes, a wire feed mechanism, a powder collection system and a gas supply system (patent RF 2093311, B22F 9/14, published 10/20/1997). The plant is equipped with a wire deformation unit, a cyclone and an electrostatic precipitator with hoppers for collecting powder, a fan, a vortex-type rebound classifier and a truncated cone installed in the classifier chamber with a gap at the lower base with the chamber wall, and the upper base of the cone is made in the form of a slot directed on the classifier rotor, and along the axis of the cone there is a branch pipe for supplying gas with powder from the reactor, and the powder collection hopper is connected to the bottom of the classifier chamber through a pipeline with a gate, while the wire deformation unit is made in the form of rings or freely rotating rollers with a guide groove, mounted in a cage that rotates around the axis of the wire drawing, using rods to move rings or rollers at a given distance from the axis of rotation of the cage. The separator of the proposed design allows you to separate only particles larger than 0.5 microns.

Known installation for the production of powders of metals, alloys and chemical compounds by electric wire explosion, containing a reactor for electric wire explosion with high-voltage and grounded electrodes connected to a source of pulsed currents, a wire feed mechanism into the reactor, a gas and powder circulation system, and a gas separation and collection unit powder (RF patent 2247631, B22F 9/14, published on March 10, 2005). The gas and powder circulation system is made in the form of tubular gas outlets, connected at one end to the reactor opposite the interelectrode gap, and at the other end to the gas separation and powder collection unit, which is made in the form of expanders connected in series by means of nozzles, each of which is equipped with a powder accumulator. In the known device, there is no separator, and the existing system of expanders does not provide separation into a separate fraction of powder with a particle size of less than 200 nm.

A device is known that contains an explosion chamber, a wire feed mechanism, a high-voltage electrode and a grounded electrode installed in the chamber and connected to a power source for electric explosion of the wire to obtain powder particles, a system for separating powder particles by size, connected to the chamber through a pipeline equipped with a fan and made with the possibility of forced circulation of nitrogen as a working gas in the chamber, and a means of controlling the pressure of the working gas in the chamber (RF patent 2699886, B22F 9/14, publ. 09/11/2019). The high-voltage electrode is configured to supply liquid nitrogen through it to the chamber for cooling the working gas. The separator of the proposed design is intended only for separating particles larger than 5 microns.

A device for producing powder materials is known (RF patent 2675188, B22F 9/14, publ. 12/17/2018), selected as a prototype. The device for producing metal powder contains a reactor, electrodes installed in the reactor and connected to a power source for electric explosion of a metal wire to obtain powder particles, a wire feed mechanism and a particle size separation system, and also contains high-voltage and grounded electrodes. The particle size separation system is made in the form of a separator installed vertically under the reactor opposite the interelectrode gap and equipped with a hopper for collecting a large fraction of powder particles, a cylindrical cyclone installed in series with respect to the separator, connected to it by a pipeline and equipped with a hopper for collecting fine powder particle size less than 5 microns, and a fan connected by pipelines to the reactor and cyclone and made with the possibility of forced circulation of the gaseous medium in the form of argon, nitrogen or helium. The design of the separator used in this invention does not allow separating micron and submicron particles larger than 200 nm from the gas stream.

The problem to be solved by the invention is the effective separation of particles in the gas flow of the electric wire explosion installation.

EFFECT: obtaining powders of metal oxides with stable dispersion and chemical composition.

The problem is solved by the fact that the complex for obtaining nanoparticles of metal oxides by electric explosion of wire contains a reactor connected by a pipeline into a single gas-flow structure, made with the possibility of feeding a metal wire from the chamber of the wire feed mechanism, a high-voltage electrode and a grounded electrode placed in the reactor to provide an electric explosion metal wire, a separator with a hopper for collecting and unloading large particles of metal oxides, a cyclone with a hopper for collecting and unloading nanoparticles of metal oxides and a centrifugal fan that provides forced circulation of the working gas according to the above design. But unlike the prototype, a cylindrical structure is used as a separator, in which a cutter is additionally installed, having the shape of a truncated cone and installed at an angle of 45 degrees relative to the separator body, and the diameter of the cutter opening is 2 times smaller than the diameter of the inlet to the separator. The separator is a gas-dynamic device in which particles larger than 200 nm in size are separated from the gas stream. Microparticles are formed as a result of end effects accompanying the process of wire dispersion by a current pulse. The aerosol is accelerated in the narrow channel of the separator, and at the outlet of the channel, low-inertia nanoparticles continue their movement with the gas flow, while large microparticles move by inertia and settle in the bin for collecting large particles.

As a separator, a cylindrical structure is used, in which a cutter having the shape of a truncated cone is additionally installed. The angle at the base of the cone is 45°. The separation process is adjusted by changing the distance L (from (L _min ) to (L _max )) from the separator inlet with a diameter d1 to the cutter outlet with a diameter d2. The value of d2 is 0.5d1, which makes it possible to maintain the constancy of the gas flow rates when passing through a hole with diameters d1 and d2. As the distance L increases, the separation efficiency with the release of particles larger than 200 nm decreases. The cutter installed in the path of the gas flow prevents the entrainment of microsized and submicron particles, therefore, the efficiency of separating particles larger than 200 nm increases.

On FIG. 1 shows a schematic diagram of an installation for the production of metal oxide powders.

The installation includes the following units: 1 - wire dispersion reactor, 2 - high-voltage electrode, 3 - grounded electrode, 4 - high-voltage power source, 5 - wire feed mechanism, 6 - particle cutter, made in the form of a truncated cone. The angle at the base of the cone is 45°. The cutter removes particles larger than 200 nm from the gas stream, 7 - a separator in which particles are separated using a cutter 6, 8 - a hopper for collecting particles larger than 200 nm, 9 - a cyclone for separating particles with dimensions 10 from the gas stream ÷200 nm, 10 - a hopper for collecting particles with dimensions of 10÷200 nm, 11 - a fan for continuous circulation of the buffer gas in the closed volume of the device (the direction of the buffer gas flow in the closed volume is shown by arrows). The principle of operation is as follows. After the conductor reaches the high-voltage electrode (2), the electrical circuit closes and a current pulse flows in the circuit, leading to explosive destruction of the wire. As a result of the electric explosion of the wire, particles with sizes from 10 nm to 5 µm are formed. Under the action of forced circulation of the gas mixture, the particles are carried out of the reactor by flow (a). After passing through a pipe with a diameter of d1, the gas stream containing particles branches into two streams (b) and (c). Flow (b) carries away particles with sizes from 0.2 to 5 μm. When the gas flow (b) passes through the cutter outlet with a diameter d2, the flow (b) branches into two flows (d) and (e). Particles in the flow (d) with sizes from 0.2 to 5 μm, upon impact with the cutter surface, are deposited in the separator (flow (e)) and collected in hopper 8. Particles smaller than 200 nm are carried away by flow (c) from the separator into cyclone 9 and deposited in the hopper 10. The described scheme of particle separation allows you to remove from the gas stream (a) particles with sizes from 0.2 to 5 microns. The separation process is adjusted by changing the distance L (from (Lmin) to (Lmax)) from the inlet to the separator with a diameter d1 to the outlet of the cutter with a diameter d2. The value of d2 is 0.5d1, which makes it possible to maintain the constancy of the velocities of the pelvic flow during the passage of a hole with diameters d1 and d2. With increasing distance L, the separation efficiency with the release of particles larger than 200 nm decreases.

Below are examples of implementation.

Example 1

ZnO powder is obtained by blasting zinc wire. The device is pre-evacuated to a residual pressure of 10 ^-1 Pa, and then filled with an oxygen-containing working gas. Set the interelectrode distance 100 mm, the frequency of explosions 0.7 Hz. The gas mixture feed rate is 2.5 m/s. The cutter is located at the maximum distance L _max from the inlet to the separator. The accumulated products of the wire explosion, represented by a mixture of nano- and microparticles, are carried out by the gas flow from the reactor 1 to the separator 7. In the separator 7, the particles are separated into two fractions. Large particles are deposited in the hopper 8 of the separator. Small particles are taken out by the gas stream from the separator 7 to the cyclone 9 and are deposited in the hopper of the cyclone 10. The purified gas from the cyclone 9 is fed through the pipeline to the reactor.

Accumulated 100 g of powder (hopper 10), which is a particle with an average size of 77±4 nm (Fig. 2).

Example 2

ZnO powder was obtained in the same modes as described in example 1. In this case, the cutter is located at a minimum distance L _min from the inlet to the separator. The accumulated wire explosion products, represented by a mixture of nano- and microparticles, are carried out by the gas flow from the reactor 1 to the separator 7. In the separator 7, the particles are separated into two fractions. Particles of a large fraction are deposited in the hopper 8 of the separator. Particles of the fine fraction are taken out by the gas stream from the separator 7 to the cyclone 9 and are deposited in the hopper of the cyclone 10. The purified gas from the cyclone 9 is fed through the pipeline to the reactor.

Accumulated 100 g of powder (hopper 10), which is a particle with an average size of 67±2 nm (Fig. 3).

Example 3

ZnO-TiO ₂ powder is obtained by exploding two twisted zinc and titanium wires. The device is pre-evacuated to a residual pressure of 10 ^-1 Pa, and then filled with an oxygen-containing working gas. Set the interelectrode distance 100 mm, the frequency of explosions 0.7 Hz. The gas mixture feed rate is 2.5 m/s. The cutter is located at the maximum distance L _max from the inlet to the separator. The accumulated wire explosion products, represented by a mixture of nano- and microparticles, are carried out by the gas flow from the reactor 1 to the separator 7. In the separator 7, the particles are separated into two fractions. Large particles are deposited in the hopper 8 of the separator. Small particles are taken out by the gas stream from the separator 7 to the cyclone 9 and are deposited in the hopper of the cyclone 10. The purified gas from the cyclone 9 is fed through the pipeline to the reactor.

Accumulated 100 g of powder (hopper 10), which is a particle with an average size of 79±5 nm (Fig. 4).

Example 4

Powder ZnO-TiO ₂ was obtained in the same modes as described in example 3. In this case, the cutter is located at a minimum distance L _min from the inlet to the separator. The accumulated wire explosion products, represented by a mixture of nano- and microparticles, are carried out by the gas flow from the reactor 1 to the separator 7. In the separator 7, the particles are separated into two fractions. Particles of a large fraction are deposited in the hopper 8 of the separator. Particles of the fine fraction are taken out by the gas stream from the separator 7 to the cyclone 9 and are deposited in the hopper of the cyclone 10. The purified gas from the cyclone 9 is fed through the pipeline to the reactor.

Accumulated 100 g of powder (hopper 10), which is a particle with an average size of 69±2 nm (Fig. 5).

Claims (1)

A complex for producing metal oxide nanoparticles by electrical explosion of a wire, containing a reactor connected by a pipeline into a single gas-flow structure, made with the possibility of feeding a metal wire from the chamber of the wire feed mechanism, a high-voltage electrode and a grounded electrode placed in the reactor to provide an electric explosion of a metal wire, a separator with a hopper for collecting and unloading large particles of metal oxides, a cyclone with a hopper for collecting and unloading nanoparticles of metal oxides and a centrifugal fan that provides forced circulation of the working gas according to the above design, characterized in that a cylindrical design is used as a separator, in which a cutter is additionally installed , having the shape of a truncated cone and installed at an angle of 45 degrees relative to the separator body, and the diameter of the cut-off hole is 2 times less than the diameter of the inlet hole to the separator.

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