RU2699886C1 - Method of producing metal powder and device for its implementation - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: group of inventions relates to production of metal powder. Method includes electric explosion of metal wire in explosion chamber with forced circulation of nitrogen as working gas. Electric explosion of wire is carried out at the value of energy introduced into wire in range from 0.6 to 0.9 of energy of sublimation of wire metal and constant cooling of working gas in chamber to temperature of not more than 40 °C by continuous supply of liquid nitrogen, wherein pressure in explosion chamber is kept at not more than 0.85 atm. Device comprises explosion chamber, wire feed mechanism installed in chamber and connected to power supply high-voltage electrode and grounded electrode for electric explosion of wire to obtain powder particles, system for separation of powder particles by size, connected to chamber by means of pipeline equipped with fan and made with possibility of forced circulation of nitrogen as working gas in chamber, and means of control of working gas pressure in chamber. High-voltage electrode is configured to feed liquid nitrogen thereto for cooling of working gas.

EFFECT: preventing sintering of powder particles.

6 cl, 5 dwg, 6 ex

Description

FIELD OF TECHNOLOGY

The invention relates to powder metallurgy, in particular to the production of bimodal powder materials containing a mixture of nano- and microparticles, in particular for the production of powder materials from heat-resistant, heat-resistant and corrosion-resistant alloys for additive technologies for the synthesis of parts of complex systems.

BACKGROUND OF THE INVENTION

Due to their small size, metal nanoparticles have a large specific surface energy, which determines their high chemical activity and the ability to form micron agglomerates. For practical applications, as a rule, the destruction of agglomerates to primary particles is required. In order to separate particle agglomerates into components, such deagglomeration methods as ultrasonic treatment and mechanical homogenization of particle agglomerates in liquid media, spraying of suspensions of nanoparticles at high pressures, etc. are used.

However, metal nanoparticles in the process of production by the EEC method form sintered agglomerates from individual nanoscale elements that are firmly connected to each other. Particles in such agglomerates are interconnected by stronger interactions than Van der Waals forces, and their destruction is a separate and difficult task. It is more efficient to prevent the formation of sintered agglomerates upon receipt of nanoparticles.

When energy (0.6–0.9) E _c is introduced into the wire, bimodal powders are formed from nano- and microparticles. When energy is introduced into the wire that is lower than the sublimation energy (0.6–0.9) E _{s, the} bulk of the EEC products are particles of the liquid phase of the alloy, the sizes of which vary in the range from units to several tens of micrometers. When particles of liquid metal collide with the surface of a high-voltage electrode, particles are deposited on the surface of the electrode. During continuous operation of the installation, the deposition of particles leads to a local formation of a growth on the surface of the electrode, the length of which can reach several centimeters. With the formation of a growth, the interelectrode distance decreases, which leads to an unpredictable decrease in the length of the exploding wire. Reducing the length of the exploding wire at a constant value of the charging voltage, depending on the type of metal, leads either to shunting the wire by current (reducing the specific energy introduced into the wire), or to reducing the volume of the exploded metal (increasing the specific energy introduced into the wire). This in turn leads to a change in the dispersed composition of the obtained powder, because the average particle size and the ratio of nano- and microparticles is determined by the specific value of the energy transferred to the wire.

A known method of producing highly dispersed powders of inorganic substances, disclosed in [RU2048277C1, publ. 20.11.1995], in which metal preforms are blown with a diameter of 0.2 - 0.7 mm under the influence of a current pulse at an energy density transmitted to the preform equal to 0, 9 sublimation energy of the metal to its ionization energy, for no more than 15 μs in a gaseous medium under a pressure of 0.5 - 10 atm. Metals and alloys having a ratio of ionization energy to sublimation energy equal to or more than 0.9 are used as a metal billet , and the ratio of specific metal's resistance to liquid and solid state, is equal to or greater than 1.

This invention solves the problem of preventing sintering of particles after they are obtained, and not during the EEC process, i.e. issues of optimizing temperature conditions inside the chamber are not being addressed. Also, with the indicated explosion parameters, bimodal powders cannot be obtained.

A known installation for producing powders of metals, alloys and chemical compounds by electric explosion of a wire, disclosed in [RU2247631C1, publ. 03/10/2005], which provides an increase in the quality of the obtained product by reducing powder agglomeration. In the proposed installation, containing a reactor for electric explosion of a wire with a high voltage and grounded electrodes connected to a source of pulsed currents, a mechanism for supplying wire to the reactor, a gas and powder circulation system and a gas separation and powder collecting unit, according to the invention, the gas and powder circulation system is made in in the form of tubular vents connected at one end to the reactor opposite the interelectrode gap, and at the other to a gas separation and powder collection unit, which is made as a follower but connected by means of nozzles of expanders, each of which is equipped with a powder accumulator, ensuring the ratio: Si / Si + 1≥1.43, where i = 1, 2 ..., S1 is the total passage area of the tubular vents, S2, S3. ..- sectional area of the connecting pipes. The main technical result is to improve the quality of the resulting product by reducing the agglomeration of powders: agglomerate content ≤ 6% wt. and diameter ≤ 2.3 μm. The use of this installation allows to reduce by 19 times the characteristic size of the agglomerates and 10 times the content of agglomerates in the resulting powder in comparison with the prototype. Offered in the known invention, the system of gas vents and expanders allows you to more carefully separate the resulting particles in size. First, separate large agglomerates, then everything is smaller and smaller, so that particles of the desired size remain in the product, namely ≤ 2.3 μm.

However, this method does not prevent the sintering of particles upon receipt, but fights the consequences, i.e. prevents sintered agglomerates from entering the marketable product.

The disadvantages of the two above analogues can be attributed to the fact that using the techniques and modes stated in them, in the process of electric explosion of wires made of chromium-nickel alloys, particles will sinter with the formation of isthmuses between particles and the formation of irregular agglomerates. The reason for this formation is the low sintering temperature of the nanoparticles and the high temperature of the working gas during the operation of an electric explosive installation.

Thus, there is a need to create a method for preventing sintering of particles during the electric explosion of wires when receiving bimodal powders from heat-resistant, heat-resistant and corrosion-resistant alloys.

SUMMARY OF THE INVENTION

The basis of the invention is the task of developing a method of electric explosion of metal wires, in which the cooling process of the explosion products would be more efficient to prevent sintering of particles of the nanoscale fraction with the formation of isthmuses between particles (the formation of sintered particles among themselves) and, accordingly, the formation of irregular agglomerates.

EFFECT: obtaining bimodal powders from heat-resistant, heat-resistant and corrosion-resistant alloys, consisting of spherical nano- and microparticles not sintered among themselves.

Another technical result is an increase in the operating time of the installation, due to a decrease in the shutdown time for cleaning the electrode, since the cooling of the high-voltage electrode prevents the formation of a build-up on its surface, which is formed as a result of surfacing of liquid metal particles.

The problem is solved in that the proposed method for producing metal powder includes an electric explosion of a metal wire in a reactor (explosive chamber) with forced circulation of the working gas.

What is new is that the wire is blown up with the amount of energy introduced into the wire in the range from 0.6 to 0.9, the sublimation energy of the metal of the wire, and the working gas is constantly cooled to a temperature of no more than 40 ° C, by continuously supplying liquid nitrogen to the explosive chamber, while for the continuous supply of liquid nitrogen, the pressure in the blast chamber is maintained no more than 0.85 atm.

The reason for the formation of sintered agglomerates during the production of powder materials from heat-resistant, heat-resistant, and corrosion-resistant alloys is the low sintering temperature of nanoparticles and the high temperature of the working gas during operation of an electric explosive installation. At temperatures above 40 ° C, metal nanoparticles sinter, forming irregularly shaped agglomerates. An effective way to prevent sintering of nanoparticles is to cool the working gas in an explosive chamber.

The working gas is cooled by periodically supplying liquid nitrogen to the blast chamber.

The problem is also solved by the fact that the proposed device for producing metal powder from heat-resistant, heat-resistant and corrosion-resistant alloys contains an explosive chamber, a grounded electrode installed in the explosive chamber and a high-voltage electrode connected via a switch to a power source to supply high voltage to it in order to realize an electric explosion metal wire to obtain powder particles, wire feeder, fan for forced circulation of the working gas, connected pipelines with a reactor (explosive chamber).

New is that the device contains means for monitoring the pressure of the working gas, and the aforementioned high-voltage electrode is configured to supply liquid nitrogen through it to the explosive chamber.

As a means of monitoring the working gas pressure, the device comprises an electronic sensor installed in the gas path of the installation.

It is advisable that the high-voltage electrode is made hollow and with at least one inlet made with the possibility of connecting the electrode to a tube that connects to a source of liquid nitrogen and at least two outlet openings made on the side of the electrode facing the wire for continuous supply of liquid nitrogen into the explosive chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 shows a schematic diagram of the installation.

In FIG. 2 shows a constructive solution of a high voltage electrode.

In FIG. 3 a and b show microphotographs of particles of a heat-resistant alloy of the ХН70Ю grade obtained by transmission electron microscopy, respectively a) without gas cooling, and b) at a gas temperature of 30 ° C, in FIG. 3 c - shows a micrograph of a bimodal powder obtained using scanning electron microscopy.

In FIG. 4 a and b show microphotographs of powder particles obtained from the heat-resistant KhN60VT alloy obtained by transmission electron microscopy, respectively: a) without gas cooling, and b) at a gas temperature of 30 ° C; in FIG. 3 c - shows a micrograph of a bimodal powder obtained using scanning electron microscopy.

In FIG. 5 a and b show micrographs of powder particles obtained from 316L corrosion-resistant alloy, respectively: a) without gas cooling, and b) at a gas temperature of 30 ° C; in FIG. 5 c - micrograph of bimodal powder obtained using scanning electron microscopy.

DETAILED DESCRIPTION OF THE INVENTION

The device contains (figure 1): 1 - high-voltage cable entry; 2 - pipelines to ensure aerosol circulation along the installation circuit (aerosol flows are indicated by arrows); 3 - electric fan; 4 - camera switch, 5 - switch; 6 - high voltage electrode; 7 — blast chamber; 8 — electric drive of the device for straightening the wire; 9 - chamber of the wire feed mechanism; 10 - coil with wire; 11 - wire feed mechanism (electric drive mechanism is not shown in the figure); 12 - low voltage electrode; 13 - separator; 14 - a vessel with liquid nitrogen; 15 - connecting brass tube for supplying liquid nitrogen; 16 - a cyclone for trapping nano- and microparticles; 17 - container for collecting and unloading nano- and microparticles; 18 - electronic pressure sensor of the working gas, 19 - cavity in the high-voltage electrode, 20 - nozzles for supplying nitrogen to the explosive chamber, 21 - nitrogen movement in the explosive chamber, W - exploding wire.

The device operates as follows.

The operation of the installation is carried out in accordance with its circuit diagram (Fig. 1). The movement of the wire W from the coil 10 towards the high-voltage electrode 6 is carried out by the feed mechanism 11 with the drive of the straightening wire 8. When the wire W closes the gap "high voltage electrode - low voltage electrode", a current pulse flows in the circuit, under which the wire W explodes.

The design of the high voltage electrode 6 is shown in FIG. 2.

The proposed design solution of the high-voltage electrode allows for continuous supply (by injection) of liquid nitrogen into the reactor through two holes 20 made on one of the bases of the high-voltage electrode 6 (the high-voltage electrode is a hollow disk with a base diameter of 100 mm and a height of 15 mm ) facing towards the exploding wire. The cavity with liquid nitrogen 19 of the high voltage electrode is connected by a brass tube 15 to a vessel 14 containing liquid nitrogen. Due to the pressure difference between the explosive chamber 7 and the vessel with liquid nitrogen 14, there is a continuous flow of nitrogen from the vessel into the explosive chamber. For the continuous flow of liquid nitrogen, the pressure in the installation should not exceed 0.85 atm. Upon reaching the specified value, which is controlled by an electronic sensor (mounted in the upper base of the cyclone to capture nano- and microparticles) of the gas pressure, a fore-vacuum deposit (not shown) is turned on to pump gas from the installation to a pressure of 0.8 atm. The cycle repeats continuously. The aerosol formed during wire explosion, represented by nano- and microparticles of alloys, interacts with cooled gas in the near-electrode region and, under the action of a gas stream from fan 3, separator 13 passes through piping 2 into a cyclone for collecting powder 16 and settles in a container 17 for collecting and unloading bimodal powders of nano- and microparticles with a particle size of less than 5 microns. The purified gas through the pipe 2 passes the fan 3 and returns to the explosive chamber. The cycle repeats continuously.

The invention is also illustrated by the following examples of obtaining powder from a heat-resistant alloy of the brand ХН70Ю, heat-resistant alloy of the brand ХН60ВТ, corrosion-resistant alloy of the brand 316L.

Example 1

Powder from nano- and microparticles of KhN70Y alloy is obtained by blasting a wire of heat-resistant alloy of the KhN70Y grade with a diameter of 0.4 mm and a length of 80 mm in a nitrogen atmosphere. Before filling with nitrogen, the device is pre-evacuated to a residual pressure of 10 ^-1 Pa. The sublimation energy of the wire material ( E _s ) is 6.2 kJ / g. An energy of the order of 0.85 E _c is supplied to the wire located in the explosive chamber 7. Energy is supplied to the wire within 3.5 μs. The fan 3 through a pipeline connecting it to the explosive chamber 7, provides a continuous supply of working gas of nitrogen at a speed of 2.5 m / s. The accumulated wire explosion products, represented by a mixture of nano- and microparticles, are fed from the blasting chamber 7 to a separator 13 by a stream of working gas of nitrogen. Particles larger than 5 microns are separated in the separator. Particles with sizes greater than 5 microns are deposited in the hopper of separator 13. Particles with sizes less than 5 microns are carried out by the flow of working gas from separator 13 to cyclone 16. Due to the vortex circulation of the gas stream in cyclone 16, particles are deposited with sizes less than 5 microns - in the cyclone hopper 17 . During the operation of the installation, the working gas nitrogen is heated. The temperature of the nitrogen working gas rises to 60 ° C. The purified gas from cyclone 16 is piped to the inlet of fan 3 and again fed into the blast chamber 7. The working gas heated to 60 ° C is circulated inside the unit. Dispersion of the wire is carried out at a working gas temperature of 60 ° C. Accumulated 120 g of powder (hopper 17), which is an agglomerate of particles.

Typical images of agglomerates of the obtained particles are shown in figure 3A.

As can be seen in the image, in the case of an electric explosion of a wire made of the KhN70Y heat-resistant alloy without cooling the working gas with liquid nitrogen, bimodal powders are formed, including agglomerates of irregularly sintered nanoparticles.

Example 2

Powder from nano- and microparticles of KhN70Y alloy is obtained by blasting a wire of heat-resistant alloy of the KhN70Y grade with a diameter of 0.4 mm and a length of 80 mm in a nitrogen atmosphere. Before filling with nitrogen, the device is pre-evacuated to a residual pressure of 10 ^-1 Pa. Sublimation energy ( E _s ) 6.2 kJ / g. An energy of the order of 0.85 E _c is supplied to the wire located in the blasting chamber 10 from the power source 1. Energy is supplied to the wire within 3.5 μs. Fan 3 carries out continuous circulation of the working nitrogen gas inside the unit at a speed of 2.5 m / s. The accumulated products of wire explosion are carried away by a gas stream into the separator 13, and particles with sizes greater than 5 μm are deposited. Particles with sizes less than 5 microns are then taken out by the flow of the working gas into the cyclone 16 and deposited in the cyclone 17 hopper. The purified gas from the cyclone 16 is piped to the inlet of fan 3 and again fed to the blast chamber 7. In the blast chamber, the gas purified from particles, with gas / vapor formed when nitrogen boils at the outlet of the high-voltage electrode. By mixing, the gas temperature drops to 30 ° C. Cooled gas circulates inside the unit. Dispersion of the wire is carried out at a working gas temperature of 30 ° C. 120 g of powder (hopper 18), which is a mixture of nano and microparticles, has been accumulated.

In FIG. Figure 3b shows a photomicrograph of a bimodal powder of a heat-resistant alloy of the ХН70Ю grade obtained by transmission electron microscopy. In FIG. 3c shows a micrograph of a bimodal powder obtained using scanning electron microscopy.

Thus, during an electric explosion of a wire with cooling of the working gas with liquid nitrogen, bimodal powders are formed, including nano- and microparticles.

Example 3

Powder from nano- and microparticles of KhN60VT alloy is obtained by exploding a wire of heat-resistant KhN60VT alloy with a diameter of 0.6 mm and a length of 70 mm in an atmosphere of a working nitrogen gas. Before filling with nitrogen, the device is pre-evacuated to a residual pressure of 10 ^-1 Pa. The sublimation energy of the wire material ( E _s ) 6.8 kJ / g An energy of the order of 0.85 E _c is supplied to the wire located in the blasting chamber 7. Energy is supplied to the wire within 5.5 μs. The working gas circulation rate of nitrogen is 2.5 m / s. The temperature of the working gas of nitrogen is 60 ° C. We accumulated 120 g of powder (hopper 18), which is an agglomerate of particles.

Typical images of agglomerates of the obtained particles are shown in figure 4A.

As can be seen in the image, during the electric explosion of a wire made of the heat-resistant KhN60VT alloy without cooling the working gas with liquid nitrogen, bimodal powders are formed, including agglomerates of irregularly sintered nanoparticles.

Example 4

Powder from nano- and microparticles of KhN60BT alloy is obtained by exploding a wire of heat-resistant alloy of the KhN60BT grade with a diameter of 0.6 mm and a length of 70 mm in a nitrogen atmosphere. Before filling with nitrogen, the device is pre-evacuated to a residual pressure of 10 ^-1 Pa. Sublimation energy ( E _s ) 6.8 kJ / g. An energy of the order of 0.85 E _c is supplied to the wire located in the blasting chamber 7. Energy is supplied to the wire within 5.5 μs. The argon working gas circulation rate inside the unit is 2.5 m / s. The purified gas from the cyclone 16 is piped to the inlet of the fan 3 and then fed back to the blast chamber 7. In the blast chamber, the gas purified from particles is mixed with the gas / vapor that forms when nitrogen boils at the outlet of the high-voltage electrode. By mixing, the temperature of the gas drops to 30 ° C and the cooled gas circulates inside the unit. Dispersion of the wire is carried out at a working gas temperature of 30 ° C. 120 g of powder (hopper 18), which is a mixture of nano and microparticles, has been accumulated.

In FIG. Figure 4b shows a photomicrograph of a bimodal powder of a heat-resistant alloy of the brand ХН60ВТ obtained using transmission electron microscopy. In FIG. 4c shows a micrograph of a bimodal powder obtained using scanning electron microscopy.

Thus, during an electric explosion of a wire with cooling of the working gas with liquid nitrogen, bimodal powders are formed, including nano- and microparticles.

Example 5

The powder of nano- and microparticles of alloy 316L is obtained by exploding a wire of a corrosion-resistant alloy of grade 316L with a diameter of 0.35 mm and a length of 80 mm in an atmosphere of nitrogen. Before filling with nitrogen, the device is pre-evacuated to a residual pressure of 10 ^-1 Pa. The sublimation energy of the wire material ( E _s ) 5.8 kJ / g An energy of the order of 0.85 E _c is supplied to the wire located in the blasting chamber 7. Energy is supplied to the wire within 3.0 μs. The working gas circulation rate of nitrogen is 2.5 m / s. The temperature of the working gas of nitrogen is 60 ° C. Accumulated 120 g of powder (hopper 17), which is an agglomerate of particles.

Typical images of agglomerates of the obtained particles are shown in figure 5A.

As can be seen in the image, during electric explosion of a wire from a corrosion-resistant alloy of grade 316L without cooling the working gas with liquid nitrogen, bimodal powders are formed, including sintered agglomerates of nanoparticles.

Example 6

The powder of nano- and microparticles of alloy 316L is obtained by exploding a wire of a corrosion-resistant alloy of grade 316L with a diameter of 0.35 mm and a length of 80 mm in an atmosphere of nitrogen. Before filling with nitrogen, the device is pre-evacuated to a residual pressure of 10 ^-1 Pa. Sublimation energy ( E _s ) 5.8 kJ / g. An energy of the order of 0.85 E _c is supplied to the wire located in the blasting chamber 7. Energy is supplied to the wire within 3.0 μs. The circulation speed of the working nitrogen gas inside the installation is 5.5 m / s. The purified gas from the cyclone 16 is piped to the inlet of the fan 3 and again enters the blast chamber 7. In the blast chamber, the gas purified from the particles is mixed with the gas / vapor that forms when nitrogen boils at the outlet of the high-voltage electrode. By mixing, the gas temperature drops to 30 ° C. Cooled gas circulates inside the unit. Dispersion of the wire is carried out at a working gas temperature of 30 ° C. 120 g of powder (hopper 18), which is a mixture of nano and microparticles, has been accumulated.

Representative images of the particles are shown in figures 5 b and c.

In FIG. 5 b, images were obtained using transmission electron microscopy; Fig. 5 c shows a micrograph of a bimodal powder obtained by scanning electron microscopy.

In an electric explosion of a wire of 316L corrosion-resistant alloy with cooling of the working gas with liquid nitrogen, bimodal powders are formed, including nano- and microparticles.

Claims (6)

1. A method of producing a metal powder, comprising an electric explosion of a metal wire in an explosive chamber with forced circulation of nitrogen as a working gas, characterized in that the electric explosion of a metal wire is carried out at a value of energy introduced into the wire in the range from 0.6 to 0, 9 the energy of sublimation of the metal wire and the constant cooling of the working gas in the chamber to a temperature of not more than 40 ° C by continuous supply of liquid nitrogen, while the pressure in the blast chamber is maintained no more than 0.85 atm . 2. The method according to claim 1, characterized in that they use a metal wire of heat-resistant, heat-resistant, corrosion-resistant alloys with a diameter of from 0.35 to 0.6 mm 3. A device for producing a metal powder, comprising an explosion chamber for electric explosion of a metal wire, a mechanism for supplying a metal wire into the chamber, a high-voltage electrode and a grounded electrode for electric explosion of a metal wire to produce powder particles installed in the chamber and connected to a power source, a particle separation system powder in size, connected to the chamber by means of a pipeline equipped with a fan and made with the possibility of forced circulation uu nitrogen as the working gas in the chamber, characterized in that it comprises a pressure control means of the working gas in the chamber, wherein the high voltage electrode is arranged to supply therethrough a liquid nitrogen chamber for cooling the working gas. 4. The device according to p. 3, characterized in that the high-voltage electrode is hollow and has at least one inlet for connecting the cavity of the high-voltage electrode with a source of liquid nitrogen and at least two outlet openings made on the surface of the high-voltage electrode facing to the side blasting metal wire for feeding liquid nitrogen into the chamber. 5. The device according to p. 3, characterized in that as a means of monitoring the pressure of the working gas, it contains an electronic sensor. 6. The device according to claim 4, characterized in that it contains a vessel for liquid nitrogen with a brass tube for supplying liquid nitrogen to the inlet of the high voltage electrode.

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