RU2590045C2 - Method of producing metal nanopowder from wastes of high speed steel in kerosene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of powders. Wastes of high speed tungsten-containing steel P6M5 are subjected to electroerosion dispersion in a reactor in a medium of a dielectric fluid by means of spark discharge between said wastes and electrodes consisting of same material. Dielectric liquid used is kerosene.

EFFECT: formation at reactor bottom of a sediment in form of spherical particles of metal nanopowder based on tungsten carbide.

1 cl, 5 dwg, 1 ex

Description

The present invention relates to the field of powder metallurgy, namely to obtain nanopowders.

Similar methods are known for producing metal powder, which are based on physicochemical processes. For example, a method of producing a metal powder by forming between the particles of arc discharges in a dielectric fluid (Russian patent No. 2116164, B22F, 1998).

The closest analogue of the claimed invention is a method for producing a metal powder by electroerosive dispersion of waste of high-speed steel P6M5, disclosed in the article by AGEEV E.V. et al. X-ray microanalysis of a powder obtained from high-speed steel wastes by electroerosive dispersion in an aqueous medium, Visnik of Sumy National Agricultural University, Seriya “Mechanization and Automation of Tombstone Processes”, issue 10 (25), 2013, p. 216-219, [on-line], [found August 17, 2015 at irbus-nbuv.gov.ua] / [1].

Its disadvantages include:

- a relatively large size of the resulting particles;

- oxidation of powder particles.

The objective of the invention is to obtain nanoscale powders based on tungsten carbide with a spherical particle shape.

The problem is solved by a method that includes electroerosive dispersion (EED) of waste of high-speed tungsten-containing steel P6M5 in a reactor in a dielectric fluid medium - in kerosene, by means of spark discharges between these wastes and electrodes consisting of the same material with the formation of a precipitate in the form of particles of a metal nanopowder at the bottom of the reactor.

DESCRIPTION

Figure 1 schematically shows the EED process: 1 - pulse generator; 2, 3 - electrodes; 4 - drops of molten material; 5 - working fluid; 6 - hard alloy plates; 7 - discharge channel; 8 - discharge point, 9 - gas bubble.

Figures 2-3 show images from a QUANTA 600 FEG scanning electron microscope, which were performed to study the shape and size of microparticles.

Figure 4 shows the results of particle size studies using the Fraunhofer method.

Table 1 presents the main phases of the BRS powder.

The technological process of obtaining nanopowders from high-speed steel waste by the EED method includes the following operations:

- collection and sorting of steel waste by grade (chemical composition);

- waste treatment (from pollution, chips);

- loading high-speed steel wastes into the reactor and connecting electrodes;

- pouring into the reactor a working fluid (distilled water or lighting kerosene);

- choice of dispersion modes;

- electroerosive dispersion;

- sedimentation and discharge of the working fluid;

- separation of the nanoscale fraction by centrifugation;

- chemical cleaning of the powder (if necessary);

- calcination of the powder in the furnace at a temperature of 150-200 ° C for 20-30 minutes;

- quality control.

The EED process is the destruction of conductive material as a result of local exposure to short-term electrical discharges between the electrodes [2]. In the discharge zone, under the influence of high temperatures, heating, melting and partial evaporation of the metal occur.

To obtain high temperature in a limited area of small volume, a large concentration of energy is required. Achieving this goal is carried out using pulsed voltage, and EED is carried out in a liquid medium that fills the gap between the electrodes, called the interelectrode gap or interelectrode gap.

Due to the fact that any smooth surface has its own macro- or microrelief, there will always be two points between two electrodes, the distance between which will be less than between other points of the electrode surfaces. When a current source (in this case, a pulsed one) is connected to the electrodes, a current flows between the electrodes and an electric field arises, the intensity of which between the nearby points of the electrodes will reach its maximum value. Under the influence of an electric field in the zone of the highest voltage, ionization of the working medium occurs with the formation of a channel with increased cross-country ability, i.e. disturbed electrical strength of the working environment. And between these two nearby points there is a breakdown of the interelectrode gap. Between the points at which the breakdown of the working medium occurred, a channel with high electrical conductivity is formed.

The cross section of the discharge channel is small, and its expansion is impeded by a magnetic field that compresses the channel. The working environment surrounding the discharge channel plays the same role. The length of the discharge channel and its diameter are very small and therefore the energy density in it reaches large values, and the temperature in this local volume is tens of thousands of degrees. At points where the discharge channel is supported by electrodes, the material is melted and vaporized from the surface of the electrodes. The working medium surrounding the discharge channel decomposes and evaporates under the influence of high temperatures. All these processes occur in very small periods of time and with the release of large energies, so they are dynamic explosive in nature.

Under the action of forces developing in the discharge channel, the liquid material and vaporous material are ejected from the discharge zone into the working medium surrounding it and freezes in it with the formation of individual particles. Wells appear on the surface of the electrodes at the site of the current pulse, which are formed due to the removal of material by a pulsed discharge. Thus, electrical erosion is carried out, as exemplified by the action of a single pulse, with the formation of one erosion hole. After the termination of the pulse discharge, the voltage at the electrodes drops. The process of deionization of the working environment begins, i.e. neutralization of charged particles and electric strength of the working medium is restored. The interelectrode gap is prepared for the passage of the next discharge. If a pulse voltage is periodically supplied to the electrodes from the generator, the process will be repeated. In this case, each new pulse discharge will occur in the place where the distance between the electrodes is minimal. If the pause between pulsed discharges is sufficient to deionize the working medium, then the process will be repeated with the formation of new erosion holes on the surface, and this is the reason for the EED process.

The powder materials obtained by the EDR of high-speed steel waste can be effectively used as a high-solid phase in the manufacture and restoration of machine parts by various surfacing methods (plasma-powder surfacing, surfacing under a flux layer, surfacing in a protective gas environment, etc.) and spraying (detonation spraying , plasma spraying, etc.), when applying galvanic coatings (chromium plating, ironing, etc.), as well as as modifiers of various cast alloys or additives in the manufacture of tools and high speed steel.

Example.

Wastes of high-speed steel grade P6M5 were dispersed in a kerosene in an experimental setup. At the same time, the electrical parameters of the installation were changed:

- pulse repetition rate of 100 Hz;

- voltage at the electrodes 200 V;

- Capacitor capacitance 55 μF.

The pulse voltage of the generator 1 is applied to the electrodes 2 and 3 and then to the waste of high-speed steel 6 (drills made of high-speed steel serve as electrodes). When a voltage of a certain value is reached, an electrical breakdown of the working medium 5 takes place, located in the interelectrode space, with the formation of a discharge channel 7. Due to the high concentration of thermal energy, the material at the discharge point 8 melts and evaporates, the working medium evaporates and surrounds the discharge channel with gaseous decomposition products 9 ( gas bubble). As a result of significant dynamic forces developing in the discharge channel and the gas bubble, droplets of molten material 4 are ejected outside the discharge zone into the working medium surrounding the electrodes and freeze in it, forming droplet-like particles (Fig. 1). Moreover, by changing the electrical parameters of the dispersion process (voltage at the electrodes, capacitance of the capacitors and pulse repetition rate), it is possible to control the width and offset of the particle size interval, as well as the performance of the process. A centrifuge is used to separate nanoparticles from large ones.

Using a QUANTA 600 FEG scanning electron microscope, a direct analysis of powder particles with a fairly high resolution was carried out. It was found that the powder obtained by the EED method from waste BRS consists of particles of regular spherical shape (or elliptical), irregular shape (conglomerates) with a particle size of from 0.01 μm to 50 μm.

X-ray microanalysis, the study of the elemental composition of powder samples was carried out on an electron-ion scanning (raster) microscope with field emission of electrons "QUANTA 600 FEG" and an energy-dispersive X-ray analyzer of the company "EDAX". It was found that the test sample of the BRS powder contains iron, oxides and iron carbide as the main minerals, and also contains a small amount of tungsten.

The proposed method for producing a metal powder from high-speed steel waste in kerosene gives the following advantages compared to known methods:

- achieved a small average size and spherical shape of the particles;

- the particle size depends on the process parameters that are controlled by the installation, and not on the mesh size of the mesh;

- adjustment of parameters can be carried out without stopping the process;

- ensures the purity of the composition of the obtained powder from impurities,

since there is no grid, and the electrodes are made of the same metal as the working material.

Information sources

1. Ageeva E.V. et al. X-ray microanalysis of a powder obtained from high-speed steel wastes by electroerosive dispersion in an aqueous medium // News of the Sumy National Agrarian University, Seria, “Mechanization and Automation of Tombstone Processes,” issue 10 (25), 2013, p. 216-219, [on-line], [found 08/17/2015 on irbus-].

2. Nemilov EF Electroerosive processing of materials. L .: Engineering, Leningrad. Otdel, 1983. - 160 p.

Claims (1)

A method of producing a metal nanopowder from the waste of high-speed tungsten-containing steel P6M5, comprising electroerosive dispersion of these wastes in a dielectric liquid medium in a reactor, characterized in that kerosene is used as a dielectric liquid, while electroerosive dispersion is carried out by means of spark discharges between these wastes and electrodes consisting of of the same material, with the formation of a precipitate in the form of particles of a metal nanopowder based on tungsten carbide on d e reactor.

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