RU2684295C1 - Method and device with a rotating magnet for electrochemical metallisation of magnetic powders - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to powder metallurgy, particularly, to electrochemical metallization of powders. Method of electrochemical metallization of magnetic powders, including loading of powder into electrolysis cell, after powder loading into electrolysis tank, under which rotating magnet or cascade of rotating magnets is placed, cathode is introduced so that powder touches its bare part. Rotary magnet or cascade of rotating magnets is turned on to provide electric contact between cathode and mass of particles, as well as between separate particles and filled with electrolyte. Anode made of deposited material or graphite is inserted into upper layer of electrolyte, current source is included and mixing is performed by means of rotating magnetic field created by magnet rotating in different planes or cascade of magnets, so as to ensure retention of powder particles near cathode with simultaneous rotation of each particle. Device for electrochemical metallization of magnetic powder comprises container from non-electroconductive material for placement of powder and electrolyte in it, under the bottom of which there is a rotating magnet or cascade of rotating magnets, made with possibility of rotation in different planes, a cathode, an anode and a current source. Cathode is made in form of graphite rod and contains isolated from contact with solution part and bare part at lower end to ensure contact with powder, and anode from deposited metal or graphite is made with possibility of its introduction into upper layer of electrolyte.EFFECT: improved conductive properties of powder due to uniformity of coating.5 cl, 1 tbl, 2 dwg, 3 ex

Description

The invention relates to powder metallurgy, in particular, to devices for electrochemical metallization of powders, the use of which includes, but is not limited to the manufacture of catalysts, magnetic solders, pigments, fillers of magnetic conductive elastomers, magnetic powders for recording devices, powders as components for pyrotechnic compositions, creation multilayer powder alloys.

There are various methods and hardware options for the process of electrochemical metallization of magnetic powders. A process is described for the electrometallization of fine particles by suspending conductive particles in an electrolyte containing ions of a deposited metal. Electrometallization is carried out by passing a direct current through suspensions of conductive powders ranging in size from 0.1-10 microns, in which particles moved by the flow of circulating liquid come into contact with the cathode, but do not reach the anode. Fluid flow can be generated by both the rotor and the pump. The cathode is a plate with which metallized particles come into contact (patent US 4908106, IPC C25D 7/00, 04/13/1990). The disadvantage is the abnormally low contact time of particles with the cathode due to the large uncertainty of the collision of particles with the cathode.

A known method of electrolytic encapsulation of conductive bulk powder materials with nickel or other metals in an automated centrifuge. Particles slide along the surface of the cathode and are removed from the metallization zone (patent US 5565079, IPC C25D 1/00, 10/15/1996). The disadvantage of this method is the low probability of contact of particles with the cathode.

A known method of electrometallization of the surfaces of powder materials, regardless of particle size and with a high speed of the process, which is cyclical in nature and consists of at least 3 independent stages in each cycle of work: mixing, sedimentation, electrometallization. The mixing step begins immediately after electrodeposition, and is carried out with sufficient intensity to disperse the particles and break the bonds that formed in the sedimentation layer by increasing the metal shell during electrodeposition (patent US 6010610, IPC C25D 7/00, 04.01.2000). The method is quite simple, however, as the authors indicate, the formation of powder aggregates during metallization in a fixed layer is very likely, which subsequently requires a dispersion step.

To prevent particles from sticking together during electrometallization of powder materials, a method is known that is carried out in a fluidized bed container that is created by vibration (US Pat. No. 6,254,757, IPC C25D 7/00, 07/03/2001). The disadvantage is the reduced likelihood of contact of the particles with the cathode in the fluidized bed mode.

A known method and apparatus for carrying out electrolytic processing of powder materials, in particular, ultrafine powders with particle sizes in the nano-region or in the region of micron fractions during planetary rotation of a flowing electrolytic cell. The planetary rotation of the cell creates a centrifugal force, under the action of which the powder material is collected and continuously mixed, which makes electrometallization uniform. An array of electrodes and a system with a roller contact make it possible to apply electric potential only to those electrodes that are in contact with the powder material being processed (patent US 2002179430, IPC C25D 17/00, 05/05/2002). The method provides both pressing the powder to the cathode and mixing the powder, however, the hardware design is very complicated, and the metallization process proceeds in a batch mode.

A known method of processing electrically conductive nanoparticles by using an electrochemical cell for dynamic processing. The method is implemented through a simple design with stirring the particles of the suspension (US patent 2009145772, IPC C02F 1/461, 06/11/2009). A significant drawback is the small degree of metallization of the particles and the high degree of coating on the cathode.

A known method and apparatus (patent US 2003038034, IPC C25D 5/00, 02.17.2003), taken as a prototype, for microencapsulation and electrodeposition of coatings on powders of ferromagnetic and magnetically soft materials with particle sizes in micron fractions or in the nano-region. The apparatus is a continuously functioning rotating flow system, including a vertical rotating cell. The cell includes an annular electrode located on the wall of the cell vessel. The rotating cell in general is a toroidal magnet or an annular array of magnets (permanent magnets or electromagnetic coils) located inside the annular cathode in a vessel for alternately exposing the powder particles to the front of the cathode ring and electrodepositing these particles with subsequent reorientation as a result of the next exposure. The disadvantage is the complex design associated with the rotation of the cathode.

The present invention is to develop a simple effective method and device for electrochemical metallization of magnetic powders in order to increase the speed and uniformity of the deposition of a metal coating on the powder particles to protect their surface from corrosion, and improve their conductive properties.

The problem is achieved in that the method of electrochemical metallization of magnetic powders, including loading the powder into the electrolytic tank, filling the container with electrolyte and mixing by means of a magnetic field created by a magnet or a cascade of magnets to ensure coating of the powder particles, characterized in that after loading the powder into the capacity of the electrolyzer, under which a rotating magnet or a cascade of rotating magnets is placed, introduce the cathode so that the powder is in contact I with its bare part, after which they include a rotating magnet or a cascade of rotating magnets to ensure electrical contact between the cathode and the mass of particles, as well as between the individual particles, fill the container with electrolyte, introduce an anode made of deposited material or graphite into the upper layer of the electrolyte, include the current source and carry out mixing by means of a rotating magnetic field created by a magnet rotating in different planes or a cascade of magnets, in such a way that it provides retention powder particles near the cathode with the simultaneous rotation of each particle, and to create a magnetic field using a permanent magnet or electromagnet. To implement this method, a device for electrochemical metallization of a magnetic powder is proposed, comprising a container of non-conductive material for placing powder and electrolyte in it, a magnet or cascade of magnets, a cathode, anode and a current source, characterized in that the cathode is made in the form of a graphite rod and contains the part isolated from contact with the solution and the bare part at the lower end to ensure contact with the powder is placed in a container of non-conductive material, the anode is from a deposited metal and or graphite configured to introducing it into the top layer of the electrolyte, while under the bottom of the container from non-conductive material disposed a rotating magnet or a cascade of rotating magnets are rotatable in different planes, wherein the anode is formed as a cylinder, a plate, a rod or brush.

In FIG. 1 is a diagram of the device, where 1 is a capacitance of non-conductive material, 2 is an electrolyte, 3 is a cathode, 4 is an insulating coating of the cathode from contact with the solution, 5 is. rotating magnet, 6 - anode.

The magnetic powder intended for metallization is placed in a container mounted on a table, a cathode is introduced before contact with the powder, a system of rotating magnets is turned on, an electrolyte solution is poured into the container, the anode is lowered into the upper electrolyte layer and a current source is turned on.

A rotating magnetic field created by a rotating magnet (a system of rotating magnets) creates a close contact of the powder with the cathode, provides continuous mixing of the powder mass near the cathode and, which is especially important, simultaneously causes the individual powder particles to rotate, remaining in electrical contact with each other, as a result whereby the electrochemical deposition of metal occurs on continuously rotating particles, thereby ensuring uniformity and continuity of the coating and no deposition occurs coating on the cathode (Fig. 1).

The advantages of the proposed device is the simplicity of design, the intensity of mixing, ease of control, as well as the possibility of its automation.

The technical result is a significant improvement in the electrically conductive properties of the metallized powder due to the uniformity of the coating. It is known that finely divided metal powders, in particular iron powders, are susceptible to corrosion and, as a result, exhibit a significantly lower ability to conduct electric current, which makes it necessary to protect the surface with another metal with lower resistance and high corrosion resistance.

To illustrate the effectiveness of electrochemical metallization according to the invention, experiments were carried out on the deposition of copper and nickel on carbonyl iron powder of grade P-10 with spherical particles 3-8 μm in size, followed by measurement of the resistance values R of the starting material and metallization products at different pressures. The measurements were carried out on the installation in the form of a cylinder with a piston, which creates pressure on the powder with different forces. In this case, at each load, the electrical resistance is measured. The installation was created on the basis of the MCP "BR 2820" LCR METER ohmmeter as described in the article "The effect of high-voltage treatment of powder compositions of Fe-Ti-C and Fe-Ti-B-C composition on the change in their electrical resistance" Sizonenko, E.I. Taftay, N.S. Pristash, A.D. Zaichenko, A.S. Torpakov // Electrical contacts and electrodes. Ser .: Composite, layered and gradient materials and coatings. - 2014 .-- 2014 .-- S. 129-133.

Based on the data obtained, the values of resistivity ρ were calculated by the formula:

где

Where

S is the cross-sectional area of the frame containing the powder sample

l - distance between contacts

Comparative measurements of the ability to conduct electric current in powders of untreated carbonyl iron, powder of carbonyl iron with a copper coating, and nickel-plated carbonyl iron with a copper sublayer are carried out. The experimental results are shown below in the plots of the specific resistance of powder samples ρ versus pressure force F _pressure. (Fig. 2) and in table 1. Figure 1 shows the curves of the change in electrical resistance on the compression pressure of the powder during measurement, where:

(1) untreated carbonyl iron powder (spherical particles, 3-8 μm),

(2) a slow carbonyl iron powder (1% Cu) in a magnet rotation mode,

(3) carbonyl iron powder with a two-layer copper-nickel coating (1% Cu, 2.5% Ni) in the rotation mode of the magnet,

(4) carbonyl iron powder with a two-layer copper-nickel coating (0.5% Cu, 0.5% Ni) coated in a mechanical stirrer mode.

For a quantitative comparison of the electrical resistance of various powders, an average pressure of 7.5 kgf / cm ² was chosen, at which a minimum scatter of the data is obtained when measuring the resistance shown in Table 1.

Index K is the index of change in resistivity, reflecting the improvement in the quality of metallized powder relative to the starting material and calculated by the formula:

K = log (ρ ₀ / ρ), where

ρ ₀ and ρ are the resistivities of the starting material and the metallization product, respectively.

Powder loading depends on the number of rotating magnets in the cascade and the size of the capacity of the electrolyzer. In the above examples, an electrolyzer with a capacity of 500 ml was used. The degree of removal of the anode from the metallized powder varies depending on the specifics of the anode process and the aggressiveness of the substances formed on the anode.

The order of the metallization experiments is described in examples 1-3. Example 1 - comparative data without rotation of the magnet. Examples 2, 3 - with the rotation of the magnet

Example 1. Copper plating and nickel plating in the stationary magnet mode (comparative example).

In a container (1) with a volume of 500 ml, 50 g of iron powder (7) is loaded (spherical particles with an average size of 3-8 μm) and the electrolyte (2) is added, which is a solution of 5 g of ammonium chloride 1 g of ethylenediaminetetraacetic acid and 0.75 g polyethylene oxide in 200 ml of distilled water (pH ≈7). A copper anode made in the form of a brush (6) is lowered into the upper electrolyte layer. The container is installed in the installation with a magnet (7) permanently mounted under the bottom, a cathode (3) is installed in the container, so that the powder material (7) is in contact with its exposed part. The process of copper plating is carried out without rotation of the magnet. Mixing of the iron powder is carried out with a mechanical stirrer immersed in the powder with a rotation speed of 120 rpm for 90 minutes The degree of deposition of copper is 0.5% by weight of iron powder.

The second stage is the process of nickel plating. 300 ml of electrolyte (2), which is a saturated solution of nickel chloride in ethylene glycol, is poured into a container, a graphite anode made in the form of a rod with a cross section of 1 cm ^{2 is} lowered into the upper electrolyte layer, a current is supplied to the electrolyzer, and a glass mechanical stirrer immersed in powder is turned on ( rotation speed 120 rpm). The process is conducted for 38 minutes at a current density of 10.0 A / dm ² (based on spot size). After the end of the process, the powder is unloaded, washed with distilled water and alcohol, and dried at 50 ° C.

The degree of precipitation is 0.5% nickel by weight of the starting carbonyl iron powder.

Local aggregation (sticking) of powder particles is observed.

Example 2. Copper in the mode of a rotating magnet.

50 g of iron powder (7) (spherical particles with an average size of 3-8 μm) are loaded into the capacity of the electrolyzer (1) with a volume of 500 ml (under the bottom of which there is an electric magnet (5). The cathode (3) is installed in the container so that the powder material comes into contact with its exposed part and a rotating magnet is turned on (the rotation speed of the magnet in this design is 60 rpm and is not limited to this value). An electrolyte (2) is poured into the container, which is a solution of 5 g of ammonium chloride 1 g of ethylenediaminetetraacetic acid and 0.75 g of polyethylene oxide in 200 ml of distilled water (pH ≈ 7), a copper anode made in the form of a brush is lowered into the upper layer of the electrolyte (6 ) and apply current to the electrolyzer. The process is conducted for 90 minutes with an average current density of 9.0 A / dm ² (based on spot size). During metallization, the copper of the anode dissolves in the electrolyte and is applied to the surface of the metallized powder. After the end of the process, the powder is unloaded, washed with distilled water and alcohol, and dried at 50 ° C.

The degree of precipitation is 1% copper by weight of the initial carbonyl iron powder.

Example 3. Nickel plating in a rotating magnet mode.

The entire amount of iron powder (7) that has been copper-plated in Example 2 is loaded into a 500 ml container (1); the cathode (3) is installed in the container so that the powder material comes into contact with its bare part and a rotating magnet (5) is turned on ( the magnet rotation speed in this design is 60 rpm and is not limited to this value). 300 ml of electrolyte (2), which is a saturated solution of nickel chloride in ethylene glycol, is poured into a container; a graphite anode made in the form of a rod with a cross section of 1 cm ^{2 is} lowered into the upper electrolyte layer and a current is applied to the electrolyzer. The process is conducted for 38 minutes at a current density of 10.0 A / dm ² (based on spot size). After the end of the process, the powder is unloaded, washed with distilled water and alcohol, and dried at 50 ° C.

The degree of precipitation is 2.5% nickel by weight of the starting carbonyl iron powder.

From the results presented in table 1, it follows that the powder obtained in the installation in the mode of mixing the powder with a magnetic field during the rotation of the magnets, shows the best results in electrical conductivity in comparison with the powder obtained without rotation of the magnets. The implementation of the proposed method in comparison with the comparative, carried out without stirring a magnetic field, allows you to increase the coefficient K from 4.75 (op. 1) to 5.95 (op. 3) when conducting copper-nickel plating of powder material and from 4.75 (op . 1) when carrying out copper-nickel plating up to 5.58 (op. 2) when carrying out only copper plating.

Claims (5)

1. The method of electrochemical metallization of a magnetic powder, including loading the powder into the electrolytic tank, filling the container with electrolyte and mixing by means of a magnetic field created by a magnet or a cascade of magnets to provide coating on the powder particles, characterized in that after loading the powder into the electrolyzer container, by which a rotating magnet or a cascade of rotating magnets is placed, a cathode is introduced so that the powder comes into contact with its exposed part, and then on A rotating magnet or a cascade of rotating magnets is provided to ensure electrical contact between the cathode and the mass of particles, as well as between the individual particles, fill the container with electrolyte, introduce an anode made of deposited material or graphite into the upper layer of the electrolyte, turn on the current source and stir by means of a rotating magnetic field created by a magnet rotating in different planes or a cascade of magnets in such a way that they ensure the retention of powder particles near the cathode simultaneously rotation of each particle. 2. The method according to p. 1, characterized in that to create a magnetic field using a permanent magnet or electromagnet. 3. Device for electrochemical metallization of a magnetic powder, containing a container of non-conductive material for placing powder and electrolyte in it, a magnet or a cascade of magnets, a cathode, anode and a current source, characterized in that the cathode is made in the form of a graphite rod and contains isolated from the contact with the solution, the part and the bare part at the lower end to ensure contact with the powder, is placed in a container of non-conductive material, the anode of the deposited metal or graphite is made with the possibility of shielding it into the upper electrolyte layer, while a rotating magnet or a cascade of rotating magnets arranged to rotate in different planes is placed under the bottom of the container of non-conductive material. 4. The device according to p. 3, characterized in that the magnet is a permanent magnet or electromagnet. 5. The device according to p. 3, characterized in that the anode is made in the form of a cylinder, plate, rod or brush.

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