Method and device for producing metal powders, preferably precious metal powders, more preferably silver powder

Abstract

In the present method and device for producing metal powders, an electrolyte solution is exposed to an electrochemical potential and ultrasonic vibrations in a thin-layer sonoelectrochemical cell with a sacrificial anode, and powder particle sizes are controlled by controlled limitation of the dwell time of electrolyte solution containing already-formed particles in the thin-layer sonoelectrochemical cell. Limitation of the dwell time within the thin-layer sonoelectrochemical cell is achieved by the continuous controlled circulation of electrolyte solution from a settling cell through the thin-layer sonoelectrochemical cell, in the process of which formed particles with predetermined sizes settle to the bottom of the settling cell. The powder production rate is 400 g / h or more. The production cost of the powder is of an order less than that of similar powders produced by chemical reduction, which is the most widely used technique to date, while production waste is several orders less.

Description

[0001] Method and device for producing metal powders, preferably noble metal powders, more preferably silver powder

[0002] Field of technology

[0003] The present invention relates to the field of production of metal powders, preferably powders of pure metals, more preferably powders of noble metals, and even more preferably silver powder, and in particular to methods and devices for the production, based on a sonoelectrochemical synthesis process, on an industrial scale of metal powders, especially noble metals, such as silver.

[0004] Prior art

[0005] Metal powders are widely used in various fields of technology, for example, in powder metallurgy, aluminum-titanium alloy is used to manufacture jet engine nozzles, or silver powders are used to manufacture conductive pastes and inks for various purposes. The average particle size of the powders used varies widely from tens of nanometers to tens of micrometers, and in many applications, the monodispersity of the powders is important.

[0006] The properties of metal powders and their cost depend on the cost of raw materials, small- or large-scale production, the shape and size of the particles, and the degree of purity.

[0007] Atomization and chemical reduction are most often used to produce powders in large volumes, while mechanical crushing and electrolysis are used for special materials produced in relatively small quantities. All atomization processes consist of three main integrated stages: melting, atomization, and solidification. Melting can be performed by methods such as vacuum induction melting, plasma arc melting, induction drop melting, or direct plasma heating. Atomization produces droplets of liquid metal that simultaneously solidify into powder particles upon cooling. These methods produce powders of all metals with particle sizes from 20 to 500 µm.It should be noted that spraying methods, despite significant energy costs, allow producing powders at a quite acceptable cost price, however, it is not possible, or difficult and inefficient, to produce metal powders with particle sizes smaller than 20 μm using these methods. In some important applications, such as the production of conductive metal pastes and inks for the electronics industry or photocells, ultrafine powders are used, such as silver and copper in the size range from 10 nm to 10 μm, and more preferably from 50 nm to 2 μm.

[0008] Currently, metal powders of the above-mentioned size range are obtained mainly by chemical reduction. It provides ample opportunities for the synthesis of high-quality metal powders with controlled morphology and particle size from several nanometers to tens of microns (e.g. [1], [2]). The main disadvantage of chemical reduction methods is the relatively high cost of the product, which is associated with both the use of expensive precursors of these metals (mainly nitrates or acetates) and the ratio of the volume of the liquid phase used to the weight of the product. The ratio of the volume of the liquid phase to the weight of the product is very high and, at best, is 300: 1, for example, to synthesize one kilogram of silver powder, the volume of the liquid phase used is 300 liters or more. In this regard, several reactors with a volume of 1000-4000 liters or more are used in the industrial process. This requires large production areas and special premises.The entire volume of the used liquid phase, saturated with toxic residues of the reducing agent, is a production waste and its quantity is significant.

[0009] The production of metal powders by electrolysis is well known. The electrolysis method allows obtaining powders of all metals and some alloys, including silver, gold, high-purity iron, nickel, manganese and chromium. This method has certain advantages over other powder production methods: it is inexpensive equipment, a single-stage, environmentally friendly process and high purity of products.

[0010] Metal powders are obtained by electrolysis from aqueous and / or non-aqueous electrolytes, using both constant (galvanostatic and potentiostatic) and periodically changing electrolysis modes. There is a strong correlation between the parameters and mode of electrolysis and the shape of the powder particles. The main shapes of powder particles obtained by electrolysis are as follows: dendrites of various shapes, spongy, needle-like, fibrous, and less often - spherical. The shape of the particles depends on the composition, temperature, mixing of the electrolyte solution, cathode material, and the nature of the metal. In large-scale production, typical particle sizes are more than 30 μm.

[0011] It should be noted that some publications describe methods for producing metal powders, such as silver, that allow producing spherical powders with particle sizes of less than 30 μm, such as [3], which describes the synthesis of powders of 50 to 200 nm in size by electrolysis. Here, a rotating cathode of a special shape is used, and silver ions formed by oxidation of the sacrificial anode are reduced by a reducing agent (hydrazine), and not on the surface of the cathode. However, the limited volume of the reactor is very quickly saturated with already formed metal particles, and this entails a change in the initial conditions of electrolysis, and the amount of reducing agent is limited. This and similar methods and devices cannot be used for large-scale production of metal powders, such as chemical reduction technology.

[0012] A method and device for producing ultrafine powders are known according to a patent [4]. According to this method and device for producing ultrafine powders, widely known as the pulse sonoelectrochemical method, electrodes are immersed in an electrolytic bath containing elements intended for forming powders in an electrolyte solution, with the cathode being a concentrator of an ultrasonic transducer, and the anode being an inert plate. A pulsed electrolysis current is created between the electrodes and ultrasonic waves are emitted from the cathode, with the electrochemical and ultrasonic pulses alternating. This method synthesizes both ceramic and purely metallic powders, mainly in the nanometer range.

[0013] This method and device are also unsuitable for the production of large volumes of metal powders, since one of the disadvantages of this method is that expensive precursors of these metals are used as raw materials, as in chemical methods of powder production.

[0014] Also known is a method and device for producing metal powders, in particular silver, by a sonoelectrochemical method using a sacrificial anode as a raw material [5]. In this method and device, two electrode rods are located at a distance from each other in a solution prepared by dissolving any of an environmentally friendly agent that reduces metal ions and an organic reducer of metal ions in pure water. The electrode rods consist of the same component as the metal particles that are desired to be obtained, so that the electrode rods dissolve in the solution under the action of electricity, and one or both of an ultrasonic generator and a stirrer are located in the solution for dispersing the metal particles in the solution to obtain particles of uniform shape. This analogue is also not suitable for producing powders of regular morphology in large volumes due to the following.

[0015] As the practice of synthesizing pure metal powders (e.g. silver, nickel, titanium) [6], [7], [8], [9] by the pulsed sonoelectrochemical method has shown, the sizes and morphology of the synthesized particles depend not only on the electrolyte composition, current density, voltage, ultrasound power, time intervals of alternating ultrasound and DC voltage actions, but also critically depend on the synthesis time interval. This is due to the fact that metal particles are conductors and therefore in a liquid electrolyte they have some negative potential relative to the anode. Therefore, metal ions are reduced not only on the cathode, but also on the already formed particles - first enlarging them, and then forming dendrites of different shapes. And this is the main reason that makes it impossible to use this potentially highly productive method for large-scale synthesis of pure metal powders with the desired particle size.

[0016] The essence of the invention

[0017] The main objective of the present invention is to create a method and device for a continuous sonoelectrochemical process for the large-scale production of metal powders and, more preferably, silver powder with a particle size range from 10 nanometers to 10 micrometers. Another objective of the present invention is to significantly reduce the cost of powders and especially silver powder compared to the chemical reduction method.

[0018] The essence of the invention is a method for producing metal powders, preferably powders of noble metals, more preferably silver powder by sonoelectrolysis using a sonoelectrochemical method, according to which the electrolyte solution is exposed to an electrochemical potential and ultrasonic vibrations in a thin-layer sonoelectrochemical cell with a sacrificial anode, the predetermined sizes of the powder particles are controlled by means of an adjustable limitation of the residence time of portions of the electrolyte solution containing already formed particles in the space of the thin-layer sonoelectrochemical cell, wherein the limitation of the residence time in the space of the thin-layer sonoelectrochemical cell is carried out by means of continuous adjustable circulation of the electrolyte solution in a settling cell through the thin-layer sonoelectrochemical cell, during which the formed particles with predetermined sizes precipitate to the bottom of the settling cell.

[0019] The above-mentioned thin-layer sonoelectrolytic cell is formed by a flat chemically inert cathode, which is also an ultrasound emitter, and the surface of a sacrificial anode, located parallel to each other, while the distance between them is set within 0.5-3 cm and kept constant throughout the production process by adjusting the position of the sacrificial anode as it is consumed.

[0020] The above-mentioned correction of the position of the sacrificial anode as it is consumed is carried out by continuously monitoring the ohmic resistance of the electrolyte.

[0021] The above-mentioned cathode, which is also an ultrasound emitter, can oscillate at frequencies ranging from 20 to 200 kHz and an intensity ranging from 5 to 120 W / cm. 2 .

[0022] The above-mentioned electrolyte solution may be aqueous, non-aqueous or mixed, single-component or multi-component. The corresponding metal salts are used as electrolytes - both separately and their mixtures, acids or bases. The solution may contain surfactants, as well as a defoamer.

[0023] The above-mentioned metal powders, preferably noble metal powders, and more preferably silver powder can be produced with an average particle size of 10 nm to 5 μm with a standard deviation of 15-20%, and the particle morphology can be either spherical or in the form of flakes or cylinders. The particle sizes and morphology of the produced powders are controlled by the composition of the electrolyte solution, ultrasound intensity, ultrasound frequency, electrolyte circulation rate, current density, and the productivity is controlled by the current strength.

[0024] The essence of the invention is also a device for producing metal powders, preferably powders of noble metals, more preferably silver powder by a sonoelectrochemical method, including a sonoelectrochemical reactor containing a metal housing, a thin-layer sonoelectrolytic cell formed by a flat chemically inert cathode, on the back side of which an ultrasonic transducer is located, and a surface of a sacrificial anode, parallel to each other, as well as a unit for correcting the position of the sacrificial anode as it is consumed and a unit for cooling the ultrasonic transducer, wherein the thin-layer sonoelectrolytic cell has an inlet and an outlet, which are connected to each other by means of tubes through a pump (preferably, but not necessarily peristaltic) and a settling cell.

[0025] According to a preferred embodiment, the side walls of the thin-layer sonoelectrolytic cell are formed by a Teflon insert, tightly mounted in the metal body of the reactor, and the ends are formed on one side by a flat titanium cathode, equipped with an ultrasonic transducer, and on the other side by the surface of the cylinder of the sacrificial anode, attached to a piston-holder, which is equipped with a screw-and-nut type translational movement mechanism for adjustable positioning of the sacrificial anode relative to the cathode as the anode material is consumed, wherein the Teflon insert is equipped with rectangular grooves located opposite each other and adjacent to the surface of the cathode, communicating with grooves of variable cross-section on the metal body, located opposite each other, and smoothly transitioning to the inlet and outlet openings of the reactor.

[0026] According to a preferred embodiment, the settling cell is a container with a volume of 1 to 10 liters, equipped with a lid similar to the head of a Drexel flask, containing a long tube for feeding the electrolyte solution to the sonoelectrolytic cell and a short tube for returning the electrolyte solution to the settling cell, and also equipped with a cooling jacket for controlling the temperature of the electrolyte solution.

[0027] One of the cells, let's call it the active space of the reactor, is a thin-layer sonoelectrochemical cell with a sacrificial anode and a cathode equipped with an ultrasonic emitter with a volume of no more than 100 ml, and the other, let's call it the passive space, is a settling cell with a volume of 1 to 10 l. A pump, preferably peristaltic, produces continuous circulation of the electrolyte solution between the reactor cells.

[0028] Metal powder particles are formed in the active space of the sonoelectrochemical reactor due to oxidation of the sacrificial anode and subsequent reduction of metal ions on the cathode, and continuous circulation of the electrolyte solution between the cells of the sonoelectrochemical reactor limits and regulates the time of presence of already formed particles in the active space of the reactor. And this is one of the factors regulating the particle size of the synthesized powders. Powder particles already formed to the required size settle to the bottom of the settling cell and subsequently do not enter the active space of the sonoelectrochemical reactor, which prevents the formation of dendrites and other structures. The ratio of the volume of the liquid phase used to the weight of the product is on average 4:1, which is at least an order of magnitude less, compared to the production of powders by chemical reduction.

[0029] The productivity of the method according to the present invention depends, as usual in electrolysis, on the current strength. In a sonoelectrochemical cell with a volume of 100 ml and an electrode surface area of ​​about 40 cm 2 Current up to 100 amperes can be used (current density 2.5 A / cm 2 ), which means that the productivity, for example, for silver powder (current efficiency 95%) will be about 380 g / hour, and for monovalent copper (in some non-aqueous electrolyte solutions) about 230 g / hour. The current density is more than 2.5 A / cm 2 leads to a significant reduction in current efficiency, so for higher currents and higher productivity, the surface area of ​​the electrodes and the volume of the sonoelectrochemical cell must be increased, but within reasonable limits.

[0030] The particle sizes of the produced powders according to the present invention from 10 nm to 10 µm are controlled by: the intensity and frequency of ultrasonic vibrations, current density, electrochemical potential, the composition of the electrolyte itself (aqueous, mixed or non-aqueous), and the rate of circulation of the electrolyte.

[0031] The electrolyte solution, after separation from the produced powder by decantation and filtration, is reused many times, which dramatically reduces the cost of the product and hazardous waste.

[0032] Brief description of graphic materials

[0033] Fig. 1 is a schematic representation of a description of a method for producing metal powders, preferably silver, according to the present invention.

[0034] Fig. 2 is a schematic representation of an apparatus for producing metal powders, preferably silver, according to an embodiment of the present invention.

[0035] Fig. 3 is a schematic representation of the reactor, and Fig. 4 is a section along A-A in Fig. 3.

[0036] Fig. 5 shows the sonoelectrochemical cell on a larger scale.

[0037] Fig. 6 is a photograph illustrating a reactor of the apparatus for producing metal powders according to the present invention. Fig. 7 is an FE-SEM image of silver powder particles obtained according to the process described in Example 1.

[0038] Fig. 8 is a field emission scanning electron microscope (FE-SEM) image of silver powder particles obtained according to the process described in Example 2.

[0039] Fig. 9 is a field emission scanning electron microscope (FE-SEM) image of silver powder particles obtained according to the process described in Example 3.

[0040] Fig. 10 is a field emission scanning electron microscope (FE-SEM) image of silver powder particles obtained according to the process described in Example 4.

[0041] Fig. 11 is a field emission scanning electron microscope (FE-SEM) image of silver powder particles obtained according to the process described in Example 5.

[0042] Fig. 12 is a field emission scanning electron microscope (FE-SEM) image of silver powder particles obtained according to the process described in Example 6.

[0043] Fig. 13 is a field emission scanning electron microscope (FE-SEM) image of copper powder particles obtained according to the process described in Example 7.

[0044] Fig. 14 is a field emission scanning electron microscope (FE-SEM) image of nickel powder particles obtained according to the process described in Example 8.

[0045] Implementation of the invention

[0046] Fig. 1 shows a diagram explaining a method for producing pure metal powders, more preferably noble metal powders and, more preferably, silver powder. A thin-layer sonoelectrochemical cell (preferably, but not necessarily of cylindrical cross-section) (1) is formed on one side by a cathode plate (2), which is provided with an ultrasonic transducer (3) on the back side, and a sacrificial anode (4) on the other side. The sacrificial anode (4) is designed with the possibility of moving in the direction of the vertical axis of the cell (1). The inlet (5) of the cell (1) is connected by means of tubes (6) through a pump (7) (preferably, but not necessarily peristaltic) to a settling cell (8) equipped with a cooling jacket. The outlet (9) of the cell (1) is directly connected to the settling cell (8) by means of a tube (10). The said settling cell (8) contains an electrolyte solution (11).In this case, the inlet tube (6) is immersed in the electrolyte solution (11), and the tip of the outlet tube (10) is located above the level of the electrolyte solution (11).

[0047] By means of a pump (7), the electrolyte solution (11) contained in the settling cell (8) is circulated through the sonoelectrochemical cell (1), i.e. through the active space of the reactor at a constant speed and is pumped back into the settling cell (8). This ensures the constant presence of the electrolyte solution in the sonoelectrochemical cell (1). Then the ultrasonic transducer (3), fixed on the back side of the cathode (2), is switched on, after which a constant voltage is applied between the sacrificial anode (4) and the cathode (2), while the positive pole of the direct current is connected to the anode, and the negative pole to the cathode.

[0048] The intensity of the oscillations of the ultrasonic transducer (3) and, consequently, the intensity of the oscillations of the cathode (2) can vary from 5 to 100 W / cm2 , and the frequency from 5 to 200 kHz. The intensity and frequency of the cathode plate oscillations (2) are the main factors determining the particle size, granulometric composition and morphology of the produced powder.

[0049] Additional factors that determine the particle size, granulometric composition and morphology of the produced powder are the current density, the circulation rate of the electrolyte solution (11) and the composition of the electrolyte solution itself (11).

[0050] The current strength between the electrodes of a sonoelectrochemical cell is 10-100 A or more at current densities <2.5 A / cm 2 mainly determines the productivity of metal powder, for example, for the production of silver powder with a productivity of 400 g / hour or more.

[0051] When the constant voltage is switched on between the electrodes, electrochemical reactions of metal oxidation on the sacrificial anode (4) begin, followed by reduction on the vibrating cathode (2), and due to circulation, the already reduced metal particles, as well as the unreduced metal ions, repeatedly pass through the sonoelectrochemical cell (1), that is, the active space of the reactor. Metal particles in the electrolyte solution (11) are conductors and have a negative potential relative to the anode (4), as a result of which the metal ions are reduced not only on the cathode (2), but also on the already formed particles, which leads to an increase in the particle size. The increase in the powder particle size continues until they reach the target value determined by the established values ​​of the intensity and oscillation frequency of the cathode (2), current density, circulation rate of the electrolyte solution (11), and the composition of the electrolyte solution itself (11).Upon reaching the target sizes, the powder particles aggregate and settle to the bottom of the settling cell (8) and then they no longer pass through the active space of the reactor and do not participate in the sonoelectrochemical reaction, thereby preventing further increase in size and the formation of dendrites or other irregular objects, the particles remain spherical or nearly spherical.

[0052] During the production process, the sacrificial anode (4) wears out and, in order to maintain the initial settings (voltage between the electrodes, current, ultrasound intensity) unchanged, as it is consumed, the sacrificial anode (4) is moved in the direction of the vertical axis of the sonoelectrochemical cell (1) in such a way that the distance between the anode (4) and the cathode (2) remains unchanged throughout the production process.

[0053] Fig. 2, 3 and 4 show a device implementing the method according to the present invention. Fig. 2 illustrates a device for producing metal powders, and in particular silver powder, according to a preferred embodiment of the present invention. In Fig. 2, 3 and 4, the same components as in Fig. 1 are assigned the same reference numerals, and a detailed description thereof will be partially omitted.

[0054] The device for producing metal powders, preferably silver powder, includes a reactor (12), a settling cell (8) and a peristaltic pump (7). The main reactor (12), including a sonoelectrochemical cell (1), contains a metal housing (13) with a Teflon insert (14). The metal housing (13) is made of stainless steel and is provided with inlet and outlet openings with nozzles (15 A) and (15 B). The sonoelectrochemical cell is formed in the cavity of the Teflon insert (14) between the surfaces of the titanium cathode (2) and the cylinder of the sacrificial anode (4). The titanium cathode (2) is simultaneously the radiating surface of the ultrasonic transducer (3) mounted on the opposite surface of the titanium cathode (2), and the diameter of the cylindrical sacrificial anode (4) (preferably made of silver) is equal to the inner diameter of the Teflon insert (14).The Teflon insert (14) is provided with rectangular grooves located opposite each other and adjacent to the cathode (2), forming the input (5) and output (9) openings of the sonoelectrochemical cell. The input (5) and output (9) openings of the sonoelectrochemical cell are directly adjacent to the openings of variable cross-section located on the metal housing (13) opposite each other, smoothly transitioning to the input and output fittings (15 A) and (15 B). The titanium plate of the cathode (2) with the ultrasonic transducer (3) is fixed on the metal housing (13) with the Teflon insert (14) in such a way as to exclude electrical contact between the cathode (2) and the housing (13). The cathode (2) with the ultrasonic transducer (3) is provided with a radiator (16), on which the legs (17) with a fan (18) for cooling the ultrasonic transducer (3) are fixed.The sacrificial anode cylinder (4) (preferably made of silver) is fixed to the piston-holder (20) by means of a bolt (19), which is equipped with a lead screw (21).

[0055] The piston-holder (20) by means of rubber gaskets (22) tightly fits to the inner walls of the Teflon insert (14). The lead screw (21) of the piston is provided with a nut (23) and guides (24) for linear movement of the piston-holder (20) as a result of rotation of the nut (23). The nut (23) is installed in the cover (25) of the reactor and is provided with a gear (26), which is connected to the drive - a stepper motor (27) with a gear (28). The stepper motor (27) is attached to the reactor body (13) by means of a drive holder (29). The reactor is provided with magnetic limit sensors-limiters (30) for limiting the range of movement of the sacrificial anode (4), which are mounted on the holder (31), fixed on the reactor body (13). The positioning carriage (32) for triggering the limit switches (30) is mounted on the end section of the lead screw (21), while the ferromagnetic head of the carriage (not shown in the drawings) is located between the limit switches (30).

[0056] The settling cell (8) is a vessel, preferably with a cooling jacket, provided with a lid (33) similar to the Drechsel Bottle Head. This lid is provided with two tubes, the central tube is long and immersed in the depth of the settling cell (8), and the side tube is short. The branch of the tube immersed in the depth of the vessel and used for sucking in the electrolyte solution is connected by a flexible tube (6) through a peristaltic pump (7) to the inlet fitting (15 A) of the reactor (12). The short side tube of the Drechsel Bottle Head is directly connected to the outlet fitting (15B) of the reactor (12) for pumping the electrolyte solution back into the settling cell (8).

[0057] In one preferred embodiment of the present invention, the temperature of the electrolyte solution is controlled by means of a settling cell (8) with a cooling jacket. In another preferred embodiment, the settling cell is placed in a thermostat bath. In yet another preferred embodiment, the temperature is controlled by means of a spiral condenser connected between the settling cell (8) and the inlet fitting (15 A) of the reactor (12).

[0058] The power supply and control unit (34) contains an ultrasound generator and a DC source which controls the DC in both galvanostatic and potentiostatic modes and also generates signals which control the production process. The output of the ultrasound generator is connected to the ultrasound converter (3), the terminals of the DC source are connected respectively: through the fastening bolt (19) to the sacrificial anode (4) - positive and to the cathode (2) through the radiator-cooler (17) - negative, and the signals which control the production process are fed to the stepper motor (27) and the limit switches (30), as shown in Fig. 2. The controls on the power supply and control unit (34) as well as the corresponding connecting cables are not shown in Fig. 2.

[0059] The device operates as follows. The lower sensor-limiter (30) is installed in such a way that the minimum distance between the anode (4) and the cathode (2) is preferably 5-10 mm, depending on the selected ultrasound frequency and the selected DC voltage. The upper sensor-limiter (30) is installed from the lower sensor-limiter at a distance exceeding the length of the cylinder of the sacrificial anode (4) by 10%. The electrolyte solution is poured into the settling cell (8) so as to fill 90% of the volume. The settling cell (8) is closed with a lid (33) similar to the Drechsel Bottle Head and it is ensured that the central tube of the Drechsel Bottle Head is immersed in the solution by approximately 5-7 cm. The connecting flexible tubes (6) and (10) between the reactor (12), the settling cell (8) and the peristaltic pump (7) are checked according to Fig. 2.

[0060] Turn on the peristaltic pump (7), set the liquid flow rate, preferably 0.5-1.5 l / min, and wait until the electrolyte circulation is established.

[0061] The frequency and intensity of ultrasonic vibrations supplied to the ultrasonic transducer are switched on and adjusted using an ultrasonic generator located on the power and control unit (34).

[0062] On the power supply and control unit (34), based on the previously measured specific resistance of the electrolyte solution and the surface area of ​​the electrodes, the desired resistance of the electrolyte is set, which is equivalent to setting the desired distance between the electrodes: preferably 1-1.5 cm. The DC source is switched on, for example in galvanostatic mode, the operating current is set, preferably from 10 to 100 A. Based on the continuous measurement of the electrolyte resistance, the power supply and control unit (34) generates a control signal to the stepper motor (26) of the sacrificial anode drive (4), thereby setting it at a predetermined distance from the cathode plate (2).

[0063] Further, during the entire production cycle, as the sacrificial anode is consumed, the control signal from the power and control unit (34) continuously adjusts the position of the anode (4) relative to the cathode (2) by a predetermined distance. The product, in this case silver powder, precipitates and collects at the bottom of the settling cell (8).

[0064] At the end of the production cycle, the DC voltage is switched off, and the sacrificial anode with the holder returns to its original position according to the corresponding signal from the power and control unit (34).

[0065] On the power and control unit (34), the ultrasonic generator is switched off. The circulation of the electrolyte is stopped, then the peristaltic pump is switched on in the reverse direction, thereby moving the remainder of the electrolyte solution contained in the sonoelectrochemical cell (1) into the settling cell (8).

[0066] The produced powder is separated from the electrolyte solution by decantation and filtration, then washed and subsequently dried in a drying cabinet at a temperature of 40-45 degrees. The decantation and filtrate of the electrolyte solution, after correction of the composition and pH, are stored for subsequent reuse.

[0067] Thus, the method and device for producing metal powders, preferably powders of noble metals and more preferably silver powder according to the present invention uses bulk metal as a source of metal, for example silver, in contrast to the most frequently used method of chemical reduction at present, where expensive precursors, salts of these metals - mainly nitrates or acetates, and sometimes very toxic reducing agents are used as a source of silver or any other metal. The ratio of the volume of the liquid phase used to the unit weight of the produced powder, according to the present invention, is 4: 1, i.e. approximately two orders of magnitude less than in the production of a similar powder by chemical reduction. All reagents (electrolyte solution in this case) are used repeatedly. Waste from production is minimal and mainly consists of liquids in the powder washing stage.Despite its modest size, the productivity of the device according to the present invention, for example for silver, is approximately the same order as the methods of chemical reduction using reactors of very impressive sizes. We illustrate this further with examples.

[0068] Example 1

[0069] A silver anode is installed in the reactor (12). 4 liters of an aqueous electrolyte solution containing 10 g / l of silver nitrate and 2 g / l of polyethyleneglycol 4000 as a stabilizer are poured into a 5-liter settling cell (8), and the pH of the electrolyte solution is adjusted to 3.5 with nitric acid. The temperature of the cooling liquid in the settling cell jacket (8) is set to 18 degrees. The settings on the power and control unit are as follows: ultrasound intensity 25 W / cm 2 , ultrasound frequency 40 kHz, galvanostatic electrolysis mode, current value 50 A (current density will be 2 A / cm 2) and the resistance of the electrolyte based on the fixed interelectrode distance of 10 mm.

[0070] The peristaltic pump, ultrasonic generator, and then the DC source are switched on alternately, with a half-minute interval. After another 30 seconds, the stationary mode of silver powder production is established.

[0071] After 5 hours, the DC source is turned off, then the ultrasound, then the remainder of the electrolyte in the sonoelectrochemical cell (1) is transferred to the settling cell (8) by reversing the start of the peristaltic pump (7).

[0072] The contents of the settling cell (8) are transferred to another five-liter vessel, settled, and then the powder is separated from the electrolyte solution by decantation and filtration. The electrolyte solution is stored separately for subsequent use, and the powder is washed first with water, then with isopropyl alcohol, and dried in a drying cabinet at a temperature of 45 degrees for 5 hours.

[0073] After drying, the weight of the produced powder is 1 kg.

[0074] Thermogravimetric analysis, after heating the powder to 1000 degrees, showed that the weight loss was 0.3%.

[0075] Analysis of scanning electron microscope images (Fig. 7) revealed that the average particle size of the powder was 0.8 μm, with a standard deviation from the average size of 0.2.

[0076] Example 2 A silver anode is installed in the reactor (12). 2 liters of an aqueous electrolyte solution containing 10 g / l of silver nitrate and 2 g / l of polyethyleneglycol 4000 as a stabilizer are poured into a 2.5 liter settling cell (8), the pH of the electrolyte solution is adjusted to 3.5 with nitric acid. The temperature of the cooling liquid in the settling cell jacket (8) is set to 18 degrees. The settings on the power and control unit are as follows: ultrasound intensity 25 W / cm 2, ultrasound frequency 40 kHz, galvanostatic electrolysis mode, current value 25 A (current density will be 1 A / cm 2 ) and the resistance of the electrolyte based on the fixed interelectrode distance of 10 mm.

[0077] The peristaltic pump, ultrasonic generator, and then the DC source are switched on alternately, with a half-minute interval. After another 30 seconds, the stationary mode of silver powder production is established.

[0078] After 5 hours, the DC source is turned off, then the ultrasound, then the remainder of the electrolyte in the sonoelectrochemical cell (1) is transferred to the settling cell (8) by reversing the start of the peristaltic pump (7).

[0079] The contents of the settling cell (8) are transferred to another five-liter vessel, settled, and then the powder is separated from the electrolyte solution by decantation and filtration. The electrolyte solution is stored separately for subsequent use, and the powder is washed first with water, then with isopropyl alcohol and dried in a drying cabinet at a temperature of 45 degrees for 5 hours.

[0080] After drying, the weight of the produced powder is 0.5 kg.

[0081] Thermogravimetric analysis, after heating the powder to 1000 degrees, showed that the weight loss was 0.3%.

[0082] Analysis of scanning electron microscope images (Fig. 8) revealed that the average particle size of the powder was 0.4 μm, with a standard deviation from the average size of 0.2.

[0083] Example 3

[0084] Example 2 is repeated with the difference that the corrected electrolyte already used in example 2 is reused as the electrolyte.

[0085] After drying, the weight of the produced powder is 0.5 kg.

[0086] Thermogravimetric analysis, after heating the powder to 1000 degrees, showed that the weight loss was 0.3%. Analysis of scanning electron microscope images (Fig. 9) revealed that the average particle size of the powder was 0.4 μm, the standard deviation from the average size was 0.2.

[0087] Example 4.

[0088] Example 2 is repeated with the difference that the ultrasound intensity is set to 50 W / cm. 2 , and the corrected electrolyte, already used twice in examples 2 and 3, is used as the electrolyte.

[0089] After drying, the weight of the produced powder is 0.5 kg.

[0090] Thermogravimetric analysis, after heating the powder to 1000 degrees, showed that the weight loss was 0.3%.

[0091] Analysis of scanning electron microscope images (Fig. 10) revealed that the average particle size of the powder was 0.2 μm, with a standard deviation from the average size of 0.2.

[0092] Example 5.

[0093] A silver anode is installed in the reactor (12). 1 liter of electrolyte solution of the following composition is poured into the settling cell (8) with a volume of 1.2 l: 40% H2O, 60% acetonitrile, 26 g / l nitric acid and 5 g / l ethylamine as a stabilizer, pH of the electrolyte solution 1. The temperature of the cooling liquid of the settling cell jacket is set to 18 degrees. The settings on the power and control unit are as follows: ultrasound intensity 25 W / cm 2 , ultrasound frequency 40 kHz, galvanostatic electrolysis mode, current value 25 A (current density will be 1 A / cm 2 ) and the resistance of the electrolyte based on the fixed interelectrode distance of 20 mm.

[0094] The peristaltic pump, ultrasonic generator, and then the DC source are switched on in turn, with a half-minute interval. After another 30 seconds, the stationary mode of silver powder production is established. For another 9 minutes, the pH of the electrolyte solution increases and becomes 5.

[0095] After 1.5 hours, the DC source is turned off, then the ultrasound, then the remaining electrolyte in the sonoelectrochemical cell (1) is transferred to the settling cell (8) by reversing the start of the peristaltic pump (7).

[0096] The contents of the settling cell (8) are transferred to another five-liter vessel, settled, then the powder is separated from the electrolyte solution by decantation and filtration. The electrolyte solution is stored separately for subsequent use, and the powder is washed first with water, then with isopropyl alcohol and dried in a drying cabinet at a temperature of 45 degrees for 5 hours.

[0097] After drying, the weight of the produced powder is 135 g.

[0098] Thermogravimetric analysis, after heating the powder to 1000 degrees, showed that the weight loss was 0.3%.

[0099] Analysis of scanning electron microscope images (Fig. 11) revealed that the average particle size of the powder was 1.5 μm, with a standard deviation from the average size of 0.2.

[0100] Example 6

[0101] A silver anode is installed in the reactor (12). 1 liter of electrolyte solution of the following composition is poured into the 1.2 liter settling cell (8): 40% H2O, 60% acetonitrile, 30 g / l unsaturated Octadecylamine nitrate, pH of the electrolyte solution is 6. The temperature of the cooling liquid of the settling cell jacket is set to 18 degrees. The settings on the power and control unit are as follows: ultrasound intensity 50 W / cm 2, ultrasound frequency 40 kHz, galvanostatic electrolysis mode, current value 21 A (current density will be 0.9 A / cm 2 ) and the resistance of the electrolyte based on the fixed interelectrode distance of 10 mm.

[0102] The peristaltic pump, ultrasonic generator, and then the DC source are switched on alternately, with a half-minute interval. After another 30 seconds, the stationary mode of silver powder production is established.

[0103] After 1.5 hours, the DC source is turned off, then the ultrasound, then the remaining electrolyte in the sonoelectrochemical cell (1) is transferred to the settling cell (8) by reversing the start of the peristaltic pump (7).

[0104] The contents of the settling cell (8) are transferred to another five-liter vessel, settled, then the powder is separated from the electrolyte solution by decantation and filtration. The electrolyte solution is stored separately for subsequent use, and the powder is washed first with water, then with isopropyl alcohol and dried in a drying cabinet at a temperature of 45 degrees for 5 hours.

[0105] After drying, the weight of the produced powder is 140 g. Thermogravimetric analysis showed that after heating the powder to 1000 degrees, the weight loss is 0.9%.

[0106] Analysis of scanning electron microscope images (Fig. 12) revealed that the average particle size of the powder was 30 nm, with a standard deviation of 0.15.

[0107] It should be noted that the proposed method and device are less productive for the production of metal powders that are in the series of standard potentials before hydrogen (Ni, Co, Fe, Zn, Zr, etc.), the reduction of which on the cathode is accompanied by the release of hydrogen (conditionally base metals). This is due to the fact that a significant share of energy is spent on secondary electrochemical reactions, such as hydrogen reduction, and at high cathode potentials and / or high cathode current densities, the reduction of metal on the cathode may stop altogether. Therefore, to maintain high productivity, it will be necessary to significantly increase the area of ​​the cathode, and therefore the overall dimensions of the device.

[0108] Next, we will illustrate the production of powders of other metals using the examples of copper and nickel on the same device as in examples 1-6 of the production of silver powder.

[0109] Example 7

[0110] A copper anode is installed in the reactor (12). 1 liter of electrolyte solution of the following composition is poured into the 1.2 liter settling cell (8): 60% H2O, 40% acetonitrile, 10 g / l ethylamine nitrate, pH of the electrolyte solution is 6. In the electrolyte of this composition, copper is oxidized and reduced monovalently, while the electrochemical equivalent is 2.63 g / A hour. The temperature of the settling cell jacket cooling liquid is set to 18 degrees. The settings on the power and control unit are as follows: ultrasound intensity 25 W / cm 2 , ultrasound frequency 40 kHz, galvanostatic electrolysis mode, current value 25 A (current density will be 1 A / cm 2 ) and the resistance of the electrolyte based on the fixed interelectrode distance of 10 mm.

[0111] The peristaltic pump, ultrasonic generator, and then the DC source are switched on alternately, with a half-minute interval. After another 30 seconds, the stationary mode of copper powder production is established.

[0112] After 1.5 hours, the DC source is switched off, then the ultrasound, then the remainder of the electrolyte in the sonoelectrochemical cell (1) is transferred to the settling cell (8) by reversing the start of the peristaltic pump (7). The contents of the settling cell (8) are transferred to another two-liter vessel, settled, then the powder is separated from the electrolyte solution by decantation and filtration. The electrolyte solution is stored separately for subsequent use, and the powder is washed first with water, then with isopropyl alcohol and dried in a drying cabinet at a temperature of 45 degrees for 5 hours.

[0113] After drying, the weight of the produced powder is 71 g.

[0114] Thermogravimetric analysis showed that after heating the powder to 1000 degrees, the weight loss was 0.96%.

[0115] Analysis of scanning electron microscope images (Fig. 13) revealed that the average particle size of the powder was 500 nm, with a standard deviation of 0.2.

[0116] Example 8

[0117] A nickel anode is installed in the reactor (12). 1 liter of electrolyte solution of the following composition is poured into the 1.2 liter settling cell (8): 1.5 molar solution of tetrabutylammonium bromide in methanol, pH of the electrolyte solution is 6. Nickel is oxidized and reduced divalently, and the electrochemical equivalent is 1.09 g / A hour. The temperature of the cooling liquid of the settling cell jacket is set to 18 degrees. The settings on the power and control unit are as follows: ultrasound intensity 50 W / cm 2 , ultrasound frequency 40 kHz, galvanostatic electrolysis mode, current value 10 A (current density will be 0.4 A / cm 2 ) and the resistance of the electrolyte based on the fixed interelectrode distance of 10 mm.

[0118] The peristaltic pump, ultrasonic generator, and then the DC source are switched on alternately, with a half-minute interval. After another 30 seconds, the stationary mode of silver powder production is established.

[0119] After 1.5 hours, the DC source is turned off, then the ultrasound, then the remainder of the electrolyte in the sonoelectrochemical cell (1) is transferred to the settling cell (8) by reversing the start of the peristaltic pump (7).

[0120] The contents of the settling cell (8) are transferred to another two-liter vessel, settled, then the powder is separated from the electrolyte solution by decantation and filtration. The electrolyte solution is stored separately for subsequent use, and the powder is washed first with water, then with isopropyl alcohol and dried in a drying cabinet at a temperature of 45 degrees for 5 hours. After drying, the weight of the produced powder is 14 g.

[0121] Thermogravimetric analysis showed that after heating the powder to 1000 degrees, the weight loss was 0.95%.

[0122] Analysis of scanning electron microscope images (Fig. 14) revealed that the average particle size of the powder was 100 nm, with a standard deviation from the average size of 0.15.

[0123] Sources of information:

[0124] 1. US patent US11548068B2 published 01 / 10 / 2023;

[0125] 2. Japanese patent JP5098098B2 published 12.12.2012;

[0126] 3. US patent application 2012 / 0091009A1, publ. 04 / 19 / 2012;

[0127] 4. WO9533871A1, published 14.12.1995, MIC: C25B1 / 00; C25C5 / 00; C25C5 / 02;

[0128] 5. patent KR100555584, published 12 / 17 / 2004, IEC: B22F9 / 16);

[0129] 6. Yehoshua Socol, Oleg Abramson, Aharon Gedanken, et al., Suspensive Electrode Formation in Pulsed Sonoelectrochemical Synthesis of Silver Nanoparticles. Langmuir 2002, 18, 4736-4740;

[0130] 7. Junjie Zhu, Suwen Liu, O. Palchik, Yuri Koltypin, and A. Gedanken, Shape-Controlled Synthesis of Silver Nanoparticles by Pulse Sonoelectrochemical Methods. Langmuir 2000, 16, 6396-6399;

[0131] 8. Li-Ping Jiang, An-Ning Wang, Yu Zhao, Jian-Rong Zhang, Jun-Jie Zhu, A novel route for the preparation of monodisperse silver nanoparticles via a pulsed sonoelectrochemical technique. Inorganic Chemistry Communications 7 2004 506-509;

[0132] 9. Foroughi, F.; Lamb, J. J.; Burheim, O.S.; Pollet, B.G. Sonochemical and Sonoelectrochemical Production of Energy Materials. Catalysts 2021, 11, 284.

Claims

Invention formula 1. A method for producing metal powders by a sonoelectrochemical method, according to which an electrolyte solution is subjected to the action of an electrochemical potential and ultrasonic vibrations in a thin-layer sonoelectrochemical cell with a sacrificial anode, the predetermined sizes of the powder particles are controlled by means of an adjustable limitation of the residence time of portions of the electrolyte solution containing already formed particles in the space of the thin-layer sonoelectrochemical cell, wherein the limitation of the residence time in the space of the thin-layer sonoelectrochemical cell is carried out by means of continuous adjustable circulation of the electrolyte solution in a settling cell through the thin-layer sonoelectrochemical cell, during which the formed particles with predetermined sizes precipitate to the bottom of the settling cell.

2. The method according to claim 1, characterized in that the thin-layer sonoelectrolytic cell is formed by a flat chemically inert cathode, which is also an ultrasound emitter, and the surface of a sacrificial anode, located parallel to each other, while the distance between them is set within 0.5-3 cm and kept constant throughout the entire production process by adjusting the position of the sacrificial anode as it is consumed.

3. The method according to item 2, characterized in that the correction of the position of the sacrificial anode as it is consumed is carried out by means of continuous monitoring of the ohmic resistance of the electrolyte.

4. The method according to I.2, characterized in that the cathode, which is also an ultrasound emitter, can oscillate at frequencies in the range from 20 to 200 kHz and an intensity in the range from 5 to 120 W / cm. 2 .

5. The method according to claim 1, characterized in that the electrolyte solution may be aqueous, non-aqueous or mixed, single-component or multi-component, and the corresponding metal salts are used as electrolytes - either separately or as mixtures thereof, acids or bases, and the solution may contain surfactants, as well as an antifoaming agent.

6. The method according to claim 1, characterized in that metal powders, preferably noble metal powders, and more preferably silver powder, are produced with an average particle size value from 10 nm to 5 μm, with a standard deviation of 15-20%, wherein The morphology of the particles can be either spherical or in the form of flakes or cylinders, and the size and morphology of the particles of the produced powders are controlled by the composition of the electrolyte solution, the intensity of ultrasound, the frequency of ultrasound, the rate of circulation of the electrolyte, the current density, and the productivity is controlled by the current strength.

7. A device for producing metal powders by a sonoelectrochemical method, comprising a sonoelectrochemical reactor containing a metal housing, a sonoelectrolytic cell formed by a flat chemically inert cathode, on the back side of which an ultrasonic transducer is located, and the surface of a sacrificial anode, parallel to each other, as well as a unit for correcting the position of the sacrificial anode as it is consumed and a unit for cooling the ultrasonic transducer, wherein the sonoelectrolytic cell has an inlet and an outlet, which are connected to each other by means of tubes through a pump and a settling cell.

8. The device according to item 7, characterized in that the side walls of the thin-layer sonoelectrolytic cell are formed by a Teflon insert tightly mounted in the metal body of the reactor, and the ends are formed on one side by a flat titanium cathode equipped with an ultrasonic transducer, and on the other side by the surface of the cylinder of the sacrificial anode attached to the piston-holder, which is equipped with a screw-and-nut type translational movement mechanism for adjustable positioning of the sacrificial anode relative to the cathode as the anode material is consumed, wherein the Teflon insert is equipped with rectangular grooves located opposite each other and adjacent to the surface of the cathode, communicating with grooves of variable cross-section on the metal body, located opposite each other, and smoothly transitioning to the inlet and outlet openings of the reactor.

9. The device according to item 7, characterized in that the settling cell is a container with a volume of 1 to 10 liters, equipped with a lid similar to the head of a Drexel flask, containing a long tube for feeding the electrolyte solution to the sonoelectrolytic cell and a short tube for returning the electrolyte solution to the settling cell, and also equipped with a cooling jacket for controlling the temperature of the electrolyte solution.

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