A method for preparing a TiB2 coating to inhibit particle agglomeration during electrophoretic deposition

Abstract

This invention discloses a method for preparing a TiB2 coating that inhibits particle agglomeration during electrophoretic deposition, comprising the following steps: First, a fluoride salt mixture is prepared and divided into two parts. One part of the fluoride salt is mixed with boron powder and titanium dioxide powder, heated to form a molten salt, and the upper layer of molten salt is extracted. After rapid cooling, crushing, and grinding, TiB2-fluoride salt composite powder is obtained. Then, the other part of the fluoride salt is heated to form a base molten salt, and the TiB2-fluoride salt composite powder is added to the base molten salt. Electrophoretic deposition is then performed using a ring-shaped graphite anode and a cathode to be deposited. This method prepares highly dispersed TiB2-fluoride salt composite powder through in-situ synthesis, and then uses a ring-shaped anode to reduce the probability of TiB2 particle agglomeration during electrophoresis, effectively inhibiting particle agglomeration and improving the TiB2 electrophoretic deposition efficiency.

Description

Technical Field

[0001] This invention belongs to the field of electrophoretic deposition for preparing surface coatings, and specifically discloses a method for preparing TiB2 coatings that inhibits particle agglomeration during electrophoretic deposition. Background Technology

[0002] Titanium diboride (TiB2) coatings, due to their high melting point, ultra-high hardness, and excellent corrosion resistance, are irreplaceable in fields such as liquid metal cooling systems for nuclear reactors, high-temperature electrode materials, and aluminum electrolysis cathodes. Particularly in the aluminum electrolysis industry, TiB2 coatings on the cathode surface represent significant technological innovation. This coating, with its excellent wettability with molten aluminum, can significantly reduce the voltage drop at the bottom of the electrolytic cell, while simultaneously shortening the electrode distance to reduce energy loss, thus substantially reducing energy consumption in aluminum electrolysis. Aluminum electrolytic cells with TiB2-coated, wettable cathodes have become a core technology for the future green transformation of the aluminum electrolysis industry.

[0003] Traditional TiB2 preparation techniques, such as plasma spraying and laser cladding, while achieving rapid deposition, suffer from drawbacks such as high porosity and low interfacial bonding strength, severely limiting the coating's lifespan under extreme conditions. In recent years, molten salt electrophoretic deposition technology has attracted significant attention due to its ability to produce dense coatings. Patent CN119530914A proposes a method for rapid boration of titanium metal surfaces using electric field-induced nano-assembly in molten salt. By applying an electric field to molten salt containing nano-TiB2, the nano-TiB2 assembles on the titanium metal surface to form a boride layer, significantly increasing the boration rate and reducing energy consumption. Patent CN114045546A introduces a method for in-situ synthesis and electrophoretic deposition of transition metal boride coatings using molten salt. By synthesizing nano-transition metal borides in molten salt and combining this with electrophoretic deposition technology, efficient coating preparation is achieved, reducing raw material costs. Invention patent CN112359395A proposes a metal boride coating and its preparation method. By adding metal boride nanoparticles to inorganic molten salt and simultaneously performing electrophoretic deposition and sintering, a dense and strongly bonded metal boride coating is prepared. In summary, molten salt electrophoretic deposition technology utilizes TiB2 nanoparticles synthesized in situ or added to a molten salt system to achieve coating deposition under the action of an electric field.

[0004] However, in existing TiB2 molten salt electrophoretic deposition technology, the problem of TiB2 particle agglomeration is unavoidable. Excessively high current density or electric field strength leads to severe TiB2 particle agglomeration, resulting in a poor-quality TiB2 coating; while insufficient current density or electric field strength results in low electrophoretic deposition efficiency and thin coatings. This problem makes it difficult to control the process parameters of existing TiB2 molten salt electrophoretic deposition technology. Therefore, how to effectively suppress the agglomeration of TiB2 particles during molten salt electrophoretic deposition and achieve efficient TiB2 coating preparation is a core technical problem that needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing TiB2 coatings that suppresses particle agglomeration during electrophoretic deposition. This method can achieve sufficient dispersion of TiB2 in molten salt and suppress particle agglomeration during the preparation of TiB2 coatings, thereby achieving efficient preparation of TiB2 coatings.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a TiB2 coating that inhibits particle agglomeration during electrophoretic deposition includes the following steps:

[0008] S1. Preparation of fluoride salt mixture: Mix one or more fluorides selected from NaF (40-60% by mass), AlF3 (40-55% by mass), and LiF, CaF2 and MgF2 (0-5% by mass). Then divide the mixture into fluoride salt A (10%-50% by mass) and fluoride salt B (the remainder).

[0009] Preparation of S2.TiB2 dispersion: Fluoride salt A is mixed with boron powder and titanium dioxide powder to form an in-situ reaction mixture. Under an inert atmosphere, the mixture is heated to 900-1100℃ and held for 3-6 hours to form molten salt. The upper layer of molten salt is extracted, cooled to room temperature, and then crushed and ground to obtain TiB2-fluoride composite powder. The mass fractions of boron powder and titanium dioxide powder in the in-situ reaction mixture are 10-30% and 20-40%, respectively.

[0010] S3. Molten Salt System Construction: Fluoride salt B is heated to 900-1100℃ under an inert atmosphere to melt, and held at that temperature for 0.5-1h to form the basic molten salt;

[0011] S4. Molten Salt Electrophoretic Deposition: The TiB2-fluoride salt composite powder described in step S2 is added to the basic molten salt described in step S3 and kept at a temperature for 1-2 hours. Then, an annular graphite anode and the cathode to be deposited are placed in the annular graphite anode. Electrophoretic deposition is performed by passing an electric current through the annular graphite anode to obtain a cathode with a TiB2 coating.

[0012] Furthermore, during the cooling process in step S2, when the temperature is greater than 600℃, the cooling rate is 30-50℃ / min.

[0013] Furthermore, in step S2, the particle size of the TiB2-fluoride salt composite powder is less than 200 mesh.

[0014] Furthermore, in step S4, the cathode to be deposited is any one of graphite, stainless steel, titanium, molybdenum, or their alloys.

[0015] Furthermore, in step S4, the shortest distance D between the side of the cathode to be deposited and the inner wall of the graphite anode is 1-10 cm, the ratio of the voltage applied to both ends of the anode and cathode to the distance D is 0.1-0.5 V / cm, and the electrophoretic deposition time is 0.5-2 h.

[0016] Furthermore, in step S4, the depth ratio of the graphite anode to the cathode to be deposited in the molten salt is 1-1.5:1.

[0017] The beneficial effects of this invention are as follows: This invention proposes a method for preparing a TiB2 coating that suppresses particle agglomeration during electrophoretic deposition. First, a highly dispersed TiB2-fluoride composite powder is prepared using an in-situ synthesis method, and then electrophoresis is performed using a ring anode, thereby effectively mitigating the agglomeration of TiB2 particles during electrophoretic deposition. Compared with existing technologies, the TiB2 particles prepared by the in-situ synthesis method are not uniform in size. Through a long-term heat preservation process, the large agglomerated particles settle, and the TiB2 in the extracted upper molten salt is stably dispersed in the fluoride. Rapid cooling avoids secondary agglomeration of TiB2 during the cooling process, thus preparing a highly dispersed TiB2-fluoride composite powder. Furthermore, in existing technologies, electrodes are often arranged opposite each other, resulting in a constant electric field strength between the electrodes. TiB2 particles are prone to agglomeration during their movement towards the cathode. However, in the ring anode electric field of this invention, the electric field strength distribution is such that the closer to the cathode surface, the greater the electric field strength, thus significantly reducing the probability of TiB2 particle agglomeration during electrophoresis. This invention significantly improves the preparation effect of TiB2 coating by suppressing the aggregation of TiB2 particles during electrophoretic deposition, and the electrophoretic deposition efficiency is also improved accordingly. Attached Figure Description

[0018] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0019] Figure 1 This is a front view of the electrophoretic deposition apparatus used in Embodiment 1 of the present invention. In the figure, 1-anode guide rod, 2-ring anode, 3-cathode to be deposited, 4-graphite crucible, 5-cathode guide rod, 6-molten salt, 7-anode guide rod.

[0020] Figure 2This is a top view of the electrophoretic deposition apparatus used in Embodiment 1 of the present invention.

[0021] Figure 3 This is a photograph of the graphite cathode surface after electrophoretic deposition in Example 1 of the present invention.

[0022] Figure 4 This is the electrophoretic deposition result observed by a metallographic microscope in Example 1 of the present invention.

[0023] Figure 5 This is a SEM-EDS image of the cross-section of the titanium cathode after electrophoretic deposition in Example 2 of the present invention. Detailed Implementation

[0024] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Example 1:

[0026] S1. Mix NaF, AlF3 and LiF at mass fractions of 50%, 45% and 5%, respectively, and then divide the mixture into fluoride salt A and fluoride salt B with mass fractions of 50% and 50%, respectively.

[0027] S2. Fluoride salt A is mixed with boron powder and titanium dioxide powder to form an in-situ reaction mixture. Under an inert atmosphere, the mixture is heated to 900°C and held for 3 hours to form molten salt. The upper layer of molten salt is extracted and cooled to 600°C at a rate of 50°C / min. Then, it is slowly cooled to room temperature. After crushing and grinding, TiB2-fluoride salt composite powder with a particle size of less than 200 mesh is obtained.

[0028] S3. Heat fluoride salt B to 900℃ under an inert atmosphere to melt it, and hold it at that temperature for 0.5h to form the basic molten salt;

[0029] S4. Add the TiB2-fluoride salt composite powder described in step S2 to the basic molten salt described in step S3, keep it at a certain temperature for 1 hour, and then place a ring-shaped graphite anode and a graphite cathode. The graphite cathode is located at the center of the ring-shaped graphite anode, and the shortest distance D from the inner wall of the graphite anode is 2 cm. The ratio of the immersion depth of the graphite anode to the graphite cathode in the molten salt is 1.25:1. A schematic diagram of the electrophoretic deposition apparatus used is shown below. Figure 1 and Figure 2 As shown, a graphite cathode with a titanium diboride coating was obtained by applying a voltage of 0.6V across the anode and cathode for 2 hours.

[0030] The images after electrophoretic deposition of graphite cathodes are shown below, using both the traditional scheme with the anode and cathode arranged opposite each other and the scheme of this embodiment. Figure 3 As shown. After electrophoresis, the graphite cathode surface in this embodiment was clean, with no large number of agglomerated particles, while the graphite cathode surface in the traditional embodiment had a large number of TiB2 agglomerated particles. Testing revealed that the titanium diboride coating in this embodiment was dense, with an average thickness of 90 μm.

[0031] Example 2:

[0032] S1. Mix NaF, AlF3, CaF2 and MgF2 at mass fractions of 45%, 50%, 2% and 3%, respectively, and then divide the mixture into fluoride salt A at 35% and fluoride salt B at 65% by mass.

[0033] S2. Fluoride salt A is mixed with boron powder and titanium dioxide powder to form an in-situ reaction mixture. Under an inert atmosphere, the mixture is heated to 1000℃ and held for 5 hours to form molten salt. The upper layer of molten salt is extracted and cooled to 600℃ at a rate of 30℃ / min. Then, it is slowly cooled to room temperature. After crushing and grinding, TiB2-fluoride salt composite powder with a particle size of less than 200 mesh is obtained.

[0034] S3. Heat fluoride salt B to 1000℃ under an inert atmosphere to melt it, and hold it at that temperature for 1 hour to form the basic molten salt;

[0035] S4. Add the TiB2-fluoride salt composite powder described in step S2 to the base molten salt described in step S3, and keep it at a constant temperature for 2 hours. Then, place a ring-shaped graphite anode and a titanium cathode in the molten salt. The titanium cathode is located at the center of the ring-shaped graphite anode, and the shortest distance D from the inner wall of the graphite anode is 1 cm. The ratio of the immersion depth of the graphite anode to the titanium cathode in the molten salt is 1:1. After applying a voltage of 0.5V to both ends of the anode and cathode and continuing for 1 hour, a titanium cathode with a titanium diboride coating is obtained.

[0036] After electrophoresis, the surface of the titanium cathode was clean, with no large number of aggregated particles appearing. The SEM-EDS results of the cross-section after electrophoresis are shown below. Figure 5 As shown. Testing revealed that the titanium diboride coating is dense, with an average thickness of 50 μm.

[0037] Example 3:

[0038] The steps are the same as in Example 2, except that in step S1, the mass fractions of NaF, AlF3, LiF, CaF2 and MgF2 are 40%, 55%, 1%, 2% and 2%, respectively, fluoride salt A accounts for 10% and fluoride salt B accounts for 90%; in step S2, the temperature is raised to 1100℃ under inert atmosphere protection and held for 6 hours to form molten salt, the upper layer of molten salt is extracted, and the temperature is cooled to 600℃ at a rate of 45℃ / min; in step S4, the cathode to be deposited is a stainless steel cathode, the shortest distance D from the inner wall of the graphite anode is 10cm, and a voltage of 2V is applied across the anode and cathode.

[0039] After electrophoresis, the stainless steel cathode surface was clean, with no large number of agglomerated particles. Testing revealed that the titanium diboride coating was dense, with a thickness of 50 μm.

[0040] Example 4:

[0041] The steps are the same as in Example 2, except that in step S1, the mass fractions of NaF and AlF3 are 60% and 40%, respectively. In step S2, the temperature is raised to 1000℃ under an inert atmosphere and held for 3 hours. In step S3, fluoride salt B is heated to 1100℃ under an inert atmosphere. In step S4, TiB2-fluoride salt composite powder is added to the base molten salt and held for 1.5 hours. The cathode to be deposited is a molybdenum alloy cathode, with a minimum distance D from the inner wall of the graphite anode of 6 cm. The immersion depth ratio of the graphite anode to the graphite cathode in the molten salt is 1.5:1. A voltage of 1.8V is applied across the anode and cathode and maintained for 0.5 hours.

[0042] After electrophoresis, the surface of the molybdenum alloy cathode was clean, with no large number of agglomerated particles. Testing revealed that the titanium diboride coating was dense, with a thickness of 30 μm.

Claims

1. A method for preparing a TiB2 coating that inhibits particle agglomeration during electrophoretic deposition, characterized in that, Includes the following steps: S1. Preparation of fluoride salt mixture: Mix one or more fluorides selected from NaF (40-60% by mass), AlF3 (40-55% by mass), and LiF, CaF2 and MgF2 (0-5% by mass). Then divide the mixture into fluoride salt A (10%-50% by mass) and fluoride salt B (the remainder). Preparation of S2.TiB2 dispersion: Fluoride salt A is mixed with boron powder and titanium dioxide powder to form an in-situ reaction mixture. Under an inert atmosphere, the mixture is heated to 900-1100℃ and held for 3-6 hours to form molten salt. The upper layer of molten salt is extracted, cooled to room temperature, and then crushed and ground to obtain TiB2-fluoride composite powder. The mass fractions of boron powder and titanium dioxide powder in the in-situ reaction mixture are 10-30% and 20-40%, respectively. S3. Molten Salt System Construction: Fluoride salt B is heated to 900-1100℃ under an inert atmosphere to melt, and held at that temperature for 0.5-1h to form the basic molten salt; S4. Molten Salt Electrophoretic Deposition: The TiB2-fluoride salt composite powder described in step S2 is added to the basic molten salt described in step S3 and kept at a temperature for 1-2 hours. Then, an annular graphite anode and the cathode to be deposited are placed in the annular graphite anode. Electrophoretic deposition is performed by passing an electric current through the annular graphite anode to obtain a cathode with a TiB2 coating.

2. The method for preparing a TiB2 coating to suppress particle agglomeration during electrophoretic deposition according to claim 1, characterized in that, During the cooling process in step S2, when the temperature is greater than 600℃, the cooling rate is 30-50℃ / min.

3. The method for preparing a TiB2 coating to suppress particle agglomeration during electrophoretic deposition according to claim 1, characterized in that, In step S2, the particle size of the TiB2-fluoride composite powder is less than 200 mesh.

4. The method for preparing a TiB2 coating to suppress particle agglomeration during electrophoretic deposition according to claim 1, characterized in that, In step S4, the cathode to be deposited is any one of graphite, stainless steel, titanium, molybdenum, or their alloys.

5. The method for preparing a TiB2 coating to suppress particle agglomeration during electrophoretic deposition according to claim 1, characterized in that, In step S4, the shortest distance D between the side of the cathode to be deposited and the inner wall of the graphite anode is 1-10 cm, the ratio of the voltage applied to both ends of the anode and cathode to the distance D is 0.1-0.5 V / cm, and the electrophoretic deposition time is 0.5-2 h.

6. The method for preparing a TiB2 coating to suppress particle agglomeration during electrophoretic deposition according to claim 1, characterized in that, In step S4, the depth ratio of the graphite anode to the cathode to be deposited in the molten salt is 1-1.5:1.

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