An inert anode having a high Cr, Ni alloy coating and a method of making the same

Abstract

The application discloses an inert anode with a high Cr, Ni alloy coating and a preparation method thereof, and belongs to the technical field of electrolytic aluminum electrodes. The high Cr, Ni alloy protective coating of the inert anode is composed of the following components: 20-25% of Cr, 38-43% of Ni, 1.3-1.7% of Cu, 0.3-0.8% of Ti, 0.3-0.8% of Mn, 2.3-2.9% of Mo, and the balance of Fe. The Cr and Mo elements in the coating can form a protective oxide film in the corrosion process, the Ni can promote the stability of the metal oxide film and improve the thermodynamic stability, the Cu can improve the conductivity of the alloy coating, the conductivity of the high Cr, Ni alloy and the oxide film is very good, the Ti element can refine the grains and reduce the intergranular corrosion trend in the alloy, and the oxide film formed on the surface of the prepared inert anode after pre-oxidation can effectively enhance the corrosion resistance in the aluminum electrolysis process, greenhouse gas is not generated, resources are saved, and the application is green and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of electrolytic aluminum electrode technology, and in particular to an inert anode with a high Cr and Ni alloy coating and its preparation method. Background Technology

[0002] As the most abundant metallic element in the Earth's crust, aluminum and its alloys have been the subject of continuous and in-depth research for many years, with the goal of replacing steel. However, due to aluminum's reactivity, elemental aluminum is almost non-existent in nature, existing instead in various aluminum compounds and aluminum ores. Therefore, the preparation of pure aluminum is the first step towards the application of aluminum and its alloys. The industrial production of aluminum mainly employs the cryolite-alumina molten electrolysis method (also known as the Hall-Herut molten salt electrolysis method). Molten cryolite is used as the solvent, alumina as the solute, carbon anode as the anode, and molten aluminum as the cathode. After a strong direct current is applied, an electrochemical reaction occurs at the two electrodes in an electrolytic cell at 950–970°C to obtain pure aluminum. However, in this process, the carbon anode generates a large amount of CO2 gas due to its participation in the reaction, resulting in a harsh industrial production environment and pollution of the natural environment.

[0003] Unlike traditional carbon anodes, anodes that do not participate in or barely participate in the reaction during electrolysis are called inert anodes. Currently, the most researched inert anode materials mainly include ceramics, cermets, and metal alloys. Among these, ceramics and cermets exhibit good inertness but relatively poor conductivity and are extremely brittle, making them prone to damage during use; their preparation is also difficult and costly. Metal alloy inert anodes, on the other hand, possess high strength and toughness, good conductivity, and excellent processing performance, making them more valuable for research and application. For example, the patent titled "A Nickel-Iron-Based Alloy Coating and Its Preparation Method and Application" (application number 202210983346.2) utilizes a nickel-iron alloy as the surface coating material for the inert anode, prepared through plasma cladding technology, and then forms an oxide film through oxidation. However, the coating composition is primarily Fe and Ni, making it difficult to guarantee the conductivity of the formed oxide film. Furthermore, the coating contains Al and rare earth elements, resulting in poor coating quality obtained through plasma cladding. The patent entitled "Surface Treatment Method for Aluminum Electrolytic Inert Anode" (application number 201310671469.3) uses a spraying method to form a protective layer on the surface of Ni-Fe inert anode. The protective layer consists of a bottom Fe-Ni-X1 alloy layer and an outer Fe-Ni-X2-O ceramic-metal layer. The overall process is complex. At the same time, due to the limitations of the spraying technology, the bonding between the alloy layer and the ceramic-metal layer is poor, the heat input is low, and the density of the protective layer is difficult to guarantee. Summary of the Invention

[0004] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, an inert anode with an oxidation-resistant and corrosion-resistant high-Cr,Ni alloy coating is provided, the inert anode comprising an alloy substrate and a high-Cr,Ni alloy protective coating on the surface of the substrate; the high-Cr,Ni alloy protective coating comprises, by mass percentage, the following: 20%–25% Cr, 38%–43% Ni, 1.3%–1.7% Cu, 0.3%–0.8% Ti, 0.3%–0.8% Mn, 2.3%–2.9% Mo, with the balance being Fe.

[0005] In the protective coating composition, Cr and Mo both form protective oxide films during corrosion, while Ni promotes the stability of the metal oxide film and improves thermodynamic stability, and Cu enhances the electrical conductivity of the alloy coating. Both high-Cr, Ni alloys and oxide films exhibit excellent electrical conductivity. Ti can refine grains and reduce the tendency for intergranular corrosion in the alloy.

[0006] Preferably, the alloy matrix comprises one of 20G, Q235 steel, and H13 steel.

[0007] In a second aspect of the present invention, a method for preparing an inert anode with a high Cr and Ni alloy coating that is simple to process, has high production efficiency, and good quality control is provided, comprising the following steps:

[0008] (1) Under set conditions, the metal component raw materials are ball-milled, dried and sieved to obtain alloy powder;

[0009] (2) Remove impurities from the surface of the alloy matrix and preheat it at a certain temperature to obtain a cladding matrix; the alloy powder is pretreated at a certain temperature to obtain cladding powder;

[0010] (3) In an inert gas atmosphere, the synchronous powder feeding method is used to clad the cladding powder on the surface of the cladding substrate to form an alloy layer by laser cladding process;

[0011] (4) The alloy layer is subjected to thermal oxidation treatment to form a dense oxide film, thereby obtaining an inert anode with a high Cr and Ni alloy coating.

[0012] Preferably, the specific method of step (1) is as follows: prepare metal component raw materials according to the composition ratio of the high Cr and Ni alloy protective coating, mix the metal component raw materials with the grinding ball in proportion, add the control agent and perform wet grinding in an inert gas atmosphere; the powder obtained after wet grinding is dried and sieved to obtain alloy powder.

[0013] More preferably, the grinding balls are made of cemented carbide and have diameters of 10mm, 5mm, and 2mm; based on a total mass of 500g of grinding balls, it contains 2 to 3 grinding balls with a diameter of 10mm, and the remaining mass consists of grinding balls with diameters of 5mm and 2mm at a mass ratio of 1 to 2:1.

[0014] More preferably, before the ball milling process, a set amount of grinding balls are first added to the ball milling device, then fine silica sand is added to submerge the grinding balls, and water is added to 1 / 2 to 2 / 3 of the volume of the ball milling device. The ball milling is carried out at a speed of 200 to 250 rpm for 20 to 30 minutes. After the process, the ball milling device and grinding balls are rinsed until no silica sand particles are left.

[0015] This operation prevents powder from sticking to the milling jar and milling balls during subsequent ball milling, effectively avoiding the problem of uneven particle refinement during ball milling.

[0016] More preferably, based on a total mass of 500g of grinding balls, the amount of the control agent added is 15-35mL; the control agent is anhydrous ethanol.

[0017] Preferably, in step (1), the ball-to-material ratio of the ball milling process is 1 to 2:1, the ball milling rate is 250 to 300 rpm, and the processing time is 6 to 7 hours.

[0018] In the preparation of high-Cr,Ni alloy protective coating cladding powder, a lower ball milling speed will result in lower powder mixing efficiency, while an excessively high speed will cause severe heat generation, leading to powder oxidation or excessive fineness, thus reducing the quality of the finished product. Considering the composition of the raw materials in this invention, an appropriate rotation speed, combined with a selected ball milling time, is used to homogenize the metal powder and achieve a preliminary alloying state, thereby improving the quality of the subsequent cladding coating.

[0019] Preferably, in step (1), the standard mesh size of the alloy powder is 100 to 300 mesh.

[0020] Preferably, in step (2), the temperature of the preheating treatment is 800-900℃ and the treatment time is 5-7h; the temperature of the pretreatment is 80-90℃ and the treatment time is 5-6h.

[0021] Preferably, in step (3), the laser power of the laser cladding process is 1500-3000W, and the voltage is 29-30V; argon is used as the working gas in the cladding process, the protective gas flow rate is 300-400L / h, and the powder feeding gas flow rate is 600-800L / h; the powder feeder rotation speed is 6-8rad / min; the laser distance from the substrate (defocusing amount) is 10-15mm, and the spot diameter is 2-4mm; during operation, the laser performs multiple overlapping claddings on the substrate from left to right, and its scanning speed is 400-450mm / min.

[0022] The powder composition selected in this invention has a high content of alloying elements. Compared with ordinary cladding processes, conventional laser power is low, resulting in insufficient heat input and poor adhesion between the cladding layer and the substrate. Conversely, excessively fast scanning speeds lead to insufficient cladding layer height and narrow width, making it difficult to meet the required forming quality. Conversely, slow scanning speeds result in low efficiency and increased dilution. To obtain a cladding layer with good forming quality, sufficient height, and wide cladding layer, the process parameters used in laser cladding (such as laser power, spot diameter, and scanning speed) are selected based on the raw material composition and the required cladding layer performance. Through prior analysis of the substrate and cladding material, and relevant preliminary experiments, the optimal process parameters for preparing the laser cladding layer were determined. These process parameters do not possess a simple linear inference relationship and are not derived from a finite number of experiments; they must be determined based on the compositional characteristics and the crystal phase of the final product.

[0023] Preferably, in step (4), the thermal oxidation treatment is carried out in an oxygen atmosphere, the treatment temperature is 800-950℃, and the treatment time is 10-15h.

[0024] Thermal oxidation treatment forms a dense oxide film containing alloying elements such as Fe, Cr, Ni, and Mo on the surface of the cladding layer, which can protect the anode material from corrosion during electrolysis.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] This invention provides an inert anode with a high Cr and Ni alloy coating that does not react during electrolysis to generate a large amount of CO2 gas and has good oxidation and corrosion resistance.

[0027] This invention provides a method for preparing an inert anode with a high Cr and Ni alloy coating. This method is simple, efficient, and has good quality control. Attached Figure Description

[0028] Figure 1In the middle, the left image is a scanning electron microscope (SEM) image of the coating microstructure of the inert anode with a high Cr and Ni alloy coating in Example 1, and the right image is a scanning electron microscope (SEM) image of the coating fusion line.

[0029] Figure 2 The microhardness curve of the coating of the inert anode with a high Cr and Ni alloy coating in Example 1 is shown.

[0030] In the figure: 1. High Cr, Ni alloy laser cladding layer; 2. 20G substrate; 3. Fusion line. Detailed Implementation

[0031] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0032] In the following embodiments:

[0033] Ar gas, purity: 99.99%.

[0034] Example 1

[0035] An inert anode with a high Cr, Ni alloy coating comprises a 20G substrate and a high Cr, Ni alloy protective coating on the substrate surface; the high Cr, Ni alloy protective coating has the following composition by mass percentage: 20% Cr, 39% Ni, 1.7% Cu, 0.3% Ti, 0.3% Mn, 2.6% Mo, with the balance being Fe.

[0036] Method for preparing inert anodes with high Cr and Ni alloy coatings:

[0037] (1) Weigh the metal components according to the above proportions; weigh 500g of stainless steel grinding balls, of which 2 grinding balls with a diameter of 10mm are taken, and the remaining mass is made up of grinding balls with diameters of 5mm and 2mm in a mass ratio of 1:1; before the ball milling begins, first add the weighed grinding balls to the ball milling jar, then add fine silica sand to submerge all the grinding balls, then add 1 / 2 volume of pure water to the ball milling jar, and ball mill at a speed of 250rpm for 20min. After the ball milling is finished, rinse the ball milling jar and grinding balls repeatedly, and clean them in an ultrasonic cleaner for 10min until there are no silica sand particles; then mix the grinding balls and metal component raw materials at a ball-to-material ratio of 1:1, add 15ml of anhydrous ethanol to the ball milling jar as a control agent, and fill it with Ar gas as a protective gas. Set the ball mill speed to 300rpm, the total ball milling time to 7h, and perform wet milling. The powder after wet milling is dried in a drying oven, and then the powder is screened using a stainless steel sieve, leaving powder with a particle size of 200 mesh to obtain alloy powder;

[0038] (2) Use an angle grinder to clean the rust and oxide layer on the surface of the 20G substrate. Use acetone or carbon tetrachloride to remove impurities and oil stains from the surface of the substrate. Then dry it in a drying oven. After drying, place the cleaned 20G substrate at 800℃ for 5 hours to prevent cracking after laser cladding. After preheating, wrap it with fireproof cotton for easy use. The powder is sieved twice to control its particle size to 200 mesh. The powder is spherical or near-spherical in shape. Dry it in a drying oven at 80℃. The dried powder is placed in a tray and evenly spread at the above temperature for 6 hours. The powder should be turned over during the drying process to obtain cladding powder.

[0039] (3) Argon is used as the working gas in the cladding process. The preparation method of synchronous powder feeding is adopted. The laser power of laser cladding is set to 2500W, the voltage is 29V, the protective gas flow rate is 350L / h, the powder feeding gas flow rate is 700L / h, the powder feeder rotation speed is 7rad / min, the laser distance from the substrate (defocusing amount) is 15mm, and the spot diameter is 3mm. Multiple overlapping cladding is performed on the substrate from left to right, and the scanning speed is 400mm / min. The cladding powder is clad on the surface of the cladding substrate to form an alloy layer through the laser cladding process.

[0040] (4) After the alloy layer is prepared, it is subjected to further surface thermal oxidation treatment. It is oxidized for 15 hours in an oxygen atmosphere at 900°C. After the treatment is completed, it is cooled with the furnace to form a dense oxide film containing alloying elements such as Fe, Cr, Ni, and Mo on the surface of the alloy layer.

[0041] The microstructure of the alloy structure in the coating of the inert anode with a high Cr, Ni alloy coating in this embodiment was observed using scanning electron microscopy (SEM). Figure 1 As shown in the two images, the structure is mainly composed of willow-leaf-shaped and fine needle-like structures. The alloy matrix appears light gray in the secondary electron SEM image, mainly composed of Ni and Fe elements, while the lath-like and numerous needle-like structures appear dark gray, mainly containing Cr and Fe elements, which are the compound precipitates of these two elements. The fusion line between the cladding layer and the substrate is smooth and flat, without cracks or inclusions, indicating a very good bond between the two. At the same time, the melting of the substrate is not intense, resulting in minimal dilution of the elements in the cladding layer.

[0042] The microhardness curve of the cladding coating was obtained by testing with a microhardness tester. For example... Figure 2As shown, it can be mainly divided into three regions: substrate, fusion zone and laser cladding layer; the hardness of 20G substrate is about 200HV, the hardness of fusion zone is basically the same as that of the base material, the hardness of laser cladding layer is about 800HV, and the hardness of laser cladding layer is basically uniform; the hardness from fusion line to cladding layer does not increase step by step, but changes abruptly, indicating that the cladding layer has good integrity and is almost not diluted.

[0043] Example 2

[0044] An inert anode with a high Cr, Ni alloy coating comprises a 20G substrate and a high Cr, Ni alloy protective coating on the substrate surface; the high Cr, Ni alloy protective coating has the following composition by mass percentage: 20% Cr, 39% Ni, 1.7% Cu, 0.8% Ti, 0.8% Mn, 2.6% Mo, with the balance being Fe.

[0045] In this embodiment, the preparation method of the inert anode with a high Cr and Ni alloy coating is consistent with that in Example 1.

[0046] In this embodiment, the use of a higher Ti content in the coating can further refine the grains of the cladding layer, thereby improving the overall strength and hardness of the coating. A higher Mn content can also make the alloy microstructure more uniform and refined, while also increasing the alloy's strength. However, when the content of these two elements increases, especially in low-carbon Ti-containing alloys, the high viscosity of the molten metal often leads to the inclusion of non-metallic impurities, which are difficult to separate and float, resulting in defects such as porosity and inclusions in the alloy. Furthermore, with the increase of manganese content, the thermal conductivity of the alloy decreases sharply, while the coefficient of linear expansion increases, causing greater internal stress during rapid heating or cooling, increasing the tendency for parts to crack. Simultaneously, its electrical conductivity decreases sharply, and its resistivity increases accordingly, which is unfavorable for use in electrolysis. Therefore, the Ti and Mn component content in this embodiment represents the upper limit corresponding to the present invention.

[0047] Example 3

[0048] The composition of the inert anode with a high Cr and Ni alloy coating in this embodiment is consistent with that in Example 1.

[0049] The preparation method of the inert anode with a high Cr and Ni alloy coating in this embodiment is basically the same as that in Example 1. The difference is that the parameters in the laser cladding process in this embodiment are as follows: the laser power is 1500W, the voltage is 29V, argon is used as the working gas in the cladding process, the protective gas flow rate is 300L / h, the powder feeding gas flow rate is 600L / h, the powder feeder rotation speed is 6rad / min, the laser distance from the substrate (defocusing amount) is 15mm, the spot diameter is 2mm, and multiple overlapping cladding is performed on the substrate from left to right, with a scanning speed of 400mm / min.

[0050] In this embodiment, the reduced laser power indicates a decrease in heat input. Therefore, the powder feeding rate needs to be adjusted to ensure that the synchronously fed alloy powder has sufficient energy to absorb and melt, bonding with the substrate to form a high-quality cladding layer. The reduced powder feeding rate implies a decrease in the thickness and width of the cladding layer; therefore, the scanning speed cannot be increased to ensure a minimal reduction. Simultaneously, the reduced spot diameter allows for more concentrated laser energy, which is beneficial for coating formation.

[0051] Example 4

[0052] The composition of the inert anode with a high Cr and Ni alloy coating in this embodiment is consistent with that in Example 1.

[0053] Method for preparing inert anodes with high Cr and Ni alloy coatings:

[0054] (1) Weigh the metal components according to the above proportions; weigh 500g of stainless steel grinding balls, of which 2 grinding balls with a diameter of 10mm are taken, and the remaining mass is made up of grinding balls with diameters of 5mm and 2mm at a mass ratio of 2:1; before the ball milling begins, add the weighed grinding balls to the ball milling jar, then add fine silica sand to submerge all the grinding balls, and then add 1 / 2 volume of pure water to the ball milling jar. Grind at a speed of 250rpm for 20min. After the grinding, rinse the ball milling jar and grinding balls repeatedly, and clean them in an ultrasonic cleaner for 10min until there are no silica sand particles; then mix the grinding balls and metal component raw materials at a ball-to-material ratio of 2:1, add 25ml of anhydrous ethanol to the ball milling jar as a control agent, and fill with Ar gas as a protective gas. Set the ball mill speed to 300rpm, the total ball milling time to 7h, and perform wet grinding. The powder after wet grinding is dried in a drying oven, and then the powder is screened using a stainless steel sieve to leave the powder with a particle size of 200 mesh, thus obtaining alloy powder;

[0055] (2) Use an angle grinder to clean the rust and oxide layer on the surface of the 20G substrate. Use acetone or carbon tetrachloride to remove impurities and oil stains from the surface of the substrate. Then dry it in a drying oven. After drying, place the cleaned 20G substrate at 900℃ for 7 hours to prevent cracking after laser cladding. After preheating, wrap it with fireproof cotton for easy use. The powder is sieved twice to control its particle size to 200 mesh. The powder is spherical or near-spherical in shape. Dry it in a drying oven at 80℃. The dried powder is placed in a tray and evenly spread at the above temperature for 6 hours. The powder should be turned over during the drying process to obtain cladding powder.

[0056] (3) Argon is used as the working gas in the cladding process. The preparation method of synchronous powder feeding is adopted. The laser power of laser cladding is set to 3000W, the voltage is 29V, the protective gas flow rate is 400L / h, the powder feeding gas flow rate is 800L / h, the powder feeder rotation speed is 8rad / min, the laser distance from the substrate (defocusing amount) is 15mm, and the spot diameter is 4mm. Multiple overlapping cladding is performed on the substrate from left to right, and the scanning speed is 450mm / min. The cladding powder is clad on the surface of the cladding substrate to form an alloy layer through the laser cladding process.

[0057] (4) After the alloy layer is prepared, it is subjected to further surface thermal oxidation treatment. It is oxidized for 10 hours in an oxygen atmosphere at 850°C. After the treatment is completed, it is cooled with the furnace to form a dense oxide film containing alloying elements such as Fe, Cr, Ni, and Mo on the surface of the alloy layer.

[0058] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. An inert anode with a high Cr, Ni alloy coating, characterized in that, The inert anode comprises an alloy substrate and a high-Cr, Ni alloy protective coating on the substrate surface; the high-Cr, Ni alloy protective coating comprises, by mass percentage: 20%~25% Cr, 38%~43% Ni, 1.3%~1.7% Cu, 0.3~0.8% Ti, 0.3~0.8% Mn, 2.3%~2.9% Mo, with the balance being Fe; The method for preparing the inert anode with a high Cr, Ni alloy coating includes the following steps: (1) Under set conditions, the metal component raw materials are ball-milled, dried and sieved to obtain alloy powder; (2) Remove impurities from the surface of the alloy matrix and preheat it at a certain temperature to obtain a cladding matrix. The preheating temperature is 800~900℃ and the treatment time is 5~7h. The alloy powder is pretreated at a certain temperature to obtain cladding powder. The pretreatment temperature is 80~90℃ and the treatment time is 5~6h. (3) In an inert gas atmosphere, the cladding powder is clad onto the surface of the cladding substrate to form an alloy layer by means of synchronous powder feeding and laser cladding process; (4) The alloy layer is subjected to thermal oxidation treatment to form a dense oxide film, thereby obtaining an inert anode with a high Cr and Ni alloy coating; the thermal oxidation treatment is carried out in an oxygen atmosphere, the treatment temperature is 800~950℃, and the treatment time is 10~15h.

2. The inert anode with a high Cr, Ni alloy coating according to claim 1, characterized in that: The alloy matrix includes one of 20G, Q235 steel, and H13 steel.

3. The inert anode with a high Cr, Ni alloy coating according to claim 1, characterized in that, The specific method of step (1) is as follows: prepare metal component raw materials according to the composition ratio of the high Cr and Ni alloy protective coating, mix the metal component raw materials with the grinding ball in proportion, add the control agent and perform wet grinding in an inert gas atmosphere; the powder obtained after wet grinding is dried and sieved to obtain alloy powder.

4. The inert anode with a high Cr, Ni alloy coating according to claim 3, characterized in that: The grinding balls are made of cemented carbide and come in three diameters: 10mm, 5mm, and 2mm. A total of 500g of grinding balls contains 2-3 grinding balls with a diameter of 10mm, and the remaining mass consists of grinding balls with diameters of 5mm and 2mm at a mass ratio of 1-2:

1. The amount of the control agent added is 15-35mL, based on a total mass of 500g of grinding balls. The control agent is anhydrous ethanol.

5. The inert anode with a high Cr, Ni alloy coating according to claim 3, characterized in that: Before the ball milling process, a set amount of grinding balls are added to the ball milling device, then fine silica sand is added to submerge the grinding balls, and water is added to 1 / 2 to 2 / 3 of the volume of the ball milling device. The ball milling is carried out at a speed of 200 to 250 rpm for 20 to 30 minutes. After the process, the ball milling device and grinding balls are rinsed until no silica sand particles are left.

6. The inert anode with a high Cr, Ni alloy coating according to claim 1, characterized in that: In step (1), the ball-to-material ratio of the ball milling process is 1~2:1, the ball milling rate is 250~300 rpm, and the processing time is 6~7 h; the standard mesh size of the alloy powder is 100~300 mesh.

7. The inert anode with a high Cr, Ni alloy coating according to claim 1, characterized in that: In step (3), the laser power of the laser cladding process is 1500~3000W and the voltage is 29~30V; argon is used as the working gas in the cladding process, the protective gas flow rate is 300~400L / h, the powder feeding gas flow rate is 600~800L / h; the powder feeder rotation speed is 6~8rad / min; the laser distance from the substrate is 10~15mm and the spot diameter is 2~4mm; during operation, the laser performs multiple overlapping claddings on the substrate from left to right, and the scanning speed is 400~450mm / min.

Images