A Yttrium-Stabilized Zirconia Gradient Coating for High-Temperature Corrosion Resistance on Tungsten Cathode Surface

Abstract

This invention relates to the field of rare earth metal electrolytic cathode protective coating technology, and more particularly to a yttrium-stabilized zirconia gradient coating for high-temperature corrosion resistance on the surface of a tungsten cathode. The invention constructs a strong, metallurgically bonded underlayer on a tungsten substrate through surface pretreatment and reactive sintering. Then, an atmospheric plasma technology is used to spray a continuously composed, creep-resistant gradient layer to buffer thermal stress. Finally, a highly dense, corrosion-resistant surface layer is constructed using sol-gel technology. This multi-scale, multi-mechanism synergistic effect constructs a high-temperature corrosion-resistant yttrium-stabilized zirconia gradient coating, fundamentally solving the problems of insufficient adhesion and poor thermal shock resistance in tungsten cathode coatings. Furthermore, it can block molten salt penetration, significantly extending the service life of the tungsten cathode in harsh environments.

Description

Technical Field

[0001] This invention relates to the field of rare earth metal electrolytic cathode protective coating technology, and in particular to a yttrium-stabilized zirconium oxide gradient coating for high-temperature corrosion resistant on the surface of a tungsten cathode. Background Technology

[0002] In the molten salt electrolysis process for producing rare earth metals, tungsten cathode materials face severe synergistic corrosion at the interface between the molten salt, air, and metal phases at high temperatures of 850-950℃. This corrosion manifests as high-temperature oxidation to generate volatile tungsten trioxide, molten salt electrochemical corrosion, and thermal corrosion induced by the salt film, leading to rapid cathode wear, reduced production efficiency, and high costs. To address these corrosion problems, the industry has explored various solutions, such as using tungsten alloys or exploring other refractory metals to improve the substrate material's resistance to high-temperature oxidation and molten salt corrosion. However, high-purity tungsten or certain alloys are difficult to completely replace tungsten in terms of overall performance and cost, while other materials may introduce problems related to conductivity, mechanical strength, or contamination of the molten salt. Alternatively, protective coatings resistant to oxidation and molten salt corrosion can be prepared on the tungsten cathode surface to isolate or slow down the direct erosion of the tungsten substrate by environmental media. However, these protective coatings are prone to cracking, peeling, or premature failure under long-term high-temperature, strong corrosion, thermal cycling, and potential physical erosion conditions, especially at the dynamically changing three-phase interface, where maintaining coating integrity is extremely difficult. Therefore, a tungsten cathode coating with strong adhesion, good thermal shock resistance, and the ability to block molten salt penetration is needed. Summary of the Invention

[0003] This invention aims to overcome the shortcomings of existing technologies and provide a yttrium-stabilized zirconia gradient coating for high-temperature corrosion resistance on the surface of a tungsten cathode. The technical approach of this invention is as follows: First, a strong metallurgically bonded underlayer is constructed on a tungsten substrate through surface pretreatment and reactive sintering. Then, an anti-creep gradient layer with continuous composition is sprayed using atmospheric plasma technology to buffer thermal stress. Finally, an extremely dense anti-corrosion surface layer is constructed by superimposing sol-gel technology. Through the synergistic effect of multiple scales and mechanisms, a high-temperature corrosion-resistant yttrium-stabilized zirconia gradient coating is constructed, fundamentally solving the problems of insufficient adhesion and poor thermal shock resistance of tungsten cathode coatings. Moreover, it can block molten salt penetration and significantly extend the service life of tungsten cathodes in harsh environments.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A yttrium-stabilized zirconium oxide gradient coating for high-temperature corrosion resistant tungsten cathode surface comprises, from the inside out: tungsten cathode substrate, strong bonding underlayer, creep resistant gradient layer, and corrosion resistant top layer;

[0006] Furthermore, the tungsten cathode substrate undergoes pretreatment before subsequent steps.

[0007] The strong-bonding underlayer is constructed using composite slurry as raw material through coating and vacuum sintering processes.

[0008] The creep-resistant gradient layer is made from tungsten powder, yttrium-stabilized zirconium oxide powder, and titanium carbide through an atmospheric plasma spraying process. Furthermore, by altering the ratio of tungsten powder to yttrium-stabilized zirconium oxide powder, a creep-resistant gradient layer with a gradient structure is constructed. The ratio of tungsten powder to yttrium-stabilized zirconium oxide powder from the inside out is 90:10, 60:40, 30:70, and 0:100, respectively. The amount of titanium carbide used is 1% of the weight of the tungsten powder and yttrium-stabilized zirconium oxide powder.

[0009] The anti-corrosion surface layer is formed by sol-gel method to form a cerium and yttrium co-doped zirconium oxide film, thereby constructing a dense anti-corrosion surface layer.

[0010] A yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode is prepared by the following steps:

[0011] Step S1: Pre-treatment of tungsten cathode surface using sandblasting process: The tungsten cathode substrate is placed in deionized water for ultrasonic cleaning, then cleaned with acetone and anhydrous ethanol for 15 minutes each, dried, and then roughened by sandblasting. After sandblasting, it is cleaned again with anhydrous ethanol to obtain the pre-treated tungsten cathode.

[0012] Step S2: Prepare a strong bonding underlayer using a slurry coating method: First, a composite slurry is coated onto the surface of the pretreated tungsten cathode using a scraping method to form a wet film layer with a thickness of 100-120µm. The wet film layer is dried at 80℃ for 12h and then transferred to a tube furnace. Under argon protection, the temperature is increased to 500-550℃ at a rate of 1℃ / min and held for 2h. Then, it is transferred to a vacuum sintering furnace for vacuum sintering, thereby forming a strong bonding underlayer on the surface of the pretreated tungsten cathode.

[0013] Step S3: Prepare an anti-creep gradient layer using atmospheric plasma spraying: First, mix tungsten powder, yttrium-stabilized zirconium oxide powder and titanium carbide according to different ratios, and ball mill them in a ball mill to obtain mixed powders with different ratios. Then, use an atmospheric plasma spraying system to spray the mixed powders with different ratios onto a strong bonding underlayer in sequence to form an anti-creep gradient layer.

[0014] Step S4: Prepare the anti-corrosion surface layer using the sol-gel method: First, prepare a cerium-yttrium co-doped sol, coat it onto the anti-creep gradient layer, heat it to 200℃ at a heating rate of 1℃ / min, hold it at that temperature for 1h, then continue heating it to 400℃ at a heating rate of 5℃ / min, hold it at that temperature for 60min, continue heating it to 600℃, hold it at that temperature for 120min, cool it, and wash it with deionized water to form the anti-corrosion surface layer.

[0015] Furthermore, in step S1: during the sandblasting process: 25-mesh white corundum sand is used, the sandblasting air pressure is 0.6-0.65MPa, the sandblasting angle is 75°, and the sandblasting time is 15s.

[0016] Furthermore, in step S2: the composite slurry is prepared by the following steps: tungsten powder, silicon powder and nickel powder are mixed to obtain a mixed powder, and then the mixed powder is added to a ball mill, and a mixture of polyvinyl butyral and ethanol is added. Under the conditions of ball-to-powder ratio of 4:1 and rotation speed of 300 rpm, the mixture is stirred and mixed for 6-8 hours to obtain the composite slurry.

[0017] In the preparation process of the composite slurry: the weight ratio of tungsten powder, silicon powder and nickel powder is 90:8-10:0.8-1, the weight ratio of polyvinyl butyral and ethanol is 3:97, and the weight ratio of mixed powder to mixed liquid is 70:30.

[0018] Furthermore, in step S2, the vacuum sintering process is as follows: under a vacuum of 0.1 MPa, the temperature is increased to 800-900℃ at a heating rate of 4-5℃ / min, held for 30-40 min, then increased to 1100-1200℃, held for 30-40 min, then increased to 1300-1400℃ again, held for 60-90 min, cooled to 700-800℃, and then cooled to room temperature.

[0019] Furthermore, in step S3: during ball milling: the ball-to-material ratio is 4:1, anhydrous ethanol is used as the medium, the rotation speed is 300 rpm, the ball milling time is 6-8 h, and after ball milling, drying is performed to obtain mixed powders with different ratios; during atmospheric plasma spraying: argon and hydrogen are used as the main gas and secondary gas respectively, the main gas flow rate is 40 L / min, the secondary gas flow rate is 4 L / min, the powder feed rate is 10 g / min, the current is 550 A, the voltage is 50 V, the spray distance is 100 mm, and the spraying angle is 90°, wherein the thickness of each layer with different ratios in the anti-creep gradient layer is 150 µm.

[0020] Furthermore, in step S4: the cerium and yttrium co-doped sol is prepared by the following steps: zirconium propoxide solution, yttrium nitrate solution, acetylacetone and n-propanol are mixed and stirred for 30 min at a stirring rate of 300 rpm and a temperature of 50°C. Then, cerium nitrate solution is added and stirring is continued for 30 min to obtain the cerium and yttrium co-doped sol.

[0021] Furthermore, the volume ratio of the zirconium propoxide solution, yttrium nitrate solution, acetylacetone, n-propanol, and cerium nitrate solution is 10-12 mL: 0.8-0.9 mL: 1 mL: 9-10 mL: 1.2-1.5 mL, wherein the zirconium propoxide solution, yttrium nitrate solution, and cerium nitrate solution all use n-propanol as the solvent, and their molar concentrations are all 0.5 mol / L.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a yttrium-stabilized zirconia gradient coating for high-temperature corrosion resistance on the surface of a tungsten cathode. First, a strong metallurgically bonded underlayer is constructed on the tungsten substrate through surface pretreatment and reaction sintering. Then, an anti-creep gradient layer with continuous composition is sprayed using atmospheric plasma technology to buffer thermal stress. Finally, an extremely dense anti-corrosion surface layer is constructed by superimposing sol-gel technology. The high-temperature corrosion resistant yttrium-stabilized zirconia gradient coating is constructed through the synergistic effect of multiple scales and multiple mechanisms, which fundamentally solves the problems of insufficient adhesion and poor thermal shock resistance of tungsten cathode coatings. Moreover, it can block molten salt penetration and significantly extend the service life of tungsten cathodes in harsh environments.

[0023] This invention employs a combination of sandblasting roughening and sintering of tungsten-silicon-nickel slurry, along with mechanical anchoring and in-situ generation of tungsten silicide metallurgical bonding mechanism, to solve the fundamental problem of weak bonding between the coating and the tungsten substrate. The generation of tungsten silicide achieves interfacial atomic bonding, and its thermal expansion coefficient is between that of tungsten and yttrium-stabilized zirconium oxide, while also playing a certain stress buffering role.

[0024] This invention employs segmented gradient spraying and the addition of titanium carbide reinforcing phases, combined with the synergistic mechanism of continuous component transition and dispersion strengthening, to solve the problems of poor creep resistance and easy cracking due to thermal mismatch in coatings at high temperatures. Its gradient structure can smoothly release thermal stress, and the two-nanometer titanium carbide particles pin the grain boundaries, significantly improving the overall high-temperature strength and toughness of the coating.

[0025] This invention employs a sol-gel process to prepare cerium-yttrium co-doped zirconia surface layers. Combined with the dual mechanism of nanoparticle stacking and sintering and rare earth ion co-stabilization, it solves the problem of molten salt easily penetrating through coating pores. The sol precursor can penetrate into the micro-defects on the surface of the gradient layer, and nanoscale pore sealing is achieved after heat treatment. Furthermore, the co-doping of cerium and yttrium further stabilizes the tetragonal phase of zirconia, improving the density, toughness, and resistance to high-temperature phase transformation of the surface layer. Detailed Implementation

[0026] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following preferred embodiments will provide a detailed description of the specific implementation methods, structures, features and effects of the present invention.

[0027] In the following examples and comparative examples: the tungsten powder was from Stardust Technology Guangdong Co., Ltd., with a size of 15-53 μm; the silicon powder was from Thermo Fisher Scientific, with a size of 325 mesh; the nickel powder was from Stardust Technology Guangdong Co., Ltd., with a size of 15-53 μm; the polyvinyl butyral was from Shanghai Aladdin Biochemical Technology Co., Ltd.; the yttrium-stabilized zirconia powder was from Hangzhou Jiayou New Materials Co., Ltd., and was 8% yttrium-stabilized zirconia powder with a size of 15-50 μm; the titanium carbide was from Qinghe County Yaoxie Metal Materials Co., Ltd., with a size of 1-3 μm.

[0028] Example 1: A yttrium-stabilized zirconium oxide gradient coating for high-temperature corrosion resistant on the surface of a tungsten cathode, comprising, from the inside out: a tungsten cathode substrate, a strong bonding underlayer, an anti-creep gradient layer, and an anti-corrosion top layer;

[0029] Furthermore, the tungsten cathode substrate undergoes pretreatment before subsequent steps.

[0030] The strong-bonding underlayer is constructed using composite slurry as raw material through coating and vacuum sintering processes.

[0031] The creep-resistant gradient layer is made from tungsten powder, yttrium-stabilized zirconium oxide powder, and titanium carbide through an atmospheric plasma spraying process. Furthermore, by altering the ratio of tungsten powder to yttrium-stabilized zirconium oxide powder, a creep-resistant gradient layer with a gradient structure is constructed. The ratio of tungsten powder to yttrium-stabilized zirconium oxide powder from the inside out is 90:10, 60:40, 30:70, and 0:100, respectively. The amount of titanium carbide used is 1% of the weight of the tungsten powder and yttrium-stabilized zirconium oxide powder.

[0032] The anti-corrosion surface layer is formed by sol-gel method to form a cerium and yttrium co-doped zirconium oxide film, thereby constructing a dense anti-corrosion surface layer.

[0033] A yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode is prepared by the following steps:

[0034] Step S1: Pre-treatment of tungsten cathode surface using sandblasting process: The tungsten cathode substrate is placed in deionized water for ultrasonic cleaning, then cleaned with acetone and anhydrous ethanol for 15 minutes each, dried, and then roughened by sandblasting. After sandblasting, it is cleaned again with anhydrous ethanol to obtain the pre-treated tungsten cathode.

[0035] Step S2: Preparation of a strong bonding underlayer using a slurry coating method: First, a composite slurry is coated onto the surface of the pretreated tungsten cathode using a scraping method to form a wet film layer with a thickness of 100µm. The wet film layer is dried at 80℃ for 12h and then transferred to a tube furnace. Under argon protection, the temperature is increased to 500℃ at a rate of 1℃ / min and held for 2h. The film is then transferred to a vacuum sintering furnace for vacuum sintering, thereby forming a strong bonding underlayer on the surface of the pretreated tungsten cathode.

[0036] Step S3: Prepare an anti-creep gradient layer using atmospheric plasma spraying: First, mix tungsten powder, yttrium-stabilized zirconium oxide powder and titanium carbide according to different ratios, and ball mill them in a ball mill to obtain mixed powders with different ratios. Then, use an atmospheric plasma spraying system to spray the mixed powders with different ratios onto a strong bonding underlayer in sequence to form an anti-creep gradient layer.

[0037] Step S4: Prepare the anti-corrosion surface layer using the sol-gel method: First, prepare a cerium-yttrium co-doped sol, coat it onto the anti-creep gradient layer, heat it to 200℃ at a heating rate of 1℃ / min, hold it at that temperature for 1h, then continue heating it to 400℃ at a heating rate of 5℃ / min, hold it at that temperature for 60min, continue heating it to 600℃, hold it at that temperature for 120min, cool it, and wash it with deionized water to form the anti-corrosion surface layer.

[0038] Furthermore, in step S1: during the sandblasting process: 24-mesh white corundum sand is used, the sandblasting air pressure is 0.6MPa, the sandblasting angle is 75°, and the sandblasting time is 15s.

[0039] Further, in step S2: the composite slurry is prepared by the following steps: tungsten powder, silicon powder and nickel powder are mixed to obtain a mixed powder, and then the mixed powder is added to a ball mill, and a mixture of polyvinyl butyral and ethanol is added. Under the conditions of ball-to-powder ratio of 4:1 and rotation speed of 300 rpm, the mixture is stirred and mixed for 6 hours to obtain the composite slurry.

[0040] In the preparation process of the composite slurry: the weight ratio of tungsten powder, silicon powder and nickel powder is 90:8:0.8, the weight ratio of polyvinyl butyral and ethanol is 3:97, and the weight ratio of mixed powder to mixed liquid is 70:30.

[0041] Furthermore, in step S2, the vacuum sintering process is as follows: under a vacuum of 0.1 MPa, the temperature is increased to 900°C at a heating rate of 5°C / min, held for 30 min, then increased to 1100°C, held for 40 min, then increased to 1300°C again, held for 90 min, cooled to 700°C, and then cooled to room temperature.

[0042] Furthermore, in step S3: during ball milling: the ball-to-material ratio is 4:1, anhydrous ethanol is used as the medium, the rotation speed is 300 rpm, the ball milling time is 6 hours, and after ball milling, drying is performed to obtain mixed powders with different proportions; during atmospheric plasma spraying: argon and hydrogen are used as the main gas and secondary gas, respectively, the main gas flow rate is 40 L / min, the secondary gas flow rate is 4 L / min, the powder feed rate is 10 g / min, the current is 550 A, the voltage is 50 V, the spray distance is 100 mm, and the spraying angle is 90°, wherein the thickness of each layer with different proportions in the anti-creep gradient layer is 150 µm.

[0043] Furthermore, in step S4: the cerium and yttrium co-doped sol is prepared by the following steps: zirconium propoxide solution, yttrium nitrate solution, acetylacetone and n-propanol are mixed and stirred for 30 min at a stirring rate of 300 rpm and a temperature of 50°C. Then, cerium nitrate solution is added and stirring is continued for 30 min to obtain the cerium and yttrium co-doped sol.

[0044] Furthermore, the volume ratio of the zirconium propoxide solution, yttrium nitrate solution, acetylacetone, n-propanol, and cerium nitrate solution is 12 mL: 0.9 mL: 1 mL: 9 mL: 1.2 mL, wherein the zirconium propoxide solution, yttrium nitrate solution, and cerium nitrate solution all use n-propanol as the solvent, and their molar concentrations are all 0.5 mol / L.

[0045] Example 2: A yttrium-stabilized zirconium oxide gradient coating for high-temperature corrosion resistant on the surface of a tungsten cathode, comprising, from the inside out: a tungsten cathode substrate, a strong bonding underlayer, an anti-creep gradient layer, and an anti-corrosion top layer;

[0046] Furthermore, the tungsten cathode substrate undergoes pretreatment before subsequent steps.

[0047] The strong-bonding underlayer is constructed using composite slurry as raw material through coating and vacuum sintering processes.

[0048] The creep-resistant gradient layer is made from tungsten powder, yttrium-stabilized zirconium oxide powder, and titanium carbide through an atmospheric plasma spraying process. Furthermore, by altering the ratio of tungsten powder to yttrium-stabilized zirconium oxide powder, a creep-resistant gradient layer with a gradient structure is constructed. The ratio of tungsten powder to yttrium-stabilized zirconium oxide powder from the inside out is 90:10, 60:40, 30:70, and 0:100, respectively. The amount of titanium carbide used is 1% of the weight of the tungsten powder and yttrium-stabilized zirconium oxide powder.

[0049] The anti-corrosion surface layer is formed by sol-gel method to form a cerium and yttrium co-doped zirconium oxide film, thereby constructing a dense anti-corrosion surface layer.

[0050] A yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode is prepared by the following steps:

[0051] Step S1: Pre-treatment of tungsten cathode surface using sandblasting process: The tungsten cathode substrate is placed in deionized water for ultrasonic cleaning, then cleaned with acetone and anhydrous ethanol for 15 minutes each, dried, and then roughened by sandblasting. After sandblasting, it is cleaned again with anhydrous ethanol to obtain the pre-treated tungsten cathode.

[0052] Step S2: Preparation of a strong bonding underlayer using a slurry coating method: First, a composite slurry is coated onto the surface of the pretreated tungsten cathode using a scraping method to form a wet film layer with a thickness of 100µm. The wet film layer is dried at 80℃ for 12h and then transferred to a tube furnace. Under argon protection, the temperature is increased to 550℃ at a rate of 1℃ / min and held for 2h. The film is then transferred to a vacuum sintering furnace for vacuum sintering, thereby forming a strong bonding underlayer on the surface of the pretreated tungsten cathode.

[0053] Step S3: Prepare an anti-creep gradient layer using atmospheric plasma spraying: First, mix tungsten powder, yttrium-stabilized zirconium oxide powder and titanium carbide according to different ratios, and ball mill them in a ball mill to obtain mixed powders with different ratios. Then, use an atmospheric plasma spraying system to spray the mixed powders with different ratios onto a strong bonding underlayer in sequence to form an anti-creep gradient layer.

[0054] Step S4: Prepare the anti-corrosion surface layer using the sol-gel method: First, prepare a cerium-yttrium co-doped sol, coat it onto the anti-creep gradient layer, heat it to 200℃ at a heating rate of 1℃ / min, hold it at that temperature for 1h, then continue heating it to 400℃ at a heating rate of 5℃ / min, hold it at that temperature for 60min, continue heating it to 600℃, hold it at that temperature for 120min, cool it, and wash it with deionized water to form the anti-corrosion surface layer.

[0055] Furthermore, in step S1: during the sandblasting process: 24-mesh white corundum sand is used, the sandblasting air pressure is 0.6MPa, the sandblasting angle is 75°, and the sandblasting time is 15s.

[0056] Further, in step S2: the composite slurry is prepared by the following steps: tungsten powder, silicon powder and nickel powder are mixed to obtain a mixed powder, and then the mixed powder is added to a ball mill, and a mixture of polyvinyl butyral and ethanol is added. Under the conditions of ball-to-powder ratio of 4:1 and rotation speed of 300 rpm, the mixture is stirred and mixed for 6 hours to obtain the composite slurry.

[0057] In the preparation process of the composite slurry: the weight ratio of tungsten powder, silicon powder and nickel powder is 90:8:0.8, the weight ratio of polyvinyl butyral and ethanol is 3:97, and the weight ratio of mixed powder to mixed liquid is 70:30.

[0058] Furthermore, in step S2, the vacuum sintering process is as follows: under a vacuum of 0.1 MPa, the temperature is increased to 800°C at a heating rate of 4°C / min, held for 30 min, then increased to 1100°C, held for 30 min, then increased to 1300°C again, held for 60 min, cooled to 700°C, and then cooled to room temperature.

[0059] Furthermore, in step S3: during ball milling: the ball-to-material ratio is 4:1, anhydrous ethanol is used as the medium, the rotation speed is 300 rpm, the ball milling time is 6 hours, and after ball milling, drying is performed to obtain mixed powders with different proportions; during atmospheric plasma spraying: argon and hydrogen are used as the main gas and secondary gas, respectively, the main gas flow rate is 40 L / min, the secondary gas flow rate is 4 L / min, the powder feed rate is 10 g / min, the current is 550 A, the voltage is 50 V, the spray distance is 100 mm, and the spraying angle is 90°, wherein the thickness of each layer with different proportions in the anti-creep gradient layer is 150 µm.

[0060] Furthermore, in step S4: the cerium and yttrium co-doped sol is prepared by the following steps: zirconium propoxide solution, yttrium nitrate solution, acetylacetone and n-propanol are mixed and stirred for 30 min at a stirring rate of 300 rpm and a temperature of 50°C. Then, cerium nitrate solution is added and stirring is continued for 30 min to obtain the cerium and yttrium co-doped sol.

[0061] Furthermore, the ratio of the volume of zirconium propoxide solution, yttrium nitrate solution, acetylacetone, n-propanol and cerium nitrate solution is 10 mL: 0.8 mL: 1 mL: 9 mL: 1.2 mL, wherein the zirconium propoxide solution, yttrium nitrate solution and cerium nitrate solution all use n-propanol as solvent and their molar concentration is 0.5 mol / L.

[0062] Example 3: A yttrium-stabilized zirconium oxide gradient coating for high-temperature corrosion resistant on the surface of a tungsten cathode, comprising, from the inside out: a tungsten cathode substrate, a strong bonding underlayer, an anti-creep gradient layer, and an anti-corrosion top layer;

[0063] Furthermore, the tungsten cathode substrate undergoes pretreatment before subsequent steps.

[0064] The strong-bonding underlayer is constructed using composite slurry as raw material through coating and vacuum sintering processes.

[0065] The creep-resistant gradient layer is made from tungsten powder, yttrium-stabilized zirconium oxide powder, and titanium carbide through an atmospheric plasma spraying process. Furthermore, by altering the ratio of tungsten powder to yttrium-stabilized zirconium oxide powder, a creep-resistant gradient layer with a gradient structure is constructed. The ratio of tungsten powder to yttrium-stabilized zirconium oxide powder from the inside out is 90:10, 60:40, 30:70, and 0:100, respectively. The amount of titanium carbide used is 1% of the weight of the tungsten powder and yttrium-stabilized zirconium oxide powder.

[0066] The anti-corrosion surface layer is formed by sol-gel method to form a cerium and yttrium co-doped zirconium oxide film, thereby constructing a dense anti-corrosion surface layer.

[0067] A yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode is prepared by the following steps:

[0068] Step S1: Pre-treatment of tungsten cathode surface using sandblasting process: The tungsten cathode substrate is placed in deionized water for ultrasonic cleaning, then cleaned with acetone and anhydrous ethanol for 15 minutes each, dried, and then roughened by sandblasting. After sandblasting, it is cleaned again with anhydrous ethanol to obtain the pre-treated tungsten cathode.

[0069] Step S2: Preparation of a strong bonding underlayer using a slurry coating method: First, a composite slurry is coated onto the surface of the pretreated tungsten cathode using a scraping method to form a wet film layer with a thickness of 120µm. The wet film layer is dried at 80℃ for 12h and then transferred to a tube furnace. Under argon protection, the temperature is increased to 550℃ at a rate of 1℃ / min and held for 2h. The film is then transferred to a vacuum sintering furnace for vacuum sintering, thereby forming a strong bonding underlayer on the surface of the pretreated tungsten cathode.

[0070] Step S3: Prepare an anti-creep gradient layer using atmospheric plasma spraying: First, mix tungsten powder, yttrium-stabilized zirconium oxide powder and titanium carbide according to different ratios, and ball mill them in a ball mill to obtain mixed powders with different ratios. Then, use an atmospheric plasma spraying system to spray the mixed powders with different ratios onto a strong bonding underlayer in sequence to form an anti-creep gradient layer.

[0071] Step S4: Prepare the anti-corrosion surface layer using the sol-gel method: First, prepare a cerium-yttrium co-doped sol, coat it onto the anti-creep gradient layer, heat it to 200℃ at a heating rate of 1℃ / min, hold it at that temperature for 1h, then continue heating it to 400℃ at a heating rate of 5℃ / min, hold it at that temperature for 60min, continue heating it to 600℃, hold it at that temperature for 120min, cool it, and wash it with deionized water to form the anti-corrosion surface layer.

[0072] Furthermore, in step S1: during the sandblasting process: 24-mesh white corundum sand is used, the sandblasting air pressure is 0.65MPa, the sandblasting angle is 75°, and the sandblasting time is 15s.

[0073] Further, in step S2: the composite slurry is prepared by the following steps: tungsten powder, silicon powder and nickel powder are mixed to obtain a mixed powder, and then the mixed powder is added to a ball mill, and a mixture of polyvinyl butyral and ethanol is added. Under the conditions of ball-to-powder ratio of 4:1 and rotation speed of 300 rpm, the mixture is stirred and mixed for 8 hours to obtain the composite slurry.

[0074] In the preparation process of the composite slurry: the weight ratio of tungsten powder, silicon powder and nickel powder is 90:10:1, the weight ratio of polyvinyl butyral and ethanol is 3:97, and the weight ratio of mixed powder to mixed liquid is 70:30.

[0075] Furthermore, in step S2, the vacuum sintering process is as follows: under a vacuum of 0.1 MPa, the temperature is increased to 900°C at a heating rate of 5°C / min, held for 40 min, then increased to 1200°C, held for 40 min, then increased to 1400°C again, held for 90 min, cooled to 800°C, and then cooled to room temperature.

[0076] Furthermore, in step S3: during ball milling: the ball-to-material ratio is 4:1, anhydrous ethanol is used as the medium, the rotation speed is 300 rpm, the ball milling time is 8 hours, and after ball milling, drying is performed to obtain mixed powders with different proportions; during atmospheric plasma spraying: argon and hydrogen are used as the main gas and secondary gas, respectively, the main gas flow rate is 40 L / min, the secondary gas flow rate is 4 L / min, the powder feed rate is 10 g / min, the current is 550 A, the voltage is 50 V, the spray distance is 100 mm, and the spraying angle is 90°, wherein the thickness of each layer with different proportions in the anti-creep gradient layer is 150 µm.

[0077] Furthermore, in step S4: the cerium and yttrium co-doped sol is prepared by the following steps: zirconium propoxide solution, yttrium nitrate solution, acetylacetone and n-propanol are mixed and stirred for 30 min at a stirring rate of 300 rpm and a temperature of 50°C. Then, cerium nitrate solution is added and stirring is continued for 30 min to obtain the cerium and yttrium co-doped sol.

[0078] Furthermore, the ratio of the volume of zirconium propoxide solution, yttrium nitrate solution, acetylacetone, n-propanol and cerium nitrate solution is 12 mL: 0.9 mL: 1 mL: 10 mL: 1.5 mL, wherein the zirconium propoxide solution, yttrium nitrate solution and cerium nitrate solution all use n-propanol as solvent and their molar concentration is 0.5 mol / L.

[0079] Comparative Example 1: Compared with Example 3, step S2 is omitted in this comparative example. That is, the tungsten substrate is only pretreated by sandblasting before proceeding directly to subsequent steps S3 and S4. Other steps are the same.

[0080] Comparative Example 2: Compared with Example 3, this comparative example changed the process of step S3, that is, directly spraying a coating with a tungsten powder and yttrium stabilized zirconium oxide gradient mass ratio of 30:70, while the other steps were the same.

[0081] Comparative Example 3: Compared with Example 3, step S4 is omitted in this comparative example, that is, the cerium-yttrium co-doped zirconium oxide anti-corrosion surface layer is not prepared, and the other steps are the same.

[0082] According to the processes of Examples 1, 2, 3, Comparative Examples 1, 2, and 3, tungsten cathode samples with surface coatings were prepared. The tungsten cathode samples and their mating pairs were bonded together with E-7 adhesive, and the bond strength was measured using a tensile testing machine at room temperature. The tungsten cathode samples were placed in a box-type muffle furnace and heated to 950°C in air atmosphere for 15 minutes, then rapidly quenched in 25°C deionized water for 3 minutes. This was considered one cycle, and the number of cycles at which visible macroscopic cracks or peeling of the coating appeared was recorded. The tungsten cathode samples were then partially immersed in a crucible containing NdF3-LiF eutectic molten salt and held at 950°C for 100 hours. After cooling, the molten salt penetration depth was measured. The test results are shown in the table below.

[0083] Table 1 Test Results

[0084]

[0085] As shown in the table, the test results indicate that, compared with Comparative Examples 1, 2, and 3, Comparative Examples 1, 2, and 3 show that: Comparative Example 1 lacked a strong-bonded underlayer, thus missing the metallurgical bonding mechanism of silicon powder reacting with the tungsten matrix to form tungsten silicide. The coating and substrate primarily relied on the mechanical anchoring force provided by sandblasting, resulting in low bonding strength. In the thermal shock test, due to the lack of an effective transition layer for thermal expansion coefficients, interfacial stress concentration led to a sharp decline in its thermal shock resistance, causing early cracking of the coating. Consequently, in molten salt corrosion, molten salt rapidly penetrated through the poorly bonded interface, leading to complete performance failure. Comparative Example 2, on the other hand, used a single-component coating... The non-gradient structure lacks the transition mechanism of continuous change in composition and thermal expansion coefficient, resulting in obvious performance abrupt interfaces inside the coating. During thermal cycling, these interfaces become the preferred sites for stress concentration and crack initiation, leading to a significant reduction in its thermal shock resistance. Molten salt also penetrates more easily along these interfaces. Since Comparative Example 3 did not prepare a sol-gel anti-corrosion surface layer, it lacked a dense surface layer with nano-sol sealing and rare earth ion co-stabilized zirconium oxide. As a result, the open pores and microcracks on the surface of the atmospheric plasma spraying gradient layer were not sealed, becoming channels for direct molten salt intrusion. Consequently, its resistance to molten salt penetration depth was much greater than that of Example 3 with a dense surface layer.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A yttrium-stabilized zirconium oxide gradient coating for high-temperature corrosion resistance on the surface of a tungsten cathode, characterized in that: From the inside out, the layers are: tungsten cathode substrate, strong bonding underlayer, creep resistant gradient layer, and corrosion resistant surface layer; The tungsten cathode substrate is pretreated before subsequent steps are performed. The strong-bonding underlayer is constructed using composite slurry as raw material through coating and vacuum sintering processes. The creep-resistant gradient layer is made from tungsten powder, yttrium-stabilized zirconium oxide powder, and titanium carbide through an atmospheric plasma spraying process. Furthermore, by altering the ratio of tungsten powder to yttrium-stabilized zirconium oxide powder, a creep-resistant gradient layer with a gradient structure is constructed. The ratio of tungsten powder to yttrium-stabilized zirconium oxide powder from the inside out is 90:10, 60:40, 30:70, and 0:100, respectively. The amount of titanium carbide used is 1% of the weight of the tungsten powder and yttrium-stabilized zirconium oxide powder. The corrosion-resistant surface layer is formed by sol-gel method to form a cerium and yttrium co-doped zirconium oxide film, thereby constructing a dense corrosion-resistant surface layer; The composite slurry is prepared by the following steps: tungsten powder, silicon powder and nickel powder are mixed to obtain a mixed powder, which is then added to a ball mill, and a mixture of polyvinyl butyral and ethanol is added. The mixture is stirred for 6-8 hours at a ball-to-powder ratio of 4:1 and a rotation speed of 300 rpm to obtain the composite slurry. In the preparation process of the composite slurry: the weight ratio of tungsten powder, silicon powder and nickel powder is 90:8-10:0.8-1, the weight ratio of polyvinyl butyral and ethanol is 3:97, and the weight ratio of mixed powder to mixed liquid is 70:

30.

2. The method for preparing a yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode according to claim 1, characterized in that: It is prepared through the following steps: Step S1: Pre-treatment of tungsten cathode surface using sandblasting process: The tungsten cathode substrate is placed in deionized water for ultrasonic cleaning, then cleaned with acetone and anhydrous ethanol for 15 minutes each, dried, and then roughened by sandblasting. After sandblasting, it is cleaned again with anhydrous ethanol to obtain the pre-treated tungsten cathode. Step S2: Prepare a strong bonding underlayer using a slurry coating method: First, a composite slurry is coated onto the surface of the pretreated tungsten cathode using a scraping method to form a wet film layer with a thickness of 100-120µm. The wet film layer is dried at 80℃ for 12h and then transferred to a tube furnace. Under argon protection, the temperature is increased to 500-550℃ at a rate of 1℃ / min and held for 2h. Then, it is transferred to a vacuum sintering furnace for vacuum sintering, thereby forming a strong bonding underlayer on the surface of the pretreated tungsten cathode. Step S3: Prepare an anti-creep gradient layer using atmospheric plasma spraying: First, mix tungsten powder, yttrium-stabilized zirconium oxide powder and titanium carbide according to different ratios, and ball mill them in a ball mill to obtain mixed powders with different ratios. Then, use an atmospheric plasma spraying system to spray the mixed powders with different ratios onto a strong bonding underlayer in sequence to form an anti-creep gradient layer. Step S4: Prepare the anti-corrosion surface layer using the sol-gel method: First, prepare a cerium-yttrium co-doped sol, coat it onto the anti-creep gradient layer, heat it to 200℃ at a heating rate of 1℃ / min, hold it at that temperature for 1h, then continue heating it to 400℃ at a heating rate of 5℃ / min, hold it at that temperature for 60min, continue heating it to 600℃, hold it at that temperature for 120min, cool it, and wash it with deionized water to form the anti-corrosion surface layer.

3. The method for preparing a yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode according to claim 2, characterized in that: In step S1: During the sandblasting process, 25-mesh white corundum sand is used, the sandblasting air pressure is 0.6-0.65MPa, the sandblasting angle is 75°, and the sandblasting time is 15s.

4. The method for preparing a yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode according to claim 2, characterized in that: In step S2: the vacuum sintering process is as follows: under a vacuum of 0.1 MPa, the temperature is increased to 800-900℃ at a heating rate of 4-5℃ / min, held for 30-40 min, then increased to 1100-1200℃, held for 30-40 min, then increased to 1300-1400℃ again, held for 60-90 min, cooled to 700-800℃, and then cooled to room temperature.

5. The method for preparing a yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode according to claim 2, characterized in that: In step S3: During ball milling: the ball-to-material ratio is 4:1, anhydrous ethanol is used as the medium, the rotation speed is 300 rpm, and the ball milling time is 6-8 hours. After ball milling, the mixture is dried to obtain mixed powders with different ratios. During atmospheric plasma spraying: argon and hydrogen are used as the main gas and secondary gas, respectively. The main gas flow rate is 40 L / min, the secondary gas flow rate is 4 L / min, the powder feed rate is 10 g / min, the current is 550 A, the voltage is 50 V, the spray distance is 100 mm, and the spraying angle is 90°. The thickness of each layer with different ratios in the anti-creep gradient layer is 150 µm.

6. The method for preparing a yttrium-stabilized zirconium oxide gradient coating resistant to high-temperature corrosion on the surface of a tungsten cathode according to claim 2, characterized in that: In step S4: the cerium and yttrium co-doped sol is prepared by the following steps: zirconium propoxide solution, yttrium nitrate solution, acetylacetone and n-propanol are mixed and stirred for 30 min at a stirring rate of 300 rpm and a temperature of 50 °C. Then, cerium nitrate solution is added and stirring is continued for 30 min to obtain the cerium and yttrium co-doped sol. The volume ratio of zirconium propoxide solution, yttrium nitrate solution, acetylacetone, n-propanol and cerium nitrate solution is 10-12 mL: 0.8-0.9 mL: 1 mL: 9-10 mL: 1.2-1.5 mL, wherein n-propanol is used as the solvent for zirconium propoxide solution, yttrium nitrate solution and cerium nitrate solution, and their molar concentration is 0.5 mol / L.

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