A method for the thermal decomposition of a nickel-based substrate surface to produce a composite coating

Abstract

The application discloses a method for preparing a composite coating on the surface of a nickel base material by thermal decomposition, which comprises the following steps: sandblasting and ultrasonic cleaning treatment of the nickel base material; coating a precursor solution containing platinum and palladium on the surface of the nickel base material, drying, and then performing thermal decomposition in an air atmosphere; repeating the operation to form a platinum-palladium mixed bottom layer; coating a precursor solution containing ruthenium, cerium and zirconium on the platinum-palladium mixed bottom layer, drying, and then performing thermal decomposition in an air atmosphere; repeating the operation to form a ruthenium-cerium-zirconium composite oxide surface layer; finally, performing annealing treatment in a hydrogen-argon mixed atmosphere, and obtaining the composite coating after furnace cooling. The obtained product comprises a nickel base material, a platinum-palladium mixed bottom layer attached to the surface of the nickel base material, and a ruthenium-cerium-zirconium composite oxide surface layer attached to the surface of the platinum-palladium mixed bottom layer. The bottom layer and the surface layer are sequentially constructed by the thermal decomposition method, so that the coating has excellent adhesion and long-term service stability in a corrosive environment.

Description

Technical Field

[0001] This invention relates to the field of metal surface coating preparation technology, and in particular to a method for preparing a composite coating by thermal decomposition on a nickel substrate surface. Background Technology

[0002] Constructing oxide coatings on metal substrates is an important means to improve the corrosion resistance and functional properties of the substrates. Thermal decomposition has become a commonly used method for preparing metal oxide coatings due to its simplicity and controllable composition. However, oxide coatings prepared by existing thermal decomposition methods still face problems such as insufficient coating density and weakened adhesion to the substrate during long-term service, especially in corrosive media environments, where active components in the coating are easily dissolved and lost, leading to functional degradation. How to significantly improve the structural integrity and corrosion resistance of the coating while maintaining its original functional properties is a pressing technical challenge in this field.

[0003] To address the aforementioned issues, existing technologies attempt to improve the coating through elemental doping or the construction of multilayer coatings. For example, Chinese patent CN103014718A discloses a cerium-containing metal oxide coating, which incorporates cerium into a ruthenium oxide coating via thermal decomposition to improve its structural stability. However, single cerium doping is insufficient to continuously suppress the dissolution and loss of active components in long-term corrosive environments. Chinese patent CN104532279A discloses a multilayer metal oxide coating, which sequentially constructs a platinum metal underlayer and a ruthenium oxide surface layer on the substrate surface. However, the pure ruthenium oxide component on the surface layer is prone to structural degradation in corrosive media, and the interfacial bonding between the underlayer and the surface layer is insufficient, making it difficult to ensure the long-term service stability of the coating.

[0004] Therefore, there is a need in the art for a method and products thereof for forming a multilayer composite oxide coating on a nickel substrate surface that is dense, has strong interlayer bonding, and exhibits excellent service stability in corrosive environments. Summary of the Invention

[0005] The main objective of this invention is to provide a method for preparing a composite coating by thermal decomposition on the surface of a nickel substrate. The bottom layer and the top layer are constructed sequentially by thermal decomposition, so that the coating has both excellent adhesion and long-term service stability in corrosive environments.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a composite coating by thermal decomposition on a nickel substrate surface, comprising the following steps: After sandblasting, the nickel substrate is subjected to ultrasonic treatment with acidic solution and then ultrasonic treatment with alkaline solution in sequence to obtain a pretreated nickel substrate with a clean surface and a roughness of Ra3.0μm~10.0μm. A mixed metal precursor solution containing platinum and palladium is coated onto the surface of the pretreated nickel substrate. After drying at 110°C to 130°C, it is thermally decomposed in air at 560°C to 600°C. The coating, drying and thermal decomposition process is repeated twice. After cooling, a platinum-palladium mixed underlayer is formed. A precursor solution containing ruthenium, cerium and zirconium is coated onto the platinum-palladium mixed substrate. After drying, it is thermally decomposed in air at 450°C to 550°C. The coating, drying and thermal decomposition process is repeated. After cooling, a ruthenium-cerium-zirconium composite oxide surface layer is formed. The nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer is annealed at 450°C to 550°C for 30 to 50 minutes in a hydrogen-argon mixed atmosphere with a volume fraction of 5% to 10%. After annealing, the substrate is cooled to room temperature in the furnace to obtain the composite coating.

[0007] Furthermore, the steps of coating the precursor solution containing ruthenium, cerium, and zirconium onto the platinum-palladium mixed substrate, drying it, and then thermally decomposing it in air at 450°C–550°C, followed by repeating the coating, drying, and thermal decomposition processes, include: Ruthenium trichloride, cerium nitrate, and zirconium oxychloride were dissolved in ethanol at a molar ratio of 50:15-35:15-35, and polyvinylpyrrolidone was added to prepare a precursor solution containing ruthenium, cerium, and zirconium with a total metal concentration of 130 g / L to 170 g / L. The precursor solution is uniformly coated on the surface of the platinum-palladium mixed substrate. After drying at 110°C to 130°C to remove the solvent, it is placed in an air atmosphere and heated to 450°C to 550°C for thermal decomposition to complete the preparation of the monolayer film.

[0008] The single-layer film preparation process was repeated five times, and after cooling, a ruthenium-cerium-zirconium composite oxide surface layer was formed on the surface of the platinum-palladium mixed substrate.

[0009] Furthermore, the amount of polyvinylpyrrolidone added is 0.3 g / L to 0.8 g / L.

[0010] Furthermore, the total metal loading of the ruthenium-cerium-zirconium composite oxide surface layer formed after cooling is 8 g / m² to 10 g / m².

[0011] Furthermore, the step of annealing the nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer in a 5%–10% (v / v) hydrogen-argon mixed atmosphere at 450°C–550°C for 30–50 minutes includes: The nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer is placed in a hydrogen-argon mixed atmosphere containing 5% to 10% hydrogen and annealed at a temperature of 450°C to 550°C for 35 to 45 minutes. After annealing, it is cooled to room temperature in the furnace.

[0012] Furthermore, the step of sequentially subjecting the nickel substrate to ultrasonic treatment with an acidic solution and then with an alkaline solution after sandblasting includes: The nickel substrate after sandblasting is immersed in a sulfuric acid solution with a mass fraction of 15% to 25% for ultrasonic treatment, and then removed and washed with water. Then, it is immersed in a sodium hydroxide solution with a mass fraction of 20% to 30% for ultrasonic treatment.

[0013] Furthermore, the step of coating the platinum and palladium precursor solution onto the surface of the pretreated nickel substrate, drying it at 110°C to 130°C, then thermally decomposing it, repeating the coating, drying, and thermal decomposition process twice, and finally cooling to form a platinum-palladium mixed underlayer, includes: Chloroplatinic acid and palladium chloride were dissolved in ethanol solvent at a molar ratio of 1:0.8 to 1:1.2 to prepare a precursor solution containing platinum and palladium with a total metal concentration of 40 g / L to 60 g / L. The precursor solution is uniformly coated on the surface of the pretreated nickel substrate. After drying at 110℃~130℃ to remove the solvent, it is placed in an air atmosphere and heated to 560℃~600℃ for thermal decomposition to complete the preparation of the single-layer bottom layer. The single-layer underlayer preparation operation was repeated twice, and after cooling, a platinum-palladium mixed underlayer was formed on the surface of the nickel substrate.

[0014] Furthermore, the total metal loading of the platinum-palladium hybrid underlayer formed on the nickel substrate surface after cooling is 1.2 g / m² to 1.8 g / m².

[0015] The present invention also provides a nickel-based product with a surface having a multilayer composite oxide coating, comprising: Nickel substrate; A platinum-palladium hybrid underlayer adhered to the surface of the nickel substrate; The ruthenium-cerium-zirconium composite oxide surface layer is attached to the surface of the platinum-palladium mixed bottom layer.

[0016] The method for preparing a composite coating by thermal decomposition on a nickel substrate provided by the present invention has the following beneficial effects: A platinum-palladium mixed underlayer and a ruthenium-cerium-zirconium composite oxide surface layer are constructed sequentially by thermal decomposition. The underlayer and the surface layer form a metallurgical bonding interface through element interdiffusion during the thermal decomposition process. Compared with the mechanical stacking method of multi-layer coatings in the prior art, the interlayer bonding force is significantly enhanced, effectively avoiding the peeling failure of the coating during service.

[0017] By simultaneously introducing cerium and zirconium into the surface layer, cerium provides electron buffering through its variable valence properties, while zirconium enhances the structural integrity of the coating by forming a stable oxide skeleton. The synergistic effect of the two effectively inhibits the dissolution and loss of active components in the coating in corrosive media, overcoming the shortcomings of existing technologies where single-element doping has limited effect on improving the overall performance of the coating.

[0018] Through the functional synergy design of the bottom and top layers, the coating possesses both excellent adhesion and long-term service stability in corrosive environments. The structural degradation rate of the coating is significantly reduced under long-term operating conditions, and its service life is significantly extended compared to existing single-doped or multi-layer coating solutions. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for preparing a composite coating on a nickel substrate by thermal decomposition, as provided in an embodiment of the present invention. Figure 2 is a scanning electron microscope image of the surface morphology of the composite coating prepared in Example 1 of the present invention; Figure 3 These are the steady-state activity test results of the composite coating in a strongly alkaline medium in the embodiments of the present invention; Figure 4 These are the results of the composite coating under strongly alkaline medium-enhanced corrosion weight loss test in the embodiments of the present invention; The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Reference Figure 1 This is a schematic flowchart of a method for preparing a composite coating on a nickel substrate by thermal decomposition, as proposed in this invention, including the following steps: S1. After sandblasting, the nickel substrate is subjected to ultrasonic treatment with acidic solution and then ultrasonic treatment with alkaline solution in sequence to obtain a pretreated nickel substrate with a clean surface and a surface roughness of Ra3.0μm~10.0μm. S2, a mixed metal precursor solution containing platinum and palladium is coated onto the surface of the pretreated nickel substrate, dried at 110°C to 130°C, and then thermally decomposed in air at 560°C to 600°C. The coating, drying, and thermal decomposition process is repeated twice, and after cooling, a platinum-palladium mixed underlayer is formed. S3, a precursor solution containing ruthenium, cerium and zirconium is coated onto the platinum-palladium mixed substrate, dried, and then thermally decomposed in air at 450°C to 550°C. The coating, drying and thermal decomposition process is repeated, and after cooling, a ruthenium-cerium-zirconium composite oxide surface layer is formed. S4, the nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer is annealed at 450°C to 550°C for 30 to 50 minutes in a hydrogen-argon mixed atmosphere with a volume fraction of 5% to 10%. After annealing, the substrate is cooled to room temperature in the furnace to obtain the composite coating.

[0022] As described in step S1 above, the nickel substrate is roughened by sandblasting. 60-mesh corundum abrasive is used and sprayed at high speed onto the nickel mesh surface under compressed air, forming a uniform rough microstructure with a surface roughness controlled between Ra 3.0 μm and Ra 10.0 μm. The micron-level rough surface formed by sandblasting increases the contact area between the substrate and the coating, which is beneficial for enhancing the mechanical bonding effect. After sandblasting, surface dust is removed, and the nickel substrate is completely immersed in acetone solution for ultrasonic cleaning for 30 minutes to remove surface oil and organic impurities. The nickel substrate is then removed and transferred to anhydrous ethanol for further ultrasonic cleaning for 10 minutes to further purify the surface, followed by rinsing with pure water. The nickel substrate is then placed in a 20% sulfuric acid solution and ultrasonically treated for 1 hour to fully dissolve the natural oxide film and residual sandblasting dust, exposing a fresh and dense metallic nickel surface. After treatment, the substrate is repeatedly rinsed with pure water until no residual acid remains. The nickel substrate is then ultrasonically treated in a 25% sodium hydroxide solution for 20 minutes to neutralize trace acid residues and deeply remove hidden oil and impurities. After removal, it is rinsed with pure water until the washing solution is neutral, first placed in a natural environment to dry the surface moisture, and then placed in a 50°C oven to dry, resulting in a clean pretreated nickel substrate with suitable roughness.

[0023] As described in step S2 above, chloroplatinic acid and palladium chloride are dissolved in ethanol at a molar ratio of 1:1 to prepare a precursor solution containing platinum and palladium with a total metal concentration of 50 g / L. The precursor solution is uniformly coated onto the surface of the pretreated nickel substrate using a brush coating method and dried at 120°C for 10 minutes to allow the solvent to fully evaporate. Subsequently, the dried nickel substrate is placed in air and heated to 580°C for 20 minutes for thermal decomposition, causing the platinum and palladium metal salts to decompose into their corresponding elemental metals and oxides, forming a dense platinum-palladium mixed film on the nickel substrate surface. This coating, drying, and thermal decomposition process is repeated three times. Each coating layer is a new film layer superimposed on the previous layer. Through multiple thermal decompositions, the film layers fuse together, and the platinum and palladium metal particles gradually grow and connect with each other. Finally, after cooling, a continuous and uniform platinum-palladium mixed underlayer is formed on the nickel substrate surface. Platinum provides high chemical stability and conductivity in the substrate, while palladium forms palladium hydride during subsequent processing, endowing the substrate with unique hydrogen absorption and buffering capabilities. The synergistic effect of platinum and palladium gives the substrate both excellent conductive transition function and resistance to hydrogen-induced damage. Multiple coating processes and thermal decomposition ensure the density of the substrate and a strong bond with the nickel substrate.

[0024] As described in step S3 above, ruthenium trichloride, cerium nitrate, and zirconium oxychloride are dissolved in ethanol solvent at a molar ratio of 50:35:15, and 0.5 g / L of polyvinylpyrrolidone is added to prepare a precursor solution containing ruthenium, cerium, and zirconium with a total metal concentration of 150 g / L. The introduction of polyvinylpyrrolidone helps to improve the dispersion uniformity of the coating solution and promotes the uniform distribution of each metal component during subsequent thermal decomposition. The precursor solution is uniformly coated onto the surface of the platinum-palladium mixed substrate by brushing and dried at 120°C for 10 minutes to allow the solvent to fully evaporate. Subsequently, the dried nickel substrate is placed in an air atmosphere and heated to 500°C for 20 minutes for thermal decomposition, causing the metal salts of ruthenium, cerium, and zirconium to decompose into their corresponding oxides, forming a ruthenium-cerium-zirconium composite oxide film layer on the surface of the platinum-palladium mixed substrate. The coating, drying, and thermal decomposition processes were repeated six times. Each time, the oxide film formed after thermal decomposition was superimposed and fused with the previous layer, gradually constructing a dense and uniformly thick ruthenium-cerium-zirconium composite oxide surface layer. After cooling, this surface layer firmly adhered to the platinum-palladium mixed substrate. In the ruthenium-cerium-zirconium composite oxide surface layer, the variable valence properties of cerium provide an electron buffer between oxidizing and reducing environments, while the zirconium oxide forms a stable framework structure. Their synergistic effect effectively inhibits the dissolution and loss of ruthenium in corrosive media, endowing the surface layer with excellent structural integrity and corrosion resistance.

[0025] As described in step S4 above, the nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer is placed in a hydrogen-argon mixed atmosphere containing 5% to 10% hydrogen and annealed at 500°C for 40 minutes. During annealing, the hydrogen in the hydrogen-argon mixed atmosphere undergoes a mild reduction reaction with the coating surface and interior, moderately regulating the chemical valence state of ruthenium in the ruthenium-cerium-zirconium composite oxide surface layer, while simultaneously promoting the further formation of palladium hydrides in the platinum-palladium mixed underlayer, thus strengthening the hydrogen buffering capacity of the underlayer. The double-layer coating undergoes moderate interfacial atomic interdiffusion at high temperature, transitioning the bonding between the underlayer and surface layer from mechanical stacking to metallurgical bonding, improving the density and bonding strength of the interface region. The cerium and zirconium oxides maintain a stable skeletal structure during annealing, without significant phase separation or agglomeration, ensuring the continued maintenance of the surface structure integrity. After annealing, the coating is slowly cooled to room temperature in the furnace to avoid coating cracking or interface delamination caused by thermal stress from rapid cooling. After this annealing treatment, the overall density, interlayer bonding strength, and structural stability of the coating are all improved, and the actual service life of the coating is significantly extended compared with the unannealed state.

[0026] The present invention will be specifically described below through examples and comparative examples.

[0027] Example 1 Pure nickel mesh was used as the nickel substrate and first underwent sandblasting roughening treatment. 60-mesh corundum abrasive was used to sandblast the surface of the nickel mesh, creating a uniformly rough microstructure with a surface roughness controlled within the range of Ra 3.0 μm to Ra 10.0 μm. After sandblasting, surface dust was removed, and the nickel mesh was completely immersed in an acetone solution for ultrasonic cleaning to remove surface oil and organic impurities. The cleaning time was 30 minutes. After removal, it was transferred to anhydrous ethanol solution for further ultrasonic cleaning for 10 minutes to further purify the surface, followed by rinsing with pure water. The cleaned nickel mesh was then placed in a 20% sulfuric acid solution for ultrasonic treatment for 1 hour to fully dissolve and remove the naturally formed oxide film and sandblasting residue, exposing a fresh and dense metallic nickel surface. After treatment, the nickel mesh was removed and repeatedly rinsed with pure water until no residual acid remained on the surface. The nickel mesh is then placed in a 25% sodium hydroxide solution and ultrasonically treated for 20 minutes to neutralize any trace acidic residue on the surface and deeply remove any hidden oil and impurities. After removal, it is rinsed with pure water until the washing solution is neutral. The surface moisture is first allowed to air dry in a natural environment, and then it is placed in an oven at 50°C to dry, resulting in a clean pretreated nickel substrate with suitable roughness.

[0028] Prepare the undercoating solution by dissolving chloroplatinic acid and palladium chloride in ethanol at a molar ratio of Pt:Pd = 1:1, controlling the total metal concentration to 50 g / L. Apply the prepared undercoating solution evenly to the surface of the pretreated nickel mesh, dry at 120°C for 10 minutes, then transfer it to an air-atmosphere heating device for thermal decomposition at 580°C for 20 minutes. Repeat the brushing, drying, and thermal decomposition process three times, controlling the total metal loading of the undercoat to reach 1.5 g / m², thus forming a platinum-palladium mixed undercoat on the nickel substrate surface.

[0029] To prepare the surface coating solution, ruthenium trichloride hydrate, cerium nitrate hexahydrate, and zirconium oxychloride octahydrate were dissolved in ethanol at a molar ratio of Ru:Ce:Zr = 50:35:15, maintaining a total metal concentration of 150 g / L. Simultaneously, 0.5 g / L of polyvinylpyrrolidone was added to the solution and stirred until completely dissolved. The surface coating solution was evenly brushed onto the surface of the platinum-palladium mixed substrate and dried at 120°C for 10 minutes. Then, it was transferred to an air-atmosphere heating device and thermally decomposed at 500°C for 20 minutes. This brushing, drying, and thermal decomposition process was repeated six times, maintaining a total surface metal loading of 9 g / m², thus forming a ruthenium-cerium-zirconium composite oxide surface layer on the platinum-palladium mixed substrate.

[0030] After all coating preparations are completed, the coated nickel substrate is placed in a hydrogen-argon mixed atmosphere with a volume fraction of 5% to 10% and annealed at 500°C for 40 minutes. After annealing, the substrate is cooled to room temperature in the furnace to obtain the finished composite coating.

[0031] The performance of the multilayer composite oxide coating samples prepared in this embodiment was tested. Steady-state activity testing was conducted in a strongly alkaline medium at a constant temperature of 85°C using a water bath. The stable operating potential of the coating was read using a steady-state testing method. Corrosion resistance stability testing was conducted in a strongly alkaline medium using an enhanced weight loss method at a temperature of 85°C. After 6 hours of continuous testing, the weight loss rate per unit area of ​​the coating was calculated.

[0032] Depend on Figure 3 It can be seen that the composite coating prepared in this embodiment exhibits a low stable operating potential and good functional activity in a strongly alkaline medium. Figure 4 As can be seen, the proportion of cerium component in this embodiment is relatively higher, which can give full play to the electron buffering effect brought about by the change of valence state, effectively inhibit the dissolution and loss of active components in strong alkaline medium, and the coating has low weight loss per unit area after the enhanced corrosion test, strong interlayer bonding, and excellent resistance to media erosion.

[0033] like Figure 2As shown in the SEM images, the coating forms a continuous, uniform, and complete coating on the nickel substrate surface. The surface is smooth and dense, without obvious macroscopic cracks, pinholes, or localized peeling defects. The coating particles are fine and uniformly distributed, perfectly conforming to the microscopic contours of the substrate, with no exposed substrate areas. This morphology indicates that after the stepwise thermal decomposition process and subsequent atmosphere annealing, the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer have a good bonding state, resulting in excellent overall film quality and a dense structure. This dense and complete coating structure effectively blocks the penetration of strongly alkaline media into the substrate, reduces the contact area between the active components and the corrosive media, and provides structural support for the coating's excellent resistance to media corrosion and long-term service stability. Figure 3 , Figure 4 The performance test results corroborate each other.

[0034] Example 2 This embodiment provides a method for preparing a multilayer composite oxide coating by thermal decomposition on a nickel substrate. The process parameters for substrate pretreatment, preparation of a platinum-palladium mixed underlayer, and final annealing are the same as in Example 1. The only difference is the molar ratio of the precursors for the ruthenium-cerium-zirconium composite oxide surface layer.

[0035] In preparing the surface coating solution, ruthenium trichloride hydrate, cerium nitrate hexahydrate, and zirconium oxychloride octahydrate were dissolved in ethanol at a molar ratio of Ru:Ce:Zr = 50:25:25, controlling the total metal concentration to 150 g / L. Simultaneously, 0.5 g / L of polyvinylpyrrolidone was added to the solution and stirred until completely dissolved. The prepared surface coating solution was uniformly brushed onto the surface of the platinum-palladium mixed substrate and dried at 120°C for 10 minutes. Then, it was transferred to an air-atmosphere heating device and thermally decomposed at 500°C for 20 minutes. This brushing, drying, and thermal decomposition process was repeated six times to control the total metal loading on the surface to reach 9 g / m², forming a ruthenium-cerium-zirconium composite oxide surface layer on the platinum-palladium mixed substrate. The annealing process was the same as in Example 1. After annealing, the surface was cooled to room temperature in the furnace to obtain the finished composite coating.

[0036] The performance of the multilayer composite oxide coating samples prepared in this embodiment was tested. Steady-state activity testing was conducted in a strongly alkaline medium at a constant temperature of 85°C using a water bath. The stable operating potential of the coating was read using a steady-state testing method. Corrosion resistance stability testing was conducted in a strongly alkaline medium using an enhanced weight loss method at a temperature of 85°C. After 6 hours of continuous testing, the weight loss rate per unit area of ​​the coating was calculated.

[0037] Depend on Figure 3 It can be seen that the composite coating prepared in this embodiment has the lowest stable operating potential among the three sets of embodiments, and exhibits the best functional activity. Figure 4As can be seen, in this embodiment, the ratio of cerium to zirconium is balanced, and the synergistic effect of the two is fully utilized. The dissolution of active components is inhibited by the electronic buffering effect of cerium, and the integrity of the coating structure is maintained by the oxide skeleton of zirconium. After the enhanced corrosion test, the coating has the smallest weight loss per unit area, no interlayer peeling, and achieves the optimal balance between activity and corrosion resistance, resulting in the best overall service performance.

[0038] Example 3 This embodiment provides a method for preparing a multilayer composite oxide coating by thermal decomposition on a nickel substrate. The process parameters for substrate pretreatment, preparation of a platinum-palladium mixed underlayer, and final annealing are the same as in Example 1. The only difference is the molar ratio of the precursors for the ruthenium-cerium-zirconium composite oxide surface layer.

[0039] In preparing the surface coating solution, ruthenium trichloride hydrate, cerium nitrate hexahydrate, and zirconium oxychloride octahydrate were dissolved in ethanol at a molar ratio of Ru:Ce:Zr = 50:15:35, controlling the total metal concentration to 150 g / L. Simultaneously, 0.5 g / L of polyvinylpyrrolidone was added to the solution and stirred until completely dissolved. The prepared surface coating solution was uniformly brushed onto the surface of the platinum-palladium mixed substrate and dried at 120°C for 10 minutes. Then, it was transferred to an air-atmosphere heating device and thermally decomposed at 500°C for 20 minutes. This brushing, drying, and thermal decomposition process was repeated six times to control the total metal loading on the surface to reach 9 g / m², forming a ruthenium-cerium-zirconium composite oxide surface layer on the platinum-palladium mixed substrate. The subsequent annealing process was the same as in Example 1. After annealing, the surface was cooled to room temperature in the furnace to obtain the finished composite coating.

[0040] The performance of the multilayer composite oxide coating samples prepared in this embodiment was tested. Steady-state activity testing was conducted in a strongly alkaline medium at a constant temperature of 85°C using a water bath. The stable operating potential of the coating was read using a steady-state testing method. Corrosion resistance stability testing was conducted in a strongly alkaline medium using an enhanced weight loss method at a temperature of 85°C. After 6 hours of continuous testing, the weight loss rate per unit area of ​​the coating was calculated.

[0041] Depend on Figure 3 It can be seen that the composite coating prepared in this embodiment exhibits a low stable operating potential and excellent functional activity in a strongly alkaline medium. Figure 4 As can be seen, after the enhanced corrosion test, the coating of the sample in this embodiment has a small weight loss per unit area, the dissolution and loss of active components are effectively suppressed, the interlayer bonding is strong and there is no peeling phenomenon, the coating structure integrity is well maintained, and it has excellent resistance to strong alkaline corrosion and long-term service stability.

[0042] Example 4 This embodiment provides a method for preparing a multilayer composite oxide coating by thermal decomposition on a nickel substrate. The process parameters for substrate pretreatment, preparation of the platinum-palladium mixed underlayer, and preparation of the ruthenium-cerium-zirconium composite oxide surface layer are the same as those in Example 1. The only difference is that after all coating preparations are completed, no hydrogen-argon mixed atmosphere annealing is performed, and the finished composite coating is obtained by natural cooling to room temperature.

[0043] The performance of the multilayer composite oxide coating samples prepared in this embodiment was tested. Steady-state activity testing was conducted in a strongly alkaline medium at a constant temperature of 85°C using a water bath. The stable operating potential of the coating was read using a steady-state testing method. Corrosion resistance stability testing was conducted in a strongly alkaline medium using an enhanced weight loss method at a temperature of 85°C. After 6 hours of continuous testing, the weight loss rate per unit area of ​​the coating was calculated.

[0044] Depend on Figure 3 It can be seen that the composite coating prepared in this embodiment still possesses good functional activity in a strongly alkaline medium, and its stable operating potential remains within a reasonable range. Figure 4 It can be seen that, due to the lack of atmospheric annealing treatment, the residual stress inside the coating was not fully eliminated, the interlayer interface bonding strength was lower than that of Example 1, the weight loss per unit area of ​​the coating after the enhanced corrosion test was higher than that of Example 1, and the dissolution inhibition effect of the active component was weaker than that of the annealed sample. This indicates that the hydrogen-argon mixed atmosphere annealing step can effectively optimize the interlayer bonding state of the coating and further improve the corrosion resistance stability and service life of the coating.

[0045] Comparative Example 1 This comparative example provides a method for preparing an oxide coating by thermal decomposition on a nickel substrate surface. The difference from Example 1 is that the preparation step of the platinum-palladium mixed underlayer is omitted, and a ruthenium-cerium-zirconium composite oxide surface layer is directly prepared on the pretreated nickel substrate surface.

[0046] When preparing the surface coating solution, ruthenium trichloride hydrate, cerium nitrate hexahydrate, and zirconium oxychloride octahydrate were dissolved in ethanol at a molar ratio of Ru:Ce:Zr = 50:35:15, controlling the total metal concentration to 150 g / L. Simultaneously, 0.5 g / L of polyvinylpyrrolidone was added to the solution and stirred until completely dissolved. The surface coating solution was uniformly brushed onto the surface of the pretreated nickel substrate and dried at 120°C for 10 minutes. Then, it was transferred to a heating device with an air atmosphere and thermally decomposed at 500°C for 20 minutes. This brushing, drying, and thermal decomposition process was repeated six times to control the total metal loading on the surface to reach 9 g / m². After coating preparation, the coated nickel substrate was placed in a hydrogen-argon mixed atmosphere with a volume fraction of 5% to 10% and annealed at 500°C for 40 minutes. After annealing, the substrate was cooled to room temperature in the furnace to obtain the finished oxide coating.

[0047] The oxide coating samples prepared in this comparative example were subjected to performance tests. Steady-state activity tests were conducted in a strongly alkaline medium at a constant temperature of 85°C using a water bath, and the stable operating potential of the coating was read using a steady-state testing method. Corrosion resistance stability tests were conducted in a strongly alkaline medium using an enhanced weight loss method at a temperature of 85°C. After 6 hours of continuous testing, the weight loss rate per unit area of ​​the coating was calculated.

[0048] Depend on Figure 3 It can be seen that the stable operating potential of the coating prepared in this comparative example is significantly higher than that of Example 1, indicating poorer functional activity. Figure 4 It can be seen that, due to the lack of transitional bonding effect of the platinum-palladium mixed underlayer, the interfacial bonding strength between the coating and the nickel substrate is insufficient. Under the corrosion of strong alkaline media, the dissolution and loss of active components are more significant. After the enhanced corrosion test, the weight loss per unit area of ​​the coating is much higher than that of Example 1, and the coating shows signs of peeling in some areas. The structural integrity and long-term service stability are not as good as the composite coating with a double-layer structure.

[0049] Comparative Example 2 This comparative example provides a method for preparing a composite coating by thermal decomposition on a nickel substrate. The difference from Example 1 is that the bottom layer is a pure platinum layer, and only chloroplatinic acid is used as the precursor salt. It does not contain palladium components. The process parameters for substrate pretreatment, surface preparation and final annealing are the same as those in Example 1.

[0050] When preparing the undercoating solution, chloroplatinic acid was dissolved in ethanol solvent, and the total metal concentration was controlled to be 50 g / L. The prepared undercoating solution was evenly brushed onto the surface of the pretreated nickel mesh, dried at 120°C for 10 minutes, and then transferred to a heating device in an air atmosphere for thermal decomposition at 580°C for 20 minutes. The above brushing, drying, and thermal decomposition operations were repeated three times to control the total metal loading of the undercoating to reach 1.5 g / m², forming a pure platinum undercoating on the nickel substrate surface. The subsequent preparation and annealing process of the ruthenium-cerium-zirconium composite oxide surface layer was completely consistent with that in Example 1. After annealing, the surface was cooled to room temperature in the furnace to obtain the finished composite coating.

[0051] The composite coating samples prepared in this comparative example were subjected to performance tests. Steady-state activity tests were conducted in a strongly alkaline medium at a constant temperature of 85°C using a water bath, and the stable operating potential of the coating was read using a steady-state testing method. Corrosion resistance stability tests were conducted in a strongly alkaline medium using an enhanced weight loss method at a temperature of 85°C. After 6 hours of continuous testing, the weight loss rate per unit area of ​​the coating was calculated.

[0052] Depend on Figure 3 It can be seen that the stable operating potential of the composite coating prepared in this comparative example is higher than that of Example 1, but its functional activity is weaker than that of the composite coating with a platinum-palladium mixed underlayer. Figure 4It can be seen that, due to the lack of synergistic buffering effect of palladium component, the interfacial compatibility between the pure platinum underlayer and the surface layer is reduced. Under the corrosion of strongly alkaline media, the degree of dissolution and loss of active components is higher than that in Example 1. After the enhanced corrosion test, the coating loses more weight per unit area and the structural stability under the fluctuation of operating conditions is insufficient. This indicates that the synergistic combination of platinum and palladium can further optimize the interfacial bonding state and resistance to media corrosion of the coating, and improve the overall service performance.

[0053] Comparative Example 3 This comparative example provides a method for preparing a composite coating by thermal decomposition on a nickel substrate. The difference from Example 1 is that the bottom layer is a pure palladium layer, and only palladium chloride is used as the precursor salt. Platinum components are not included. The process parameters for substrate pretreatment, surface preparation and final annealing are the same as those in Example 1.

[0054] When preparing the undercoating solution, palladium chloride was dissolved in ethanol solvent, and the total metal concentration was controlled to be 50 g / L. The prepared undercoating solution was evenly brushed onto the surface of the pretreated nickel mesh, dried at 120°C for 10 minutes, and then transferred to a heating device in an air atmosphere for thermal decomposition at 580°C for 20 minutes. The above brushing, drying, and thermal decomposition operations were repeated three times to control the total metal loading of the undercoating to reach 1.5 g / m², forming a pure palladium undercoating on the nickel substrate surface. The subsequent preparation and annealing process of the ruthenium-cerium-zirconium composite oxide surface layer was completely consistent with that in Example 1. After annealing, the surface was cooled to room temperature in the furnace to obtain the finished composite coating.

[0055] The composite coating samples prepared in this comparative example were subjected to performance tests. Steady-state activity tests were conducted in a strongly alkaline medium at a constant temperature of 85°C using a water bath, and the stable operating potential of the coating was read using a steady-state testing method. Corrosion resistance stability tests were conducted in a strongly alkaline medium using an enhanced weight loss method at a temperature of 85°C. After 6 hours of continuous testing, the weight loss rate per unit area of ​​the coating was calculated.

[0056] Depend on Figure 3 It can be seen that the stable operating potential of the composite coating prepared in this comparative example is higher than that of Example 1, but its functional activity is inferior to that of the composite coating with a platinum-palladium mixed underlayer. Figure 4 It can be seen that the chemical stability of the single palladium component substrate is weaker than that of the platinum-palladium synergistic system. Under long-term corrosion in a strongly alkaline medium, the interlayer interface protection capability decreases, the degree of dissolution and loss of active components is higher than in Example 1, and the coating loses more weight per unit area after the enhanced corrosion test. Combining the test results of Comparative Example 2 and this comparative example, it can be seen that the substrate formed by mixing platinum and palladium in a certain proportion can simultaneously exert the high stability of platinum and the buffering effect of palladium. The synergistic effect of the two is significantly better than that of the single component substrate, and can more effectively improve the overall service performance of the coating.

[0057] comprehensive Figure 3 and Figure 4The test results were compared and analyzed to determine the steady-state activity and resistance to strong alkaline corrosion of each group of samples. This analysis clarified the influence of the underlying structure, component ratio, and annealing process on the service performance of the composite coating.

[0058] Compared to Comparative Example 1, Example 1 employs a two-layer structure design with a platinum-palladium mixed bottom layer and a ruthenium-cerium-zirconium composite surface layer. Figure 3 The steady-state operating potential is significantly reduced, and the functional activity is significantly improved. Figure 4 The weight loss per unit area after the medium-strength corrosion test decreased significantly, and the coating structure integrity was better. This indicates that the platinum-palladium hybrid underlayer can form a well-adapted transition interface between the substrate and the surface layer, which not only improves the bonding strength between the coating and the substrate, but also provides a stable bearing base for the functional components of the surface layer, effectively mitigating the erosion of the interface by the strong alkaline medium and preventing overall coating peeling and rapid loss of active components.

[0059] Comparing Example 1, Comparative Example 2, and Comparative Example 3, it is evident that neither a single-component pure platinum substrate nor a pure palladium substrate can achieve optimal performance. The pure platinum substrate of Comparative Example 2 exhibits good chemical stability but insufficient interfacial buffering capacity; while the pure palladium substrate of Comparative Example 3 possesses some buffering effect, its own corrosion resistance is relatively weak. Both... Figure 3 The steady-state operating potentials in all cases were higher than those in Example 1. Figure 4 The weight loss per unit area in both cases was greater than that in Example 1. The mixed underlayer formed by the proportional blending of platinum and palladium in Example 1 can simultaneously leverage the high chemical stability of platinum and the interfacial buffering effect of palladium. The two work synergistically to improve the overall performance of the underlayer, thereby optimizing the activity and corrosion resistance of the entire coating system.

[0060] Examples 1, 2, and 3 used different cerium-zirconium molar ratios. All three groups of samples exhibited good service performance, but their performance emphases differed. Figure 3 and Figure 4 As can be seen, Example 2, with its balanced cerium-zirconium ratio, exhibits the lowest steady-state operating potential and minimal weight loss per unit area, achieving an optimal balance between activity and corrosion resistance, resulting in the best overall performance. Example 1, with its higher cerium content, demonstrates a more significant valence buffering effect and a superior inhibitory effect on the dissolution of active components. Example 3, with its higher zirconium content, exhibits a more robust oxide framework structure, resulting in stronger coating structural integrity and peel resistance. This demonstrates that by adjusting the cerium-zirconium ratio, the coating's anti-dissolution performance or structural stability can be selectively optimized to meet different service requirements.

[0061] Comparing Example 1 and Example 4, it can be seen that the sample that has not undergone annealing in a hydrogen-argon mixed atmosphere, Figure 3 The steady-state operating potential increases slightly. Figure 4The weight loss per unit area increased significantly. This indicates that annealing can effectively eliminate residual stress generated during coating preparation, promote appropriate diffusion of interlayer elements and strengthen interfacial bonding, further improve the interfacial bonding strength and structural density of the coating, thereby enhancing the long-term service stability of the coating in strongly alkaline media.

[0062] In summary, this invention constructs a two-layer composite structure on a nickel substrate surface using a stepwise thermal decomposition process, consisting of a platinum-palladium mixed underlayer and a ruthenium-cerium-zirconium composite oxide surface layer. Combined with precise substrate pretreatment and atmosphere annealing, this achieves a synergistic improvement in the composite coating's functional activity and resistance to strong alkaline corrosion. First, the invention uses sandblasting roughening and multi-step ultrasonic cleaning to control the substrate surface morphology and cleanliness, creating a suitable bearing interface for the coating. Then, a platinum-palladium mixed transition underlayer and a ruthenium-cerium-zirconium functional surface layer are prepared sequentially. The interfacial compatibility and buffering effect of the platinum and palladium components in the underlayer enhance the bonding strength between the coating and the substrate. The valence state buffering effect of cerium and the oxide framework of zirconium in the surface layer inhibit the dissolution of active components and maintain the integrity of the coating structure. Finally, annealing in a hydrogen-argon mixed atmosphere eliminates residual stress and further optimizes the interlayer bonding state.

[0063] Through multiple examples and comparative studies, it was verified that adjusting the cerium-zirconium composition ratio can directionally optimize the performance emphasis of the coating. The overall performance of the two-layer synergistic system is significantly better than that of solutions without an underlying structure or with a single-component underlying layer. Annealing treatment can further improve the long-term service stability of the coating. This method offers strong process controllability, and the prepared composite coating has a dense structure and strong interlayer bonding. It exhibits excellent service reliability in strongly alkaline media environments and is suitable for functional modification processing of various metal substrate surfaces.

[0064] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a composite coating by thermal decomposition on a nickel substrate surface, characterized in that, Includes the following steps: After sandblasting, the nickel substrate is subjected to ultrasonic treatment with acidic solution and then ultrasonic treatment with alkaline solution in sequence to obtain a pretreated nickel substrate with a clean surface and a roughness of Ra3.0μm~10.0μm. A mixed metal precursor solution containing platinum and palladium is coated onto the surface of the pretreated nickel substrate. After drying at 110°C to 130°C, it is thermally decomposed in air at 560°C to 600°C. The coating, drying and thermal decomposition process is repeated twice. After cooling, a platinum-palladium mixed underlayer is formed. A precursor solution containing ruthenium, cerium and zirconium is coated onto the platinum-palladium mixed substrate. After drying, it is thermally decomposed in air at 450°C to 550°C. The coating, drying and thermal decomposition process is repeated. After cooling, a ruthenium-cerium-zirconium composite oxide surface layer is formed. The nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer is annealed at 450°C to 550°C for 30 to 50 minutes in a hydrogen-argon mixed atmosphere with a volume fraction of 5% to 10%. After annealing, the substrate is cooled to room temperature in the furnace to obtain the composite coating.

2. The method for preparing a composite coating by thermal decomposition on a nickel substrate surface according to claim 1, characterized in that, The steps of coating a precursor solution containing ruthenium, cerium, and zirconium onto the platinum-palladium mixed substrate, drying it, and then thermally decomposing it at 450°C–550°C in air, followed by repeating the coating, drying, and thermal decomposition processes, include: Ruthenium trichloride, cerium nitrate, and zirconium oxychloride were dissolved in ethanol at a molar ratio of 50:15-35:15-35, and polyvinylpyrrolidone was added to prepare a precursor solution containing ruthenium, cerium, and zirconium with a total metal concentration of 130 g / L to 170 g / L. The precursor solution was uniformly coated on the surface of the platinum-palladium mixed substrate. After drying at 110°C to 130°C to remove the solvent, it was placed in an air atmosphere and heated to 450°C to 550°C for thermal decomposition to complete the preparation of the monolayer film. The single-layer film preparation process was repeated five times, and after cooling, a ruthenium-cerium-zirconium composite oxide surface layer was formed on the surface of the platinum-palladium mixed substrate.

3. The method for preparing a composite coating by thermal decomposition on a nickel substrate surface according to claim 2, characterized in that, The amount of polyvinylpyrrolidone added is 0.3 g / L to 0.8 g / L.

4. The method for preparing a composite coating by thermal decomposition on a nickel substrate surface according to claim 2, characterized in that, The total metal loading of the ruthenium-cerium-zirconium composite oxide surface layer formed after cooling is 8 g / m² to 10 g / m².

5. The method for preparing a composite coating by thermal decomposition on a nickel substrate surface according to claim 1, characterized in that, The step of annealing the nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer in a 5%–10% (v / v) hydrogen-argon mixed atmosphere at 450°C–550°C for 30–50 minutes includes: The nickel substrate with the platinum-palladium mixed underlayer and the ruthenium-cerium-zirconium composite oxide surface layer is placed in a hydrogen-argon mixed atmosphere containing 5% to 10% hydrogen and annealed at a temperature of 450°C to 550°C for 35 to 45 minutes. After annealing, it is cooled to room temperature in the furnace.

6. The method for preparing a composite coating by thermal decomposition on a nickel substrate surface according to claim 1, characterized in that, The steps of subjecting the nickel substrate to sandblasting followed by sequential ultrasonic treatment with an acidic solution and then with an alkaline solution include: The nickel substrate after sandblasting is immersed in a sulfuric acid solution with a mass fraction of 15% to 25% for ultrasonic treatment, and then removed and washed with water. Then, it is immersed in a sodium hydroxide solution with a mass fraction of 20% to 30% for ultrasonic treatment.

7. The method for preparing a composite coating by thermal decomposition on a nickel substrate surface according to claim 1, characterized in that, The steps of coating a platinum and palladium precursor solution onto the surface of the pretreated nickel substrate, drying it at 110°C to 130°C, thermally decomposing it, and repeating the coating, drying, and thermal decomposition process twice, followed by cooling to form a platinum-palladium mixed underlayer, include: Chloroplatinic acid and palladium chloride were dissolved in ethanol solvent at a molar ratio of 1:0.8 to 1:1.2 to prepare a precursor solution containing platinum and palladium with a total metal concentration of 40 g / L to 60 g / L. The precursor solution is uniformly coated on the surface of the pretreated nickel substrate. After drying at 110℃~130℃ to remove the solvent, it is placed in an air atmosphere and heated to 560℃~600℃ for thermal decomposition to complete the preparation of the single-layer bottom layer. The single-layer underlayer preparation operation was repeated twice, and after cooling, a platinum-palladium mixed underlayer was formed on the surface of the nickel substrate.

8. The method for preparing a composite coating by thermal decomposition on a nickel substrate surface according to claim 7, characterized in that, The total metal loading of the platinum-palladium hybrid underlayer formed on the nickel substrate surface after cooling is 1.2 g / m² to 1.8 g / m².

9. A nickel-based product with a multilayer composite oxide coating on its surface, characterized in that, include: Nickel substrate; A platinum-palladium hybrid underlayer adhered to the surface of the nickel substrate; The ruthenium-cerium-zirconium composite oxide surface layer is attached to the surface of the platinum-palladium mixed bottom layer.

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