A liquid sodium-based nickel-platinum alloy coating preparation device and a preparation method thereof

Abstract

The application relates to a liquid sodium-based nickel-platinum alloy coating preparation device and a preparation method thereof, wherein metal sodium, a platinum source and a workpiece to be plated are placed in a graphite crucible, and the amount of the metal sodium can completely immerse the workpiece to be plated after being melted; a sealing assembly can completely accommodate the graphite crucible and form a closed cavity; a heating assembly provides a heating temperature of 700-800 DEG C, and is used for providing high-temperature reaction conditions for the formation of the nickel-platinum alloy coating. Through the liquid sodium as the plating solvent, the plating assembly, the sealing assembly and the heating assembly, the platinum atoms can be uniformly diffused on the surface of the workpiece, the platinum atoms and the nickel atoms can be interdiffused to form an atomic-level alloying combination, the micropore and crack defects easily appearing in the plating layer in the traditional process can be effectively avoided, the coating and the substrate are more firmly combined, the coating thickness can be flexibly regulated through the heating time, and a relatively thick coating meeting the requirements can be stably prepared.

Description

Technical Field

[0001] This invention relates to platinum-nickel alloy coatings, and more specifically to an apparatus and method for preparing nickel-platinum alloy coatings based on liquid sodium. Background Technology

[0002] Nickel-platinum (NiPt) alloy coatings, as a class of advanced functional materials with excellent performance, possess outstanding high-temperature oxidation resistance, excellent corrosion resistance, and good electrical conductivity. Their composition and microstructure can be customized according to specific application requirements, making them promising for applications in modern industrial technology. In the aerospace field, this coating effectively protects high-temperature components of turbine engines from high-temperature oxidation and thermal corrosion. In the catalysis field, thanks to the high catalytic activity of platinum and the excellent chemical stability of nickel, nickel-platinum alloys have become catalysts that combine high efficiency and low cost. In the biomedical field, nickel-platinum coatings on the surface of implantable medical devices exhibit excellent biocompatibility; therefore, the preparation technology of nickel-platinum alloy coatings has attracted much attention.

[0003] Currently, various methods for preparing nickel-platinum alloy coatings have been developed in the industry, and these methods have been applied in specific scenarios:

[0004] Electroplating is widely used in the preparation of NiAlPt thermal barrier coatings for gas turbine blades. However, the utilization rate of platinum salts in the plating solution is low, and untreated plating solutions can easily cause environmental pollution. At the same time, due to factors such as uneven mass transfer in the liquid phase, organic impurity contamination, metallic impurity contamination, extreme process conditions, and uneven current distribution, the prepared coatings usually have micropores and cracks.

[0005] Electrochemical deposition can deposit two or more metals simultaneously to form metal composites and can precisely control the elemental atomic ratio of NiPt alloys. However, it also suffers from coating defects and plating solution contamination problems similar to those of electroplating.

[0006] Magnetron sputtering can prepare ultrathin NiPt films with a thickness of less than 100 nanometers and has been widely used in the production of oxygen reduction reaction electrodes. However, this technology is difficult to prepare thicker nickel-platinum alloy films. If we try to deposit films with a thickness of more than micrometers, not only will the quality of the film decrease, but there will also be problems such as long time consumption and a significant increase in cost.

[0007] Synchronous arc plasma deposition generates nanoscale metal particles by applying an electric arc discharge to the target metal. The resulting film is thinner than that produced by magnetron sputtering, but it still cannot meet the requirements for preparing thicker coatings.

[0008] Fluidized bed reactor atomic layer deposition (FBR-ALD) is an advanced process for the large-scale synthesis of catalysts, which can rapidly prepare uniform atomic-scale metal nanoparticles in a cost-effective and efficient manner. However, this process is difficult to form uniform coatings on complex geometries (such as turbine blade cavities) and is not suitable for preparing large-sized uniform films.

[0009] Supercritical fluid chemical deposition (SFCD) is a supercritical fluid-based technology that can deposit metals, metal oxides, alloys and ceramic materials in the form of thin films or nanoparticles onto crystal substrates, support materials and polymers. It has attracted much attention in the field of functional materials development. However, this technology requires a supercritical fluid generator and a precision pressure / temperature control system. The complex equipment configuration limits its widespread application. Summary of the Invention

[0010] To address the problems of existing technologies, such as micropores and cracks in the coating, low platinum source utilization and environmental pollution, difficulty in preparing thick films, uneven coating on complex-shaped workpieces, and complex equipment, this invention aims to provide a nickel-platinum alloy coating preparation device and method based on liquid sodium.

[0011] The nickel-platinum alloy coating preparation apparatus based on liquid sodium according to the present invention includes a coating component, a sealing component, and a heating component. The coating component includes a graphite crucible, metallic sodium, a platinum source, and a workpiece to be coated. The metallic sodium, platinum source, and workpiece are all placed inside the graphite crucible, and the amount of metallic sodium is sufficient to completely submerge the workpiece after melting. The sealing component can completely contain the graphite crucible and form a closed cavity. The heating component provides a heating temperature of 700-800°C to provide high-temperature reaction conditions for the formation of the nickel-platinum alloy coating.

[0012] In a preferred embodiment, the platinum source is a platinum wire.

[0013] In a preferred embodiment, the workpiece to be coated is a nickel-based alloy workpiece or other alloy workpiece coated with a nickel coating.

[0014] In a preferred embodiment, the sealing assembly is a stainless steel crucible that has been sealed to form a closed cavity using an argon arc welding machine.

[0015] In a preferred embodiment, the nickel-platinum alloy coating preparation apparatus further includes an environmental protection component, which is a glove box that houses or is adapted to house the heating component. The heating component is a pit furnace or a high-temperature furnace built into the glove box.

[0016] The method for preparing a nickel-platinum alloy coating based on liquid sodium according to the present invention includes the following steps: S1, ultrasonically cleaning and drying the workpiece to be coated, the platinum source, the graphite crucible, and the sealing assembly; S2, placing metallic sodium, the platinum source, and the workpiece to be coated in an inert gas environment, and then placing the graphite crucible into the sealing assembly to form a closed cavity; S3, placing the sealing assembly in a heating assembly and heating at 700-800°C to melt the metallic sodium, dissolve the platinum source in the liquid sodium, and allow platinum atoms to diffuse uniformly through the liquid sodium to the surface of the workpiece to be coated and interdiffuse with nickel atoms in the workpiece to form a nickel-platinum alloy coating.

[0017] In a preferred embodiment, the inert gas environment in step S2 is provided by a glove box, wherein the oxygen content in the glove box is ≤0.1ppm and the water content is ≤0.1ppm.

[0018] In a preferred embodiment, in step S2, the workpiece to be coated is suspended in the graphite crucible by a nickel wire.

[0019] In a preferred embodiment, in step S1, acetone, anhydrous ethanol and deionized water are used sequentially for ultrasonic cleaning, and then each component is dried; wherein, the drying temperature of the graphite crucible is 650-750℃ and the drying time is 5-15 hours; the drying temperature of the workpiece to be coated, the platinum source and the sealing assembly is 100-120℃ and the drying time is 24-48 hours.

[0020] In a preferred embodiment, the method for preparing the nickel-platinum alloy coating further includes opening the seal after the heating component has cooled naturally to room temperature, removing the workpiece to be coated, and obtaining a finished product with a dense nickel-platinum alloy coating on its surface.

[0021] This invention uses liquid sodium as a coating solvent, along with coating, sealing, and heating components. This not only achieves uniform diffusion of platinum atoms on the workpiece surface and their interdiffusion with nickel atoms to form an atomic-level alloy bond, effectively avoiding micropores and cracks common in traditional coating processes, but also ensures a stronger bond between the coating and the substrate. Furthermore, it eliminates the need for a plating bath, using platinum wire directly as the platinum source, significantly improving platinum source utilization. The entire process generates no waste liquid discharge, and the non-biotoxic nature of metallic sodium completely solves the problem of plating bath pollution. Simultaneously, the coating thickness can be flexibly controlled by heating time, enabling the stable preparation of thicker coatings that meet requirements, overcoming the limitations of traditional techniques in producing thick films. The excellent wettability of liquid sodium can completely coat all surfaces of complex-shaped workpieces, ensuring a uniform coating on complex geometric structures and solving the problem of uneven coating on complex-shaped workpieces in traditional processes. Attached Figure Description

[0022] Figure 1This is a simplified assembly diagram of the nickel-platinum alloy coating preparation apparatus according to the present invention.

[0023] Figure 2 These are surface SEM images of NiPt layers prepared at 700°C for different times according to the nickel-platinum alloy coating preparation process of the present invention.

[0024] Figure 3 These are cross-sectional SEM images of NiPt layers prepared at 700°C for different times according to the nickel-platinum alloy coating preparation process of the present invention.

[0025] Figure 4 These are SEM images of the surface and cross-sectional morphology of the NiPt layer prepared on a 316H workpiece using the nickel-platinum alloy coating preparation process according to the present invention. Detailed Implementation

[0026] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0027] like Figure 1 As shown, the nickel-platinum alloy coating preparation apparatus based on liquid sodium according to the present invention includes a sealing component A and a coating component B, wherein the sealing component A is wrapped around the outside of the coating component B to provide a closed reaction environment, and the coating component B is the core execution unit to realize the nickel-platinum alloy coating.

[0028] See Figure 1 The sealing assembly A includes a first crucible 1 and a crucible lid 2, which cooperate to provide a sealed reaction environment. In a preferred embodiment, the first crucible 1 and the crucible lid 2 are sealed by welding with a weld seam 11 of an argon arc welding machine, forming a completely sealed cavity after welding. This prevents liquid sodium leakage and the entry of outside air during heating, while also avoiding safety hazards caused by the diffusion of liquid sodium vapor. In a preferred embodiment, the first crucible 1 and the crucible lid 2 are made of 304 stainless steel. In a preferred embodiment, the first crucible 1 is a cylindrical structure with an open top, and its size ensures that it can completely accommodate the coating assembly B, ensuring that the coating assembly B can be disposed inside the first crucible 1 and the crucible lid 2.

[0029] See Figure 1 The coating component B includes a second crucible 3, metallic sodium 4, platinum source 5, workpiece 6, and nickel wire.

[0030] The second crucible 3 is an open-top crucible, its size ensuring complete containment of the workpiece 6, metallic sodium 4, and platinum source 5. In a preferred embodiment, the second crucible 3 is made of high-purity graphite. The second crucible 3 is dried before assembly to ensure no moisture remains inside.

[0031] The sodium metal 4 is in a block form and is preferably laid at the bottom of the interior of the second crucible 3. In a preferred embodiment, the purity of the sodium metal 4 is ≥99.5 wt%, for example, purchased from Shanghai Hushi Laboratory Equipment Co., Ltd. The amount of sodium metal 4 used is determined by the size of the second crucible 3 and the dimensions of the workpiece 6, with the key requirement being that the liquid sodium formed after heating and melting can completely immerse the workpiece 6.

[0032] Among them, platinum source 5 is a filamentous platinum wire, dispersed in the second crucible 3, which can directly contact metallic sodium 4, serving as a supply source of platinum. It should be understood that... Figure 1 The sodium metal 4 and platinum source 5 are shown as a mixed block for ease of drawing only. In a preferred embodiment, the platinum wire has a diameter of 0.5 mm and a purity ≥99.95 wt%. The amount of platinum source 5 is positively correlated with the surface area of ​​the workpiece 6; for example, a preferred amount is 7.5 mg / cm². 2 (i.e., 75g / m) 2 ).

[0033] Workpiece 6 is the core component to be coated, and its material includes nickel-based alloys or other alloys coated with nickel. The grade of the nickel-based alloy is not limited; in a preferred embodiment, workpiece 6 is a GH3535 nickel-based alloy. Other alloys coated with nickel can be formed using electroplating; in a preferred embodiment, the thickness of the nickel coating is ≥10μm, and purity is not required. In a preferred embodiment, workpiece 6 is a 15mm×10mm×2mm sheet cut from metal. The coating surface of workpiece 6 undergoes pretreatment, including sequential polishing with 80 to 2000 grit silicon carbide sandpaper and polishing with 0.05mm alumina polishing liquid to ensure a smooth surface without protrusions or oxide layers. In a preferred embodiment, workpiece 6 is suspended in the second crucible 3 by a nickel wire, with both ends of the nickel wire connected to the inner wall of the second crucible 3 and workpiece 6 respectively, so that workpiece 6 is suspended in metallic sodium 4, ensuring that all surfaces of workpiece 6 can fully contact the liquid sodium and improve coating uniformity.

[0034] The nickel-platinum alloy coating preparation apparatus based on liquid sodium according to the present invention further includes an environmental protection component. In a preferred embodiment, the environmental protection component is a glove box, providing an inert gas environment, such as an argon inert environment, with an internal oxygen content ≤0.1ppm and a water content ≤0.1ppm, to provide an oxygen-free and water-free environment for the special drying treatment of the second crucible 3 and the assembly of the coating components, thereby preventing oxidation of the metallic sodium 4, the workpiece 6, and the platinum source 5 during the assembly process.

[0035] The apparatus for preparing a nickel-platinum alloy coating based on liquid sodium according to the present invention further includes a heating component, which provides stable high-temperature reaction conditions for the coating component and is used to heat the sealed coating component as a whole. In a preferred embodiment, the heating component is a pit furnace. The pit furnace can be integrated inside the glove box or placed separately as an independent device inside the glove box. Its maximum heating temperature can reach 800°C, and it is used to heat the sealing component A and the coating component B, providing the reaction temperature required for the formation of the nickel-platinum alloy coating. In a preferred embodiment, the furnace chamber dimensions of the pit furnace are D100mm × H100mm.

[0036] The nickel-platinum alloy coating preparation apparatus based on liquid sodium according to the present invention further includes a pretreatment component, which is independent of the sealing component A, the coating component B, and the heating component, and is used to clean and dry the sealing component A and the coating component B. The pretreatment component includes an ultrasonic cleaner and a vacuum drying oven. The ultrasonic cleaner is used to ultrasonically clean the workpiece 6, platinum source 5, second crucible 3, first crucible 1, and crucible lid 2. Its interior can contain three cleaning media: acetone, anhydrous ethanol, and deionized water. The ultrasonic vibration of the media removes oil, impurities, and oxide layers from the surface of the components. The vacuum drying oven is used to dry the cleaned workpiece 6, platinum source 5, first crucible 1, and crucible lid 2. Its heating temperature can be adjusted to 110°C, eliminating the need for additional vacuum control; drying of the components is achieved solely through high temperature.

[0037] The following is a brief description of the preparation process of the nickel-platinum alloy coating based on liquid sodium according to the present invention.

[0038] Pretreatment steps: Place the workpiece 6, platinum source 5, second crucible 3, first crucible 1, and crucible lid 2 into an ultrasonic cleaner in sequence, and perform ultrasonic cleaning with acetone, anhydrous ethanol, and deionized water respectively to remove surface oil, impurities, and oxide layers; after cleaning, place the workpiece 6, platinum source 5, first crucible 1, and crucible lid 2 into a vacuum drying oven and bake at 110℃ for 24 to 48 hours until completely dry; place the second crucible 3 into a pit furnace in a glove box and dry at 700℃ for 12 hours to remove internal moisture.

[0039] Assembly steps: Transfer the dried workpiece 6, platinum source 5, second crucible 3, first crucible 1, crucible lid 2, and cut block sodium metal 4 into a glove box; in the glove box, first lay the sodium metal 4 at the bottom of the second crucible 3, then disperse the platinum source 5 into the second crucible 3 to contact the sodium metal 4; suspend the workpiece 6 in the second crucible 3 with nickel wire; place the second crucible 3 containing sodium metal 4, platinum source 5, and workpiece 6 into the first crucible 1, and cover it with crucible lid 2.

[0040] Sealing step: Use an argon arc welding machine to seal the open ends of the first crucible 1 and the crucible lid 2 to form a closed cavity.

[0041] Heating reaction steps: The sealed first crucible 1 and crucible lid 2 are removed from the glove box and placed into a pit furnace. The pit furnace temperature is set to 700℃ for heating. After metallic sodium 4 melts into liquid sodium, it can dissolve a large amount of platinum source 5. Utilizing the continuous dissolution and deposition of atoms in the liquid sodium, platinum atoms diffuse uniformly to the surface of workpiece 6, interdiffusion with nickel atoms in workpiece 6 to form a NiPt alloy coating. The heating time is controlled according to the target coating thickness: after 4 hours of heating, the coating thickness is 3.25 μm; after 8 hours of heating, the coating thickness is 4.47 μm; after 15 hours of heating, the coating thickness is 5.57 μm… It should be understood that below 700℃, coating formation is relatively slow, and above 800℃, the vapor pressure of liquid sodium is high, which may cause danger.

[0042] Cooling and part removal steps: After heating to the preset time, turn off the pit furnace. After the first crucible 1 and crucible cover 2 have cooled to room temperature naturally, open the seal with an argon arc welding machine and take out the workpiece 6 from the second crucible 3. Use anhydrous ethanol to clean the sodium residue on the surface of the workpiece 6 to obtain the finished product with a dense nickel-platinum alloy coating. That is, a dense platinum-nickel alloy coating is obtained on the surface of nickel-based alloys and other alloys plated with nickel coating.

[0043] See Figure 2 The figures show SEM images of the surface morphology of the NiPt layer deposited on the nickel-based alloy workpiece. (a) corresponds to the NiPt coating surface prepared by heating for 15 h, (b) corresponds to the NiPt coating surface prepared by heating for 24 h, (c) corresponds to the NiPt coating surface prepared by heating for 48 h, (d) corresponds to the NiPt coating surface prepared by heating for 150 h, (e) corresponds to the NiPt coating surface prepared by heating for 800 h, and (f) corresponds to the NiPt coating surface prepared by heating for 1500 h. As can be seen from the figures, the NiPt coating surfaces prepared at different heating times have no visible pores or cracks, exhibiting a dense and smooth morphology. This proves that the coating prepared by the present invention has excellent surface quality, and the surface state can remain stable after long-term heating, further verifying the structural reliability of the coating.

[0044] See Figure 3The images show backscattered SEM images of the cross-sectional morphology of NiPt layers deposited on nickel-based alloy workpieces. (a) shows the NiPt coating section after 15 hours of heating, with a thickness of 5.57 μm; (b) shows the NiPt coating section after 24 hours of heating, with a thickness of 6.17 μm; (c) shows the NiPt coating section after 48 hours of heating, with a thickness of 8.85 μm; (d) shows the NiPt coating section after 150 hours of heating, with a thickness of 12.57 μm; and (e) shows the NiPt coating section after 800 hours of heating. The layer thickness is 15.28 μm. (f) corresponds to the NiPt coating section after heating for 1500 h, with a coating thickness of 17.42 μm. As shown in the figure, the NiPt coatings prepared under different heating times maintain a dense structure, are completely integrated with the substrate, have a clear interface with the workpiece substrate, are tightly bonded, and have no gaps, pores, peeling, cracks, or other defects. This proves that the NiPt coating prepared by this invention is firmly bonded to the nickel-based alloy workpiece substrate, and the coating is dense and defect-free inside. The thickness increases regularly with heating time, further verifying the stability and reliability of the process of this invention.

[0045] See Figure 4 The figures show SEM images of the surface and cross-sectional morphology of the NiPt layer deposited on a 316H workpiece. (a1) and (a2) correspond to the surface of the NiPt coating after 48 hours of heating, and (b1) and (b2) correspond to the cross-section of the NiPt coating after 48 hours of heating. As can be seen from the figures, the NiPt coating prepared on the surface of the workpiece with the iron-based alloy substrate has no visible pores or cracks, and exhibits a dense and flat morphology. The cross-section maintains a dense structure, is completely integrated with the substrate, has a clear interface with the workpiece substrate, and is tightly bonded without gaps, pores, peeling, cracks, or other defects. This proves that the NiPt coating prepared by this invention is firmly bonded to the iron-based alloy workpiece substrate, and the coating is dense and defect-free inside, verifying the applicability of this invention to other alloy workpieces.

[0046] This invention uses liquid sodium as the coating solvent. Leveraging the excellent wettability of liquid sodium, it completely coats all surfaces of the workpiece 6 (including complex geometries such as turbine blade cavities, holes with a diameter ≥2mm, and workpiece gaps with a spacing <0.5mm), solving the problem that existing processes such as FBR-ALD cannot form a uniform coating on complex-shaped workpieces. Simultaneously, liquid sodium can dissolve a large amount of platinum, allowing platinum atoms to be deposited on the workpiece surface through uniform atomic diffusion. These platinum atoms interdiffusion with nickel atoms to form an atomic-level alloy bond, i.e., forming a solid solution or intermetallic compound through interdiffusion, without obvious interfacial gaps. The coating and substrate are metallurgically bonded. Combined with the heat treatment effect of high-temperature heating, coating stress is completely eliminated, solving the defects of micropores and cracks in existing electrodeposition processes, and producing a dense nickel-platinum alloy layer. Figure 2 and Figure 3SEM images of the cross-section and surface showed no visible pores or cracks. Workpiece 6 consisted of multiple 15mm×10mm×2mm sample combinations, each sample having a 2mm diameter hole, and the inter-surface distance between samples was <0.5mm. The results showed no difference in the NiPt thickness on the surface of each sample, indicating that the present invention can be applied to complex shapes and is almost unaffected by the shape of the sample surface.

[0047] Moreover, this invention eliminates the need for plating solutions, directly using platinum wire as the platinum source, thus avoiding the problems of low platinum salt utilization and plating solution contamination in electroplating processes. Sodium metal is non-toxic, and the entire process generates no waste liquid, making it environmentally friendly. Furthermore, the coating thickness of this invention can be precisely controlled by heating time to meet the requirements for thick coating preparation, overcoming the limitations of processes such as magnetron sputtering in preparing micron-level thick films. The coating adheres tightly to the workpiece substrate (SEM images show that the NiPt layer is completely fused with the nickel substrate), without pores or cracks, and exhibits stable performance. Additionally, this invention uses only conventional equipment such as a glove box, pit furnace, and argon arc welding machine, eliminating the need for complex equipment such as supercritical fluid generators. The operation steps are simple, the equipment configuration is reasonable, lowering the technological threshold and facilitating industrial application.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A device for preparing a nickel-platinum alloy coating based on liquid sodium, characterized in that, The nickel-platinum alloy coating preparation apparatus includes a coating component, a sealing component, and a heating component. The coating component includes a graphite crucible, metallic sodium, a platinum source, and a workpiece to be coated. The metallic sodium, platinum source, and workpiece are all placed inside the graphite crucible, and the amount of metallic sodium is sufficient to completely submerge the workpiece after melting. The sealing component can completely contain the graphite crucible and form a closed cavity. The heating component provides a heating temperature of 700-800°C to provide high-temperature reaction conditions for the formation of the nickel-platinum alloy coating.

2. The nickel-platinum alloy coating preparation apparatus according to claim 1, characterized in that, The platinum source is a platinum wire.

3. The nickel-platinum alloy coating preparation apparatus according to claim 1, characterized in that, The workpiece to be coated is a nickel-based alloy workpiece or other alloy workpieces coated with a nickel coating.

4. The nickel-platinum alloy coating preparation apparatus according to claim 1, characterized in that, The sealing assembly is a stainless steel crucible that has been sealed to form a closed cavity using an argon arc welding machine.

5. The nickel-platinum alloy coating preparation apparatus according to claim 1, characterized in that, The nickel-platinum alloy coating preparation apparatus also includes an environmental protection component, which is a glove box that houses or is adapted to house the heating component. The heating component is a pit furnace or a high-temperature furnace built into the glove box.

6. A method for preparing a nickel-platinum alloy coating based on liquid sodium, characterized in that, The method for preparing the nickel-platinum alloy coating includes the following steps: S1, the workpiece to be coated, platinum source, graphite crucible and sealing components are subjected to ultrasonic cleaning and drying. S2, In an inert gas environment, place metallic sodium, platinum source and workpiece to be coated in a graphite crucible, and then place the graphite crucible into a sealing assembly to form a closed cavity. S3. The sealing component is placed in the heating component and heated at 700-800℃ to melt the metallic sodium. The platinum source dissolves in the liquid sodium, and the platinum atoms diffuse uniformly through the liquid sodium to the surface of the workpiece to be coated and interdiffuse with the nickel atoms in the workpiece to form a nickel-platinum alloy coating.

7. The method for preparing a nickel-platinum alloy coating according to claim 6, characterized in that, The inert gas environment in step S2 is provided by a glove box, wherein the oxygen content in the glove box is ≤0.1ppm and the water content is ≤0.1ppm.

8. The method for preparing a nickel-platinum alloy coating according to claim 6, characterized in that, In step S2, the workpiece to be coated is suspended in the graphite crucible by a nickel wire.

9. The method for preparing a nickel-platinum alloy coating according to claim 6, characterized in that, In step S1, acetone, anhydrous ethanol and deionized water are used sequentially for ultrasonic cleaning, and then each component is dried. The drying temperature of the graphite crucible is 650-750℃ and the drying time is 5-15 hours. The drying temperature of the workpiece to be coated, the platinum source and the sealing assembly is 100-120℃ and the drying time is 24-48 hours.

10. The method for preparing a nickel-platinum alloy coating according to claim 6, characterized in that, The method for preparing the nickel-platinum alloy coating also includes opening the seal after the component to be heated has cooled naturally to room temperature, removing the workpiece to be coated, and obtaining a finished product with a dense nickel-platinum alloy coating on its surface.

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