A method for electroplating a nickel-zinc alloy on the surface of a uranium metal fuel

Abstract

The application relates to a method for electroplating a nickel-zinc alloy on the surface of uranium metal fuel, comprising the following steps: removing the oxide layer on the surface of the uranium metal fuel; placing the uranium metal fuel with the removed oxide layer in a ferric chloride solution for immersion etching activation; placing the immersion-etching-activated uranium metal fuel as a cathode in an electrolyte containing zinc ions and nickel ions for electroplating, so as to obtain a nickel-zinc alloy coating on the surface of the uranium metal fuel. The nickel-zinc alloy coating obtained on the surface of the uranium metal fuel by the method has the characteristics of bright appearance, low toxicity, small hydrogen brittleness, good toughness, good weldability and the like, and the surface protection and corrosion resistance of the uranium metal fuel are significantly improved, and the service life and safety of the uranium metal fuel are improved, so that the uranium metal fuel is suitable for use in harsh industrial atmospheres and severe marine environments, and the method has the advantages of simplified preparation process, high production efficiency and low production cost, thereby helping to promote the further development of the uranium metal fuel in the fields of national defense and nuclear energy.

Description

Technical Field

[0001] The invention relates to the field of electroplating chemical industry, in particular to a method for electroplating nickel-zinc alloy on the surface of uranium metal fuel. Background Art

[0002] Uranium has important strategic value in the fields of national defense and nuclear energy due to its unique nuclear properties. However, the chemical properties of uranium are very active and it is easily affected by chemical and electrochemical reactions in the environmental medium, which leads to corrosion and the generation of various corrosion products, thus affecting its physical and chemical properties and nuclear reaction performance. In order to improve the stability of uranium in a specific environment, uranium is usually processed into uranium metal fuel. Compared with unprocessed uranium, the corrosion resistance of uranium metal fuel in the atmosphere has been greatly improved. However, when uranium metal fuel is in a high humidity atmosphere or in contact with aqueous solutions, its corrosion resistance will be significantly reduced. In addition, chloride ions Cl in the atmosphere and aqueous solutions - This can damage the density of the oxide film on the surface of uranium metal fuel, significantly accelerating its corrosion. In terms of physical and chemical properties, surface corrosion of uranium metal fuel can lead to changes in mechanical properties, volume changes, and even pulverization. In terms of nuclear reactivity, surface corrosion can alter the nuclear reactivity characteristics of uranium metal fuel, reducing its efficiency and potentially causing safety incidents. This, in turn, can affect the reliability of uranium metal fuel storage and use. Specifically, uranium metal fuel cannot be stored for long periods in dry areas, and its storage time in coastal and industrial areas is even shorter. Therefore, before storage and use, uranium metal fuel must undergo rigorous anti-corrosion treatment to extend its storage life and ensure its good performance during storage, while also maintaining its nuclear reactivity and guaranteeing the safe and stable operation of nuclear energy systems.

[0003] Currently, electroplating a coating on a metal surface is a common method for improving the corrosion resistance of a metal, such as electroplating a Zn, Ni single metal coating, or a Zn / Ni composite coating on a workpiece surface. The Zn / Ni composite coating comprises the following steps: chemically degreasing the workpiece; activating the degreased workpiece in hydrochloric acid and then rinsing with pure water; electroplating the activated workpiece in an electrolyte for zinc plating, then electroplating the zinc-plated workpiece with nickel, and rinsing the workpiece with running water after the nickel plating is complete; passivating the electroplated workpiece and then rinsing it with running water; sealing the passivated workpiece in a sealant, and then drying the workpiece to obtain a Zn / Ni composite coating. This method is complex, has low production efficiency, and high production costs, making it unsuitable for actual production. Furthermore, the above method is mainly applied to metal materials such as copper and iron. When applied to uranium metal fuel, the corrosion resistance of the coating obtained on the surface of the uranium metal fuel is relatively weak. Therefore, there is an urgent need to develop a corrosion-resistant treatment method for uranium metal fuel to effectively improve its corrosion resistance and production efficiency, thereby promoting the further development of uranium metal fuel in the fields of national defense and nuclear energy. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to overcome the defects or shortcomings of the prior art and provide a method for electroplating nickel-zinc alloy on the surface of uranium metal fuel.

[0005] A method for electroplating nickel-zinc alloy on the surface of uranium metal fuel comprises the following steps:

[0006] S1. Remove the oxide layer on the surface of uranium metal fuel;

[0007] S2. Placing the uranium metal fuel with the oxide layer removed in a ferric chloride solution for etching and activation;

[0008] S3. The etched and activated uranium metal fuel is used as a cathode and placed in an electrolyte containing zinc ions and nickel ions for electroplating, thereby obtaining a nickel-zinc alloy coating on the surface of the uranium metal fuel.

[0009] Compared with the prior art, the nickel-zinc alloy coating obtained on the surface of the uranium metal fuel by the method of the present invention has the characteristics of bright appearance, low toxicity, low hydrogen embrittlement, good toughness, good weldability, and excellent protective and decorative properties. It significantly improves the surface protection and corrosion resistance of the uranium metal fuel, thereby increasing the service life and safety of the uranium metal fuel, making it suitable for storage and use in harsh industrial atmospheres and harsh marine environments. In addition, the method has the advantages of simplified preparation process, high production efficiency, and low production cost, thereby helping to promote the further development of uranium metal fuel in the fields of national defense and nuclear energy.

[0010] In one embodiment, in step S2, the concentration of ferric chloride is 1200-1500 g / L, and the etching time is 10-60 s.

[0011] In one embodiment, the concentration of ferric chloride is 1300-1400 g / L, and the etching activation time is 10-30 s.

[0012] In one embodiment, in step S3, the electrolyte is an alkaline electrolyte containing 0.1-0.2 mol / L zinc ions and 0.01-0.1 mol / L nickel ions.

[0013] In one embodiment, the electrolyte contains 10-15 g / L zinc oxide, 8-16 g / L nickel sulfate hexahydrate, 120-130 g / L sodium hydroxide, 0.5-1 g / L ethylenediamine, 50-60 g / L triethanolamine, and 15 mL / L ammonia water.

[0014] In one embodiment, in step S3, the cathode current density of the electroplating is 6-12 A / dm 2 .

[0015] In one embodiment, the electroplating time is 30-90 minutes and the temperature is 25-55°C.

[0016] In one embodiment, the cathode current density of the electroplating is 8-10A / dm 2 .

[0017] In one embodiment, in step S1, the surface of the uranium metal fuel is polished with 100-300 grit sandpaper to remove the oxide layer.

[0018] In one embodiment, the zinc content in the nickel-zinc alloy coating is 65-85 wt %, and the nickel content is 10-20 wt %.

[0019] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 These are macroscopic morphologies of the nickel-zinc alloy coatings of Examples 1-9; wherein, sample #1 to sample #9 represent the nickel-zinc alloy coatings obtained in Examples 1-9, respectively.

[0021] Figure 2 This is the SEM image of the nickel-zinc alloy coating of Example 1.

[0022] Figure 3 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 1.

[0023] Figure 4 This is the SEM image of the nickel-zinc alloy coating of Example 2.

[0024] Figure 5 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 2.

[0025] Figure 6 This is the SEM image of the nickel-zinc alloy coating of Example 3.

[0026] Figure 7 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 3.

[0027] Figure 8 This is the SEM image of the nickel-zinc alloy coating of Example 4.

[0028] Figure 9 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 4.

[0029] Figure 10 This is the SEM image of the nickel-zinc alloy coating of Example 5.

[0030] Figure 11 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 5.

[0031] Figure 12 This is the SEM image of the nickel-zinc alloy coating of Example 6.

[0032] Figure 13 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 6.

[0033] Figure 14 This is the SEM image of the nickel-zinc alloy coating of Example 7.

[0034] Figure 15 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 7.

[0035] Figure 16 This is the SEM image of the nickel-zinc alloy coating of Example 8.

[0036] Figure 17 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 8.

[0037] Figure 18 This is the SEM image of the nickel-zinc alloy coating of Example 9.

[0038] Figure 19 This is the EDS energy spectrum of the nickel-zinc alloy coating of Example 9.

[0039] Figure 20 The micromorphology of the nickel-zinc alloy coating of Example 8 at different cycles in the cyclic salt spray test; among them, (a) is 7 cycles; (b) is 10 cycles; (c) is 15 cycles; (d) is 19 cycles; and (e) is 30 cycles. DETAILED DESCRIPTION

[0040] This paper analyzes the reasons why uranium metal fuel electroplated with Zn / Ni composite coatings using existing techniques exhibits weak corrosion resistance. Prior art Zn / Ni composite coating methods primarily target common base metals such as copper and iron. The coating structure, from the inside out, consists of the base metal, zinc coating, and nickel coating. For these base metals, the zinc and nickel coatings provide a synergistic protective effect: Zinc has a high chemical activity (low standard electrode potential) and preferentially undergoes oxidation in corrosive environments. This means that the zinc coating inhibits base metal corrosion through sacrificial anodic protection. Furthermore, nickel is chemically stable and less susceptible to corrosion. Furthermore, the nickel coating typically has a lower porosity than the zinc coating, filling the pores on the zinc coating surface and forming a dense physical barrier that effectively isolates the corrosive medium from the base metal, thereby protecting the base metal.

[0041] However, for the uranium metal fuel of the present invention, the situation is different. The standard electrode potential of uranium is lower than that of zinc, which means that uranium is more likely to lose electrons and be oxidized than zinc. Therefore, when zinc and uranium are in contact with the external environment at the same time, the uranium metal fuel will react first, resulting in a weaker corrosion resistance of the coating. The present invention further analyzes the reasons why zinc and uranium are in contact with the external environment at the same time: when the zinc coating thickness is insufficient or the current density is improperly controlled, the porosity of the zinc coating is high. Although the subsequent nickel electroplating can cover some of the gaps, it is difficult to fill them completely. The remaining pores will become the starting point of corrosion. The corrosive medium can contact the uranium metal fuel through these pores, accelerating the corrosion of the uranium metal fuel. Secondly, during the electroplating process, an oxide film is easily formed on the surface of the zinc coating or impurities are adsorbed, which will reduce the bonding strength between the nickel coating and the zinc coating, forming microcracks or pores at the bonding interface. The corrosive medium can invade along the gaps, further accelerating the corrosion of the uranium metal fuel. In addition, humidity or chloride ion-containing environments (such as marine environments) will accelerate the corrosion of zinc and uranium. After the zinc coating is corroded, loose corrosion products (such as Zn(OH)2, ZnCl2·4Zn(OH)2) are easily generated, causing the coating to expand, crack, or even peel off, weakening the protective effect of the nickel coating, allowing the corrosive medium to directly contact the uranium metal fuel, accelerating the corrosion of uranium.

[0042] In addition, for base metal and uranium metal fuel, the Zn / Ni composite coating may expose the zinc coating while isolating the metal from the external environment, causing red rust to occur, thereby affecting the use of the metal and the performance of the coating. The existing method for solving this problem is to passivate and seal the coating after electroplating to form a dense passivation film on the surface of the Zn / Ni composite coating, thereby preventing the zinc coating from being partially exposed, thereby improving the corrosion resistance of the Zn / Ni composite coating and improving the appearance of the Zn / Ni composite coating. However, this method is inefficient and is not conducive to actual production. Therefore, the present invention hopes to improve the electroplating method so that the coating still has strong surface protection and corrosion resistance without passivation and sealing.

[0043] Based on this, the present invention attempts to adjust the order and ratio of zinc and nickel electroplating, and finds that the improvement of simultaneously electroplating zinc and nickel on the surface of uranium metal fuel to form a nickel-zinc alloy coating can solve the problem of weak bonding between the zinc coating and the nickel coating, and can reduce the porosity and hydrogen embrittlement rate of the nickel-zinc alloy coating. By improving the ability of the coating to isolate the uranium metal fuel from the external environment and improving the chemical stability of the coating itself, the corrosion resistance of the electroplated uranium metal fuel is improved.

[0044] However, uranium metal fuel coated with a nickel-zinc alloy electroplating layer is susceptible to coating shedding during use. This shedding exposes the uranium metal fuel to the external environment, leading to corrosion. Research has found that existing methods, which use acidic solutions such as hydrochloric acid to etch and activate the metal before electroplating, are not suitable for uranium metal fuel. This is because hydrochloric acid has a low etching rate for uranium metal, and hydrogen ions inhibit its dissolution. Although bulk uranium metal dissolves rapidly in concentrated hydrochloric acid, the dissolution rate decreases with increasing acidity. Hydrochloric acid, on the other hand, has a high etching rate for other metallic elements in the uranium metal fuel (such as possible impurities or alloying components), resulting in increased surface roughness and an uneven microstructure. This uneven surface condition weakens the bonding between the coating and the uranium metal fuel surface and reduces alloy phase stability. Under environmental stress or electrochemical action, the coating easily peels from the uranium metal fuel surface, accelerating coating failure. In addition, an oxide layer is easily formed on the surface of uranium metal fuel, which hinders the etching effect of the etching activation solution on the surface of the uranium metal fuel, resulting in insufficient bonding between the coating and the surface of the uranium metal fuel. If an acidic solution is used to remove the oxide layer on the surface of the uranium metal fuel, the hydrogen ions in the acidic solution may increase the etching rate between the uranium metal and other metal elements, resulting in further reduction of roughness and uniformity.

[0045] In order to achieve suitable roughness and uniformity on the surface of the uranium metal fuel and improve the bonding strength between the coating and the uranium metal fuel surface, the present invention explores methods for removing the oxide layer of the uranium metal fuel and etching and activation methods. The research found that polishing the uranium metal fuel surface with sandpaper followed by etching and activation with ferric chloride can significantly improve the quality of the coating. Compared with traditional etching solutions such as hydrochloric acid, ferric chloride has a more uniform etching effect. Sanding before etching and activation has a dual effect. On the one hand, sanding can remove the oxide layer on the surface of the uranium metal fuel, allowing the ferric chloride to fully etch the freshly exposed surface of the uranium metal fuel. On the other hand, sanding and ferric chloride work together to achieve suitable roughness and uniformity on the surface of the uranium metal fuel, thereby improving the bonding strength between the coating and the uranium metal fuel surface and preventing the coating from falling off the uranium metal fuel surface. According to tests, the nickel-zinc alloy coating prepared by the method of polishing-ferric chloride etching-electroplating nickel-zinc alloy in the present invention produces Zn(OH)2·2H2O substance after the initial corrosion and white rust appear. This substance can be evenly and densely covered on the surface of the coating and is not easy to conduct electricity, thereby protecting the coating and preventing the coating from red rust. That is, after removing the passivation and sealing, the nickel-zinc alloy coating obtained by the method of the present invention still has excellent surface protection and corrosion resistance, can meet the production requirements of enterprises, and thus helps to simplify the preparation process of electroplated nickel-zinc alloy, improve production efficiency, and reduce production costs.

[0046] Based on the above-mentioned preparation design ideas, the method of electroplating nickel-zinc alloy on the surface of uranium metal fuel of the present invention is described in detail below:

[0047] S1. Use sandpaper to polish the surface of the uranium metal fuel to remove the oxide layer.

[0048] S2. Placing the uranium metal fuel with the oxide layer removed in a ferric chloride solution for etching and activation; rinsing the etched and activated uranium metal fuel with nitric acid and / or deionized water to remove etching products.

[0049] S3. The washed, etched and activated uranium metal fuel is used as a cathode and placed in an electrolyte containing zinc ions and nickel ions for electroplating to obtain a nickel-zinc alloy coating on the surface of the uranium metal fuel.

[0050] Based on the above method of electroplating nickel-zinc alloy on the surface of uranium metal fuel, the present invention further conducted experimental operations and verifications on various parameters, which are described in detail below.

[0051] Examples 1-9

[0052] Example 1-9 provides a method for electroplating nickel-zinc alloy on the surface of uranium metal fuel, comprising the following steps:

[0053] S1. Sand the uranium metal fuel surface with 100-300 grit sandpaper for 5 minutes to remove the oxide layer.

[0054] S2. The uranium metal fuel from which the oxide layer has been removed in step S1 is placed in a 1200-1500 g / L ferric chloride solution at 25° C. for etching and activation for 10-60 seconds; the etched and activated uranium metal fuel is rinsed with nitric acid to remove the etching products remaining on the surface of the uranium metal fuel, and then rinsed alternately with deionized water and nitric acid two to three times.

[0055] S3: Connect the activated uranium metal fuel after washing and etching in step S2 to the cathode and immerse it in the electrolyte for electroplating: use the uranium metal fuel as the cathode and the platinum mesh as the anode, and the cathode current density is 6-12A / dm 2 The electroplating temperature is 25-55°C and the electroplating time is 30-60 minutes. A nickel-zinc alloy coating is formed on the surface of the uranium metal fuel. The electrolyte comprises 10-15 g / L zinc oxide, 8-16 g / L nickel sulfate hexahydrate, 120-130 g / L sodium hydroxide, 0.5-1 g / L ethylenediamine, 50-60 g / L triethanolamine, and 15 mL / L ammonia water.

[0056] The specific process parameters of Examples 1-9 are shown in Table 1 below.

[0057] The macroscopic morphology of the nickel-zinc alloy coatings obtained on the surface of uranium metal fuel in Examples 1-9 (i.e., Samples 1# to 9#) is as follows: Figure 1 As shown, the surface morphology of the nickel-zinc alloy coating (sample #5) prepared in Example 5 is poor, while the morphology of the nickel-zinc alloy coating (sample #8) prepared in Example 8 is good.

[0058] The microstructure of the nickel-zinc alloy coating was analyzed by SEM, and the nickel-zinc alloy coating was subjected to EDS elemental analysis to observe the morphology and composition of the nickel-zinc alloy coating. Figure 2-19 As shown in Table 2, the nickel-zinc alloy coatings obtained in Examples 1-9 contain more than 85wt% of zinc and nickel, as well as a small amount of carbon and oxygen, and do not contain uranium, indicating that the formed nickel-zinc alloy coatings are dense. Among them, the total content of zinc and nickel in the nickel-zinc alloy coating obtained in Example 8 is the highest, reaching 94.58wt%. According to Examples 4-5, as the plating time increases, the zinc content of the nickel-zinc alloy coating gradually increases, while the content of nickel gradually decreases. In addition, a comprehensive comparison of Examples 1-9 shows that the nickel content of the nickel-zinc alloy coatings with a plating time of 90min is all lower than 13wt%, and its corrosion resistance may be relatively low.

[0059] Table 1 Process parameters of steps S1-S3 in Examples 1-9

[0060]

[0061] Table 2 Zn content and Ni content of nickel-zinc alloy coatings in Examples 1-9

[0062]

[0063] Test Method

[0064] According to the macroscopic morphology of the coating, the 5# sample with poor surface morphology and the 8# sample with good morphology were selected for cyclic salt spray test to evaluate the corrosion resistance of the nickel-zinc alloy coating: each cycle was 24 hours, including 8 hours of salt spray and 16 hours of rest. The experimental temperature of the salt spray box was 35±2℃, the salt solution used was 5% NaCl by mass, and the pH was about 7.2.

[0065] The experimental results show that the 5# and 8# samples remain intact after 30 cycles, and the corrosion resistance can meet the production requirements of the enterprise. Compared with the 8# sample of Example 8, the performance of the 5# sample of Example 5 is slightly worse and there are more cracks. Among them, the microscopic morphology of the 8# sample of Example 8 at different cycles is shown in the following figure. Figure 20 As shown in the figure, after the nickel-zinc alloy coating undergoes initial corrosion and white rust appears, Zn(OH)2·2H2O substance is produced. This substance can evenly and densely cover the surface of the coating, is not easy to conduct electricity, and plays a protective role for the coating. At the same time, the presence of Ni in the coating makes the reaction difficult to proceed, which plays an inhibitory role, increases the potential of the entire corrosion, prevents the cathode reaction from proceeding, and thus slows down the corrosion reaction of the Zn-Ni alloy coating.

[0066] In summary, the uranium metal fuel having a nickel-zinc alloy and the method for electroplating a nickel-zinc alloy on the surface of the uranium metal fuel provided by the present invention have the following advantages:

[0067] (1) The nickel-zinc alloy coating on the surface of the uranium metal fuel of the present invention has the characteristics of bright appearance, low toxicity, low hydrogen embrittlement, good toughness, good weldability, excellent protective and decorative properties, etc. The coating does not contain uranium element and can effectively isolate the uranium metal fuel from the external environment, thereby providing the product (uranium metal fuel with the coating) with good surface protection and corrosion resistance, improving the service life and safety of the product, enabling the product to meet the production requirements of the enterprise, and being suitable for storage and use in harsh industrial atmospheres and harsh marine environments.

[0068] (2) Compared with the existing method of electroplating nickel-zinc alloy on the surface of the workpiece, the method of the present invention has the advantages of simplified preparation process, high production efficiency and low production cost, which improves the economic benefits of uranium metal fuel processing and is helpful for actual production.

[0069] (3) Compared with the Zn, Ni single metal coating or Zn / Ni composite coating obtained on the surface of uranium metal fuel by existing methods, the nickel-zinc alloy electroplating layer obtained by the present invention performs better in terms of corrosion resistance and mechanical properties, which reduces the frequency of maintenance and replacement of the product during long-term use, thereby indirectly improving the overall production efficiency.

[0070] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for electroplating nickel-zinc alloy on the surface of uranium metal fuel, characterized in that: Including steps: S1. Remove the oxide layer on the surface of the uranium metal fuel. Use 100-300 mesh sandpaper to polish the surface of the uranium metal fuel to remove the oxide layer. S2, placing the uranium metal fuel with the oxide layer removed in a ferric chloride solution for etching and activation, wherein the concentration of the ferric chloride is 1200-1500 g / L and the etching and activation time is 10-60 seconds; S3, the uranium metal fuel activated by etching is used as a cathode and placed in an electrolyte containing zinc ions and nickel ions for electroplating to obtain a nickel-zinc alloy coating on the surface of the uranium metal fuel, wherein the electrolyte is an alkaline electrolyte containing 0.1-0.2 mol / L zinc ions and 0.01-0.1 mol / L nickel ions, and the cathode current density of the electroplating is 6-12 A / dm 2 The electroplating time is 30 minutes and the temperature is 40-55°C; The zinc content in the nickel-zinc alloy coating is 65-76.23 wt %, and the nickel content is 16.36-20 wt %.

2. The method according to claim 1, wherein: The concentration of the ferric chloride is 1300-1400 g / L, and the etching activation time is 10-30 s.

3. The method according to claim 2, wherein: The electrolyte contains 10-15 g / L of zinc oxide, 8-16 g / L of nickel sulfate hexahydrate, 120-130 g / L of sodium hydroxide, 0.5-1 g / L of ethylenediamine, 50-60 g / L of triethanolamine and 15 mL / L of ammonia water.

4. The method according to claim 3, wherein: The cathode current density of the electroplating is 8-10A / dm 2 .

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