Method for electroplating nickel-zinc alloy on surface of uranium metal fuel

Abstract

The invention relates to a method for electroplating a nickel-zinc alloy on the surface of uranium metal fuel. The method comprises the following steps: removing an oxide layer on the surface of the uranium metal fuel; the uranium metal fuel with the oxide layer removed is placed in a ferric trichloride solution to be etched and activated; and the etched and activated uranium metal fuel serves as a cathode and is placed in an electrolyte containing zinc ions and nickel ions for electroplating, and the nickel-zinc alloy coating is obtained on the surface of the uranium metal fuel. The nickel-zinc alloy coating obtained on the surface of the uranium metal fuel through the method has the advantages of being bright in appearance, low in toxicity, small in hydrogen embrittlement, good in toughness, good in weldability and the like, the surface protection performance and corrosion resistance of the uranium metal fuel are remarkably improved, then the service life of the uranium metal fuel is prolonged, and the safety of the uranium metal fuel is improved; the uranium metal fuel is suitable for being stored and used in severe industrial atmosphere and harsh marine environment, and the method has the advantages of simplified preparation process, high production efficiency and low production cost, so that further development of the uranium metal fuel in the fields of national defense and nuclear energy is promoted.

Description

Technical Field

[0001] The present invention relates to the field of electroplating chemicals, and particularly to a method for electroplating a 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, uranium has very active chemical properties and is extremely vulnerable to the influence of chemical and electrochemical actions in environmental media, and thus corrodes and generates various corrosion products, which in turn affect 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 the uranium metal fuel is in a high-humidity atmosphere or in contact with an aqueous solution, its corrosion resistance will significantly decrease. In addition, chloride ions Cl - in the atmosphere and aqueous solution will damage the compactness of the oxide film on the surface of the uranium metal fuel, and have an obvious accelerating corrosion effect on the uranium metal fuel. In terms of physical and chemical properties, the surface corrosion of uranium metal fuel may lead to problems such as changes in its mechanical properties, volume changes, and even pulverization; in terms of nuclear reaction performance, surface corrosion will change the nuclear reaction characteristics of uranium metal fuel, resulting in a decrease in its nuclear reaction efficiency, and may even trigger safety accidents, thus affecting the reliability of storage and use of uranium metal fuel, that is, uranium metal fuel cannot be stored in dry areas for a long time, and has a shorter storage time in coastal and industrial areas. Therefore, before storing and using uranium metal fuel, it is necessary to carry out strict anti-corrosion treatment on it to extend its storage time, ensure its good performance during storage, while maintaining its nuclear reaction performance, and ensure the safe and stable operation of the nuclear energy system.

[0003] At present, electroplating a coating on the metal surface is a common method to improve the corrosion resistance of the metal. For example, electroplating single metal coatings of Zn or Ni or Zn / Ni composite coatings on the surface of workpieces. Among them, electroplating a Zn / Ni composite coating includes the following steps: chemically degreasing the workpiece; activating the degreased workpiece in hydrochloric acid and then rinsing it with pure water; placing the activated workpiece in an electrolyte for electroplating zinc, and then electroplating nickel on the workpiece after electroplating zinc. After electroplating nickel is completed, rinse the workpiece with running water; passivate the electroplated workpiece and then rinse it with running water; place the passivated workpiece in a sealing agent for sealing and then dry it to obtain a workpiece with a Zn / Ni composite coating. This method has a complex process, low production efficiency, and high production cost, which is not conducive to actual production. Moreover, 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 uranium metal fuel is 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 deficiencies 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 includes the steps: S1. Remove the oxide layer on the surface of uranium metal fuel; S2. Immerse and activate the uranium metal fuel with the oxide layer removed in a ferric chloride solution; S3. Use the immersed and activated uranium metal fuel as the cathode and place it in an electrolyte containing zinc ions and nickel ions for electroplating to obtain a nickel-zinc alloy coating on the surface of uranium metal fuel.

[0006] Compared with the prior art, the nickel-zinc alloy coating obtained on the surface of uranium metal fuel by the method of the present invention has the characteristics of bright appearance, low toxicity, small hydrogen embrittlement, good toughness, good weldability, excellent protective decoration, etc., significantly improving the surface protection and corrosion resistance of uranium metal fuel, thereby improving the service life and safety of uranium metal fuel, making it suitable for storage and use in harsh industrial atmospheres and severe marine environments, and this method has the advantages of simplified preparation process, high production efficiency, and low production cost, thus contributing to the further development of uranium metal fuel in the fields of national defense and nuclear energy.

[0007] In one embodiment, in step S2, the concentration of ferric chloride is 1200 - 1500 g / L, and the etching time is 10 - 60 s.

[0008] In one embodiment, the concentration of ferric chloride is 1300 - 1400 g / L, and the etching activation time is 10 - 30 s.

[0009] In one embodiment, in step S3, the electrolyte is an alkaline electrolyte containing 0.1 - 0.2 mol / L of zinc ions and 0.01 - 0.1 mol / L of nickel ions.

[0010] In one embodiment, 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.

[0011] In one embodiment, in step S3, the cathode current density of the electroplating is 6 - 12 A / dm 2 。

[0012] In one embodiment, the electroplating time is 30 - 90 min, and the temperature is 25 - 55 °C.

[0013] In one embodiment, the cathode current density of the electroplating is 8 - 10 A / dm 2 。

[0014] In one embodiment, in step S1, the surface of the uranium metal fuel is polished with 100 - 300 - mesh sandpaper to remove the oxide layer.

[0015] In one embodiment, the zinc content in the nickel - zinc alloy coating is 65 - 85 wt%, and the nickel content is 10 - 20 wt%.

[0016] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the macroscopic morphology diagram of the nickel - zinc alloy coatings of Examples 1 - 9; among them, sample #1 - sample #9 respectively represent the nickel - zinc alloy coatings obtained in Examples 1 - 9.

[0018] Figure 2 It is the SEM diagram of the nickel - zinc alloy coating of Example 1.

[0019] Figure 3 It is the EDS spectrum diagram of the nickel - zinc alloy coating of Example 1.

[0020] Figure 4 It is the SEM diagram of the nickel - zinc alloy coating of Example 2.

[0021] Figure 5 It is the EDS spectrum diagram of the nickel - zinc alloy coating of Example 2.

[0022] Figure 6 SEM image of the nickel-zinc alloy coating of Example 3.

[0023] Figure 7 EDS spectrum of the nickel-zinc alloy coating of Example 3.

[0024] Figure 8 SEM image of the nickel-zinc alloy coating of Example 4.

[0025] Figure 9 EDS spectrum of the nickel-zinc alloy coating of Example 4.

[0026] Figure 10 SEM image of the nickel-zinc alloy coating of Example 5.

[0027] Figure 11 EDS spectrum of the nickel-zinc alloy coating of Example 5.

[0028] Figure 12 SEM image of the nickel-zinc alloy coating of Example 6.

[0029] Figure 13 EDS spectrum of the nickel-zinc alloy coating of Example 6.

[0030] Figure 14 SEM image of the nickel-zinc alloy coating of Example 7.

[0031] Figure 15 EDS spectrum of the nickel-zinc alloy coating of Example 7.

[0032] Figure 16 SEM image of the nickel-zinc alloy coating of Example 8.

[0033] Figure 17 EDS spectrum of the nickel-zinc alloy coating of Example 8.

[0034] Figure 18 SEM image of the nickel-zinc alloy coating of Example 9.

[0035] Figure 19 EDS spectrum of the nickel-zinc alloy coating of Example 9.

[0036] Figure 20 Microscopic morphologies of the nickel-zinc alloy coating of Example 8 at different cycles in the cyclic salt spray test; where (a) is the 7th cycle; (b) is the 10th cycle; (c) is the 15th cycle; (d) is the 19th cycle; (e) is the 30th cycle. Detailed implementation manners

[0037] The present invention analyzes the reasons for the weak corrosion resistance of uranium metal fuel with electroplated Zn / Ni composite coatings using existing technologies: In existing technologies, the method of electroplating Zn / Ni composite coatings mainly targets common substrate metals such as copper and iron. The coating structure from the inside out is the substrate metal, zinc coating, and nickel coating. For these substrate metals, the zinc coating and nickel coating play a synergistic protective role: Zinc has a higher chemical activity (low standard electrode potential) and preferentially undergoes an oxidation reaction in a corrosive environment, that is, the zinc coating can inhibit the corrosion of the substrate metal by sacrificial anode protection. At the same time, nickel has strong chemical stability and is not prone to corrosion reactions. Moreover, the porosity of the nickel coating is usually lower than that of the zinc coating, which can fill the pores on the surface of the zinc coating, forming a dense physical barrier to effectively isolate the contact between the corrosive medium and the substrate metal, thereby protecting the substrate metal.

[0038] 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 preferentially, resulting in weak corrosion resistance of the coating. The present invention further analyzes the reasons for the simultaneous contact of zinc and uranium with the external environment: When the thickness of the zinc coating is insufficient or the current density is not properly controlled, the porosity of the zinc coating is relatively high. Although subsequent electroplating of nickel can cover some of the voids, it is difficult to completely fill them. The remaining pores will become the starting points of corrosion, and 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 or impurities are easily formed on the surface of the zinc coating, 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 the presence of chloride ions (such as in a marine environment) will accelerate the corrosion of zinc and uranium. After the zinc coating corrodes, loose corrosion products (such as Zn(OH)2, ZnCl2·4Zn(OH)2) are easily generated, resulting in swelling, cracking, and even peeling of the coating, weakening the protective effect of the nickel coating, and enabling the corrosive medium to directly contact the uranium metal fuel, accelerating the corrosion of uranium.

[0039] In addition, for matrix metals and uranium metal fuels, while the Zn / Ni composite coating isolates the metal from contact with the external environment, there may be a problem that part of the zinc coating is exposed and red rust appears, which in turn affects the use of the metal and the performance of the coating. The existing method to solve 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, preventing part of the zinc coating from being exposed, thereby improving the corrosion resistance of the Zn / Ni composite coating and improving the appearance of the Zn / Ni composite coating. However, the efficiency of this method is low and it 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.

[0040] Based on this, the present invention attempts to adjust the sequence and ratio of electroplating zinc and nickel, and finds that electroplating zinc and nickel simultaneously on the surface of uranium metal fuel to form a nickel-zinc alloy coating can solve the problem of weak bonding force 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 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.

[0041] However, when the uranium metal fuel after electroplating the nickel-zinc alloy coating is used, there is a problem that the coating is easily peeled off. The peeling off of the coating will expose the uranium metal fuel to the external environment, and then corrosion will occur. After research, it is found that the existing method uses acidic solutions such as hydrochloric acid to etch and activate the metal before electroplating, but this method is not applicable to uranium metal fuel. Because the etching rate of hydrochloric acid on metallic uranium is low, and hydrogen ions can inhibit the dissolution of metallic uranium. Although the massive metallic uranium dissolves rapidly in concentrated hydrochloric acid, its dissolution rate decreases instead as the acidity increases. However, the etching rate of hydrochloric acid on other metal elements in uranium metal fuel (such as possible impurities or alloy components) is high, which will lead to an increase in the surface roughness of uranium metal fuel and an uneven microstructure. This uneven surface state will result in insufficient bonding force between the coating and the surface of uranium metal fuel and a decrease in the stability of the alloy phase. Under environmental stress or electrochemical action, the coating is easily peeled off from the surface of uranium metal fuel, accelerating the failure of the coating. In addition, an oxide layer is easily formed on the surface of uranium metal fuel, hindering the etching effect of the etching and activation solution on the surface of uranium metal fuel, resulting in insufficient bonding force between the coating and the surface of uranium metal fuel. If an acidic solution is used to remove the oxide layer on the surface of uranium metal fuel, the hydrogen ions in the acidic solution may exacerbate the etching rate between uranium metal and other metal elements, leading to further reduction in roughness and uniformity.

[0042] In order to form a suitable roughness and uniformity on the surface of uranium metal fuel and improve the bonding force between the coating and the surface of uranium metal fuel, the present invention explores the methods for removing the oxide layer and the etching activation method of uranium metal fuel. It is found that by polishing the surface of uranium metal fuel with sandpaper and then performing etching activation with ferric chloride, the coating quality can be significantly improved: compared with traditional etching solutions such as hydrochloric acid, the etching effect of ferric chloride is more uniform; and sandpaper polishing before etching activation has a dual effect. On the one hand, sandpaper polishing can remove the oxide layer on the surface of uranium metal fuel, enabling ferric chloride to fully etch the freshly exposed surface of uranium metal fuel. On the other hand, the combined action of polishing and ferric chloride forms a suitable roughness and uniformity on the surface of uranium metal fuel, thereby improving the bonding force between the coating and the surface of uranium metal fuel and preventing the coating from peeling off the surface of uranium metal fuel. After testing, when the nickel-zinc alloy coating prepared by the method of polishing-ferric chloride etching-electroplating nickel-zinc alloy in the present invention shows white rust during initial corrosion, a substance of Zn(OH)2·2H2O is generated, which can uniformly and densely cover the surface of the coating and is not easily conductive, thus playing a protective role for the coating and preventing the coating from showing red rust. That is, after removing 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 the enterprise, and thus helps to simplify the preparation process of electroplating nickel-zinc alloy, improve production efficiency, and reduce production costs.

[0043] Based on the above preparation design idea, the method for electroplating nickel-zinc alloy on the surface of uranium metal fuel of the present invention is described in detail as follows: S1. Polish the surface of uranium metal fuel with sandpaper to remove the oxide layer.

[0044] S2. Place the uranium metal fuel with the oxide layer removed in a ferric chloride solution for etching activation; rinse the etched and activated uranium metal fuel with nitric acid and / or deionized water to remove the etching products.

[0045] S3. Use the rinsed and etched and activated uranium metal fuel as the cathode and place it in an electrolyte containing zinc ions and nickel ions for electroplating to obtain a nickel-zinc alloy coating on the surface of uranium metal fuel.

[0046] Based on the method for electroplating nickel-zinc alloy on the surface of uranium metal fuel, the present invention further conducts experimental operations and verifications on various parameters, which are described in detail as follows.

[0047] Examples 1-9 Examples 1-9 provide a method for electroplating nickel-zinc alloy on the surface of uranium metal fuel, including the following steps: S1. Polish the surface of uranium metal fuel with 100-300 mesh sandpaper for 5 minutes to remove the oxide layer.

[0048] S2. Place the uranium metal fuel with the oxide layer removed in step S1 into a 1200 - 1500 g / L ferric chloride solution at 25°C for etching and activation for 10 - 60 seconds; rinse the etched and activated uranium metal fuel with nitric acid to remove the residual etching products on the surface of the uranium metal fuel, and then alternately rinse it with deionized water and nitric acid two to three times.

[0049] S3. Connect the etched and activated uranium metal fuel rinsed in step S2 to the cathode and immerse it in the electrolyte for electroplating: use the uranium metal fuel as the cathode, a platinum mesh as the anode, with a cathode current density of 6 - 12 A / dm 2 , the electroplating temperature is 25 - 55°C, and the electroplating time is 30 - 60 min. After electroplating, a nickel - zinc alloy coating is obtained on the surface of the uranium metal fuel. Among them, the electrolyte includes 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.

[0050] Among them, the specific process parameters of Examples 1 - 9 are shown in Table 1 below.

[0051] The macroscopic morphologies of the nickel - zinc alloy coatings (i.e., Sample 1# - Sample 9#) obtained on the uranium metal fuel in Examples 1 - 9 are as Figure 1 shown. Among them, the surface morphology of the nickel - zinc alloy coating (Sample 5#) prepared in Example 5 is relatively poor, and the morphology of the nickel - zinc alloy coating (Sample 8#) prepared in Example 8 is better.

[0052] Use SEM to analyze the microstructure of the above - mentioned nickel - zinc alloy coating, and conduct EDS elemental analysis on the nickel - zinc alloy coating to observe the morphology and composition of the nickel - zinc alloy coating. Refer to Figure 2-19 and Table 2. The nickel - zinc alloy coatings obtained in Examples 1 - 9 contain more than 85 wt% of zinc and nickel elements, as well as a small amount of carbon and oxygen elements, and do not contain uranium elements, indicating that the formed nickel - zinc alloy coating is dense. Among them, the total content of zinc and nickel elements in the nickel - zinc alloy coating obtained in Example 8 is the highest, reaching 94.58 wt%. According to Examples 4 - 5, as the electroplating time increases, the zinc element content in the nickel - zinc alloy coating gradually increases, while the nickel element content gradually decreases. In addition, by comprehensively comparing Examples 1 - 9, it can be seen that the nickel content in the nickel - zinc alloy coating with an electroplating time of 90 min is lower than 13 wt%, and its corrosion resistance may be lower.

[0053] Table 1 Process parameters of steps S1 - S3 in Examples 1 - 9

[0054] Table 2 Zn content and Ni content in the nickel - zinc alloy coatings in Examples 1 - 9

[0055] Testing method According to the macroscopic morphology of the coating, Sample No. 5 with a relatively poor surface morphology and Sample No. 8 with a better morphology were selected for the cyclic salt spray test to evaluate the corrosion resistance of the nickel-zinc alloy coating: Each cycle was 24 h, including 8 h of salt spray and 16 h of intermittent time. The experimental temperature of the salt spray chamber was 35 ± 2 °C, and the salt solution was 5% NaCl by mass fraction, with a pH of approximately 7.2.

[0056] The experimental results showed that Samples No. 5 and No. 8 still remained unbroken after 30 cycles, and the corrosion resistance effect could meet the enterprise production requirements. Compared with Sample No. 8 in Example 8, Sample No. 5 in Example 5 had slightly worse performance and more cracks. Among them, the measurement results of the microscopic morphology of Sample No. 8 in Example 8 at different cycles are as Figure 20 shown. After white rust appeared in the initial corrosion of the nickel-zinc alloy coating, a substance of Zn(OH)2·2H2O was generated, which could uniformly and densely cover the surface of the coating, was not easily conductive, and played a protective role for the coating; at the same time, the presence of Ni in the coating made the reaction not easy to proceed, played an inhibitory role, increased the potential of the entire corrosion occurrence, prevented the cathode reaction from proceeding, and thus slowed down the corrosion reaction of the Zn-Ni alloy coating.

[0057] In summary, the uranium metal fuel with nickel-zinc alloy provided by the present invention and the method for electroplating nickel-zinc alloy on the surface of uranium metal fuel have the following advantages: (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, small hydrogen embrittlement, good toughness, good weldability, excellent protective decoration, etc. The coating does not contain uranium elements, can effectively isolate the uranium metal fuel from the external environment, thus providing good surface protection and corrosion resistance for the product (uranium metal fuel with coating), improving the service life and safety of the product, enabling the product to meet the enterprise production requirements, and being suitable for storage and use in harsh industrial atmospheres and severe marine environments.

[0058] (2) Compared with the existing methods for electroplating nickel-zinc alloy on the surface of workpieces, the method of the present invention has the advantages of simplified preparation process, high production efficiency, and low production cost, improving the economic benefits of uranium metal fuel treatment and contributing to actual production.

[0059] (3) Compared with the Zn and Ni elemental metal coatings or Zn / Ni composite coatings obtained on the surface of uranium metal fuel by the existing methods, the nickel-zinc alloy electroplated coating obtained by the present invention shows better performance in terms of corrosion resistance and mechanical properties, reducing the frequency of maintenance and replacement during the long-term use of the product, and thus indirectly improving the overall production efficiency.

[0060] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A method for electroplating a nickel-zinc alloy on the surface of uranium metal fuel, characterized in that, Including the steps: S1. Remove the oxide layer on the surface of the uranium metal fuel; S2. Place the uranium metal fuel with the oxide layer removed into a ferric chloride solution for etching and activation; S3. Use the etched and activated uranium metal fuel as the cathode and place it 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.

2. The method according to claim 1, characterized in that: In step S2, the concentration of the ferric chloride is 1200 - 1500 g / L, and the time for etching and activation is 10 - 60 s.

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

4. The method according to claim 1, wherein: In step S3, the electrolyte is an alkaline electrolyte containing 0.1 - 0.2 mol / L of zinc ions and 0.01 - 0.1 mol / L of nickel ions.

5. The method according to claim 4, 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.

6. The method according to claim 4, wherein: The cathode current density of the electroplating is 6-12 A / dm 2 .

7. The method according to claim 4, wherein: The time for electroplating is 30 - 90 min, and the temperature is 25 - 55 °C.

8. The method according to claim 6, characterized in that: The cathode current density of the electroplating is 8 - 10 A / dm 2 .

9. The method according to claim 1, wherein: In step S1, polish the surface of the uranium metal fuel with 100 - 300 mesh sandpaper to remove the oxide layer.

10. The method according to any one of claims 1-9, characterized in that: The content of zinc in the nickel-zinc alloy coating is 65 - 85 wt%, and the content of nickel is 10 - 20 wt%.

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