Water boiling oxidation method for nuclear-grade extrusion forming aluminum material
The automated boiling oxidation method solves the stability and safety issues of manual boiling oxidation processes, achieves the preparation of a uniform oxide film on the aluminum surface, is suitable for large-scale production, avoids the appearance of yellow streaks and watermarks, and meets the requirements of nuclear-grade extruded aluminum materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-04-03
AI Technical Summary
The existing manual boiling oxidation process has poor stability, low production efficiency, and high safety risks. In addition, yellow streaks and large-area watermarks are easily found on the surface of aluminum materials, which cannot meet the needs of large-scale production.
An automated boiling oxidation method is adopted, which removes impurities by treating with nitric acid at room temperature, combined with hot and cold water rinsing, to control the oxide film thickness between 200nm and 500nm, avoiding the formation of yellow streaks and watermarks. The process parameters are controlled by a robotic arm and equipment.
It achieves uniformity and stability of the oxide film on the aluminum surface, reduces safety risks, is suitable for large-scale production, and ensures the protective effect of the oxide film and the quality of the aluminum material.
Smart Images
Figure CN121781131A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of surface treatment technology for cladding tubes, and particularly relates to a water-boiling oxidation method for nuclear-grade extruded aluminum materials. Background Technology
[0002] The main component of the tubular fuel element cladding tube is aluminum alloy, which is prone to corrosion in humid environments and difficult to store. Therefore, it needs to be anodized to enhance its corrosion resistance. However, the oxide film generated by traditional anodizing is only 10μm to 15μm thick, and this oxide film will peel off after the fuel is installed in the reactor, increasing the irradiance index inside the reactor.
[0003] Previous studies have shown that controlling the oxide film at the nanometer scale can effectively reduce the in-pile irradiance index. Currently, the oxide film thickness prepared by manual boiling oxidation process is only 200 nm to 500 nm, which meets the size requirements for reducing the in-pile irradiance index while achieving a protective function.
[0004] However, the process parameters and operation of the water boiling oxidation process, which relies on manual operation, cannot be guaranteed to be consistent, making it difficult to guarantee the yield. During the operation, there is a risk that the aluminum material may come into contact with the tank wall and undergo electrochemical corrosion or be bumped. In addition, the quantity processed each time by manual operation is limited, which cannot be applied to large-scale production. Furthermore, the water boiling oxidation process involves the use of nitric acid and high-temperature liquids, which poses a high safety risk during operation. Summary of the Invention
[0005] The main objective of this application is to provide a water-boiling oxidation method for nuclear-grade extruded aluminum materials, which solves the problems of poor stability, low production efficiency, and high safety risks associated with manual water-boiling oxidation processes.
[0006] Another objective of this application is to provide a water-boiling oxidation method for nuclear-grade extruded aluminum materials, which solves the problem of yellow streaks and large-area watermarks appearing on the surface of extruded aluminum materials after automated water-boiling oxidation.
[0007] To achieve the above objectives, this application provides the following technical solution:
[0008] A method for boiling oxidation of nuclear-grade extruded aluminum materials includes:
[0009] Step 1: Perform preliminary cleaning of the fuel element to reduce impurities on the element surface;
[0010] Step 2: Immerse the fuel element in nitric acid to completely erode impurities on the surface of the fuel element and regenerate a uniform, porous white oxide pre-film.
[0011] Step 3: Remove nitric acid from the surface of the fuel element using hot water at a temperature of 50℃~70℃;
[0012] Step 4: Immerse the fuel element in nitric acid to remove the yellow / gray streaks formed by residual substances on the surface of the fuel element after high-temperature nitric acid immersion.
[0013] Step 5: Remove nitric acid from the surface of the fuel element using hot water at a temperature of 50℃~70℃;
[0014] Step 6: During the cold water rinsing process, repeatedly wipe the surface of the fuel element to remove impurities generated by the reaction between the fuel element and aluminum;
[0015] Step 7: Immerse the fuel element in deionized water at a temperature exceeding 80°C for sealed storage, and prepare a nanoscale oxide film through the reaction of aluminum and water;
[0016] Step 8: Dry the fuel element.
[0017] As one feasible approach, in step 1, acetone or ethanol is used to perform preliminary cleaning of the fuel element. After the pretreatment is completed, the acetone or ethanol is allowed to completely evaporate before proceeding to step 2.
[0018] As an feasible approach, in step 2, after the fuel element is installed into the mounting bracket, the angle between the fuel element and the horizontal plane is adjusted to 10° to 40°.
[0019] As one feasible method, in step 2, the fuel element is immersed in nitric acid with a mass fraction of 65% to 68% and a temperature of 70°C to 90°C for 5 to 15 minutes using a robotic arm.
[0020] As an feasible approach, in step 3, the hot water immersion time is 0.5 min to 1 min.
[0021] As one feasible approach, in step 4, the fuel element is immersed in nitric acid with a mass fraction of 65%–68% for 5–15 minutes using a robotic arm.
[0022] As an feasible approach, in step 5, the hot water immersion time is 0.5 min to 1 min.
[0023] As an feasible approach, in step 6, the fuel element surface is rinsed with cold water using circulating water while it is still wet.
[0024] As an feasible approach, in step 7, the water is sealed and stored for 20 to 60 minutes, with a pH of 5 to 8 and a conductivity not exceeding 2.0 μS / cm.
[0025] As one feasible approach, in step 8, the fuel element is dried using a blower.
[0026] Compared with the prior art, the boiling oxidation method for nuclear-grade extruded aluminum materials provided in this application has the following advantages:
[0027] This application uses room temperature nitric acid treatment to remove oil from aluminum materials after high temperature nitric acid etching. Due to the slow movement of the automated equipment, the nitrite adsorbed by the aluminum oxide cannot be washed off in time. This causes the nitrite to redissolve, thus avoiding the influence of nitrite on the growth of the aluminum oxide film during the boiling oxidation process and eliminating the yellow streaks on the surface of the aluminum material after automatic boiling oxidation.
[0028] This application reduces the bonding strength between impurities and the aluminum substrate during the nitric acid treatment process by controlling the process temperature, so that the impurities can be effectively removed by wiping, thus avoiding large-area watermarks on the aluminum surface after automatic boiling oxidation.
[0029] This application utilizes the reaction between aluminum and hot water to prepare oxide films with a size of 200nm to 500nm through a water-boiling oxidation technique.
[0030] This application avoids the introduction of additional chemical substances by adjusting the original process and parameters. Attached Figure Description
[0031] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the technical description will be briefly introduced below.
[0032] Figure 1 A flowchart of the boiling oxidation method for nuclear-grade extruded aluminum materials provided in this application;
[0033] Figure 2 X-ray diffraction (XRD) patterns of the original sample, the sample with yellow / gray stripes, and the sample without yellow / gray stripes provided for this application;
[0034] Figure 3 Scanning electron microscope (SEM) and energy scattering spectrum (EDS) images of the yellow / gray striped area and the normal area of the sample provided in this application at different magnifications;
[0035] Figure 4 SEM image of the automatically boiled water oxidation sample provided in this application;
[0036] Figure 5 Auger electron spectroscopy (AES) test results for the automatically boiled oxidized samples provided in this application;
[0037] Figure 6 SEM images of traditional water-boiling oxidation samples provided in this application;
[0038] Figure 7 AES test results for the conventional water-boiling oxidation sample provided in this application. Detailed Implementation
[0039] The following detailed description provides further details on specific implementation methods.
[0040] like Figures 1 to 7 As shown, this application provides a water-boiling oxidation method for nuclear-grade extruded aluminum materials, comprising the following steps:
[0041] Step 1: Pre-treatment. Use acetone or ethanol to perform preliminary cleaning of the fuel element to reduce impurities on the element surface.
[0042] The pretreatment process involves using acetone or ethanol to initially clean the fuel elements through soaking and wiping, reducing oil and other impurities on the element surface and preventing the introduction of excessive impurities during nitric acid immersion, thus extending the service life of nitric acid. After pretreatment, it is essential to ensure that the acetone (anhydrous ethanol) completely evaporates to avoid residual organic solvents reacting with nitric acid and undergoing a nitration reaction that is difficult to remove.
[0043] Step 2: High-temperature nitric acid immersion. The fuel element is immersed in nitric acid to completely erode impurities on the surface of the fuel element and regenerate a uniform, porous white oxide pre-generated film.
[0044] After the fuel element is installed in the mounting bracket, the angle between the fuel element and the horizontal plane is adjusted to 10° to 40° to prevent a large amount of nitric acid from rushing into and out of the fuel element during the immersion / removal of the fuel element, which could cause damage from shaking. This also ensures that the nitric acid in the fuel element is completely drained when the nitric acid is removed. The fuel element is then immersed in nitric acid with a mass fraction of 65% to 68% and a temperature of 70°C to 90°C for 5 to 15 minutes by a robotic arm. This ensures that impurities are completely etched away and a uniform, porous white oxide pre-generated film is regenerated on the surface of the fuel element.
[0045] Step 3: Hot water immersion. Nitric acid on the surface of the fuel element is removed by hot water at a temperature of 50℃~70℃.
[0046] Hot water immersion is completed automatically by the equipment. The nitric acid on the surface of the fuel element is quickly removed by hot water. The immersion time is 0.5 min to 1 min, and the water temperature should be strictly controlled between 50℃ and 70℃.
[0047] If the immersion temperature exceeds 70℃, the reaction rate between aluminum and water will be significantly accelerated, and an uneven oxide film will be rapidly generated on the surface of the fuel element. This will affect the growth of the oxide film in the boiling process, resulting in large-area watermarks. Furthermore, impurities adsorbed by the fuel element in nitric acid will also enter the oxide film during the reaction between aluminum and hot water, making them difficult to remove through subsequent processes.
[0048] In addition, excessively high temperatures can cause the surface of the fuel element to dry rapidly as it moves through the various tanks of the automated equipment, causing impurities dissolved in the water to combine with the surface of the fuel element and become difficult to remove.
[0049] Step 4: Room temperature nitric acid immersion. Immerse the fuel element in nitric acid to remove the yellow / gray streaks formed by the residue on the surface of the fuel element after the high temperature nitric acid immersion in Step 2.
[0050] After the fuel element is immersed in high-temperature nitric acid (step 2), its surface temperature is high. The residual nitric acid on the element surface evaporates rapidly during the transfer to hot water (step 3), resulting in impurities remaining and exhibiting yellow / gray streaks. These impurities are tightly bonded to the substrate and cannot be removed by water washing; they must be dissolved with room-temperature nitric acid. The room-temperature nitric acid immersion is automatically completed by a robotic arm immersing the fuel element in 65%–68% nitric acid for 5–15 minutes.
[0051] By comparing the X-ray diffraction (XRD) patterns of samples in their original state, with yellow / gray streaks, and without yellow / gray streaks, the composite peak signal of alumina and aluminum at around 45° disappeared in samples with / without acid stains.
[0052] Combining scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) images of the yellow / gray striped area and the normal area at different magnifications, it can be seen that the morphology, size and elemental composition of the sample are not significantly different at micron-level magnification. It is preliminarily judged that the appearance of yellow / gray stripes is caused by the adsorption of some solutes in nitric acid by porous alumina on the surface of the fuel element. This adsorption is usually caused by the interaction between functional groups on the surface of alumina film and nitrogen oxides or iron ions, with the scale ranging from molecular to nano-cluster level.
[0053] Due to adsorption, deionized water with a pH of 6-7 has poor solubility for nitrogen oxides and nitrates, making it difficult to effectively remove acid residues. Therefore, it is necessary to lower the pH of the cleaning solution to increase its solubility for nitrogen oxides and nitrates. Concentrated nitric acid at room temperature (65%-68%) has a pH far less than 1, providing a suitable pickling environment for the nitrogen oxides and nitrates adsorbed by alumina. This allows the chemicals that form yellow / gray streaks to redissolve without introducing additional chemicals into the process, meeting nuclear-grade cleanliness requirements.
[0054] In addition, the main reactions in nitric acid are the reaction of aluminum with nitric acid to produce aluminum nitrate and aluminum oxide, and the reaction of aluminum oxide with aluminum nitrate to produce aluminum nitrate, such as... Figure 4 As shown, with the formation of alumina, the reaction between aluminum and aluminum nitrate is inhibited, and the main reaction becomes the reaction between alumina and nitric acid. The reaction rate is affected by temperature, and the reaction rate at room temperature is almost negligible. By measuring the mass change of the sample in nitric acid at mass fractions of 65%–68%, 80℃, and room temperature (as shown in Table 1), it can be seen that the reaction rate between the fuel element and aluminum at high temperature is about 50 times that at room temperature.
[0055] Therefore, immersion in room temperature nitric acid for 5 to 10 minutes can dissolve impurities adhering to the fuel element from high-temperature nitric acid without corroding the fuel element surface or introducing other elements, and eliminate yellow / gray streaks on the surface.
[0056] Table 1 Results of Cold Nitric Acid Immersion Test
[0057]
[0058] Step 5: Hot water immersion. Remove residual nitric acid from the surface of the fuel element by immersion in nitric acid at room temperature (step 4) using hot water at a temperature of 50℃~70℃.
[0059] After immersion in ambient temperature nitric acid, the fuel element temperature is low, and the residual nitric acid on the surface evaporates slowly. No impurities remain during the transfer to hot water (step 5), so they can be directly removed by hot water immersion. The hot water immersion process is the same as the previous hot water washing process (step 3), with an immersion time of 0.5 min to 1 min, and the water temperature should be strictly controlled between 50℃ and 70℃.
[0060] Step 6: Cold water rinsing. During the cold water rinsing process, repeatedly wipe the surface of the fuel element to further remove impurities generated by the reaction between the fuel element surface and aluminum.
[0061] The cold water rinsing process is achieved by a combination of automated equipment and manual labor. The cold water rinsing is carried out by circulating water. During the cold water rinsing process, workers use lint-free cloths to repeatedly wipe the surface of the fuel element to further remove impurities generated by the reaction between the fuel element surface and aluminum.
[0062] This process must be carried out before the surface of the fuel element is dry. If the fuel element has dried, the surface impurities will strongly adsorb onto the alumina pre-grown film, making it difficult to remove by physical means. This will affect the nucleation and growth of alumina in the initial stage of subsequent boiling oxidation, causing the oxide film to turn yellow locally. Therefore, the workpiece dried before the cold water flow needs to be re-immersed in high-temperature nitric acid to etch the alumina pre-grown film contaminated by impurities.
[0063] Step 7: Boiling. The fuel element is sealed and stored in deionized water at a temperature exceeding 80°C, and a nanoscale oxide film is prepared through the reaction of aluminum and water.
[0064] The boiling process is automated. A robotic arm immerses the fuel element in deionized water at a temperature exceeding 80°C (below the local boiling point) for 20-60 minutes, sealing it for preservation. A nanoscale oxide film is then prepared through the reaction of aluminum and water. The reaction process is as follows: Figure 5 As shown.
[0065] During the reaction, aluminum ions react with water to nucleate on the surface of the pre-grown oxide film, and then grow into a film as the reaction progresses. The nucleation effect of alumina on the fuel element surface on the pre-grown film determines the consistency of the oxide film surface appearance. Therefore, it is necessary to remove impurities from the surface of the pre-grown oxide film and strictly control the pH value of the deionized water to be between 5 and 8 and the conductivity to not exceed 2.0 μS / cm.
[0066] Step 8: Dry the fuel element.
[0067] The drying process takes place outside the equipment and requires that the fuel elements be completely dry. A blower can be used to assist in the drying process.
[0068] SEM and AES (sputtering rate 17 nm / min) were performed on samples subjected to automated boiling oxidation (pretreatment - high-temperature nitric acid immersion at 85℃ for 10 min - hot water rinsing at 60℃ for 0.5 min - room temperature nitric acid immersion for 10 min - hot water rinsing at 60℃ for 0.5 min - cold water rinsing - boiling at 90℃ for 40 min - drying). The results showed that the oxide film was formed by a dense packing of microspheres of 10–30 μm (e.g., ...). Figure 6 As shown), the oxide film thickness is approximately 425–442 nm. SEM and AES (sputtering rate 17 nm / min) were performed on samples subjected to traditional water-boiling oxidation (pretreatment—high-temperature nitric acid immersion at 85°C for 10 min—hot water washing at 80°C for 0.5 min—cold water rinsing—boiling at 90°C for 40 min—drying). It was found that the oxide film was also formed by the close packing of microsphere structures (e.g., ...). Figure 6 As shown in the figure, the oxide film thickness is approximately 425 nm to 442 nm, consistent with the automatically boiled oxidation sample. Therefore, this proves that the automated boiled oxidation process can replace the traditional manual boiled oxidation process.
[0069] In summary, this application addresses the shortcomings of manual boiling oxidation and the characteristics of pickling and boiling film formation on aluminum alloys by providing an automated process for preparing high-quality nanoscale oxide films on the surface of nuclear-grade extruded aluminum alloys.
[0070] This application uses machinery to replace manual water boiling oxidation. The automated program ensures a stable and controllable process, effectively avoiding risks such as contact between aluminum and the tank wall and collisions during transportation. It also overcomes the limitations of human labor, enabling large-scale batch oxidation while reducing safety risks.
[0071] This application effectively overcomes the shortcomings of automated equipment's inherent lack of flexibility, which leads to prolonged intervals between water boiling oxidation processes and prevents timely nitric acid cleaning. This avoids the formation of yellow or light gray streaks and the increase in nitrite and nitrate ion content in the water after reactor loading, ensuring the surface quality of the aluminum and the water quality within the reactor. By controlling the hot water temperature, the application solves the problem of uneven oxide film growth during the hot water immersion process due to insufficient rinsing of fuel elements in hot water. This avoids the formation of watermarks and delamination within the oxide film after water boiling oxidation, which reduces the substrate adhesion and ensures the appearance and protective function of the oxide film. Furthermore, the automated water boiling oxidation process does not introduce other chemical substances compared to the original manual process, meeting nuclear-grade cleanliness requirements.
[0072] The above description is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application.
Claims
1. A method for boiling and oxidizing nuclear-grade extruded aluminum materials, characterized in that, include: Step 1: Perform preliminary cleaning of the fuel element to reduce impurities on the element surface; Step 2: Immerse the fuel element in nitric acid to completely erode impurities on the surface of the fuel element and regenerate a uniform, porous white oxide pre-film. Step 3: Remove nitric acid from the surface of the fuel element using hot water at a temperature of 50℃~70℃; Step 4: Immerse the fuel element in nitric acid to remove the yellow / gray streaks formed by residual substances on the surface of the fuel element after high-temperature nitric acid immersion. Step 5: Remove nitric acid from the surface of the fuel element using hot water at a temperature of 50℃~70℃; Step 6: During the cold water rinsing process, repeatedly wipe the surface of the fuel element to remove impurities generated by the reaction between the fuel element and aluminum; Step 7: Immerse the fuel element in deionized water at a temperature exceeding 80°C for sealed storage, and prepare a nanoscale oxide film through the reaction of aluminum and water; Step 8: Dry the fuel element.
2. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 1, acetone or ethanol is used to perform preliminary cleaning of the fuel element. After the pretreatment is completed, the acetone or ethanol is allowed to evaporate completely before proceeding to step 2.
3. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 2, after installing the fuel element into the mounting bracket, adjust the angle between the fuel element and the horizontal plane to 10° to 40°.
4. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 2, the fuel element is immersed in nitric acid with a mass fraction of 65% to 68% and a temperature of 70°C to 90°C for 5 to 15 minutes using a robotic arm.
5. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 3, the hot water immersion time is 0.5 min to 1 min.
6. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 4, the fuel element is immersed in 65%–68% nitric acid by a robotic arm for 5–15 minutes.
7. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 5, the hot water immersion time is 0.5 min to 1 min.
8. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 6, the fuel element surface is rinsed with cold water using circulating water while it is still wet.
9. The boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 7, the water is sealed and stored for 20 to 60 minutes, with a pH of 5 to 8 and a conductivity not exceeding 2.0 μS / cm.
10. The water-boiling oxidation method for nuclear-grade extruded aluminum materials according to claim 1, characterized in that, In step 8, the fuel element is dried using a blower.