Anodic oxide film layer sealing solution and sealing process based on permanganate

Abstract

The invention provides a permanganate-based anodic oxide film layer sealing solution and a sealing process, the sealing solution is composed of permanganate, nitrate and molybdate, the use of materials is not limited by regulations, the sealing solution is environment-friendly, and the cost of chemical raw materials is low; the preparation process of the solution is simple to operate, is carried out at room temperature and does not need special equipment support; under a dark condition, the solution has a relatively long storage period, and can be processed into a liquid / solid preparation for transportation and sales. By means of the sealing solution and the sealing process method, high-corrosion-resistance sealing of the anodic oxide film can be achieved, and after reasonable sealing, the corrosion resistance of the anodic oxide film can reach the neutral salt mist corrosion resistance level of 336 h.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a sealing solution for anodized films based on permanganate and its sealing process. Background Technology

[0002] Anodizing is a metal surface treatment technology that generates an alumina film on the surface of aluminum alloys through an electrochemical reaction, widely used to improve the corrosion resistance of aluminum alloys. Due to the inherent characteristics of the "electric field-assisted acid dissolution mechanism," the generated alumina film contains an array of vertically arranged channels. These channels have a large pore volume, providing pathways for corrosive media to penetrate into the substrate, hindering the optimization of the corrosion resistance of the anodized film. To overcome the drawbacks caused by the channel structure, anodized parts are usually directly immersed in a specific chemical solution. At this time, a certain chemical reaction is artificially constructed within the channels, generating chemically stable products that fill the pores. This post-anodizing treatment method is referred to in the industry as the chemical sealing of the anodized film.

[0003] There are numerous research and application cases related to the sealing of anodic oxide films. To date, the chemical sealing of anodic oxide films has mainly undergone the following processes:

[0004] The first stage involves sealing the anodic oxide film using hot water or steam. Water molecules react with the anodic aluminum oxide to form boehmite, and the increased volume helps to seal the pores. Although the sealed anodic oxide film improves corrosion resistance, it is still difficult to achieve the stable corrosion resistance required for aerospace engineering applications.

[0005] The second stage: To further enhance the corrosion resistance of the anodic oxide film, dichromate is currently mainly used for sealing. Hexavalent chromium, with its strong oxidizing properties, reacts with aluminum compounds in the pores to form aluminum chromate, aluminum dichromate, and other chemically stable substances. These substances not only seal the pores but also achieve secondary passivation of the pores through hydration in humid environments, thus achieving a higher level of corrosion resistance. For example, HB 5362, "Quality Inspection of Corrosion Resistance of Commonly Used Metal Protective Coatings for Aircraft," in the aerospace industry, stipulates that anodic oxide films sealed with dichromate should have a neutral salt spray resistance level exceeding 336 hours.

[0006] Phase Three: In recent years, due to environmental regulations restricting the use of dichromates, the industry has begun to experiment with using transition metal compounds such as nickel and cobalt salts to seal anodic oxide films. The hydrotalcite structure formed within the pores has a lamellar, layered, and amorphous characteristic, which improves the corrosion resistance of the film to some extent. Furthermore, it has been reported that some commercial nickel and cobalt sealants already meet the corrosion resistance requirements of MIL-PRF-8625F.

[0007] Phase Four: With the rapid development of rare earth science, the industry has noticed that some special properties of rare earth metals can be used to seal the pores of anodic oxide films. For example, lanthanum and cerium possess valence electron transfer properties, which help resist the coordination and oxidation of halide ions. However, a series of cerium salt-based sealing agents have recently been developed, but their sealing effect is still not as good as that of dichromates and needs further optimization.

[0008] Phase 5: Industry scholars proposed the concept of organic-inorganic hybrid sealing, which involves doping an inorganic sealing solution system dominated by rare earth metal ions and transition metal ions with organosilicon resins, silane coupling agents or other organic film-forming substances to improve the corrosion resistance of the film by increasing the hydrophobicity of the film surface.

[0009] Currently, the requirements for aerospace aluminum alloy anodizing film technology mainly focus on evaluating the reliability, stability, and sustainability of the protection level of the process (including the sealing process). Because an organic coating forms on the surface of the anodized film after organic sealing, affecting the bonding strength between the subsequent coating resin and the film, the aerospace industry primarily uses inorganic chemical sealing for the chemical sealing of aluminum alloy anodized films, specifically employing sealing technologies such as dichromates, nickel salts, or cobalt salts. However, with the increasing emphasis on cleaner production and environmental awareness, relevant environmental protection laws and policies require surface treatment companies to gradually abandon the use of environmentally harmful chemical sealing solutions. Referring to GB 21900-2008 "Electroplating Pollutant Emission Standard," the use of heavy metal ions such as nickel, cobalt, and chromium should be restricted.

[0010] Therefore, it is necessary to explore a more environmentally friendly anodic oxide film sealing process. Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of existing anodic oxide film sealing processes in terms of environmental protection, and to provide an anodic oxide film sealing solution based on permanganate and its sealing process.

[0012] To achieve all the above objectives, this invention discloses a permanganate-based anodic oxide film sealing solution and sealing process.

[0013] A permanganate-based anodic oxide film sealing solution, characterized by the following composition:

[0014] Permanganate 10g / L-50g / L;

[0015] Nitrate levels: 1 g / L - 25 g / L;

[0016] Molybdate 0.1 g / L - 5 g / L;

[0017] pH adjuster as needed, adjust the pH of the solution to 4-8;

[0018] Deionized water balance;

[0019] Thus, the prepared solution will be purplish-red in color.

[0020] Furthermore, the permanganate is Mn-containing 7+ A mixture of one or more soluble salts; such as potassium permanganate, sodium permanganate, ammonium permanganate, etc.

[0021] The nitrate is one or a mixture of several salts of alkali metals, alkaline earth metals, and light metals containing nitrate ions; for example: sodium nitrate, lithium nitrate, potassium nitrate, barium nitrate, aluminum nitrate, etc.

[0022] The molybdate is a Mo-containing... 6+ It is a mixture of one or more soluble salts, such as sodium molybdate, potassium molybdate, ammonium molybdate, lithium molybdate, etc.

[0023] Furthermore, the pH adjuster is an inorganic acid, an inorganic base, an organic acid, or an organic base;

[0024] The inorganic acid is nitric acid, sulfuric acid, hydrochloric acid, or hydrofluoric acid;

[0025] The inorganic base is sodium hydroxide, potassium hydroxide, or ammonia.

[0026] The organic acid is acetic acid, citric acid, or malic acid;

[0027] The organic base is monoethanolamine, diethanolamine, or triethanolamine.

[0028] Furthermore, the conductivity of the deionized water is ≤5 uS / cm.

[0029] Meanwhile, this invention provides a method for preparing the above-mentioned permanganate-based anodic oxide film sealing solution, characterized in that: under continuous stirring, the other raw materials (i.e., permanganate, nitrate, and molybdate; the order of dissolution can be adjusted, but the previous raw material should be completely dissolved before adding the next) are dissolved one by one in deionized water. Then, the pH adjuster is added to adjust the pH of the solution to 4-8, thus completing the preparation. The purpose of continuous stirring during the preparation process is to promote the dissolution of the raw materials.

[0030] Furthermore, the specific steps are as follows:

[0031] S1. While stirring continuously, add permanganate to a small amount of deionized water in portions until it is completely dissolved;

[0032] S2. While stirring continuously, add nitrate to the solution obtained in S1 in portions until it is completely dissolved;

[0033] S3. While stirring continuously, add molybdate in portions to the solution obtained in S2 until it is completely dissolved;

[0034] S4. While stirring continuously, add deionized water to make up the solution volume to the target solution volume;

[0035] S5. Add a pH adjuster to the solution obtained in S4 until the pH value of the solution is 4-8, and the preparation is complete.

[0036] Furthermore, the present invention also provides a method for sealing an anodic oxide film using the above-mentioned permanganate-based anodic oxide film sealing solution, characterized by comprising the following steps:

[0037] 1) Immerse the anodized aluminum alloy parts in an anodized film sealing solution heated to 80-90℃ for 20-30 minutes;

[0038] 2) After removal, thoroughly clean the aluminum alloy parts with running water. When the cleaning water is colorless, it is considered that the cleaning is complete.

[0039] 3) Dry and clean the aluminum alloy parts, and then seal them with an anodized film.

[0040] Furthermore, in step 3), the drying temperature is 50-80℃ and the time is 30-60min.

[0041] Furthermore, the aluminum alloy parts are subjected to Type II sulfuric acid anodizing according to HB / Z 233 "Aluminum and Aluminum Alloy Sulfuric Acid Anodizing Process"; the aluminum alloy parts are 2024-T3 aluminum alloy test pieces (non-clad aluminum).

[0042] The principle of this invention:

[0043] The core innovation of this invention lies in employing a permanganate system to achieve a dual sealing mechanism of "oxidative precipitation + structural repair". Its technical principle can be broken down into the following key steps:

[0044] First, permanganates (such as potassium permanganate) release strongly oxidizing Mn2 in heated acidic to near-neutral solutions. 7+ Ions. When anodized aluminum alloy is immersed in solution, Mn 7+ The MnO2 permeates along the membrane pores and undergoes a redox reaction with the active aluminum on the pore walls, generating MnO2 (manganese dioxide) and hydrated alumina, which have extremely low solubility. These products are deposited in the pores as nanoparticles, physically filling the pores and forming the first barrier. Simultaneously, unreacted MnO2 adsorbed in the membrane pores / pores... 7+Salt can remain purple for a very long period of time (macroscopically manifested as a film that remains purple, the purple color being due to Mn). 7+ The characteristic color of chromium acts as an oxidant to repassivate internally degraded components, thus exhibiting chromium-like self-healing properties.

[0045] Secondly, the addition of nitrates acts as an "oxidation enhancer." At high temperatures, nitrates decompose to produce nitrogen oxides and nascent oxygen, which on the one hand strengthens the oxidative environment of permanganate and promotes the activation of aluminum in the pore walls; on the other hand, through micro-area pH regulation, it avoids drastic local pH fluctuations that could lead to film dissolution, thus ensuring the uniformity of the deposition reaction.

[0046] The key innovation lies in the introduction of molybdate. Molybdate ions ( It also possesses a unique "self-healing" property: if microcracks or localized damage occur in the membrane during use, the infiltrated moisture will cause molybdate to form aluminum molybdate colloid at the damaged site, dynamically sealing the newly formed defects. This "damage response" mechanism complements the static sealing / self-healing properties of permanganate, significantly improving the reliability of the membrane during long-term service.

[0047] Under the synergistic effect of the three components, the sealed membrane forms a dense composite structure with manganese oxide as the framework and molybdate as the repair agent. For example... Figure 3 As shown, the treated film exhibits a uniform surface state; after 336 hours of neutral salt spray testing ( Figure 4 There were still no signs of corrosion after that, which meets the basic requirements of aviation standard HB 5362.

[0048] Advantages of this invention:

[0049] 1. The permanganate-based anodic oxide film sealing solution developed in this invention has the advantages of simple composition and low material cost. The manufacturing process does not require special equipment support, and it is easy to package and transport, thus having market promotion prospects.

[0050] 2. The materials required for the anodic oxide film sealing solution based on permanganate developed in this invention are not subject to regulatory restrictions, and it has the advantage of being more environmentally friendly than traditional dichromate sealing technology, and is not within the key control scope of GB 21900-2008 "Electroplating Pollutant Emission Standard".

[0051] 3. The permanganate-based anodic oxide film sealing process developed in this invention is simple to operate, requires no special equipment support or additional special processing, and can enable the anodic oxide film to exhibit excellent corrosion resistance performance that meets the requirements of HB 5362 "Quality Inspection of Corrosion Resistance of Commonly Used Metal Protective Coatings for Aircraft".

[0052] 4. Under light-protected conditions, the sealing solution of this invention has a long shelf life and can be processed into liquid / solid formulations for transportation and sale. Using the sealing solution and sealing process of this invention, high corrosion resistance of anodic oxide films can be achieved. After proper sealing, the corrosion resistance of the anodic oxide film can reach a neutral salt spray corrosion resistance level of 336 h. In particular, the aluminum alloy sample (2024-T3) sealed by the sealing solution and process of this invention can reach a level of non-corrosion under neutral salt spray exceeding 1000 h. Attached Figure Description

[0053] Figure 1 Images of the permanganate blocking solution prepared in Example 1 and images of the impregnated sample;

[0054] Figure 2 Anodized sample prepared according to HB / Z 233;

[0055] Figure 3 To complete the anodic oxidation of the sample after permanganate sealing;

[0056] Figure 4 The sample condition after 336 hours of neutral salt spray corrosion. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the embodiments. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Steps not specifically described in the embodiments are all existing technologies and will not be described in detail here.

[0058] Example 1

[0059] The composition and formulation of a permanganate-based anodic oxide film sealing solution are as follows:

[0060] Potassium permanganate (AR): 36 g / L;

[0061] Sodium nitrate (AR): 10 g / L;

[0062] Aluminum nitrate (AR): 10 g / L;

[0063] Ammonium molybdate (AR): 3 g / L;

[0064] pH adjuster: Nitric acid / ammonia solution, as needed.

[0065] The remainder is deionized water (≤5 uS / cm);

[0066] Color: purplish-red (e.g.) Figure 1 (as shown)

[0067] A method for preparing a permanganate-based anodic oxide film sealing solution (500 mL) specifically includes the following steps:

[0068] S1: Add 150mL of deionized water to the container;

[0069] S2: While stirring continuously, add 18g of potassium permanganate to the container in several batches until it is completely dissolved;

[0070] S3: While stirring continuously, add 5g of sodium nitrate and 5g of aluminum nitrate to the container in several batches until completely dissolved;

[0071] S4: While stirring continuously, add 1.5g of ammonium molybdate to the container in portions until completely dissolved;

[0072] S5: While stirring continuously, continue to add deionized water to the container until the solution volume reaches 500 mL;

[0073] S6: While stirring continuously, adjust the pH of the solution to 5.6 using nitric acid / ammonia.

[0074] A method for sealing an anodic oxide film based on permanganate specifically includes the following steps:

[0075] 1) Heat the sealing solution obtained above to 90°C and set aside for later use;

[0076] 2) Select 2024-T3 aluminum alloy specimens (non-clad aluminum) and prepare Class II sulfuric acid anodizing samples according to HB / Z 233 "Sulfuric Acid Anodizing Process for Aluminum and Aluminum Alloys" (e.g. Figure 2 (as shown)

[0077] 3) Immerse the anodized sample obtained in step 2) in the sealing solution of step 1) and keep it for 30 min;

[0078] 4) Thoroughly wash the sealed sample from step 3) in running water;

[0079] 5) Place the cleaned sample from step 4) in a warm air bath at approximately 50°C for 60 minutes to dry. Figure 3 As shown in the figure, 90 indicates 90℃ and 30 indicates 30 minutes.

[0080] Example 2

[0081] The composition and formulation of a permanganate-based anodic oxide film sealing solution are as follows:

[0082] Potassium permanganate (AR): 16 g / L;

[0083] Barium nitrate (AR): 4 g / L;

[0084] Aluminum nitrate (AR): 1 g / L;

[0085] Sodium nitrate (AR): 1 g / L;

[0086] Sodium molybdate (AR): 0.1 g / L;

[0087] Ammonium molybdate (AR): 0.1 g / L;

[0088] pH adjuster: Nitric acid / ammonia solution, as needed.

[0089] The remainder is deionized water (≤5 uS / cm);

[0090] Color: Purple-red (same as in Example 1);

[0091] A method for preparing a permanganate-based anodic oxide film sealing solution (500 mL) specifically includes the following steps:

[0092] S1: Add 150mL of deionized water to the container;

[0093] S2: While stirring continuously, add 8g of potassium permanganate to the container in several batches until it is completely dissolved;

[0094] S3: While stirring continuously, add 2g of barium nitrate, 0.5g of aluminum nitrate, and 0.5g of sodium nitrate to the container in portions until completely dissolved;

[0095] S4: While stirring continuously, add 0.05g sodium molybdate and 0.05g ammonium molybdate to the container in portions until completely dissolved;

[0096] S5: While stirring continuously, continue to add deionized water to the container until the solution volume reaches 500 mL;

[0097] S6: While stirring continuously, adjust the pH of the solution to 4.1 using nitric acid / ammonia.

[0098] A method for sealing an anodic oxide film based on permanganate specifically includes the following steps:

[0099] 1) Heat the sealing solution obtained above to 85°C and set aside for later use;

[0100] 2) Select 2024-T3 aluminum alloy specimens (non-clad aluminum) and prepare Type II sulfuric acid anodizing specimens according to HB / Z 233 "Sulfuric Acid Anodizing Process for Aluminum and Aluminum Alloys" (same as in Example 1);

[0101] 3) Immerse the anodized sample obtained in step 2) in the sealing solution described in step 1) and keep it for 30 minutes;

[0102] 4) Thoroughly wash the sealed sample from step 3) in running water;

[0103] 5) Place the cleaned sample from step 4) in a warm air bath at approximately 60°C for 45 minutes to dry. The effect is similar to that of Example 1.

[0104] Example 3

[0105] The composition and formulation of a permanganate-based anodic oxide film sealing solution are as follows:

[0106] Sodium permanganate (AR): 48 g / L;

[0107] Barium nitrate (AR): 4 g / L;

[0108] Aluminum nitrate (AR): 20 g / L;

[0109] Sodium nitrate (AR): 1 g / L;

[0110] Sodium molybdate (AR): 4.8 g / L;

[0111] pH adjuster: Nitric acid / ammonia solution, as needed.

[0112] The remainder is deionized water (≤5 uS / cm);

[0113] Color: Purple-red (same as in Example 1);

[0114] A method for preparing a permanganate-based anodic oxide film sealing solution (500 mL) specifically includes the following steps:

[0115] S1: Add 150mL of deionized water to the container;

[0116] S2: While stirring continuously, add 24g of potassium permanganate to the container in several batches until it is completely dissolved;

[0117] S3: While stirring continuously, add 2g of barium nitrate, 10g of aluminum nitrate, and 0.5g of sodium nitrate to the container in portions until completely dissolved;

[0118] S4: While stirring continuously, add 2.4g of sodium molybdate to the container in portions until completely dissolved;

[0119] S5: While stirring continuously, continue to add deionized water to the container until the solution volume reaches 500 mL;

[0120] S6: While stirring continuously, adjust the pH of the solution to 7.5 using nitric acid / ammonia.

[0121] A method for sealing an anodic oxide film based on permanganate specifically includes the following steps:

[0122] 1) Heat the sealing solution obtained above to 90°C and set aside for later use;

[0123] 2) Select 2024-T3 aluminum alloy specimens (non-clad aluminum) and prepare Type II sulfuric acid anodizing specimens according to HB / Z 233 "Sulfuric Acid Anodizing Process for Aluminum and Aluminum Alloys" (same as in Example 1);

[0124] 3) Immerse the anodized sample obtained in step 2) in the sealing solution described in step 1) and keep it for 30 minutes;

[0125] 4) Thoroughly wash the sealed sample from step 3) in running water;

[0126] 5) Place the cleaned sample from step 4) in a warm air bath at approximately 60°C for 60 minutes to dry. The effect is similar to that of Example 1.

[0127] According to the neutral salt spray test method specified in GB 10125, the corrosion resistance of the sealed sample from Example 1 was tested, and the results are as follows: Figure 4 As shown, the third-party testing agency determined that the product met the technical requirements of HB 5362 "Quality Inspection of Corrosion Resistance of Commonly Used Metal Protective Coatings for Aircraft", namely, no white or gray-black corrosion products were found after 336 hours.

[0128] In summary, the anodic oxide film sealing solution prepared by this invention is not only environmentally friendly, but also has excellent sealing performance, and has great application prospects in the aerospace industry.

[0129] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A permanganate-based anodic oxide film sealing solution, characterized in that, The composition is as follows: Permanganate 10g / L-50g / L; Nitrate levels: 1 g / L - 25 g / L; Molybdate 0.1 g / L - 5 g / L; pH adjuster to adjust the pH of the solution to 4-8; Deionized water balance.

2. The anodic oxide film sealing solution according to claim 1, characterized in that: The permanganate is Mn-containing 7+ A mixture of one or more soluble salts; The nitrate is one or a mixture of several salts of alkali metals, alkaline earth metals and light metals containing nitrate ions. The molybdate is a Mo-containing... 6+ A mixture of one or more soluble salts.

3. The anodic oxide film sealing solution according to claim 1 or 2, characterized in that: The pH adjuster is an inorganic acid, inorganic base, organic acid, or organic base; The inorganic acid is nitric acid, sulfuric acid, hydrochloric acid, or hydrofluoric acid; The inorganic base is sodium hydroxide, potassium hydroxide, or ammonia. The organic acid is acetic acid, citric acid, or malic acid; The organic base is monoethanolamine, diethanolamine, or triethanolamine.

4. The method for preparing the permanganate-based anodic oxide film sealing solution according to any one of claims 1-3, characterized in that: While continuously stirring, dissolve all other ingredients except the pH adjuster in deionized water one by one and in portions. Then add the pH adjuster to adjust the pH of the solution to 4-8 to complete the preparation.

5. The method for preparing the anodic oxide film sealing solution based on permanganate according to claim 4, characterized in that, Includes the following steps: S1. While stirring continuously, add permanganate to deionized water in portions until completely dissolved; S2. While stirring continuously, add nitrate to the solution obtained in S1 in portions until it is completely dissolved; S3. While stirring continuously, add molybdate in portions to the solution obtained in S2 until it is completely dissolved; S4. While stirring continuously, add deionized water to make up the solution volume to the target solution volume; S5. Add a pH adjuster to the solution obtained in S4 until the pH value of the solution is 4-8, and the preparation is complete.

6. A method for sealing an anodic oxide film using the permanganate-based anodic oxide film sealing solution according to any one of claims 1-3, characterized in that, Includes the following steps: 1) Immerse the anodized aluminum alloy parts in an anodized film sealing solution heated to 80-90℃ for 20-30 minutes; 2) After removal, clean the aluminum alloy parts with running water; 3) Dry and clean the aluminum alloy parts, and then seal them with an anodized film.

7. The method according to claim 6, characterized in that: In step 3), the drying temperature is 50-80℃ and the time is 30-60 minutes.

8. The method according to claim 6, characterized in that: The aluminum alloy parts are subjected to Class II sulfuric acid anodizing in accordance with HB / Z 233 "Sulfuric Acid Anodizing Process for Aluminum and Aluminum Alloys".

Images