Sample preparation method for observing surface morphology of medium-high voltage formed foil

Abstract

The invention discloses a sample preparation method for observing the surface appearance of a medium-high voltage formed foil, which comprises the following steps: cutting the formed foil into a strip-shaped sample with a specific size, grinding and polishing, carrying out primary ultrasonic cleaning, putting into a special alkaline corrosive liquid for treatment, carrying out secondary ultrasonic cleaning, and finally observing by using a scanning electron microscope. The alkaline corrosive liquid comprises various components such as potassium hydroxide and sodium silicate, and the components have a synergistic effect and are prepared under the conditions of optimized temperature, stirring rotation speed and the like. The sample preparation method has remarkable advantages, and compared with a traditional method, the use of chemicals easy to explode is avoided, so that the safety is greatly improved; the operation process is standard, parameters are clear, simplicity and convenience are achieved, and repeatability is good; by accurately controlling the corrosion process, the sample preparation effect is good, and the surface appearance can be clearly presented; meanwhile, the components of the used corrosive liquid are environment-friendly, and environmental pollution is reduced. The method has a wide application prospect in the related scientific research and production fields of electronic materials.

Description

Technical Field

[0001] The present invention relates to the technical field of medium and high voltage formation foils, and particularly to a sample preparation method for observing the surface morphology of medium and high voltage formation foils.

Background Art

[0002] The medium and high voltage formation foil, fully known as the medium and high voltage anode foil for aluminum electrolytic capacitors, is an essential key raw material for aluminum electrolytic capacitors. As a main component of various household appliances, computers, communication equipment, and automation equipment, etc., the performance of aluminum electrolytic capacitors directly affects the overall operation status of these electronic devices. Moreover, the quality of the formation foil is closely related to the performance and service life of aluminum electrolytic capacitors, and thus indirectly determines the quality of the entire electronic unit.

[0003] With the rapid development of electronic technology, the application scenarios of aluminum electrolytic capacitors have been continuously expanded, and the market's demand for their miniaturization, long life, and high integration has become increasingly urgent. Among the numerous research directions for improving the performance of aluminum electrolytic capacitors, high specific capacitance has become a popular field at present. According to the capacitance formula of the capacitor C = εoεrS / δ (where C represents capacitance, εo and εr represent the vacuum permittivity and relative permittivity respectively, and S and δ represent the area and thickness of the dielectric oxide film), since εo and εr are fixed natural constants, if we want to increase the capacitance of the capacitor, we can only start from two aspects: increasing the area of the dielectric oxide film or reducing the thickness of the oxide film. However, if the oxide film is too thin, the capacitor is easily broken down during operation; if the thickness is too high, it will block the etching holes, resulting in a significant reduction in the effective area of the oxide film, which will also affect the capacitance of the capacitor. Therefore, exploring a sample preparation method that can accurately observe the surface morphology of the formation foil is crucial for studying the thickness growth law of the dielectric oxide film.

[0004] Currently, the Chinese invention patent application with the publication number CN117388301A proposes a method for detecting the surface hole morphology of the medium and high voltage formation foil of aluminum electrolytic capacitors. This method first grinds the formation foil, then uses the electrochemical corrosion method to remove the aluminum matrix between the oxide films, then uses transparent tape to stick and remove the corrosion products, and finally performs secondary electrochemical corrosion. The processed formation foil can then be placed under a scanning electron microscope for observation. However, this method has obvious defects: firstly, the electrochemical corrosion solution used contains perchloric acid. As the currently known strongest inorganic oxyacid, perchloric acid not only has flammability, strong corrosiveness, and strong irritation, but is also a strong oxidant. When it comes into contact or mixes with organic substances, reducing agents, and flammable substances (such as sulfur, phosphorus, etc.), it is extremely easy to cause combustion and explosion. It will decompose at room temperature and explode when heated. It belongs to an easily manufacturable explosive chemical and has a large potential safety hazard; secondly, after using transparent tape to stick off the corrosion products, the adhesive of the tape will remain on the surface of the formation foil, which will undoubtedly interfere with the subsequent observation of the surface of the formation foil and lead to deviation in the observation results.

[0005] The disclosure of the above background art content is only for assisting in understanding the inventive concept and technical solution of the present invention, and it does not necessarily belong to the prior art of this patent application. Without clear evidence indicating that the above content was publicly available on the filing date of this patent application, the above background art should not be used to evaluate the novelty and inventiveness of this application.

Summary of the Invention

[0006] The object of the present invention is to propose a sample preparation method for observing the surface morphology of medium and high voltage forming foils, so as to solve the technical problems in the above-mentioned prior art, such as the use of easily explosive chemicals, low safety factor, the adhesive residue affecting surface observation, and poor sample preparation effect.

[0007] To this end, the present invention adopts the following technical solutions:

[0008] A sample preparation method for observing the surface morphology of medium and high voltage forming foils, comprising the following steps:

[0009] S1. Cutting treatment: Cut the forming foil into rectangular strip samples;

[0010] S2. Grinding and polishing treatment: Press one end of the strip sample processed in step S1 firmly with one hand, and gently press the other end on the abrasive paper of a metallographic sample grinding and polishing machine, and grind and polish the forming foil for 3 - 5 seconds until the ground and polished surface shows a gray color with metallic luster;

[0011] S3. First ultrasonic cleaning: Put the strip sample polished in step S2 into an ultrasonic cleaning machine for cleaning for 4 - 6 minutes. After the cleaning time reaches, turn off the power of the ultrasonic cleaning machine, and use tweezers to take out the strip sample from the cleaning tank and place it on a clean filter paper to drain the water;

[0012] S4. Alkaline corrosion treatment: Pour the prepared alkaline corrosion solution into a clean plastic beaker, and the liquid level height should be able to completely immerse the strip sample; use tweezers to put the strip sample ultrasonically cleaned for the first time in step S3 into the alkaline corrosion solution to ensure that the strip sample is completely immersed in the solution; at room temperature, let the strip sample soak in the alkaline corrosion solution for 12 - 18 minutes;

[0013] S5. Second ultrasonic cleaning: Pour out the water in the cleaning tank of the ultrasonic cleaning machine and refill it with water; use tweezers to take out the strip sample treated by alkaline corrosion in step S4 from the corrosion solution and put it into the cleaning tank for ultrasonic cleaning; after the cleaning time ends, turn off the power of the cleaning machine, and use tweezers to take out the strip sample from the cleaning tank and place it on a clean filter paper to let it air dry;

[0014] S6. Scanning electron microscope observation: After the strip-shaped sample treated in step S5 and dried is sputter-coated with gold for 2 - 3 minutes, it is pasted onto the sample stage of the scanning electron microscope with conductive adhesive, ensuring that the sample is firmly fixed and in the correct position; observe the surface morphology of the strip-shaped sample.

[0015] Preferably, in step S1, the formed foil is cut into rectangular strip-shaped samples with a length of 3 - 6 cm and a width of 2 cm.

[0016] Preferably, in step S2, the abrasive paper of the metallographic sample grinding and polishing machine is 1000 - 2000 mesh, and the turntable speed is 100 - 200 r / min.

[0017] Preferably, in step S3, the power of the ultrasonic cleaning machine is 200 - 240 W.

[0018] Preferably, the components of the alkaline etching solution in step S4 include 1.2 - 1.8 g of potassium hydroxide, 1.7 - 2.3 g of sodium silicate, 0.05 - 0.1 g of polyvinylpyrrolidone, 2.8 - 3.2 g of potassium sodium tartrate, 1.0 - 1.5 g of EDTA disodium, 1.0 - 1.5 g of citric acid, and 95 - 105 mL of deionized water.

[0019] Preferably, the components of the alkaline etching solution in step S4 are specifically 1.5 g of potassium hydroxide, 2 g of sodium silicate, 0.08 g of polyvinylpyrrolidone, 3 g of potassium sodium tartrate, 1.2 g of EDTA disodium, 1.3 g of citric acid, and 100 mL of deionized water.

[0020] Preferably, the preparation method of the alkaline etching solution in step S4 is as follows:

[0021] a. Weigh potassium hydroxide and add it to a blender containing the measured deionized water, and stir until it is completely dissolved;

[0022] b. Weigh sodium silicate and polyvinylpyrrolidone, dry-mix polyvinylpyrrolidone and sodium silicate evenly, and add them to the above solution in small amounts and multiple times for reaction, while continuously stirring during the reaction; after all the mixture of sodium silicate and polyvinylpyrrolidone is added to the solution, keep the solution in a constant temperature water bath at 45 - 55 °C until sodium silicate is fully dissolved to form a uniform solution;

[0023] c. Weigh potassium sodium tartrate and EDTA disodium, first add potassium sodium tartrate and stir until it is dissolved, then add EDTA disodium. The stirring time after adding potassium sodium tartrate is 5 - 7 minutes until the solution is clear and transparent; the stirring time after adding EDTA disodium is 5 - 7 minutes until the solution is evenly mixed;

[0024] d. Weigh citric acid and add it in small portions while continuously stirring. Maintain the stirring speed in step c. After all the citric acid is added to the solution, stir for 3 - 5 min until the solution is homogeneous to obtain an alkaline etching solution.

[0025] Preferably, in the preparation method of the alkaline etching solution, the stirring speed in step a is set to 200 - 300 r / min and the stirring time is 3 - 5 min; the stirring speed in step b is set to 300 - 400 r / min and the stirring time is 10 - 15 min; the stirring speed in step c is set to 200 - 300 r / min.

[0026] Preferably, in the preparation method of the alkaline etching solution, the dissolution temperature in step a is controlled at ≤35°C; the reaction temperature in step b is controlled at 40 - 50°C; after adding disodium EDTA in step c, the reaction temperature is controlled at 55 - 65°C.

[0027] Preferably, in step S5, the power of the ultrasonic cleaner is 200 - 240 W and the cleaning time is 8 - 12 min.

[0028] The sample preparation method for observing the surface morphology of medium - high voltage formed foils provided by the present invention significantly improves the clarity of surface morphology observation and the integrity of the oxide film structure through the selection and synergistic effect of specific process parameters. The following is an explanation from the perspectives of technical principles and parameter necessity:

[0029] 1. Cutting treatment: Cut the formed foil into rectangular strip - shaped samples to provide samples of appropriate size for subsequent processing and observation, facilitating operation and fixation, and ensuring the consistency and representativeness of the samples.

[0030] 2. Grinding and polishing treatment: Use a metallographic sample grinding and polishing machine and abrasive paper to grind and polish the strip - shaped samples. Remove some impurities and oxide layers on the surface of the formed foil through mechanical friction, making the surface show a gray color with metallic luster. During this process, using abrasive paper with a mesh number of 1000 - 2000 can remove surface impurities and oxide layers while avoiding excessive wear that may cause damage to the microstructure. Below 1000 mesh may result in too deep scratches, and above 2000 mesh will be inefficient and difficult to expose the metal substrate. When the turntable speed is <100 r / min, the grinding and polishing efficiency is low and local overheating is likely to occur; when the speed is >200 r / min, the oxide film may be deformed due to frictional heat. Appropriate abrasive paper mesh number and turntable speed can effectively improve the surface flatness without damaging the internal structure of the formed foil, preparing for subsequent etching treatment and observation. After grinding and polishing, the exposure of the metal substrate provides a uniform reaction interface for the etching solution, avoiding uneven etching caused by surface unevenness.

[0031] 3. First ultrasonic cleaning: The ultrasonic cleaning machine utilizes the cavitation effect generated by high-frequency vibration to form numerous tiny bubbles in the cleaning liquid. These bubbles rupture when they come into contact with the surface of the strip sample, generating a powerful impact force that peels off the debris, impurities, etc. remaining during the grinding and polishing process from the surface of the strip sample and disperses them into the cleaning liquid, thereby achieving the purpose of cleaning. A power of 200 - 240W and a cleaning time of 4 - 6 minutes can ensure the cleaning effect while avoiding damage to the formed foil caused by over-cleaning.

[0032] 4. Alkaline corrosion treatment: Multiple components in the alkaline corrosion liquid act synergistically to perform corrosion treatment on the surface of the formed foil. Potassium hydroxide, as a strong alkaline corrosion agent, reacts with the aluminum matrix to form soluble potassium meta-aluminate. At the same time, the aluminum oxide film is relatively stable under alkaline conditions, thereby achieving selective corrosion of the aluminum matrix; sodium silicate, as a corrosion inhibitor, acts synergistically with potassium hydroxide and hydrolyzes to generate SiO3 2— to form a protective aluminum silicate layer with Al 3+ inhibiting the excessive dissolution of the oxide film. At the same time, the hydrolyzed SiO3 2— can complex with metal ions to form a protective aluminum silicate layer and improve the uniformity of corrosion; excessive potassium hydroxide will cause excessive corrosion of the matrix, and insufficient sodium silicate will cause the protective layer to fail. Polyvinylpyrrolidone, as a dispersant, has a dispersing and protecting effect, which can prevent the agglomeration and re-deposition of metal ions during the corrosion process, making the corrosion more uniform. Its role is to prevent the gelation of sodium silicate and stabilize the corrosion liquid. Too little dosage cannot inhibit agglomeration, and too much may hinder the reaction activity. Potassium sodium tartrate and EDTA disodium, as complexing agents, chelate the generated Al 3+ ions. Through complexation, they form stable complexes with metal ions, further promoting the dissolution of the aluminum matrix and inhibiting the re-deposition of metal ions, maintaining the continuity and uniformity of the corrosion reaction; potassium sodium tartrate preferentially complexes with Al 3+, EDTA disodium enhances chelation, while citric acid, as an environmentally friendly surfactant, can not only adjust the pH value of the solution, but also complex with metal ions to improve corrosion uniformity, reduce the environmental load at the same time. The three work together to ensure corrosion uniformity and avoid local over-corrosion. By precisely controlling the composition, concentration and reaction conditions of the etching solution, selective corrosion of the aluminum substrate is achieved while maintaining the integrity of the oxide film, so as to better observe the surface morphology of the etched foil. In the etching solution preparation process, stirring control and temperature control are also very important. The dry mixing pretreatment of sodium silicate and PVP in step b can avoid local gelation caused by direct addition, and the temperature-controlled stirring in stages ensures that each component is fully dissolved and functions: in step a, KOH is dissolved at a temperature ≤ 35 °C because low temperature can prevent the solution from splashing or the components from decomposing due to the violent heat release of KOH; in step b, sodium silicate is dissolved at 45 - 55 °C because heating can promote the hydrolysis of sodium silicate, and the dispersion effect of PVP is the best at this temperature; in step c, EDTA is added at 55 - 65 °C because high temperature enhances the complexing ability of EDTA, ensuring the stable complexation of metal ions and avoiding redeposition.

[0033] 5. Second ultrasonic cleaning: Once again, utilize the cavitation effect of the ultrasonic cleaner to remove the residual corrosion products and alkaline etching solution on the surface of the strip-shaped sample after alkaline corrosion treatment, ensure the surface is clean, and avoid the influence of residual substances on the SEM observation results. A power of 200 - 240 W and a cleaning time of 8 - 12 min can effectively remove residual impurities.

[0034] 6. SEM observation: After the processed strip-shaped sample is sputter-coated with gold for 2 - 3 min, it is pasted on the SEM sample stage with conductive adhesive. The surface of the sample is scanned by an electron beam to generate signals such as secondary electrons, so as to obtain a high-resolution surface morphology image for detailed observation and analysis of the microstructure of the etched foil surface.

[0035] The beneficial effects of the present invention compared with the prior art include:

[0036] 1. High safety: Compared with the traditional sample preparation method using highly explosive chemicals such as perchloric acid, the alkaline etching solution used in the present invention has relatively safe components, avoiding the risks of strong oxidizing properties, inflammability and explosiveness, reducing environmental hazards and operation risks, and reducing potential hazards to operators and the experimental environment.

[0037] 2. Good sample preparation effect: The optimized sample preparation steps and specially formulated alkaline etching solution achieve efficient selective corrosion of the aluminum substrate, while avoiding excessive dissolution of the oxide film, effectively avoiding excessive or insufficient local corrosion. Through the synergistic effect of multiple components, the redeposition of metal ions is reduced, ensuring that the observed surface morphology is more realistic and clear. At the same time, two ultrasonic cleanings can completely remove particle residues, ensure the accuracy and reliability of SEM observation results, improve the quality and accuracy of sample preparation, and facilitate in-depth research on the surface microstructure of chemical foil.

[0038] 3. Easy operation: The parameters of each step are clear, such as grinding and polishing time, cleaning time, ultrasonic power, corrosion liquid composition and reaction conditions, which have specific ranges and preferred values, making it easy for operators to operate according to standard procedures, reducing the difficulty of operation and improving the repeatability of the experiment.

[0039] 4. Strong environmental protection: Most of the ingredients in the alkaline corrosive solution are relatively environmentally friendly substances, and the entire sample preparation process does not involve chemicals that are harmful to the environment, which reduces the pollution of chemical waste to the environment and is in line with the concept of green chemistry.

[0040] 5. Wide adaptability: This sample preparation method can be applied to medium and high voltage formed foils of different specifications and characteristics. By adjusting some parameters (such as the proportion of etching liquid components, reaction time, etc.), it can meet diverse research needs and provide a reliable and universal sample preparation technology for scientific research and production in related fields.

Brief Description of the Drawings

[0041] Figure 1 This is the surface morphology of the untreated chemically formed foil.

[0042] Figure 2 This is the surface morphology of the chemically formed foil observed in Example 1 of the present invention.

[0043] Figure 3 This is the surface morphology of the chemically formed foil observed in Example 2 of the present invention.

[0044] Figure 4 This is the surface morphology of the chemically formed foil observed in Example 3 of the present invention. [Specific implementation method]

[0045] The features and technical advantages of the present invention have been broadly described above so as to better understand the detailed description of the present invention. Other features and advantages of the present invention will be described below. Those skilled in the art should understand that the disclosed concepts and specific embodiments can be easily used as a basis to modify or design other structures to achieve the same purpose of the present invention. Those skilled in the art should also recognize that such equivalent configurations do not deviate from the spirit and scope of the present invention. The novel features considered to be the characteristics of the present invention, its structural and operational methods, as well as further purposes and advantages, will be better understood from the following description in conjunction with the accompanying drawings. However, it should be deeply understood that each feature provided is only for description and illustration, and is not intended to limit the definition of the present invention.

[0046] Example 1

[0047] A sample preparation method for observing the surface morphology of medium and high voltage formed foils, comprising the following steps:

[0048] S1. Cutting treatment: Cut the formed foil into a rectangular strip with a length of 4 cm and a width of 2 cm. The surface morphology diagram of the untreated formed foil is shown in Figure 1 ;

[0049] S2. Grinding and polishing treatment: Press one end of the strip sample processed by step S1 with one hand, and gently press the other end on the 2000-mesh abrasive paper of the metallographic sample grinding and polishing machine. The turntable speed is 200 r / min, and grind and polish the formed foil for 3 seconds until the ground and polished surface presents a gray color with metallic luster;

[0050] S3. First ultrasonic cleaning: Put the strip sample ground and polished by step S2 into an ultrasonic cleaning machine and clean it for 5 min. The power of the ultrasonic cleaning machine is 240 W. After the cleaning time reaches, turn off the power of the ultrasonic cleaning machine, and use tweezers to take out the strip sample from the cleaning tank and place it on a clean filter paper to drain the water;

[0051] S4. Alkaline corrosion treatment: Pour the prepared alkaline corrosion solution into a clean plastic beaker, and the liquid level height should be able to completely immerse the strip sample; use tweezers to put the strip sample ultrasonically cleaned for the first time in step S3 into the alkaline corrosion solution to ensure that the strip sample is completely immersed in the solution; in a normal temperature environment, let the strip sample soak in the alkaline corrosion solution for 15 min;

[0052] S5. Second ultrasonic cleaning: Pour out the water in the cleaning tank of the ultrasonic cleaning machine and refill it with water; use tweezers to take out the strip sample treated by alkaline corrosion in step S4 from the corrosion solution and put it into the cleaning tank for ultrasonic cleaning; the power of the cleaning machine is 240 W and the cleaning time is 10 min; after the cleaning time ends, turn off the power of the cleaning machine, use tweezers to take out the strip sample from the cleaning tank and place it on a clean filter paper to let it air dry;

[0053] S6. Scanning electron microscope observation: After the strip samples processed in step S5 and dried are sputter-coated with gold for 2 - 3 minutes, they are pasted onto the sample stage of the scanning electron microscope with conductive glue, ensuring that the samples are firmly fixed and in the correct position; observe the surface morphology of the strip samples.

[0054] The specific components of the alkaline etching solution in step S4 are 1.5 g of potassium hydroxide, 2 g of sodium silicate, 0.08 g of polyvinylpyrrolidone, 3 g of potassium sodium tartrate, 1.2 g of EDTA disodium, 1.3 g of citric acid, and 100 mL of deionized water. The preparation method of the alkaline etching solution is as follows:

[0055] a. Weigh potassium hydroxide and add it to a blender containing the measured deionized water and stir until completely dissolved; set the stirring speed at 250 r / min and the stirring time at 4 min; control the dissolution temperature at ≤ 35 °C;

[0056] b. Weigh sodium silicate and polyvinylpyrrolidone, dry-mix polyvinylpyrrolidone and sodium silicate evenly, and add them to the above solution in small amounts and multiple times for reaction. Control the reaction temperature at 45 °C and keep stirring during the reaction; set the rotation speed at 350 r / min and the stirring time at 15 min; after all the mixture of sodium silicate and polyvinylpyrrolidone is added to the solution, keep the solution in a constant temperature water bath at 50 °C until the sodium silicate is fully dissolved to form a uniform solution;

[0057] c. Weigh potassium sodium tartrate and EDTA disodium. First, add potassium sodium tartrate and stir until dissolved, then add EDTA disodium. The stirring time after adding potassium sodium tartrate is 6 min until the solution is clear and transparent; the stirring time after adding EDTA disodium is 7 min, and control the reaction temperature at 60 °C until the solution is mixed evenly; set the stirring speed at 280 r / min;

[0058] d. Weigh citric acid, add it in small amounts and multiple times and keep stirring, maintaining the stirring speed in step c. After all the citric acid is added to the solution, stir for 5 min until the solution is uniform to obtain the alkaline etching solution.

[0059] The observed surface morphology diagram of the formed foil is shown in Figure 2The following features can be observed from the figure: The surface of the etched foil presents a complex three-dimensional network structure, which consists of a large number of interlaced and irregularly shaped holes and the oxide film around the holes. These holes vary in size and are relatively evenly distributed, and the thickness of the oxide film is also relatively uniform. The contour of the microstructure is clear, indicating that the etching treatment is relatively uniform without local over-etching or under-etching. This uniform etching effect helps to better reveal the true microstructure of the etched foil, facilitating the analysis of its performance and quality. It can be seen that the sample preparation method of the present invention, from steps such as cutting, grinding and polishing, cleaning to alkaline etching treatment, can effectively reveal the surface microstructure of medium and high voltage etched foils. The special composition and preparation conditions of the alkaline etching solution, as well as the precisely controlled parameters of each step, enable the surface of the etched foil to be uniformly etched, obtaining clear and representative microstructure images, providing a reliable basis for in-depth research on the performance and quality of medium and high voltage etched foils.

[0060] Example 2

[0061] A sample preparation method for observing the surface morphology of medium and high voltage etched foils, comprising the following steps:

[0062] S1. Cutting treatment: Cut the etched foil into a rectangular strip sample with a length of 5 cm and a width of 2 cm.

[0063] S2. Grinding and polishing treatment: Press one end of the strip sample processed in step S1 firmly with one hand, and gently press the other end on the 1800-mesh abrasive paper of the metallographic sample grinding and polishing machine. The turntable speed is 180 r / min, and grind and polish the etched foil for 4 seconds until the ground and polished surface shows a gray color with metallic luster.

[0064] S3. First ultrasonic cleaning: Put the strip sample ground and polished in step S2 into an ultrasonic cleaning machine and clean it for 5 min. The power of the ultrasonic cleaning machine is 220 W. After the cleaning time reaches, turn off the power of the ultrasonic cleaning machine, take out the strip sample from the cleaning tank with tweezers, and place it on a clean filter paper to drain the water.

[0065] S4. Alkaline etching treatment: Pour the prepared alkaline etching solution into a clean plastic beaker, and the liquid level height should be able to completely immerse the strip sample; use tweezers to put the strip sample ultrasonically cleaned for the first time in step S3 into the alkaline etching solution to ensure that the strip sample is completely immersed in the solution; in a normal temperature environment, let the strip sample soak in the alkaline etching solution for 15 min.

[0066] S5. Second ultrasonic cleaning: Drain the water in the cleaning tank of the ultrasonic cleaner and refill it with water; Use tweezers to take out the strip-shaped sample that has undergone the alkaline corrosion treatment in step S4 from the corrosion solution and put it into the cleaning tank for ultrasonic cleaning; The power of the cleaner is 220W and the cleaning time is 10 minutes; After the cleaning time ends, turn off the power of the cleaner, use tweezers to take out the strip-shaped sample from the cleaning tank, place it on a clean filter paper, and let it air dry;

[0067] S6. Scanning electron microscope observation: After spraying gold on the strip-shaped sample that has been processed and dried in step S5 for 2 - 3 minutes, paste it on the sample stage of the scanning electron microscope with conductive glue, ensuring that the sample is firmly fixed and in the correct position; Observe the surface morphology of the strip-shaped sample.

[0068] The composition and preparation method of the alkaline corrosion solution in step S4 are the same as those in Example 1.

[0069] The observed surface morphology diagram of the formed foil is shown in Figure 3 . It can be observed from the figure that the surface of the medium - high voltage formed foil presents a three - dimensional network structure, which is composed of a large number of intersecting and irregularly shaped holes and an oxide film with a uniform thickness around. The overall pore density fluctuates little, indicating that the corrosion process has a high degree of uniformity. This uniform corrosion effect ensures that the microscopic structure of the formed foil surface can be truly presented.

[0070] Example 3

[0071] A sample preparation method for observing the surface morphology of medium - high voltage formed foil, including the following steps:

[0072] S1. Cutting treatment: Cut the formed foil into a rectangular strip - shaped sample with a length of 3 cm and a width of 2 cm;

[0073] S2. Grinding and polishing treatment: Press one end of the strip - shaped sample that has been cut in step S1 firmly with one hand, and gently press the other end on the 1500 - mesh abrasive paper of the metallographic sample grinding and polishing machine. The turntable speed is 150 r / min, and grind and polish the formed foil for 5 seconds until the ground and polished surface shows a gray color with metallic luster;

[0074] S3. First ultrasonic cleaning: Put the strip - shaped sample that has been ground and polished in step S2 into the ultrasonic cleaner for cleaning for 6 minutes. The power of the ultrasonic cleaner is 200W. After the cleaning time reaches, turn off the power of the ultrasonic cleaner, use tweezers to take out the strip - shaped sample from the cleaning tank, and place it on a clean filter paper to drain the water;

[0075] S4. Alkaline corrosion treatment: Pour the prepared alkaline corrosion solution into a clean plastic beaker, and the liquid level height should be able to completely immerse the strip - shaped sample; Use tweezers to put the strip - shaped sample that has been first ultrasonically cleaned in step S3 into the alkaline corrosion solution, ensuring that the strip - shaped sample is completely immersed in the solution; At room temperature, let the strip - shaped sample soak in the alkaline corrosion solution for 15 minutes;

[0076] S5. Second ultrasonic cleaning: Drain the water in the cleaning tank of the ultrasonic cleaner and refill it with water; Use tweezers to take out the strip-shaped sample that has undergone the alkaline corrosion treatment in step S4 from the corrosion solution and place it in the cleaning tank for ultrasonic cleaning; The power of the cleaner is 200W and the cleaning time is 12 minutes; After the cleaning time ends, turn off the power of the cleaner, use tweezers to take out the strip-shaped sample from the cleaning tank, place it on a clean filter paper, and let it air dry;

[0077] S6. Scanning electron microscope observation: After the strip-shaped sample that has been processed and dried in step S5 is sputter-coated with gold for 2 - 3 minutes, it is pasted on the sample stage of the scanning electron microscope with conductive glue to ensure that the sample is firmly fixed and in the correct position; Observe the surface morphology of the strip-shaped sample.

[0078] The composition and preparation method of the alkaline corrosion solution in step S4 are the same as those in Example 1.

[0079] The observed surface morphology diagram of the formed foil is shown in Figure 4 . It can be clearly observed from the figure that the surface of the medium-high voltage formed foil presents a multi-level pore composite structure, and a three-dimensional network system composed of nano- to micron-scale pore channels intertwined is formed on the material surface. The main pore channels are distributed in irregular polygons, and fractal branch structures can be seen in some areas. The microscopic structure has clear contours, indicating that the corrosion treatment is uniform without over-corrosion or under-corrosion, ensuring the accurate presentation of the true microscopic structure of the formed foil. This ideal effect benefits from the sample preparation method of the present invention. From ensuring the consistency of the samples during cutting, to removing impurities by grinding and polishing, to precisely controlling the cleaning and alkaline corrosion parameters, as well as the reasonable composition and preparation conditions of the special alkaline corrosion solution, each step is closely coordinated, enabling the surface of the formed foil to be uniformly corroded, obtaining a clear and representative microscopic structure image, providing a reliable basis for in-depth research on its performance and quality.

[0080] Those skilled in the art will recognize that numerous variations to the above description are possible, so the embodiments are merely used to describe one or more specific embodiments. The above-described embodiments are only a description of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a sample for observing the surface morphology of a medium- and high-pressure electrochemically formed foil, characterized in that: The following steps are involved: S1. Cutting process: Cut the formed foil into rectangular strips; S2. Grinding and polishing: Press one end of the strip sample cut in step S1 with one hand, and gently press the other end on the sandpaper of the metallographic sample grinding and polishing machine with one hand, and grind and polish the foil for 3-5 seconds until the polished surface presents a gray color with a metallic luster; S3. First ultrasonic cleaning: Put the strip sample after polishing in step S2 into an ultrasonic cleaning machine for 4-6min. After the cleaning time is reached, turn off the power of the ultrasonic cleaning machine, remove the strip sample from the cleaning tank with tweezers, and place it on a clean filter paper to drain the water; S4. Alkaline corrosion treatment: Pour the prepared alkaline corrosion solution into a clean plastic beaker, and the liquid level should be high enough to completely immerse the strip sample; use tweezers to place the strip sample that has been ultrasonically cleaned for the first time in step S3 into the alkaline corrosion solution, ensuring that the strip sample is completely immersed in the solution; at room temperature, let the strip sample soak in the alkaline corrosion solution for 12-18 minutes; S5. Second ultrasonic cleaning: pour out the water in the ultrasonic cleaning tank and add water again; use tweezers to remove the strip sample treated with alkaline corrosion in step S4 from the corrosion solution and put it into the cleaning tank for ultrasonic cleaning; after the cleaning time is over, turn off the power of the cleaning machine, use tweezers to remove the strip sample from the cleaning tank, place it on a clean filter paper, and let it air dry; S6. Scanning electron microscope observation: After the strip sample processed and dried in step S5 is sprayed with gold for 2-3 minutes, it is pasted on the sample stage of the scanning electron microscope with conductive glue to ensure that the sample is firmly fixed and correctly positioned; the surface morphology of the strip sample is observed.

2. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 1, characterized in that: In the step S1, the formed foil is cut into rectangular strips with a length of 3-6 cm and a width of 2 cm.

3. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 1, characterized in that: In the step S2, the sandpaper of the metallographic sample grinding and polishing machine is 1000-2000 mesh, and the turntable speed is 100-200r / min.

4. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 1, characterized in that: The power of the ultrasonic cleaning machine in step S3 is 200-240W.

5. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 1, characterized in that: The components of the alkaline etching solution in step S4 include 1.2-1.8 g potassium hydroxide, 1.7-2.3 g sodium silicate, 0.05-0.1 g polyvinyl pyrrolidone, 2.8-3.2 g potassium sodium tartrate, 1.0-1.5 g EDTA-disodium, 1.0-1.5 g citric acid, and 95-105 mL deionized water.

6. A method for preparing a sample for observing the surface morphology of a medium- and high-pressure chemically formed foil according to claim 1, characterized in that: The components of the alkaline etching solution in step S4 are specifically 1.5 g potassium hydroxide, 2 g sodium silicate, 0.08 g polyvinyl pyrrolidone, 3 g potassium sodium tartrate, 1.2 g EDTA-disodium, 1.3 g citric acid, and 100 mL deionized water.

7. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 5 or 6, characterized in that: The preparation method of the alkaline etching solution is as follows: a. Weigh potassium hydroxide and add it to a blender filled with deionized water and stir until completely dissolved; b. Weigh sodium silicate and polyvinyl pyrrolidone, dry-mix polyvinyl pyrrolidone and sodium silicate, add small amounts and multiple times to the above solution for reaction, and stir continuously during the reaction; after all the mixture of sodium silicate and polyvinyl pyrrolidone is added to the solution, place the solution in a constant temperature water bath maintained at 45-55°C until the mixture is fully dissolved to form a uniform solution; c. Weigh potassium sodium tartrate and disodium EDTA, first add potassium sodium tartrate and stir to dissolve, then add disodium EDTA, stir for 5-7 minutes after adding potassium sodium tartrate, until the solution is uniform; stir for 5-7 minutes after adding disodium EDTA, until the solution is uniform; d. Weigh citric acid, add it in small amounts several times and continue stirring, maintain the stirring speed of step c, and stir for 3-5 minutes until all the citric acid is added to the solution until the solution is uniform to obtain an alkaline etching solution.

8. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 7, characterized in that: In the preparation method of the alkaline corrosive solution, the stirring speed of step a is set to 200-300 r / min, and the stirring time is 3-5 min; the stirring speed of step b is set to 300-400 r / min, and the stirring time is 10-15 min; and the stirring speed of step c is set to 200-300 r / min.

9. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 7, characterized in that: In the preparation method of the alkaline etching solution, step a controls the dissolution temperature to be ≤35° C.; step b controls the reaction temperature to be 40-50° C.; and step c controls the reaction temperature to be 55-65° C. after adding disodium EDTA.

10. A sample preparation method for observing the surface morphology of medium- and high-pressure chemically formed foil according to claim 1, characterized in that: In step S5, the power of the ultrasonic cleaning machine is 200-240W, and the cleaning time is 8-12 minutes.

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