Reagent and method for expanding electrical steel extraction replicated carbon film

Abstract

The invention discloses a reagent and a method for unfolding an electrical steel extraction replica carbon film, and belongs to the field of metal material sample preparation. The carbon film developing reagent is composed of absolute ethyl alcohol and deionized water, the absolute ethyl alcohol accounts for 2%-10% by volume, and the deionized water accounts for 90%-98% by volume. The surface tension of the carbon film developing reagent meets the requirement that the carbon film is fully developed while the carbon film is kept complete, a sample is not polluted, and two-phase particles are not dissolved.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of metal material specimens, and particularly relates to a method for preparing an extraction carbon replica sample for a transmission electron microscope of a metal material. Background Art

[0002] Electrical steel (mainly including grain-oriented silicon steel and non-grain-oriented silicon steel) is mainly used for making the iron cores of various motors and transformers, and plays an irreplaceable important role in the fields of electric power, electronics and mechanical industries. It is an energy-saving material with the largest output and consumption in the field of magnetic alloys. Common precipitation phases in electrical steel include MnS, AlN, Cu2S, SiO2, and composite precipitation of multiple elements, etc. These precipitations are usually between a few nanometers and a few hundred nanometers, and the complete morphology and distribution can only be observed with the aid of a transmission electron microscope. To successfully observe the precipitation of two-phase particles in electrical steel, the primary task is to prepare a "qualified" electron microscope sample. Generally, there are mainly two types of samples for electron microscope observation: extraction carbon replica samples and metal thin film samples. When using metal thin film samples to observe two-phase particles in steel, it is mainly limited by the thin area of the sample. When the thin area is good, the observable area is a ring with a radius of dozens of micrometers, and when it is bad, it is only a few micrometers. Secondly, dislocations, grain boundaries and extinction fringes in the steel will all affect the observation and statistics of two-phase particles. Therefore, many researchers prefer to use extraction carbon replicas to statistically analyze the size and distribution of two-phase particles in steel.

[0003] The extraction carbon replica can not only show the surface relief of the sample, but also extract some fine constituent phases, such as second-phase particles, with a carbon film, and can maintain their original distribution in the sample. Its greatest advantage is that in addition to being able to observe the size, morphology and distribution of these small particles under a transmission electron microscope, their phases can also be determined by electron diffraction. The specific preparation method is as follows: ① Select a suitable etchant so that it dissolves the matrix material of the sample (such as the ferrite matrix in steel) faster than the second-phase particles, so that these particles protrude from the surface of the sample; ② On the surface of the deeply etched metallographic specimen, evaporate and deposit a carbon film with a certain thickness (about 20 nm), and then use a needle tip or a small knife to scratch the carbon film into small squares smaller than the sample copper mesh; ③ Place the specimen with carbon spraying and scratched grids into a container containing the etchant for secondary etching (or electrolytic polishing) to further dissolve the matrix material, so that the carbon film together with the second-phase particles protruding from the surface of the specimen is separated from the matrix; ④ Transfer the separated carbon film to a certain chemical reagent for washing to dissolve the remaining matrix, and finally transfer it to alcohol for washing, pick it up with a sample copper mesh, and dry it for observation. After the carbon film is washed clean in the fourth step, it needs to be picked up with a copper mesh. Before picking up with the copper mesh, the carbon film needs to be fully unfolded without any wrinkles. However, in the actual experiment, the carbon film usually curls up in alcohol. How to fully unfold the carbon film and keep its shape intact has become a difficult problem that troubles people.

[0004] After separation from the substrate, the carbon film of the carbon replica extracted from electrical steel often curls together and exhibits poor integrity. Some researchers place the film in a beaker of tap water, using the water's surface tension to fully unfold the carbon film. However, excessive tension causes the film to become fragmented, severely damaging its integrity. To fully unfold and maintain the integrity of the carbon film, a suitable developing reagent is needed that does not contaminate the sample, exhibits low surface tension, or corrode the dissolved secondary particles. Summary of the Invention

[0005] The present invention aims to provide a carbon film developing reagent and a sample preparation method for carbon replica extraction of electrical steel by transmission electron microscopy. The surface tension of the carbon film developing reagent satisfies the requirement of fully developing the carbon film while keeping the carbon film intact, without contaminating the sample or dissolving the two-phase particles.

[0006] A reagent for developing an electrical steel extraction replica carbon film consists of anhydrous ethanol and deionized water, wherein the anhydrous ethanol accounts for 2%-10% and the deionized water accounts for 90%-98% by volume, preferably the anhydrous ethanol accounts for 2%-8% and the deionized water accounts for 92%-98%.

[0007] A method for developing a replica carbon film extracted from electrical steel, which utilizes the above reagent to develop the carbon film.

[0008] A method for preparing a carbon replica sample of electrical steel extracted by transmission electron microscopy comprises the following steps:

[0009] Step 1: Mechanically grind the electrical steel sample and mechanically polish it until there are no scratches on the surface, and clean the polishing paste;

[0010] Step 2: Immerse the polished surface of the sample in a 2-6% (volume percentage) nitric acid alcohol (anhydrous ethanol) solution and etch until the sample surface changes color, that is, the metallographic structure can be vaguely seen. Quickly clean the etching solution on the sample surface with anhydrous ethanol and blow it dry, then place it in the sample box;

[0011] Step 3: Place the sample in the sample chamber of the high vacuum coater and evacuate to 8×10 -5 mba or above, evaporate a carbon film with a thickness of about 10-20nm on the surface of the sample, release the vacuum and take out the sample;

[0012] Step 4: Scratch off the carbon film around the edges of the sample. Use a blade to carve small squares of about 2mm-3mm in length and width on the sample coating surface. Then immerse the sample in a nitric acid solution with a concentration of about 8-12% (volume percentage) until the carbon film peels off.

[0013] Step 5: After the carbon film falls off, remove it with a grid and place it in anhydrous ethanol to wash off the nitric acid solution on the carbon film until the anhydrous ethanol becomes colorless.

[0014] Step 6: Prepare the carbon film developing reagent using the above developing reagent ingredients. To ensure the integrity and density of the carbon film, it is necessary to prepare reagents with different surface tensions. The reagents are composed of anhydrous ethanol and deionized water. The surface tension coefficient of water at 293K is 72.75×10 -3 N·m -1 , anhydrous ethanol is 22.32×10 -3 N·m -1 . The experiment found that the surface tension of deionized water was too large, causing the carbon film to easily break into a large number of small pieces, and the tension of anhydrous ethanol was too small, so the carbon film was curled up and could not be fully unfolded. After adding a small amount of anhydrous ethanol to deionized water, the tension of the mixed solution was slightly smaller than that of the aqueous solution. Under the appropriate solution ratio, the carbon film was completely unfolded and the carbon film was intact. In terms of volume percentage, the proportion of anhydrous ethanol in the mixed reagent is between 2% and 10%, and the proportion of deionized water is between 90% and 98%. If the proportion of anhydrous ethanol is too low, the tension of the mixed reagent is too large, which will cause the carbon film to break. If the proportion of anhydrous ethanol is too high, the tension of the mixed reagent is insufficient, and the carbon film cannot be fully unfolded.

[0015] Step 7: Use a grid to transfer the carbon film to a carefully tempered carbon film developing reagent. Once the carbon film is fully developed, scoop it up with a copper mesh and place it on clean filter paper. The carbon film will adhere tightly to the copper mesh. Dry the copper mesh under a 100W infrared lamp. This completes the preparation of the extracted carbon replica sample.

[0016] Furthermore, in step 1, the sample is cut into small pieces of (5-20 mm) × (5-20 mm), mounted with the surface facing down using a mounting machine, and the sample is mechanically ground using 180-240#, 400-600#, and 800-1200# sandpaper in sequence, and mechanically polished until there are no scratches on the surface, and the polishing paste is cleaned.

[0017] Furthermore, in step 2, the polished surface of the sample is immersed in a 2-6% (volume percentage) nitric acid alcohol (anhydrous ethanol) solution and corroded for 30-90 seconds until the surface of the sample changes color, and the metallographic structure can be vaguely seen.

[0018] Furthermore, in step 4, the carbon film and the inlay around the edges of the sample are cut apart, and a blade is used to carve small squares of about 2 mm to 3 mm in length and width on the sample coating surface.

[0019] Furthermore, in step 4, the sample is immersed in an 8-12% by volume nitric acid anhydrous ethanol solution for 5-20 minutes until the carbon film peels off.

[0020] Further, in step 5, after the carbon film falls off, pick up the carbon film with a grid and put it into a weighing bottle filled with anhydrous ethanol to wash off the nitric acid alcohol solution on the carbon film. Usually, the carbon film needs to be washed with anhydrous ethanol more than twice until the anhydrous ethanol in the weighing bottle shows colorless, then cover the bottle cap and store it.

[0021] Further, in step 7, pick up the carbon film with a Φ3mm copper mesh and place it on a clean filter paper.

[0022] Further, in step 7, bake the copper mesh under an infrared baking lamp with a power of 50 - 200W for about 30 seconds to 1 minute until the sample is dried.

[0023] Further, the electrical steel includes grain-oriented silicon steel or non-oriented silicon steel.

[0024] Advantages of the present invention:

[0025] (1) The carbon film unfolding reagent of the present invention can fully unfold the carbon film without wrinkles;

[0026] (2) The integrity and adhesion of the carbon film are good. After being picked up by the copper mesh and dried, it is not easy to fall off from the copper mesh and does not contaminate the transmission electron microscope sample chamber;

[0027] (3) The carbon film unfolding reagent is composed of anhydrous ethanol and deionized water. After baking and volatilization, there are no residual elements, it does not contaminate the sample, has no acidity or alkalinity, and does not dissolve the two-phase particles;

[0028] (4) The method for preparing the extraction carbon replica sample is simple and easy to operate, and has strong practicability. Description of the drawings

[0029] Figure 1 It is a diagram of the carbon film stored in the weighing bottle;

[0030] Figure 2 It is an effect diagram of the carbon film put into a mixed solution of 3% alcohol and 97% deionized water;

[0031] Figure 3 It is an effect diagram of the carbon film put into 100% deionized water;

[0032] Figure 4 It is an effect diagram of the carbon film put into a mixed solution of 15% alcohol and 85% deionized water;

[0033] Figure 5 It is an effect diagram of the complete carbon film tightly attached to the copper mesh. Detailed implementation manners

[0034] The following further illustrates the detailed implementation manners of the present invention in conjunction with the embodiments.

[0035] Example 1: Taking non-oriented silicon steel as an example, illustrate the method for preparing the extraction carbon replica sample of electrical steel.

[0036] 1) Cut the non-oriented silicon steel 35ADG1800 sample into small pieces of 10 mm × 10 mm, mount them well with a mounting machine with the surface facing downwards, mechanically grind the samples successively with 200#, 500#, and 800# sandpapers, and mechanically polish them until there are no scratches on the surface, then clean the polishing paste thoroughly;

[0037] 2) Immerse the polished surface of the sample in a nitric acid alcohol solution with a concentration (volume percentage) of 4% for about 40 seconds. The metallographic structure can be faintly seen on the surface of the sample. Quickly clean the etching solution on the surface of the sample with absolute ethanol and dry it with a hair dryer, then place it in a sample box;

[0038] 3) Place the sample in the sample chamber of a Leica ACE600 high-vacuum coating instrument, evacuate to 5 × 10 -5 mbar, evaporate a carbon film with a thickness of about 15 nm on the surface of the sample, and take out the sample after releasing the vacuum;

[0039] 4) Cut the carbon film at the edges of the sample from the mounting material, scratch small squares with a length and width of about 2 mm - 3 mm on the coated surface of the sample with a blade, and then immerse the sample in nitric acid alcohol with a concentration (volume percentage) of about 10% for about 10 minutes until the carbon film peels off;

[0040] 5) After the carbon film peels off, fish out the carbon film with a carrier grid and put it into a weighing bottle filled with absolute ethanol, wash the nitric acid alcohol on the carbon film. Usually, the carbon film needs to be washed with absolute ethanol more than twice until the absolute ethanol in the weighing bottle shows colorless, then cover the bottle cap and store it (as Figure 1 shown), and the carbon film is mostly curled;

[0041] 6) Transfer the carbon film with a carrier grid to a mixed solution of 3% alcohol and 97% deionized water by volume (as Figure 2 shown). After the carbon film unfolds fully, fish up the carbon film with a Φ3 mm copper mesh and place it on a clean filter paper. The carbon film will adhere tightly to the copper mesh. Bake the copper mesh under an infrared baking lamp with a power of 100 W for about 1 minute until the sample is dried, and the preparation of the non-oriented silicon steel extraction carbon replica sample is completed (as Figure 5 shown), and the complete carbon film adheres tightly to the copper mesh.

[0042] Comparative Example 1

[0043] In step 6) of Example 1, transfer the carbon film prepared in step 5) with a carrier grid to a 100% deionized water solution. The carbon film breaks due to excessive solution tension (as Figure 3 shown).

[0044] Comparative Example 2

[0045] In Step 6) of Example 1, the carbon film prepared in Step 5) was transferred to a mixed solution of 15% alcohol and 85% deionized water by means of a support grid. The carbon film could not be fully unfolded due to insufficient tension of the mixed solution (as Figure 4 shown).

[0046] Example 2: Taking grain-oriented electrical steel as an example to illustrate the preparation method of an extraction carbon replica sample of electrical steel.

[0047] 1) Cut the grain-oriented electrical steel 27AG100 sample into small pieces of 15 mm × 15 mm, mount it with a mounting machine with the surface facing down, and mechanically grind the sample successively with 200#, 500#, and 800# sandpapers, and mechanically polish it until there are no scratches on the surface. Clean the polishing paste;

[0048] 2) Immerse the polished surface of the sample in a nitric acid alcohol solution with a concentration (volume percentage) of 4% for about 40 seconds. The metallographic structure can be faintly seen on the surface of the sample. Quickly clean the etching solution on the surface of the sample with absolute ethanol and blow it dry with a hair dryer, and place it in a sample box;

[0049] 3) Place the sample in the sample chamber of a Leica ACE600 high-vacuum coating instrument, evacuate to 5×10 -5 mbar, evaporate a carbon film with a thickness of about 15 nm on the surface of the sample, and take out the sample after releasing the vacuum;

[0050] 4) Cut the carbon film at the edges of the sample, use a blade to scratch small squares with a length and width of about 2 mm - 3 mm on the coated surface of the sample, and then immerse the sample in a nitric acid alcohol with a concentration (volume percentage) of about 10% for about 10 minutes until the carbon film peels off;

[0051] 5) After the carbon film peels off, use a support grid to fish out the carbon film and put it into a weighing bottle filled with absolute ethanol, and wash the nitric acid alcohol on the carbon film. Usually, the carbon film needs to be washed with absolute ethanol more than twice until the absolute ethanol in the weighing bottle shows colorless. Cover the bottle cap and store it;

[0052] 6) Transfer the carbon film to a mixed solution of 5% alcohol and 95% deionized water by means of a support grid. After the carbon film is fully unfolded, use a Φ3 mm copper grid to fish out the carbon film and place it on a clean filter paper. The carbon film will adhere tightly to the copper grid. Place the copper grid under an infrared baking lamp with a power of 100 W and bake it for about 1 minute. The sample is dried, and the preparation of the extraction carbon replica sample of grain-oriented electrical steel is completed.

[0053] Example 3: Taking ultra-high magnetic induction non-oriented electrical steel as an example to illustrate the preparation method of an extraction carbon replica sample of electrical steel.

[0054] 1) Cut the non-oriented electrical steel 50W1000 sample into small pieces of 12 mm × 12 mm. Fix the samples with the surface facing down using an embedding machine. Mechanically grind the samples successively with 240#, 600#, and 1000# sandpapers, and mechanically polish until there are no scratches on the surface. Clean the polishing paste thoroughly.

[0055] 2) Immerse the polished surface of the sample in a 5% (by volume) nitric acid alcohol solution for about 50 seconds. The metallographic structure can be faintly seen on the surface of the sample. Quickly clean the etching solution on the surface of the sample with absolute ethanol and dry it with a hair dryer. Place it in a sample box.

[0056] 3) Place the sample in the sample chamber of a Leica ACE600 high-vacuum coating instrument. Evacuate to 7 × 10 -5 mbar, and evaporate a carbon film with a thickness of about 12 nm on the surface of the sample. Take out the sample after releasing the vacuum.

[0057] 4) Cut the carbon film at the edges of the sample away from the embedding material. Use a blade to scratch small squares with a length and width of about 2 mm - 3 mm on the coated surface of the sample. Then immerse the sample in a nitric acid alcohol solution with a concentration of about 9% (by volume) for about 15 minutes until the carbon film peels off.

[0058] 5) After the carbon film peels off, use a support grid to fish out the carbon film and put it into a weighing bottle filled with absolute ethanol. Wash the nitric acid alcohol on the carbon film. Usually, the carbon film needs to be washed with absolute ethanol more than twice until the absolute ethanol in the weighing bottle shows colorless. Cover the bottle cap and store it.

[0059] 6) Transfer the carbon film to a mixed solution of 4% (by volume) alcohol and 96% deionized water using a support grid. After the carbon film is fully unfolded, use a Φ3 mm copper mesh to fish out the carbon film and place it on a clean filter paper. The carbon film will adhere tightly to the copper mesh. Bake the copper mesh under an infrared baking lamp with a power of 100 W for about 40 seconds until the sample is dried. The preparation of the extraction carbon replica sample of the ultra-high magnetic induction non-oriented electrical steel is completed.

Claims

1. A reagent for developing the extraction replica carbon film of electrical steel, characterized in that, It is composed of absolute ethanol and deionized water. By volume percentage, the proportion of absolute ethanol is 2%-10%, and the proportion of deionized water is 90%-98%.

2. A method for unfolding the extraction replica carbon film of electrical steel, characterized in that, Use the reagent described in claim 1 to develop the carbon film.

3. A method for preparing a transmission electron microscope extraction carbon replica sample of electrical steel, characterized in that, It includes the following steps: Step 1: Mechanically grind the electrical steel sample and mechanically polish it until the surface has no scratches. Step 2: Immerse the polished surface of the sample in a nitric acid absolute ethanol solution with a volume percentage of 2-6%, and corrode it until the surface of the sample changes color, that is, the metallographic structure can be seen. Clean the corrosion solution on the surface of the sample with absolute ethanol and dry it. Step 3: Place the sample in the sample chamber of a high-vacuum coating instrument, evacuate the vacuum to 8×10 -5 mbar or above, evaporate a carbon film with a thickness of 10 - 20 nm on the surface of the sample, and take out the sample after releasing the vacuum; Step 4: Scratch off the carbon film on the four edges of the sample, use a blade to scratch squares on the coated surface of the sample, and then immerse the sample in a nitric acid absolute ethanol solution with a volume percentage of 8-12% until the carbon film peels off. Step 5: After the carbon film peels off, use a carrier grid to fish out the carbon film and put it into absolute ethanol for cleaning until the absolute ethanol shows colorless. Step 6: Prepare the carbon film developing reagent: Prepare the reagent according to the composition described in claim 1. Step 7: Use a carrier grid to transfer the carbon film into the carbon film developing reagent. After the carbon film is fully developed, use a copper mesh to fish out the carbon film and place it on a clean filter paper. Place the copper mesh under an infrared baking lamp to dry it to obtain an extracted carbon replica sample.

4. The preparation method according to claim 3, characterized in that, In step 1, cut the sample into small pieces of (10-15mm)×(10-15mm), fix it with an embedding machine with the surface facing down, and successively use 180-240#, 400-600#, and 800-1200# sandpapers to mechanically grind the sample and mechanically polish it until the surface has no scratches. Clean the polishing paste.

5. The preparation method according to claim 3, characterized in that, In step 2, immerse the polished surface of the sample in a nitric acid absolute ethanol solution with a volume percentage of 2-6% and corrode it for 30-90s until the surface of the sample changes color, that is, the metallographic structure can be seen.

6. The preparation method according to claim 3, characterized in that, In step 4, cut the carbon film on the four edges of the sample from the embedding material, and use a blade to scratch small squares with a length and width of 2mm-3mm on the coated surface of the sample.

7. The preparation method according to claim 3, characterized in that, In step 4, immerse the sample in a nitric acid absolute ethanol solution with a volume percentage of 8-12% and soak it for 5-20min until the carbon film peels off.

8. The preparation method according to claim 3, characterized in that, In step 5, after the carbon film peels off, use a carrier grid to fish out the carbon film and put it into a weighing bottle containing absolute ethanol, wash off the nitric acid absolute ethanol solution on the carbon film, and wash the carbon film with absolute ethanol more than twice until the absolute ethanol in the weighing bottle shows colorless. Cover the bottle cap and store it.

9. The preparation method according to claim 3, characterized in that, In step 7, use a Φ3mm copper mesh to fish out the carbon film and place it on a clean filter paper; place the copper mesh under an infrared baking lamp and bake it at a power of 50-200W for 30 seconds - 1 minute until the sample is dried.

10. The preparation method according to claim 3, characterized in that, The electrical steel includes grain-oriented silicon steel or non-grain-oriented silicon steel.

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