A method for preparing an indium metallographic sample

Abstract

The application belongs to the field of metallographic detection, and particularly discloses a preparation method of a metal indium metallographic sample. The application uses an aqueous nitric acid solution as an electrolyte to prepare the metal indium metallographic sample through electrolytic corrosion and electrolytic polishing. The method is suitable for preparing the metal indium metallographic sample, effectively avoids deformation and a smearing layer generated in the sample preparation process, thereby avoiding metallographic false images caused by the deformation layer and the smearing layer, and showing a real indium metallographic phase. Moreover, the method can greatly reduce the preparation difficulty and preparation time of the indium metallographic sample.

Description

Technical Field

[0001] This invention belongs to the field of metallographic testing, and specifically relates to a method for preparing an indium metallographic sample. Background Technology

[0002] Indium, as an important strategic resource, is widely used in various fields, such as in the fabrication of TCO transparent conductive oxide coated glass and CIGS copper indium gallium selenide solar cells. Elemental indium is also frequently used to fabricate sputtering targets. The size and uniformity of indium grains are crucial parameters determining the sputtering effect of the target. Metallographic analysis is a convenient, rapid, and efficient method for observing and analyzing metal grains. Because indium has excellent plasticity and is extremely soft, existing traditional metallographic sample preparation methods, such as mechanical polishing, inevitably produce deformation and smearing layers on the indium surface, creating metallographic artifacts and hindering accurate observation of the indium metallographic structure. Therefore, there is an urgent need to develop a method for preparing metallographic samples that can accurately observe the indium metallographic structure. Summary of the Invention

[0003] To address the problem of metallographic artifacts appearing in indium when preparing indium metallographic samples using conventional metallographic sample preparation methods, this invention provides a method for preparing indium metallographic samples. This method is suitable for preparing elemental indium (purity ≥ 99.8%) metallographic samples, effectively avoiding deformation and smearing layers that occur during sample preparation, thus preventing metallographic artifacts caused by these layers and revealing the true indium metallographic structure.

[0004] To achieve the above objectives, the following technical solution is adopted:

[0005] A method for preparing an indium metallographic sample includes the following steps:

[0006] (1) Sampling: Indium metal is cut using a water jet or wire cutting to obtain an indium metal sample;

[0007] (2) Electrolytic corrosion: The indium metal sample is subjected to electrolytic corrosion in an electrolyte, the voltage of which is 2-3V; the electrolyte is a 21-25% mass concentration aqueous solution of nitric acid.

[0008] (3) Cleaning and drying: The indium metal sample after electrolytic corrosion is cleaned and dried to obtain an indium metallographic sample.

[0009] The principle of indium electrolytic etching metallographic visualization: Nitric acid solution is a strong acid and a strong oxidizing electrolyte. When electricity is applied, it reacts with indium in a series of reactions, dissolving the indium to form purple, high-molecular-weight complex ions, which are used to form thin films. However, at voltages of 2-3V, the solution is insufficient to form a thin film, and the corrosion effect is weak. Due to the large number of dislocations and other defects at grain boundaries, they are most easily corroded, and the corrosion rate is relatively fast, so they appear as obvious thick lines in the metallographic image. Inside the grains, the atoms are neatly arranged, the corrosion rate is slow, and a smooth surface can be preserved. Twin interfaces also have dislocations and other defects, but fewer defects, so the corrosion is less obvious compared to grain boundaries, appearing as less noticeable thin lines in the metallographic image.

[0010] As a preferred embodiment of the present invention, in step (1), wire cutting or water jet cutting is used to ensure that the sample does not deform inside. The indium sample is preferably a cube with a side length ≥ 20 mm.

[0011] The wire cutting is preferably slow wire cutting, and the water jet is also known as high-pressure water jet cutting.

[0012] In a preferred embodiment of the present invention, in step (1), the purity of the indium metal is greater than or equal to 99.8%.

[0013] In a preferred embodiment of the present invention, in step (1), the indium metal sample further requires the following pretreatment steps:

[0014] (1a) Surface treatment: The indium metal sample is surface treated so that the surface roughness Ra of the indium metal sample is ≤1.6μm and the flatness is ≤0.1mm;

[0015] (1b) Electropolishing: The surface-treated indium sample is electropolished in an electrolyte solution, wherein the voltage of the electropolishing is 5-10V; and the electrolyte solution is a 21-25% mass concentration aqueous solution of nitric acid.

[0016] (1c) Cleaning and drying: Clean and dry the electropolished indium sample.

[0017] Electropolishing principle: A schematic diagram of electropolishing is attached. Figure 1 As shown, after the indium sample comes into contact with the electrolyte, an electrochemical reaction occurs on the surface of the indium sample upon the application of an electric current, resulting in the dissolution and corrosion of the indium sample surface. The reaction occurring on the sample surface is as follows: In-ne - →In n+ .

[0018] Nitric acid solution is a strong acid and a strong oxidizing electrolyte. When electricity is applied, it reacts with indium in a series of reactions, dissolving the indium to form purple, high-molecular-weight complex ions, which are used to form thin films. Nitric acid solution also has good electrical conductivity; the higher the voltage and current, the stronger its corrosiveness.

[0019] When an electric current is applied, the solution forms a thin film of varying thickness on the sample surface. Due to the continuous agitation of the electrolyte, the film diffuses and flows faster in the raised areas of the sample surface, resulting in a thinner film; conversely, the film flows slower in the recessed areas, resulting in a thicker film. Since the film has a certain resistance, the current density is higher in thinner areas and lower in thicker areas. The dissolution rate is faster at the corresponding raised areas and lower at the recessed areas. This process gradually transforms the sample surface into a plateau, eventually forming a glossy, polished surface.

[0020] When the voltage is too high, the solution becomes too corrosive, gas is generated on the sample surface, and adsorbed bubbles cause pitting corrosion, resulting in poor polishing effect on the surface of the indium sample.

[0021] In a preferred embodiment of the present invention, in step (1a), the surface treatment is performed using a slow wire cutting method.

[0022] In step (1a), the surface treatment can be performed using a slow wire cutting method to ensure that the internal structure does not deform.

[0023] In a preferred embodiment of the present invention, in step (1b), the electrolytic polishing current density is 2.0-3.5 A / cm². 2 The electrolyte flow rate is 15-20 mL / cm. 2 The electropolishing time is 250-400s.

[0024] As a further preferred embodiment of the present invention, in step (1b), the voltage of the electropolishing is 5V, and the current density is 2.4-2.8A / cm². 2 The electrolyte flow rate is 20 mL / cm. 2 The electropolishing time is 300-320s.

[0025] Electropolishing can achieve a maximum electrolytic depth of 2mm, completely removing the surface stress layer; the Stell ElectroPol-5 equipment is preferred as a polishing machine or electrolytic etching equipment.

[0026] In a preferred embodiment of the present invention, the cleaning and drying in step (1c) specifically involves rinsing with water for more than 20 seconds to remove residual electrolyte on the surface, rinsing with anhydrous ethanol for more than 10 seconds to remove surface moisture, and then drying the residual liquid on the surface with cold air.

[0027] In a preferred embodiment of the present invention, in step (2), the current density of the electrolytic corrosion is 1-2 A / cm². 2 The electrolyte flow rate is 15-20 mL / cm.2 The electrolytic corrosion time is 30-60 seconds.

[0028] As a further preferred embodiment of the present invention, in step (2), the voltage of the electrolytic corrosion is 2.5V, and the current density is 1.1-1.5A / cm². 2 The electrolyte flow rate is 15 mL / cm. 2 The electrolytic corrosion time is 40-60 seconds.

[0029] As a preferred embodiment of the present invention, in step (3), the cleaning and drying specifically involves: rinsing with water for more than 20 seconds to remove residual electrolyte on the surface, rinsing with anhydrous ethanol for more than 10 seconds to remove surface moisture, and then drying the residual liquid on the surface with cold air.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The method for preparing the indium metallographic sample of the present invention enables the indium metallographic sample to display a true and accurate indium metallographic structure, and can also display twin boundaries in the metallographic structure.

[0032] (2) The method for preparing indium metallographic samples of the present invention can greatly reduce the difficulty of preparing indium metallographic tests, and operators do not need much experience in metallographic preparation to produce accurate metallographic results.

[0033] (3) The special properties of indium make grinding and polishing of metallographic samples using traditional mechanical polishing methods extremely difficult, taking more than 1 hour, and the results are not necessarily accurate. The indium metallographic sample preparation method of the present invention can greatly reduce the preparation time. The two steps of electrolytic polishing and etching only take 4-8 minutes, and the results are stable. Attached Figure Description

[0034] Figure 1 This is a simplified diagram of the electrolysis process.

[0035] Figure 2 This is an EBSD image of metallic indium from Example 1.

[0036] Figure 3 The image shows the metallographic image of the indium metallographic sample from Example 1.

[0037] Figure 4 This is an EBSD image of metallic indium from Example 2.

[0038] Figure 5 The image shows the metallographic image of the indium metallographic sample from Example 2.

[0039] Figure 6 This is an EBSD image of 2N8 metallic indium from Example 3.

[0040] Figure 7 The image shows the metallographic image of the 2N8 indium metallographic sample from Example 3.

[0041] Figure 8 The image shows the metallographic image of the 2N8 indium metallographic sample from Example 3.

[0042] Figure 9 The image shows the metallographic image of the indium metallographic sample of Comparative Example 1.

[0043] Figure 10 The image shows the metallographic image of the indium metallographic sample in Comparative Example 2.

[0044] Figure 11 The diagram shows the preparation process flow of Examples 2 and 3.

[0045] Figure 12 The diagram shows the cutting and sampling process in Examples 1 and 2. ① is the surface that contacts the glass mold, serving as the mirror surface (i.e. the surface to be tested) in Example 1, and ② is the water jet sampling and cutting surface that does not contact the glass mold, serving as the surface to be tested in Example 2. Detailed Implementation

[0046] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below through specific comparative examples and embodiments.

[0047] Example 1

[0048] Electrolytic corrosion reveals the as-cast metallographic structure of pure indium.

[0049] (1) Sampling: 4N5 pure indium is melted on a smooth glass mold and allowed to fully contact the glass before cooling, solidifying, and demolding to obtain an indium ingot. The surface of the indium ingot that contacts the glass mold during solidification is designated as the mirror surface (i.e., the attached surface). Figure 12 (①) The indium connected to the mirror surface of the indium ingot is sampled and cut into a 25*25*25mm metal indium sample using a water jet. The mirror surface does not need to be cut, and the mirror surface is protected from scratches and contact throughout the process. The sampling process ensures that the sample is not bumped, subjected to heavy pressure, or deformed.

[0050] (2) EBSD Scan: EBSD scanning of the mirror surface ① of the indium sample yielded a clear image of the grain morphology, revealing twins within the grains, as shown in the attached image. Figure 2 As shown.

[0051] (3) Electrolytic corrosion: The indium sample ① was placed in a Steer ElectroPol-5 instrument for electrolytic corrosion. A 21-25 wt% nitric acid aqueous solution was used as the electrolyte. The voltage was set to 2.5 V and the current density to 1.1-1.5 A / cm². 2Electrolyte flow rate 15 (the default value displayed on this device; all electrolyte flow rates mentioned below are values ​​displayed on this device), electrolytic corrosion time 40s, to obtain the sample after electrolytic corrosion.

[0052] (4) Cleaning and drying: Rinse the sample after electrolytic corrosion with pure water for 30s to remove the residual electrolyte on the surface, then rinse with anhydrous ethanol for 10s to remove the surface moisture, and then use a hair dryer to blow the cold air for 40s to dry the residual liquid on the surface to obtain the indium metallographic sample.

[0053] (5) Metallographic observation: The indium metallographic sample was observed using a metallographic microscope. The results are shown in the appendix. Figure 3 As can be seen, the grain boundaries in the indium phase are clear, and twin boundaries can be observed. The twin boundaries can be clearly distinguished from the grain boundaries, which is consistent with the results of EBSD.

[0054] When preparing indium metallographic samples using metallographic sample preparation methods such as mechanical polishing and cutting, it is unavoidable that a deformation layer and a smear layer will be generated on the indium surface, forming a metallographic illusion of metallic indium, which makes it impossible to accurately observe the metallographic structure of metallic indium. In this embodiment, the metallographic test surface is the ① side that contacts the glass mold. This surface has not been cut or mechanically polished, which can avoid the generation of a deformation layer and a smear layer on the indium surface. As a standard surface, it can display the true metallographic structure of metallic indium.

[0055] Example 2

[0056] (1) Sampling: 4N5 pure indium was melted on a smooth glass mold and allowed to fully contact the glass before cooling, solidification, and demolding to obtain an indium ingot (the same indium ingot as in Example 1, as shown in the attached figure). Figure 12 (As shown). A 25*25*25mm metallic indium sample was cut from the indium ingot using a water jet. During the sampling process, it was ensured that the sample was not subject to impact, heavy pressure, or deformation. This embodiment uses [the method described in the original text]. Figure 12 Surface ② in the diagram is the surface to be tested.

[0057] (2) Surface treatment: The metal indium sample is cut to the surface ② where metallographic preparation is required using a slow wire EDM machine to a roughness of Ra < 1.6 μm and a flatness of < 0.1 mm.

[0058] (3) Electropolishing: The surface-treated indium sample ② was placed in a Steer ElectroPol-5 instrument for electropolishing. The electrolyte was a 21-25 wt% nitric acid aqueous solution, the electropolishing voltage was 5V, and the electropolishing current density was 2.4-2.8A / cm². 2 The flow rate of the electropolishing electrolyte was 20, and the electropolishing time was 300s, resulting in a bright electropolished indium sample.

[0059] (4) Cleaning and drying: Rinse the polished indium sample with pure water for 30 seconds to remove the residual electrolyte on the surface, then rinse with anhydrous ethanol for 10 seconds to remove the surface moisture, and then use a hair dryer to blow the cold air for 40 seconds to dry the residual liquid on the surface.

[0060] (5) EBSD Scan: The electrolysis region of the sample was scanned using EBSD. The results are shown in the attached figure. Figure 4 As shown, a clear image of the grain morphology can be observed, and twins are found in the grains.

[0061] (6) Electrolytic corrosion: The sample was placed in a Steer ElectroPol-5 instrument for electrolytic corrosion. The electrolyte was a 21-25 wt% nitric acid aqueous solution. The electrolytic corrosion voltage was 2.5 V, and the electrolytic corrosion current density was 1.1-1.5 A / cm². 2 The electrolyte flow rate was 15, and the electrolytic corrosion time was 40s, resulting in an electrolytically etched indium sample.

[0062] (7) Cleaning and drying: Rinse the electrolytically etched indium sample with pure water for 30 seconds to remove the residual electrolyte on the surface, then rinse with anhydrous ethanol for 10 seconds to remove the surface moisture, and then use a hair dryer to blow the cold air for 40 seconds to dry the residual liquid on the surface to obtain the indium metallographic sample.

[0063] (8) Metallographic observation: The indium metallographic sample was observed using a metallographic microscope. The results are shown in the appendix. Figure 5 As can be seen, the grain boundaries of indium are clear, and twin boundaries can be observed. The twin boundaries can be clearly distinguished from the grain boundaries, which is consistent with the results of EBSD. The metallographic sample preparation method of the present invention can show the true metallographic structure of indium.

[0064] In this embodiment, after surface treatment and electrolytic polishing, the surface ② is cut and polished, inevitably producing a deformation layer and a paste layer on the indium surface. However, after being processed by the method of the present invention, it is used as the metallographic test surface. The results show that the metallographic structure of the indium in this embodiment is consistent with that in Example 1, which once again proves that the metallographic sample preparation method of the present invention can show the true metallographic structure of the indium.

[0065] Example 3

[0066] (1) Sampling: 2N8 pure indium is melted on a smooth glass mold and allowed to fully contact the glass before cooling, solidifying, and demolding to obtain an indium ingot. The indium ingot is then sampled and cut into 25*25*25mm metal indium samples using a water jet. During the sampling process, the sample must be free from impacts, heavy pressure, or deformation (in this embodiment, the surface to be tested is the water jet sampling cut surface of the non-contact glass mold).

[0067] (2) Surface treatment: The surface of the indium sample that needs to be prepared for metallographic analysis (the surface that does not contact the glass mold) is cut to a roughness of Ra < 1.6 μm and a flatness of < 0.1 mm using a slow wire EDM machine.

[0068] (3) Electropolishing: The surface-treated indium sample was placed in a Stereo ElectroPol-5 instrument for electropolishing. The electrolyte was a 21-25 wt% nitric acid aqueous solution, the electropolishing voltage was 5V, and the electropolishing current density was 2.4-2.8 A / cm². 2 The flow rate of the electropolishing electrolyte was 20, and the electropolishing time was 320s, resulting in a bright electropolished indium sample.

[0069] (4) Cleaning and drying: Rinse the polished indium sample with pure water for 30 seconds to remove the residual electrolyte on the surface, then rinse with anhydrous ethanol for 10 seconds to remove the surface moisture, and then use a hair dryer to blow the cold air for 40 seconds to dry the residual liquid on the surface.

[0070] (5) EBSD Scan: The electrolysis region of the sample was scanned using EBSD. The results are shown in the attached figure. Figure 6 As shown.

[0071] (6) Electrolytic corrosion: The sample was placed in a Steer ElectroPol-5 instrument for electrolytic corrosion. The electrolyte was a 21-25 wt% nitric acid aqueous solution. The electrolytic corrosion voltage was 2.5 V, and the electrolytic corrosion current density was 1.1-1.5 A / cm². 2 The electrolyte flow rate was 15, and the electrolytic corrosion time was 60s, resulting in an electrolytic corrosion sample of indium metal.

[0072] (7) Cleaning and drying: Rinse the electrolytically etched indium sample with pure water for 30 seconds to remove the residual electrolyte on the surface, then rinse with anhydrous ethanol for 10 seconds to remove the surface moisture, and then use a hair dryer to blow the cold air for 40 seconds to dry the residual liquid on the surface to obtain the indium metallographic sample.

[0073] (8) Metallographic observation: The indium metallographic sample was observed using a metallographic microscope. The results are shown in the appendix. Figure 7 and 8 As can be seen, the grain boundaries of indium are clear, and the morphology of 2N8 indium grains is dendritic.

[0074] Comparative Example 1

[0075] (1) 4N5 pure indium is melted on a smooth glass mold and allowed to fully contact the glass before cooling, solidifying, and demolding to obtain an indium ingot. The indium ingot is then sampled and cut into 25*25*25mm metal indium samples using a water jet. During the sampling process, the samples must be free from impacts, heavy pressure, or deformation.

[0076] (2) The surface of the indium metal sample (the surface to be tested in this comparative example is the water jet sampling and cutting surface of the non-contact glass mold) was polished and smoothed (mechanical polishing) by using 600 grit, 1200 grit, 2500 grit, 3000 grit, 4000 grit and 5000 grit sandpaper in sequence.

[0077] (3) Polish the sample to a bright surface on a polishing cloth using a 0.5μm diamond suspension (mechanical polishing).

[0078] (4) Immerse the polished indium metal sample in 68% nitric acid for 15 seconds and remove it (chemical etching).

[0079] (5) Rinse the chemically etched indium sample with pure water for 30 seconds to remove the residual etching solution on the surface, then rinse with anhydrous ethanol for 10 seconds to remove the surface moisture, and then use a hair dryer to blow the cold air for 40 seconds to dry the residual liquid on the surface to obtain the indium metallographic sample.

[0080] (6) The indium metallographic sample was observed using a metallographic microscope, and the results are shown in the appendix. Figure 9 A large number of fine grains were found, which were completely different from the cast grains in Example 1. The surface of the metallographic sample prepared in this comparative example was composed of recrystallized grains from the sample deformation layer, and the grain boundaries were blurred, making it impossible to show twins and thus unable to represent the true metallographic structure.

[0081] Comparative Example 2

[0082] (1) 2N8 indium was melted on a smooth glass mold and allowed to fully contact the glass before cooling, solidifying, and demolding to obtain an indium ingot (the same indium ingot as in Example 1). The indium ingot was then sampled and cut into 25*25*25mm metal indium samples using a water jet. During the sampling process, the samples were ensured to be free from impacts, heavy pressure, or deformation.

[0083] (2) Use a sharp blade to cut the sample surface to be tested flat in one stroke (the surface to be tested in this comparative example is the water jet sampling and cutting surface of a non-contact glass mold), with a roughness Ra < 1.6 μm (mechanical cutting).

[0084] (3) Immerse the sample in 68% nitric acid for 60 seconds and remove it (this is chemical corrosion).

[0085] (4) Rinse the chemically etched indium sample with pure water for 30 seconds to remove the residual etchant on the surface, then rinse with anhydrous ethanol for 10 seconds to remove the surface moisture, and then use a hair dryer to blow the cold air for 40 seconds to dry the residual liquid on the surface to obtain the indium metallographic sample.

[0086] (5) The indium metallographic sample was observed using a metallographic microscope, and the results are shown in the appendix. Figure 10A large number of fine grains can be observed on the sample surface. These grains are completely different from the cast grains in Example 3. These grains are recrystallized grains of the deformed layer of the sample and cannot show dendrites, so they cannot represent the true metallographic structure.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an indium metallographic sample, characterized in that, Includes the following steps: (1) Includes the following processes 1a-1d: (1a) Sampling: Indium metal is cut using a water jet or wire cutting to obtain an indium metal sample; the purity of the indium metal is greater than or equal to 99.8%; (1b) Surface treatment: The indium metal sample is surface treated so that the surface roughness Ra of the indium metal sample is ≤1.6μm and the flatness is ≤0.1mm; (1c) Electropolishing: The surface-treated indium sample is electropolished in an electrolyte solution, wherein the voltage of the electropolishing is 5-10V; the electrolyte solution is a 21-25% mass concentration nitric acid aqueous solution; (1d) Cleaning and drying: The electrolytically polished indium sample is cleaned and dried; (2) Electrolytic corrosion: The indium metal sample is subjected to electrolytic corrosion in an electrolyte, the voltage of which is 2-3V; the electrolyte is a 21-25% mass concentration nitric acid aqueous solution; (3) Cleaning and drying: The indium metal sample after electrolytic corrosion is cleaned and dried to obtain an indium metallographic sample.

2. The method for preparing an indium metallographic sample as described in claim 1, characterized in that, In step (2), the current density of the electrolytic corrosion is 1-2 A / cm², and the electrolyte flow rate is 15-20 mL / cm². 2 The electrolytic corrosion time is 30-60 seconds.

3. The method for preparing an indium metallographic sample as described in claim 2, characterized in that, In step (2), the voltage for electrolytic corrosion is 2.5V, the current density is 1.1-1.5A / cm², and the electrolyte flow rate is 15 mL / cm². 2 The electrolytic corrosion time is 40-60 seconds.

4. The method for preparing an indium metallographic sample as described in claim 1, characterized in that, In step (1b), the current density for electropolishing is 2.0-3.5 A / cm², and the electrolyte flow rate is 15-20 mL / cm². 2 The electropolishing time is 250-400s.

5. The method for preparing an indium metallographic sample as described in claim 4, characterized in that, In step (1b), the current density is 2.4-2.8 A / cm², and the electrolyte flow rate is 20 mL / cm². 2 The electropolishing time is 300-320s.

6. The method for preparing an indium metallographic sample as described in claim 1, characterized in that, In step (1a), the surface treatment is performed using slow wire cutting.

7. The method for preparing an indium metallographic sample as described in claim 1, characterized in that, In step (1c), the cleaning and drying specifically involves rinsing with water for more than 20 seconds to remove residual electrolyte on the surface, rinsing with anhydrous ethanol for more than 10 seconds to remove surface moisture, and then drying the residual liquid on the surface with cold air.

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