Preparation method of aerolite EBSD sample

Abstract

The invention provides a preparation method of a meteorite EBSD sample. The preparation method of the meteorite EBSD sample comprises the following steps: (1) cutting, cleaning and drying blocky meteorite to obtain slices; embedding and fixing the obtained slices; (2) grinding the embedded sample in the step (1) by using abrasive paper, and then polishing the sample by using diamond polishing paste and polishing cloth; and (3) carrying out vibration polishing on the sample polished in the step (2), cleaning and drying to obtain the aerolite EBSD sample. The method provided by the invention solves the problems of low polishing efficiency, long time and poor polishing effect in the existing sample preparation technology. The meteorite surface which is high in quality, smooth and unstressed is prepared through multi-stage grinding, two-stage mechanical polishing and vibration polishing of the polishing solution with the unique proportion, and the method can be widely applied to preparation of extraterrestrial samples (meteorite and lunar soil) EBSD samples.

Description

Technical Field

[0001] This invention belongs to the field of extraterrestrial sample crystallographic information detection technology, and relates to a method for preparing meteorite EBSD samples. Background Technology

[0002] To meet the demands of deep space exploration, the study of extraterrestrial samples (meteorites, lunar soil) is a core component driving the development of space science. Extraterrestrial samples are rocks and soils collected from celestial bodies such as the Moon, Mars, and asteroids, primarily composed of different types of minerals. Minerals are products of various geological processes, and their unique crystal structures are closely related to their chemical composition and rock occurrence. Therefore, obtaining accurate crystallographic information is crucial for understanding mineral types and their underlying geological history, aiding in mineral identification and crystal structure characterization in extraterrestrial sample research. Scanning electron microscopy backscatter diffraction (EBSD) can meet the needs of mineral crystallographic structure analysis of extraterrestrial samples.

[0003] EBSD testing places extremely high demands on sample preparation, requiring a smooth surface free of deformation stress. Otherwise, lattice distortion will occur, resulting in unclear Kikuchi patterns and making accurate analysis impossible. Compared to metal and terrestrial rock samples, extraterrestrial samples have complex mineral compositions and undergo extreme temperatures, pressures, and rapid cooling during impacts, leading to complex residual stresses and lattice distortions within them. These stress layers are deeper, more persistent, and more difficult to completely eliminate than those in metals and terrestrial rocks. Therefore, the preparation of extraterrestrial samples such as meteorites and lunar regolith is challenging, and the analytical process is complex. Few domestic and international institutions use EBSD technology to study their crystallographic structures.

[0004] The main methods for removing stress layers from sample surfaces include ion polishing, vibratory polishing, and electropolishing. Ion polishing equipment is expensive and requires a certain level of conductivity from the sample. However, extraterrestrial samples contain non-conductive or low-conductive mineral phases, leading to reduced polishing efficiency or surface charge accumulation, affecting EBSD signal quality. Furthermore, high-energy ion beams cause slight bombardment damage to the surface of extraterrestrial samples, especially for soft or easily phase-transformed minerals (such as olivine), potentially introducing amorphous layers or artifacts that interfere with EBSD calibration. Electropolishing is effective for metallic phases but is not suitable for extraterrestrial samples with multiple mineral phases, as it is difficult to achieve uniform removal of all phases. Vibratory polishing uses high-frequency horizontal vibrations to perform atomic-level ablation micromachining on the sample surface, gradually releasing residual stress within the sample and ultimately achieving fine polishing of the sample surface. It causes less damage to brittle materials like meteorites, avoids introducing residual stress or plastic deformation, and is suitable for the fine processing of multiphase materials. However, the method of vibratory polishing of meteorites using silicon dioxide or aluminum oxide polishing liquid also has certain limitations: (1) the polishing efficiency is low, especially for mineral phases with high hardness; (2) for severely deformed samples, a longer polishing time is required to completely remove the damaged layer; (3) in some cases, it may be difficult to obtain the ideal surface finish and remove stress.

[0005] Currently, the preparation of extraterrestrial EBSD samples is time-consuming and laborious, and the results are not ideal, resulting in a low level of research on the mineral crystal structure of extraterrestrial samples (such as meteorites and lunar soil). Therefore, there is an urgent need to develop a method for preparing EBSD samples of extraterrestrial objects. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing meteorite EBSD samples. This method solves the problems of low polishing efficiency, long processing time, and poor polishing results in existing sample preparation techniques. This invention prepares a high-quality, smooth, and stress-free meteorite surface through multi-stage grinding, two-stage mechanical polishing, and vibration polishing with a uniquely formulated polishing slurry. In the grinding stage, seven different grit sandpapers are used to grind the meteorite surface from coarse to fine. In the mechanical polishing stage, two different grit diamond polishing pastes and polishing cloths are used to mechanically polish the meteorite surface from large to small. The most crucial stage is vibration polishing, which uses a polishing slurry prepared with 0.02-micron amorphous silica and 3% hydrogen peroxide, combined with synthetic rayon polishing cloth, to vibrately polish the meteorite surface. This method can be widely applied to the preparation of extraterrestrial samples (meteorites, lunar soil) EBSD samples.

[0007] The technical solution of the present invention is as follows: A method for preparing a meteorite EBSD sample includes the following steps: (1) Cut, clean and dry the block meteorite to obtain slices; then mount and fix the obtained slices; (2) Grind the sample that was inlaid in step (1) with sandpaper, and then polish the sample with diamond polishing paste and polishing cloth; (3) Vibration polishing was performed on the sample polished in step (2), and after cleaning and drying, meteorite EBSD sample was obtained.

[0008] According to a preferred embodiment of the present invention, the cleaning in step (1) is rinsing with deionized water; the drying is drying at 80°C to 100°C.

[0009] According to a preferred embodiment of the present invention, the length and width of the slice in step (1) are both less than 1 inch, and more preferably, the length and width of the slice are 1~2 cm and the thickness is 1~2 mm.

[0010] According to a preferred embodiment of the present invention, the embedding in step (1) is performed by cold embedding using an epoxy resin embedding agent. The specific steps of the embedding are as follows: adding a curing agent to an epoxy resin, wherein the volume ratio of epoxy resin to curing agent is 2 to 4:1, stirring evenly to obtain an epoxy resin embedding agent; placing the slice at the bottom of a mold with a diameter of 1 inch, pouring in the epoxy resin embedding agent, and curing at room temperature for 6 to 9 hours; the curing agent and epoxy resin are not specifically limited, and commonly used types in the art are acceptable.

[0011] According to a preferred embodiment of the present invention, the grinding step in step (2) is as follows: the surface of the meteorite sample is ground sequentially with sandpaper of 80~120 mesh, 220~320 mesh, 600~800 mesh, 1000~1500 mesh, 2500~3000 mesh, 4000~5000 mesh, and 6000~7000 mesh, and the grinding is stopped after each mesh of sandpaper has been ground until the frictional force has no change.

[0012] According to a preferred embodiment of the present invention, the polishing process in step (2) is as follows: the automatic polishing machine is set to a chassis speed of 130~150 rpm and a power head speed of 60 rpm, with both rotating in the same direction and a loading force of 5N. First, the sample surface is polished for 3~5 minutes using diamond polishing paste with a particle size of 0.5 micrometers and synthetic rayon polishing cloth. Then, the sample surface is polished for 3~5 minutes using diamond polishing paste with a particle size of 0.1 micrometers and synthetic rayon polishing cloth until the sample surface is flat and smooth and free of scratches. After polishing, the sample is cleaned with deionized water or anhydrous ethanol and dried with cold air.

[0013] According to a preferred embodiment of the present invention, the polishing liquid for vibration polishing in step (3) is prepared by the following method: a 0.02-micron non-crystalline silica polishing liquid is mixed with a 3wt% hydrogen peroxide solution at a volume ratio of 4 to 6:1 and stirred evenly to obtain the polishing liquid.

[0014] According to a preferred embodiment of the present invention, the vibration polishing step (3) is as follows: the sample is fixed at the bottom of a 400-gram fixture, and then 1 to 4 200-gram counterweights are added to the fixture and placed in the polishing disc of the vibration polishing machine; polishing liquid is poured in to submerge the polishing surface of the sample, the vibration frequency is 7200 rpm, the amplitude percentage is set to 40 to 60, and the sample is moved along the maximum diameter of the polishing disc for 6 to 10 hours until the surface is smooth and the stress, deformation layer and oxide layer on the sample surface are removed.

[0015] According to a preferred embodiment of the present invention, the cleaning in step (3) is to clean the sample using deionized water or anhydrous ethanol; the drying is to dry the sample using cold air.

[0016] The technical features and beneficial effects of this invention are as follows: 1. The precision operation of the present invention in the sandpaper grinding and diamond polishing paste mechanical polishing stages improves the smoothness and gloss of the meteorite surface more than coarse grinding and polishing, laying a solid foundation for the efficiency of subsequent vibration polishing and stress relief.

[0017] 2. The vibration polishing method used in this invention does not introduce residual stress or plastic deformation, does not damage the surface of extraterrestrial samples, and is suitable for the fine processing of extraterrestrial samples with various mineral phases.

[0018] 3. In the vibration polishing stage, this invention utilizes a polishing slurry composed of silica polishing slurry and hydrogen peroxide, which significantly improves the polishing efficiency of meteorite sample surfaces, shortens polishing time, reduces the difficulty of stress removal, results in lower stress residue, higher EBSD calibration rate, and more accurate phase boundary characterization.

[0019] 4. The meteorite EBSD sample prepared by this invention has good characterization effect and can be extended to the preparation of lunar soil EBSD samples. Attached Figure Description

[0020] Figure 1 Scanning electron microscope (SEM) image of the Martian meteorite EBSD sample prepared in Example 1.

[0021] Figure 2 The EBSD calibration diagrams of the Martian meteorite EBSD sample prepared in Example 1 are shown in Figure a, where Figure a is the inverse pole diagram and Figure b is the phase diagram.

[0022] Figure 3 The image is a scanning electron microscope (SEM) image of the lunar meteorite EBSD sample prepared in Example 2.

[0023] Figure 4 Figure 2 shows the EBSD calibration diagram of the lunar meteorite EBSD sample prepared in Example 2, where Figure a is the inverse pole figure and Figure b is the phase diagram. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0025] The synthetic rayon polishing cloth used in the examples is Biao Le polishing cloth, model 407222 Microcloth polishing cloth 12in, with adhesive backing.

[0026] Example 1 A method for preparing a meteorite EBSD sample includes the following steps: (1) Using a diamond wire saw, the blocky Martian meteorite (Martian meteorite NWA13366-1) sample was cut into 10mm×10mm×1mm slices, rinsed with deionized water, and dried at 90℃ for 15 minutes.

[0027] (2) Mix EpoxiCure 2 epoxy resin and EpoxiCure 2 curing agent in a volume ratio of 4:1 and stir evenly to obtain epoxy resin embedding agent.

[0028] (3) Place the meteorite slice obtained in step (1) at the bottom of a mold with a diameter of 1 inch, pour in the prepared epoxy resin insert, and cure at room temperature for 6 hours.

[0029] (4) After the epoxy resin embedding agent has completely solidified, the surface of the meteorite sample is ground sequentially with sandpaper of 80 mesh, 220 mesh, 800 mesh, 1000 mesh, 3000 mesh, 5000 mesh, and 7000 mesh. The grinding time for each mesh is controlled at 5 to 10 minutes. Grinding is stopped when the friction of each mesh of sandpaper no longer changes. Finally, the sample surface is ground until there are no obvious undulations under an optical microscope. Then, the sample surface is polished with 0.5-micron diamond polishing paste and synthetic rayon polishing cloth. The Biao Le automatic grinding and polishing machine is set with the chassis rotating. The speed was 150 rpm, the power head speed was 60 rpm, both rotated in the same direction, the applied force was 5 N, and the polishing time was 5 minutes. Then, the sample was further polished using 0.1 micron diamond polishing paste and synthetic rayon polishing cloth. The Biao Le automatic polishing machine was set with the chassis speed at 130 rpm, the power head speed at 60 rpm, both rotated in the same direction, the applied force was 5 N, and the polishing time was 3 minutes. The sample surface was flat and smooth without scratches. After polishing, the sample was washed with deionized water and dried with cold air.

[0030] (5) Fix the mechanically polished sample to the bottom of the 400g fixture of the VibroMet 2 vibratory polisher, add a 200g counterweight on the fixture, and place it in the polishing disc of the VibroMet 2 vibratory polisher.

[0031] (6) Mix 0.02-micron non-crystalline silica polishing slurry and 3wt% hydrogen peroxide solution in a volume ratio of 5:1 to obtain polishing slurry. Then pour the prepared polishing slurry into the polishing pad, which must submerge the sample polishing surface.

[0032] (7) Turn on the machine, set the vibration frequency to 7200 rpm, set the amplitude percentage to 50, and move the sample along the maximum diameter of the polishing disc for 8 hours until the surface is smooth and the stress, deformation layer and oxide layer on the sample surface are removed.

[0033] (8) The sample obtained in step (7) was washed with deionized water and dried with cold air to obtain the Martian meteorite EBSD sample.

[0034] Figure 1 The image shows a scanning electron microscope (SEM) image of the Martian meteorite EBSD sample prepared in this embodiment, which has a clear morphology and is free of scratches.

[0035] Figure 2 The EBSD calibration diagrams of the Martian meteorite EBSD sample prepared for this example are shown in Figure a, which is an inverse pole figure that clearly shows the crystallographic orientation distribution of grains in the microstructure of the meteorite; Figure b is a phase diagram with clear phase boundaries. The overall calibration rate is over 90%, which is lower than that of some metals. This is because the crystal structure of feldspar in the meteorite collapsed under high-intensity impact, resulting in vitrification of the grains and the absence of Kikuchi patterns.

[0036] Example 2 A method for preparing a meteorite EBSD sample includes the following steps: (1) Using a diamond wire saw, the blocky lunar meteorite (lunar meteorite NWA6950) sample was cut into slices of 10mm×10mm×2mm, rinsed with deionized water, and dried at 90℃ for 15 minutes.

[0037] (2) Mix EpoxiCure 2 epoxy resin and EpoxiCure 2 curing agent in a volume ratio of 4:1 and stir evenly to obtain epoxy resin embedding agent.

[0038] (3) Place the meteorite slice obtained in step (1) at the bottom of a mold with a diameter of 1 inch, pour in the prepared epoxy resin insert, and cure at room temperature for 6 hours.

[0039] (4) After the epoxy resin embedding agent has completely solidified, the surface of the meteorite sample is ground sequentially with sandpaper of 80 mesh, 220 mesh, 800 mesh, 1000 mesh, 3000 mesh, 5000 mesh, and 7000 mesh. The grinding time for each mesh is controlled at 5 to 10 minutes. Grinding is stopped when the friction of each mesh of sandpaper no longer changes. Finally, the sample surface is ground until there are no obvious undulations under an optical microscope. Then, the sample surface is polished with 0.5-micron diamond polishing paste and synthetic rayon polishing cloth. The Biao Le automatic grinding and polishing machine is set with the chassis rotating. The speed was 150 rpm, the power head speed was 60 rpm, both rotated in the same direction, the applied force was 5 N, and the polishing time was 5 minutes. Then, the sample was further polished using 0.1 micron diamond polishing paste and synthetic rayon polishing cloth. The Biao Le automatic polishing machine was set with the chassis speed at 130 rpm, the power head speed at 60 rpm, both rotated in the same direction, the applied force was 5 N, and the polishing time was 3 minutes. The sample surface was flat and smooth without scratches. After polishing, the sample was washed with deionized water and dried with cold air.

[0040] (5) Fix the mechanically polished sample to the bottom of the 400g fixture of the VibroMet 2 vibratory polisher, add a 200g counterweight on the fixture, and place it in the polishing disc of the VibroMet 2 vibratory polisher.

[0041] (6) Mix 0.02-micron non-crystalline silica polishing slurry and 3wt% hydrogen peroxide solution in a volume ratio of 5:1 to obtain polishing slurry. Then pour the prepared polishing slurry into the polishing pad, which must submerge the sample polishing surface.

[0042] (7) Turn on the machine, set the vibration frequency to 7200 rpm, set the amplitude percentage to 60, and move the sample along the maximum diameter of the polishing disc for 6 hours until the surface is smooth and the stress, deformation layer and oxide layer on the sample surface are removed.

[0043] (8) The sample obtained in step (7) was washed with deionized water and dried with cold air to obtain the lunar meteorite EBSD sample.

[0044] Figure 3 The image shows a scanning electron microscope (SEM) image of the lunar meteorite EBSD sample prepared in this embodiment, which has a clear morphology and is free of scratches.

[0045] Figure 4 The EBSD calibration diagrams of the lunar meteorite EBSD sample prepared for this example are shown in Figure a, which is an inverse pole figure that clearly shows the crystallographic orientation distribution of grains in the microstructure of the meteorite; Figure b is a phase diagram with clear phase boundaries. The overall calibration rate is over 85%, which is lower than that of some metals. This is because the crystal structure of feldspar in the meteorite collapsed under high-intensity impact, resulting in vitrification of the grains and the absence of Kikuchi patterns.

[0046] In summary, this invention proposes a novel EBSD preparation method for preparing extraterrestrial meteorite samples with complex mineral compositions. This invention also has some applicability to lunar soil samples. The preparation method of this invention improves sample preparation efficiency and surface quality, significantly enhances calibration rates, and advances the application of EBSD technology in extraterrestrial sample research.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a meteorite EBSD sample, characterized in that, The steps include the following: (1) Cut, clean and dry the block meteorite to obtain slices; then mount and fix the obtained slices; (2) Grind the sample that was inlaid in step (1) with sandpaper, and then polish the sample with diamond polishing paste and polishing cloth; (3) Vibration polishing was performed on the sample polished in step (2), and after cleaning and drying, meteorite EBSD sample was obtained.

2. The method for preparing meteorite EBSD samples according to claim 1, characterized in that, The cleaning in step (1) is to rinse with deionized water; the drying is to dry at 80℃~100℃.

3. The method for preparing meteorite EBSD samples according to claim 1, characterized in that, The length and width of the slice in step (1) are both less than 1 inch. Preferably, the length and width of the slice are 1~2 cm and the thickness is 1~2 mm.

4. The method for preparing meteorite EBSD samples according to claim 1, characterized in that, The embedding in step (1) is a cold embedding using an epoxy resin embedding agent. The specific steps of the embedding are as follows: add the curing agent to the epoxy resin, the volume ratio of epoxy resin to curing agent is 2~4:1, stir evenly to obtain the epoxy resin embedding agent; place the slice at the bottom of a mold with a diameter of 1 inch, pour in the epoxy resin embedding agent, and cure at room temperature for 6~9 hours.

5. The method for preparing a meteorite EBSD sample according to claim 1, characterized in that, The grinding steps in step (2) are as follows: use sandpaper of 80~120 mesh, 220~320 mesh, 600~800 mesh, 1000~1500 mesh, 2500~3000 mesh, 4000~5000 mesh and 6000~7000 mesh in sequence to grind the surface of the meteorite sample. Stop grinding each grit of sandpaper when the frictional force no longer changes.

6. The method for preparing a meteorite EBSD sample according to claim 1, characterized in that, The polishing process described in step (2) is as follows: The automatic polishing machine is set to a chassis speed of 130~150 rpm and a power head speed of 60 rpm, with both rotating in the same direction. The loading force is 5N. First, the sample surface is polished for 3~5 minutes using diamond polishing paste with a particle size of 0.5 micrometers and synthetic rayon polishing cloth. Then, the sample surface is polished for 3~5 minutes using diamond polishing paste with a particle size of 0.1 micrometers and synthetic rayon polishing cloth until the sample surface is flat, smooth, and free of scratches. After polishing, the sample is cleaned with deionized water or anhydrous ethanol and dried with cold air.

7. The method for preparing a meteorite EBSD sample according to claim 1, characterized in that, The polishing slurry for vibration polishing in step (3) is prepared by the following method: 0.02-micron non-crystalline silica polishing slurry is mixed with 3wt% hydrogen peroxide solution at a volume ratio of 4~6:1 and stirred evenly to obtain the polishing slurry.

8. The method for preparing a meteorite EBSD sample according to claim 1, characterized in that, The vibration polishing steps described in step (3) are as follows: fix the sample at the bottom of a 400-gram fixture, add 1 to 4 200-gram counterweights on the fixture, and place it in the polishing disc of the vibration polishing machine; pour in polishing liquid to submerge the polishing surface of the sample, set the vibration frequency to 7200 rpm, set the amplitude percentage to 40 to 60, and move the sample along the maximum diameter of the polishing disc for 6 to 10 hours until the surface is smooth and the stress, deformation layer and oxide layer on the sample surface are removed.

9. The method for preparing a meteorite EBSD sample according to claim 1, characterized in that, The cleaning in step (3) involves cleaning the sample with deionized water or anhydrous ethanol; the drying involves drying with cold air.

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