A method for preparing a target for micro-area analysis of lunar dust particles below 10 μm

Abstract

The application discloses a preparation method of a target suitable for micro-area analysis of lunar dust particles below 10 microns, and belongs to the technical field of micro-area mineral component analysis, and solves the problem that the existing lunar soil sample preparation method cannot meet the target preparation requirement of lunar dust particles below 10 microns. The preparation method comprises the following steps: preparing a lunar soil-ethanol suspension A, removing coarse particle debris to obtain a lunar soil-ethanol suspension B containing fine particle debris; performing low-speed centrifugal treatment on the lunar soil-ethanol suspension B, so that the fine particle debris is spatially zoned according to the particle size difference in the ethanol medium, and a lunar soil-ethanol mixed solution containing target fine particles is obtained; dropping the lunar soil-ethanol mixed solution on a glass plate to deposit in a defined deposition area; after the target fine particles are deposited in the defined deposition area, resin embedding is performed to obtain a resin target; and the resin target is finely polished in stages to obtain a sample target. The application realizes effective separation, dispersion and stable target preparation of lunar dust particles below 10 microns.

Description

Technical Field

[0001] This invention belongs to the field of micro-area mineral composition analysis technology, and specifically relates to a method for preparing a micro-area analysis target suitable for lunar dust particles smaller than 10 μm. Background Technology

[0002] With the return of lunar samples by Chang'e 5 and its continued output of original findings, and Chang'e 6's achievement of the first-ever automated sample return from the far side of the moon, my country's lunar sample research has entered a new stage of refinement and systematization. Developing sample preparation technologies suitable for trace and ultrafine lunar dust particles is crucial for improving the efficiency of scientific output and independent analysis capabilities of returned samples, as well as for future lunar resource development, in preparation for subsequent lunar and deep space exploration missions.

[0003] Lunar regolith is a complex aggregate of particles formed on the lunar surface under the combined effects of long-term meteorite / micrometeorite impacts, solar wind intrusion, cosmic ray irradiation, and space weathering. It is a crucial material carrier for studying the formation and evolution of the Moon, the process of lunar surface material modification, space weathering mechanisms, and the state of lunar resources. Research shows that lunar regolith preserves various rock fragments, mineral debris, glassy components, and information about their surface modification, and can record the long-term evolutionary history of the Moon. Furthermore, lunar regolith mineral particles are important reservoirs of volatiles such as solar wind-derived water, as well as metallic and non-metallic resources.

[0004] Lunar regolith is precious and irreplaceable, and its composition is highly heterogeneous, thus micro-area in-situ analysis methods offer significant advantages. Compared to wet chemical analysis, micro-area methods can comprehensively characterize the morphology, chemical composition, microstructure, and surface modification features of individual particles or local areas while preserving the original state of the sample to the greatest extent possible. This avoids the loss of crucial information due to overall fragmentation, mixing, or large-scale processing. Especially for fine-grained minerals, glass, and metals in lunar regolith, key information such as intragranular and intergranular relationships, surface weathering traces, impact edges, melt edges, and adhering substances are often directly related to their formation. Therefore, a reliable and effective sample preparation process is an important prerequisite for micro-area analysis.

[0005] However, existing methods for preparing lunar regolith samples are generally more suitable for larger, screened rock fragments or mineral crystals. Lunar regolith itself has a wide range of particle sizes, including both coarse particles and a large number of fine particles smaller than 10 μm. For example, the average particle size of lunar regolith from Chang'e 5 / 6 is about 5 μm, with approximately 95% of the particles being smaller than 10 μm. For samples with such significant particle size differences, it is often difficult to simultaneously capture the surface condition of particles of different sizes when using conventional methods such as target preparation and polishing to prepare analytical resin targets.

[0006] Specifically, traditional methods face at least two problems when processing lunar dust particles smaller than 10 μm: First, high-precision micro-area surface analysis typically requires a flat and easily locatable analytical surface, while grinding, polishing, or surface leveling steps in conventional sample preparation are more suitable for larger particles. When the target surface is processed to meet analytical requirements, smaller particles are prone to burial, dragging, detachment, or even loss due to over-polishing, making it difficult to retain effective analytes. Second, lunar dust particles, due to their unique formation, have complex and irregular morphologies, low overall sphericity, and significant adhesion and cohesion. Especially at the fine-grained scale, the irregular morphology, van der Waals forces, electrostatic interactions, and surface energy effects between particles are more prominent, easily leading to aggregation, adhesion, and stacking. Therefore, lunar dust samples smaller than 10 μm (including 10 μm) are not only difficult to effectively separate from other particle size ranges, but even if successfully separated, it is difficult to achieve uniform dispersion and single-particle exposure on the analytical target surface, thus limiting subsequent micro-area analysis and the interpretation of scientific implications.

[0007] In summary, existing lunar soil sample preparation methods are mainly suitable for larger particles. For ultrafine lunar dust particles smaller than 10 μm (especially 1–10 μm), there are technical challenges such as difficulty in picking them up, easy agglomeration, difficulty in retention, and unfavorable conditions for subsequent micro-area analysis. Therefore, there is an urgent need to develop a method for preparing targets suitable for micro-area analysis of lunar dust particles smaller than 10 μm. Summary of the Invention

[0008] Based on the above analysis, this invention aims to provide a method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm, addressing the problem that existing lunar soil sample preparation methods are mainly applicable to larger particles and cannot meet the target preparation requirements for lunar dust particles smaller than 10 μm (including 10 μm). The preparation method provided by this invention is a target preparation method for lunar dust particles smaller than 10 μm, especially 1-10 μm particles. It can effectively pick up particles of this size from mixed lunar soil and achieve uniform distribution on the analysis target surface while avoiding particle adhesion, thereby providing a stable, locatable, and representative sample carrier for subsequent micro-area surface analysis.

[0009] The objective of this invention is achieved as follows: A method for preparing a micro-target suitable for analyzing lunar dust particles smaller than 10 μm, comprising: Step S1: Prepare lunar soil-ethanol suspension A; Step S2: Remove coarse rock fragments from lunar soil-ethanol suspension A under a microscope to obtain lunar soil-ethanol suspension B containing fine rock fragments; Step S3: Perform low-speed centrifugation on lunar soil-ethanol suspension B to cause the fine rock fragments to spatially separate according to their particle size differences in the ethanol medium, with the target fine particles being enriched in the suspension in the central region. Step S4: Extract the suspension in the central region to obtain a lunar soil-ethanol mixture containing the target fine particles; Step S5: Mark the defined deposition area on a glass plate, and drop the lunar soil-ethanol mixture into the defined deposition area; allow the sediment to stand for a predetermined time, allowing the ethanol to fully evaporate, and the target fine particles to be deposited in the defined deposition area, thus obtaining the sample before resin embedding; Step S6: Perform resin embedding on the sample before resin embedding to prepare a resin target.

[0010] Furthermore, it also includes: Step S7: Perform progressive fine polishing on the resin target to obtain a sample target with a flat surface suitable for micro-area analysis.

[0011] Further, in step S1, the lunar soil-ethanol suspension A is prepared in an inert gas environment.

[0012] Further, in step S2, coarse rock fragments are removed from the lunar soil-ethanol suspension A under a microscope. The coarse rock fragments include rock fragments with a particle size greater than N, mineral grains, and glass components. Where N = n × 10 μm, and n is an integer not less than 8.

[0013] Furthermore, in step S3, the lunar soil-ethanol suspension B is centrifuged at low speed using a slow centrifuge. The speed of the slow centrifuge is 20-60 rpm, and the centrifugation time is 1-10 minutes.

[0014] Furthermore, the slow centrifuge has a rotation speed of 30 rpm and a centrifugation time of 3 to 8 minutes.

[0015] Further, in step S4, the suspension in the central region is extracted using a 50 μL pipette.

[0016] Further, step S5 includes: Step S51: Mark the defined deposition area on the glass plate, and use a pipette to drop the aspirated lunar soil-ethanol mixture onto the defined deposition area on the glass plate; Step S52: Place the glass plate with the lunar soil-ethanol mixture added in a Class 100 clean bench and let it stand for a predetermined time to allow the ethanol to evaporate completely. The target fine particles are deposited and retained in the defined area, and the particles are initially dispersed to form a sample before resin embedding.

[0017] Further, step S51 includes: Step S511: First, apply traceless double-sided tape to the surface of the glass plate; Step S512: Mark two concentric circles with diameters of 2.54 cm and 1 cm on the glass plate. The circular area with a diameter of 1 cm is the defined deposition area.

[0018] Furthermore, step S6 specifically includes: After the ethanol has evaporated in step S5, the deposition area is embedded in epoxy resin using a mold with a diameter of 2.54 cm to form a resin target preform. The resin target blank is placed in a drying oven for drying and curing to obtain the resin target before polishing.

[0019] Further, step S7 specifically involves using micron-sized diamond polishing paste with particle sizes ranging from coarse to fine to perform multiple fine polishing steps on the resin target, with a polishing level of at least three.

[0020] Furthermore, the polishing level is three-stage, with diamond polishing pastes with particle sizes of 0.5 micrometers, 0.25 micrometers, and 0.1 micrometers used sequentially to polish the resin target in three stages.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: a) The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm provided by the present invention disperses lunar soil samples in anhydrous ethanol and combines steps such as coarse particle removal, low-speed centrifugation for zoning and extraction of the central region. This method can effectively separate and enrich lunar dust particles smaller than 10 μm, especially 1~10 μm, from mixed lunar soil with a large particle size range, thereby solving the problem that the existing technology is difficult to effectively pick out ultrafine lunar dust particles.

[0022] b) The method for preparing a target suitable for micro-area analysis of lunar dust particles smaller than 10 μm provided by the present invention involves adding a droplet of the target fine particle suspension to a predetermined and limited deposition area, and using a volatilization deposition method to uniformly disperse and spread the lunar dust particles on the target surface. This method can effectively reduce the degree of adhesion, agglomeration and stacking of fine lunar dust particles during the sample preparation process, improve particle dispersibility and single particle exposure, and thus optimize the subsequent micro-area analysis conditions.

[0023] c) The method for preparing micro-area analysis targets for lunar dust particles smaller than 10 μm provided by the present invention, through the process route of "first separating the target fine particles, and then performing limited area deposition and resin embedding", effectively avoids the problem of fine particles being buried, falling off or difficult to retain due to excessive particle size difference in the traditional whole sample preparation process, and helps to improve the retention rate of lunar dust particles smaller than 10 μm in the final analysis target.

[0024] d) The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm provided by the present invention completes the dispersion, extraction, deposition and target preparation process of lunar soil samples under nitrogen-filled environment and clean conditions. Anhydrous ethanol is used as the dispersion medium, which can reduce the influence of external moisture, impurities and air disturbance on the original state of fine lunar dust particles, thus making it more conducive to preserving their original morphology, surface features and occurrence state.

[0025] e) The method for preparing micro-area analysis targets for lunar dust particles smaller than 10 μm provided by this invention can provide stable and reliable sample targets for micro-area analysis of the mineral composition, chemical composition, surface morphology, particle structure, glassy components, and occurrence states of metallic and non-metallic components of ultrafine lunar dust particles. The analytical test results obtained using the sample targets prepared by this invention can provide accurate data support for identifying the occurrence forms, particle size distribution characteristics, surface modification states, and potential usability of resource components in lunar soil. This has positive significance for resource evaluation on the Moon and other extraterrestrial bodies, verification of in-situ resource utilization technologies, and deep space resource development.

[0026] In this invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages will become apparent from the description or be learned by practicing the invention. The objectives and other advantages of this invention can be realized and obtained through the description and drawings; furthermore, the analysis results of fine lunar dust particles obtained based on the sample target prepared according to this invention can further serve the comprehensive evaluation of the composition, occurrence state, and development and utilization potential of lunar and other extraterrestrial resources. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings. Figure 1 This is a schematic diagram of the operation process for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm, as provided by the present invention. Figure 2 This is a schematic diagram illustrating the spatial zoning of fine lunar soil particles in an ethanol medium according to particle size differences, as provided by the present invention. Figure 3 The image shows a comparison of the analytical target prepared using existing target preparation methods (left image) and the analytical target prepared using the method of this invention (right image) under a microscope.

[0028] Figure label: 1. Central region; 2. First intermediate transition zone region; 3. Second intermediate transition zone region; 4. Edge region; 5. Petri dish; 6. Isolated large particles. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] To facilitate understanding of the embodiments of this application, further explanation and description will be provided below with reference to the accompanying drawings and specific embodiments. These embodiments do not constitute a limitation on the embodiments of this application. In the drawings, the dimensions and relative dimensions of components may be exaggerated for clarity and / or descriptive purposes. When exemplary embodiments can be implemented differently, a specific process sequence may be performed in a different order than that described. For example, two consecutively described processes may be performed substantially simultaneously or in the reverse order of their description. Furthermore, the same reference numerals denote the same components.

[0031] The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, unless the context clearly indicates otherwise, the singular forms “a” and “the” are intended to include the plural forms as well. Furthermore, when the terms “comprising” and / or “including” and variations thereof are used in this specification, it indicates the presence of the stated features, integrals, steps, operations, parts, components, and / or groups thereof, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, parts, components, and / or groups thereof. It should also be noted that, as used herein, the terms “substantially,” “about,” and other similar terms are used as approximate terms rather than as terms of degree, thus explaining the inherent biases in measurements, calculated values, and / or provided values ​​that would be recognized by one of ordinary skill in the art.

[0032] Example 1

[0033] One specific embodiment of the present invention discloses a method for preparing a micro-area analytical target suitable for lunar dust particles smaller than 10 μm. This method is particularly suitable for preparing micro-area analytical targets for tiny lunar dust samples, especially for separating lunar dust particles with a particle size of less than or equal to 10 μm (preferably 1~10 μm) from mixed lunar soil samples and uniformly dispersing them on the surface of the analytical target. The prepared analytical target can be used for subsequent electron microscopy, electron probe microanalysis, secondary ion mass spectrometry, and other micro-area in-situ analyses. With the help of micro-area in-situ analysis technology, it is possible to obtain information on the morphology, composition, structure, and spatial relationships of lunar dust particles at a microscale, which is especially important for precious and irreplaceable lunar soil samples.

[0034] The preparation method for targets suitable for micro-area analysis of lunar dust particles smaller than 10 μm is described in the following procedure: Figure 1 The preparation method includes the following steps: Step S1: Dispersion pretreatment of lunar soil samples to prepare lunar soil-ethanol suspension A under an inert gas environment.

[0035] In a nitrogen-protected glove box, use a 304 stainless steel sample spoon to take out 2-5 mg of the thoroughly mixed lunar soil sample and transfer the lunar soil sample to a petri dish; add 99.9% analytical grade anhydrous ethanol to the petri dish so that the anhydrous ethanol liquid level covers the surface of the lunar soil sample, thereby obtaining lunar soil-ethanol suspension A.

[0036] In one alternative embodiment, in a nitrogen-protected glove box, a portion of 99.9% analytical grade anhydrous ethanol is added to a clean petri dish beforehand, forming an ethanol layer at the bottom of the dish. Then, a 304 stainless steel sample spoon is used to remove the thoroughly mixed lunar soil sample, and the lunar soil sample is transferred in batches to the petri dish for infiltration, with further additions made at the end. Specifically, before adding the lunar soil sample to the petri dish, V1 volume of anhydrous ethanol is added to the petri dish to form an ethanol layer at the bottom. 1-2 mg of lunar soil sample is then added to the petri dish, allowing it to contact and be initially infiltrated by the anhydrous ethanol. A small amount of anhydrous ethanol (V2 volume) is then added to the initially infiltrated petri dish, followed by the addition of another 1-2 mg of lunar soil sample, which contacts the previously added anhydrous ethanol to complete the infiltration. This process of adding lunar soil sample in batches and replenishing ethanol is repeated until the total amount of lunar soil sample added reaches 2-5 mg, and all lunar soil samples are fully infiltrated. After all lunar soil samples have been infiltrated, V is added to the petri dishes. n+1Volumes of anhydrous ethanol are added, ensuring the ethanol level completely covers the surface of the soaked lunar soil sample, thus obtaining lunar soil-ethanol suspension A. This staged addition of lunar soil sample and anhydrous ethanol reduces splashing, floating, local aggregation, and adhesion to the container walls during the transfer of trace amounts of lunar soil sample, improving the stability and repeatability of sample dispersion pretreatment. It should be noted that the volume of anhydrous ethanol added each time is V1, V2, ..., V... n ,,V n+1 Except for the last time V was added n+1 Volumetric ethanol is used to create a liquid layer above the surface of the lunar soil sample; the remaining amounts of anhydrous ethanol added each time are V1~V. n The amount added should be such that it can wet the lunar soil sample added in the corresponding batch without forming a liquid layer above the surface of the lunar soil sample. The specific amount should be adjusted according to the amount of lunar soil added in the corresponding batch.

[0037] Using a nitrogen-filled glove box for the above operations can reduce the chance of the sample coming into contact with moisture and impurities in the air, thereby reducing the impact of environmental pollution and hygroscopic effects on the dispersion state of fine lunar dust particles. On the other hand, anhydrous ethanol can be used as a dispersion medium to fully wet the lunar soil particles and form a suspension system that can be further graded without introducing the surface tension effect of the aqueous phase.

[0038] In some embodiments, the amount of anhydrous ethanol added is preferably just enough to cover the surface of the lunar soil sample while leaving a certain liquid thickness. That is, after adding anhydrous ethanol to the petri dish and letting it stand for a period of time, the lunar soil sample precipitates and separates into layers with the anhydrous ethanol. After precipitation, the thickness of the anhydrous ethanol liquid layer above the surface of the lunar soil sample is 1-5 mm, that is, the height of the anhydrous ethanol liquid level is 1-5 mm higher than the surface of the lunar soil sample after precipitation.

[0039] Step S2: Remove coarse rock fragments from lunar soil-ethanol suspension A under a microscope to obtain lunar soil-ethanol suspension B containing fine rock fragments.

[0040] The coarse-grained rock fragments include rock fragments, mineral grains, and glass components with a particle size greater than N, where N = n × 10 μm, and n is an integer not less than 8. This means that the critical value for distinguishing between coarse and fine-grained rock fragments is N, which is an integer multiple of 10 μm. In practice, the value of n can be determined according to the actual particle size composition of different types of lunar or asteroidal regolith samples. For example, n can be taken as an integer from 8 to 15, that is, the value of N can be adjusted to 80 μm, 120 μm, or 150 μm. The principle of adjustment is to be able to clearly distinguish between the coarse-grained rock fragment components and the target fine-grained rock fragment components.

[0041] For example, the petri dish containing lunar soil-ethanol suspension A from step S1 is observed under a stereomicroscope. Using a 304 stainless steel picking needle and tweezers, rock fragments, mineral crystals, and glass components with a particle size greater than n×10μm (e.g., greater than 100μm) in lunar soil-ethanol suspension A are picked out one by one to reduce the interference of coarse particles on the subsequent fine particle separation and extraction process. This step S2, by removing significantly larger particle components in advance, narrows the particle size distribution range of the remaining particle system in the suspension, thereby improving the identification and extraction accuracy of fine particle enrichment areas in subsequent centrifugation. For original lunar soil samples with extremely large particle size differences, if this step is not performed, larger particles are prone to causing local disturbances during subsequent processing, which is not conducive to the enrichment and extraction of lunar dust particles smaller than 10μm.

[0042] Step S3: Perform low-speed centrifugation on lunar soil-ethanol suspension B to cause fine rock fragments to spatially separate in the ethanol medium according to their particle size differences. The target fine particles are enriched in the suspension in the central region, that is, lunar dust particles with a particle size of less than 10 μm are distributed in the suspension in the central region of the spatial separation.

[0043] The culture dish 5, containing lunar soil-ethanol suspension B with fine-grained rock debris after step S2, was placed in a slow centrifuge for low-speed centrifugation. This caused the fine-grained lunar soil particles in the culture dish to spatially separate according to their particle size differences in the ethanol medium, with the target fine particles (lunar dust particles ≤10μm) concentrated in the central region of the suspension. The spatial zoning of the particles exhibited a distribution pattern similar to that of barred galaxies, rather than a strictly regular ring shape. After low-speed centrifugation, the spatial distribution of lunar dust particles in culture dish 5 showed the following pattern: lunar dust particles ≤10μm were distributed in the central region 1. From the central region 1 outwards, it can be roughly divided into a first intermediate transition zone region 2, a second intermediate transition zone region 3, and an edge region 4. (See [reference]). Figure 2From the center of the ring outwards, the particle size gradually increases. The particles in the first intermediate transition zone 2 are larger than 10 μm and less than or equal to 30 μm; the particles in the second intermediate transition zone 3 are larger than 30 μm and less than or equal to 100 μm; and the particles in the outermost edge zone 4 are rock fragments or mineral crystals larger than 100 μm, which are isolated large particles. Experimental observations show that under the aforementioned low-speed centrifugation conditions, fine lunar soil particles exhibit size-related zoning at the bottom of the petri dish or in the liquid distribution area. Smaller particles are enriched in the central region, while relatively larger particles are more distributed in the peripheral region or other non-central regions. This allows for the initial enrichment of lunar dust particles smaller than 10 μm. This step is one of the key technical points for obtaining lunar dust particles smaller than or equal to 10 μm. Unlike the screening or simple static sedimentation techniques commonly used in existing technologies, this embodiment uses low-speed centrifugation to achieve gentle particle size separation of lunar soil particles in the liquid phase, thereby avoiding the problems of low efficiency, large sample loss, easy particle adhesion to the screen and electrostatic adsorption of traditional mechanical screening for ultrafine particles.

[0044] In some embodiments, the centrifugation time can be adjusted according to the size of the petri dish, the volume of anhydrous ethanol, and the amount of sample. For example, the centrifugation time is 1 to 10 minutes, preferably 3 to 8 minutes. When performing low-speed centrifugation, the speed of the slow centrifuge can be adjusted in the range of 20 to 60 rpm, preferably 30 rpm, as long as a identifiable particle size distribution can be formed.

[0045] Step S4: Extract the suspension enriched with target fine particles in the central region of the spatial band to obtain a lunar soil-ethanol mixture containing target fine particles.

[0046] Specifically, a 50 μL pipette is used to extract the fine-particle-enriched suspension distributed in the central region in step S3, thereby obtaining a lunar soil-ethanol mixture enriched with lunar dust particles of ≤10 μm, preferably 1~10 μm. When using the 50 μL pipette, the aspiration operation should be performed as quietly as possible without disturbing the particle distribution in the outer regions to reduce the mixing of larger particles into the target fine-particle component. The volume of liquid aspirated by the pipette can be adjusted according to the range of the central region and the degree of fine-particle enrichment. The purpose of this step is to separate the target fine-particle-enriched portion formed after low-speed centrifugation from the original mixed lunar soil system, providing a sample source for subsequent preparation of micro-area analysis targets. Compared with the traditional method of directly picking fine particles from the whole lunar soil sample, this embodiment first achieves particle size separation through centrifugation, and then extracts the fine-particle-enriched region through micro-pipettes, thereby significantly improving the acquisition efficiency of lunar dust particles with a particle size ≤10 μm.

[0047] In one alternative embodiment, in order to form a more refined and well-defined particle size distribution, the low-speed centrifugation process is carried out in a two-stage centrifugation manner.

[0048] The first stage of centrifugation is a rapid pre-segmentation stage, with the following operating parameters: a slow centrifuge speed of 50-60 rpm and a centrifugation time of 2-3 minutes. In this stage, relatively high low-speed centrifugation conditions cause larger lunar soil particles or those with higher equivalent density to preferentially migrate radially and gradually accumulate towards the outer edge of the petri dish; simultaneously, smaller lunar dust particles, due to their lower migration rate, remain mainly in the area near the center. This stage of treatment can quickly increase the spatial distance between coarse and fine particles, forming a preliminary central fine-particle enrichment zone and an outer coarse-particle enrichment zone.

[0049] The second stage of centrifugation is a slow-speed, fine-grained zoning stage, with the following operating parameters: a slow centrifuge speed of 20-30 rpm and a centrifugation time of 4-5 minutes. This stage continues the radial sorting process of particles under lower speed conditions, further stabilizing and refining the initial zoning formed in the first stage. Simultaneously, the lower speed reduces disturbances to the established zoning structure caused by liquid reflux, local eddies, and particle resuspension, decreasing the probability of fine particles being carried to the outer region or coarse particles re-mixing into the central region. Through this stage, lunar soil particles can form a clearer particle size gradient distribution in the ethanol medium; that is, the central region is dominated by fine particles with a diameter ≤10 μm, preferably 1-10 μm, gradually increasing in particle size towards the outer edge, while the edge region shows relatively coarse particles or discontinuous coarse particle enrichment zones.

[0050] The advantages of the two-stage centrifugation process described above are as follows: the first stage can quickly establish the spatial displacement difference between particles of different sizes using a high rotation speed, avoiding indistinct banding caused by excessive processing time at low rotation speeds; the second stage can stabilize and refine the preliminary banding results under milder conditions, avoiding excessive particle migration, edge accumulation, or enhanced liquid disturbance caused by continuous high rotation speeds. Therefore, the two-stage centrifugation method balances banding efficiency and accuracy, and is more conducive to obtaining a lunar soil-ethanol suspension enriched with target fine particles in the central region of the petri dish.

[0051] Step S4: Extract the suspension enriched with target fine particles in the central region of the spatial band to obtain a lunar soil-ethanol mixture containing target fine particles.

[0052] Specifically, after completing the low-speed centrifugation and banding in step S3, the culture dish is kept horizontal to avoid shaking or tilting that could damage the banding structure. Subsequently, the central fine particle enrichment region is identified under stereomicroscope or microscopic observation conditions, and the suspension is slowly aspirated from the central fine particle enrichment region using a 50 μL pipette to obtain a lunar soil-ethanol mixture enriched with lunar dust particles ≤10 μm in diameter, preferably 1~10 μm.

[0053] During aspiration, the pipette tip should be as close as possible to the central fine particle enrichment area, avoiding contact with the particle layer deposited at the bottom of the culture dish. The aspiration speed should be slow and stable to minimize the impact of liquid disturbance on the peripheral coarse particle zone. Preferably, the aspiration depth after the pipette tip is inserted into the liquid surface should be such that the suspension in the central area can be aspirated without scraping off the coarse particles at the bottom. The volume of a single aspiration can be adjusted according to the size of the central area and the degree of fine particle enrichment; for example, the volume of a single aspiration is 10-50 microliters. When the central area is large or the content of the target fine particles is low, multiple small aspirations can be used to complete the extraction, thereby improving the recovery rate of the target fine particles and reducing the probability of coarse particle contamination.

[0054] In this step, the central fine-particle enrichment region is the target sampling area formed by low-speed centrifugation in step S3. Since larger particles preferentially migrate to the outer edges during centrifugation, while smaller lunar dust particles migrate relatively shorter distances, the central region can relatively enrich target fine particles with a diameter ≤10 μm. By performing micro-pipette extraction on this region, the target fine particles can be separated from the original mixed lunar soil system, providing a sample source for subsequent target-defined area deposition, resin embedding, and micro-area analysis target preparation.

[0055] Compared to traditional methods that involve manually picking fine particles directly from whole lunar soil samples, this step does not rely on the operator identifying and picking fine particles one by one from the mixed particles. Instead, it first uses two-stage low-speed centrifugation to create particle size bands, and then performs targeted micro-absorption from the fine particle enrichment areas. Therefore, this step can reduce the difficulty of manual picking, reduce sample loss, improve the acquisition efficiency and extraction stability of lunar dust particles with a particle size ≤10μm, and help reduce the interference of larger particles on the subsequent micro-area analysis target preparation.

[0056] Step S5: Mark the defined deposition area on the glass plate, and drop the lunar soil-ethanol mixture obtained in step S4 into the defined deposition area; allow the sediment to stand for a predetermined time, allowing the ethanol to fully evaporate, and the target fine particles to be deposited in the defined deposition area, thus obtaining the sample before resin embedding.

[0057] Step S51: Mark the defined deposition area on the glass plate, and use a pipette to drop the aspirated lunar soil-ethanol mixture onto the defined deposition area on the glass plate.

[0058] Step S511: First, apply traceless double-sided tape to the surface of the glass plate. The traceless double-sided tape is used to temporarily fix the particle deposition area during the subsequent target preparation process, and at the same time, it plays the role of limiting the droplet diffusion range and facilitating resin embedding into the target.

[0059] Step S512: Mark two concentric circles with diameters of 2.54 cm and 1 cm on the glass plate using a waterproof marker. The 1 cm diameter circle defines the deposition area. Using a 50 μL pipette, drop the lunar soil-ethanol mixture extracted in step S4 into the 1 cm diameter circle, allowing the target fine particles to deposit within the defined deposition area. The 1 cm diameter circle controls the distribution density of the lunar soil fine particles on the target surface, preventing excessive particle dispersion and a low effective particle count per unit area, and also preventing excessively small droplet areas that could lead to overly dense, clumped, and stacked particles.

[0060] Compared with the prior art of directly dripping a solution containing fine particles onto any substrate surface, this embodiment precisely controls the deposition range by pre-setting a concentric circle region on a glass plate. This ensures that the target fine particles remain within the predetermined region after the ethanol evaporates, facilitating subsequent resin target preparation, polishing, and microscopic positioning analysis.

[0061] Step S52: Place the glass plate with the lunar soil-ethanol mixture added in a Class 100 clean bench and let it stand for a predetermined time to allow the ethanol to evaporate completely. The target fine particles are deposited and retained in the defined area, and the particles are initially dispersed to form a sample before resin embedding.

[0062] Specifically, after adding the lunar soil-ethanol mixture to the defined deposition area in step S51, the glass plate is placed in a Class 100 clean bench and left to stand for a predetermined time until the ethanol completely evaporates, allowing the target fine particles to deposit and remain within the defined area. Using a Class 100 clean bench can effectively reduce environmental particulate contamination and prevent foreign dust from mixing into high-value lunar dust samples. Before the ethanol evaporates, auxiliary operations such as adding small amounts in stages, dot-matrix or spiral distribution, short-term horizontal low-speed rotation, and adding blank areas under microscopic observation can be used to ensure that the lunar soil-ethanol mixture covers the 1cm defined deposition area as evenly as possible. Specifically, the lunar soil-ethanol mixture obtained in step S4 can be divided into multiple micro-droplets and added sequentially from the center to the edge, so that different droplets partially contact or slightly connect, thereby reducing local particle accumulation caused by a single concentrated drop. After the addition is completed, the glass plate can be rotated horizontally at low speed or gently oscillated for a short time to promote the slow spread of the liquid within the defined area, but the liquid should be prevented from crossing the boundary of the defined area. Subsequently, the particle distribution is observed under a stereomicroscope. For sparsely populated areas, a small amount of additional droplets can be applied to improve the uniformity of the target fine particles' coverage throughout the defined area. These auxiliary operations reduce edge enrichment, particle agglomeration, and excessively thick local deposition that occur during ethanol evaporation, thereby improving the effectiveness of subsequent resin embedding and micro-area analysis. The above process creates a relatively dispersed initial particle distribution within the defined area of ​​lunar soil particles, with double-sided adhesive serving a fixing function. This embodiment utilizes a "liquid-phase transfer followed by controlled evaporation" method to achieve relatively uniform spreading of the target fine particles within the defined area of ​​the target surface, reducing particle accumulation and local adhesion problems caused by direct dry picking.

[0063] In some implementations, the glass plate after adding the lunar soil-ethanol mixture needs to be left to stand in a Class 100 clean bench for 20 to 60 minutes, preferably 25 to 40 minutes, such as 30 minutes. This time range ensures that the ethanol evaporates completely while avoiding unnecessary environmental pollution caused by excessively long sample standing time, thus balancing the requirements of evaporation efficiency and sample purity.

[0064] To improve ethanol evaporation efficiency, a low-vacuum assisted evaporation method can also be used. Specifically, a glass plate with a lunar soil-ethanol mixture added is placed in a clean vacuum dryer, a clean vacuum chamber, or a low-vacuum container purged with nitrogen. While keeping the glass plate horizontal, the chamber pressure is slowly reduced, allowing the ethanol to evaporate more rapidly under a low-vacuum environment. The low-vacuum conditions are designed to prevent significant boiling, bubbling, splashing, or particle migration of the droplets. For example, the chamber pressure can be controlled at 40-80 kPa, preferably 50-70 kPa, and the processing time can be 5-20 minutes, preferably 8-15 minutes. During the vacuuming process, a gradual pressure reduction method is preferred, slowly lowering the pressure to the target range, and maintaining the evaporation process while observing stable droplet edges and no significant splashing or bubble disturbance.

[0065] When using a low-vacuum assisted evaporation method, the ethanol evaporation time can be shortened while reducing the environmental exposure risks associated with prolonged static storage. Simultaneously, because the low-vacuum conditions avoid violent boiling and rapid airflow disturbances, the possibility of target fine particles being carried away from the defined deposition area by liquid disturbances can be reduced, ensuring that the target fine particles remain primarily deposited within the defined area. Therefore, sample preparation efficiency can be improved while maintaining sample purity and particle distribution stability.

[0066] In some implementations, a stereomicroscope can be used to observe whether the liquid in the lunar soil-ethanol mixture has completely evaporated and whether the particles are stably attached, to determine whether the target fine particles have reached a suitable state within the defined deposition area, i.e., effective deposition has been achieved. Here, "effective deposition" refers to a situation where the target fine particles are relatively uniformly spread within the defined area of ​​the target surface, with almost no particle accumulation or local adhesion.

[0067] Step S6: Perform resin embedding on the sample before resin embedding to prepare the resin target.

[0068] After the ethanol evaporates completely in step S5, an epoxy resin embedding target is prepared by using a mold with a diameter of 2.54 cm to embed the deposition area of ​​the sample before resin embedding, forming a resin target preform. Then, the resin target preform is placed in a drying oven for drying and curing treatment to obtain the resin target before polishing. The epoxy resin is used to embed and fix the fine dust particles that have been deposited and dispersed within the area defined by the glass plate, thereby obtaining an analytical target suitable for subsequent polishing and micro-area analysis.

[0069] In some embodiments, the epoxy resin can be a conventional low-shrinkage analytical sample preparation resin. The resin-to-curing agent ratio can be performed according to the product instructions. To achieve full curing and ensure target quality, the curing temperature is 50-70°C, and the curing time is 24-48 hours.

[0070] For example, a forced-air drying oven is used, with the drying temperature set at 60°C and the curing time at 36 hours. Using a 60°C forced-air drying oven for extended curing helps improve the integrity and mechanical stability of the resin during curing, reducing the risk of particle detachment during subsequent polishing.

[0071] The curing time and temperature can be adjusted appropriately based on the actual thickness of the resin embedding to ensure effective curing while avoiding excessively high temperatures that could alter the properties of the particles. If the resin embedding thickness is large, the curing time can be extended (e.g., to 48 hours) or the drying temperature can be increased (e.g., to 65℃) to ensure complete internal curing of the resin. If the resin embedding thickness is small, the curing time can be shortened (e.g., extended to 24 hours) and the drying temperature can be lowered (e.g., to 50℃).

[0072] Step S7: Perform progressive fine polishing on the resin target to obtain a sample target with a flat surface suitable for micro-area analysis.

[0073] Specifically, a micron-sized diamond polishing paste with particle sizes ranging from coarse to fine is used to perform progressively fine polishing on the resin target, with at least three polishing levels. The specific operation is as follows: The cured resin target from step S6 is taken out, and diamond polishing pastes with particle sizes of 0.5 microns, 0.25 microns, and 0.1 microns are used sequentially to polish the resin target, with each polishing session lasting 10 to 20 minutes. No coolant is added during the polishing process, thereby obtaining a smooth target surface suitable for micro-area analysis. This embodiment uses micron-sized diamond polishing paste with particle sizes ranging from coarse to fine for progressive polishing, ensuring target surface smoothness while reducing excessive disturbance to the surface of tiny lunar dust particles. Simultaneously, the absence of coolant during polishing avoids the localized shedding, migration, or cross-contamination of extremely fine particles due to liquid flow. After the above steps, a micro-area analysis target enriched with lunar dust particles smaller than 10 microns (mainly 1 to 10 microns) and relatively dispersed on the target surface is obtained, suitable for subsequent micro-area surface analysis using electron microscopy, electron probe microanalysis, and secondary ion mass spectrometry.

[0074] See Figure 3 The left image is a microscopic image of an analytical target prepared using existing target preparation methods, and the right image is a microscopic image of an analytical target prepared using the method of the present invention. It can be clearly seen from the images that the analytical target prepared by the method of the present invention does not show any adhesion, agglomeration or stacking of fine lunar dust particles, has good particle dispersion, and better exposure of individual mineral particles.

[0075] Compared with the prior art, the method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm provided in this embodiment has at least one of the following beneficial effects: 1. In view of the problem that traditional methods are difficult to effectively separate target fine particles from mixed lunar soil due to the large particle size range and complex composition of lunar soil samples, this invention disperses the lunar soil sample in anhydrous ethanol and combines steps such as coarse particle removal, low-speed centrifugation for zoning and extraction of the central region. This can effectively separate and enrich lunar dust particles smaller than 10 μm, especially 1~10 μm, from mixed lunar soil with a large particle size range, thereby solving the problem that existing technologies are difficult to effectively pick out ultrafine lunar dust particles.

[0076] 2. To address the problem that 1-10μm lunar dust particles are prone to adhesion, agglomeration, and stacking due to surface forces during sample preparation, making it difficult to achieve single-particle dispersion and spreading, this invention adds a suspension of target fine particles to a predetermined and limited deposition area and uses a volatilization deposition method to spread the lunar dust particles on the target surface. This effectively reduces the degree of adhesion, agglomeration, and stacking of fine lunar dust particles during sample preparation, improves particle dispersibility and single-particle exposure, and thus improves the conditions for subsequent micro-area analysis.

[0077] 3. Existing common sample preparation methods such as embedding, grinding, and polishing are difficult to balance the retention of large and small particles when processing lunar soil samples with large particle size differences. This can easily lead to the loss, detachment, or ineffective exposure of fine particles. This invention avoids the problems of loss, detachment, or ineffective retention of fine particles caused by large particle size differences in traditional whole sample preparation by adopting a processing route of "first separating the target fine particles, and then performing limited area deposition and resin embedding". This is beneficial to improving the retention rate of lunar dust particles smaller than 10 μm in the final analytical target.

[0078] 4. This invention completes the dispersion, extraction, deposition and target preparation of lunar soil samples under nitrogen-filled and clean conditions, and uses anhydrous ethanol as the dispersion medium, which can significantly reduce the influence of external moisture, impurities and air disturbance on the original state of fine lunar dust particles, and help to preserve their original morphology, surface features and occurrence state.

[0079] 5. To address the problem that existing technologies struggle to preserve the original morphology, composition, and surface structure information of lunar dust samples, this invention offers a clear and simple operational process. It enables the effective separation, dispersion, and stable target preparation of lunar dust particles smaller than 10 μm, especially those between 1 and 10 μm, providing a stable and reliable sample carrier for subsequent electron microscopy, electron probe microanalysis, secondary ion mass spectrometry, and other in-situ micro-area analyses. Furthermore, the equipment and experimental conditions used are readily achievable, exhibiting good repeatability and practicality, making it particularly suitable for the preparation of micro-area analytical targets for ultrafine lunar dust particles in precious trace lunar soil samples.

[0080] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above description is only a specific embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a micro-area analysis target suitable for lunar dust particles smaller than 10 μm, characterized in that, include: Step S1: Prepare lunar soil-ethanol suspension A; Step S2: Remove coarse rock fragments from lunar soil-ethanol suspension A under a microscope to obtain lunar soil-ethanol suspension B containing fine rock fragments; the coarse rock fragments include rock fragments with a particle size greater than N, mineral grains, and glass components; where N = n × 10 μm, and n is an integer not less than 8; Step S3: Perform low-speed centrifugation on lunar soil-ethanol suspension B to cause the fine rock fragments to spatially separate according to their particle size differences in the ethanol medium, with the target fine particles being enriched in the suspension in the central region. Step S4: Extract the suspension in the central region to obtain a lunar soil-ethanol mixture containing the target fine particles; Step S5: Mark the defined deposition area on a glass plate, and drop the lunar soil-ethanol mixture into the defined deposition area; allow the sediment to stand for a predetermined time, allowing the ethanol to fully evaporate, and the target fine particles to be deposited in the defined deposition area, thus obtaining the sample before resin embedding; Step S6: Perform resin embedding on the sample before resin embedding to prepare a resin target.

2. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 1, characterized in that, Also includes: Step S7: Perform progressive fine polishing on the resin target to obtain a sample target with a flat surface suitable for micro-area analysis.

3. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 2, characterized in that, In step S1, the lunar soil-ethanol suspension A is prepared under an inert gas environment.

4. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 1, characterized in that, In step S3, the lunar soil-ethanol suspension B is centrifuged at low speed using a slow centrifuge. The speed of the slow centrifuge is 20-60 rpm, and the centrifugation time is 1-10 minutes.

5. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 4, characterized in that, The slow centrifuge operates at 30 rpm and centrifuges for 3 to 8 minutes.

6. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 1, characterized in that, In step S4, the suspension in the central region is extracted using a 50 μL pipette.

7. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 1, characterized in that, Step S5 includes: Step S51: Mark the defined deposition area on the glass plate, and use a pipette to drop the aspirated lunar soil-ethanol mixture onto the defined deposition area on the glass plate; Step S52: Place the glass plate with the lunar soil-ethanol mixture added in a Class 100 clean bench and let it stand for a predetermined time to allow the ethanol to evaporate completely. The target fine particles are deposited and retained in the defined area, and the particles are initially dispersed to form a sample before resin embedding.

8. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 1, characterized in that, Step S51 includes: Step S511: First, apply traceless double-sided tape to the surface of the glass plate; Step S512: Mark two concentric circles with diameters of 2.54 cm and 1 cm on the glass plate. The circular area with a diameter of 1 cm is the defined deposition area.

9. The method for preparing a micro-area analysis target for lunar dust particles smaller than 10 μm according to claim 1, characterized in that, Step S6 is as follows: After the ethanol has evaporated in step S5, the deposition area is embedded in epoxy resin using a mold with a diameter of 2.54 cm to form a resin target preform. The resin target blank is placed in a drying oven for drying and curing to obtain the resin target before polishing.

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