Preparation method of powder particle section observation sample and sample

Abstract

The invention provides a preparation method of a powder particle section observation sample and the sample, and relates to the technical field of material microstructure analysis. The preparation method comprises the following steps: mixing powder particles with a binder to obtain a mixture, coating the surface of a supporting substrate with the mixture to form a thin layer, and curing the thin layer; cutting the cured thin layer to obtain a thin layer with an initial cross section; fixing the thin layer with the initial cross section on the sample table, and enabling the initial cross section to protrude from the sample table; the protruding initial cross-section is ion milled using an ion beam to obtain a final analysis cross-section. According to the invention, the particles and the binder are pre-mixed and coated to form a film, so that firm fixation of the particles is ensured; mechanical pre-cutting and ion fine grinding are combined, so that the sample preparation efficiency is improved, and a non-damage high-quality section capable of truly reflecting the internal structure of the material is obtained.

Description

Technical Field

[0001] This invention relates to the field of material microstructure analysis technology, specifically to a method for preparing a sample for observing the cross-section of powder particles and the sample itself. Background Technology

[0002] In fields such as materials science, chemical engineering, geological exploration, and biomedicine, the internal microstructure of powder materials, such as pores, grain boundaries, and phase distribution, plays a decisive role in their macroscopic properties. Therefore, accurate observation of the internal morphology of powder particles is crucial for materials development, performance optimization, and failure analysis.

[0003] In the field of materials synthesis, studying the internal morphology of powder particles allows us to understand the nucleation and growth mechanisms of powders during synthesis, thereby optimizing synthesis processes and improving material quality and performance. For example, in the preparation of metal powders, different preparation processes lead to different structural features within the powder particles, such as pores and inclusions. These features directly affect the density, strength, and other properties of the subsequently sintered products. In the field of catalysts, the internal morphology of powder catalysts is closely related to the distribution of active sites. Studying their internal structure helps to reveal the essence of catalytic reactions and develop more efficient catalysts.

[0004] Currently, obtaining the internal morphology of particles mainly relies on preparing cross-sections of the particles and then observing them using equipment such as scanning electron microscopes. Traditional mechanical grinding and polishing methods, when processing discrete, small powder particles, are prone to mechanical stress that can easily cause particle breakage, detachment, or damage such as scratches and deformation on the sample surface, making it difficult to reflect their true internal structure. While focused ion beam methods can precisely cut individual particles, their sample preparation efficiency is extremely low, their cost is high, and their processing area is very limited, making them unsuitable for large-scale particle analysis requiring statistical significance.

[0005] Ion milling technology utilizes high-energy ion beams for non-contact physical exfoliation of samples, avoiding mechanical damage and making it an ideal technique for obtaining high-quality cross-sections. Some existing methods attempt to apply this technology to powder samples, for example, by spraying or dispersing powder particles onto a substrate coated with a binder for fixation, followed by ion milling. However, this fixation method easily leads to uneven particle distribution, agglomeration, or insufficient bonding between the particles and the binder. During subsequent cutting and milling processes, particles easily detach from the matrix, resulting in sample preparation failure and ultimately failing to obtain a flat, complete, and effective analytical cross-section containing a large number of particles. Therefore, developing a method that can efficiently and stably prepare non-destructive, high-quality powder particle cross-sections is a pressing technical challenge in this field. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the purpose of this invention is to provide a method for preparing a powder particle cross-section observation sample and the sample itself.

[0007] A method for preparing a powder particle cross-section observation sample according to the present invention includes the following steps: The powder particles are mixed with a binder to obtain a mixture, the mixture is coated on the surface of a support substrate to form a thin layer, and the thin layer is cured. The cured thin layer is cut to obtain a thin layer with an initial cross-section; The thin layer with the initial cross-section is fixed to the sample stage, and the initial cross-section protrudes from the sample stage; The protruding initial cross-section is ion-milled using an ion beam to obtain the final analytical cross-section.

[0008] Preferably, the step of forming the thin layer specifically includes: The powder particles are premixed with the adhesive, and the resulting mixture is then coated onto the surface of the support substrate to form the thin layer.

[0009] Preferably, the adhesive is an instant adhesive, and the supporting substrate is a copper foil.

[0010] Preferably, the adhesive is epoxy resin, and the step of curing the thin layer includes heating the thin layer.

[0011] Preferably, in the ion milling step, the ion beam energy is 10kV to 15kV, and the swing angle of the sample stage is ±30 degrees to ±50 degrees.

[0012] Preferably, the powder particles are one or more of lithium battery electrode material powder, metal powder, or ceramic powder.

[0013] A powder particle cross-section sample provided by the present invention includes: Support substrate; A thin layer is cured and disposed on the support substrate, the thin layer being composed of an adhesive and a plurality of powder particles encapsulated in the adhesive; The thin layer has an analytical section formed by ion milling, and the analytical section exposes the internal structure of the plurality of powder particles.

[0014] Preferably, the powder particles are lithium battery cathode material particles.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention ensures that each particle is effectively wrapped and firmly fixed by the binder by pre-mixing powder particles with binder and coating them into a film. This fundamentally solves the problems of uneven particle distribution and easy detachment caused by existing spraying methods, and significantly improves the stability of subsequent processing.

[0016] 2. This invention can fix a large number of powder particles on the same substrate, and obtain a large number of particle cross sections through a single ion milling process, which greatly improves the analysis efficiency and meets the needs of statistical analysis of samples in industrial research and development.

[0017] 3. This invention adopts a two-step strategy of "mechanical pre-cutting + ion fine grinding", which not only utilizes the high efficiency of mechanical cutting, but also completely eliminates the mechanical damage layer through subsequent ion grinding, and finally obtains a smooth and stress-free ideal cross section that can truly reflect the original internal structure of the material.

[0018] 4. This invention has no special requirements on the type or size of powder particles and is applicable to the internal structure analysis of various powder materials such as metals, ceramics, and polymers. Attached Figure Description

[0019] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A flowchart illustrating a method for preparing a cross-sectional sample of powder particles provided in this application embodiment; Figure 2 This is a schematic diagram of the sample loading structure provided in an embodiment of this application; Figure 3 This is a schematic diagram of the surface morphology of powder particles before ion milling, according to an embodiment of this application. Figure 4 This is a schematic diagram of the first cross-sectional morphology of powder particles after ion milling, according to an embodiment of this application. Figure 5 This is a schematic diagram of the second cross-sectional morphology of powder particles after ion milling, according to an embodiment of this application.

[0020] Explanation of reference numerals in the attached figures: 1. Cured thin layer containing particles; 2. Supporting substrate; 3. Fixed sample stage. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0022] This application provides a specific method for preparing and observing cross-sectional samples of lithium battery cathode material powder particles. (Refer to...) Figure 1 This method fully demonstrates the entire process from sample preparation to final observation. It aims to obtain a high-quality cross-section that accurately reflects the internal microstructure of nickel-cobalt-manganese ternary cathode material (NCM material) powder particles through a series of precisely controlled steps. Specifically, the method includes a particle fixation and film formation step S10, an initial cross-section preparation step S20, a sample loading step S30, an ion milling step S40, and a morphology observation step S50.

[0023] First, the particle fixation and film formation step S10 is performed. The core purpose of this step is to firmly and uniformly fix the discrete micro-powder particles in the substrate to form a whole that facilitates subsequent processing. Specifically, a clean support substrate 2 is prepared. In one embodiment of this application, a high-purity oxygen-free copper foil with a size of approximately 7 mm × 7 mm and a thickness of approximately 0.015 mm is preferably used as the support substrate 2. It is understood that copper foil is chosen because of its good conductivity, which is beneficial for reducing charge accumulation effects in subsequent scanning electron microscopy observations; at the same time, copper foil also has suitable flexibility and strength, making it easy to handle. Before operation, it is necessary to ensure that the surface of the copper foil is free of oil, oxide layer and other contaminants. For example, it can be cleaned by wiping with solvents such as ethanol or acetone, and then dried with compressed air.

[0024] Next, the adhesive is prepared. As an optional implementation, this embodiment uses a fast-curing cyanoacrylate adhesive (commonly known as instant adhesive), such as the commercially available Tamiya 87139 instant adhesive. The advantage of using this type of instant adhesive is its rapid curing; it can form a cured layer with sufficient strength at room temperature in a short time, thereby significantly shortening the waiting time for sample preparation. During operation, a dropper or directly from the adhesive bottle can be used to carefully take one drop of the instant adhesive solution and add it to the center of a clean copper foil surface.

[0025] Then, the NCM material powder to be observed (approximately 2 mg) was added to the binder. For example... Figure 3The diagram schematically illustrates the original surface morphology of these particles before treatment. They typically appear as secondary spherical particles composed of numerous tiny primary particles aggregated together, with an uneven surface. To ensure uniform dispersion of the powder particles in the binder, a sharp tool (such as a clean toothpick tip) is used to quickly and gently stir the droplet until the NCM powder particles are fully wetted and uniformly dispersed by the instant adhesive, thus preventing particle agglomeration. It should be noted that this premixing step is crucial to ensuring that a large number of well-dispersed particles can be observed on the final cross-section. Compared to the existing method of applying adhesive first and then sprinkling powder, this method allows each particle to be fully coated with the binder, thereby greatly enhancing the bonding force between the particles and the cured substrate.

[0026] After mixing, the particle-binder mixture needs to be coated onto the surface of the support substrate 2 to form a thin layer of uniform thickness. In this embodiment, a simple and effective coating method can be used: a clean, lint-free cloth is laid flat over the mixture, gentle and uniform pressure is applied, and the cloth is quickly dragged across the mixture in a horizontal direction. The smooth surface of the cloth is used to coat the high-viscosity mixture into a film with a thickness of approximately tens to hundreds of micrometers. This thickness range ensures complete embedding of the particles without being too thick, which would increase the difficulty of subsequent cutting and grinding.

[0027] After coating, the support substrate 2 with the particle-containing thin layer is left to stand at room temperature in a dry environment. Due to the use of instant adhesive, the curing process is usually completed within 30 minutes. After the adhesive is fully cured, a composite structure is obtained in which the particle-containing cured thin layer 1 is firmly attached to the support substrate 2, in which a large number of NCM powder particles are stably embedded in the cured adhesive matrix, forming a solid whole.

[0028] After particle fixation and film formation are completed, the initial cross-section preparation step S20 is performed. This step aims to create a flat initial cross-section on the solidified thin layer, suitable for subsequent ion milling. Specifically, the sample prepared in the previous step is placed on a flat, stable cutting pad. A sharp blade (such as a surgical blade or a new utility knife) is used, roughly perpendicular to the sample surface, to quickly and decisively cut from top to bottom. Understandably, while this rapid cutting method may produce plastic deformation, scratches, and stress damage layers at the microscopic scale due to mechanical action, it macroscopically yields a relatively flat "blade-cut surface," thus providing an ideal starting plane for subsequent fine ion milling and greatly improving sample preparation efficiency.

[0029] The process then proceeds to sample loading step S30, the purpose of which is to precisely fix the sample with its initial cross-section onto the sample stage for ion milling. (Refer to...) Figure 2In this embodiment, a specially made copper block is used as the fixed sample stage 3 (for example, its dimensions can be 4 mm thick, 18 mm wide, and 16 mm high). Copper is chosen to ensure good electrical and thermal conductivity. A piece of conductive tape with a width of 8 mm (such as carbon conductive tape from the Rixin brand) is taken and pasted onto the top surface of the fixed sample stage 3 after the support substrate 2, which has been cut in step S20. A key feature is the precise adjustment of the position of the support substrate 2 so that its edge with the kerfed surface protrudes from the top edge of the fixed sample stage 3 by a preset height (in this embodiment, the protrusion height is set to about 1 mm). The purpose of this setting is to ensure that during the subsequent ion polishing process, the ion beam can bombard the entire initial cross-section without being blocked by the edge of the fixed sample stage 3, thereby ensuring a complete and uniform polishing effect.

[0030] After sample loading is completed, the core step of ion polishing, S40, is performed. The fixed sample stage 3, with the sample loaded, is placed into the sample chamber of the ion polishing equipment. In this embodiment, the equipment used is the SEMPREP SMART cross-section ion polisher manufactured by Technoorg Linda in Hungary, and the sample stage is installed on the matching 90-degree cross-section sample stage adapter. Accordingly, process parameters that are crucial to the final cross-section quality need to be set. In this embodiment, the following preferred parameters are set for NCM materials and instant adhesive substrates: the ion gun energy is set to 12 kV, which is sufficient to effectively peel the material without introducing excessive thermal damage; the sample stage swing angle is set to ±40 degrees to eliminate the "curtain effect" streaks that may be caused by a single ion beam incident angle, resulting in a smoother cross-section; the sample stage tilt angle (relative to the ion beam incident direction) is set to 7 degrees; and the processing time is set to 1 hour. After the equipment is started, the high-energy argon ion beam performs continuous and precise physical peeling of the sample's protruding initial cross-section in a high vacuum environment, removing the material atomically layer by atomically in a non-contact manner, thereby completely eliminating the damage layer and stress layer introduced by mechanical cutting in step S20.

[0031] After one hour of ion milling, a smooth, stress-free, and scratch-free final analytical section was formed on the original cutting plane. The NCM powder particles embedded on it were precisely "cut open," revealing their true internal structure.

[0032] Finally, the morphology observation step S50 is performed. The sample, after ion milling, along with the fixed sample stage 3, is directly transferred to the sample chamber of the scanning electron microscope for observation. In this embodiment, the equipment used is a Phenom Pharos field emission scanning electron microscope manufactured by Thermo Fisher Scientific. It is understood that since the entire sample system (including copper foil, copper plate, and conductive tape) has good conductivity, high-resolution imaging is usually possible without additional gold or carbon sputtering treatment on the sample surface. The electron beam is focused on the final analytical section, and clear observation can be achieved by adjusting the magnification. Figure 4 and Figure 5 As shown, the final analytical section reveals a large number of NCM particles that have been smoothly cut open, exhibiting a clear internal morphology. This clearly distinguishes each spherical secondary NCM particle from numerous smaller (typically submicron-level) primary particles (i.e., grains) that are either tightly or loosely packed. Furthermore, grain boundaries between primary particles, gaps and pores due to incomplete sintering or inherent material properties, and even microcracks that may occur within the particles due to cycling are all clearly visible. These high-quality microstructural images provide invaluable and intuitive experimental evidence for in-depth analysis of the rate performance, cycle stability, and failure mechanism of this cathode material.

[0033] This application provides a method for preparing powder particle cross-section observation samples. By combining a pre-mixing and coating process of powder particles with a binder to form a film, along with a two-step cross-section preparation strategy of "mechanical pre-cutting + protruding loading + ion fine grinding," this method effectively solves the problems of difficult, easily damaged, and inefficient powder sample preparation in existing technologies. This method not only stably and efficiently obtains a large number of high-quality, non-damaging cross-sections of powder particles, but also, through adjustments to material and process parameters, is widely applicable to various types of powder systems, from lithium battery materials to ceramics and metals, providing strong technical support for the microstructure analysis of materials. It is understood that the sample itself prepared by this method—a composite thin layer containing a large number of powder particles embedded in the binder and possessing an ion-milled cross-section on a supporting substrate—also constitutes a product with a novel structure.

[0034] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method of preparing a sample for cross-section observation of a powder particle, characterized by, The method comprises the following steps: mixing powder particles with a binder to obtain a mixture, coating the mixture on a surface of a support substrate to form a thin layer, and curing the thin layer; cutting the cured thin layer to obtain a thin layer with an initial cross section; fixing the thin layer with the initial cross section on a sample stage and protruding the initial cross section from the sample stage; ion milling the protruding initial cross section by using an ion beam to obtain a final analysis cross section.

2. The method of preparing a powder particle cross-section observation sample according to claim 1, characterized by, The step of forming a thin layer specifically comprises: pre-mixing the powder particles with the binder, and then coating the obtained mixture on the surface of the support substrate to form the thin layer.

3. The method of preparing a cross-section observation sample of powder particles according to claim 2, characterized by, The binder is a quick-drying adhesive, and the support substrate is a copper foil.

4. The method of preparing a cross-section observation sample of powder particles according to claim 2, characterized by, The binder is an epoxy resin, and the step of curing the thin layer comprises heating the thin layer.

5. The method of preparing a cross-section observation sample of powder particles according to claim 1, characterized by, In the step of ion milling, the ion beam energy is 10 kV to 15 kV, and the sample stage swing angle is ±30 degrees to ±50 degrees.

6. The method of preparing a cross-sectioned sample of powder particles according to claim 1, wherein The powder particles are one or more of lithium battery electrode material powder, metal powder, or ceramic powder.

7. A powder particle cross-section sample, characterized by, It comprises: a support substrate; curing a thin layer disposed on the support substrate, the thin layer being composed of a binder and a plurality of powder particles wrapped in the binder; wherein the thin layer has an analysis cross section formed by ion milling the thin layer, and the analysis cross section exposes the internal structure of the plurality of powder particles.

8. The powder particle cross-section sample of claim 7, wherein, The powder particles are lithium battery positive electrode material particles.

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