A method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information

Abstract

The present invention provides a method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information. The method includes: Step 1, preparing a sample of a ceramic matrix nanocomposite and designing a synchrotron radiation nano-CT imaging experiment; Step 2, acquiring a nano-CT projection sequence and performing CT reconstruction and three-dimensional visualization; Step 3, establishing a three-dimensional high-order nearest neighbor index model of nanoparticles within any spatially interested region in the sample; Step 4, qualitatively and quantitatively characterizing the three-dimensional distribution pattern of nanoparticles and obtaining the multi-scale information of nanoparticles according to the analysis and calculation of the three-dimensional high-order nearest neighbor index model.

Description

Technical Field

[0001] The present invention relates to the technical fields of analysis and characterization of particle distribution and X-ray computed tomography, and particularly relates to a method for analyzing the three-dimensional distribution of nanoparticles in a nanocomposite reconstructed by synchrotron radiation nano-CT based on three-dimensional high-order nearest neighbor index analysis and obtaining multi-scale information of the nanoparticles. Background Art

[0002] Ultra-high temperature ceramic materials have characteristics such as high melting point (>3000 °C), high hardness (>20 GPa), low density (6.08 g / cm3), excellent electrical and thermal conductivity, corrosion resistance, and oxidation resistance, which have attracted more and more attention from scientists. Adding nanoparticles into ceramic matrix grains or grain boundaries is of great significance for improving the performance of ceramic composites. For example, adding nanoparticles at the nanoscale to the ceramic matrix can enhance its oxidation resistance and mechanical properties. Adjusting the ratio and dispersion degree of nanoparticles can further increase its oxidation resistance, density, and mechanical properties. It can be seen that the aggregation distribution and agglomeration degree of nanoparticles are very important for the comprehensive performance and reliability of the composite material. Therefore, evaluating the three-dimensional distribution of nanoparticles in the ceramic matrix has always been the key in the development and research of nanocomposites.

[0003] The three-dimensional high-order nearest neighbor distance index (Nearest Neighbour Index, NNI) is a method for analyzing the mean value of the nearest neighbor distances between points in three-dimensional space, and is used to characterize and analyze the distribution law of point sets in three-dimensional space.

[0004] SEM, TEM, and X-ray diffraction have been widely used to observe the dispersion and aggregation of nanoparticles in ceramic products of nanocomposites. However, these technical methods are time-consuming, destructive, and limited to the characterization of two-dimensional slices, which will distort the actual morphology or particle distribution, and cannot represent the particle morphology and distribution in the three-dimensional volume. Nano-CT can obtain non-destructive three-dimensional nano-scale tomographic structure imaging, and is widely used in many research fields such as biomedicine, microsystem manufacturing, and materials science.

[0005] Currently, there is no relevant report on combining three-dimensional NNI with nano-CT to analyze and characterize the three-dimensional distribution of nanoparticles inside nanocomposites and obtain clustering information. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention proposes a method for analyzing the three-dimensional distribution of nanoparticles and obtaining its multi-scale information. This method non-destructively qualitatively and quantitatively characterizes the three-dimensional distribution characteristics of nanoparticles in the region of interest (ROI) of the three-dimensional space of the ceramic nanocomposite and obtains the clustering information of the nanoparticles.

[0007] The technical solution of the present invention is as follows: A method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information, comprising the following steps:

[0008] Step 1, prepare a sample of a ceramic matrix nanocomposite and design a synchrotron radiation nano-CT imaging experiment;

[0009] Step 2, obtain a nano-CT projection sequence and perform CT reconstruction and three-dimensional visualization;

[0010] Step 3, establish a three-dimensional high-order NNI model of nanoparticles within any spatial ROI in the sample;

[0011] Step 4, qualitatively and quantitatively characterize the three-dimensional distribution pattern of nanoparticles according to the analysis and calculation of the three-dimensional high-order nearest neighbor index model and obtain the multi-scale information of the nanoparticles.

[0012] Beneficial effects:

[0013] Compared with the method for characterizing the distribution of nanoparticles in traditional nanocomposites in the embodiments of the present invention, this method performs synchrotron radiation nano-CT three-dimensional imaging on the nanocomposite sample, performs segmentation processing and three-dimensional visualization on the three-dimensional CT volume image of the sample, can realize the three-dimensional non-destructive internal visualization of nanoparticles in the nanocomposite, and at the same time establish a three-dimensional high-order NNI mathematical model of the ROI in the sample, and qualitatively and quantitatively characterize the three-dimensional distribution of nanoparticles in the nanocomposite by calculating the three-dimensional NNI and the corresponding Z value of the nanoparticles within the ROI of the nanocomposite sample, and obtain multi-scale information such as the distance and size between nanoparticle clusters. Description of the drawings

[0014] Figure 1 It is a flowchart of a method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information provided by an embodiment of the present invention;

[0015] Figure 2 It is a prepared ceramic composite sample provided by an embodiment of the present invention and fixed on a test bench with a pin. Figure (a) is a loading table with the sample, Figure (b) is an enlarged image, and Figure (c) is a microscopic image of the sample;

[0016] Figure 3 It is the nano-CT system configuration provided by an embodiment of the present invention;

[0017] Figure 4 It is to perform circumferential scanning on a rotating test bench to obtain scanning data, perform logarithmic demodulation and stitching to obtain a complete CT projection sequence provided by an embodiment of the present invention;

[0018] Figure 5 It is the image segmentation and three-dimensional visualization process of the whole sample provided by an embodiment of the present invention;

[0019] Figure 6 It is a three-dimensional visualization schematic diagram of nanoparticles in an irregular three-dimensional ROI in the sample provided by the embodiment of the present invention;

[0020] Figure 7 It is the three-dimensional high-order NNI of the ROI provided by the embodiment of the present invention k -k curve. Specific implementation manner

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0022] According to an embodiment of the present invention, as Figure 1 shown, in view of the problems that the nanoparticles in the ceramic matrix nanocomposite need to qualitatively and quantitatively characterize the nanoparticle distribution and further explore the clustering information, the embodiment of the present invention proposes a method for analyzing and characterizing the three-dimensional distribution of nanoparticles in the nanocomposite reconstructed by synchrotron radiation nano-CT based on three-dimensional high-order NNI and obtaining multi-scale information of the nanoparticles. The specific steps of the method are as follows:

[0023] Step S101, prepare a sample of the ceramic matrix nanocomposite and design a synchrotron radiation nano-CT imaging experiment;

[0024] Step S102, obtain the nano-CT projection sequence and perform CT reconstruction and three-dimensional visualization;

[0025] Step S103, establish a three-dimensional high-order NNI model of the nanoparticles in any spatial ROI in the sample;

[0026] Step S104, qualitatively and quantitatively characterize the three-dimensional distribution pattern of the nanoparticles and obtain the multi-scale information of the nanoparticles according to the analysis and calculation of the three-dimensional high-order nearest neighbor index model.

[0027] Further, in step S101, a sample of the ceramic matrix nanocomposite is prepared by spark plasma sintering. It is sintered at a temperature of 1700 °C and contains powder particles with a mass fraction of 5%. The imaging field of view of the nano-CT is 60×60×60 mm 3 , physically crush the nanocomposite and screen it with a 250-mesh sieve to obtain a sample with a required size.

[0028] In the design of the nano-CT imaging experiment, a sample with dimensions meeting certain requirements and a good shape is observed and selected using an optical microscope, fixed to the end of a large-headed pin with epoxy resin glue, and the large-headed pin is inserted into the sample loading platform. The X-rays of the synchrotron radiation accelerator are focused and penetrate the sample fixed on the sample holder. After passing through the sample, the X-rays are focused on the zone plate and received by the detector. The system integrates the X-ray microscope drive device and nano-CT technology. Benefiting from the high-performance X-ray zone plate, nano-CT can observe this nano-composite material sample with a resolution of 100 nm.

[0029] Furthermore, the data obtained by the detector in step S102 are the projection data of the ceramic matrix nano-composite material sample after specified scaling. In the 360° circumferential rotation scan, the detector will collect X-ray signals at each angular position to obtain a series of tomographic information. After logarithmic demodulation and stitching of these data, a series of CT projection sequences are obtained.

[0030] The ART algorithm shown in formula (1) is used for reconstruction to obtain the CT image.

[0031]

[0032] Among them, k represents the number of iterations, λ represents the relaxation parameter, r i , x, p i are all in vector form.

[0033] Volume rendering of three-dimensional images. First, the image is filtered through a median filter of a given pixel to suppress noise slice by slice. Then, the maximum inter-class variance method is used to segment the ceramic matrix and nano-particles. Finally, the ceramic matrix is placed in a semi-transparent state, and the segmented semi-transparent ceramic matrix and nano-particles are synthesized, and the VG Studio Max is used to present the quantitative relationship between the two, and the three-dimensional distribution of nano-particles in the transparent ceramic matrix is observed. Comparing with the two-dimensional slice images, it can be found that the three-dimensional volume image more comprehensively reflects the three-dimensional distribution of nano-particles in the sample. The nano-particles are randomly distributed throughout the sample, and aggregates of different sizes can be clearly observed in many regions. The discreteness and distribution of nano-particles in the ceramic matrix can be clearly observed in different research regions. Take an ROI to observe the discreteness of nano-particles in the ceramic matrix, and the nano-particles are distributed in three-dimensional space and are clearly displayed.

[0034] Furthermore, the three-dimensional high-order NNI in step S103 is a key index for quantitatively analyzing the three-dimensional distribution of nano-particles in three-dimensional space. The establishment of its mathematical model mainly includes three steps: First, select an ROI with any spatial form in the sample under study. Among the particles in the ROI, select any nano-particle i, and record the set of distances between the center of gravity of i and the centers of gravity of other nano-particles as {W i}, the k-th order nearest neighbor distance of particle i can be expressed as W i (k) , k = 1, 2, 3, … ≤ n - 1. Second, calculate the three-dimensional first-order NNI (i.e., NNI1) and the three-dimensional first-order Z value (i.e., Z1), as shown in formulas (2) and (3). Third, calculate the three-dimensional k-th order NNI (i.e., NNI k ), as shown in formula (4).

[0035]

[0036]

[0037]

[0038] α, β, γ are constant terms, λ is the spatial density, n is the total number of nanoparticles, (3k - 2)!!! is the triple factorial, i.e., (3k - 2)!!! = (3k - 2)·(3k - 5)!!! =... = (3k - 2)·(3k - 5)·(3k - 8)...(3·1 - 2).

[0039] Furthermore, in step S104, an irregular-shaped hemispherical ROI with a radius of 200 voxels in the sample is selected to analyze the three-dimensional distribution of nanoparticles in this region. Through the calculation of the three-dimensional high-order NNI model of this ROI, it is known that the NNI1 of the ROI is 0.22, indicating that the nanoparticles are in a aggregated distribution. From the NNI k -k curve showing a first-order stepped shape, it can be seen that there are two clusters in the ROI, and the k values (i.e., k 11 and k 12 ) at the bottom and top of the first-order step are the numbers of the two clusters respectively, and the d(NN) value (i.e., d(NN) k12 ) value at the top of the first-order step represents the distance between the two clusters.

[0040] To prove the effectiveness of the above embodiments, the embodiments of the present invention conducted the following experiments, and the steps are as follows:

[0041] (1) After preparing the ceramic matrix nanocomposite by spark plasma sintering, take a sample block of corresponding size, fix it with epoxy resin glue at the end of a large-headed pin, and insert the large-headed pin into the sample holder of the inspection table as Figure 2 shown.

[0042] (2) Configure the nano-CT system as Figure 3 shown, rotate the inspection table to perform circumferential scanning to obtain 720 projections, and perform logarithmic demodulation and splicing on the projections to obtain a complete CT projection sequence as Figure 4 shown.

[0043] (3) After obtaining the complete CT projection sequence, use the CT reconstruction algorithm shown in formula (1) to reconstruct the projection sequence. After segmenting and pseudo-color synthesizing the reconstruction result, volume rendering is performed to complete three-dimensional visualization as Figure 5 shown.

[0044] Figure 6 This is a three-dimensional visualization view of nanoparticles in an irregular three-dimensional ROI in the sample provided by the embodiment of the present invention. After three-dimensionally visualizing the sample, a part of the irregular area is denoted as ROI, as Figure 7 shown. It can be seen that the ROI is an irregular hemispherical body. The three-dimensional NNI-related formulas and inferences shown in formulas (2)-(4) can be used to qualitatively and quantitatively characterize the distribution of particles in the ROI and obtain multi-scale information of the particles. The ROI is an irregular hemispherical body. After calculation, since the value of the three-dimensional NNI1 of the ROI is 0.22 < 1, it can be known that the particle distribution in the ROI is an aggregated distribution. From the NNI k -k curve showing the first-level step shape, it can be seen that there are two clusters in the ROI, and the k 11 and k 12 values are the numbers of the two clusters respectively, and the d(NN) k12 value represents the distance between the two clusters. This analysis conclusion matches the visual effect of the three-dimensional visualization.

[0045] The embodiment of the present invention combines the three-dimensional NNI mathematical model and nano-CT technology to analyze and characterize the three-dimensional distribution of nanoparticles inside the nanocomposite and obtain the clustering information of the nanoparticles, which can non-destructively qualitatively and quantitatively characterize the distribution form of the nanoparticles inside the nanocomposite and obtain multi-scale information of the nanoparticles.

[0046] Although the above describes the illustrative specific embodiments of the present invention for the understanding of those skilled in the art in the technical field of the present invention, and it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the technical field, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

Claims

1. A method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information, characterized in that, It includes the following steps: Step 1: Prepare samples of ceramic matrix nanocomposites and design synchrotron radiation nano-CT imaging experiments; Step 2: Obtain nano-CT projection sequences and perform CT reconstruction and three-dimensional visualization; Step 3: Establish a three-dimensional high-order nearest neighbor index model for nanoparticles in any spatially interesting region of the sample; Step 4: Qualitatively and quantitatively characterize the three-dimensional distribution pattern of nanoparticles and obtain multi-scale information of nanoparticles according to the analysis and calculation of the three-dimensional high-order nearest neighbor index model; In the said Step 3, establishing a three-dimensional high-order nearest neighbor index model for nanoparticles in any spatially interesting region of the sample specifically includes: The three-dimensional high-order NNI is a key index for quantitatively analyzing the three-dimensional distribution of nanoparticles in three-dimensional space. The establishment of its mathematical model mainly includes three steps: First, select an ROI with any spatial form in the samples under study. Among the particles within the ROI, select any nanoparticle i, and denote the set of distances between the center of gravity of particle i and the centers of gravity of other nanoparticles as {W i}, and the k-th nearest neighbor distance of particle i can be expressed as W i (k) , where k = 1, 2, 3, … ≤ n - 1; Second, calculate the three-dimensional first-order NNI and three-dimensional first-order Z value of the ROI, as shown in formulas (1) and (2): （1） （2） is the constant term, λ is the spatial density, and n is the total number of nanoparticles; Third, calculate the three-dimensional k-order NNI of the ROI, as shown in formula (3): （3） is the constant term, and (3k - 2)!!! is the triple factorial, that is: ; For the distribution pattern of particles within the spatial region studied by three-dimensional first-order NNI qualitative characterization, the corresponding three-dimensional first-order Z value can quantitatively characterize the degree of particle aggregation. For three-dimensional high-order NNI, for NNI with different k values k , NNI k -k curves are obtained, and multi-scale information on nanoparticle clustering can be obtained by analyzing the curves.

2. The method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information according to claim 1, characterized in that: In the said Step 1, preparing samples of ceramic matrix nanocomposites and designing synchrotron radiation nano-CT imaging experiments specifically includes: Samples of ceramic matrix nanocomposites were prepared by spark plasma sintering, specifically including: sintering powder particles containing 5% by mass at a temperature of 1700 °C, and the imaging field of view of nano-CT was 60×60×60 mm 3 , physically pulverizing the nanocomposite and screening it with a 250-mesh sieve to obtain samples meeting the size requirements; In nano-CT imaging, observe and select some samples with an optical microscope, fix them at the end of a large-headed pin with epoxy resin glue, insert the large-headed pin into the sample loading platform, the X-rays of the synchrotron radiation accelerator are focused to penetrate the sample fixed on the sample loading platform, and after passing through the sample, the X-rays are focused on the zone plate and received by the detector.

3. The method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information according to claim 1, characterized in that: In the said Step 2, obtaining nano-CT projection sequences and performing CT reconstruction and three-dimensional visualization specifically includes: Obtain CT projection sequences. The data obtained by the detector are the projection data of the scaled ceramic matrix nanocomposite sample. In the 360° circumferential rotation scan, the detector will collect X-ray signals at each angular position to obtain a series of projection information. After logarithmic demodulation and splicing of the said projection data, a series of complete CT projection sequences are obtained; Reconstruct the tomographic images of the sample. Use the CT reconstruction algorithm to reconstruct a series of complete projection sequences to obtain the tomographic images of the nanocomposite sample; Volume render the three-dimensional image of the sample. First, filter out the noise of the image through a median filter of a given pixel, then use the maximum inter-class variance method to segment the ceramic matrix and nanoparticles. Finally, place the ceramic matrix in a semi-transparent state, synthesize the segmented semi-transparent ceramic matrix and nanoparticles, and use VG Studio Max to present the quantitative relationship between the two, and observe the three-dimensional distribution of nanoparticles in the transparent ceramic matrix.

4. The method for analyzing the three-dimensional distribution of nanoparticles and obtaining their multi-scale information according to claim 1, characterized in that: In the said Step 4, qualitatively and quantitatively characterizing the three-dimensional distribution pattern of nanoparticles and obtaining multi-scale information of nanoparticles according to the analysis and calculation of the three-dimensional high-order nearest neighbor index model specifically includes: Select an irregularly shaped hemispherical ROI with a radius of 200 voxels in the sample, and analyze and calculate the three-dimensional distribution characteristics and multi-scale information of the nanoparticles in this region according to the three-dimensional high-order NNI model established in Step 3.

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