X-ray powder diffraction method for determining the macroscopic composition and microstructure of carbon materials
By establishing structural models of amorphous carbon and graphite-like carbon, and combining full-spectrum fitting and the Rietveld method, the XRD patterns were accurately decomposed, solving the error problem in the determination of microstructural parameters of carbon materials, and realizing high-precision data calculation and standardization.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF COAL CHEM CHINESE ACAD OF SCI
- Filing Date
- 2023-06-13
- Publication Date
- 2026-05-26
AI Technical Summary
Existing technologies are insufficient to accurately determine the microstructural parameters of amorphous carbon, graphitic carbon, and graphitized carbon in carbon materials. XRD diffraction peak separation methods suffer from large errors, are greatly affected by human factors, and face difficulties in data sharing and communication.
The PONCKS method was used to establish structural models of amorphous carbon and graphite-like carbon. By fitting the full spectrum and dividing the peaks, combined with the Rietveld method, the XRD pattern was accurately decomposed into background scattering, amorphous carbon, graphite crystal and graphite-like carbon peaks, and the content and microstructure parameters of each component were calculated.
It enables precise calculation of the microstructure parameters of carbon materials, reduces human error, ensures high data reliability, and supports the standardization of carbon material research and production.
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Figure CN116735633B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of carbon material testing technology, specifically a method for determining the macroscopic composition and microstructure of carbon materials using X-ray powder diffraction. Background Technology
[0002] Carbon materials are characterized by their light weight, high strength, high temperature resistance, corrosion resistance, good fatigue resistance and damage tolerance, electrical and thermal conductivity, and high plasticity. They have been widely used in aerospace, machinery, electronics, electrical appliances, nuclear energy, metallurgy, chemical and other fields. With the advancement of science and technology, mankind is increasingly discovering the infinite development possibilities contained in carbon materials.
[0003] Currently, research technology on carbon materials in China is still immature, and systematic research on their structure is insufficient. Methods for controlling the microscopic structure of carbon materials have not been mastered, and there is no effective theoretical basis to guide production. Relying mainly on experience or continuous trial and error can easily lead to misdirection and prolong research and development time. For example, while the general process flow for carbon fiber is clear, the control of different parameters and changes in the process during production will affect the final performance of the carbon material product. At the same time, the relationship between product performance and microstructure can also guide the manufacturing process flow and parameters. Therefore, studying the evolution law of the microstructure of carbon materials during carbonization and graphitization is crucial. Providing theoretical guidance for the production of carbon materials is of great significance, providing a theoretical basis for parameter control during the production process. Analyzing the impact of microstructural differences on performance is of great application value in clarifying the relationship between carbon material structure and performance, guiding structural control, and providing a theoretical basis for improving product performance.
[0004] Currently, the main methods for studying carbon materials include X-ray powder diffraction, Raman spectroscopy, transmission electron microscopy, and scanning electron microscopy. Scanning electron microscopy primarily studies the morphology of materials; transmission electron microscopy mainly observes the microstructure and microstructure of carbon materials; Raman spectroscopy can characterize structural information such as lattice defects, layer number, and morphology of carbon materials; and X-ray powder diffraction pattern analysis can obtain the interlayer spacing (d) of graphite crystallites. 002 and the thickness L of the microcrystalline wafer stack in this structure. C The structural parameters of graphite wafers include the packing width La of the microcrystalline basal plane. X-ray diffraction (XRD) and Raman spectroscopy can reflect the statistically significant size and degree of graphitization of graphite layers. Scanning, transmission, and Raman spectroscopy are all point or very small area scans, which are not macroscopically representative. The homogeneity of the sample has a great influence on the test results, resulting in poor macroscopic representativeness.
[0005] X-ray powder diffraction, as a method capable of determining both the macroscopic content and microscopic crystal structure of phases, has been widely applied thanks to continuous software upgrades and methodological innovations. The method for determining the microscopic crystal structure parameters of phases involves using the initial crystal structure parameters of each phase (obtained from sources such as literature or crystal structure databases), followed by software refinement of the X-ray powder diffraction pattern to obtain precise microscopic crystal structure parameter values. For calculating the content of each phase in a sample, if all phases are crystalline, the content can be calculated using the Rietveld full-spectrum fitting method. If an amorphous phase exists, it can be obtained through full-spectrum fitting using internal and external standard methods. However, if there is more than one amorphous phase, only the content of the mixture of amorphous phases can be obtained, not the content of each individual phase.
[0006] Extensive experimental data in the literature have demonstrated that most carbon materials, such as graphite and carbon fibers, contain amorphous carbon, graphitic carbon-like carbon, and graphitized carbon. In calculating the microstructure parameters of carbon materials, the key is to accurately determine the positions of the peaks needed for the calculation. However, because amorphous carbon, graphitic carbon-like carbon, and graphite coexist in carbon material samples, the XRD diffraction pattern of carbon materials is a superposition of the scattering spectra of the crystal structure of amorphous carbon, graphitic carbon-like carbon, and graphitized carbon, and the background scattering. The XRD spectra exhibit high peak-background ratios, asymmetrical peak shapes, and overlapping peaks of different phases. Typically, XRD diffraction peaks are not symmetrical, making peak position determination difficult. Current methods for determining peak positions include the peak apex method, the center of full width at half maximum (FWHM) method, and the centroid method. However, these methods have very large errors and cannot accurately characterize the true nature of carbon materials. Although peak separation is widely accepted, current multi-peak separation methods use computer peak-splitting software to decompose aliased and asymmetrical (002) diffraction peaks into several symmetrical peaks. While this fitting method can approximate the actual situation, current fitting methods either emphasize mathematical analysis or physical essence, and the necessary structural model for fitting has not yet been established. This makes it difficult to handle masked or weakly intensified diffraction peaks, leading to some deviations in the results. Different methods yield significantly different peak positions, thus limiting its widespread acceptance and application. Currently, the literature methods and standards for X-ray diffraction determination of carbon materials do not truly analyze X-ray diffraction. Figure 5 The physical meaning of elements (peak position, diffraction intensity, full width at half maximum, morphological distribution, symmetry) and their relationship with the structure are greatly affected by human factors in operation. Data from different people and different laboratories vary greatly, which is not conducive to data sharing and communication. Summary of the Invention
[0007] To address the aforementioned technical problems, the purpose of this invention is to provide a method for determining the macroscopic composition and microstructure of carbon materials using X-ray powder diffraction.
[0008] X-ray diffraction patterns are the external manifestation of the internal microstructure of a sample. Carbon materials include amorphous carbon, graphitic carbon, and graphitized carbon (the d-type of graphite crystals). 002 The XRD pattern (with values between 0.3354 nm and 0.3440 nm) is the result of the combined effects of these phases, and also includes factors such as background scattering, instrument broadening, and crystallite broadening. The description of graphitic carbon in carbon materials can be obtained by full-spectrum fitting of the graphite crystal structure. Instrument broadening and crystallite broadening can be controlled during the fitting process by adjusting instrument parameters and fitting software parameters. For the fitting of background scattering functions, amorphous carbon, and graphitic carbon-like structures, we will refer to the PONCKS method, select appropriate model samples, and establish background scattering function, amorphous carbon structure models, and graphitic carbon-like structure models with practical physical meaning that can accurately describe the experimental XRD pattern through full-spectrum fitting. These established structural models will be directly applied to the despectral fitting of carbon materials, accurately decomposing the XRD pattern into background scattering peaks, amorphous carbon peaks, graphite crystal peaks, and graphitic carbon-like peaks. Furthermore, according to the Rietveld method, the content and crystallite structure parameters of each component will be obtained. This research aims to achieve accurate peak separation of carbon materials, obtain precise results using correct computational models, and present objective and accurate data. It reveals the correspondence between the microstructure of carbon materials and their X-ray diffraction patterns, providing data support and theoretical guidance for the product development, engineering applications, and production of carbon materials.
[0009] To achieve the above objectives, the present invention specifically adopts the following technical solution:
[0010] A method for determining the macroscopic composition and microstructure of carbon materials using X-ray powder diffraction includes the following steps:
[0011] The first step is to establish amorphous carbon structure models and graphite-like carbon structure models using experimental or simulation methods.
[0012] The second step is the quantitative calculation of the macroscopic composition of carbon materials;
[0013] The third step is to calculate the microstructure parameters of the carbon material.
[0014] Furthermore, in the first step, the steps for establishing the amorphous carbon structure model and the graphite carbon structure model using experimental methods are as follows:
[0015] First, an amorphous carbon structure model and background scattering curve function are established, specifically as follows:
[0016] S1: Select high-purity amorphous carbon and corundum samples respectively, mix them according to the mass ratio, and grind them to obtain a mixture sample;
[0017] S2: Collect XRD spectra of high-purity amorphous carbon and mixture samples respectively; First, import the spectrum of the high-purity amorphous carbon sample into the XRD full-spectrum fitting software, add amorphous carbon for full-spectrum peak shape fitting, after fitting, display and fix the background scattering curve, delete the added amorphous carbon peaks, assume a crystal structure model for amorphous carbon, specify structural parameter values, obtain the volume V value of the unit cell, refine the grain size function Cry size L, after fitting, fix the Cry size L value and all peak intensities; turn on the intensity scaling factor and fit again, after fitting, replace the XRD spectrum of amorphous carbon with the XRD spectrum of the mixture sample, and import the crystal structure file of corundum. At this time, turn on the background scattering curve function, refine the grain size function Cry size L of corundum, and import the fitting parameters related to the instrument parameters for full-spectrum fitting analysis.
[0018] S3: Based on the mass percentages of amorphous carbon and corundum in the mixture, as well as the ZMV value of corundum and the V value of the unit cell volume of amorphous carbon, calculate the overall ZM value of amorphous carbon; substitute this value into the fitted crystal structure parameters of amorphous carbon mentioned above and fit again. After fitting, obtain the quantitative result that is the same as the content of the prepared mixture sample. The structural model obtained at this time is the structural model file of amorphous carbon; save it as the structural model file of amorphous carbon.
[0019] Secondly, a graphite-like carbon structure model is established, specifically as follows:
[0020] Select ungraphitized carbon material samples containing amorphous carbon and graphitic carbon, and acquire their XRD spectra. Import these spectra into XRD full-spectrum fitting software, and simultaneously import the background scattering curve function and amorphous carbon structure model established in steps S1-S3. Then, import the graphite structure file as the initial model for the graphitic carbon structure for full-spectrum fitting. During fitting, changes in the atomic positions in the graphite structure model are allowed. After fitting, the XRD spectrum of graphitic carbon can be obtained, and the structure model file of graphitic carbon can be exported.
[0021] Furthermore, the high-purity amorphous carbon sample in step S1 is obtained by one of the following methods: using finished amorphous carbon products, obtaining amorphous carbon samples from the carbon material preparation process, or obtaining amorphous carbon samples from coal samples by removing volatile matter and ash; the mixing of the two according to a mass ratio specifically means that the mass ratio of amorphous carbon to corundum cannot be less than 1.
[0022] Furthermore, in step S2, the collected spectrum of high-purity amorphous carbon is imported into XRD full-spectrum fitting software, and amorphous carbon peaks are added for full-spectrum peak shape fitting. Specifically, 2-3 amorphous carbon peaks are manually added for full-spectrum peak shape fitting. A crystal structure model is assumed for amorphous carbon, and the assumed amorphous carbon crystal structure model is a crystal structure model with space group P4 or P22. When assigning values to the variables of the fine-tuning grain size function Cry size L, the values should not exceed 3.5 nm.
[0023] Furthermore, in step S3, the overall ZM value (ZM) of amorphous carbon is calculated based on the mass percentages of amorphous carbon and corundum in the mixture, as well as the ZMV value of corundum and the V value of the unit cell volume of amorphous carbon. a The formula used for the calculation is as follows: (1)
[0024] In the formula: Wa is the mass percentage of amorphous carbon in the mixture, Sa is the proportion factor of amorphous carbon, Va is the cell volume of amorphous carbon; Ws is the mass percentage of corundum in the mixture, Ss is the proportion factor of corundum, and (ZMV)s is the ZMV value of the corundum sample.
[0025] Furthermore, in the first step, the steps for establishing the amorphous carbon structure model and the graphite-like carbon structure model using simulation calculation methods are as follows:
[0026] (1) Collect the XRD spectrum of a carbon material sample;
[0027] (2) Molecular mechanical simulation calculations were performed using graphite crystal structure. The structure and parameters were continuously adjusted, and the XRD spectrum of the structure was calculated to make its spectrum close to the XRD spectrum of graphite-like carbon, so as to obtain the initial structural model of graphite-like carbon.
[0028] (3) Based on the graphite-like structure model in step (2), continue to perform molecular mechanics simulation calculations, calculate the XRD spectrum of the structure, make it close to the XRD spectrum of amorphous carbon, and obtain the initial structure model of amorphous carbon.
[0029] (4) The initial structural models of amorphous carbon and graphite-like carbon obtained above are loaded into the full spectrum fitting software. The XRD spectrum of the carbon material sample collected in step (1) is fitted with peaks. The initial structural models of amorphous carbon and graphite-like carbon are continuously adjusted. When the fitting reaches the required convergence index, the structural model obtained is the structural model of amorphous carbon and graphite-like carbon. It can be directly saved as a structural file and directly called in the quantitative calculation of macroscopic composition and microscopic structural parameters of carbon materials.
[0030] Furthermore, the second step of quantitatively calculating the macroscopic composition of carbon materials involves the following steps: using the amorphous carbon structure model and graphite-like carbon structure model established in the first step, as well as the crystal structure of graphite, the XRD spectrum of the carbon material sample to be tested is fitted and peaked using full-spectrum fitting software. After fitting, the overlapping peaks are decomposed into four parts: background scattering peaks, amorphous carbon peaks, graphite crystal peaks, and graphite-like carbon peaks. At the same time, accurate unit cell parameters, precise peak positions, and peak intensities are obtained. The content of each component in the carbon material is calculated according to the Rietveld quantitative method.
[0031] Furthermore, the third step involves calculating the parameters of the carbon material's microstructure, including the average interplanar spacing d of the 002 crystal plane of the carbon material. 002 Graphitization degree The graphite microcrystal layer stacking thickness Lc and basal plane stacking width La are determined as follows: The peak position obtained from the fitting in the second step, i.e., the 2θ angle value, is input into the XRD spectrum of the carbon material sample to be tested. The peak position is fixed using fitting software to perform peak phase full spectrum fitting. After fitting, the half-peak width or integral intensity of the peak is obtained. Using Bragg's formula, the average interplanar spacing d of the 002 crystal plane of the carbon material is calculated from the 002 diffraction angle value in the XRD spectrum. 002 Then calculate the degree of graphitization. Then, the 002 diffraction peak of the graphite crystal in the XRD diffraction pattern is used to calculate the stacking thickness Lc of the graphite microcrystal layer; the basal stacking width La of the graphite microcrystal is calculated using the 110 diffraction peak.
[0032] The Bragg formula is as follows:
[0033] d002=λ / 2sin(θ) (2)
[0034] In the formula: d 002 θ is the average interplanar spacing of the 002 crystal plane of the carbon material, in nm; θ is the Bragg angle of the 002 crystal plane diffraction, in °; λ is the incident wavelength, in nm.
[0035] Graphitization degree The calculation formula is as follows: (3)
[0036] In the formula: Graphitization degree, unit (%); d 002 The average interplanar spacing of the 002 crystal plane is expressed in nm.
[0037] The formulas for calculating the lamination thickness Lc and the substrate width La are as follows:
[0038] L hkl =Kλ / βcosθ (4)
[0039] In the formula: L hkl λ is the average crystallite size perpendicular to the hkl crystal plane, in nm; θ is the Bragg angle of the hkl crystal plane diffraction, in °; λ is the incident wavelength, in nm; K is the shape factor; β is the full width at half maximum (FWHM) or integral intensity of the diffraction peak, in radians (nm).
[0040] When the value of K in formula (4) is 0.89, L hkl The value is the stacking thickness Lc of the graphite microcrystal layer;
[0041] When the value of K in formula (4) is 1.84, L hkl The value is the basal packing width La of the graphite microcrystals.
[0042] Furthermore, the X-ray diffractometer test conditions used to acquire the XRD diffraction pattern are as follows: a CuKα light source with Ni filter is used, the scanning step size is 0.02 degrees, the scanning speed is not greater than 2° / min, the 2θ angle indication error of the X-ray diffractometer is within ±0.02°, and the 2θ angle repeatability is expressed as standard deviation and shall not exceed 0.002°.
[0043] Furthermore, when performing full-spectrum fitting, instrument parameter files, including goniometer radius, light source files, and instrument slit width, need to be included.
[0044] Compared with the prior art, the present invention has the following beneficial effects:
[0045] This invention employs the innovative approach of the PONKCS method. Through in-depth research on carbon material samples, it establishes background scattering curve functions, amorphous carbon, and graphitic carbon structural models. These models are closely related to actual crystal structures and accurately describe the X-ray diffraction patterns of crystals. By using these structural models and full-spectrum fitting peak division, the X-ray diffraction pattern of carbon materials is scientifically and accurately decomposed into four parts: background scattering, amorphous carbon, graphitic carbon, and graphitic carbon. By substituting these components into the structural model for full-spectrum fitting peak division and by fixing peak positions and fitting peak shapes, not only can the microstructural parameters of each phase in the carbon material be accurately calculated, but also the percentage content of each phase can be obtained. This method is more accurate and reliable than existing methods for calculating microstructural parameters. Furthermore, it is the first method proposed to solve the calculation of the content of amorphous carbon, graphitic carbon, and graphitic carbon in carbon materials. This method is also simple to operate, eliminates human error, facilitates data sharing and standardization, and plays a significant role in promoting the research and production of carbon materials. Attached Figure Description
[0046] Figure 1This is the peak shape fitting spectrum of the carbon black sample in Example 1 of the present invention;
[0047] Figure 2 The full spectrum fitting results are for the carbon black and corundum mixture sample in Example 1 of this invention;
[0048] Figure 3 In Example 1 of this invention, the full spectrum fitting peaks of the ungraphitized carbon material are amorphous carbon and graphite-like carbon.
[0049] Figure 4 The graphite-like carbon structure model obtained by simulation calculation method in Embodiment 1 of the present invention;
[0050] Figure 5 The calculated XRD pattern of graphitic carbon obtained by simulation in Example 1 of this invention;
[0051] Figure 6 Based on the invention, an amorphous carbon structure model, a graphite-like structure model, and a full spectrum fitting of the background scattering curve function and graphite crystal structure file were used to fit the carbon felt sample, and the peak results and content of each phase were obtained.
[0052] Figure 7 After the full spectrum of the carbon felt sample in Example 1 of this invention is fitted, the peak positions and peak shapes of each component are used to perform full spectrum fitting with fixed peak positions and peak shapes to obtain the integrated intensity of each peak and calculate the microstructure parameters of the graphite component.
[0053] Figure 8 XRD patterns of polyacrylonitrile carbon felts at different graphitization temperatures;
[0054] Figure 9 Full spectrum fitting peak division results for carbon felt samples treated at 1000℃;
[0055] Figure 10 Full spectrum fitting peak division results for carbon felt samples treated at 1500℃;
[0056] Figure 11 Full spectrum fitting peak division results for carbon felt samples treated at 2000℃;
[0057] Figure 12 The peak-splitting results of the full spectrum fitting for the T800 carbon fiber sample;
[0058] Figure 13 The results of peak segmentation fitting of the full spectrum of imported graphite;
[0059] Figure 14 The full spectrum fitting peak division results of the graphite sample obtained by graphitization treatment #4 (2450℃);
[0060] Figure 15The full spectrum fitting peak division results of the graphite sample obtained by graphitization treatment #5 (2900℃);
[0061] Figure 16 The results are the full-spectrum fitting peaks of the carbon black and graphite mixture in Example 2. Detailed Implementation
[0062] To better explain the technical solution of the present invention, the present invention will be described in complete and detailed manner below with reference to the accompanying drawings in the embodiments of the present invention and through specific implementation methods.
[0063] In this embodiment, the X-ray powder diffractometer used was a BRUKER D8 Advance A25 X-ray diffractometer from Germany. Test conditions: Ni-filtered CuKα radiation (λ=0.15406nm), tube voltage 40kV, tube current 40mA, scan step size 0.02 degrees, scan speed 1.2s / step. The carbon material sample was ground to 200-300 mesh, and the carbon fiber was cut into short fibers less than 0.5mm.
[0064] Example 1
[0065] A method for determining the macroscopic composition and microstructure of carbon materials using X-ray powder diffraction includes the following steps:
[0066] The first step involves establishing amorphous carbon structure models and graphite-like carbon structure models using experimental methods.
[0067] First, an amorphous carbon structure model and background scattering curve function are established, specifically as follows:
[0068] S1: Select a high-purity amorphous carbon sample. In this embodiment, carbon black from the finished amorphous carbon product is used, or activated carbon can also be used. The amorphous carbon sample can be obtained from the carbon material preparation process, or from a coal sample after removing volatile matter and ash. Then, the carbon black and corundum sample are mixed in a 1:1 mass ratio and ball-milled to a mesh size of 200-300 to obtain a uniformly mixed sample.
[0069] S2: Collect XRD spectra of high-purity amorphous carbon and mixture samples respectively. First, import the collected high-purity amorphous carbon spectrum into XRD full-spectrum fitting software, such as TOPAS, Jade, GSAS, etc. Manually add 2-3 amorphous carbon peaks for full-spectrum peak shape fitting. After fitting, display the background scattering curve, and then fix the background curve so that it is not refined in subsequent fittings. Delete the added amorphous carbon peaks, assume a crystal structure model for amorphous carbon, with space group P4, cell parameters a=1, c=70, and obtain the volume V value of this cell. Use this assumed crystal structure model to perform crystal structure refinement full-spectrum fitting, assign a value of 3.5nm to the crystallite size function Cry size L, and refine this function through full-spectrum fitting. After fitting, fix the Cry size L value and all peak intensities; turn on the intensity scaling factor, give it an initial value of 0.00001, and fit again. After fitting, replace the XRD spectrum of amorphous carbon with the XRD spectrum of the prepared mixture sample, and import the crystal structure file of corundum. At this point, turn on the background scattering curve function, refine the crystal size function Crysize L of corundum, and import the fitting parameters related to the instrument parameters for Rietveld full-spectrum fitting quantitative analysis. The above assumes a crystal structure model for amorphous carbon; the P22 crystal structure model can also be used.
[0070] S3: The overall ZM value (ZM) of amorphous carbon is calculated based on the mass percentages of amorphous carbon and corundum in the mixture, as well as the ZMV value of corundum and the V value of the unit cell volume of amorphous carbon. a Then, substitute this value into the crystal structure parameters of the amorphous carbon that have been fitted above and fit it again. After the fitting is completed, the quantitative result with the same content as the prepared mixture sample is obtained. At this time, the structural model is the structural model of amorphous carbon. Save it as the structural model file of amorphous carbon. In this way, the model of amorphous carbon and the background scattering curve function can be directly used as the structural file in the full spectrum fitting of carbon material samples.
[0071] The overall ZM value of amorphous carbon (ZM) a It is calculated according to formula (1). (1)
[0072] In the formula: Wa is the mass percentage of amorphous carbon in the mixture, Sa is the proportion factor of amorphous carbon, Va is the cell volume of amorphous carbon; Ws is the mass percentage of corundum in the mixture, Ss is the proportion factor of corundum, and (ZMV)s is the ZMV value of the corundum sample.
[0073] The peak shape fitting spectrum of amorphous carbon (carbon black) is as follows: Figure 1 As shown. The full-spectrum fitting results of the mixture sample prepared from carbon black and corundum are as follows. Figure 2 As shown.
[0074] Secondly, a graphite-like micro-carbon structure model is established, specifically as follows:
[0075] With graphite crystals (d 002 Compared to values between 0.3340 nm and 0.3354 nm, the interlayer spacing d of graphitic carbon is... 002 Greater than 0.3354 nm. The graphite structure model in carbon materials is fitted using the crystal structure parameters of graphite, while the graphite-like carbon structure model is established using the crystal structure parameters of graphite to create an initial model.
[0076] Ungraphitized carbon material samples were selected, containing only amorphous carbon and graphitic carbon phases. XRD spectra of these samples were acquired and imported into XRD full-spectrum fitting software. The background scattering curve function and amorphous carbon structural model established in steps S1-S3 were imported, and then a graphite structure file was imported as the initial model for the graphitic carbon-like structure file. Full-spectrum fitting was performed, allowing variations in atomic positions within the graphite structure model. This was because, except for the graphitic carbon-like structure, other models had already established accurate structural models describing the XRD spectra of these samples. Once the fitting reached convergence, the XRD spectrum of the graphitic carbon-like structure was obtained, and the structural model file could be exported. This file could be directly used in the fitting of carbon material samples.
[0077] The peaks after full-spectrum fitting of the above-mentioned ungraphitized carbon material samples are amorphous carbon and graphitic carbon, such as... Figure 3 As shown.
[0078] In addition, simulation calculation methods were used to establish amorphous carbon structure models and graphite-like structure models, as detailed below:
[0079] (1) Collect the XRD spectrum of a carbon material sample;
[0080] (2) Molecular mechanical simulation calculations were performed using graphite crystal structure. The structure and parameters were continuously adjusted, and the XRD spectrum of the structure was calculated to make its spectrum close to the XRD spectrum of graphite-like carbon, so as to obtain the initial structural model of graphite-like carbon.
[0081] (3) Based on the graphite-like structure model in step (2), continue to perform molecular mechanics simulation calculations, calculate the XRD spectrum of the structure, make it close to the XRD spectrum of amorphous carbon, and obtain the initial structure model of amorphous carbon.
[0082] (4) The initial structural models of amorphous carbon and graphite-like carbon obtained above are loaded into the full spectrum fitting software. The XRD spectra of the carbon material samples collected in step (1) are fitted with peaks. The initial structural models of amorphous carbon and graphite-like carbon are continuously adjusted. When the fitting reaches the required convergence index, the structural model obtained at this time is the structural model of amorphous carbon and graphite-like carbon. It can be directly saved as a structural file and directly called in the quantitative calculation of macroscopic composition and microscopic structural parameters of carbon materials.
[0083] The graphite-like structure model obtained from the above simulation calculations is as follows: Figure 4 As shown, the XRD pattern of graphite-like carbon obtained from simulation calculations is as follows. Figure 5 As shown.
[0084] The second step is the quantitative calculation of the macroscopic composition of carbon materials.
[0085] The graphite structure model in carbon materials is known. In the first step, we obtained the graphite-like structure model, the amorphous carbon structure model, and the background scattering curve function of carbon materials by experimental and simulation methods, respectively. Now, we select a carbon felt sample (cut into short fibers less than 0.5 mm) to perform quantitative calculations on the macroscopic composition of carbon materials.
[0086] XRD patterns of the carbon felt sample were collected, and full-spectrum fitting and peak decomposition were performed using TOPAS software. After fitting, overlapping peaks were decomposed into four parts with clear physical meaning: background scattering peaks, amorphous carbon peaks, graphite crystal peaks, and graphite-like carbon peaks. Accurate unit cell parameters, precise peak positions, and peak intensities were obtained simultaneously. The content of each component in the carbon material was calculated using the Rietveld quantitative method. Specific fitting and peak decomposition results are shown below. Figure 6 As shown, the amorphous carbon content in the carbon felt sample was 56.14%, the graphite-like carbon content was 30.46%, and the graphite content was 13.40%, calculated using the Rietveld quantitative method.
[0087] The third step is the parameter calculation of the microstructure of carbon materials.
[0088] X-ray diffraction analysis can determine the degree of ordered arrangement of carbon materials (the degree of graphitization) and calculate the size of graphite microcrystals. Furthermore, the relationship between the material's microstructure and properties can be studied. The parameters of the carbon material's microstructure include the average interplanar spacing d of the 002 crystal plane. 002 Graphitization degree The thickness Lc of the graphite microcrystal layer and the basal plane packing width La are calculated. The peak positions (2θ angle values) obtained in the second step are input into the XRD spectrum of the carbon material sample. Peak positions are fixed using fitting software to perform full-spectrum peak shape fitting. After fitting, the half-maximum width or integral intensity of the peak is obtained. Using Bragg's formula, the average interplanar spacing d of the 002 crystal planes of the carbon material is calculated from the 002 diffraction angle positions in the XRD spectrum. 002 Then calculate the degree of graphitization. Then, the 002 diffraction peak of the graphite crystal in the XRD diffraction pattern is used to calculate the stacking thickness Lc of the graphite microcrystal layer; the basal stacking width La of the graphite microcrystal is calculated using the 110 diffraction peak.
[0089] The Bragg formula is as follows:
[0090] The Bragg formula is used as follows:
[0091] d 002 =λ / 2sin(θ) (2)
[0092] In the formula: d 002 θ is the average interplanar spacing of the 002 crystal plane of the carbon material, in nm; θ is the Bragg angle of the 002 crystal plane diffraction, in °; λ is the incident wavelength, in nm.
[0093] Graphitization degree The calculation formula is as follows: (3)
[0094] In the formula: d represents the degree of graphitization (%), 0.3440 nm is the interlayer spacing of completely ungraphitized carbon, and 0.3354 nm is the interlayer spacing of ideal graphite crystals. 002 The average interplanar spacing of the 002 crystal plane;
[0095] The formulas for calculating the graphite microc wafer layer thickness Lc and the substrate packing width La are as follows: (4)
[0096] In the formula: L hkl λ is the average crystallite size perpendicular to the hkl crystal plane, in nm; θ is the Bragg angle of the hkl crystal plane diffraction, in °; λ is the incident wavelength, in nm; K is the shape factor; β is the full width at half maximum (FWHM) or integral intensity of the diffraction peak, in radians (nm).
[0097] When the value of K in formula (4) is 0.89, L hklThe value is the stacking thickness Lc of the graphite microcrystal layer;
[0098] When the value of K in formula (4) is 1.84, L hkl The value is the basal packing width La of the graphite microcrystals.
[0099] like Figure 7 As shown, after fitting the full spectrum of the carbon felt sample, the peak positions and peak shapes of each component are used to perform full spectrum fitting with fixed peak positions and shapes to obtain the integrated intensity of each peak. The microstructure parameters of the graphite component can then be calculated.
[0100] The following calculations of the macroscopic composition and microstructure of carbon felt materials with different graphitization temperatures were performed using the method of this invention. The degree of graphitization in the materials was observed, and the feasibility and accuracy of the method of this invention were verified.
[0101] 1. Polyacrylonitrile carbon felts with different graphitization temperatures were selected from the same sample: Sample 1 (1000℃), Sample 2 (1500℃), and Sample 3 (2000℃), which were three samples with different graphitization temperatures of high, medium and low.
[0102] The sample was cut into short fibers less than 0.5 mm, and XRD pattern data was collected for testing. Figure 8 As shown. Using the method of this invention, the amorphous carbon structure model, graphite-like carbon structure model, background scattering curve function, and graphite crystal structure file were subjected to XRD spectrum full-spectrum fitting and peak division, and the results are as follows. Figure 9-11 As shown,
[0103] The macroscopic composition and microstructure parameters of the above three samples were calculated using the method of the present invention.
[0104] from Figure 9 The fitting peak results show that for a sample processed at 1000℃, the amorphous carbon content is 88.15%, the graphitic carbon content is 11.85%, and the graphitic d... 002 The interplanar spacing is 0.346644 nm, and the sample has not yet begun to graphitize.
[0105] from Figure 10 The fitting peak results show that the graphite-like content of the sample treated at 1500℃ increases to 63.13%, and the interlayer spacing is 0.345560nm, which is smaller than that of the sample treated at 1000℃.
[0106] from Figure 11 The fitting peak results show that the graphite structure is basically formed in the sample treated at 2000℃, d 002The value is 0.344432nm, the graphite content is 45.82%, there is a small amount of graphite-like structure, and the amorphous carbon content is 49.20%. Using the peaks phase full spectrum fitting method, the graphite structure Lc=4.516nm and La=5.742nm were obtained by analysis and calculation using formula (4).
[0107] 2. Select T800 carbon fiber samples and imported graphite samples.
[0108] The T800 carbon fiber sample has a graphite content of 14.34%, d 002 The value is 0.340444 nm, the graphite-like content is 5.85%, and the d 002 The wavelength is 0.344615 nm, and the amorphous carbon content is 79.82%, indicating that graphitization is just beginning in this sample. Based on the graphitization calculation formula, the degree of graphitization of the graphite component in the sample is calculated to be 46.51%. The full-spectrum fitting peak results of the T800 carbon fiber sample are as follows... Figure 12 As shown.
[0109] XRD patterns of imported graphite, such as Figure 13 As shown. After testing and analysis, it was found that the system contained only the graphite phase. After fitting, d was obtained. 002 The value is 0.3364 nm, and the calculated degree of graphitization is 88.37%.
[0110] 3. Using the same carbon source sample, graphite samples 4# (2450℃) and 5# (2900℃) were obtained by graphitizing at different temperatures.
[0111] The peak-splitting results of the XRD spectra of samples #4 and #5 obtained using the method of this invention are as follows: Figure 14 , 15 As shown in the figure. Analysis of the XRD patterns reveals that sample #5 has a higher content of graphite microcrystalline phase than sample #4, and its graphite crystal structure is also closer to that of standard graphite. Sample #4 has a lower dg... 002 The value is 0.340498 nm, and the d of sample #5 is... 002 The value is 0.339514 nm. The crystal micro parameters of samples 4# and 5# can be obtained by analyzing and calculating using formula (4). The La and Lc of sample 4# are 12.7 nm and 8.1 nm, respectively, and the La and Lc of sample 5# are 21.0 nm and 14.6 nm, respectively. The La and Lc grain sizes of graphite crystals in sample 5# are also larger than those in sample 4#.
[0112] Example 2
[0113] A certain proportion of amorphous carbon and imported graphite were prepared, ground and mixed to form a mixture sample, and the macroscopic composition and microstructure parameters of the carbon material in the mixture sample were determined using the method of the present invention.
[0114] 0.1326 g of amorphous carbon (carbon black) and 0.2148 g of imported graphite were weighed and ground to obtain a homogeneous mixture sample. The XRD pattern of this mixture sample was collected, and peak fitting was performed using the background scattering curve function and amorphous carbon structure model obtained by the above method. The results are as follows: Figure 16 As shown, quantitative calculations using the Rietveld method yielded an amorphous carbon content of 60.70% and a graphite content of 39.30%, which is close to the results of the prepared mixture. The prepared mixture contained 38.17% amorphous carbon and 61.83% by mass, with an error of only 1.13%. Microstructural parameter d 002 The value is 0.3366 nm, which indicates that the peak separation results of the method of the present invention are accurate and reliable.
[0115] The above descriptions are merely representative embodiments of different types of samples of the present invention and do not limit the technical scope of the present invention. For those skilled in the art, any modifications, equivalent substitutions, and improvements made based on the technical route and concept of the present invention will not affect the optimization effect of these examples. Therefore, the patent protection scope of the present invention should be determined by the aforementioned claims.
Claims
1. A method for determining the macroscopic composition and microstructure of carbon materials by X-ray powder diffraction, characterized in that, Includes the following steps: The first step involves establishing amorphous carbon structure models and graphite-like carbon structure models using experimental or simulation methods; among them, The steps for establishing amorphous carbon structure models and graphitic carbon structure models using experimental methods are as follows: First, an amorphous carbon structure model and background scattering curve function are established, specifically as follows: S1: Select high-purity amorphous carbon and corundum samples respectively, mix them according to the mass ratio, and grind them to obtain a mixture sample; S2: Collect XRD spectra of high-purity amorphous carbon and mixture samples respectively; First, import the spectrum of the high-purity amorphous carbon sample into the XRD full-spectrum fitting software, add amorphous carbon for full-spectrum peak shape fitting, after fitting, display and fix the background scattering curve, delete the added amorphous carbon peaks, assume a crystal structure model for amorphous carbon, specify structural parameter values, obtain the volume V value of the unit cell, refine the grain size function Cry size L, after fitting, fix the Cry size L value and all peak intensities; turn on the intensity scaling factor and fit again, after fitting, replace the XRD spectrum of amorphous carbon with the XRD spectrum of the mixture sample, and import the crystal structure file of corundum. At this time, turn on the background scattering curve function, refine the grain size function Cry size L of corundum, and import the fitting parameters related to the instrument parameters for full-spectrum fitting analysis. S3: Based on the mass percentages of amorphous carbon and corundum in the mixture, as well as the ZMV value of corundum and the V value of the unit cell volume of amorphous carbon, calculate the overall ZM value of amorphous carbon; substitute this value into the fitted crystal structure parameters of amorphous carbon mentioned above and fit again. After fitting, obtain the quantitative result that is the same as the content of the prepared mixture sample. The structural model obtained at this time is the structural model file of amorphous carbon; save it as the structural model file of amorphous carbon. Secondly, a graphite-like carbon structure model is established, specifically as follows: Select ungraphitized carbon material samples containing amorphous carbon and graphitic carbon, collect their XRD spectra, import the spectra into XRD full spectrum fitting software, and simultaneously import the background scattering curve function and amorphous carbon structure model established in steps S1-S3. Then import the graphite structure file as the initial model for graphitic carbon structure and perform full spectrum fitting. During fitting, the atomic positions in the graphite structure model are allowed to change. After the fitting is completed, the XRD spectrum of graphitic carbon can be obtained, and the structure model file of graphitic carbon can be exported. The steps for establishing amorphous carbon structure models and graphite-like carbon structure models using simulation calculation methods are as follows: (1) Collect the XRD spectrum of a carbon material sample; (2) Molecular mechanical simulation calculations were performed using graphite crystal structure. The structure and parameters were continuously adjusted, and the XRD spectrum of the structure was calculated to make its spectrum close to the XRD spectrum of graphite-like carbon, so as to obtain the initial structural model of graphite-like carbon. (3) Based on the graphite-like structure model in step (2), continue to perform molecular mechanics simulation calculations, calculate the XRD spectrum of the structure, make it close to the XRD spectrum of amorphous carbon, and obtain the initial structure model of amorphous carbon. (4) The initial structural models of amorphous carbon and graphite-like carbon obtained above are loaded into the full spectrum fitting software. The XRD spectrum of the carbon material sample collected in step (1) is fitted with peaks. The initial structural models of amorphous carbon and graphite-like carbon are continuously adjusted. When the fitting reaches the required convergence index, the structural model obtained at this time is the structural model of amorphous carbon and graphite-like carbon. It can be directly saved as a structural file and directly called in the quantitative calculation of macroscopic composition and microscopic structural parameters of carbon materials. The second step is the quantitative calculation of the macroscopic composition of carbon materials. Specifically, using the amorphous carbon structure model and graphite-like carbon structure model established in the first step, as well as the crystal structure of graphite, the XRD spectrum of the carbon material sample to be tested is fitted and peaked using full-spectrum fitting software. After fitting, the overlapping peaks are decomposed into four parts: background scattering peaks, amorphous carbon peaks, graphite crystal peaks, and graphite-like carbon peaks. At the same time, accurate unit cell parameters, precise peak positions, and peak intensities are obtained. The content of each component in the carbon material is calculated according to the Rietveld quantitative method. The third step is the calculation of the microstructure parameters of the carbon material; the parameters of the carbon material microstructure include the average interplanar spacing d of the 002 crystal plane of the carbon material. 002 Graphitization degree The graphite microcrystal layer stacking thickness Lc and the substrate stacking width La.
2. The method for determining the macroscopic composition and microstructure of carbon materials by X-ray powder diffraction according to claim 1, characterized in that, The high-purity amorphous carbon sample in step S1 is obtained by one of the following methods: using finished amorphous carbon products, obtaining amorphous carbon samples from the carbon material preparation process, or obtaining amorphous carbon samples from coal samples by removing volatile matter and ash; the two are mixed according to a mass ratio, specifically the mass ratio of amorphous carbon to corundum cannot be less than 1.
3. The method for determining the macroscopic composition and microstructure of carbon materials by X-ray powder diffraction according to claim 1, characterized in that, In step S2, the collected spectrum of high-purity amorphous carbon is imported into XRD full-spectrum fitting software, and amorphous carbon peaks are added for full-spectrum peak shape fitting. Specifically, 2-3 amorphous carbon peaks are manually added for full-spectrum peak shape fitting. A crystal structure model is assumed for amorphous carbon, and the assumed amorphous carbon crystal structure model is a crystal structure model with space group P4 or P22. When refining the grain size function Cry size L, the value assigned to the variable of the function Cry size L should not be greater than 3.5 nm.
4. The method for determining the macroscopic composition and microstructure of carbon materials by X-ray powder diffraction according to claim 1, characterized in that, In step S3, the overall ZM value (ZM) of amorphous carbon is calculated based on the mass percentages of amorphous carbon and corundum in the mixture, as well as the ZMV value of corundum and the V value of the unit cell volume of amorphous carbon. a The formula used for the calculation is as follows: （1） In the formula: Wa This represents the mass percentage of amorphous carbon in the mixture. S a V is the proportion factor for amorphous carbon. a The volume of the unit cell for amorphous carbon; W s This represents the mass percentage of corundum in the mixture. S s ZMV is the proportion factor for corundum. s This represents the ZMV value of the corundum sample.
5. The method for determining the macroscopic composition and microstructure of carbon materials by X-ray powder diffraction according to claim 1, characterized in that, The parameters of the microstructure of the carbon material include the average interplanar spacing d of the 002 crystal plane of the carbon material. 002 Graphitization degree The graphite microcrystal layer stacking thickness Lc and basal plane stacking width La are determined as follows: The peak position obtained from the fitting in the second step, i.e., the 2θ angle value, is input into the XRD spectrum of the carbon material sample to be tested. The peak position is fixed using fitting software to perform peaksphase full-spectrum fitting. After fitting, the half-peak width or integral intensity of the peak is obtained. Using Bragg's formula, the average interplanar spacing d of the 002 crystal plane of the carbon material is calculated from the 002 diffraction angle value in the XRD spectrum. 002 Then calculate the degree of graphitization. Then, the 002 diffraction peak of the graphite crystal in the XRD diffraction pattern is used to calculate the stacking thickness Lc of the graphite microcrystal layer; the basal stacking width La of the graphite microcrystal is calculated using the 110 diffraction peak. The Bragg formula is as follows: d 002 =λ / 2sin(θ) (2) In the formula: d 002 λ is the average interplanar spacing of the 002 crystal plane of the carbon material, in nm; θ is the Bragg angle of the 002 crystal plane diffraction, in degrees; λ is the incident wavelength, in nm. The formula for calculating the degree of graphitization g is as follows: （3） In the formula: Graphitization degree, in % d 002 is the average interplanar spacing of the 002 crystal plane, in nm; The formulas for calculating the lamination thickness Lc and the substrate width La are as follows: （4） In the formula: L hkl λ is the average crystallite size perpendicular to the hkl crystal plane, in nm; θ is the Bragg angle of the hkl crystal plane diffraction, in degrees; λ is the incident wavelength, in nm; K is the form factor; β is the full width at half maximum (FWHM) or integral intensity of the diffraction peak, in radians (nm). When the value of K in formula (4) is 0.89, L hkl The value is the stacking thickness Lc of the graphite microcrystal layer; When the value of K in formula (4) is 1.84, L hkl The value is the basal packing width La of the graphite microcrystals.
6. The method for determining the macroscopic composition and microstructure of carbon materials by X-ray powder diffraction according to any one of claims 1-5, characterized in that, The X-ray diffractometer test conditions used to acquire XRD diffraction patterns are as follows: a CuKα light source with Ni filter is used, the scanning step size is 0.02 degrees, the scanning speed is not greater than 2° / min, the 2θ angle indication error of the X-ray diffractometer is within ±0.02°, and the 2θ angle repeatability is expressed as standard deviation and shall not exceed 0.002°.
7. The method for determining the macroscopic composition and microstructure of carbon materials by X-ray powder diffraction according to any one of claims 1-5, characterized in that, When performing full-spectrum fitting, the instrument parameter file needs to be included, including the goniometer radius, light source file, and instrument slit width.