A method for testing average pore size and orientation factor of high thermal conductive carbon fiber

Abstract

The application discloses a high-thermal-conductivity carbon fiber average pore size and orientation factor testing method, which comprises the following steps: preparing a fiber sample; performing a small-angle X-ray scattering test on the fiber sample to obtain a two-dimensional scattering pattern; obtaining a half-height width of an azimuth curve according to the two-dimensional scattering pattern; and obtaining the average pore size and the orientation factor f of the fiber according to the half-height width L and the orientation factor f v . The scattering pattern obtained by the application has high resolution, can be used for high-resolution analysis of the fine structure state of the high-thermal-conductivity carbon fiber, and can be used for accurate quantitative analysis of the average pore size and the orientation factor of the high-thermal-conductivity carbon fiber.

Description

Technical Field

[0001] This invention relates to a method for testing the average pore size and orientation factor of high thermal conductivity carbon fibers, belonging to the field of quantitative testing technology. Background Technology

[0002] High thermal conductivity mesophase pitch carbon fiber (MP-CF) is a type of high-performance carbon fiber made from high-purity spinnable mesophase pitch as raw material through processes such as melt spinning, oxidation carbonization, and high-temperature graphitization. The advantages of MP-CF lie in its high thermal conductivity and high modulus. Its axial thermal conductivity can reach over 1000 W / (m•K), and its modulus can reach over 800 GPa. Thanks to its high modulus and high thermal conductivity, MP-CF offers significant advantages in lightweight applications in aerospace and advanced industrial equipment, while also serving as a structural load-bearing material and a functional material for heat protection and conduction. It is a high-end carbon fiber variety with great development potential.

[0003] High thermal conductivity mesophase pitch carbon fibers possess unparalleled thermal conductivity compared to traditional metallic thermally conductive materials, which is closely related to their highly ordered graphite microcrystalline structure. During the preparation process of high thermal conductivity mesophase pitch carbon, in addition to the highly ordered microcrystalline structure, various defects are also generated internally, such as microcrystalline defects and micropore defects (micropores, cracks). The microstructure and microdefect structure of a material determine its properties; the microstructure of carbon fibers determines its final properties. Therefore, the relationship between the characterization of microstructure and performance has become a hot topic for researchers both domestically and internationally.

[0004] Due to the imperfect stacking of structural units in high thermal conductivity mesophase pitch carbon fiber, there are a large number of defects, most of which are micropores with preferred orientation. These defects have a huge impact on the properties of high thermal conductivity mesophase pitch carbon fiber materials (especially thermal conductivity).

[0005] Accurately and quantitatively characterizing the complex microporous defects of highly thermally conductive carbon fibers with preferred orientation, and speculating on the correlation between the micro-mesoscale structure and thermal conductivity of these fibers, has always been a technical challenge of common concern to researchers. Traditional gas adsorption or mercury intrusion porosimetry methods for testing closed-pore structures only allow the medium to penetrate the open pores, not the closed pores. For fiber systems with both open and closed pores, adsorption methods have limitations in detecting pore structure. SEM is primarily used to observe pore information on the outer surface of fibers and the microscopic morphology of radial cross-sections. TEM can observe micron-sized pores, but its field of view is small and lacks statistical accuracy. Micro-nano CT technology can also obtain internal three-dimensional structural information without damaging the sample, allowing for three-dimensional reconstruction of the internal pore structure and obtaining parameters such as pore size, distribution, and porosity. However, it cannot accurately identify structures with high aspect ratios and high orientation. Summary of the Invention

[0006] The purpose of this invention is to overcome the aforementioned shortcomings and provide a method for testing the average pore size and orientation factor of high thermal conductivity carbon fibers. This method solves the technical problems of inaccurate calculation and large errors in the average pore size and orientation factor due to the inability to separate signals. The scattering pattern obtained by this invention has high resolution, enabling high-resolution analysis of the fine structural state of high thermal conductivity carbon fibers and precise quantitative analysis of the average pore size and orientation factor.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for testing the average pore size and orientation factor of high thermal conductivity carbon fibers, comprising: (1) Preparation of fiber samples; (2) Small-angle X-ray scattering test was performed on the fiber sample to obtain a two-dimensional scattering pattern; (3) Obtain the half-width and height of the azimuth curve based on the two-dimensional scattering pattern. ; (4) According to Obtain the average pore size of the fiber L and orientation factor .

[0008] Furthermore, the method for preparing the fiber sample in step (1) includes: (1.1) Drip alcohol into the fiber to release static electricity in the fiber; (1.2) Attach the fibers after static electricity has been released onto the hard sheet; (1.3) The fibers adhered to the hard sheet are sorted to remove fuzz and crimp, so that the fibers are straight and untwisted, and a fiber sample is obtained.

[0009] Furthermore, the conditions for performing small-angle X-ray scattering tests on the fiber samples in step (2) include: X-ray voltage ≥40kV, X-ray voltage ≥40mA, exposure time: 10s~20s, distance between sample and detector when selecting this equipment to characterize the maximum structural size.

[0010] Furthermore, the detector used in step (2) small-angle X-ray scattering test is a two-dimensional detector.

[0011] Furthermore, step (3) obtains the half-width at half-maximum (WHM) of the azimuth curve based on the two-dimensional scattering pattern. The methods include: like Figure 4 and Figure 5 The azimuth angles with a width of 0.011 obtained at different q positions are integrated, and the Lorentzian function is used to fit the azimuth integral curve to obtain the full width at half maximum (FWHM). q is the scattering vector; Specific methods include: (3.1) Based on the two-dimensional scattering pattern, slice it in concentric circles to obtain the azimuth curves of different slice widths near different q values; q value is the scattering vector in the two-dimensional scattering pattern; (3.2) Fit the azimuth integral curve with a function to obtain the full width at half maximum (FWHM). , The width is at half the height of the peak.

[0012] Furthermore, in step (3.1), the method for obtaining azimuth curves for different slice widths near different q values ​​includes: By sampling the two-dimensional scattering pattern several times, the corresponding azimuth curves for different slice widths (0.0015, 0.002, 0.006) near different q values ​​are obtained; q value is the scattering vector in the two-dimensional scattering pattern. Integrating the azimuth curve and fitting it with either the Gaussian or Lorentzian function yields results from different function fittings. .

[0013] Furthermore, step (4) is based on the half-width of the azimuth curve. Obtain the average pore size of the fiber L and orientation factor The methods include: according to The s~sB curve is obtained by fitting, where s=q / 2π, q=(4πsinθ) / λ, θ is the diffraction angle, and λ is the X-ray wavelength; Based on the s~sB curve and the following formula

[0014] ; Among them, the average pore size of the fiber L and orientation factor The average pore size of the fiber was obtained based on the intercept and slope of the s~sB curve, respectively. L and orientation factor .

[0015] Furthermore, when sampling the two-dimensional scattering pattern, the interval between two adjacent samples is 0.0015.

[0016] Furthermore, the number of data points included in the azimuth integral corresponding to each intercept is ≥400.

[0017] Furthermore, the fitting function for the azimuth integral is the Lorentzian function.

[0018] Compared with the prior art, the present invention has at least one of the following advantages: (1) By adjusting the sample preparation method, exposure time, Sq distance, spot position and other parameters during small-angle X-ray scattering test, the present invention enables the parameters to work together to obtain high resolution of scattering pattern of high thermal conductivity carbon fiber. This avoids problems such as inaccurate calculation of average pore size and orientation factor due to the inability to separate signals, and large errors. It realizes high resolution analysis of fine structure state of high thermal conductivity carbon fiber, which is convenient for accurate quantitative analysis of average pore size and orientation factor of high thermal conductivity carbon fiber. (2) This invention has the characteristics of quantitative analysis of the average pore size and orientation factor of high thermal conductivity carbon fiber, good reversibility, reliable data, etc., with small average deviation; (3) The present invention has the advantages of simple sample preparation method and easy operation, and is easy to promote and apply. Attached Figure Description

[0019] Figure 1 The small-angle X-ray scattering pattern of the high thermal conductivity carbon fiber provided in Embodiment 1 of the present invention; Figure 2 A schematic diagram of fitting the tangent integral using the Lorentzian function; Figure 3 Schematic diagram of the fitting curve of tangent integral s~sB of high thermal conductivity carbon fiber; Figure 4 A schematic diagram of azimuth integrals with a width of 0.011 obtained for different q positions; Figure 5 This is a schematic diagram of fitting the azimuth integral curve using the Lorentzian function. Detailed Implementation

[0020] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0021] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0022] Small-angle X-ray scattering (SAXS) is an important method for studying the microporous structure inside materials. SAXS studies the intensity distribution near the origin of reciprocal lattice space. While the three-dimensional intensity distribution near the origin of reciprocal lattice space is spherically symmetric, the two-dimensional intensity distribution is circularly symmetric (two-dimensionally centrosymmetric). However, this is not the case for high thermal conductivity carbon fibers. Their diffraction patterns near the origin of reciprocal lattice space are not circularly symmetric, but only centrosymmetric in diameter. This necessitates obtaining high-resolution (sample and instrument conditions) two-dimensional SAXS pattern data and performing detailed analysis of the scattering pattern data.

[0023] This invention provides a method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber. By using appropriate sample preparation methods and instrument conditions, a high-resolution two-dimensional small-angle scattering pattern is obtained. The scattering pattern is analyzed using Ruland streek, and the average pore size and orientation factor of high thermal conductivity carbon fiber are obtained by optimizing technical parameters such as cutting spacing, data points, and fitting function.

[0024] This invention is achieved through the following technical solution: This invention discloses a method for testing the average pore size and orientation factor of high thermal conductivity carbon fibers, comprising the following steps: Step 1: The fiber sample obtained by placing the high thermal conductivity carbon fiber on a stable hard sheet is straight and untwisted, with no obvious fuzz or crimp. Step 2: Perform small-angle X-ray scattering test on the fiber sample to obtain a 2D scattering pattern and complete the test. During the test, the X-ray voltage is ≥40kV, the X-ray voltage is ≥40mA, the exposure time is 10s~20s, and the distance between the sample and the detector is selected when the maximum structural size in the system is measured in the equipment. Step 3: Obtain the average aperture size based on the analysis of the obtained 2D scattering pattern. L and orientation factor Quantitative analysis. Using the theoretical basis of the Ruland analytical preferred orientation system (Ruland streak), the obtained images of oriented carbon fibers are integrated in concentric circles. The resulting azimuth curve's half-width at half-maximum (FWHM) is... See equation (1) and equation (2): (1) (2) In the formula: s = q / 2π, q = (4πsinθ) / λ, θ is the diffraction angle. The unit is radians.

[0025] The average pore size and orientation factor of high thermal conductivity carbon fibers are obtained by linear fitting of the s~sB curve.

[0026] In an optional embodiment, the fiber sample described in step 1 is directly adhered to the metal small-angle scattering instrument sample holder. The fiber will be dispersed. Due to the adhesion between the tape and the metal sample holder, and the brittle and hard characteristics of the high thermal conductivity fiber, the fiber is easy to break and produce burrs.

[0027] In an optional embodiment, the fiber sample described in step 1 is dripped with alcohol to release static electricity and directly adhered to the metal small angle scattering instrument sample holder. Because the alcohol affects the adhesion between the tape and the metal sample holder, the resulting fiber sample is prone to peeling and instability.

[0028] In an optional embodiment, the fiber sample described in step 1 is dripped into alcohol to release static electricity and adhere to the prepared stable sample hard sheet. The stable hard sheet with the fiber sample attached is then glued to the metal sample holder with adhesive tape. The resulting fiber sample is straight and without twist, and has no obvious fuzz or crimp.

[0029] In an optional embodiment, step 3 involves obtaining the average aperture size and orientation factor quantitatively based on the obtained 2D scattering pattern analysis. When integrating the image of the 2D scattering pattern, the integration is performed using the smallest possible cut interval to obtain the full width at half maximum (FWHM) data of the curve, thus obtaining the pore length and average aperture size.

[0030] In an optional embodiment, step 3 involves obtaining the average aperture size and orientation factor quantitatively based on the obtained 2D scattering pattern analysis. When integrating the image of the 2D scattering pattern, more data points are collected for integration to obtain the full width at half maximum (FWHM) data of the curve, thus obtaining the average aperture size.

[0031] In an optional embodiment, step 3 involves obtaining the average aperture size and orientation factor quantitatively based on the obtained 2D scattering pattern analysis. During the integration of the 2D scattering pattern image, a suitable fitting function is used to fit the curve, obtaining the full width at half maximum (FWHM) data of the curve to obtain the average aperture size.

[0032] In an alternative embodiment, small-angle X-ray scattering testing employs a 2D detector.

[0033] In an alternative embodiment, the analysis of the 2D scattering pattern is based on Ruland streak theory.

[0034] In one optional embodiment, when integrating the 2D scattering pattern in successive cycles, the cutting interval is 0.0015, resulting in the azimuth curve of a certain slice.

[0035] In an optional embodiment, the 2D scattering pattern is integrated in successive cycles, and then fitted to the azimuth curve to obtain the full width at half maximum (FWHM) of the curve. The number of data points selected is ≥400.

[0036] In an optional embodiment, the full width at half maximum (FWHM) of the curve is obtained by fitting the 2D scattering pattern to the azimuth curve. The Lorentzian function was used for fitting.

[0037] Example: Example 1 Step 1: The fiber sample is dripped into alcohol to release static electricity and sticks to the prepared stable sample hard sheet. Then, the stable hard sheet with the fiber sample is attached is glued to the metal sample holder with tape. The resulting fiber sample is straight and without twist, with no obvious fuzz or crimp. Step 2: Perform small-angle X-ray scattering (SAXS) on the fiber sample to obtain the following results. Figure 1 The 2D scattering pattern was tested, with the following conditions: X-ray voltage ≥40kV, X-ray voltage ≥40mA, exposure time: 10s~20s, and sample distance from detector: 1050mm.

[0038] Step 3: Based on the obtained 2D scattering pattern analysis, the average aperture size and orientation factor are quantitatively analyzed. Using the theoretical basis of the Ruland analytical preferred orientation system (Ruland streak), the image of the oriented carbon fibers is integrated in concentric circles. Different data points (60°) are used with cutting intervals of 0.0015, 0.002, and 0.006. After integration, different Lorentzian fitting functions are used to obtain the full width at half maximum (FWHM) of the resulting azimuth curve. ,like Figure 2 , Figure 2 The horizontal axis φ in the figure represents the angular range of the scattering signal of the slice. Substituting into formula (1), the average pore size and orientation factor of the high thermal conductivity carbon fiber are obtained by linear fitting of the s~sB curve, as shown in Table 1 and Figure 3 The average deviation of the data obtained by using a cutting spacing of 0.0015 is relatively small.

[0039] Table 1. Average pore size and orientation factor of high thermal conductivity carbon fibers obtained with different cutting spacings.

[0040] Example 2 Step 1: The fiber sample is dripped into alcohol to release static electricity and sticks to the prepared stable sample hard sheet. Then, the stable hard sheet with the fiber sample is attached is glued to the metal sample holder with tape. The resulting fiber sample is straight and without twist, with no obvious fuzz or crimp. Step 2: Perform small-angle X-ray scattering test on the fiber sample to obtain a 2D scattering pattern and complete the test. During the test, the X-ray voltage is ≥40kV, the X-ray voltage is ≥40mA, the exposure time is 10s~20s, and the distance between the sample and the detector is 1050mm.

[0041] Step 3: Based on the obtained 2D scattering pattern analysis, the average aperture size and orientation factor are quantitatively analyzed. Using the theoretical basis of the Ruland analytical preferred orientation system (Ruland streak), the image of the oriented carbon fibers is integrated in concentric loops. Different data points (200, 400, and 600) are used with a cutting spacing of 0.0015. After integration, different Lorentzian fitting functions are used to obtain the full width at half maximum (FWHM) of the resulting azimuth curve. Substituting into formula (1), the average pore size and orientation factor of the high thermal conductivity carbon fiber were obtained by linear fitting of the s~sB curve, as shown in Table 2. The average deviation of the data obtained by using a cutting spacing of 0.0015 was relatively small.

[0042] In an optional embodiment, step 3 involves obtaining the average aperture size and orientation factor quantitatively based on the obtained 2D scattering pattern analysis. When integrating the image of the 2D scattering pattern, different data points (200, 400, 600) are used to obtain the full width at half maximum (FWHM) of the curve, and the resulting pore length is shown in Table 2. The average deviation of the data obtained using data point 600 is relatively small.

[0043] Table 2. Average pore size and orientation factor of high thermal conductivity carbon fibers obtained at different data points.

[0044] Example 3 Step 1: The fiber sample is dripped into alcohol to release static electricity and sticks to the prepared stable sample hard sheet. Then, the stable hard sheet with the fiber sample is attached is glued to the metal sample holder with tape. The resulting fiber sample is straight and without twist, with no obvious fuzz or crimp. Step 2: Perform small-angle X-ray scattering test on the fiber sample to obtain a 2D scattering pattern and complete the test. During the test, the X-ray voltage is ≥40kV, the X-ray voltage is ≥40mA, the exposure time is 10s~20s, and the distance between the sample and the detector is 1050mm.

[0045] Step 3: Based on the obtained 2D scattering pattern analysis, the average aperture size and orientation factor are quantitatively analyzed. Using the theoretical basis of the Ruland analytical preferred orientation system (Ruland streak), the image of the oriented carbon fibers is integrated in concentric loops. Different data points (60°) are used with a cutting spacing of 0.0015. After integration, the Gaussian-Lorentzian curve fitting function is used to fit the curve, and the half-width at half-maximum (FWHM) of the resulting azimuth curve is obtained. Substituting into formula (1), the average pore size and orientation factor of high thermal conductivity carbon fiber are obtained by linear fitting of the s~sB curve, as shown in Table 3.

[0046] Table 3. Average aperture size and orientation factor obtained from different fitting functions

[0047] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0048] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for testing the average pore size and orientation factor of high thermal conductivity carbon fibers, characterized in that, include: (1) Preparation of fiber samples; (2) Small-angle X-ray scattering test was performed on the fiber sample to obtain a two-dimensional scattering pattern; (3) Obtain the half-width and height of the azimuth curve based on the two-dimensional scattering pattern. ; (4) According to Obtain the average pore size of the fiber L and orientation factor .

2. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 1, characterized in that, Step (1) involves the following method for preparing fiber samples: (1.1) Drip alcohol into the fiber to release static electricity in the fiber; (1.2) Attach the fibers after static electricity has been released onto the hard sheet; (1.3) The fibers adhered to the hard sheet are sorted to remove fuzz and crimp, so that the fibers are straight and untwisted, and a fiber sample is obtained.

3. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 1, characterized in that, The conditions for small-angle X-ray scattering testing of the fiber sample in step (2) include: X-ray voltage ≥40kV, X-ray voltage ≥40mA, exposure time: 10s~20s, distance between sample and detector when selecting this equipment to characterize the maximum structural size.

4. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 1, characterized in that, Step (2) The detector used for small-angle X-ray scattering test is a two-dimensional detector.

5. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 1, characterized in that, Step (3) Obtain the half-width and height of the azimuth curve based on the two-dimensional scattering pattern. The methods include: Integrating the azimuth angles obtained at different q positions, and fitting the azimuth integral curve using the Lorentzian function, yields the full width at half maximum (FWHM). ; Specific methods include: (3.1) Based on the two-dimensional scattering pattern, slice it in concentric circles to obtain the azimuth curves of different slice widths near different q values; q value is the scattering vector in the two-dimensional scattering pattern; (3.2) Fit the azimuth integral curve with a function to obtain the full width at half maximum (FWHM). , The width is at half the height of the peak.

6. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 5, characterized in that, In step (3.1), the method for obtaining azimuth curves for different slice widths near different q values ​​includes: By sampling the two-dimensional scattering pattern several times, the corresponding azimuth curves of different slice widths near different q values ​​are obtained; q value is the scattering vector in the two-dimensional scattering pattern. Integrating the azimuth curve and fitting it with either the Gaussian or Lorentzian function yields the full width at half maximum (FWHM) obtained from different function fittings. .

7. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 1, characterized in that, Step (4) Based on the half-width of the azimuth curve Obtain the average pore size of the fiber L and orientation factor The methods include: according to The s~sB curve is obtained by fitting, where s=q / 2π, q=(4πsinθ) / λ, θ is the diffraction angle, and λ is the X-ray wavelength; The average pore size of the fiber is obtained based on the s~sB curve and the following formula. L and orientation factor : ； Among them, the average pore size of the fiber L and orientation factor The average aperture size is obtained from the intercept and slope of the s~sB curve, respectively. L and orientation factor .

8. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 6, characterized in that, When sampling the two-dimensional scattering pattern, the interval between two adjacent samples is 0.0015.

9. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 6, characterized in that, The number of data points included in the azimuth integral corresponding to each intercept is ≥400.

10. The method for testing the average pore size and orientation factor of high thermal conductivity carbon fiber according to claim 6, characterized in that, The fitting function for the azimuth integral is the Lorentzian function.

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