X-ray microscopy is an elegant chemical imaging technique that bridges the gap between light
microscopy and electron microscopy. Vital information on the chemical state (valency, surface
functionality), chemical composition, three-dimensional (3D) chemical structure (order, disorder,
rupture), and chemical imaging can be obtained from X-ray microscopy. In the current original
research article, X-ray microscopy is used as a characterization tool to examine the microstructural
features of commercial carbon fibers. Pitch-based (NX100) and polyacrylonitrile (PAN)-based
(T700SC) CFs chosen as representative examples for the two major classes of CF feedstock were
examined using XRM. A homemade and simple sample preparation technique was developed by gluing
the single filament of the carbon fiber (3 mm height) to the flat end of the office pin, which was
subsequently held vertically above the XRM sample holder. The XRM imaging instrument was operated
at a voltage of 50 kV and at a power of 4.0 W all through the 3D structural characterization of the
carbon fibres. Cross-sectional imaging of the carbon fibers (NX100) showed core shell type structure
with a clear contrast in the X-ray absorption in the outer and the inner regions of the fiber. From the
outer region to the inner region of the fiber (though the structure remained the same), the density of the
graphitic structure increased significantly. The core of the pitch-based fibers is highly crystalline
compared to the PAN-based fibers. This observation provided additional support for the conclusions
drawn from the CFs’ XRD and Raman analyses. The 3D microstructural images of the cross-section of
the CFs were constructed using TXM3DVIEWER software. In addition, the 3D microstructure of the
whole of the single filament of CFs was constructed with the same software. The difference in the 3D
microstructure of the NX100 and T700SC is due to the difference in the feedstock as well as the
processing conditions. The microstructure of the CFs deduced from XRM is discussed in detail in
comparison with the scanning transmission X-ray microscope images of the pitch-based (YSH50H) and
PAN-based (M46J) carbon fibers reported in literature. Analogous to the present XRM investigation,
the state-of-the-art STXRM studies also showed that the raw material had a considerable impact on the
distribution of the π-orbital-orientated domains in the CF structure.

🔒 This is a subscription article

Full text is available to subscribers and institutional members. Please choose an option below to access it.

1. X-ray microscopy analysis (XRM) of fiber-reinforced composite materials [Online]. AZO Material. 2013, April 22. Available from: https://www.azom.com/article.aspx?ArticleID=8530#:~:text=X%2Dray%20microscopy%20(XRM)%20offers%20quantitative%2C%20three%2D,to%20observe%20micro%2Dstructural%20changes.
2. Sayre D, Chapman HN. X-ray microscopy. Acta Cryst. 1995;A51:237–252. doi:10.1107/S0108767394011803.
3. Harano T, Murao R, Takeichi Y, Kimura M, Takahashi Y. Observation of the interface between resin and carbon fiber by scanning transmission X-ray microscopy. J Phys Conf Ser. 2017;849:012023. doi:10.1088/1742-6596/849/1/012023.
4. Jacobsen C. X-ray Microscopy: Advances in Microscopy and Microanalysis. Cambridge, UK: Cambridge University Press; 2020.
5. Falcone R, Jacobsen C, Kirz J, Marchesini S, Shapiro D, Spence New directions in X-ray microscopy. Contemp Phys. 2011;52(4):293–318. doi:10.1080/00107514.2011.589662.
6. Cosslett VE, Nixon WC, X-ray Microscopy. Cambridge, UK: Cambridge University Press; 1960.
7. Vogtmann J, Klingler A, Rief T, Gurka M. 3D X-ray microscopy as a tool for in depth analysis of the interfacial interaction between a single carbon fiber and an epoxy matrix after mechanical loading. J Compos Sci. 2021;5(5):121. doi:10.3390/jcs5050121.
8. Kimura M, Watanabe T, Oshima S, Takeichi Y, Niwa Y, Kitazawa R, et al. Nano-to macroscale In Situ observation of microcrack formation in carbon fiber-reinforced plastic under loading using synchrotron transmission X-ray microscopy. AIP Conf Proc. 2023;2990(1):020008. doi:10.1063/5.0169168.
9. Pournoori N, Soares GC, Lukić B, Isakov M, Belone MCL, Hokka M, et al. In situ damage characterization of CFRP under compression using high-speed optical, infrared and synchrotron X-ray phase-contrast imaging. Compos Part A Appl Sci Manuf. 2023;175:107766. doi:10.1016/j.compositesa.2023.107766.
10. Kimura M, Obayashi I, Kido D, Niwa Y, Gao X, Akagi K. Finding “Trigger Sites” of Reactions Among Heterogeneous Materials from X-ray Microscopic Big Data Using Persistent Homology. In TMS Annual Meeting & Exhibition Supplemental Proceedings. TMS 2024. The Minerals, Metals & Materials Series. Cham, Switzerland: Springer; 2024. 784–792. doi:10.1007/978-3-031-50349-8_67.
11. Yamane H, Oura M, Yamazaki N, Ishihara T, Hasegawa K, Ishikawa T, et al. Visualizing interface-specific chemical bonds in adhesive bonding of carbon fiber structural composites using soft X-ray microscopy. Sci Rep. 2022;12(1):16332. doi:10.1038/s41598-022-20233-4.
12. Takahashi K, Shoya R, Matsuo T, Sato W, Nakamura T, Takeuchi A, et al. X-ray nanoimaging of a transversely embedded carbon fiber in epoxy matrix under static and cyclic loads. Sci Rep. 2022;12(1):8843. doi:10.1038/s41598-022-12724-1.
13. Lu T, Chen X, Wang H, Zhang L, Zhou Y. Comparison of low-velocity impact damage in thermoplastic and thermoset composites by non-destructive three-dimensional X-ray microscope. Polym Test. 2020;91:106730. doi:10.1016/j.polymertesting.2020.106730.
14. Rosemeier M, Lester C, Antoniou A, Fahrenson C, Manousides N, Balzani C. Determination of as-built properties of fiber reinforced polymers in a wind turbine blade using scanning electron and high-resolution X-ray microscopy. Compos Part C Open Access. 2022;9:100310. doi:10.1016/j.jcomc.2022.100310.
15. Staab F, Prescher M, Balle F, Kirste L. 3D X-ray microscopy of ultrasonically welded aluminum/fiber-reinforced polymer hybrid joints. Mater. 2021;14(7):1784. doi:10.3390/ma14071784.
16. Kimura M, Takeichi Y, Watanabe T, Niwa Y, Kimijima KI. Finding degradation trigger sites of structural materials for airplanes using X‐Ray microscopy. Chem Record. 2019;19(7):1462–1468. doi:10.1002/tcr.201800203.
17. Wang A, Li S, Zhang S, Zhang S, Liu Z, Yan K. Enhancing CFRP laminates with plasma jet arrays: A study of interlaminar mechanical properties. Polym Compos. 2024;45(11):10190–10203. doi:10.1002/pc.28466.
18. de Oliveira MM, Runqvist L, Poot T, Uvdal K, Carastan DJ, Selegård L. Hybrid nanofiller-enhanced carbon fiber-reinforced polymer composites (CFRP) for lightning strike protection (LSP). ACS Omega. 2024;9(33):35567–35578. doi:10.1021/acsomega.4c03272.
19. Yang C, Zhu D, Yang F, Liu Q, Sun C, Lei K, et al. Quantitative analysis based on atomic force microscopy characterization of interfacial properties between carbon fibers and epoxy resin subjected to hygrothermal and thermal treatments. Compos Sci Technol. 2020;198:108278. doi:10.1016/j.compscitech.2020.108278.
20. Raimondo M, Naddeo C, Vertuccio L, Lafdi K, Sorrentino A, Guadagno L. Carbon-based aeronautical epoxy nanocomposites: effectiveness of atomic force microscopy (AFM) in investigating the dispersion of different carbonaceous nanoparticles. Polym. 2019;11(5):832. doi:10.3390/polym11050832.
21. Fard MY. Carbon nanotube network and interphase in buckypaper nanocomposites using atomic force microscopy. Int J Mech Sci. 2021;212:106811. doi:10.1016/j.ijmecsci.2021.106811.
22. Liu L, Jia C, He J, Zhao F, Fan D, Xing L, et al. Interfacial characterization, control and modification of carbon fiber reinforced polymer composites. Compos Sci Technol. 2015;121:56–72. doi:10.1016/j.compscitech.2015.08.002.
23. Pulidindi IN. Crystallinity of commercial carbon fibers from X-ray diffraction (XRD) studies. Int J Photochem Photochem Res. 2023;1(1):17–27.
24. Pulidindi IN. Raman spectroscopy for the determination of relative crystallinity of carbon fibers. Int J crystall Mater. 2024;1(1):30–37.
25. Cheng A, Zhang Y, Zhong WH, Li ZP, Cheng DJ, Lin YX, et al. Few layer MoS2 embedded in N-doped carbon fibers with interconnected macro pores for ultrafast sodium storage. Carbon. 2020;168:691–700. doi:10.1016/j.carbon.2020.07.008.
26. Harano T, Takeichi Y, Usui M, Arai Y, Murao R, Negi N, et al. Observation of distribution of π-orbital-oriented domains in PAN- and pitch-based carbon fibers using scanning transmission X-ray microscopy. Appl Sci. 2020;10(14):4836. doi:10.3390/app10144836.
27. Pulidindi IN, Gedanken A. Surface modification of carbon fibers. Preprints. 2023. doi:10.20944/preprints202308.2053.v1.
28. Patel D, Joshi M, Joshi Y, Pulidindi IN, Selvaraj S. Direct synthetic routes of MXenes and their application in carbon fiber reinforced plastics (CFRPs) as supplementary sizing layer. Int J Crystall Mater, 2024;1(1):7–13
29. Pulidindi IN. Diglycidyl ether of bisphenol A (DGEBA) based epoxy sizing agent induces surface polarity in carbon fibers. IJCM. 2024.
30. Pulidindi IN. New insight into the composition and structure of sizing agent from NMR spectroscopy. J Photochem Photochem Res. 2024.

X-ray microscopy is an elegant chemical imaging technique that bridges the gap between light
microscopy and electron microscopy. Vital information on the chemical state (valency, surface
functionality), chemical composition, three-dimensional (3D) chemical structure (order, disorder,
rupture), and chemical imaging can be obtained from X-ray microscopy. In the current original
research article, X-ray microscopy is used as a characterization tool to examine the microstructural
features of commercial carbon fibers. Pitch-based (NX100) and polyacrylonitrile (PAN)-based
(T700SC) CFs chosen as representative examples for the two major classes of CF feedstock were
examined using XRM. A homemade and simple sample preparation technique was developed by gluing
the single filament of the carbon fiber (3 mm height) to the flat end of the office pin, which was
subsequently held vertically above the XRM sample holder. The XRM imaging instrument was operated
at a voltage of 50 kV and at a power of 4.0 W all through the 3D structural characterization of the
carbon fibres. Cross-sectional imaging of the carbon fibers (NX100) showed core shell type structure
with a clear contrast in the X-ray absorption in the outer and the inner regions of the fiber. From the
outer region to the inner region of the fiber (though the structure remained the same), the density of the
graphitic structure increased significantly. The core of the pitch-based fibers is highly crystalline
compared to the PAN-based fibers. This observation provided additional support for the conclusions
drawn from the CFs’ XRD and Raman analyses. The 3D microstructural images of the cross-section of
the CFs were constructed using TXM3DVIEWER software. In addition, the 3D microstructure of the
whole of the single filament of CFs was constructed with the same software. The difference in the 3D
microstructure of the NX100 and T700SC is due to the difference in the feedstock as well as the
processing conditions. The microstructure of the CFs deduced from XRM is discussed in detail in
comparison with the scanning transmission X-ray microscope images of the pitch-based (YSH50H) and
PAN-based (M46J) carbon fibers reported in literature. Analogous to the present XRM investigation,
the state-of-the-art STXRM studies also showed that the raw material had a considerable impact on the
distribution of the π-orbital-orientated domains in the CF structure.

🔒 This is a subscription article

Full text is available to subscribers and institutional members. Please choose an option below to access it.

1. X-ray microscopy analysis (XRM) of fiber-reinforced composite materials [Online]. AZO Material. 2013, April 22. Available from: https://www.azom.com/article.aspx?ArticleID=8530#:~:text=X%2Dray%20microscopy%20(XRM)%20offers%20quantitative%2C%20three%2D,to%20observe%20micro%2Dstructural%20changes.
2. Sayre D, Chapman HN. X-ray microscopy. Acta Cryst. 1995;A51:237–252. doi:10.1107/S0108767394011803.
3. Harano T, Murao R, Takeichi Y, Kimura M, Takahashi Y. Observation of the interface between resin and carbon fiber by scanning transmission X-ray microscopy. J Phys Conf Ser. 2017;849:012023. doi:10.1088/1742-6596/849/1/012023.
4. Jacobsen C. X-ray Microscopy: Advances in Microscopy and Microanalysis. Cambridge, UK: Cambridge University Press; 2020.
5. Falcone R, Jacobsen C, Kirz J, Marchesini S, Shapiro D, Spence New directions in X-ray microscopy. Contemp Phys. 2011;52(4):293–318. doi:10.1080/00107514.2011.589662.
6. Cosslett VE, Nixon WC, X-ray Microscopy. Cambridge, UK: Cambridge University Press; 1960.
7. Vogtmann J, Klingler A, Rief T, Gurka M. 3D X-ray microscopy as a tool for in depth analysis of the interfacial interaction between a single carbon fiber and an epoxy matrix after mechanical loading. J Compos Sci. 2021;5(5):121. doi:10.3390/jcs5050121.
8. Kimura M, Watanabe T, Oshima S, Takeichi Y, Niwa Y, Kitazawa R, et al. Nano-to macroscale In Situ observation of microcrack formation in carbon fiber-reinforced plastic under loading using synchrotron transmission X-ray microscopy. AIP Conf Proc. 2023;2990(1):020008. doi:10.1063/5.0169168.
9. Pournoori N, Soares GC, Lukić B, Isakov M, Belone MCL, Hokka M, et al. In situ damage characterization of CFRP under compression using high-speed optical, infrared and synchrotron X-ray phase-contrast imaging. Compos Part A Appl Sci Manuf. 2023;175:107766. doi:10.1016/j.compositesa.2023.107766.
10. Kimura M, Obayashi I, Kido D, Niwa Y, Gao X, Akagi K. Finding “Trigger Sites” of Reactions Among Heterogeneous Materials from X-ray Microscopic Big Data Using Persistent Homology. In TMS Annual Meeting & Exhibition Supplemental Proceedings. TMS 2024. The Minerals, Metals & Materials Series. Cham, Switzerland: Springer; 2024. 784–792. doi:10.1007/978-3-031-50349-8_67.
11. Yamane H, Oura M, Yamazaki N, Ishihara T, Hasegawa K, Ishikawa T, et al. Visualizing interface-specific chemical bonds in adhesive bonding of carbon fiber structural composites using soft X-ray microscopy. Sci Rep. 2022;12(1):16332. doi:10.1038/s41598-022-20233-4.
12. Takahashi K, Shoya R, Matsuo T, Sato W, Nakamura T, Takeuchi A, et al. X-ray nanoimaging of a transversely embedded carbon fiber in epoxy matrix under static and cyclic loads. Sci Rep. 2022;12(1):8843. doi:10.1038/s41598-022-12724-1.
13. Lu T, Chen X, Wang H, Zhang L, Zhou Y. Comparison of low-velocity impact damage in thermoplastic and thermoset composites by non-destructive three-dimensional X-ray microscope. Polym Test. 2020;91:106730. doi:10.1016/j.polymertesting.2020.106730.
14. Rosemeier M, Lester C, Antoniou A, Fahrenson C, Manousides N, Balzani C. Determination of as-built properties of fiber reinforced polymers in a wind turbine blade using scanning electron and high-resolution X-ray microscopy. Compos Part C Open Access. 2022;9:100310. doi:10.1016/j.jcomc.2022.100310.
15. Staab F, Prescher M, Balle F, Kirste L. 3D X-ray microscopy of ultrasonically welded aluminum/fiber-reinforced polymer hybrid joints. Mater. 2021;14(7):1784. doi:10.3390/ma14071784.
16. Kimura M, Takeichi Y, Watanabe T, Niwa Y, Kimijima KI. Finding degradation trigger sites of structural materials for airplanes using X‐Ray microscopy. Chem Record. 2019;19(7):1462–1468. doi:10.1002/tcr.201800203.
17. Wang A, Li S, Zhang S, Zhang S, Liu Z, Yan K. Enhancing CFRP laminates with plasma jet arrays: A study of interlaminar mechanical properties. Polym Compos. 2024;45(11):10190–10203. doi:10.1002/pc.28466.
18. de Oliveira MM, Runqvist L, Poot T, Uvdal K, Carastan DJ, Selegård L. Hybrid nanofiller-enhanced carbon fiber-reinforced polymer composites (CFRP) for lightning strike protection (LSP). ACS Omega. 2024;9(33):35567–35578. doi:10.1021/acsomega.4c03272.
19. Yang C, Zhu D, Yang F, Liu Q, Sun C, Lei K, et al. Quantitative analysis based on atomic force microscopy characterization of interfacial properties between carbon fibers and epoxy resin subjected to hygrothermal and thermal treatments. Compos Sci Technol. 2020;198:108278. doi:10.1016/j.compscitech.2020.108278.
20. Raimondo M, Naddeo C, Vertuccio L, Lafdi K, Sorrentino A, Guadagno L. Carbon-based aeronautical epoxy nanocomposites: effectiveness of atomic force microscopy (AFM) in investigating the dispersion of different carbonaceous nanoparticles. Polym. 2019;11(5):832. doi:10.3390/polym11050832.
21. Fard MY. Carbon nanotube network and interphase in buckypaper nanocomposites using atomic force microscopy. Int J Mech Sci. 2021;212:106811. doi:10.1016/j.ijmecsci.2021.106811.
22. Liu L, Jia C, He J, Zhao F, Fan D, Xing L, et al. Interfacial characterization, control and modification of carbon fiber reinforced polymer composites. Compos Sci Technol. 2015;121:56–72. doi:10.1016/j.compscitech.2015.08.002.
23. Pulidindi IN. Crystallinity of commercial carbon fibers from X-ray diffraction (XRD) studies. Int J Photochem Photochem Res. 2023;1(1):17–27.
24. Pulidindi IN. Raman spectroscopy for the determination of relative crystallinity of carbon fibers. Int J crystall Mater. 2024;1(1):30–37.
25. Cheng A, Zhang Y, Zhong WH, Li ZP, Cheng DJ, Lin YX, et al. Few layer MoS2 embedded in N-doped carbon fibers with interconnected macro pores for ultrafast sodium storage. Carbon. 2020;168:691–700. doi:10.1016/j.carbon.2020.07.008.
26. Harano T, Takeichi Y, Usui M, Arai Y, Murao R, Negi N, et al. Observation of distribution of π-orbital-oriented domains in PAN- and pitch-based carbon fibers using scanning transmission X-ray microscopy. Appl Sci. 2020;10(14):4836. doi:10.3390/app10144836.
27. Pulidindi IN, Gedanken A. Surface modification of carbon fibers. Preprints. 2023. doi:10.20944/preprints202308.2053.v1.
28. Patel D, Joshi M, Joshi Y, Pulidindi IN, Selvaraj S. Direct synthetic routes of MXenes and their application in carbon fiber reinforced plastics (CFRPs) as supplementary sizing layer. Int J Crystall Mater, 2024;1(1):7–13
29. Pulidindi IN. Diglycidyl ether of bisphenol A (DGEBA) based epoxy sizing agent induces surface polarity in carbon fibers. IJCM. 2024.
30. Pulidindi IN. New insight into the composition and structure of sizing agent from NMR spectroscopy. J Photochem Photochem Res. 2024.