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Carbon fiber (CF) reinforced composites are widely used due to their excellent properties. However, the smooth surface and few functional groups of CFs can lead to fiber fractures and pullout, which reduce the service life of the composites. The overall performance of composites can be improved by growing carbon nanotubes (CNTs) on the CF surface. Before this, CF surface should be modified to enhance the loading amount of catalyst particles and thus make the CNTs more uniform. In this paper, CNTs were grown on a CF surface by one-step chemical vapor deposition to prepare multi-scale CNTs/CF reinforcements, and the effects of different methods on the CF surface modification were explored. After setting four intensities of electrochemical anodic oxidation, i.e., 50 C/g, 100 C/g, 150 C/g and 200 C/g, it was found that the distribution and quantity of CNTs were improved under both the 100 C/g and 150 C/g conditions. Considering the influence of electrical intensity on the (002) interplanar spacing of CFs, which affects the mechanical properties of the samples, 100 C/g was finally selected as the optimal electrochemical treatment intensity. This finding provides a reference for continuous and large-scale modification of CF surfaces to prepare CNTs/CF multi-scale reinforcements. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were synthesized under different catalyst compositions and reduction conditions. The effects of the catalyst, reduction temperature and reduction time on the surface morphology, graphitization, and single filament tensile strength of the prepared CNTs/CF samples were investigated. When nickel was used as the catalyst and copper as the catalyst promoter, with the increase of copper concentration, the catalytic activity increased. Thus, the carbon source was consumed more completely, improving the abundance of CNTs with good graphitization. And the effect of repairing CF defects was more obvious, hence the single filament tensile strength accordingly increased. Besides, the increase of catalyst reduction temperature and reduction time intensified the etching of CF by catalyst, and decreased the single filament tensile strength of CF. With the deposition of CNTs, the tensile strength of CF was enhanced in varying degrees. When the concentration of cooper was 0.01 mol/L with the reduction time of 10 min and reduction temperature of 450 °C, CNTs/CF had the highest tensile strength, which can reach up to 4.51 GPa. We determined that bimetallic catalysts could adjust the catalytic activity of nickel. The change of reduction time and temperature would affect the quality of CNTs, which was helpful to obtain high quality CNTs on CF surface and improve the mechanical properties of CNTs/CF and its composites. [ABSTRACT FROM AUTHOR]

Highly efficient and multifunctional electromagnetic wave (EMW) absorbers which can be easily processed are desirably required. Herein, cupric ammonia is creatively adopted as the catalyst precursor of the in-situ growth of carbon nanotubes (CNTs) onto carbon fiber (CF) during chemical vapor deposition. Typically, when prepared at 750 °C, N/S co-doped bamboo-like amorphous CNTs/CF was successfully synthesized, while some Cu nanoparticles were remained in CNT forests. The sample obtains an excellent absorption toward EMWs, demonstrating a minimal reflection loss of −59.28 dB at 14.1 GHz with an ultrathin thickness of 1.42 mm. Concurrently, it is over a relatively broad effective absorption bandwidth (EAB) of 3.3 GHz (12.3–15.6 GHz) with 31% loading in the paraffin matrix. And the EAB value of CA-700 reaches 3.7 GHz (14.3–18 GHz) at merely 1.45 mm. The satisfying attenuation performance mainly originates from the synergistic effects of continuous three-dimensional conducting networks, abundant interfaces, sufficient defects, and the well impedance matching. Moreover, all as-prepared samples could be potentially used as reinforcements of resin matrix composites with high strength. Therefore, a facile route is provided to produce thin, lightweight, superior and high-strength EMW absorbing materials based on CF and CNTs. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were prepared by chemical vapor deposition after electrochemical anodization and catalyst impregnation. The results showed that after the electrochemical anodization, the CFs were oxidatively etched and the surface roughness increased, which is helpful to form a uniform catalyst coating on the surface of CF. Under the current of 0.4 A and 0.6 A, CNTs can grow evenly on the surface of CF. Within a certain range, with the increase of growth time, the density and length of CNTs are improved. The CNTs/CF reinforcement prepared at the current intensity of 0.4 A and the growth time of 8 min has the best comprehensive performances compared with other as-fabricated samples. The tensile strength of the sample can reach a high value of 4.56 GPa, and the wettability of resin has an effective improvement. [ABSTRACT FROM AUTHOR]

Exploring carbon materials is promising for innovative electromagnetic wave (EMW) absorption materials, nevertheless challenged by balancing efficient EMW absorption and continuous large-scale fabrication. In this work, CNTs/CNFs@CF with inimitable 3D network hierarchical structures are fabricated as EMW absorbers via the chemical vapor deposition method. Through detailed characterization of its morphology, structure, composition, and magnetic properties, the material obtained optimal electromagnetism parameters and showed exceptional EMW absorption performance. Herein, the minimum reflection loss (RL min) was −66.00 dB at 1.00 mm and the maximum effective absorption bandwidth of 4.48 GHz was obtained at 1.29 mm. In addition, good mechanical properties with a single-filament tensile strength of 4.99 GPa were achieved, thereby expanding the range of applications. Undoubtedly, CNTs/CNFs@CF realizes the synergy of multiple synergistic loss mechanisms and impedance matching for EMW absorption. In summary, this implies a good prospect for the continuous large-scale preparation of ultrathin and efficient EMW absorbers. • CNTs/CNFs@CF with 3D network hierarchical structures are fabricated for facile synthesis. • The synergistic effect of impedance matching and strong attenuation is realized. • Combined with excellent mechanical properties, expanding the range of applications. [ABSTRACT FROM AUTHOR]

• Hierarchical Co 3 O 4 /Co@CNFs/CNTs/CF hybrids are fabricated by a scalable approach. • Magnetic-dielectric loss and ideal impedance produce super microwave absorption. • A RL min of −60.85 dB at 1.22 mm and an EAB of 4.24 GHz at 1.38 mm are obtained. • The SRL of CFF650 outperforms many previous prominent carbon-based composites. • CST simulation results confirm the stealth potential in practical application. Aiming to solve the aggravating electromagnetic radiation issues, high-performance electromagnetic wave (EMW) absorbers are urgently required. Recently, integrating carbonaceous and magnetic materials to obtain dielectric-magnetic double EMW loss has been intensively explored. Here, Co 3 O 4 /Co@carbon nanofibers/carbon nanotubes anchored on carbon fiber (Co 3 O 4 /Co@CNFs/CNTs/CF) hybrids (CFFs) with distinctive heterostructure were synthesized by annealing ZIF-67@CF and catalytic chemical vapor deposition, and deliver great superiorities in microwave dissipation. Specifically, when at a low filling ratio of 25 wt% in paraffin wax, CFF650 acquires a superb minimum reflection loss up to −60.85 dB at only 1.22 mm together with a broad effective absorption bandwidth of 4.24 GHz at merely 1.38 mm. Remarkably, the specific reflection loss of CFF650 achieves an unexpected value, comparable to many distinguished carbon-based composites previously reported. Besides, the simulation of radar cross section values ascertains the fulfilling stealth ability of CFFs under radar detection. These excellent characteristics benefit from the diverse components and unique heterostructures, which form rich conductive networks, plentiful heterogeneous interfaces, appropriate defect polarization and dipole polarization, sufficient magnetic loss as well as optimal impedance matching. Combined with the feasible and efficient fabrication method, this work offers a significant promise of CF-based composites for practical applications in EMW absorption. [ABSTRACT FROM AUTHOR]

This article provides a method for growing carbon nanotubes (CNTs) on carbon fibers (CFs) using a one-step method at low temperatures using Fe Ni bimetallic catalysts in a chemical vapor deposition (CVD) furnace. It was found that the best surface morphology, and tensile strength of 4.55 GPa, could be obtained by controlling the CVD process at 550 °C, 3.5 cm/min, and 0.45:0.30 L/min hydrogen to acetylene gas ratio, which is 6.56 % higher compared to Desized CFs. This proves that enhancement effect of CNTs on CFs. Subsequently, wettability tests and microstructure analysis were performed for quasi-vacuum CNTs/CF and continuous CNTs/CF under the optimal process, demonstrating that the bond strength of CF and resin was also significantly improved. The catalyst under this optimal process has a low etching effect on CFs, and the grown CNTs have a clear structure with good coaxiality and wall uniformity, which can effectively improve the performance of CNTs/CFs. [Display omitted] • Fe Ni catalyzed CNTs on the surface of CFs were employed using one-step-CVD. • The best sample showed a 6.56 % increase in tensile strength over desized CFs. • The CNTs/CF prepared by CVD have excellent performance in practice. [ABSTRACT FROM AUTHOR]

Cu nanoparticles were loaded on the surface of continuous carbon fibre (CF) and catalysed the growth of carbon nanotubes (CNTs) by continuous catalytic chemical vapour deposition. The results of Cu and traditional catalysts were contrastively studied in terms of surface morphology, microstructure and mechanical properties. It is reflected that the CNTs grown from Cu catalysts are in suitable distribution, with unique bamboo‐like structure and higher graphitisation degree. The carbon nanotube–carbon fibre utilising Cu catalyst has 53.0% higher interfacial shear strength than the pristine fibre, and shows advantage in tensile strength over its counterparts of traditional catalysts. Above all, a "loading–catalysis–reinforcing" mechanism was established, which theoretically and systematically explains how the nature of different catalyst metals affects the various stages in the process of growing CNT on the surface of continuous CF. This research expands the catalyst options, and develops the catalysis mechanism that offers an important theoretical guidance for the process optimization. [Display omitted] • Cu nanoparticle growing bamboo-like carbon nanotube on continuous carbon fibre. • Novel catalyst optimising tensile and interfacial strength simultaneously. • A "loading–catalysis–reinforcing" mechanism instructive to catalyst engineering. [ABSTRACT FROM AUTHOR]