Search

Mesophase pitch is usually prepared by radical polymerization or catalytic polymerization from coal tar, petroleum, and aromatic compounds, and the catalytic synthesis of mesophase pitch from pure aromatic compounds is more controllable in the preparation of high-quality mesophase pitch. However, the corrosive and highly toxic nature of the catalyst has limited the further development of this method. In this study, mesophase pitch was synthetized using ethylene tar and naphthalene as raw materials and boron trifluoride diethyl etherate as a catalyst. The effect of the catalytic reaction on the structure and properties of the mesophase pitch was investigated. The results show that naphthalene plays an important role in the mesophase content and reaction pressure (from above 6 MPa to 2.35 MPa). Mesophase pitch with fine-flow texture can be prepared by introducing more methylene groups, naphthenic structures, and aliphatic hydrocarbons during synthesis. Carbon fibers prepared from mesophase pitch show a split structure, and the thermal conductivity is 730 W/(m·K). This work provides theoretical support for lower toxicity and causticity and for reaction-controlled technology for the synthesis of high-purity mesophase pitch. [ABSTRACT FROM AUTHOR]

Carbon fibers produced from mesophase pitch are superior in many properties such as high thermal conductivity and high tensile modulus, which originated from the high graphitizability and high carbon yield of the raw materials. Any variation in mesophase pitch microstructure will be inherited in derived carbon fibers. Herein, we monitored the microcrystal structure evolution of carbon fiber derived from thermal soaked mesophase pitch and the caused variation in mechanical properties. Results showed that mesophase pitch with prolonged soaking time from 1 to 12 h produced the carbon fibers with improved microcrystal structure, reduced diameter, and crack angle, contributing to an apparent increase in tensile strength from 1.70 to 2.72 GPa and tensile modulus from 152 to 246 GPa. Thermal soaking upon elevated temperature from 320 to 335 °C also contributes an improvement in microcrystalline development. However, the attendant increment in diameter and open crack angle lead to deterioration in tensile strength and modulus, the highest value of which is only 1.53 GPa and 190 GPa. This work provides useful information on thermal soaking parameter selection and is of particular interest for future optimization of carbon fiber production. [ABSTRACT FROM AUTHOR]

High alignment of graphene in mesophase pitch-based carbon fibers endows them with excellent properties such as high thermal conductivity and ultrahigh modulus. However, the weak interlayer interaction between large planar molecules leads to unwanted open crack in circular carbon fiber, leading to low strain-to-failure and low utilization rate in composite manufacturing. It remains a challenge to produce split-free circular carbon fiber while keeping a high degree of alignment of graphite layers. Herein, a die swell manipulating strategy is employed to address the problem through elaborating spinneret design. By applying an exit angle of 30° at the spinneret, the stored stress and shear-induced orientation of crystallites during the capillary flow were relaxed at the exit to enhance the die swell. The disoriented texture of fibers prevents the carbon fibers from splitting while still maintaining high degree of molecular alignment. The obtained carbon fibers present 20% higher of tensile strength, and more than twice of the compressive strength than the split ones, without sacrificing their superior thermal properties, which is up to 512 W·m−1·K−1. The work provides valuable insights into the design of carbon fiber for structural and functional integration materials in aerospace and beyond. [ABSTRACT FROM AUTHOR]

This study is focused on a novel high-thermal-conductive C/C composite used in heat-redistribution thermal protection systems. The 3D mesophase pitch-based carbon fiber (CFMP) preform was prepared using CFMP in the X (Y) direction and polyacrylonitrile carbon fiber (CFPAN) in the Z direction. After the preform was densified by chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP), the 3D high-thermal-conductive C/C (CMP/C) composite was obtained. The prepared CMP/C composite has higher thermal conduction in the X and Y directions. After an ablation test, the CFPAN becomes needle-shaped, while the CFMP shows a wedge shape. The fiber/matrix and matrix/matrix interfaces are preferentially oxidized and damaged during ablation. After being coated by SiC coating, the thermal conductivity plays a significant role in decreasing the hot-side temperature and protecting the SiC coating from erosion by flame. The SiC-coated CMP/C composite has better ablation resistance than the SiC-coated CPAN/C composite. The mass ablation rate of the sample is 0.19 mg·(cm−2·s−1), and the linear ablation rate is 0.52 μm·s−1. [ABSTRACT FROM AUTHOR]

The development of graphite crystals determines the thermal conductivity of carbon/carbon (C/C) composites. Nevertheless, its connection with dynamic thermal response behavior is not completely clear, especially for the high-thermal-conductive C/C (HTC-C/C) composites. This study investigates the influence of the different graphite crystal developments on the thermal response behavior of HTC-C/C composites by controlled graphitization. The results show that when the graphitization degree increases from 77.9% to 87.7%, the thermal conductivity of HTC-C/C composites in the X/Y direction increases from 311.84 W·m−1·K−1 to 453.05 W·m−1·K−1, and that in the Z direction increases from 23.13 W·m−1·K−1 to 66.17 W·m−1·K−1. The temperature distributions on the X–Y and Y-Z surfaces exhibit distinct "lattice-like" and "stripe-like" features, aligning with the arrangement of mesophase-pitch-based carbon fibers. By increasing the graphitization degree and reducing porosity, the thermal conduction of HTC-C/C composites can be significantly enhanced. The in-plane thermal conductivity is primarily governed by the graphitization degree, while the out-of-plane thermal conductivity is mainly dominated by the porosity in HTC-C/C composites. [ABSTRACT FROM AUTHOR]

• The reliable connection of CFRP and high-strength steel is successfully realized. • The properties of hybrid joints are assessed by the maximum drawing load. • Linear oscillating laser heat source is beneficial to reducing the thermal damage of CFRP plate. • The bond between resin and carbon fiber wire is destroyed, which deteriorates the performance of steel/CFRP joint. In this paper, a novel laser rivet welding method is explored for joining CFRP to high-strength steel. The steel plate is locked between steel rivet and CFRP plate by plug riveting, while the connection between steel plate and rivet are obtained by laser welding based on the coupling of the rotation of displacement machine and linear oscillation of laser heat source. The mechanical properties of hybrid joints are assessed by the maximum drawing load, and microstructure, laser energy and temperature field distribution of joints are also investigated. The results show that the hybrid joints are categorized into steel plate/steel rivet welding area (SRA), CFRP plate/steel plate mechanical contact area (SCA) and CFRP plate/steel rivet riveting area (RCA). When laser heat source oscillates in a straight line, the peak value of laser energy reduces, while the transverse area of laser energy increases, which is beneficial to reducing the thermal damage of CFRP plate. At the optimal parameter, the melting depth in SRA is reasonably controlled, the interface temperature in SCA is lower than that of CFRP resin decomposition, and there is no gap in SCA, the fracture mode of joints presents the characteristic of CFRP matrix tearing failure, and the maximum drawing load of joint reaches 2500 N. However, when the melting depth increases to the thickness of steel plate, the heat effect on CFRP plate becomes severe, and the bond between the resin and carbon fiber wire in base material is destroyed, which deteriorates the performance of steel/CFRP joint. [ABSTRACT FROM AUTHOR]

Mesophase-pitch-based carbon fiber (MPCF) reinforced polymer (MPCFRP) composites show great potential for aerospace applications due to their excellent thermal conductivity and dimensional stability. However, the low compressive strength severely limits their application in high load-bearing areas. To address this issue, MPCF-A with a split-radial structure and MPCF-B with a skin-core structure were meticulously prepared by fiber structure regulation. The compression failure behavior of MPCFs at the monofilament and the microregion levels was investigated using the tensile recoil method and in-situ micropillar compression technique. MPCF-A exhibits the failure mode of petal-like lamellar separation due to axial crack penetrating along the (002) crystal plane of graphite layers, with the compressive strength of the core region (391 MPa) being higher than that of the skin region (360 MPa). Conversely, MPCF-B demonstrates a large transverse fracture in the skin region during damage, along with uniform microcracks in the core region. Notably, the compressive strength of the core region (547 MPa) significantly exceeds that of the skin region (456 MPa). Furthermore, the compressive strength of MPCF-B monofilaments (583 MPa) is higher than that of MPCF-A (462 MPa), attributed to factors such as the smaller graphite crystallite size (L a = 36.54 nm, L c = 26.75 nm), lower crystallite orientation (Z = 10.21°, R = 0.25), smaller pore size (R g = 9.56 nm), and higher amorphous carbon content (g = 69.77%, K = 20.38). Consequently, the compressive strength of MPCFRP-B (232 MPa) is enhanced by 30.3% compared to MPCFRP-A. [ABSTRACT FROM AUTHOR]

High-purity rayon-based carbon fiber (CF Ray) felt holds significant promise for applications in thermal protection systems and semiconductor crystal growth furnaces. This study employs halogen gas purification and high-temperature purification techniques in the fabrication of high-purity CF Ray felt. Additionally, the influence of the purification process on the thermal insulation and oxidation resistance of CF Ray felt is investigated. The glow discharge mass spectrometer analysis reveals that purification at a lower temperature of 2300 °C achieves a purity level of 6.9 ppm, surpassing both purified CF Ray felt without halogen at 2300 °C (56.1 ppm) and high-temperature treated CF Ray felt at 3000 °C (10.4 ppm). Thermal insulation and dynamic-static oxidation resistance tests show that the properties of CF Ray felt are concurrently affected by the heat treatment temperature. Compared to high-temperature purification, halogen gas purification operates at lower temperatures, preventing the graphitization of CF Ray , thereby ensuring high purity while enhancing thermal insulation and demonstrating relatively superior oxidation resistance. This study offers novel insights into the preparation and performance adjustment of high-purity CF Ray felt. [Display omitted] [ABSTRACT FROM AUTHOR]

• The C/C-SiC composite with 221.1 W∙m−1K−1 in X and Y direction was fabricated. • The CF MP /C skeleton acted as the thermal diffusion channels during ablation. • The composite showed better ablation resistance due to surface temperature reduction. The novel three dimensional highly thermal conductive carbon/carbon-silicon carbide (C/C-SiC) composite was successfully prepared using the mesophase-pitch-based carbon fibers and pyrocarbon as the thermal diffusion channels. The results show that the highly thermal conductive C/C-SiC composite with 221.1 W m−1K−1 in the ablation direction exhibits a smaller temperature gradient, and the surface temperature is 470 °C lower than that of the lowly thermal conductive C/C-SiC composite. The mass and linear ablation rates of the highly thermal conductive C/C-SiC composite are 0.56 mg·cm−2 s−1 and 0.11 μm·s−1, respectively. [ABSTRACT FROM AUTHOR]

Mesophase-pitch-based carbon fiber (MPCF) reinforced polymer (MPCFRP) have excellent properties such as high thermal conductivity and high modulus, but the significant anisotropy and surface inertness of MPCF result in the poor interlaminar thermal conductivity and interface bonding of MPCFRP, which greatly limits its application. To address this issue, MPCF-A with split-radial structure was prepared through fiber structure modulation. Compared with the conventional skin-core fiber (MPCF-B), the higher surface roughness and chemical activity of MPCF-A contribute to stronger mechanical locking and chemical bonding between fibers and resin, meanwhile open wedge crack and better graphite microcrystalline structure of MPCF-A play a positive role in increasing the contact points and reducing the phonon scattering in the heat transfer. Therefore, the interlaminar shear strength (40.7 MPa) and interlaminar thermal conductivity (2.09 W/(m·K)) of MPCFRP-A are 9.12% and 27.4% higher than those of MPCFRP-B, respectively, on the basis of the excellent in-plane thermal conductivity (322.8 W/(m·K)). This study provides a reliable guide to improve the interlayer performance of MPCFRP by tailoring the fiber microstructure. [ABSTRACT FROM AUTHOR]

The high-thermal-conductive Carbon/Carbon (HTC-C/C) composites using mesophase-pitch-based carbon fibers (CF MP) as heat conduction carriers are promising thermal management materials in high-tech fields. The composites undergo a complex dynamic temperature variation in practical application and their thermal response behavior and the enhancing effect of CF MP are not clear. The one-dimensional, two-dimensional and three-dimensional HTC-C/C composites were prepared with thermal conductivity of 528 W·m−1·K−1, 429 W·m−1·K−1 and 437 W·m−1·K−1 in the CF MP direction, respectively, and the thermal response behaviors were investigated by infrared thermal imager. The results reveal that the graphitized CF MP with azimuth angle 7.69°, graphitization degree 75.49% and thermal conductivity 700 W·m−1·K−1 can transfer heat efficiently in the composite. The temperature variation and distribution of composites are all determined by the CF MP arrangement and have a good corresponding relationship with the size and shape of pore defects. In comparison with one-dimensional composite, the two-dimensional and three-dimensional composites exhibit pronounced "striped" and "grid-like" temperature distribution, respectively. • The HTC-C/C composites with different structure were fabricated. • The CF MP acts as fast heat conduction channels. • The dynamic thermal response behavior of HTC-C/C composites are investigated. [ABSTRACT FROM AUTHOR]

• A two-directional Cf/Al composite with a thermal conductivity of 305.5 W∙m−1∙K−1 is fabricated. • The CF MP acts as fast heat conduction channels. A two directional high thermal conductive carbon fiber reinforced aluminum matrix composite with low interface damage is prepared by a vacuum hot-pressure diffusion method using the mesophase-pitch-based carbon fiber (CF MP) cloth as fast heat conduction channels. The fiber/matrix interface is composed of an amorphous gradient transition layer between aluminum matrix and CF MP rather than Al 4 C 3 interface phase, thus endowing the continuous heat conduction channels in the composite. The composites deliver the high thermal conductivity of 305.5 W∙m−1∙K−1 in the X (Y) direction and the low volume density of only 2.53 g∙cm−3 when the fiber volume fraction reaches 30 vol%. The high thermal conductivity of the composite is attributed to the highly oriented fast heat transfer effect of the CF MP , the isotropic heat transfer effect of the aluminum matrix and the low-damage CF MP /aluminum interface. This study opens a new avenue to design and select the high thermal conductivity and lightweight thermal management materials for the aerospace field. [ABSTRACT FROM AUTHOR]

A three-dimensional ZrC–SiC-modified Carbon/Carbon composite having high thermal conductivity is prepared to significantly reduce the ablation rate and improve dimensional stability of composites used in thermal protection systems. The mesophase-pitch-based carbon fibers/pyrocarbon skeleton is designed as the thermal diffusion channel using the intermediate state mesophase-pitch-based carbon fibers and chemical vapor infiltration method. After successive graphitization and polymer precursor impregnation and pyrolysis, the obtained ZrC–SiC-modified carbon/carbon composite exhibits a high thermal conductivity of 206.5 W m−1 K−1 in the X(Y) direction. The ablation results indicate that the composite exhibits a surface temperature of 241 °C, which is lower than that of the composite without mesophase-pitch-based carbon fibers, thus verifying the improved ablation resistance. The linear and mass ablation rates of the composite are found to be 0.33 μm s−1 and 0.56 mg cm−2 s−1, respectively. The thermal conduction mechanism of the ZrC–SiC-modified carbon/carbon composite near the ablation center is investigated to show the combined phonon heat conduction and thermal radiation. This study provides a protocol for the design and construction of modified carbon/carbon composites having high thermal conductivity for application in hypersonic vehicles. • A C/C–ZrC–SiC composite with a thermal conductivity of 206.5 W m−1 K−1 in the ablation direction was fabricated. • The CF MP /C skeleton acted as the thermal diffusion channels during ablation. • The composite showed improved ablation resistance due to a reduction in surface temperature. [ABSTRACT FROM AUTHOR]