Pitch-based Carbon Fibers Research Articles

Raman Scattering for Tensile Testing of Polyacrylonitrile-Based and Pitch-Based Single Carbon Fibers

Raman Scattering for Tensile Testing of Polyacrylonitrile-Based and Pitch-Based Single Carbon Fibers

Evaluation of the relationship between the number of surface and internal defects and stress in inorganic fibers

To better utilize the mechanical properties of ceramics fibers, it is very important to understand the ceramics fiber distribution. The strength distribution of ceramics fibers is strongly dependent on defects that are present in or on the surface of the material. When the defects are large, the location of the defects is identified by observing the fracture surface, and the strength of the material is analyzed based on the results. However, in recent years, defects in high-strength ceramics such as carbon fibers have become so small that it is very difficult to analyze the location of such defects. To overcome this problem, a defect analysis method has been developed based on the observation that the tensile strength of fibers decreases when tensile tests are performed in liquids. In this study, a new model that considers both surface and internal defects of fibers was introduced into this analysis method, and the newly developed method was applied to quantitatively separate surface and internal defects of polyacrylonitrile-based fibers, pitch-based carbon fibers, SiC fibers, and glass fibers in air, water, and organic solvents. The number of internal and external defects was expressed as a function of stress. Based on the number of defects, the influence of surface defects was significant for glass fibers, polyacrylonitrile-based carbon fibers, silicon carbide fibers, and pitch-based carbon fibers, in that order. This method is useful for analyses of surface defects in fibers.

Study on spinnability, thermal stability and microstructure of modified isotropic pitch by adding polyacrylonitrile melt blending

Asphalt samples modified by melting isotropic asphalt with polyacrylonitrile (PAN) are obtainable. Investigations were conducted on the spinnability, microstructure, and thermal stability of the modified asphalt. The results demonstrate that pan40w modified asphalt possesses the highest spinnability stability. Additionally, there is a reduction in viscosity within the smooth range, a slight increase in the flow point, and an enhancement in spinnability. Compared to other modified asphalt samples, PT403 containing 0.3 % PAN exhibited the highest comprehensive performance, characterized by a molecular weight of 400,000, enhanced spinnability, a larger and more uniform microcrystal size, and improved thermal stability. This study employs a distinctive modification scheme and provides a cogent explanation of the corresponding mechanisms, potentially contributing to the advancement of producing cost-effective pitch-based carbon fibers from petroleum by-products.

Ablative property and mechanism of pitch-based carbon fiber modified C/C composites with high thermal conductivity

The novel C/C composites with thermal transport function were prepared using the mesophase-pitch carbon fibers (CFMP) as the thermal diffusion channels. The introduction of CFMP greatly improved the microstructure, thermal properties, and ablative resistance of the C/C composites. During the graphitization process, compared with PAN fibers (CFPAN), CFMP was more likely to be graphitized to form a highly ordered three-dimensional graphite structure. The highly organized microcrystalline structure of CFMP resulted in a tight interface with PyC that lessened the likelihood of flaws and cracks during graphitization. CFMP, which acted as a thermal conduction skeleton, significantly improved the thermal conductivity of C/C composites. After 3000 °C HTT, the thermal conductivity of C/C-3000-Z composites was increased to 51.70 and 225.02 W/(m K) in the XY and Z planes, respectively. During the ablation process, C/C-3000-Z specimen exhibited a lower temperature gradient and less thermal stress owing to the outstanding thermal properties and fewer defects. After 30 s ablation, the temperature difference of surface and backside was only 495.9 °C, and the mass and linear ablation rates were 0.3 μm/s and 0.9 mg/s, respectively.

Enhancing electrical insulation and thermal conductivity in polydimethylsiloxane polymer nanocomposites through silica coating on carbon fibers

Mesophase pitch-based carbon fibers (MPCFs) exhibit high thermal conductivity (∼900Wm−1K−1) and are considered to be an important candidate for future thermal management. However, MPCFs lead to an increase in the electrical conductivity of nanocomposites due to the low volume electrical resistivity (∼10−3 Ω cm). The development of MPCFs nanocomposites with high thermal conductivity and good electrical insulation remains a challenging problem. In order to solve the problem, we utilized the surfactant cetyltrimethylammonium bromide (CTAB) as an anchor for hydrolysis, and employed a sol-gel method to deposit a silica coating on MPCFs (silica@MPCFs). Silica@MPCFs was used as the filler for polydimethylsiloxane (PDMS) matrix. The nanocomposites exhibit commendable thermal conductivity (achieving 1.52 Wm−1K−1) and excellent volume electrical insulation (exceeding 1013 Ω cm) at a 30 vol% concentration. Notably, both the thermal conductivity and volume electrical insulation exceed MPCFs/PDMS. This approach to electrical insulation treatment holds substantial potential for the future preparation of high-performance nanocomposites of electronic devices.

Molecular origin of viscoelasticity and influence of methylation in mesophase pitch

The viscoelastic and thermomechanical properties of pitches are responsible for their melt-spinning behavior, a critical step for manufacturing high-performance pitch-based carbon fibers. Here, we systematically explore the impact of methyl group modifications on the viscoelastic and thermal properties of mesophase pitches. We employ a range of atomistic modeling approaches, including Density Functional Theory (DFT), Density Functional Tight Binding (DFTB), and Classical Molecular Mechanics (MM), to provide detailed insights into the molecular interactions and structural changes. Our results revealed the molecular mechanisms that promote layered structures leading to the anisotropic nature of the viscoelastic behavior of mesophase pitch. Furthermore, we propose a modified molecular representation of naphthalene-based mesophase pitch based on the analysis of x-ray diffraction measurements. This study provides fundamental insights into the molecular structures of mesophase pitch and the role of methyl groups controlling its viscosity, which offer valuable insights into mesophase-based carbon fiber production.

Development of ultra-high temperature ceramic matrix composites for hypersonic applications via reactive melt infiltration and mechanical testing under high temperature

AbstractIn the ongoing development of hypersonic technologies, material advancements play a key role in meeting the ever-increasing thermomechanical demands of these applications. Ultra-High Temperature Ceramic Matrix Composites (UHTCMCs) offer a promising solution for components operating under such extreme conditions. Their outstanding thermomechanical properties, including high temperature and thermal shock resistance, excellent thermal conductivity and mechanical strength, position them as ideal candidates for applications in fields like leading edges or inlet ramps for ramjets and scramjets. Due to their remarkable material composition, UHTCMCs are capable of operating in temperature regimes that surpass 1700 °C during their operation times under oxidizing atmospheres. At the German Aerospace Center (DLR), a UHTCMC material based on carbon fibres and a zirconium diboride matrix is being developed utilizing Reactive Melt Infiltration (RMI). With RMI, the orientation of the reinforcement fibres can be tailored, to enable the material to fulfill the demanding load requirements. The reactive melt infiltration process comprises three stages: preform fabrication, pyrolysis, and the actual melt infiltration. The foundation for important material properties of the final ceramic, including the matrix composition, is established in the preform production, which is a crucial step in the process. A boron- and zirconium diboride-based slurry is infiltrated into pitch-based carbon fibre fabric. Subsequently, the preforms are consolidated, pyrolysed, and infiltrated with molten Zr2Cu to obtain the UHTC matrix by in situ reaction with the preform elements. Scanning Electron Microscopy (SEM) and Energy-dispersive X-Ray Spectroscopy (EDX) enable the examination of the microstructural features, including the arrangement and distribution of zirconium diboride within the matrix. Mechanical evaluation of the UHTCMCs is conducted via 3-point bending tests at both room temperature and at elevated temperature at 900 °C. It has been demonstrated that Ultra-High Temperature Ceramic Matrix Composites can be produced by means of reactive melt infiltration, and that they retain their strength even at elevated temperatures.

Effect of aromatization degree of mesophase pitch on cracks and mechanical properties of mesophase pitch-based carbon fibers

The aromatization degree of MP is closely related to the orientation of carbon fibers, which determines their properties. To investigate the effect of the aromatization degree of MP on the properties of carbon fibers, this study prepared MP with varying aromatization degrees using the self-pressurization/N2-blowing two-stage thermal condensation method with refined coal tar pitch as raw material. Mesophase pitch-based carbon fibers (MPCFs) were obtained through melt spinning, pre-oxidation, and carbonization processes. Results show that the C/H atomic ratio rises from 2.067 to 2.318 as the aromatization degree of MP increases. After carbonization at 1300 ℃, the microcrystalline structure of MPCFs becomes ordered, with obvious axial radiation in the cross-section. The carbon layers in MPCFs are tightly stacked in parallel, significantly improving tensile strength and modulus. When the C/H atomic ratio of MP exceeds 2.262, the resulting MPCFs exhibit a maximum tensile strength of 1389 MPa and a maximum tensile modulus of 167 GPa. However, when the C/H atomic ratio of MP exceeds 2.318, the excessive aromatization degree makes the MPCFs structure prone to cracking due to circumferential volume shrinkage, and the appearance of cracks reduces the tensile strength of MPCFs.

High-Performance Multifunctional Carbon Fibrous Sponges Derived from Pitch.

3D carbon-based porous sponges are recognized for significant potential in oil absorption and electromagnetic interference (EMI). However, their widespread application is hindered by a common compromise between high performance and affordability of mass production. Herein, a novel approach is introduced that involves laser-assisted micro-zone heating melt-blown spinning (LMHMS) to address this challenge by creating pitch-based submicron carbon fibers (PSCFs) sponge with 3D interconnected structures. These structures bestow the resulting sponge exceptional characteristics including low density (≈20mgcm-3), high porosity (≈99%), remarkable compressibility (80% maximum strain), and superior conductivity (≈628 Sm-1). The resultant PSCF sponges realize an oil/organic solvent sorption capacity over 56g/g and possess remarkable regenerated ability. In addition to their effectiveness in cleaning up oil/organic solvent spills, they also demonstrated strong electromagnetic shielding capabilities, with a total shielding effectiveness (SE) exceeding 60dB across the X-band GHz range. In virtue of extreme lightweight of ≈20mgcm-3, the specific SE of the PSCF sponge reaches as high as ≈1466dB cm3g-1, surpassing the performance of numerous carbon-based porous structures. Thus, the unique blend of properties renders these sponges promising for transforming strategies in addressing oil/organic solvent contaminations and providing effective protection against EMI.

Strategy for a high thermal conductivity and low thermal resistance under compression of oriented carbon fiber with spherical alumina thermal interface material

Thermal pads prepared with pitch-based carbon fibre (CF) orientation have garnered widespread attention due to their generally higher through-plane thermal conductivity. However, these thermal pads must undergo compression during the assembly process. When the compression exceeds a certain threshold, the orientation degree of the CFs inside the thermal pad can change, leading to a reduction in thermal conductivity. In this study, spherical alumina and CF were utilized to optimize thermal transfer stability under compression. The results demonstrate that the composites can still maintain efficient and stable heat transfer even when compressed by 25 %, which represents a more than 60 % improvement compared to pure CF-oriented composites. Furthermore, the relative motion between spherical alumina and CF, driven by their significant morphological differences, enhances the degree of CF orientation during the orientation process. With only 11.8 wt% CF loading, the composite achieved an impressive through-plane thermal conductivity of up to 20.4 W·m−1·K−1.

Carbon fibers from bitumen-derived asphaltenes: Strategies for optimizing melt spinnability and improving mechanical properties

The demand for low-cost carbon fibers with exceptional mechanical properties continues to grow across various industries. Bitumen-derived asphaltenes have emerged as a promising alternative to polyacrylonitrile (PAN), yet asphaltenes are a complex mixture of compounds, and the fundamental understanding of which asphaltenes are melt spinnable is not clearly understood. In this study, we utilized three distinct types of asphaltenes, each exhibiting notably distinct thermal softening temperatures (Ts) and aromaticity. The optimal melt processing conditions of asphaltenes were determined by dynamic rheology tests. Moreover, we introduced a novel strategy to facilitate the melt spinning of non-spinnable samples by preparing 100 % asphaltene blends with a low Ts asphaltene at different weight fractions. By this means, we achieved continuous melt spinning of precursor fibers. After careful selection of the stabilization and carbonization conditions, uniform carbon fibers were obtained from asphaltenes, which had the highest tensile strength (∼570 MPa) and modulus (∼60 GPa) values, comparable to isotropic pitch-based carbon fibers. Further post-processing of the as-spun fiber resulted in a significant increase in tensile properties, ∼1.1 GPa for strength and ∼91 GPa for modulus. Overall, this study identified spinnable asphaltene precursor characteristics and fiber post-processing methods for achieving low-cost, high-quality carbon fibers from asphaltenes.

Highly thermally conductive composites of graphene fibers

Carbon fiber-based polymer composites have rich electric and thermal functions, the merit of weight lightness to meet important applications in thermal management. Graphene fiber, a newly emerged carbonaceous fiber, features high thermal conductivity that surpasses conventional carbon fibers. For the realistic applications of graphene fiber, fiber composite is one necessary form but still remains unexplored. Here, we prepared graphene fiber based polymer composites and achieved high specific thermal conductivity up to 363 W∙cm3∙m−1∙K−1∙g−1, outperforming composites of mesophase pitch-based carbon fiber. Graphene fiber composites with a fiber content of 59 vol% have a low density of 1.53 g∙cm−3 and high axial thermal conductivity of 553 W∙m−1∙K−1. For the high breakage elongation of graphene fiber, graphene fiber composites can be fabricated to adapt sharp curvature structures. This work develops polymer composites of graphene fiber and their high thermal conductivity can have extensive applications in thermal management.

Controllable synthesis of naphthalene-derived isotropic pitch with linear molecular structure via Blanc chloromethylation–dechlorination reaction

Isotropic pitches with high softening points were controllably synthesized using naphthalene (NAP) via Blanc chloromethylation–dechlorination. Under mild conditions, chloromethyl was introduced into the NAP ring in the presence of chloromethylation reagent. The chloromethylation products of NAP are mainly composed of 1-chloromethylnaphthalene (1-CMNP) and a small amount of 1,4-dichloromethylnaphthalene (1,4-DCMNP). The results of the thermodynamic and kinetic calculations confirmed that the alpha-hydrogen on the NAP ring was more susceptible to being substituted by chloromethyl during chloromethylation, resulting in the formation of 1-CMNP and 1,4-DCMNP. High-quality isotropic pitches with linear methylene-bridged NAP ring structures, characterized by high purity, a high H/C ratio, 100 % solubility in quinoline, and excellent spinnability, were obtained after thermal dechlorination polymerization. Due to their homogeneous isotropic phase, appropriate viscosity, and outstanding spinnability, the as-synthesized pitches were adopted as precursors to prepare isotropic pitch-based carbon fibers via melt spinning. Additionally, the investigation of the carbonization behavior of the as-synthesized pitches showed that the naphthalene-derived isotropic pitch obtained at a polymerization temperature of 380 °C had a 57 % carbon yield at 800 °C, and its derived semi-cokes displayed an isotropic texture, even when carbonized at 550 °C.

Mesophase pitch-based high performance carbon fiber production using coal extracts from mild direct coal liquefaction

Mild direct coal liquefaction (autogenous pressure, no catalyst, no H2 gas) of Springfield coal in fluid catalytic cracking decant oil is shown to effectively produce coal extract precursors to spinnable mesophase pitch. This work demonstrates that the coal extract can be thermally treated to obtain mesophase pitch in a facile one-step process, bypassing the production of an intermediate isotropic pitch. Furthermore, the presence of 25 wt.% coal in the initial slurry can increase the yield to mesophase pitch nearly twofold and yield to carbon fiber by approximately 70%. The coal extract-derived mesophase pitch was melt-spun and heat treated to produce carbon fiber with graphitic texture, high modulus (>400 GPa) and tensile strength up to 943 MPa. Overall, this work demonstrates that coal can be effectively utilized to markedly amplify the mesophase pitch and carbon fiber yield from fluid catalytic cracking decant oil by relatively simple processing, while conserving utility as a precursor to high performance carbon fiber and potentially other high value graphitic products.

Vertically aligned and conformal BN-coated carbon fiber to achieve enhanced thermal conductivity and electrical insulation of a thermal interface material

Due to excellent thermal conductivity, high aspect ratio, and low density, mesophase pitch-based carbon fibers (MPCFs) are highly desired in electronic packaging. However, their thermal conductivity is hard to present in the polymer matrix because of the disordered stacking and low filling. Moreover, few researches are focused on the enhancement of the electrical insulation performance for MPCFs. Herein, we report vertically aligned and insulating boron nitride (BN) coated carbon fiber (CF) powders as significant fillers for polymer composites, endowing markedly improved thermal conductivity and electrical insulation. The high-quality BN coating layer on the surface of the CF is produced by a cooling precipitation method and high-temperature treatment with ingenious use of solubility properties, exhibiting a conformal, dense, and highly crystalline structure. This preparation method overcomes the limitations of coating thickness and particle agglomeration, resulting in a 31-fold enhancement of the electrical resistivity of the CF powders. After orientation treatment in a silicone rubber matrix, such CF@BN-filled pads exhibit good thermal conductivity, significantly improved insulation performance, and excellent mechanical properties. Among them, the optimized pad achieves a thermal conductivity of 12.06 W m−1 K−1, a volume resistivity of 50 × 108 Ω cm and a breakdown voltage of 3100 V mm−1, exceptional flexibility, and a favorable compression ratio (@45 psi) of 41.7 %. This work provides unique insights into constructing carbon fiber fillers as well as the preparation of high thermal conductivity composites, thereby expanding the application scenarios of carbon fiber powder in electronic packaging.

High stiffness 3D-printed continuous pitch carbon fiber reinforced polymer composites

This study presents a method for 3D printing very high stiffness pitch-based carbon fiber (CF) reinforced polylactic acid (PLA) composites using a modified open-source 3D printer. The fused filament fabrication (FFF) technique was used to fabricate the samples with alternating layers of PLA and PLA-coated pitch CF. The tensile Young’s modulus of the 3D-printed composite samples was measured to characterize the effect of different grades and volume fractions of pitch CF on the behaviour of the printed composites. Three grades of pitch CF which have different Young’s modulus were used with volume fractions ranging from 2.4 to 8.4%. Tensile tests showed that the K1392U CF reinforced composite with a 7.3% volume fraction demonstrated the highest improvement in Young’s modulus of 850% compared to neat 3D-printed PLA. This improvement is notably higher than any previous 3D-printed carbon-based composites at a relatively low volume fraction of CF. Statistical analysis showed increased Young’s modulus in all of 3D-printed composite samples tested. The experimental values were compared to the Halpin-Tsai model and suggest that some degree of fibre breakage occurred during the 3D printing process owing to the relative stiffness of the pitch-based fibers. Future directions and suggestions for process improvements are discussed.

Assessment of the anisotropy development of mechanical properties of pitch-based carbon fibers

Carbon fiber XN-P9 derived from anisotropic pitch was heat treated at different temperatures (2000, 2500, and 3000℃) and the mechanical properties of those single filament in various directions were tested with some methods we have developed. The anisotropy of the mechanical properties of those pitch-based carbon fibers was evaluated to be developed by heat treatment. As a comparison, the properties of carbon fiber XN-05 derived from isotropic pitch were also tested. The ratio of the longitudinal tensile modulus to the shear modulus of XN-05 fiber was approximately 3. In contrast, for pristine XN-P9 fiber, the longitudinal tensile modulus was more than nine times greater than the shear modulus, and the difference between these moduli increased with the elevating heat treatment temperatures. It was suggested that the anisotropy of mechanical properties of pitch-based carbon fibers was developed by heat treatment. In compressive deformation in the transverse direction to the fiber axis, a yielding and a softening was clearly observed with the elevating heat treatment temperature. The effect of anisotropy development on the span-length dependence of flexural modulus obtained from the three-point bending test of the single filament was assessed.

Preparation of spinnable mesophase pitch from pyrolyzed fuel oil by pressurized heat treatment and its application of carbon fiber

Petroleum residues are produced as by-products of petroleum refining. Recently, various effective non-fuel uses of petroleum residues have been considered toward a carbon-neutral society. Pyrolysis fuel oil (PFO) is one of the petroleum residues. Advanced utilization of PFO for future non-combustion applications is required. In this study, Mesophase pitch-based carbon fibers (MPCF) were successfully produced from PFO. Spinnable mesophase pitch (SMP), a precursor of MPCF, was prepared using PFO as a raw material through the pressurized heat treatment at 420°C-430 °C. PFO is from the naphtha catalytic cracking process for ethylene production and is mainly composed of 2–4 condensed polycyclic aromatic hydrocarbons (PAHs). The high temperature pressurized heat treatment could result in the PFO-derived SMPs with yield of 23.0 wt% and excellent spinnability. On the other hand, without pressurized heat treatment, the yield was 8.5 wt%. This indicates that pressurized heat treatment significantly contributed to the yield improvement. In addition, the preference for the conversion of PFO molecules into highly condensed PAHs via cata-condensation during pressurized heat treatment at 420°C-430 °C was observed, which may be the main reason for the high yield and excellent spinnability of the resulting SMPs. As a result, the obtained PFO-derived SMPs though the such high-temperature pressurized heat treatment provided the typical radial-random transversal textures and general mechanical performances of MPCF: The tensile strength and Young's modulus of the PFO-derived MPCF graphitized at 2400 °C showed high values of 1.9–2.7 GPa and 554–635 GPa, respectively.

Preparation processes and thermal conductivities of magnetic field- and torsional vibration-induced superoriented carbon fiber composites

With the advancement of semiconductor technology, advanced electronic devices have become increasingly efficient, highly integrated and multifunctional, producing a large amount of heat during operation, thus decreasing the device efficiency and increasing the requirements for thermal interface materials. The use of a magnetic field to prepare pitch-based carbon fibers (CFs) with ultrahigh axial thermal conductivities and aspect ratios is a promising method for preparing thermal interface materials. However, past methods are not adequately simple or effective. Herein, we propose a simple, efficient method for preparing a novel thermally conductive CF interface material with a superoriented and closely arranged structure. The thermal conductivity of the vertical plane can reach 82.026 W m-1 K-1, which is higher than that of many other alloys. During the experiment, we prove that the torsional vibration of the vibrating plate can greatly resolve the issue of powder bridging generated during preparation. In addition, we discover and explain the heat return conduction phenomenon through numerical simulation. Our innovative preparation process and our analysis of thermal conduction can provide a new method and unique view for the design of thermal interface materials.

Effect of isopropyl chloride addition in AlCl3 catalytic system on the formation of coal tar pitch-based mesophases

Mesophase pitch is a high-quality precursor for the synthesis of high-performance pitch-based carbon fibers. The mesophase content, texture and softening point are the most important factors for the structure, properties and spinnability of mesophase pitch (MP). Herein, we report a novel approach for the preparation of mesophase pitch with high anisotropic content and low softening point by AlCl3 catalytic pyrolysis in the presence of isopropyl chloride (PrCl). The variation of anisotropic content and mesophase texture under different PrCl additions and the effect of the introduction of isopropyl on the molecular stacking of aromatic lamellar molecules were investigated. The results confirmed that, except for their role in improving catalytic activity, carbocation co-catalysts can improve the structure and molecular assembly of aromatic molecules through the introduction of alkyl groups. The reaction of isopropyl chloride (PrCl) as a co-catalyst catalyzed pyrolysis of medium-temperature coal pitch at 370 ℃ for 8 h produced a bulk mesophase with a content close to 100 %. Compared to the AlCl3 system (without PrCl), the AlCl3-PrCl system can catalyze the preparation of mesophases at lower temperatures. In addition, it is logical that the introduction of isopropyl group significantly increases the stacking spacing of the mesophase pitch layer molecules, which can effectively improve the mobility of the aromatic layer molecules resulting in the growth of mesophase. The fusion texture and anisotropic content of mesophase pitch were significantly improved by replacing the nucleophilic reagent of the AlCl3-catalyzed system. This work provides feasible ideas for the preparation of high-performance coal tar based mesophase pitch.