Search Results (6)

Mesophase pitch is regarded as a profoundly promising candidate for the production of advanced carbon-based multifunctional materials such as carbon fibers, carbon microspheres, and carbon foams owing to its excellent intrinsic properties. Consequently, a deeper understanding of pyrolytic chemistry is indispensable for the efficient and environmentally friendly utilization of mesophase pitch. In this study, details about the structure compositions and microscopic morphologies of petroleum-driven mesophase pitch (pMP) were investigated through ultimate, FTIR, XPS, and ¹³C-NMR analyses. Furthermore, a large-scale molecular model of typical pMP with 11,835 atoms was constructed to unveil the comprehensive pyrolysis behaviors and the underlying reactions. Significantly, the evolution of specific chemical bonds and the decomposition of crucial molecular fragments were elucidated within an amalgamation of experimental TG-FTIR/MS and ReaxFF MD simulation. Accordingly, three fundamental reaction stages were artificially divided, including the low-temperature reaction, rapid thermal decomposition, and the molecular condensation reaction. During the rapid thermal decomposition stage, the cleavages of C–C and C–O bonds cooperatively contributed to the formation of C₂H₄ and H₂O gaseous products. As the temperature escalated to the molecular condensation stage, the pyrolysis process was governed by the dehydrogenation condensation, accompanied by an augmentation of C–C and H–H bonds and a diminution of C–O and C–H bonds. Additionally, the rare graphitization phenomenon was observed, suggesting a remarkable degree of structural organization in pMP. Overall, the results of ReaxFF MD simulations complement experimental observations, successfully reproducing the microstructure of pMP and atomic-scale pyrolysis behavior, thereby providing invaluable insights for the rational guidance of efficient utilization of pMP and other related carbonaceous precursors. Full article

A polarized light microscope (PLM) was utilized to examine the optical textures of mesophase pitch (MP) and MP-derived fibers, which aimed to reveal the arrangement and orientation characteristics of pitch molecules and to clarify the evolution and transformation mechanism of carbonaceous microcrystalline from pitch fibers to graphitized fibers. The results found that there were distinct optical textures in MP, where one side exhibited a transition from a flattening plane to a mountain-like undulating plane. This transition corresponded to the arrangement of pitch molecules, resembling stacked lamellar structures reminiscent of curved paper. Meanwhile, the optical textures of fibers revealed that the blue substance was wrapped around the red grain-like domains in the longitudinal section and confirmed that the red part belonged to the pyridine insoluble fraction of MP and the blue part belonged to its pyridine-soluble fraction. After graphitization, the red part was transformed into graphite sheets and the blue part was transformed into an amorphous carbon layer which was wrapped around the graphite sheets, forming a carbonaceous microcrystalline package-like bag. Therefore, this study provided a comprehensive interpretation of the structural evolution mechanism of MP and MP-derived fibers based on their macro-optical textures and micro-nanostructures. Full article

In order to achieve the high-value utilization of heavy tar for the production of enhanced-performance graphite foam carbon, the carbon mesophase was ready from the heavy component of low-temperature coal tar, and the coal tar was modified by styrene-butadiene-styrene (SBS), polyethylene (PE) and ethylene-vinyl-acetate (EVA) copolymers. The order degree of the carbonite mesophase was analyzed using a polarizing microscope test, Fourier transform infrared spectroscopy and X-ray diffraction to screen out the most suitable copolymer type and addition amount. Furthermore, the mechanism of modification by this copolymer was analyzed. The results showed that adding SBS, PE and EVA to coal tar would affect the order of carbonaceous mesophase; however, at an addition rate of 10.0 wt.%, the linear-structure SBS copolymer with a styrene/butadiene ratio (S/B) of 30/70 exhibited the optimal degree of ordering in the carbonaceous mesophase. Its foam carbon prepared by polymer modification is the only one that forms a graphitized structure, with d₀₀₂ of 0.3430 nm, and the maximum values of Lc and La are 3.54 nm and 2.22 nm, respectively. This is because, under elevated pressure and high-temperature conditions, SBS underwent chain scission, releasing a more significant number of methyl and other free radicals that interacted with the coal tar constituents. As a result, it reduced the affinity density of heavy coal tar molecules, enhanced fluidity, promoted the stacking of condensed aromatic hydrocarbons and increased the content of soluble carbonaceous mesophase, ultimately leading to a more favorable alignment of the carbonaceous mesophase. Full article

In this study, graphite, the most stable form of carbon, was examined for its hexagonal crystalline structure with specific dimensions (a_o = 2.46 Ǻ; c_o = 6.70 Ǻ). Its framework comprises parallel carbon atom planes, forming regular hexagons (side length 1.415 Ǻ) and 120° angles between adjacent atoms. Two structural variations exist: hexagonal symmetry (1-2-1-2-1-2 planes) and rhomboidal symmetry (1-2-3-1-2-3 planes). The aim of this research was to produce high-density graphite utilizing carbonaceous raw materials. Graphite-based materials often exhibit high porosity, necessitating additional treatment. In this study, we successfully obtained mesophase tar pitch (yield: 45%), a pivotal raw material, and high-density graphite. The resulting graphite underwent characterization for physical properties (apparent and real density, porosity, and compression strength), demonstrating conformity with the existing literature data. Full article

In this study, we investigated the synergistic effects of thermally conductive hybrid carbonaceous fillers of mesophase pitch-based carbon fibers (MPCFs) and reduced graphene oxides (rGOs) on the thermal conductivity of polymer matrix composites. Micro-sized MPCFs with different lengths (50 μm, 200 μm, and 6 mm) and nano-sized rGOs were used as the thermally conductive fillers used for the preparation of the heat-dissipation polymer composites. For all MPCF fillers with a different length, the thermal conductivity values of the MPCF/epoxy composites were proportional to the MPCF length and loading amount (0–50 wt%) of MPCFs. For an MPCF:rGO weight ratio of 49:1 (total loading amount of 50 wt%), the thermal conductivity values of MPCF-rGO/epoxy composites loaded with MPCFs of 50 μm, 200 μm, and 6 mm increased from 5.56 to 7.98 W/mK (approximately 44% increase), from 7.36 to 9.80 W/mK (approximately 33% increase), and from 11.53 to 12.58 W/mK (approximately 9% increase) compared to the MPCF/epoxy composites, respectively, indicating the synergistic effect on the thermal conductivity enhancement. The rGOs in the MPCF-rGO/epoxy composites acted as thermal bridges between neighboring MPCFs, resulting in the formation of effective heat transfer pathways. In contrast, the MPCF-rGO/epoxy composites with MPCF:rGO weight ratios of 48:2 and 47:3 decreased the synergistic effect more significantly compared to rGO content of 1 wt%, which is associated with the agglomeration of rGO nanoparticles. The synergistic effect was inversely proportional to the MPCF length. A theoretical approach, the modified Mori-Tanaka model, was used to estimate the thermal conductivity values of the MPCF-rGO/epoxy composites, which were in agreement with the experimentally measured values for MPCF-rGO/epoxy composites loaded with short MPCF lengths of 50 and 200 μm. Full article

The Maier-Saupe model for binary mixtures of uniaxial discotic nematogens, formulated in a previous study [1], is used to compute and characterize orientational entropy [2] and orientational specific heat. These thermodynamic quantities are used to determine mixture type (ideal or non-ideal) which arise due to their different intrinsic properties, determined by the molecular weight asymmetry ΔMw and the molecular interaction parameter β. These molecular properties are also used to characterize the critical concentration where the mixture behaves like a single component system and exhibits the minimum nematic to isotropic (NI) transition temperature (pseudo-pure mixture). A transition within the nematic phase takes place at this specific concentration. According to the Maier-Saupe model, in a single mesogen, entropy at NI transition is a universal value; in this work we quantify the mixing effect on this universal property. The results and analysis provide a new tool to characterize molecular interaction and molecular weight differences in mesogenic mixtures using standard calorimetric measurements. Full article