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Mesophase pitch-based carbon fibers are ideally suited for applications where the rapid dissipation of heat is important (structural composites, printed circuit substrates, etc.). However, control of texture is essential in order to optimize fiber properties, especially thermal conductivity. Because ribbon-shaped mesophase pitch-based carbon fibers possess a highly linear texture, these fibers are...
The optical texture of cokes obtained at 500°C (60 minutes soak time) from a range of pitches, coal-tar and petroleum pitches and from the extrography fractions of three of the pitches, was related to the chemical composition of the parent material. Small differences observed in the amount of polyaromatic hydrocarbons and basic nitrogen polyaromatic compounds present in vacuum-distilled and thermally...
Naphthalene-derived mesophase pitch (NMP) was chemically modified with p-benzoquinone (BQ) at relatively low temperature, then carbonized and graphitized. An activated Diels-Alder reaction between NMP molecules and BQ occurred at 115°C followed by a dehydration reaction at 158°C. The modified NMP changed its texture from anisotropic to isotropic with increasing BQ concentration. The carbon yield...
Naphthalene based synthetic isotropic pitch was found to give spinnable precursors which carried 10-100 μm anisotropic spheres of 45 and 50 vol% in the isotropic matrix, when the pitch was heat-treated at 375 and 380°C for 20 and 23 hours, respectively. The spun fiber was stabilized and carbonized into a carbon fiber, which showed anisotropic belts running along the fiber axis, suggesting that both...
Delayed coking is a thermal process to convert petroleum residues to a solid coke material. Processes occurring in a delayed coker are complicated and attempts have been made, at the laboratory level, to simulate industrial delayed coking. Although the latter studies are useful, it is impossible to scale-down to the laboratory level. Industrial delayed coking is a turbulent process and such movements...
A series of semi-cokes, containing from virtually 0 to 100% mesophase, were produced from the THF-soluble fraction of a soft coal tar pitch. The mesophase contents were estimated by high temperature in situ 1 H NMR and optical microscopy with extremely close agreement being obtained between the two techniques. Quantitative solid state 13 C NMR measurements using the single pulse...
The objective of this study is to search for a method, involving control over the pressures within a pyrolyzing system, to produce non-coalesced mesophase spheres of required sizes. Semicokes were studied from pyrolyses of a petroleum residue, R1, carried out in a tube reactor, 440–445°C, 1.0 MPa pressure, and soak times 1.0–2.0 h. In some pyrolyses, pressures were reduced from 1.0 to 0.1 MPa and...
The literature of the kinetics and mechanisms of formation of anisotropic semicokes from petroleum residues is reviewed. The concepts of mesophase, of self-assembly of mesogens, and of liquid-crystals are described. Values are reported of reaction order, rate constants and activation energies (98–345 kJmol −1 ). Limitations of analytical methods are critically discussed. Stages in the transformation...
Mesocarbon Microbeads (MCMB) carrying five different types of hexagon alignment, parallel, deformed onion-like, longitude-like, longitude-like with disclination, and Brooks/Taylor (latitude-like) were prepared and examined in their performances as an anode of a Li-ion battery. The first two beads were prepared from naphthalene isotropic pitch without any inert materials, and the next two were from...
The microstructure and the deposition rate of pyrocarbon deposited from propane have both been studied as a function of gas phase residence time (t r ) and reactor temperature (T) in the vicinity of 1000 o C and at a constant pressure of 2 kPa. Transitions between two different types of laminar microstructures, smooth laminar (SL) and rough laminar (RL), have been observed. Simultaneously,...
The influence of defects on the phase-boundary movement in the stage transformation from random stage (dilute stage 1) to stage 4 of lithium-graphite intercalation compounds was investigated using highly oriented pyrolytic graphite (HOPG). Potential-step chronoamperometry and in situ optical microscopy coupled with micro Raman spectroscopy were used to clarify macroscopic and microscopic influence...
During carbonization anisotropic domains, i.e. local molecular orientation (LMO), occurs. Their final size coincides with resolidification, fixing up the further properties of carbons. Five samples [pitch (Ashland 240), heavy petroleum products and kerogen increasingly cross-linked by oxygen] were studied by optical microscopy after heat treatment at increasing heating rates (0.5°Cmin −1 and...
A low QI, impregnation coal-tar pitch was used to study the efficiency and mechanism of densification of a carbonised 2-D C/C preform by a low-pressure impregnation/carbonisation processing route. Changes occurring in the porous structure of the preform as densification proceeded were followed by weight and density measurements as well as by analysis of optical microscope images of polished sections...
The tensile strength of carbon/carbon composites (C/Cs) was examined as a function of the density in the range above ρ=1.6 g/cm 3 . Three processing routes of preformed yarn, resin char, and HIP processes were adopted to densify the C/C composites. The density was increased to 1.95 g/cm 3 through these routes. The interfacial strength between the fiber and matrix was significantly...
Carbon/carbon composite films were prepared by using polycarbodiimide (PCDI) as a starting matrix and the inhomogeneous microtexture of the matrix developed by the internal stress arising during carbonization was investigated. The internal stress was produced due to constraint of the volume reduction of the matrix by the filler and, as a result, anisotropic regions were developed in the matrix around...
The kinetics of mesophase formation for three petroleum residues of different aromaticities (R1, R2 and R3) have been followed by optical microscopy (anisotropic content 'A') and solvent extraction (insolubility in heptane (HI), toluene (TI) and 1-methyl-2-pyrrolidinone (NMPI)). Kinetics of mesophase formation followed as development of HI, TI, NMPI and 'A', approximate to apparent first order kinetics...
Development of inhomogeneous microtexture in a glass-like carbon film from polycarbodiimide (PCDI) has been investigated in relation to the internal stress arising during carbonization. The PCDI films were pre-oxidized through a low-temperature heat-treatment in air and carbonized at temperatures up to 1300 o C. Under severe pre-oxidation conditions, the PCDI near the film surface was oxidized...
The effect of silicon on the pyrolysis of a petroleum residue has been studied. In this work, controlled co-pyrolysis of an aromatic petroleum residue and triphenylsilane, TPS, as a silicon source, under 1 MPa nitrogen atmosphere and at 440 o C is performed. Soaking time was varied between 1.5 and 6 h, and the silicon concentration added to the petroleum residue ranged from 0 to 2 wt%. Silicon...
A review of literature on various kinds of pyrocarbons is given. Their characterization by optical microscopy, TEM imaging (transmission electron microscopy) and diffraction techniques is discussed. Various models are also described critically, as well as the possible mechanisms of deposition.
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