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The micromechanical behavior of continuous fiber ceramic composites was studied using micro-Raman spectroscopy (MRS). Unidirectional carbon/carbon composites were probed using MRS, and it was shown that the microstrains in the composite constituents could be determined as the materials were loaded to increasing strain levels. The unidirectional C/C specimens were strained in both cantilever beam-type...
A unique process for conversion of monolithic wood structures to carbons that retain the cellular structure of the wood without the formation of cracks and other defects associated with charcoal materials is described. A variety of wood species are carbonized to produce the materials which are characterized using TGA, density, dimensional changes, acoustic velocity, SEM and mechanical testing. We...
Transient temperature and thermal stress distributions of a cylindrical rod which is locally heated eccentrically at an end surface are analyzed on the basis of thermoelastic theories. These results give a theoretical background of the fracture of graphite electrodes used in steel-making arc furnaces, which is occasionally found when electrodes are operated under high-power conditions. An experimental...
Previous studies have shown that lamellae of mesophase pitch prefer to be oriented parallel to a magnetic field. In the present work the matrix mesophase layers of the C/C composites were oriented perpendicular to the carbon fibers by a 8000 G magnetic field. This study is concerned with the internal friction of unidirectional C/C composites produced by the method of the present research. It is...
PAN-based carbon fibers were stabilized under various tensions in the presence of air at 230°C and sequentially activated at 950°C following carbonization. The prepared carbon fibers were tested for their SO 2 adsorption capacity using a thermogravimeter. The magnitude of tension during stabilization and gas environment were varied to study their effects on SO 2 adsorption capacity...
Preparation of dense carbon materials without use of any binder was attempted, effect of grinding treatment on the characteristics of raw petroleum needle coke and on the properties of the sintered carbon compacts was investigated, and the sintering mechanizm of the coke after grinding was discussed. It was found that the coke particle size and crystalline size was decreased and the specific surface...
A green mix composed of 65% pitch coke powder and 35% petroleum pitch (Ashland A 240) was shaped into cylindrical bodies, 30 mm in diameter and 30 mm in height. The bodies were treated with flowing pure oxygen at 200°C and pressures of 0.1 MPa and 1 MPa. The kinetics of oxidation were analyzed by measuring the oxygen uptake, radial temperature gradients in the body, formations of CO 2 and...
This paper describes the different procedures applied for the preparation of general purpose carbon fibers from four coal tar pitches. The four raw materials have a low softening point (of about 373 K) for this application and, hence, must be subjected to a treatment before spinning to increase this temperature. The treatments applied are the following: (i) heating in N 2 , (ii) heating...
The diverse shapes in which vapour grown carbon fibres can be produced were studied using scanning electron microscopy and laser diffraction. Fibres with a cylindrical shape were characterised by tensile testing. It is shown that the Weibull distribution function is well adapted to interpret the fibres' strength data. On the other hand, the fragmentation method cannot be used to assess the quality...
A theoretical approach has been developed to model the vibrational modes of amorphous, two-dimensional materials. The method considers that the vibrational density of states is composed primarily of states originating from embedded ring structures of medium-range order. The materials are modeled as continuous random networks comprised of a statistical distribution of symmetric, planar rings with...
The PAN (polyacrylonitrile) based carbon fiber composites were prepared from mixtures of chopped carbon fibers and phenolic resin. Two different carbon fibers were obtained by carbonization of stabilized PAN fiber precursors in nitrogen at 1073 and 1273 K, respectively. Samples of activated carbon fiber composites (ACFCs) were prepared from the carbon fiber composites by activation in carbon dioxide...
Post spinning modifications play an important role in improving the mechanical properties, density and structure of PAN fibres. Post spinning modifications affect the thermal and kinetic parameters during stabilization and alter the overall stabilization mechanism. The present paper presents a review of the different types of post spinning modifications previously attempted on PAN fibres and the...
Theoretical Young's moduli have been estimated for carbon fibers composed of single-walled fullerene nanotubules aligned in the direction of the tubule axis. In the limit of infinitely long tubules, the fibers can have a Young's modulus comparable to that of diamond. Exploiting this property of nanotubule fibers, we investigate a new carbon composite composed of layered nanotubule fibers and diamond...
Naphthalene-based mesophase ribbon fibres were studied in the present work. The fibres were surface treated in a plasma reactor and their mechanical and surface characteristics determined before and after the surface oxidation. The dispersive and non-dispersive components of the surface energy were obtained by contact angle measurements using a tensiometric method, and the surface oxygen content...
Amorphous carbon films free of hydrogen, deposited at room temperature by magnetron sputtering, were found to exhibit amorphous diamond character. The films were studied during deposition with real time and in situ spectroscopic ellipsometry (SE), from which the transparency, spectral dependence and composition were determined. Raman spectroscopy and X-ray reflectivity were also used to investigate...
Diamond-like carbon (DLC) does not have a unique composition but consists of a mixture of amorphous and crystalline phases. It is otherwise known as amorphous hydrogenated carbon. This paper reviews the preparation and properties of DLC films and their use in infrared optical, mechanical, electronic and biomedical applications.
The effect of air exposure and visible light illumination on the microhardness, plasticity and dislocation mobility in the C 60 single crystals was investigated. Microhardness values for defined structural states of the fullerene (pristine, oxygen-intercalated, photo-oxidized) are reported. It has been shown that oxygen intercalation in the fullerene lattice during air-aging in the dark results...
Carbon/carbon (C/C) composites are known for their high heat of ablation, high thermal shock resistance and enhanced vibration damping. However, due to the numerous processing steps involved, C/C composites contain a high percentage of process related defects. The geometry created by the tows, variations in stacking sequence of lamina, flow characteristics of the precursor and formation of closed...
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