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Carbon fibers were grown on alumina substrates by vapor phase decomposition of benzene in the presence of hydrogen in a tubular reactor. The effect of lengthening duration and temperature on the average fiber length was studied at two different benzene concentrations (13.2 and 18.6 mol%). In the temperature range (1283-1353 K) investigated, the maximum average fiber length increased with an increase...
Carbonaceous grains for binderless moulding were prepared by control of the preheat-treatment of the naphthalene-derived mesophase pitch. The carbonized and graphitized discs were evaluated in terms of physical properties and textures. Carbon disc of strikingly high bulk density, 2.04 g/cm 3 , high compressive strength, 1.94 tf/cm 2 , and large shrinkage ratio, 15.9%, was obtained...
Stabilization is an important step for producing pitch-based carbon fiber. In this paper, gas formation rates and weight change during oxidative stabilization, which is most commonly employed as the stabilization method, were measured continuously for three pitch-based yarns, using a mass spectrometer and a thermogravimetric analyzer, respectively. From these measurements, change in the amount of...
Upon exposure to room-temperature fluorine, intercalated carbon fibers (containing either bromine alone or iodine and bromine together) become heavier and less stable. For Amoco P-100 graphitized carbon fibers, which were intercalated with 18 wt% bromine, 1 hour of fluorine exposure resulted in a large weight increase but caused only a small decrease in thermal stability. An additional 89 hours...
An analysis of hydrogen in Vapour-grown carbon fibres by secondary ions mass spectrometry (SIMS) technique allows recognition of the main role of hydrogen in the graphitizing process and mechanical properties. It is known that VGCF have a duplex structure, consisting on an inner core and an outer coating. From our SIMS analysis, it is proven that the hydrogen content of the core is greater than...
The reactivity of fine-weave pierced 3D carbon-carbon composites in air at temperatures up to 3000°C was studied. The corrosion morphology and microstructure of oxidized samples were investigated by XPS, SEM, and XRD techniques, and the non-equilibrium nature of the oxidation process was pointed out. A thermochemical ablation model of C-C composites controlled by gas phase diffusion and reaction...
Carbon-carbon (C-C) composites are considered an emerging technology critical to several military and commercial applications. However, C-C composites' inherent susceptibility to air oxidation at temperatures above 500°C greatly limits their use to primarily price-insensitive military and space applications. Over the past several decades huge R&D efforts were conducted to develop an effective...
Unidirectional carbon fiber reinforced carbon composites (C-C composites) with different matrix textures were prepared from six matrix precursors. Two composites with an optically isotropic matrix showed tensile strength and modulus values that increased on heat treatment of the samples at a high temperature. Composites with an anisotropic matrix, having preferred orientation parallel to fiber surface,...
Boron nitride (BN), derived from borazine oligomers, was examined as a means of enhancing the oxidation resistance of carbon fiber-carbon matrix composites (C-C). To clarify the widely held impression that BN suffers from a hydrolytic instability, a systematic investigation of the accelerated hydrolysis of BN at 700°C was carried out. These results showed that the stability to moisture was directly...
Carbon-carbon composites have been coated with silica and zircon prepared by sol-gel technique and with methylsilsesquioxane, a preceramic polymer. The effect of processing parameters for preparation of the sols and coating procedure on coating morphology has been studied. Oxidation behaviour of uncoated and coated carbon-carbon composites has been studied. Coatings with continuous and uniform structure,...
C-SiC binary matrix composites, made from a porous C-C preform infiltrated with SiC, are mechanically characterized under tensile, compressive, flexural, and shear loading. The results of these tests show that the materials exhibit non-brittle fracture and have excellent strength. The oxidation behavior of the materials has been studied. Measured mass loss data from the C-SiC binary matrix composites...
The formation and oxidation resistance of surface oxide layers formed on carbon-B 4 C-SiC composites with two different B 4 C-SiC ratios were investigated at elevated temperatures in dry and moist atmospheres. From SEM observation, X-ray diffraction analysis, EPMA, and ESCA measurements of the samples before and after oxidation, it was found that the oxidation resistance depended...
Carbon (graphite) fibers have been coated with amorphous alumina-silica (Al 2 O 3 ) x (SiO 2 ) y thin films by metal organic chemical vapor deposition (MOCVD) using [Al(OSiEt 3 ) 3 ] 2 as a single-source precursor. The adhesion of the alumina-silica films to the carbon fibers and/or the films' flexibility is a function of the residual...
After the formation of a concentration gradient of SiC within a carbon-carbon composite, a zircon (ZrSiO 4 ) thin film was coated on the surface. Oxidation-resistance tests of the treated C-C composites were then carried out. A concentration gradient of SiC was produced by heating the C-C composite in silicon powder at 1450°C for 3 hours. The concentration of SiC along the direction of...
Two methods have been employed to prepare boron-doped carbon materials. One method utilized ion implantation to dope the surface region of vitreous carbon with up to 12 atomic % boron. The other method used CVD to prepare ∼ 1-2 micron thick carbon coatings with various boron contents (0 to 15 atomic %). The quantitative compositional analysis of these materials was performed with the electron microprobe...
Oxidation protection systems or carbon-carbon composites have met limited success, particularly between 900 and 1500°C where internal glass inhibitors are relied upon to protect the composite. This study investigated potential halogenated glass protection systems for the protection of structural carbon-carbon composites. A series of fluoride and fluoroborate glass compositions were selected based...
Three commercial carbons (an activated cloth and two rayon-derived carbon cloths) were used as substrates for the preparation of low- and high-temperature carbon-carbon (C-C) composites by the liquid-phase impregnation/carbonization (LPIC) technique. A petroleum pitch was used as the matrix precursor. The carbon cloths were subjected to thermal treatment (in inert atmosphere) or activation (in CO...
The nucleation and growth of silica deposited by CVD on various carbon substrates was studied with the goal of enhancing the effectiveness of oxidation protection coatings for carbon-carbon composites. In this study, the surfaces of graphitized carbon blacks and carbon fibers were characterized with scanning probe microscopy, chemical and physical adsorption, and flow microcalorimetry techniques...
The oxidation behavior of reactive carbon fibers, such as ex-Pan T300, is studied in oxidizing environments by means of TGA and tensile strength measurements. Different carbide coatings are investigated with a view to fiber protection during an air exposition at high temperature. Thin, continuous, and uniform films of TiC, SiC, B 4 C, or B 4 C/SiC multilayers are obtained by an RCVD...
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