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Chemical vapour infiltration is simulated by deposition of pyrolytic carbon on planar boron nitride substrates and carbon fibers in a hot-wall tubular reactor at about 1100 o C for varied pressure and flow-velocity of methane. The degree of orientation of the deposited graphite-like domains can be monitored via orientation and temperature dependence of the electron spin resonance parameters...
The structural properties of carbon/carbon-composites fabricated by chemical vapor infiltration (CVI) were studied by polarized light microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) on a micrometer and nanometer scale. The types of carbon bonds were estimated by electron-energy-loss spectroscopy (EELS). Using a methane/hydrogen gas mixture at a temperature...
Carbon depositions from ethene, ethine, propene, butadiene and benzene were studied in a flow reactor at a temperature of 1000 o C, constant hydrocarbon partial pressures and increasing hydrogen partial pressures. Analogous studies with methane were performed at 1100 o C. Carbon deposition rates and corresponding compositions of the gas phase were determined. In the case of the C ...
Pyrolytic carbon films were deposited on boron nitride substrates during plug-flow of a methane/argon gas mixture through a hot-wall tubular reactor at 100 kPa and 1100 o C. Of particular interest is the time resolved development of chemical reactions within the free reactor volume, which is projected to the formed structures along the reactor axis. Spatially resolved electron spin resonance...
Boron-substituted polyaromatic mesophases were synthesized by co-pyrolysis of a coal tar pitch with pyridine–borane using boron contents of 0.5 and 1%. After removal of residual isotropic material by extraction with tetrahydrofuran, the mesophases were milled to a particle size of d≤10 μm and compacted to bodies. These bodies were sintered at 1300°C and subsequently high-temperature treated at 1600,...
The chemical vapor deposition of carbon from methane was investigated at an ambient pressure of about 100 kPa, a methane partial pressure of 10 kPa and temperatures ranging from 1050–1125°C. Carbon deposition rates and compositions of the gas phase as a function of residence time have been determined using a substrate with a surface area/reactor volume ratio of 40 cm −1 . Increasing temperatures...
Carbon deposition from a methane–hydrogen mixture (pCH 4 =17.5 kPa, pH 2 =2.5 kPa) was studied at an ambient pressure of about 100 kPa and a temperature of 1100°C, using deposition arrangements with surface area/reactor volume ratios, [A S /V R ], of 10, 20, 40 and 80 cm −1 . Steady-state deposition rates and corresponding compositions of the gas phase as a...
Chemical vapor infiltration of pyrolytic carbon was studied at a temperature of 1100°C and total pressures of 20, 30 and 50 kPa using methane/hydrogen mixtures with molar ratios of 7:1, 6:1, 5:1, and 4:1. Cylindrically shaped porous alumina ceramics, 20 mm in height and 16 mm in diameter, were used as the substrate. The pore diameters range from 1 to 36 μm; the total porosity amounts to 23%. The infiltration...
Chemical vapour infiltration of pyrocarbon is analysed with respect to (i) the nature of the hydrocarbon (carbon source), (ii) the pyrolysis chemistry and kinetics of homogeneous gas phase reactions, (iii) the kinetics of heterogeneous pyrocarbon deposition reactions, (iv) pore diffusion in the Fick and Knudsen regime, (v) total pressure, (vi) initial partial pressure of the hydrocarbon, (vii) inert...
This paper is concerned with the role of carbon fibre coatings in the production of carbon fibre-reinforced carbons from high tenacity (HT) carbon fibres and phenolic resin as a matrix precursor. In order to reduce the adhesion of the matrix to the carbon fibre surface, various HT carbon fibres were coated with polyldimethylsiloxane) and poly(methylphenylsiloxane) using solutions of these materials...
Commercially surface-treated HT carbon fibres were coated with phenolic resin in order to reduce the adhesion of the phenolic resin matrix to the fibre surface. Unidirectional (UD) composites were fabricated using uncoated and coated fibres and a standard phenolic resin as matrix: the fibre volume fraction of the green composites was 60 vol%. The composites were carbonized at 1000 C and treated at...
Iron benzoate and naphthoate were studied as catalyst precursors of an iron-catalyzed pyrolysis of a coal-tar pitch as a technical hydrocarbon mixture and of anthracene as an aromatic model compound. The results are compared with those obtained with ferrocene, which has been studied previously. Both iron compounds are decomposed by formation of iron clusters at a much lower temperature than ferrocene...
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