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A carbon fibre felt with a fibre volume fraction of 7% was densified by chemical vapour infiltration of pyrolytic carbon from methane at about 1100 o C using an isothermal, isobaric process. Specimens of 1mm 3 size were cut out and analysed by electron spin resonance (ESR) in as-infiltrated form and after annealing at 2200 or 2900 o C. The temperature and orientation dependence...
Chemical vapor infiltration of a 2D carbon fiber preform with a 0/0/90/90 o fiber architecture and a fiber volume fraction of 22.5% was investigated as a function of methane pressure at various temperatures as well as a function of infiltration time at constant pressure. Inside-outside densification was obtained at the most attractive temperature of 1095 o C up to 29 kPa resulting...
Capillaries, 1.1 mm in diameter and 17.0 or 32.5 mm in length, were infiltrated at a temperature of 1100 o C and methane pressures from 5 to 30 kPa. Layer thickness and carbon texture were determined at cross-sections of 2, 16 and 32 mm from the open end of the capillaries using polarized light microscopy. Average deposition rates, determined from layer thickness and infiltration time, as...
The kinetics of carbon deposition from methane were studied over broad ranges of pressures, temperatures and reciprocal surface area/volume ratios. Based on these results, it was possible to distinguish between a growth and a nucleation mechanism of carbon deposition and to select conditions for the preparation of well-defined samples for texture analysis by transmission electron microscopy and selected...
The chemistry of carbon deposition from methane as a function of methane pressure was studied at a temperature of 1100 o C and surface area/volume ratios of 0.8 and 3.2 mm -1 by analysis of both gaseous and condensing, i.e. aromatic reaction products. Conversion of methane as well as the yields of the hydrocarbons formed increase with increasing pressure. The surface area/volume...
Pyrocarbon layers were deposited from methane on planar substrates (pyrolytic boron nitride) at a temperature of 1100 o C and residence times of 0.1, 0.5 and 2.5 s. The depositions were performed in a hot-wall reactor with the substrates oriented parallel to the gas flow. Transmission electron microscopy was applied to study the texture and the structure of the carbon layers on a micrometer...
A carbon fiber felt with a fiber volume fraction of 7.1% was infiltrated at temperatures of 1070 and 1095 o C and methane pressures from 5 to 30 kPa to confirm the inside-outside densification derived from model studies with capillaries 1 mm in diameter. Bulk densities and residual open porosities were determined as a function of infiltration depth at various heights of the felt. The texture...
A distinction between a growth and a nucleation mechanism is not sufficient to draw direct conclusions in relation to the texture of pyrolytic carbon. This is determined by the carbon formation mechanisms, which are analogous or at least similar to the mechanisms of aromatic growth. The latter mechanisms are reviewed in the first part of the paper with special consideration of structural chemical...
Capillaries, 1 mm in diameter and 17 mm in depth, were infiltrated at a temperature of 1100 o C and pressures of 20 kPa (pure methane) and 30 kPa (methane-hydrogen mixture (7:1)). The residence time of the gas in the deposition reactor was 0.5 s, at the lower pressure of 20 kPa, residence times of 1 and 2 s were studied additonally. The thickness of the deposited carbon layers was determined...
Chemical vapor infiltration of pyrocarbon was studied at 1100 o C and methane pressures ranging from 5 to 100kPa. A cylindrically shaped porous alumina ceramic, 20mm in height and 16mm in diameter, was used as the substrate. The pore diameters of the porous ceramic range from 1 to 36μm and the total porosity amounts to 23%. Theoretical considerations based on the Weisz modulus and the pore...
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