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Ethane, ethylene, acetylene, propane and neopentane have been pyrolyzed at 1173 K, and methane at 1372 K in a flow system, and the volatile pyrolysis products analyzed. Eleven aromatic hydrocarbons, containing 14 or fewer carbon atoms, accounted for 98 + % of the liquid products recovered in each case. Benzene was the main product, followed by naphthalene. No compounds with branched chains or multiple...
Pyrocarbon deposition from ethylene, acetylene and 1,3-butadiene was studied with a vertical hot-wall reactor at ambient pressure and 1000°C; initial partial pressures of the hydrocarbons and residence time were varied. Steady-state pyrocarbon deposition rates and corresponding compositions of the gas-phase were determined. Reaction models describing homogeneous gas-phase and heterogeneous pyrocarbon...
Pyrocarbon deposition from propylene and benzene was studied at ambient pressure and 1000°C using a vertical hot-wall reactor. Initial partial pressures of the hydrocarbons and residence time were varied; the influence of hydrogen in the feed gas was additionally studied. Gaseous and liquid reaction products were analyzed by on-line gas chromatography. The results are discussed in terms of homogeneous...
Pyrocarbon deposition from methane was studied at ambient pressure and a temperature of 1100°C using a vertical hot-wall reactor with a honeycomb structure as substrate. Compared to the deposition tube used in previous studies this substrate exhibits a 15-fold increase in surface area. The methane initial partial pressure was varied up to 75 kPa, and the residence time up to 1 second. The results...
Pyrocarbon deposition from methane was studied at ambient pressure and 1100°C using a vertical hot-wall deposition reactor; the methane initial partial pressure was varied up to 75 kPa and the residence time up to 1 second. The influence of hydrogen partial pressure was studied at constant methane partial pressure. Steady-state pyrocarbon deposition rates and corresponding compositions of the gas-phase...
Chemical vapor infiltration of pyrocarbon with methane as the carbon source was studied at a total pressure of 20 kPa, a temperature of 1100°C and methane partial pressures from 2.5 to 20 kPa. A cylindrically-shaped porous alumina ceramic, 20 mm in height and 16 mm in diameter, was used as the substrate. The pore entrance diameters of the porous ceramic range from 1 to 36 μm; the total porosity...
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...
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...
Gas phase analyses and kinetic studies were carried out in-situ during the CVD of pyrocarbon from a methane/carbon tetrachloride mixture at low pressure (2 kPa) and constant flow rate (50 sccm). At low temperatures (<800 o C), it is assumed that pyrocarbon is formed from chlorinated intermediate species with an apparent activation energy of 180 kJ/mol. At higher temperatures, the apparent...
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 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...
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.
Carbon-carbon composites are produced by chemical vapor deposition/chemical vapor infiltration (CVD/CVI) processes. Models of carbon-carbon composite production processes will help reduce production costs. Reliable process models must, however, include details of the gas phase kinetics in order to identify optimal conditions. We have combined detailed gas phase kinetics, surface kinetics, and a pore...
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...
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...
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...
Carbon deposition from ethene, ethine and propene as a function of pressure was studied at various temperatures and two different surface area/volume ratios. Deposition rates as a function of pressure of all hydrocarbons indicate Langmuir-Hinshelwood kinetics which suggests that the deposition process is controlled by the heterogeneous surface reactions (growth mechanism). These kinetics are favored...
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