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A mathematical model is presented for the description of the chemical vapor deposition of SiC on continuous fibers bundles consisting of several hundreds or even several thousands of individual filaments. Based on chemical engineering kinetics, the model predicts the mean layer thickness and the layer thickness distribution on the monofilaments of the bundle. The model presupposes that the kinetics...
Carbon nitride thin films were deposited using an ArF excimer laser to ablate a target of 3,5 diamino 1,2,4 triazole (guanazole) in a reactive atmosphere of ammonia. Films were obtained at room temperature onto crystalline silicon and aluminium substrates. The dependence of the film properties on the ammonia pressure is reported. Films were characterized systematically by profilometry, Fourier Transform...
A new model for the description of adsorption kinetics in heterogeneous activated carbon is presented in this paper. The activated carbon particle is composed of the fluid phase and the adsorbed phase, the latter of which is heterogeneous. This heterogeneity is assumed to be described by a distribution in the energy of interaction between the two phases. This distribution is obtained from the information...
Real-time Raman measurement is performed to study the thermal relaxation process of lattice disorder in graphite at 388K irradiated to 3×10 18 ionsm −2 with 3keV He + . It is evident from the changes in the first order Raman spectra after termination of irradiation that the annihilation of defects is governed by a second order reaction.
Thermally stimulated desorption of phenylethanol bound by partial carbonization to a silica gel surface was studied. The different pathways of uni- and bimolecular desorption were investigated by temperature-programmed desorption processes mass spectrometry (TPD MS). A simple approach for describing the desorption process is proposed. Approximations are introduced which allow the derivation of non-isothermal...
A commercial anthracene oil was polymerized with anhydrous aluminium trichloride in the temperature range of 250-325 o C. The kinetics of the process and the conversion of anthracene oil were monitored by thermogravimetric analysis, solubility parameters and carbon yield. The reactivity of the major anthracene oil components was monitored by gas chromatography. The cokes obtained at 900 ...
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...
Emissions of nitrogen oxides during combustion pose a major environmental problem and hence there is considerable interest in reducing the NOx levels encountered during pulverised coal combustion. The chemically bound nitrogen in the fuel is known to account for up to 80% of total NOx. Whilst the homogeneous production pathways of NOx from the nitrogen present in the coal volatiles are relatively...
The kinetics of mesophase formation for three petroleum residues of different aromaticities (R1, R2 and R3) have been followed by optical microscopy (anisotropic content 'A') and solvent extraction (insolubility in heptane (HI), toluene (TI) and 1-methyl-2-pyrrolidinone (NMPI)). Kinetics of mesophase formation followed as development of HI, TI, NMPI and 'A', approximate to apparent first order kinetics...
Temperature-programmed oxidation (TPO) with evolved CO and CO 2 analysis has been used to determine the kinetics of charcoal and graphite combustion at low O 2 partial pressures (1.3–6.1 kPa). Simulations of the TPO profiles provide accurate optimized rate parameters, including oxygen and carbon reaction orders, for four assumed reaction steps. Resultant activation energies indicate...
Carbon deposition from light hydrocarbons and especially from methane is a homogeneous-heterogeneous process in which complex gas phase reactions in series are competing with complex surface reactions. Models of these deposition processes, proposed for carbon deposition from methane, are used to simulate deposition profiles in capillaries, 1 mm in diameter. The influence of the length of the reaction...
Capillaries, 1.1 mm in diameter and 17 or 32.5 mm in length, were infiltrated by carbon deposition from methane at temperatures of 1100 and 1125 o C, methane pressures ranging from 10 to 30 kPa, and various flow rates of the gas corresponding to residence times of 0.08, 0.2 and 0.5 s. The deposition gradients from the mouth to the depth of the capillaries basically increase, at least as long...
Acetylene was pyrolysed at 893 and 1019 K, at pressures between 31.5 and 109 Torr, and at residence times between 23 and 451 ms. By electron microscopy, carbon nanotubes were observed to be formed on the quartz surface. Carbon formation was monitored by laser extinction at unusually low conversions (0.1-1.5%). Formation of gaseous products was followed by gas chromatography. Boosting the radical concentration...
The present study has been undertaken aiming: (1) to provide an experimental procedure for measurement of characteristics of mesophase sphere formation from a coal tar pitch upon heating at 673-723 K in terms of the time-dependent changes in the population density and the radius distribution of the spheres and (2) to prove that the nucleation, growth and coalescence of the spheres are essential for...
In a fixed bed reactor, the rate of carbon black oxidation by NO 2 is significant for temperatures above 300 o C, leading to NO, CO and CO 2 formation. The presence of O 2 in the feed gas increases the rate of oxidation, as well as the presence of water. A cumulative effect is observed when both water and oxygen are present. An oxygen balance shows that oxygen atoms...
The chemical kinetics of carbon fiber deposition using Laser Chemical Vapor Deposition (LCVD) was studied. Using methane as the precursor at a total pressure of 78.4 kPa, the activation energy was 176 kJ/mol and the order of the reaction was 3.47. Using propylene as the primary reagent at a total pressure of 21.3 kPa, the activation energy was 286 kJ/mol and the order of the reaction was 1.90. The...
Ab initio calculations have been performed to determine the energetics of oxygen atoms adsorbed onto graphene planes and the possible reaction path extracting carbon atoms in the form of carbon monoxide. From the energetics it is confirmed that this reaction path will not significantly contribute to the gasification of well ordered carbonaceous chars. Modelling results which explore this limit are...
Carbon films are deposited on fused quartz substrates by CO 2 laser-induced chemical vapor deposition (LCVD) using a novel open-air coating system. The hydrocarbon precursor gases are methane, propane and butane. The deposition rates of the three hydrocarbon gases are determined by measuring the mass of the carbon film deposited at constant temperature, and validated by film thickness measurements...
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