Evaluation of Isothermal Chemical Vapor Infiltration with Langmuir‐Hinshelwood Type Kinetics
| Autor: | R. Moene, Michiel Makkee, J. Schoonman, J.P. Dekker, J.A. Moulijn |
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| Rok vydání: | 1994 |
| Předmět: |
Reactions on surfaces
Renewable Energy Sustainability and the Environment Chemistry Kinetics Thermodynamics Condensed Matter Physics Thiele modulus Isothermal process Surfaces Coatings and Films Electronic Optical and Magnetic Materials Adsorption Chemical vapor infiltration Materials Chemistry Electrochemistry Physical chemistry Deposition (phase transition) Porosity |
| Zdroj: | Journal of The Electrochemical Society. 141:282-290 |
| ISSN: | 1945-7111 0013-4651 |
| DOI: | 10.1149/1.2054700 |
| Popis: | A model has been developed for the mathematical description of isothermal chemical vapor infiltration (ICVI) processes. Three types of adsorption of the reactive species are incorporated into the kinetic equations: weak associative adsorption, strong associative adsorption, and dissociative adsorption. The kinetic models are based on Langmuir-Hinshelwood equations. Weak associative adsorption of the reactive species gives rise to an exponentially shaped final deposition profile, whereas strong associative and dissociative adsorption result in a sigmoidally shaped deposition profile in the pore. This profile originates from a shift in deposition mechanism from a layered growth (weak associative adsorption) to a moving front growth (strong associative and dissociative adsorption). For weakly adsorbing reactive species, the residual porosity of a preform can be decreased by lowering the process pressure. With strong associative or dissociative adsorption, the reverse effect can be found at the investigated process conditions. This effect is caused by the change in reaction-rate dependence of the concentration inside the pore. Application of the concept of a generalized Thiele modulus shows that for all investigated kinetic models the residual porosity of densified preforms is smaller than 1% when the Thiele modulus is kept below 0.02. For weak associative adsorption, this region can be achievedmore » by lowering the pressure. With strong associative and dissociative adsorption of the active species, it is realized by an increase in concentration and pressure.« less |
| Databáze: | OpenAIRE |
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