Evaluation of isothermal chemical vapor infiltration with Langmuir-Hinshelwood type kinetics
- Delft Univ. of Technology (Netherlands). Dept. of Chemical of Chemical Process Technology
- Delft Univ. of Technology (Netherlands). Lab. for Applied Inorganic Chemistry
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 achieved by lowering the pressure. With strong associative and dissociative adsorption of the active species, it is realized by an increase in concentration and pressure.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 142221
- Journal Information:
- Journal of the Electrochemical Society, Vol. 141, Issue 1; Other Information: PBD: Jan 1994
- Country of Publication:
- United States
- Language:
- English
Similar Records
Catalytic site ensembles: A context to reexamine the Langmuir-Hinshelwood kinetic description
Modeling the Effects of Microwave Heating on Densification in Chemical Vapor Infiltration