Chemical vapor infiltration: modelling solid matrix deposition for ceramic composites reinforced with layered woven fabrics

Chung, Gui-Yung; McCoy, Benjamin J.; Smith, J. M.; Cagliostro, D. E.

doi:10.1016/0009-2509(92)80022-5

Cited by 23 publications

(19 citation statements)

References 9 publications

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“…The model for infiltration of S i c and TiB2 is based on the same geometry as used for the staggered-hole model (Chung et al, 1992). Mass transfer of the reactant gases is considered to occur only by diffusion.…”

Section: Model Developmentmentioning

confidence: 99%

“…Deposition in the gaps in each ply stops when the radius of outer filaments is equal to r,, the plugging radius. The procedure for evaluating r, is explained previously (Chung et al, 1992). The model is developed by solving mass-balance equations for gas-phase concentrations of reactants DDS and TiCI, for the three parts of the system (holes, spaces, and gaps) combined with equations for the change with time of the dimensions of the system.…”

Section: Model Developmentmentioning

confidence: 99%

“…The model is developed by solving mass-balance equations for gas-phase concentrations of reactants DDS and TiCI, for the three parts of the system (holes, spaces, and gaps) combined with equations for the change with time of the dimensions of the system. Mass-balance equations for each component are the same as shown in the previous article (Chung et al, 1992), except that one more suffix is needed to identify the reactant species. Two sets of mass-balance equations, one set for DDS and the other for Tic],, are solved.…”

Section: Model Developmentmentioning

confidence: 99%

“…These prior models all refer to homogeneous geometry within the sample. In contrast, the models of Chung et al (1991Chung et al ( , 1992 for layered plies of woven tows (rectangular bundles of filaments) consider the detailed distribution of void spaces and surfaces within the sample. The Chung et al models were for aligned holes (Chung et al, 1991) and maximum staggering (Chung et al, 1992) of the holes through the plies.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, the models of Chung et al (1991Chung et al ( , 1992 for layered plies of woven tows (rectangular bundles of filaments) consider the detailed distribution of void spaces and surfaces within the sample. The Chung et al models were for aligned holes (Chung et al, 1991) and maximum staggering (Chung et al, 1992) of the holes through the plies. These models considered diffusion in the voids and deposition on the surfaces in the holes between tows, spaces between plies, and gaps around filaments.…”

Section: Introductionmentioning

confidence: 99%

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Chemical vapor infiltration: Dispersed and graded depositions for ceramic composites

et al. 1993

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A structured-geometry model for dispersed and graded deposits was developed for chemical vapor infiltration of multiply-woven substrates of carbon filters. An earlier model was modified to allow for two reactants in the feed. The modelpredicts gas-phase concentration profiles in the voids of substrates and deposition amounts of two reactants as a function of time and location. Results are shown for feeding reactant gases simultaneously for dispersed deposition and periodically for the study of the graded deposition for a typical substrate. The variation in relative contents of reactants in the feed with time shows how the composition of the deposit varies. Porosities and changes of dimensions with time everywhere in the substrate are also predicted. This is an advantage of the structured-geometry model us. a simplified homogeneous geometry for the substrate. Such a simplification may preclude predicting failure, such as delamination, which would require a local description of the composite structure.Sensitivity to input parameters such as temperature, pressure, and reactant feed concentration is discussed, and two substrate geometries are compared.The behavior of the system is predicted to be dominated by the times to fill gaps between filaments at the ply surfaces and the outermost space between plies. Furthermore, faster kinetics and slower reactant diffusion favor deposition of one material near the surface of a ply or the matrix and the other near the center of the ply or matrix. By manipulating feed rates of reactants, uniformity of material and overall porosity of the composites are predicted to be enhanced.

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Section: Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Chemical vapor infiltration: Dispersed and graded depositions for ceramic composites

et al. 1993

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Graded deposition by chemical vapor infiltration of woven fabrics

et al. 1995

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Chemical vapor infiltration into woven fabrics produces lightweight composites of excellent physical and chemical properties. Deposition of two substances (graded deposition) can provide better thermal stability, corrosion and stress resistance than dcposition of a single substance (Kawai, 1990). The usual fabric consists of several plies of tows woven into a single layer. Each tow is a bundle of filaments (1,000 or more). Commonly those filaments are of carbon with a radius of the order of 4 X cm. There are three void regions in a fabric: (1) holes between the tows that run from ply to ply; (2) spaces between the plies; and (3) gaps around the individual filaments in a tow. Chung et al. (1992) gives a complete description of the geometry of a 13 ply fabric. Deposition occurs by gaseous diffusion into the three void regions with simultaneous chemical reaction to produce the solid deposit.Uniform deposition (densification) and limited void space throughout the fabric are desirable for optimum mechanical properties. The recently developed discrete model has the advantage of predicting the amount of deposition as a function of position and time anywhere in thc multilaycred fabric. The total amount of deposition at any location is the sum of deposit on the filaments (that is, in the gaps), in the spaces and on the walls of the holes. Chung et al. (1993) have recently extended the model to graded deposition of Sic and TiB,, utilizing available information on the kinetics of deposition and diffusivities of thc gaseous precursors, dichloro-dimethylsilane (DDS) and TiCI, (with BCI,). This model can be used to predict deposition profiles in the direction perpendicular to the plane of the plies, that is, in terms of the number of plies. Thus, the uniformity of dcposition can be calculated as a function of the geometry of the fabric (size of holes and spaces, filament spacing and fila-

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Carbide, Nitride and Boride Materials Synthesis and Processing

Weimer¹

1997

254

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Chemical vapor infiltration: modelling solid matrix deposition for ceramic composites reinforced with layered woven fabrics

Cited by 23 publications

References 9 publications

Chemical vapor infiltration: Dispersed and graded depositions for ceramic composites

Chemical vapor infiltration: Dispersed and graded depositions for ceramic composites

Graded deposition by chemical vapor infiltration of woven fabrics

Carbide, Nitride and Boride Materials Synthesis and Processing

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