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Measurement of Gas Transport through Fiber Preforms and Densified Composites for Chemical Vapor Infiltration
Author(s) -
Starr Thomas L.,
Hablutzel Nicole
Publication year - 1998
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1998.tb02481.x
Subject(s) - materials science , composite material , braid , chemical vapor infiltration , composite number , porosity , permeability (electromagnetism) , fiber , gaseous diffusion , membrane , chemistry , electrode , biology , genetics
Gas transport via pressure‐driven permeation or via concentration‐driven diffusion is a key step in the chemical vapor infiltration (CVI) process. This paper describes methods for the measurement of these properties for CVI preforms and partially infiltrated composites. Results are presented for Nicalon‐fiber cloth layup preforms and composites, Nextel‐fiber braid preforms and composites, and a Nicalon‐fiber three‐dimensional (3‐D) weave composite. The permeability of Nicalon cloth layup preforms is strongly dependent on the packing density over the range of 29‐40 vol% but is only weakly dependent on the orientation of the alternating cloth layers. The specimen‐to‐specimen variation is high (standard deviation of 20%), which reflects the statistical nature of the interlayer separation and alignment. This variability also affects the results for the partially densified specimens, where the permeability values for specimens of similar density can be very different. Trends in the diffusion factor results are similar to those for permeability, which reflects the fact that both transport parameters are dependent on the structure of the same pore network, although in somewhat different ways. The permeability of Nextel braid preforms is dependent on the thread count and the weight for cloths with similar construction and packing density. The gas permeability of the finer wave (6.3 tows/cm (16 tows/in.)) is approximately one‐half that of the coarser weave (3.5 tows/cm (9 tows/in.)). Results are reported for a small number of infiltrated composites with Nextel fiber reinforcement. Attempts to mount a Nicalon‐fiber 3‐D weave preform specimen have been unsuccessful. Results for a small number of composite specimens with 3‐D weave reinforcement are reported.