Intrinsic hydrogen transport constants in the CFC matrix and fibres derived from isovolumetric desorption experiments

The manufacture of carbon fibre composites (CFC) requires models differenti ating the transport mechanisms in the CFC fibres and in the matrix. A non-s tationary model was developed for isovolumetric desorption experiments (IDE ) and checked with results for a well-characterised homogeneous material (N i). The apparent transport constants for three CFC (N112, NS31 and N11) fro m Societe Europeenne de Propulsion (SEP), were derived. However, the fittin g of the experimental hydrogen release using the homogeneous model is unsat isfactory, in that the experimental curve shows two overlapping time consta nts. The analysis of the hydrogen paths served to build a non-homogeneous d iffusive model that fits accurately the experimental release. The intrinsic values of the fibre and the matrix derived for the three CFC studied are c omparable. Values for the hydrogen diffusivity in the matrix are 6-7 orders of magnitude higher than in the fibres. The determinant role of fibres on the hydrogen solubility in the studied CFC is shown. (C) 1999 Elsevier Scie nce B.V. All rights reserved.