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

The manufacture of carbon fibre composites (CFC) requires models differentiating the transport mechanisms in the CFC fibres and in the matrix. A non-stationary model was developed for isovolumetric desorption experiments (IDE) and checked with results for a well-characterised homogeneous material (Ni). The apparent transport constants for three CFC (N112, NS31 aud N11) from Societe Europeenne de Propulsion (SEP), were derived. However, the fitting of the experimental hydrogen release using the homogeneous model is unsatisfactory, in that the experimental curve shows two overlapping time constants. The analysis of the hydrogen paths served to build a non-homogeneous diffusive model that fits accurately the experimental release. The intrinsic values of the fibre and the matrix derived for the three CFC studied are comparable. 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. (orig.)