Structure and oxidation of C/C composites: role of the interface

The oxidation of N ex-PAN carbon fibre preform as well as the oxidation of the related carbon/carbon (C/C) composites are compared with the oxidation of their counterparts based on M ex-PAN carbon fibres. The oxidation test i s conducted on polished specimens by thermogravimetry. In order to localise and quantify the oxidation, SEM observation was performed on the specimens before and after the test. Whatever the matrix, oxidation of the composite is controlled by the oxidation of the preform itself. The N preform oxidiz es more slowly than the M reference. The oxidation features of M-based mate rials are related to catalytic effects because of the presence of pitting a t the interface. Oxidation of N-based composites is localised on the extern al surface and at the fibre/matrix interface. In the matrix, oxidation is c ontrolled by the anisotropy of the pyrocarbon: smooth laminar pyrocarbon (C /C1) oxidising more slowly at the surface than rough laminar pyrocarbon (C/ C2), but deeper in the bulk at the fibre/matrix interface. (C) 2001 Publish ed by Elsevier Science Ltd.