Reactivity and molecular structure of silicon carbide fibres derived from polycarbosilanes

The thermal behaviour of Nicalon NML 202 fibres was carried out in the absence and in the presence of oxygen. The gaseous species produced and the oxygen balance were determined with a mass spectrometer. Three samples were studied: the desized initial fibre, this fibre after treatment with hydrofluoric acid, and a polycrystalline silicon carbide powder. It was shown that (i) the initial fibre has still an organic character, (ii) it contains a silica-rich layer, and (iii) beneath the silica-rich sheath the bulk of the fibre contains free carbon embedded in a silicon carbide-based network.