期刊199Continuous SiC-based model monofilaments with a low free carbon content- Part I- From the pyrolysis of a polycarbosilane precursor under an atmosphere of hydrogen.pdfVIP

Continuous SiC-based model monofilaments with a low free carbon content Part I: From the pyrolysis of a polycarbosilane precursor under an atmosphere of hydrogen A. TAZI HEMIDA, R. PAILLER, R. NASLAIN Laboratoire des Composites Thermostructuraux UMR 47, CNRS-SEP-UB1, Domaine Universitaire 3, Alle e de La Boe tie, 33600 Pessac, France Pyrolysis of a Yajima-type polycarbosilane (PCS) has been performed under an atmosphere of hydrogen on both bulk samples and model monofilaments up to 1000 C, in order to reduce the free carbon content of the resulting ceramics. The organic/inorganic transition occurs within the 400800 C temperature range, with mainly an evolution of CH . At 1000 C, it yields an hydrogenated amorphous ceramic with a C/Si atomic ratio and a free carbon content significantly lower than for its counterpart obtained under inert atmosphere (namely, 1.18 and 9 at % versus 1.72 and 27 at %). Hydrogen is thought to favour the release of the pendent methyl groups of the PCS via demethanation radical reactions. Continuous model filaments were produced via the melt spinning of the PCS, electron beam curing, pyrolysis under hydrogen up to 1000 C, and a final heat treatment under argon up to 1600 C. The ceramic fibres exhibit a C/Si atomic ratio of 1.10, a free carbon content of 8 at %, a Young’s modulus of 260300 GPa and a tensile failure stress of 2100 MPa. Their thermal stability is limited to 1400 C due to some oxygen contamination during the process. 1. Introduction