Abstract:The evolvement of oxygen from polyaluminocarbosilane(PACS) to Si-Al-C-(O) fibers and its effect on properties were investigated by element analysis, solid-state 27Al nuclear magnetic resonance(NMR), Fourier transform infrared spectroscopy(FT-IR), thermo-gravimetric analyses(TGA), scanning electron microscope(SEM) and X-ray diffraction(XRD). Element analysis of PACS precursor polymer gives an empirical formula of SiC2.1H11.1O0.12Al0.024. 27Al NMR spectra mass gain shows that the oxygen of cured PACS fibers comes from aluminum aletylacetanate (Al(AcAc)3) and the curing process. Oxygen content can be regarded as a constant mass during the pyrolysis process. During the sintering process of Si-Al-C-O fibers into Si-Al-C fibers, oxygen and carbon decreases with the release of a small amount of CO and/or SiO. Oxygen has a positive effect on the ceramic yield while has a negative effect on the crystallization of Si-Al-C-O fibers. It has great influence on mechanical properties of Si-Al-C-O and excellent tensile strength is usually obtained at the oxygen content of 8%-10%. The Si-Al-C-(O) fibers have excellent thermal stability and creep resistance.

Key words: polyaluminocarbosilane; PACS; SiC fibers; Si-Al-C-(O) fibers; evolutions; properties