THERMAL-BEHAVIOR OF A POLYTITANOCARBOSILANE-DERIVED FIBER WITH A LOW-OXYGEN CONTENT - THE TYRANNO LOX-E FIBER

The chemical composition, microstructure and mechanical properties of Tyranno Lox-E fibre were studied in the as-received state and after an nealing in inert atmosphere. The fibre consists of SiC nanocrystals of 2-3 nm, free carbon aggregates of 4-5 distorted aromatic layers and 1 -3 nm in length and an amorphous silicon (titanium) oxycarbide phase. Except for evolution of residual hydrogen and a slight densification, the fibre is chemically and structurally stable and retains a high str ength up to 1300 degrees C. Beyond 1300 degrees C, superficial degrada tion resulting from decomposition of the oxycarbide into SiO(g) and CO (g) induces a decrease of strength. Compared with bulk polycrystalline SiC, the fibre has a low creep resistance at high temperature, mainly because of the nanometric size of the SiC crystals but also because o f the presence at the grain boundary of the oxycarbide phase (viscous and chemically unstable) and of the poorly organized free carbon phase (chemically and structurally unstable). (C) 1998 Chapman & Hall.