The Effect of Oxygen Content on Pyrolysis-Suppression of Si-Ti-C-O Fibers Coated with Surface Oxide Layers

Abstract

The pyrolysis of two types of amorphous Si-Ti-C-O fibers (Tyranno T-1 (18%O) and T-2 (13%O) coated with oxide layers of various thicknesses was investigated in an argon stream at 1673K. The oxide layers thicknesses of 0.12, 0.21, 0.42 and 0.65μm were formed on the surface of the fibers by the heat treatment in an oxygen stream at 1673K. The fibers with oxide layers of various thicknesses were heated rapidly at 1673K and kept at this temperature in an argon stream continuously monitoring the weight change with a thermoba-lance. After cooling the crystal structure and morphology of the fibers were examined with X-ray diffraction and SEM observation, respectively. The pyrolysis of all T-2 fibers with oxide layers of the above thicknesses was suppressed significantly. On the other hand, the T-1 fiber with an oxide layer 0.12μm thick pyrolyzed completely, and growth and coalescence of β-SiC crystal were observed. The pyrolysis of the T-1 fiber with oxide layers of 0.21, 0.42 and 0.65μm thick was suppressed significantly, and this pyrolytic behavior was similar to that of the T-2 fiber. The oxide layer of fibers was removed by chemical etching treatment, then the microstructure of the etched fibers was observed with TEM and their tensile strength was measured at room temperature. As the thickness of oxide layer decreased, crystallization of β-SiC in the fiber was inhibited and the tensile strength of the fiber increased. At the same thickness of oxide layer, the tensile strength of the T-2 fiber was larger than that of the T-1 fiber.