Structural evolution and associated properties on conversion from Si-C-O-Al ceramic fibers to Si-C-Al fibers by sintering

Abstract

Ceramic fibers with the Si-C-O-Al composition were prepared by melt-spinning of polyaluminocarbosilane (PACS), initial curing in air and then thermal curing, before finally being pyrolyzed at 1300 °C. The ceramic fibers so-obtained were sintered at 1800 °C in argon to produce Si-C-Al ceramic fibers as a super high temperature-resistant reinforcement. When the Si-C-O-Al fibers were sintered to the Si-C-Al ceramic fibers, the structural evolution and the associated properties were studied in comparison to PCS-derived Si-C-O ceramic fibers with respect to tensile strength, creep resistance, electrical resistivity, morphology, and crystalline grain size using 29Si MAS NMR, 13C MAS NMR, AES, XRD and SEM. The Si-C-O-Al ceramic fibers had low creep resistance because they contained high levels of silicon oxycarbide, poorly organized SiC crystalline grains at the nanometer level and high levels of free carbon. The electrical resistivity of the Si-C-O-Al ceramic fibers was high due to the high level of silicon oxycarbide. However, the Si-C-Al ceramic fibers were strongly resistant to creep due to a silicon oxycarbide free structure, a well-organized and crystallized SiC content and a lower content of free carbon. The absence of silicon oxycarbide in the Si-C-Al ceramic fibers is responsible for their low electrical resistivity and high tensile strength retention at high temperature.