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

摘要

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 deg C. The ceramic fibers so-obtained were sintered at 1800 deg 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 ceramicc fibers, the structural evolution and the associated properties were studied in comparison to PSC-derived Si-C-O ceramic fibers with respet to tensile strength, creep resistance, electrical resitivity, morphology, and crystalline grain size using, ~28Si MAS NMR, ~13C MAS NMR, AEX, 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 resisitivity of the Si-C-O-Al ceramic fibers was high due to the high level of silicon oxycarbide free structure, a well-organized and crystallined 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 resitivity and high tensile strength retention at high temperature.