| Si-B-N-C ceramic fiber has been a novel structural and functional ceramic fiber with high temperature resistance, oxidation resistance, creep resistance, high strength and wave-absorbing characteristics. It can not only-be used as a continuously ceramic fiber to enhance the ceramic composite, which will effectively resolve its brittleness, but also meet the requirements for structural wave-absorbing materials in military field.As the performances of Si-B-N-C ceramic fiber are mainly depended on two factors, one is the characteristics of its precursor fiber and the other is the changes occurredon structure, morphology and element composition during thermolysis process, which is based on the mechanism on chemical changes in each thermolysis stage.Thus,the thermolysis process from PBSZ precursor fiber to Si-B-N-C ceramic fiber was studied by FTIR, NMR, EA and etc., while the performances of ceramic fiber were characterized by TEM, XPS and etc. The results are followed:1. Infusible treatment stage:After treated in ammonia for6h under280℃, the cross-linking precursor fiber was obtained with improved thermal stability and high degree cross-linking. The polycondensationbetween-NH(CH3) and N-H, and alsoamong-NH(CH3) groups were happened in this stage, as a result, a stable network structure was formed in this molecular.2. Ceramic convention with flowing nitrogen:The organic groups would be released by methane, and the structure of Si3N3hexatomic ring and SiN2B ring were formed in this stage. Furthermore, the fiber remained amorphous during the ceramic convention.3. Characteristics of Si-B-N-C ceramic fiber:The obtained Si-B-N-C ceramic fiber performed excellent high temperature resistance and oxidation resistance, meanwhile, it was amorphous, compact, and non-defect on morphology. Furthermore, a multi-layer structure was formed on its surface after oxidation treatment under high temperature, which effectively prevents Si-B-N-C ceramic from oxidation. |
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