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Please use this identifier to cite or link to this item: http://hdl.handle.net/1860/271

Title: Carbothermal synthesis of coatings on SiC fibers
Authors: Chen, Linlin
Keywords: Protective coatings;Carbon fibers;Ceramic coating
Issue Date: 19-Mar-2004
Abstract: Four kinds of protective coatings FFcarbide derived carbon (CDC), boron nitride (BN), Al-O-N and BN doped Al-O-N (BAN) have been successfully synthesized on the surface of SiC fibers on the target to enhance the mechanical properties and oxidation resistance of the coated SiC fibers for the application as the reinforcements in the Ceramic Matrix Composites (CMCs) in the high temperatures. First of all, CDC coatings have been uniformly produced on Tyranno ZMI SiC fibers with good thickness control within nanometer accuracy by the chlorination in the temperature range of 550-700ºC at atmospheric pressure. Kinetics of the carbon coating growth on the fibers has been systematically studied and thus a good foundation was set up for the further coating synthesis. BN coatings have been synthesized on the surface of SiC powders, fibers and fabrics by a novel carbothermal nitridation method. Non-bridging has been achieved in the BN-coated fiber tows by the nitridation in ammonia at atmospheric pressure in a temperature below 1200ºC, which is lower compared to the traditional BN synthesis method and does not cause the degradation of the coated-fibers. BN coatings on the carbon nanotubes have also been formed and unlike the common methods, no additional dopant (such as metal catalyst) is introduced into the system during the BN coatings syntheses, thus the contamination of the final product is avoided. A novel Al-O-N coating has been explored with the most impressive point is that a more than 65% improvement in the tensile strength (up to ~5.1GPa) and a three-time increase in the Weibull modulus compared to the as-received fibers are resulted by the formation of 200nm Al-O-N coating on the SiC fibers. It exceeds the strength of all other small diameter SiC fibers reported in the literature. Furthermore, BAN coating has also been produced on the surface of SiC fibers and about 20% enhancement in mechanical strength is achieved compared to that of the original fibers. Oxidation experiments of the SiC fibers with four kinds of coatings under 1000ºC and 1200ºC in air have been carried out and better oxidation resistance of the coated fibers are presented compared to the as-received fibers. In summary, exploration of various coatings synthesis for the SiC fibers has been successfully conducted in this work. The coating material suitable for the SiC fibers should be chosen properly according to its specific application in the CFCCs and well thickness-control to meet the corresponding requirements.
URI: http://dspace.library.drexel.edu/handle/1860/271
Appears in Collections:Drexel Theses and Dissertations

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