| Summary: | 博士 === 大同大學 === 材料工程學系(所) === 100 === Carbon nanotubes(CNTs) and carbon nanofibers(CNFs) have drawn a lot of research interest because of their superior mechanical properties. In this study, addition of CNTs or CNFs into phenolic resin to fabricate CNTs- or CNFs- reinforced carbon fabric/phenolic resin composites or their corresponding carbon/carbon composites was investigated. CNTs- or CNFs- reinforced carbon fabric/phenolic resin composites were fabricated using vacuum bag hot pressing technique. The as-cured composites were then carbonized and graphitized in inert atmosphere to convert into carbon/carbon composites. In addition to the three-phase composites, CNTs- or CNFs- reinforced two-phase composites, including phenolic resin matrix and carbon matrix composites, were also investigated. The mechanical properties and fracture behavior were studied using three-point bending test for all specimens, and the influence of different loadings of nano-reinforcements was also discussed. Flexural strength and modulus of carbon fabric/phenolic resin composites were found to increase by 25.8 % and 35.6 %, respectively, for 0.3 wt% CNT (10-20 nm) addition, and also increase by 40.3 % and 29.8 % for CNF addition with the same amount. The enhanced flexural properties were due to the increased interlaminar shear strength resulted from the CNT or CNF addition. The flexural strength of carbon fabric/carbon matrix composites after a 2000℃ heat treatment was increased by 16.7 % for a CNF addition of 0.5 wt%, presumably because that the suitable interfacial strength was formed after 2000℃ heat treatment. The formation of graphitic rods with a CNT or CNF in the center was observed in CNTs- or CNFs- reinforced carbon/carbon composites heat treated at 2000℃. The number of graphitic rods for CNT reinforced composites was more than that of CNF reinforced composites, because of structure difference between CNT and CNF. Carbon nanosheets were found to grow on the surface of interior pores in carbon matrix after 1400℃ heat treatment. The thickness of carbon nanosheets increased with increasing heat treatment temperature. For two-phase composites, an increase of 9.0 % for flexural strength was measured with a 0.5 wt% addition of CNFs. The flexural moduli were improved for both CNT- and CNF- reinforced phenolic resin composites with a 0.5 wt% loading. For the flexural strength of CNT- and CNF- reinforced two-phase carbon/carbon composites, better reinforcing results were found for CNTs reinforcement as compared to the CNFs at 1000 and 1400℃ heat-treated temperature. With the addition of surfactant, sodium dodecyl- benzene sulfonate (NaDDBS), flexural strength of CNT-reinforced carbon/carbon composites after 2000℃ and 2400℃ heat treatments was enhanced.
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