Carbon fibers were uniformly coated with carbon nanotubes by catalytic decomposition of acetylene using thermal chemical vapor deposition technique at 700 °C. The nanotube coated fibers were employed for the fabrication of unidirectional multi-scale composites with epoxy matrix. As the carbon nanotubes were directly grown on carbon fibers they remain firmly attached with the fiber substrate therefore they are anticipated to modify the interfacial characteristics of the composites and in turn considerably alter the mechanical behavior. Moreover, the direct growth of carbon nanotubes on fiber facilitates uniform distribution of carbon nanotubes in the polymer matrix. The composite specimens made of carbon nanotubes coated fibers showed a significant enhancement of 48% and 85% in the tensile and flexure strength respectively as compared to composites made of carbon fibers undergone similar thermal cycle but without carbon nanotubes growth. The morphology of carbon nanotubes coating on carbon fibers was examined at nano-level using high resolution TEM which showed growth of carbon nanotubes with different morphology and diameter ranging from 5-50 nm. Specimens failed in tensile were further investigated for fractographic analysis using SEM which showed improved fiber/matrix interfacial bonding indicated by less fiber pull out.
Keywords: Carbon fibers, carbon nanotubes, composites, surface morphology, electron microscopy, mechanical properties, Raman spectra, fractograpgy
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