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PHYS 8990 Topic

Carbon nanotube-reinforced ceramic composites

Zhengwei Pan

Owing to their exceptional stiffness and strength, carbon nanotubes (CNTs) have long been considered to be an ideal reinforcement for light-weight, high-strength, and high-temperature-resistant ceramic matrix composites (CMCs). However, the research and development in CNT-reinforced CMCs have been greatly hindered due to the challenges related to manufacturing. Currently, the fabrication of CNT-CMCs mainly follows a disperse-mix-sintering strategy. The manufacturing problems thus encountered include, but are not limited to: (1) poor dispersion of nanotubes in the matrix: the nanotubes tend to form aggregates, which initiate cracks in composites, rather than reinforcing them; (2) damages of nanotubes during processing: surface modification, mechanical mixing and high-temperature sintering all often damage nanotube structures, comprising their properties; and (3) poor interfacial bonding between the nanotubes and the surrounding matrix: the nanotubes usually localize at the grain boundaries of the matrix material as ropes or bundles, which cannot create effective interfacial load transfer between the two.

In order to overcome these problems, we proposed to fabricate CNT-CMCs using chemical vapor infiltration (CVI), a technique that is being widely used to fabricate commercial carbon-fiber CMCs (C/SiC). So far, we have successfully fabricated several technologically important CNT-reinforced ceramic composites, including CNT/SiC, CNT/B, CNT/B4C, and CNT/C. Remarkably, the synthesis of CNT/C composite showed that the new carbon layer (i.e., grapheme) can be homo-epitaxially formed on the existing CNT surface, which may lead to the understanding of how the carbon nanotubes are formed, a critical question that has not be answered yet.

In this project, the students will have an opportunity to grow CNTs, to fabricate CNT-composites, to characterize CNT and CNT-composites using scanning electron microscope and transmission electron microscope, to measure the mechanical properties of the CNT-composites using an atomic force microscope, and to investigate the formation mechanisms of the composites. 

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