Microstructural analysis of the failure mechanisms of carbon nanofibers and inorganic fulerene-type tungsten disulfide
Cook, Jamie E.
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This thesis summarizes the failure mechanisms found in carbon nanofibers (CNF) and inorganic fullerene-type tungsten disulfide (IF-WS2) nanoparticles treated with diverse pressure loading methods. CNF were generated using nickel as catalyst and ethylene as carbon source, while IF-WS2 was acquired commercially. Approaches utilized to induce failure include the use of a gas gun, ultrasonic treatment and impact with military rounds. Samples were characterized using electron microscopy, powder x-ray diffraction, energy dispersive x-ray spectroscopy, and BET surface area analysis. CNF produced from nickel showed agglomeration from all testing methods but no evidence of fiber breakage or delamination. IF-WS2 failure modes observed were related, primarily, to the transition between 3D and 2D polymorphs, with subsequent agglomeration of the plate-like 2D structure, producing larger particle sizes. The secondary mechanism identified was delamination of IF-WS2, which, in contrast to the former, gave origin to smaller particulates. The failure modes identified herein were used to re-design the CNF material and test it using the gas gun. CNF with larger diameter distributions were grown from palladium catalyst, producing ultralow density carbon foam. This architecture presented viscoelastic properties that recovered the original shape after unloading, not showing evidence of failure under the gas gun test regime employed.
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