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Fracture toughness of void-site-filled skutteruditesEilertsen, James S. 07 December 2011 (has links)
Thermoelectric materials are playing an increasingly significant role in the global effort to develop sustainable energy technologies. Consequently, the demand for materials with greater thermoelectric efficiency has stimulated the development of state-of-the-art interstitially doped skutterudite-based materials. However, since intermetallics are often embrittled by interstitial substitution, optimal skutterudite-based device design, manufacture, and operation require thorough assessment of the fracture toughness of interstitially doped skutterudites. This research determines whether the fracture toughness of skutterudites is sacrificed upon interstitial doping. Both pure and interstitially doped cobalt antimonide skutterudites were synthesized via a solid-state technique in a reducing atmosphere with antimony vapor. Their crystal structures were analyzed by X-ray diffraction, and then sintered by hot uniaxial pressing into dense pellets. The electronic properties of the sintered samples were characterized. Fracture toughness of the pure Co₄Sb₁₂ and interstitially doped In₀.₁Co₄Sb₁₂ samples was evaluated by the Vicker's indentation technique and by loading beam-shaped singe-edge vee-notched bend specimens (SEVNB) in 4-point flexure. The intrinsic crack-tip toughness of both materials was determined by
measuring the crack-tip opening displacements (COD's) of radial cracks introduced from Vicker's indentations. The intrinsic crack-tip toughness of both pure Co₄Sb₁₂ and interstitially doped In₀.₁Co₄Sb₁₂ were found to be similar, 0.523 and 0.494 MPa√m, respectively. The fracture toughness of both pure and interstitially doped skutterudites, derived from SEVNB specimens in 4-point flexure were also found to be statistically identical, 0.509 and 0.574 MPa√m , respectively, and are in agreement with the intrinsic crack-tip toughness values. However, the magnitude of the toughness was found to be much lower than previously reported. Moreover, fracture toughness values derived from Vickers's indentations were found to be misleading when compared to the results obtained from fracture toughness tests carried out on the micronotched (SEVNB) specimens loaded in 4-point flexure. / Graduation date: 2012
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Novel nanocomposite synthesis for high-performance thermoelectricsEilertsen, James S. 06 January 2013 (has links)
Thermoelectric materials are playing a larger role in the global effort to
develop diverse, efficient, and sustainable energy technologies: primarily through
power-generating thermoelectric modules. The principal components of
thermoelectric modules are solid-state thermoelectric materials – typically heavily
doped semiconductors – that convert heat directly into electricity. However, this
conversion efficiency is too low to supplant traditional energy technologies – severely
limiting the distribution of clean and sustainable thermoelectric energy technologies.
Efforts to enhance thermoelectric efficiency, which have been underway for decades,
have been slow to realize appreciable gains in thermoelectric efficiency. However, a
key advance in improving efficiency – the New Paradigm in thermoelectric material
research – has been the development of thermoelectric nanocomposites.
Thermoelectric nanocomposites show improved efficiency; however, they are often
synthesized from highly toxic elements via energetically intense and costly synthesis
procedures. Therefore, this research focuses on the discovery and development of a
novel procedure for synthesizing thermoelectric nanocomposites – attrition enhanced
nanocomposite synthesis – from open cage-like skutterudite-based materials. With
further optimization, high-performance power-generating thermoelectric materials can
be produced via this technique. Therefore, attrition-enhanced nanocomposite
synthesis may play a small, though instrumental, role in achieving sustainable
electrical power. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Jan. 6, 2012 - Jan. 6, 2013
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