Doctoral thesis

Characterization of chrysotile, tellurium and iImogolite nanotubes



Thèse de doctorat: Université de Fribourg, 2008

English The discovery of C60 (R. Smalley et al.) and carbon nanotubes CNTs (S. Iijima) in 1985 and 1991 respectively was a milestone in the field of nanoscience. Since 1991, WS2, MoS2, BN, Se, Te nanotubes were synthesized and analyzed. These nanotubes are promising materials for many applications in the field of catalysis, electronic, polymer synthesis, etc. In this study, we characterized the crystallographic and chemical properties of two natural and one synthetic nanotubes: 1) chrysotile nanotubes 2) tellurium nanotubes and 3) imogolite nanotubes. An introductory chapter gives general information on the crystallography, crystal chemistry, thermal stability, synthesis of the materials. A second chapter contains a published or submitted paper on a specific aspect of the treated nanotube material. The first nanotube material presented is chrysotile, which is nanotubular mineral of the serpentine family. A formalism derived from the description of carbon nanotubes has been developed. A potential application of chrysotile nanotubes as template for metallic nanowires manufacturing is proposed. An important parameter for such a procedure is the thermal stability of the nanotube. We show that chrysotile dehydroxilation takes place around 490‰ and that the tubular morphology is stable up to 700‰ (at atmospheric pressure). Metals with a melting temperature under 700‰ can potentially be injected in chyrsotile nanotubes to produce metallic nanowires. Successful injections of Mercury and Lead were performed under high pressure conditions (4-10 Kbar). In the second case study the synthesis of tellurium nanotubes through physical vapor deposition (PVD) is presented. Tellurium is a metallic element used for the synthesis of semiconducting materials such as Bi2Te3, CdTe and ZnTe. The synthesis of tellurium nanotubes through wet chemical routes has already been achieved by several research groups. In this study we show that tellurium nanotubes can also be synthesized through physical vapor deposition between 150‰ and 200‰ without using any catalyst or template. The nanotubes show a crystallographic preferred orientation relative to the silicon wafer used as target, the (001) plane of the tellurium nanotubes being parallel to the (111) plane of the silicium. In the third case study the tubular and bundle crystallographic structure of imogolite nanotubes is investigated. Imogolite is a natural nanotubular mineral discovered in volcanic soils of the Kyushu Island (Japan). Imogolite can also be synthesized through aqueous solution. A numerical rigidbody model of the structure of individual imogoli2te nanotubes and bundles has been developed and 3 calculations of powder X-ray patterns were performed. The structural model proposed by Cradwick et al. in the '70 is confirmed. We show that the 'bundle geometry' of imoglite can be monoclinic or tetragonal. The X-rays patterns calculated in this study may eventually be used in future work and may permit better interpretations of the measured x-rays spectrums.
Faculté des sciences et de médecine
Département de Géosciences
  • English
  • Ressource en ligne consultée le 11.08.2009
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