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Title page for etd-0810110-135829


URN etd-0810110-135829 Statistics This thesis had been viewed 1957 times. Download 0 times.
Author Syuan-You Huang
Author's Email Address No Public.
Department Materials Engineering
Year 2009 Semester 2
Degree Master Type of Document Master's Thesis
Language Chinese&English Page Count 128
Title Synthesis of HfNiSn and NbCoSn Stannide Materials and their Thermoelectric Properties
Keyword
  • half-Heusler
  • mechanical alloying
  • hot-pressing
  • X-ray diffraction
  • structure evolution
  • structure evolution
  • X-ray diffraction
  • hot-pressing
  • mechanical alloying
  • half-Heusler
  • Abstract The HfNiSn and NbCoSn alloys with half-Heusler structure have been regarded as possessing excellent thermoelectric properties. Such alloys have MgAgAs-type crystal structure. In this study, starting compositions of stoichiometric Hf1Ni1Sn1, Nb1Co1Sn1 and in their vicinity were selected to carry out mechanical alloying. The milled powder mixtures were subjected to annealing treatment to observe the structural changes, and to vacuum hot-pressing to produce bulk materials in order to explore the feasibility of generating thermoelectric alloys with a single HfNiSn or NbCoSn phase. X-ray diffraction analysis was employed to analyze the structure of the powders and bulk materials, and with the Rietveld refinement the characteristics of each phase were analyzed. X-ray diffraction results showed that for the starting Hf1Ni1Sn1 composition, regardless of milling or milling plus subsequent annealing, a single phase of half-Heusler HfNiSn powder could be produced. As for the starting Nb1Co1Sn1 composition, prolong milling produces no crystalline phase. Instead, an amorphous structure is finally obtained. If an annealing treatment was further imposed on such an amorphous structure, a single phase of half-Heusler NbCoSn powder was obtained. For other compositions in the vicinity of stoichiometric Hf1Ni1Sn1 , milling on these powders produces less pure half-Heusler HfNiSn together with small amounts of other phases. When these milled powders were undergone annealing treatment, a half-Heusler HfNiSn phase was dominated and accompanied by Hf2Ni2Sn, HfNi2, or Ni3Sn4 and Ni3Sn2 mixture phase. For the above-mentioned two stoichiometric Hf1Ni1Sn1 and Nb1Co1Sn1 compositions, hot-pressing the milled powders and followed by densification produce bulk materials with a single half-Heusler HfNiSn and NbCoSn phase, and the values of figure of merit at room temperature for these two alloys are 0.007 and 0.005, respectively.
    Advisor Committee
  • Hsin-ming Wu - advisor
  • Chia-jung Hu - co-chair
  • Pee-yew Lee - co-chair
  • Files indicate not accessible
    Date of Defense 2010-07-27 Date of Submission 2010-08-10


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