Structure and high-temperature properties of Ti{sub 5}Si{sub 3} with interstitial additions

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This study was motivated by the fact that previous research on the structure and properties of Ti{sub 5}Si{sub 3} showed unacceptably inconsistent results. The primary reason for these inconsistencies was interstitial contamination of Ti{sub 5}Si{sub 3} by carbon, nitrogen and oxygen. Thus, this study measured the effects that these interstitial atoms have on some of the previously reported properties. These properties include crystalline structure, thermal expansion anisotropy, electronic structure and bonding, and high temperature oxidation resistance. In Chapter 2 of this study, the lattice parameters and atomic positions of Ti{sub 5}Si{sub 3} as a function of carbon, nitrogen or oxygen ... continued below

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Medium: P; Size: 121 pages

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Williams, Jason December 1, 1999.

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  • Ames Laboratory
    Publisher Info: Ames Lab., IA (United States)
    Place of Publication: Iowa

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This study was motivated by the fact that previous research on the structure and properties of Ti{sub 5}Si{sub 3} showed unacceptably inconsistent results. The primary reason for these inconsistencies was interstitial contamination of Ti{sub 5}Si{sub 3} by carbon, nitrogen and oxygen. Thus, this study measured the effects that these interstitial atoms have on some of the previously reported properties. These properties include crystalline structure, thermal expansion anisotropy, electronic structure and bonding, and high temperature oxidation resistance. In Chapter 2 of this study, the lattice parameters and atomic positions of Ti{sub 5}Si{sub 3} as a function of carbon, nitrogen or oxygen content were measured via x-ray and neutron diffraction. Comparing these lattice parameters to those reported in other studies on supposedly pure Ti{sub 5}Si{sub 3} confirmed that the majority of the previous studies had samples with a considerable amount of interstitial impurities. In fact, the lattice parameter trends given in Chapter 2 can be used to estimate the types and level of impurities in these studies. Furthermore, Chapter 2 discusses how atomic positions change as interstitial atoms are incorporated into the lattice. These changes in atomic separations suggest that strong bonds form between the interstitial atoms and the surrounding titanium atoms. This is in full agreement with the electronic structure calculations given in Chapter 4. These calculations show that bonding does occur between titanium d-states and interstitial atom p-states at the expense of bonding between some of the titanium and silicon atoms. In addition, carbon seems to be the most strongly bonded interstitial atom. Knowledge of the exact interstitial content and its effect on bonding is important because Chapters 3 and 5 have shown that interstitial atoms have a marked effect on the thermal expansion and oxidation resistance. As discussed in Chapter 3, all interstitial atoms lower the thermal expansion anisotropy of Ti{sub 5}Si{sub 3} due to the formation of bonds between the interstitial atom and the surrounding titanium atoms. Although interstitial atoms do have an effect on the thermal expansion of Ti{sub 5}Si{sub 3}, these effects were not strong enough to explain all the scatter of previous studies. These studies most likely suffered from systematic errors as a result of poor experimental design. The experimental procedure used in this study was designed to significantly reduce these systematic errors.

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Medium: P; Size: 121 pages

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OSTI as DE00754837

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  • Other Information: TH: Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US)

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  • Report No.: IS-T-1898
  • Grant Number: W-7405-ENG-82
  • Office of Scientific & Technical Information Report Number: 754837
  • Archival Resource Key: ark:/67531/metadc702527

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • December 1, 1999

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  • Sept. 12, 2015, 6:31 a.m.

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  • March 23, 2016, 7:52 p.m.

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Williams, Jason. Structure and high-temperature properties of Ti{sub 5}Si{sub 3} with interstitial additions, thesis or dissertation, December 1, 1999; Iowa. (digital.library.unt.edu/ark:/67531/metadc702527/: accessed September 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.