Doctoral Dissertations

Keywords and Phrases

Ultra-high Temperature Ceramics; Zirconium diboride

Abstract

"Oxidation behavior has restricted the development of ZrB₂-based ceramics for aerospace and hypersonic flight vehicles applications. The research presented in this dissertation focuses on the effect of transition metal (TM) additives on oxidation behavior of ZrB₂ ceramics. In the first stage of the research, the effect of Nb additions on the morphology of the oxide particles and stability of the protective B₂O₃ glassy layer, which formed on the top surface during oxidation, was investigated. Addition of Nb increased the thickness of the glassy layer and, as a result, improved the oxidation resistance of ZrB₂ after oxidation at 1500⁰C. Next, the oxidation behavior of nominally pure ZrB₂ and (Zr,W)B₂ after oxidation at temperatures ranging from 800 to 1600⁰C was studied. Two oxidation stages before and after significant evaporation of B₂O₃ at about 1100⁰C were recognized for nominally pure ZrB₂. Higher stability for the WO₃-B₂O₃ glassy layer compared to pure B₂O₃ resulted in a shift in the onset of the second oxidation regime toward higher temperatures for (Zr,W)₂ specimens and resulted in higher oxidation resistance for (Zr,W)B₂ compared to nominally pure ZrB₂. In the third stage of the research, the effects of TM-oxides such as WO₃, Nb₂O₅, or ZrO₂ on weight loss and structure of B₂O₃ glasses was studied. Thermogravimetric analysis performed on (TM-oxide)-B₂O₃ glasses indicated that TM-oxide additions reduced the evaporation of B₂O₃. Since no change in the structure of the glasses was detected, it was concluded that the increased stability of (TM-oxide)-B₂O₃ glasses compared to pure B₂O₃ was due to the lower activity of B₂O₃ in (TM-oxide)-B₂O₃glasses. Finally, comparison of the effects of W, Mo, or Nb on oxidation behavior of ZrB₂ at 1600⁰ showed that Mo and Nb were the most effective additives for improving the oxidation resistance of ZrB₂"--Abstract, page iv.

Advisor(s)

Fahrenholtz, William

Committee Member(s)

Hilmas, Greg
Brow, Richard K.
Watts, Jeremy Lee, 1980-
Switzer, Jay A., 1950-

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Materials Science and Engineering

Sponsor(s)

National Hypersonic Science Center for Materials and Structures

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2014

Journal article titles appearing in thesis/dissertation

  • Oxidation of zirconium diboride with niobium additions
  • Effects of temperature and the incorporation of W on the oxidation behavior of ZrB₂ ceramics
  • Effect of transition metal oxide additions on the structure of B₂O₃ glasses
  • Effects of transition metals on the oxidation behavior of ZrB₂ ceramics

Pagination

xiii, 138 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2014 Maryam Kazemzadeh Dehdashti, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Ceramic materials -- Mechanical propertiesCeramics -- Thermal propertiesZirconium -- Thermal propertiesBorides -- Thermal propertiesOxidationTransition metals

Thesis Number

T 10533

Electronic OCLC #

894224342

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