Keywords and Phrases
Ultra-high Temperature Ceramics; Zirconium diboride
"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.
Brow, Richard K.
Watts, Jeremy Lee, 1980-
Switzer, Jay A., 1950-
Materials Science and Engineering
Ph. D. in Materials Science and Engineering
National Hypersonic Science Center for Materials and Structures
Missouri University of Science and Technology
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
xiii, 138 pages
© 2014 Maryam Kazemzadeh Dehdashti, All rights reserved.
Dissertation - Open Access
Ceramic materials -- Mechanical properties
Ceramics -- Thermal properties
Zirconium -- Thermal properties
Borides -- Thermal properties
Electronic OCLC #
Kazemzadeh Dehdashti, Maryam, "Improving the oxidation resistance of diboride-based ceramics" (2014). Doctoral Dissertations. 2336.