Doctoral Dissertations


"Solid solution formation in spinel based systems proved to be a viable approach to decreasing thermal conductivity. Samples with systematically varied additions of MgGa₂O₄ to MgAl₂O₄ were prepared and thermal diffusivity was measured using the laser ash technique. Additionally, heat capacity was measured using differential scanning calorimetry and modeled for the MgAl₂O₄-MgGa₂O₄ system. At 200⁰C thermal conductivity decreased 24% with a 5 mol% addition of MgGa₂O₄ to the system. The solid solution continued to decrease the thermal conductivity by 13% up to 1000⁰C with 5 mol% addition. The decrease in thermal conductivity ultimately resulted in a decrease in heat flux when applied to a theoretical furnace lining, which could lead to energy savings in industrial settings.

The MgAl₂O₄-Al₂O₃ phase equilibria was investigated to fully understand the system and the thermal properties at elevated temperatures. The solvus line between MgAl₂O₄ and Al₂O₃ has been defined at 79.6 wt% Al₂O₃ at 1500⁰C, 83.0 wt% Al₂O₃ at 1600⁰C, and 86.5 wt% Al₂O₃ at 1700⁰C. A metastable region has been identified at temperatures up to 1700⁰C which could have significant implications for material processing and properties. The spinel solid solution region has been extended to form an infinite solid solution with Al₂O₃ at elevated temperatures. A minimum in melting at 1975⁰C and a chemistry of 96 wt% Al₂O₃ rather than a eutectic is present.

Thermal properties in the MgAl₂O₄-Al₂O₃ system were investigated in both the single phase solid solution region and the two phase region. The thermal diffusivity decreased through the MgAl₂O₄ solid solution region and was at a minimum through the entire metastable (nucleation and growth) region. As Al₂O₃ became present as a second phase the thermal diffusivity increased with Al₂O₃ content. There was an 11.7% increase in thermal diffusivity with a change in overall chemistry of 85.20 wt% Al₂O₃ to 87.71 wt% Al₂O₃, due to the drastic change in final chemistry (38.3 wt% Al₂O₃) caused by the nucleation and growth region in the system"--Abstract, page iv.


Smith, Jeffrey D.

Committee Member(s)

Reidmeyer, Mary R.
Samaranayake, V. A.
Miller, F. Scott, 1956-
Huebner, Wayne


Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering


United States. Department of Energy


Missouri University of Science and Technology

Publication Date

Summer 2012

Journal article titles appearing in thesis/dissertation

  • Solid solution effects on the thermal properties of compounds in the MgAl₂O₄-MgGa₂O₄ system
  • Metastability in the MgAl₂O₄-MgGa₂O₃ system
  • Thermal properties in the MgAl₂O₄-MgGa₂O₃ system


xiii, 158 pages

Note about bibliography

Includes bibliographical references.


© 2012 Kelley Rae O'Hara, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Subject Headings

Phase rule and equilibrium
Spinel -- Thermal properties
Thermal conductivity -- Measurement

Thesis Number

T 10034

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