Masters Theses

Keywords and Phrases

Cation Disorder; High Entropy; Inversion; Mechanical Activation; Neutron Diffraction; Spinel

Abstract

"This research focuses on the processing and the effects that has on the cation disorder of magnesium-aluminate spinel based (MgAl2O4) ceramics. The first goal of this project was to determine the effects of high-energy milling, i.e., mechanical activation, on cation disorder (inversion) within the spinel structure. First, 1:1 molar ratios of MgO:Al2O3 ceramics were processed using two green processing methods, ball milling (XD) and SPEX milling (mechanical activation, MA) followed by a subsequent annealing treatment in air to form a single spinel phase in each powder sample. Neutron diffraction analysis was employed to determine the cation site occupancy and revealed that overall mechanical activation resulted in a lower degree of cation site inversion compared to the non-activated materials, about 0.12 was the largest value returned for the MA materials and 0.13 was the lowest value out of the XD samples. The second portion of this project was to investigate the synthesis, densification behavior, and crystallographic site occupancy for a high-entropy spinel (HES) (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)Al2O4. This was compared to several other compositions including a MgAl2O4, NiAl2O4 and (Mg0.5Ni0.5)Al2O4 (MAS, NAS, NMAS) specimens produced using the same methods. Each composition reacted to form a single phase, but analysis of x-ray diffraction (XRD) patterns revealed that the HES specimen had a degree of inversion of 0.4. The NAS and NMAS samples were also highly inverted whereas the MAS material had minimal cation disorder."--Abstract, page iv.

Advisor(s)

Fahrenholtz, William

Committee Member(s)

Watts, Jeremy Lee, 1980-
Huebner, Wayne

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Materials Science and Engineering

Comments

This research was partially funded by the Enabling Materials for Extreme Environments signature area at Missouri S&T. The research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The authors would like to thank the Advanced Materials Characterization Lab at Missouri S&T for use of the characterization equipment.

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2021

Journal article titles appearing in thesis/dissertation

  • Mechanical activation and cation site disorder in MgAl2O4
  • Synthesis and characterization of a high entropy spinel

Pagination

ix, 59 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2021 Cole Alexander Corlett, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 11831

Electronic OCLC #

1280062242

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