Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

First Advisor

Mufit Akinc

Abstract

Phase relations and microstructure development were studied in the binary systems Ce [subscript]2O[subscript]3 (CeO[subscript]2)-Ce [subscript]2Si[subscript]2O[subscript]7, Ce [subscript]2O[subscript]3(CeO[subscript]2)-Al [subscript]2O[subscript]3 and Al [subscript]2O[subscript]3-Ce [subscript]2Si[subscript]2O[subscript]7 within the ternary CeO[subscript]2-Al [subscript]2O[subscript]3-SiO[subscript]2 in inert (pure argon and vacuum) and reducing (argon + 10% H[subscript]2) atmospheres in the temperature range 900° to 1970°C. High temperature phases were quenched by conventional quenching methods to determine the high temperature phase equilibria. Differential thermal analyses (DTA) were used to determine the liquidi and to monitor the solid state phase transformations. Microstructure development, as a function of temperature and composition, was investigated with SEM and optical microscopy. Binary phase diagrams, for the systems Ce [subscript]2O[subscript]3-Ce [subscript]2Si[subscript]2O[subscript]7 and Al [subscript]2O[subscript]3-Ce [subscript]2Si[subscript]2O[subscript]7, were suggested. The binary compounds that form in these systems as well as in the Ce [subscript]2O[subscript]3-Al [subscript]2O[subscript]3 binary were synthesized as pure substances and characterised by XRD and DTA. New XRD patterns were suggested for Ce[subscript]4.67(SiO[subscript]4][subscript]3O, tetragonal Ce [subscript]2Si[subscript]2O[subscript]7, monoclinic Ce [subscript]2Si[subscript]2O[subscript]7, Ce [subscript]2SiO[subscript]5, tetragonal CeAlO[subscript]3 and CeAl [subscript]11O[subscript]18. Cerium hexaaluminate, CeAl [subscript]11O[subscript]18, was determined to have a magnetoplumbite-like crystal structure rather than [beta]-alumina. The melting and decomposition points of these binary compounds were determined, with the exception of CeAlO[subscript]3. Ce[subscript]4.67(SiO[subscript]4][subscript]3O, cerium oxygen apatite, was shown to be able to absorb nitrogen in its structure from the nitrogen-bearing starting oxides used in its synthesis or even from gaseous reaction atmospheres. The presence of nitrogen in cerium oxygen apatite, when the stoichiometric compound was doped with ppm-level Si[subscript]3N[subscript]4, was confirmed by neutron diffraction experiments. Nitrogen was found to occupy the non-silicon-bonded oxygen sites of the lattice.

DOI

https://doi.org/10.31274/rtd-180813-13055

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Ahmet Cuneyt Tas

Language

en

Proquest ID

AAI9321216

File Format

application/pdf

File Size

221 pages

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