Date of Award

Summer 8-2017

Embargo Period

8-21-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Advisor(s)

Bryan A. Webler

Abstract

This project studied the inclusion behavior before and after reoxidation. It focuses on the changes in inclusion size distributions and the mechanism by which reoxidation changes inclusion chemistries. This study examined the behavior of inclusions in laboratory heats after deoxidation with 0.1 wt% Al, Ca treatment, and reoxidation. MgO and Al2O3 crucibles were employed in the experiments to track the evolution of MgAlO4 spinel inclusions and Al2O3 inclusions. For both crucibles, experiments with different Ca and S level and 100 ppm O additions were attempted. Samples were taken at various points after the different additions were made up to 20 minutes after reoxidation. Automated SEM/EDS microanalysis was used to analyze the inclusions detected on polished cross sections and inclusion compositions were studied over this time span. Size distributions were analyzed by calculating population density functions (PDF) of spinels, alumina and calcium aluminate formed at different time and compared to confirm the mechanism of inclusion formation. Electrolytic etching was performed on the sample surface and the morphology of inclusions was observed by manual SEM/EDS. After reoxidation new Al2O3 and/or spinel (MgAl2O4) inclusions formed. The inclusions that were present from deoxidation and Ca treatment became richer in Al2O3. The presence of excess CaS was found to decrease the amount of oxides that formed upon reoxidation. The shape of PDFs could be used to identify inclusions that formed due to reoxidation. Several suggested mechanisms for the inclusion chemistry and size distribution mechanisms are presented.

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