THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Tuesday, October 31, 2017

10:00 AM

in MRDC 3515

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Thomas Rudzik

"Sintering: Development of a Combined In-situ Characterization Technique and a Specific Application in Segregated Network Formation"

Committee Members:

Prof. Rosario Gerhardt, Advisor, MSE

Prof. Robert Speyer, MSE

Prof. Faisal Alamgir, MSE

Prof. Chaitanya Deo, ME

Prof. Kyriaki Kalaitzidou, ME

Dr. Jan Ilavsky, Argonne National Lab

Abstract:

Sintering is the primary method of fabrication for crystalline ceramics due to its advantage of facilitating fully dense samples at a fraction of the melting temperature. However, there are multiple codependent factors which influence the final microstructure of the sintered product and the properties it will possess. This makes it very difficult to determine the processing parameters necessary to achieve the desired properties in the material without resorting to a brute-force trial-and-error approach. The primary hurdles which have prevented the development of accurate process models are the inability of any one characterization method to completely characterize the porous microstructures of powder compacts and the fact that the microstructure at any point in the sintering process determines how the microstructure will continue to evolve. Therefore, a complete understanding of the sintering process would require employment of a combination of in-situ characterization techniques which, when used in conjunction throughout the entire sintering process, would give a complete picture of the microstructural evolution.

In this work, such a combined characterization technique has been explored, in which small angle scattering methods and ac impedance spectroscopy are carried out in-situ during the sintering of ceramic powders. A series of progressive testing procedures has shown that the concepts are sound, proved that the proposed testing methods work, and provided guidance toward successful implementation of the complete testing method.

In addition to the processing temperature advantage, sintering methods can also achieve unique microstructures and material properties, extending their potential to materials which are traditionally made via melt processing, including polymers, metals, and ceramic glasses. One promising application is the formation of percolated network composites by using sintering to induce segregation of the filler material, which minimizes the percolation threshold. Composites consisting of a borosilicate glass matrix with ITO, the predominant transparent conducting oxide, incorporated as the filler material have been fabricated using both the HP and SPS methods, with the goal of achieving a combination of both good electrical conductivity and optical properties. It is shown that the network segregation made possible through sintering results in a transition in the composites from electrically insulating to conducting at a very low concentration of ITO, but at the cost of degrading optical properties. Comparison of the samples made using HP and SPS has revealed a very unexpected trend, where identical processing parameters have resulted in higher porosity in the SPS samples, contrary to the multitude of papers in the literature which have reported densification at lower temperatures and in less time than HP. Detailed investigation has revealed that the SPS processing parameters which are usually reported in the literature may not actually be the dominant factors in that sintering process, and the resulting lack of comparability between samples made using different SPS equipment may be responsible for the lack of consensus on the mechanisms responsible for densification in SPS.