Understanding phase transformations during flash sintering

Improving the efficiency of synthesis methods in addition to establishing methods to produce novel materials or materials that are difficult to synthesize are driving factors in research for materials science. Flash sintering is both a method to densify ceramics within seconds and a method to rapidly synthesize materials. With the ability to use volatile precursors, avoid complete oxidation of elements, and locally cause transformations, flash sintering also provides a method of synthesizing compositions that would be difficult to produce conventionally. Although flash sintering is a technique with great potential to improve or expand upon current synthesis methods, the mechanisms have not been fully established. A variety of facets of flash sintering are presented in this thesis, all with the goal of understanding the mechanism of flash sintering so that it can be tailored and utilized for synthesis. By comparing two systems that are reduced during flash sintering, one with large contact resistance and the other with little contact resistance, the ability to utilize contact resistance for local heating to cause a phase transformation is shown. A method of predicting when a phase transformation will form will be discussed in addition to how kinetics and activation energy affect this prediction. An approach to using in situ Raman spectroscopy as a quantitative method to monitor defects during flash sintering is described. The effects of green body resistance and selected flash parameters on the flash temperature and the resulting phases are shown. By studying reduction reactions as model systems and utilizing in situ Raman to monitor defects and phases, we can gain further understanding of the mechanisms of flash sintering for its application as a versatile synthesis technique.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste