Committee Members:

• Prof. Rosario Gerhardt, Advisor, MSE
• Prof. Robert Speyer, MSE
• Prof. Chaitanya Deo, ME/NRE

Spark-Plasma Sintered SiCw-Al2O3 Composites and the Influence of 3YSZ on their Microwave Heating Behavior

Abstract:

Ceramic composites consisting of an alumina (Al2O3) matrix and silicon carbide whisker (SiCw) reinforcing phase have found traditional commercial uses as high-performance tooling and wear parts due to their exceptional hardness, thermal shock resistance, and chemical inertness. However, more recently they have also found use as microwave heating elements, primarily due to the microwave absorption properties of SiC, which displays resonance in the microwave frequency range allowing for rapid and uniform volumetric heating. Similarly, 3 mol% yttria stabilized zirconia (3YSZ) displays strong microwave absorption properties, experiencing a thermal runaway effect, causing the material to uncontrollably heat up to temperatures above 1000C. As such, 3YSZ has the potential to increase heating rates and maximum temperatures reached of microwave-based material technologies.

The first section of this research establishes the percolation threshold of spark-plasma sintered (SPS) SiCw-Al2O3 composites to compare to other SiCw-Al2O3 composites made with varying densification methods. Once the percolation threshold was established, a composition was chosen to add 3YSZ as an additional filler phase in attempt to influence the microwave heating behavior of the composite. While SiC can transfer electromagnetic energy to thermal energy due to the establishment of polarized and dielectric loss caused by the external electric field, 3YSZ displays thermal runaway due to a small increase in the loss factor. Thus, adding 3YSZ to a SiCw-Al2O3 composite in small volume contents can potentially induce more controlled thermal runaway in the bulk composite behavior. In the later sections of this thesis, numerical simulation work was done to study the electromagnetic microwave heating behaviors of both SiCw-Al2O3 composites of varying compositions as well as the 3YSZ-SiCw-Al2O3 composites. Localized thermal hotspots were observed in eclectically percolated SiCw-Al2O3 composites and more conducting 3YSZ-SiCw-Al2O3 composites demonstrating the tie between microwave absorption and electrical conductivity in these samples. This work provides in the initial groundwork in understanding the bulk electrical and microwave heating behaviors of 3YSZ-SiCw-Al2O3 composites.