Final Defense: Camilla McCormack

Event Date: September 21, 2023
Time: 1:30 P.M.
Location: ARMS 2237 or via WebEx
Priority: No
School or Program: Materials Engineering
College Calendar: Show

"Reaction Processing and Characterization of Al2O3/Cr Ceramic/Metal Composites"

Camilla McCormack, MSE PhD Candidate 

Advisor: Professor Kenneth Sandhage

WebEx Link

ABSTRACT

To decrease the use of fossil fuels that generate greenhouse gases, there has been a push to find alternative processes for electricity generation. An attractive renewable alternative is to use solar-thermal energy for grid-level electricity production. One method used to generate electricity from the conversion of solar-thermal energy is concentrated solar power (CSP) via the power tower paradigm, which involves an array of mirrors that concentrate sunlight to a spot on a tower. The focused sunlight raises the temperature of a heat transfer fluid which later transfers the thermal energy to a working fluid that expands so as to spin a turbine to generate electricity. Current CSP plants have a peak operation temperature of 550℃, but improvements to the heat exchanger are integral to increasing the peak operation temperature of such plants to >750℃ (for enhanced thermal-to-electrical conversion efficiency). Ceramic/metal composites (cermets) have been proposed for use as heat exchangers in these CSP plants due to the high-temperature creep resistance of the ceramic component and high-temperature toughness of the metal component. One potential material that has an attractive combination of properties for this application is the alumina/chromium (Al2O3/Cr) cermet, given the high-temperature rigidity and creep resistance of Al2O3 and the high-temperature toughness of Cr. Compared to other oxidation-resistant oxide/metal cermets, the Al2O3 and Cr components of this cermet have a relatively close average linear thermal expansion match from 25℃ to 750℃, which is advantageous due to the thermal gradients and thermal cycling of the heat exchanger during operation.

In this dissertation, the Al2O3/Cr cermet was produced via reaction forming (RF) or reactive melt infiltration (RMI). The RF method involves the reaction of Cr2O3 and Al constituent powder mixtures at elevated temperatures and modest pressures to obtain dense Al2O3/Cr plates. The RMI method involves immersing a shaped porous Cr2O3 preform into an Al or Al-Cr alloy bath to infiltrate and react to form Al2O3/Al-Cr plates. For both methods, the plate microstructure was analyzed for the various reaction conditions. The adiabatic temperature increase for the reaction between Cr2O3 and Al liquid or Al-Cr liquid alloys was calculated. The properties of RF Al2O3/Cr composites were evaluated as a function of temperature and compared to the expected behavior of such mixtures as predicted by various models for such ceramic-matrix composites. Lastly, the reaction kinetics between dense, polycrystalline Cr2O3 and a liquid Al-35at% Cr alloy were experimentally determined at various temperatures and compared to models based on different rate-limiting steps.

2023-09-21 13:30:00 2023-09-21 14:30:00 America/Indiana/Indianapolis Final Defense: Camilla McCormack ARMS 2237 or via WebEx