Hello ME Community,

Co-Advisors: Dr. Ronghui Ma and Dr. Ruey-Hung Chen

Title: Mono-Directional and Bi-Directional Freeze Casting of Porous Copper with Lamellar Morphology from Cupric Oxide Suspensions for Applications Involving Thermal and Fluid Transport

Abstract: 
Freeze casting is a porous material processing method that enables the fabrication of directionally aligned pore structures through controlled solidification. In this process, solidifying ice crystals act as temporary templates that reject suspended particles or solutes. Subsequent sublimation removes the ice, leaving a porous particle scaffold. Compared to other porous material processing methods, freeze casting indirectly controls pore formation through solidification behavior, allowing pore characteristics to be manipulated using principles established in alloy solidification theory.
Although freeze-cast materials have been identified for applications such as bio-ceramics,  electrodes, and filtration. etc., the lack of understanding of the process often results in a discrepancy between the desired pore structure and the fabricated structures.  Since solidification underpins the freeze-casting process, this work focuses on understanding the role of freezing kinetics in determining pore morphology, specifically in porous copper fabricated with copper oxide particles. Two key solidification parameters, solidification front velocity and temperature gradient, are manipulated to investigate their effects on pore structure. The influence of particle concentration and additives is also examined, recognizing that suspensions introduce coupled thermal and solute fields during solidification. Both mono-directional and bi-directional freeze-casting configurations are explored, as each produces distinct pore structures. Separate experimental systems are employed to investigate how freezing parameters affect pore structures in mono-directional and bi-directional freezing conditions, and the resulting morphological changes by controlling the two key parameters are systematically analyzed.
Building upon this understanding of process–structure relationships, the work further demonstrates the importance of linking processing conditions to material properties for engineering applications. Two examples are presented. The effective thermal conductivity of infiltrated mono-directional porous copper illustrates how controlled pore alignment influences heat transport. The wickability of bi-directionally frozen porous copper highlights the role of pore morphology in fluid transport behavior. Together, these examples demonstrate how fundamental understanding of freeze-casting solidification enables tunable porous materials with application-specific performance.