There are numerous applications of porous ceramics, including electrodes for solid oxide fuel cell, membranes and filters, and thermal insulation.  Most of these applications utilize uniform isotropic porous ceramics. Directional freeze-casting offers a novel way to make porous ceramics with tailored microstructures. Using this process, followed by partial sintering, we are able to fabricate ceramics with directionally aligned and hierarchical porosity. Freeze-casting involves directional freezing of a liquid suspension and then sublimation of the solvent by freeze drying in order to achieve uni-directional pores. Overall porosity and pore size and alignment can be controlled by several variables including: solvent to powder ratio, freezing rate, and sintering temperature. Our research focuses on two different applications of anisotropic porous zirconia ceramics. One project focuses on creating filters for catalytic hydrogen peroxide decomposition. Hydrogen peroxide (H₂O₂) is an undesirable byproduct and hindrance of a new process to produce chlorine using solar radiation. Porous ceramics provide the means of developing a filter with sufficient surface area and structure for photochemical reactor solutions to be continuously scrubbed of H₂O₂; thereby enabling unhindered chlorine production by this photochemical process at levels sufficient for water purification. The other project focuses on developing a glass-infiltrated reusable ablative ceramic surface for high temperature aeronautical applications. Porous yttrium stabilized zirconia is used as a substrate through which glass can be both initially infiltrated and subsequently drawn to a high temperature surface through capillary action for ablative purposes. At high use temperatures, the glass rises in the capillaries reaching the hot surface where it is ablated. The heating required for ablation reduces the surface temperature of the system.

Lithium batteries have been used in electronics and increasingly in hybrid and all electrical vehicles due to their lightweight and improved electrochemical performance. However, there are still several limitations with these batteries including slow charging rate, incomplete discharge and cyclic degradation in performance. Most of these problems have been related to the performance of the cathode. This project is focused on optimizing the microstructure of the porous cathode. We are investigating LiMnPO₄, which has a high theoretical capacity (171 mAh g-1) and better electrochemical stability compared to other lithium-based metal oxide cathode materials. Unfortunately LiMnPO₄ has a low electrical conductivity, which is improved by mixing it with carbon.  LiMnPO₄ powder is synthesized using the polyol process. This produces extremely fine high surface area particles. By using directional freeze casting with different weight percentages of solids and freezing rates, it is possible to create aligned pores throughout the structure, which have the potential to increase the energy density and reduce the transport distances. We are making cathodes with a broad range of microstructures and investigating their electrochemical performance.  Another process to enhance the performance is through partial sintering to make cathodes with uniform porous microstructures. By controlling the sintering temperature between 500 º-700º C, cathodes with a range of uniform isotropic porosity are being made. Structural and physical characterization will be conducted for both types of cathodes to evaluate the microstructure. The electrochemical performance of the two types of cathodes at different densities will be compared in order to optimize the microstructure.

Chemostats are a continuous culture system in which cells are grown in a tightly controlled, chemically constant environment where culture density is constrained by limiting specific nutrients. Unlike batch cultures, the selective pressure imposed in a chemostat is constant. This has made them a desirable tool for evolution and competition experiments. Traditionally chemostat experiments with S. cerevisiae have been constrained due to the limited number of cultures that can be run at once. In order to solve this problem our team is working with a new culturing system that allows 64 chemostats to be run simultaneously. In our experiment we evolved 32 biological replicates of haploid MATa yeast cells under constant sulfur-limitation for 250 generations. We are now using a variety of techniques including whole genome sequencing of evolved populations to characterize mutations that have been selected for during the course of these evolutions. Changes in the genome can be correlated to changes in relative fitness, which we assayed through competition with a GFP (a green fluorescent protein that exhibits bright green fluorescence when exposed to ultraviolet blue light) expressing ancestral strain every 50 generations. Ultimately it is our hope that higher replicate number will better reveal the spectrum of genes important for adaptive growth in a sulfur-limited environment. Furthermore we would like to use these methods to understand what genes are important in a wide variety of nutrient limited environments.