Porous Materials via Freeze Casting: 3D MXene, Ceramics, and Their Composites for Energy Storage Applications

 Freeze casting, an innovative materials processing technique, offers significant potential to create porous structures with high surface-to-volume ratio for high performance devices. This thesis presents a comprehensive study on the fabrication of porous structures using 2D MXene nanomaterials, silica, and alumina, with a focus on achieving controllable interconnected porosity and demonstration of such structures for steelmaking and energy storage. This thesis is divided into three sections. The first part of the thesis examines the freeze casting process for fabricating porous ceramics using silica and camphene. A full-factorial design of experiments is conducted to correlate freeze casting parameters with pore characteristics. Variables like solid loading, particle size, cooling temperature, and distance from the cooling surface are scrutinized. The fabricated samples are cross-sectioned and analyzed using scanning electron microscopy and image processing, yielding detailed data on areal porosity, pore size, shape, and orientation. The study successfully demonstrates the ability to steer pore orientation using bidirectional freezing, supported by a finite-element model, providing a quantitative understanding of the effects of freeze casting parameters on the part porosity. In the second part, the research establishes the suitability of freeze-cast alumina for high-temperature applications such as structural ceramics for molten metal and glass processing. Specific tests such as gas permeability, dilatometry and steel penetration tests for porous alumina are carried out in collaboration with Vesuvius Plc., a global leader in molten metal flow engineering and technology, towards this goal. By varying process parameters like solid loading and freezing conditions, the study creates alumina with microscale, interconnected, and directional pores, achieving controlled gas permeability and mechanical strength. The optimized alumina exhibits 70% porosity, impressive gas permeability, high compressive strength, and a suitable dynamic elastic modulus; along with consistent performance under high temperatures, as evidenced by the steel penetration tests. These findings highlight the potential of freeze-cast alumina in advanced industrial applications. The final part of the thesis addresses the challenge of assembling MXene nanomaterials in 3D space without restacking. A novel material system is introduced, comprising a 3D MXene network on a porous ceramic backbone, fabricated using freeze casting. This MXene-infiltrated porous silica (MX-PS) system demonstrates high conductivity and effective performance as supercapacitor electrodes. The successful creation of 3D architectures of 2D MXenes opens new avenues in various fields, including energy storage and catalysis. Overall, this thesis contributes significantly to the literature on porous ceramics and MXene-based nanomaterials, providing valuable insights into their controllable and scalable manufacturing, characterization, and application in high-performance devices and industrial settings.