Silicon-Based Porous Ceramics via Freeze-Casting Preceramic Polymers

The use of preceramic polymers to create silicon-based ceramics offers a pathway to high-temperature creep resistant and chemically resistant materials. However, large shrinkages that accompany polymer pyrolysis often result in cracking, which limit components to thin fibers and plates, and porous solids produced by foaming. Proposed here is a research direction that builds on the foundation of ceramic processing from preceramic polymers, while broadening their formability using directional freeze casting. Compared to other porous material forming methods, directional freeze casting affords anisotropic continuous pores, whose size, shape and tortuosity can be tuned, and hence, opens new avenues for application. An added benefit of preceramic polymers is their ability to be functionalized resulting in more complex chemistries and hierarchical microstructures. Because these materials provide a new class of freeze-cast solids, of interest are their pore network characteristics, explored using synchrotron techniques and flow experiments, as well as their mechanical properties as related to their anisotropic pores and complex wall structures, not yet treated in conventional models for porous materials.