Study of Pore Development in Silicon Oxycarbide Ceramics to Understand the Microstructural Evolution
Silicon oxycarbide (SiOC) is a ceramic obtained through the heating of a polymer precursor, which undergoes partial decomposition to go from an organic polymer to an inorganic ceramic. The microstructure of SiOC is not uniform at the nanometer scale, and contains nanometer sized silicon dioxide, carbon, and silicon carbide. Porous SiOC has shown great promise in applications such as lithium ion batteries, gas separation, and thermal barriers. The microstructure, and thus the properties of the SiOC, is influenced by the initial polymer and the processing conditions. In this thesis, SiOC is fabricated using a base polysiloxane polymer using different gases during heating, different additives that change the initial polymer chemical composition or polymer shape, and polymers with different reactive groups. Porosity was introduced into the SiOC ceramics through either etching the SiOC with hydrofluoric acid, which removes the silicon dioxide and produces pores with diameters less than 20 nanometers, or through decomposition during heating of a certain polymer in a two polymer mixture, producing pores that are dozens of microns in diameter. The effects of the processing parameters on the porosity and pore size are used to understand the differences in the microstructure during pyrolysis.