Mechanical properties and molecular structure of silicon carbide hybrid glasses [electronic resource]

Silicon carbide hybrid glasses are a class of hybrid organic-inorganic glasses which contain inorganic network bonds and organic monovalent bonds. They exhibit not only excellent thermal and chemical stability, but also unique multi-functionality that is tunable by controlling chemical composition, the number of monovalent bonds, and additional porosity. Perhaps the most significant advantage of silicon carbide hybrid glasses is that they are processed without moisture-sensitive bonds, and therefore they are in theory insensitive to "moisture-assisted cracking, " which significantly deteriorates the mechanical integrity of moisture-sensitive materials. These attractive properties make silicon carbide hybrid glasses promising candidates for emerging nanoscience and energy applications that require protection from moisture and harsh environments. However, the successful integration and application of silicon carbide hybrid glasses are limited by their fragile nature due to the reduced network connectivity and lack of plasticity of the glasses. The central theme of this dissertation is to investigate the fundamental connection between the molecular structure and resulting mechanical properties of silicon carbide hybrid glasses to obtain design guides to improve their mechanical properties, which enables the integration and application of the glasses. The crucial role of glass network connectivity and plasticity in the mechanical properties of the silicon carbide hybrid glasses was first demonstrated. It was shown that the cohesive fracture energy of the silicon carbide hybrid glasses can be dramatically improved by conferring plasticity to the glasses through the incorporation of carbon chains into the molecular structure without sacrificing their excellent thermal and chemical stability. The silicon carbide hybrid glasses with plasticity were also used as toughening layers to dramatically improve adhesion in nanoscale thin-film structures. It was then demonstrated that silicon carbide hybrid glasses exhibited a low sensitivity to moisture-assisted cracking even though they were processed without moisture-sensitive bonds. This low sensitivity was due to the formation of Si--O--Si bonds at Si--Hx bonds in the glasses after the deposition process. A new atomistic kinetic fracture model that incorporates the role of moisture-insensitive bonds was developed to quantitatively predict the low sensitivity and crack growth velocity of the glasses. The developed atomistic kinetic fracture model was further employed to explore how the sensitivity of the glasses to moisture-assisted cracking changed with varying Si--O--Si bonds. Finally, the applicability of a new silicon carbide hybrid glass to an industrial application was explored. This new glass exhibited mechanical properties superior to traditional silica-based hybrid glasses and insensitivity to moisture-assisted cracking.

Keywords: Materials Science and Engineering
Advisor: Dauskardt R. H. (Reinhold H.) primary advisor. Thesis advisor
Nix William D. advisor. Thesis advisor
Stebbins Jonathan Farwell advisor. Thesis advisor