9626735 Stebbins The proposed studies will use nuclear magnetic resonance (NMR) spectroscopy at ambient temperature to determine the effects of varying fictive temperature on glass structure, which will constrain temperature effects on liquid structure in the vicinity of the glass transition. In situ, high resolution, high temperature NMR on boron, oxygen, sodium, aluminum, and silicon nuclides will be used to determine temperature effects on average coordination environment. The effects of observed structural changes on entropy, enthalpy, activities, molar volumes, and other properties will be assessed using simple thermodynamic models. At lower temperatures but still in the liquid range, static and magic angle spinning NMR will be used to observe exchange among structural species and measure their exchange rates. Spin- lattice relaxation times will be measured to gain dynamical information over wider ranges in temperature. These results for molecular-scale dynamics will be compared to shear relaxation times derived from existing data on viscosity, and to data on electrical conductivity and diffusivity. Models linking the microscopic and macroscopic will be formulated and tested. %%% Silicate and borosilicate glasses, and their corresponding high temperature liquids, are of wide-ranging importance in industry and society. In order to formulate accurate predictive models for the properties of glasses and glass melts, fundamental data on their atomic-scale structure and dynamics are required. The work proposed here will extend our group's extensive studies of simple silicate glasses and liquids to borate, borosilicate, and boroaluminate-systems in order to address basic, but poorly understood questions about these technologically more relevant materials. The focus of this project is to use nuclear magnetic resonance (NMR) spectroscopy to acquire quantitative structural and dynamical information at ambient and high temperature, and to interpret and model existing macroscopic thermodynamic and transport property data in light of these new findings. ***
