Structure and Dynamics in Boron-Containing Oxide Glasses and Liquids: High-Resolution and High-Temperature Nuclear Magnetic Resonance Studies

拟议的研究将使用环境温度下的核磁共振（NMR）光谱来确定不同有效温度对玻璃结构的影响，这将限制玻璃化转变附近液体结构的温度影响。在原位，对硼、氧、钠、铝和硅核素的高分辨率、高温核磁共振将用于确定温度对平均配位环境的影响。观察到的结构变化对熵、焓、活度、摩尔体积和其他性质的影响将使用简单的热力学模型进行评估。在温度较低但仍在液体范围内的情况下，静态和魔角自旋核磁共振将用于观察结构物质之间的交换并测量它们的交换率。将测量自旋晶格弛豫时间，以在更宽的温度范围内获得动力学信息。这些分子尺度动力学的结果将与现有粘度数据得出的剪切松弛时间、电导率和扩散率数据进行比较。将制定并检验微观与宏观相联系的模型。硅酸盐和硼硅酸盐玻璃及其相应的高温液体在工业和社会上具有广泛的重要性。为了对玻璃和玻璃熔体的性质建立准确的预测模型，需要有关其原子尺度结构和动力学的基本数据。这里提出的工作将我们小组对简单硅酸盐玻璃和液体的广泛研究扩展到硼酸盐、硼硅酸盐和硼铝酸盐体系，以解决这些技术上更相关的材料的基本问题，但人们对这些问题知之甚少。该项目的重点是利用核磁共振（NMR）波谱技术获取环境和高温下的定量结构和动力学信息，并根据这些新发现对现有宏观热力学和输运性质数据进行解释和建模。＊＊＊

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. ***