Disorder and Dynamics in Silicate and Aluminosilicate Liquids, Glasses, and Crystals: Nuclear Magnetic Resonance Studies

StebbinsEAR-0104926这项建议是为了重新资助一项研究地球科学感兴趣的结晶、玻璃和熔融硅酸盐和氧化物的原子级结构和动力学的计划。该计划强调应用核磁共振技术来获取基础数据，以帮助更好地理解和预测在地球化学、岩石学和地球物理中感兴趣的过程。核磁共振是一种特定于元素的实验技术，可以提供H、Li、B、C、O、F、Na、Mg、Al、Si、P、K等原子周围局部结构的定量数据。在晶体和非晶态溶胶和液体中，向外延伸到第二原子近邻的距离，有时甚至更远。它对相对较慢的时间尺度(几秒到纳秒)的原子运动也是唯一敏感的，特别是在扩散、相变和粘性流动等过程中。这项研究工作的一个不同寻常的能力是原位，高温核磁共振，温度高达1500摄氏度。在以前的资助下，这个项目已经产生了关于玻璃和熔体中阳离子和阴离子的配位环境，组成，温度和压力如何改变结构，以及这些变化如何影响热力学和输运性质的一系列结果。特别强调了量化液体中结构无序的程度，并将其与构型熵和粘度联系起来；晶态硅酸盐和铝硅酸盐中的相关无序问题也是高度优先的。在本供资期间，在确定铝硅酸盐玻璃和熔体中的Al-Si有序度方面取得了重大进展，包括首次使用17O“三量子”核磁共振(“3QMAS”)直接计算Al-O-Al氧的比例。独立于29Si核磁共振数据建立的有序统计热力学模型得到了这些结果的很好支持，并允许预测和与性质数据进行比较。用这种方法进行的其他研究为我们理解铝硅酸盐熔体中水溶解的复杂过程和发现沸石中严格的“铝回避”的变化做出了新的贡献。对于后者，包括“五量子”技术在内的新的核磁共振方法已经显示出显著提高的光谱分辨率。新安装的14.1Tesla光谱仪(600 MHz 1H频率)和斯坦福大学的18.8T仪器(800 MHz)大大提高了分辨率和灵敏度，这对研究微小(1-10 mg)高压样品特别有用，以确定熔体和含铝镁钙钛矿等地幔矿物的结构变化。如果这项提议得到资助，其中许多项目将继续并延长。一个特别的重点将是量化温度对熔体结构的影响，这是一个关键但知之甚少的问题，也是理解熔体性质的核心。这项工作的一个主要工具将是最近建造的快速淬火装置，它将允许在广泛的“虚构温度”范围内对熔体结构进行采样，即使是小的、昂贵的、同位素丰富的样品也是如此。此外，高温核磁共振将直接用于表征铝硅酸盐熔体中的动力学。晶态硅酸铝(包括骨架和片状硅酸盐矿物)的无序及其对骨架氧和水之间特定位置交换速率的影响的研究将继续进行。在高压玻璃方面的合作将继续下去，以探索阳离子和阴离子配位的同时变化以及记录熔体结构压力效应的不同P/T路径；关于场地占有率和上、下地幔矿物有序性/无序性的合作也将扩大。将继续开发新的核磁共振方法和技术，这些方法和技术应该在地球科学内外具有广泛的适用性。

StebbinsEAR-0104926 This proposal is for renewed funding for a program of research on atomic-scale structure and dynam-ics of crystalline, glassy, and molten silicates and oxides of interest to the Earth Sciences. This program emphasizes the application of techniques of Nuclear Magnetic Resonance (NMR) to obtain fundamental data to help better understand and predict processes of interest in geochemistry, petrology, and geophys-ics. NMR is an element-specific experimental technique that can provide quantitative data on local struc-ture around atoms such as H, Li, B, C, O, F, Na, Mg, Al, Si, P, K (etc.) in crys-talline and amorphous sol-ids and liquids, out to distances of second atom neighbors and some-times beyond. It is also uniquely sen-sitive to atomic motions at relatively slow time scales (seconds to nanoseconds), that are particularly in-teresting in processes such as diffusion, phase transitions, and viscous flow. An unusual capability of this research effort is in situ, high tempera-ture NMR to temperatures up to 1500 degrees C. Under previous funding, this project has produced a wide range of results on coordination en-vironments of both cations and anions in glasses and melts, how composition, temperature and pressure change the structure, and how these changes affect thermodynamic and transport prop-erties. In particular, quantifying the extent of structural disorder in liquids, and relating this to configurational entropy and viscosity, have been emphasized; related questions of disorder in crystalline silicates and aluminosilicates have also been of high priority. During the current funding period, significant progress has been made in determining the degree of Al-Si ordering in aluminosilicate glasses and melts, including for the first time the use of 17O "triple quantum" NMR ("3QMAS") to directly count the proportions of Al-O-Al oxygens. A statistical thermodynamic model of the ordering, formulated independently from 29Si NMR data, is well supported by these results and allows prediction and comparison with data on properties. Other studies using this method have made new contributions to our understanding of the complex process of water dis-solution in aluminosilicate melts and to detect variations from strict "aluminum avoidance" in zeolites. For the latter, new NMR methods including "five quantum" techniques have shown dramatically en-hanced spectral resolution. A newly installed 14.1 Tesla spectrometer (600 MHz 1H frequency), and ac-cess to an 18.8 T instrument at Stanford (800 MHz), have allowed dramatic improvements in resolution and sensitivity, which have been especially useful in studying tiny (1 to 10 mg) high pressure samples to determine structural changes in melts and in mantle minerals such as Al-bearing MgSiO3 perovskite. Many of these projects will continue and be extended if this proposal is funded. A particular emphasis will be on quantifying the effects of temperature on melt structure, a critical and poorly understood issue that is at the heart of understanding melt properties. A major tool in this effort will be a recently con-structed fast quench apparatus that will allow sampling of the melt structure from a wide range of "fictive temperatures", even for small, expensive, isotopically enriched samples. Further in situ, high temperature NMR will be used to characterize dynamics in aluminosilicate melts directly. Studies will continue of disorder in crystalline aluminosilicates (including framework and sheet silicate minerals), and its effects on the site-specific rates of exchange among framework oxygens and H2O. Collaborations on high pres-sure glasses will continue, to explore simultaneous changes in both cation and anion coordination and dif-ferent P/T pathways for recording pressure effects on melt structure; collaborations on site occupancy and order/disorder in upper and lower mantle minerals will also be extended. New NMR methods and tech-nologies will continue to be developed which should have a wide range of applicability both within and outside of the Earth Sciences.