Silicate and aluminosilicate materials make up most of the minerals, rocks, and magmas that are at the center of geological processes. Particularly for those processes that take place at the high pressures and temperatures of the Earth's interior (and thus that are hard to observe directly), our ability to interpret what has happened in past Earth history from the geological record, and thus to predict what might take place in the future (for example, when and how volcanoes erupt), depends on a fundamental understanding of how the atomic-scale structure controls material behavior. This research program focuses on measuring this structure for synthetic, somewhat simplified analogs of solid and molten minerals and their glassy equivalents, to provide input for more accurate modeling of critical properties such as density, viscosity, heat capacity, and energy. In particular, the structures of disordered materials, which cannot be readily addressed by other, more conventional methods, are studied using Nuclear Magnetic Resonance (NMR) spectroscopy.
NMR is uniquely capable for quantifying the short- to intermediate-range structures of crystalline minerals that contain certain common types of structural disorder, and of molten materials and the glasses produced by rapid cooling of melts. This method will be the primary research tool in this program. Among the structural questions that will be addressed include the critical, but still poorly known, effects of temperature and pressure on the arrangements of atoms around, and distances between, such ions as silicon, aluminum, oxygen, sodium, calcium and magnesium, which are among the predominant constituents of natural minerals and magmas. The increase of disorder among these ions, which is the primary effect of the very high temperatures of volcanic processes, and their increasingly dense packing at the enormous pressures of the Earth's interior, will be measured. The results will be analyzed in terms of structural models for their bulk physical properties, which in term are needed to predict geological processes. New methods for structural studies, using NMR in materials containing magnetic ions such as iron and rare earth elements, will be developed. These studies will be important not only for geological materials, but also for ceramic and glass materials that are critical to a number of advanced technologies, including fuel cells, optical data fibers and substrates for computer screens and solar cells. Results from this project should lead to significant improvements in our fundamental understanding of many types of silicate materials, as well as to the development of new methods for their analysis.
