Paramagnetic interactions in nuclear magnetic resonance spectroscopy of geologic materials
Abstract/Contents
- Abstract
- This thesis documents the findings and results of our work toward the application of solid-state Nuclear Magnetic Resonance (NMR) spectroscopy to geological materials containing paramagnetic species. Commonly encountered and geologically important paramagnetic species include ions of most of the transition metals and the rare earth elements that have unpaired electrons and will be magnetized in the presence of an external magnetic field. Interactions between the magnetic moments of the paramagnetic ion and the NMR nucleus have important implications for the NMR experiment. Early studies, especially those conducted in the first decade after the wide acceptance of Magic-Angle Spinning NMR (MAS-NMR), pointed out that even modest concentrations of a paramagnetic ion in natural minerals, such as a few % Fe in a feldspar, could cause signal loss and low signal to noise, peak broadening, and "smearing" of the intensity from the isotropic peak to the spinning sidebands with resultant loss of information about chemical shift anisotropy. This early work prompted most solid-state NMR spectroscopists studying geological materials to work almost solely on synthetic non-paramagnetic materials. However, in this work, the argument is advanced that in many cases, valuable structural information can be obtained for paramagnetic geological materials, especially information concerning short-range ordering in solid solutions that cannot be determined using more traditional long-range diffraction techniques. The first two studies presented herein document the presence of distinct paramagnetically shifted NMR resonances in the 27Al and 29Si NMR spectra of two Dora Maira pyrope garnets and in the 31P NMR spectra of a suite of REE3+-bearing synthetic monazite (LaPO4) and xenotime (YPO4). By comparing the number of these peaks and their positions and intensities to the known crystal structures of these materials, peak assignments can be made to specific geometric configurations of the NMR-active atom and the paramagnetic species. Higher quality data for REE3+-beearing synthetic monazite and xenotime are presented later using homogeneous flux-grown material. Peaks related to 31P having more than one neighboring paramagnetic REE3+ are observed and their relative intensities provide evidence of random distributions of cation species in these solid solutions. Additionally, a study is presented on Fe- and Al-bearing MgSiO3 perovskite, an important lower mantle phase. The magnitude of 27Al and 29Si NMR signal loss compared to the concentration of Fe in these materials provides strong evidence of short-range ordering of charge-balancing Fe3+ and Al3+.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2014 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Palke, Aaron Craig |
|---|---|
| Associated with | Stanford University, Department of Geological and Environmental Sciences. |
| Primary advisor | Stebbins, Jonathan Farwell |
| Thesis advisor | Stebbins, Jonathan Farwell |
| Thesis advisor | Brown, G. E. (Gordon E.), Jr |
| Thesis advisor | Mao, Wendy (Wendy Li-wen) |
| Advisor | Brown, G. E. (Gordon E.), Jr |
| Advisor | Mao, Wendy (Wendy Li-wen) |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Aaron Craig Palke. |
|---|---|
| Note | Submitted to the Department of Geological and Environmental Sciences. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2014. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2014 by Aaron Palke
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