Files in this item
|(no description provided)|
|Title:||High-Resolution Solid-State Silicon-29 Nuclear Magnetic Resonance Studies of Minerals and Glasses (Nmr, Aluminum, Silicates, Structure)|
|Author(s):||Smith, Karen Ann|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||High-resolution silicon-29 magic-angle sample spinning studies of minerals and glasses are a useful tool in the effort to understand more about mineral and glass structure.
Over one hundred mineral and glass samples were studied, including representatives from all polymerization types. Paramagnetic impurities were found to broaden peaks, and cause apparent chemical shift anistropy (CSA). The results for silicates in general include: some overlap between the chemical shift ranges for different polymerizations, a wide range of CSAs and asymmetry parameters ((eta)), which are related to symmetry and structure, and silicon-29 chemical shift is affected by both tetrahedral and octhedral aluminum.
Three correlations between silicon-29 chemical shift and crystal structure are presented. The correlation between silicon-29 chemical shift and Si-O bond distances is generally quite poor, while the correlations between chemical shift and the total (Brown and Shannon) cation-oxygen bond strength sum is much better. For individual polymerizations a good correlation can be found between the chemical shift and sec <TOT. However, on a global scale, the bond strength correlation is better.
For phyllosilicates, in addition to the results presented above, evidence was found of Al/Si disorder in the tetrahedral sites of most of the samples studied. In feldspar silicates the Al/Si order/disorder and exsolution effects were readily observed. Albite and microcline were found to be completely ordered, while sanidine was completely Al/Si disordered. The spectra of the intermediate plagioclases exhibited narrow peaks from the volumes of different endmembers, although much of the signal intensity is attributed to the strained sites between volumes.
The spectra of glasses in the CaO-MgO-SiO(,2) region were generally broad and featureless, implying a virtual continuum of sites with slightly different Si-O bond lengths and Si-O-Si bond angles. However, by comparing the peak breadths against that of SiO(,2) glass (which must contain only tectosilicates), estimates of the types of polymerizations in the glass could be found. For the diopside-Cats glass system both silicon-29 and aluminum-27 spectra were run. The silicon-29 and aluminum-27 spectra of the glasses were again broad and featureless. The aluminum chemical shifts were in the range for tetrahedral aluminum. No signal was seen from octahedral aluminum.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
|Date Available in IDEALS:||2014-12-15|