Multinuclear NMR Investigations of Sol-Gel Systems
Irwin, Alan Dale
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https://hdl.handle.net/2142/70388
Description
Title
Multinuclear NMR Investigations of Sol-Gel Systems
Author(s)
Irwin, Alan Dale
Issue Date
1987
Doctoral Committee Chair(s)
Jonas, Jiri
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Abstract
The inorganic polymeric materials known as oxide glasses are normally prepared by the fusion of refractory oxides, followed by rapid cooling to avoid devitrification. A topic of current interest in materials research is the preparation of oxide glasses by the hydrolysis and polymerization of metal alkoxides in solution to form a gel, which may then be fired to form a glass. This so-called sol-gel process represents the synthesis of an inorganic polymer in a manner analogous to that in which organic polymers have traditionally been prepared.
Much work has been and continues to be done toward preparing specific materials by the sol-gel process, and toward determining the physical characteristics of sol-gel derived materials. However, there remains a great need for basic understanding of the chemistry involved. The effects of processing variables such as starting reagents, temperature, pressure, pH, etc. cannot be optimally controlled or exploited without a knowledge of the chemistry of polymer-forming metal alkoxide systems.
Recent advances in instrumentation and methods have made pulse Fourier transform nuclear magnetic resonance (NMR) spectroscopy a powerful technique for studying the chemistry of inorganic oxide systems in both the liquid and solid states. This thesis describes the application of these NMR techniques to the sol-gel systems SiO$\sb2$, B$\sb2$O$\sb3$-SiO$\sb2$, Al$\sb2$O$\sb3$-SiO$\sb2$ and Na$\sb2$O-Al$\sb2$O$\sb3$-SiO$\sb2$.
It is demonstrated that in the borosilicate system, borosiloxane bonds do not result from co-polymerization in the sol; rather they are formed during heat treatment above 150$\sp\circ$C, after water has been driven out. The degree of cross-linking in SiO$\sb2$ gels prepared under different catalytic conditions is monitored during heat treatment. While the initial gels vary greatly in their degree of cross-linking, the products after heating to 800$\sp\circ$C are very similar. In aluminosilicate gels, aluminosiloxy bonds are formed by the time of gelation, the aluminum occupying tetrahedral (AlO$\sb4$) $\sp-$ sites which are charge balanced by octahedral cationic aluminum species. The addition of sodium as a counter ion enables the octahedral aluminum to convert to (AlO$\sb4$) $\sp-$. The aluminum environment is also shown to be dependent on the type of aluminum starting alkoxide employed.
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