Files in this item
|(no description provided)|
|Title:||Multinuclear NMR Investigations of Sol-Gel Systems|
|Author(s):||Irwin, Alan Dale|
|Doctoral Committee Chair(s):||Jonas, Jiri|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|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.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.
|Date Available in IDEALS:||2014-12-15|