Chemistry and Fundamentals of the Sol-Gel Process

The Sol-Gel Handbook Synthesis, Characterization, and Applications, First Edition. 

In the following, the chemical and physical principles behind the individual steps of sol-gel processing will be discussed in more detail. 

---

Condensation of silanol species is of major industrial importance as the mechanism by which siloxane backbone polymers are formed. Mono-, di-, tri-, and tetrafunctional silanol species are all used extensively in these processes and products. As a result, many studies of condensation mechanisms have been published. Most infer primary chemistry from the condensed products obtained [8, 10, 11, 17, 23, 24, 28. 31, 57, 58], Accurate determination of rate data and mechanistic insights can provide fundamental support for these processes and others, such as sol-gel processes and treatment of mineral fillers and glass fibers with solutions of reacting silanols. 

Barsan N, Schweizer-Berberich M, Gopel W (1999) Fundamental and practical aspects in the design of nanoscaled SnOj gas sensors. A status report. Fresenius J Anal Chem 365 287-304 Belin T, Epron F (2005) Characterization methods of carbon nanotubes a review. Mater Sci Eng B 119 105-118 Brinker CJ, Scherer GW (1989) Sol-gel science the physics and chemistry of sol-gel processing. Academic, New York... 

The chemistry of the aqueous sol-gel process is quite complex due to metal and the double role of water as ligand and solvent as well as due to the large number of reaction parameters that have to be stricdy controlled (hydrolysis and condensation rate of the metal oxide precursors, pH, temperature, method of mixing, rate of oxidation, the nature and concentration of anions, etc.) in order to provide good reproducibility of the synthesis protocol. Another fundamental problem of aqueous sol-gel chemistry is that the as-synthesized precipitates are generally amorphous. The required postsynthetic annealing step to induce the crystallization process prevents any subtle control over crystal size and shape. For the preparation of bulk metal oxides, like the ceramic pigment case, these limitations play only a minor role however, in the case of nanoparticle synthesis, they constitute a major concern. 

Materials chemistry is a field of high priority internationally, in terms of both fundamental and applied science. Research contributions to the advancement of this field come from a wide range of scientists who develop the synthetic processes, perform the fundamental characterizations, and employ the materials in a wide range of applications. During recent years, sol-gel chemistry has become a major topic of research in materials science and synthesis. 

One of the separate branches that have reached a qualitatively different stage of their development are sol-gel technologies, which had come a long way from the black box method to the understanding of the chemistry of the process and the order of the major part of the stages that happen under various conditions. Even more successful were the scientists who created the so-called liquid silicon - a polysilane polymer that, under the influence of UV, transforms into polycrystalline silicon, which allows a fundamental change in the production of integrated circuits. 

---