Overview of the Sol–Gel Process

The first studies on sol–gel processing have been very much focused on the possibility of obtaining bulk gels and through these glasses from a low temperature route. With the time this first idea has been almost abandoned and sol-gel inorganic chemistry has become something different. Nowadays it is an almost ubiquitous process in nano-chemistry to prepare a variety of different materials in the form of films, membranes, nanoparticles, aerogels, mesoporous and microporous materials, self-assembled materials, etc. This change of perspective has brought to an unexpected success of inorganic and hybrid sol-gel chemistry which is now a very popular tool for nanoscience. At the same time, part of the interest in the basic chemistry of the process has been lost which has also made many people unaware of the fundamental scientific background. The complexity of sol-gel chemistry represents a natural limitation to our capability of giving very detailed and fine descriptions of complex processes. In this chapter, some basic elements of sol-gel chemistry would be introduced with the purpose of giving a general overview and describing the main properties of sol-to-gel transition which is the physical-chemical phenomenon that characterizes the process.