Wikipedia's definition of a microwave oven is as follows: A microwave oven is a household appliance used primarily for the rapid heating of food, by stirring the water molecules it contains under the effect of microwave radiation. But while this technology was initially used mainly in the kitchen, and eventually in very specific industrial applications, for the past twenty years or so microwave ovens have been widely used in chemistry laboratories to activate chemical reactions, and also to prepare so-called "advanced materials" of great interest in new technologies. What initially seemed like a revolution in synthetic chemistry is now finding a wide range of applications in laboratories, and these methods are becoming increasingly popular, not only in the laboratory but also in industrial processes. Microwave activation is currently used in a wide variety of fields, from supported-phase organic synthesis to the preparation of functional nanomaterials. The main advantage is that microwave-assisted reactions significantly reduce reaction times. Yields are improved and, occasionally, the selectivity of certain manufacturing processes is positively influenced by this technology.
With its considerable time and energy savings, the application of microwaves to activate chemical reactions can be considered part of "green chemistry". This becomes even more obvious when we avoid the use of organic solvents, which are always expensive, toxic, polluting and dangerous. This is the case with so-called "dry-phase" synthesis reactions, i.e. in the absence of the usual solvents. The organic reagent permeates the inorganic solid, which acts as a sort of solvent.
To fully understand the mechanisms of microwave action, we first need to consider the fundamental concepts and interaction of electromagnetic waves with matter, particularly polar substances. Firstly, the decisive importance of microwave absorption by water molecules, followed by their energetic transformation into molecular rotational movements and subsequent heating of the water molecules' immediate environment. Applications are known not only in the organic synthesis chemistry processes already mentioned, but also in inorganic synthesis, and especially in the preparation of ceramic materials, solid-state reactions, hydrothermal synthesis and so on. These applications will be illustrated with selected examples. The polymerization of various types of monomer and the preparation of functional and structural composites, as well as the microwave-assisted manufacture of other advanced materials, will also be the subject of this presentation.
