On the changes and reactions in metal oxides under microwave irradiation

Metal oxides are the starting point to obtain many ceramic materials and the microwave heating an appropiate preparative route for their sintering or boundary joining, particularly in those cases where at least one component shows an efficient microwave energy absorption [1–4]. The microwave heating takes place via dielectric losses, through a complex process in which the electromagnetic fields of the incident radiation induce motions of electrons and ions and rotate charge systems such as dipoles. The resistance to these induced motions results in an internal volumetric heating, with a reversal thermal gradient and flow of heat compared to conventional heating methods (convection and conduction) [5, 6]. This opens the possibility of a rapid and selective heating of a component in a given mixture of phases [7, 8]. These and many other applications of the microwave heating for the preparation of metal oxides-based materials are supported in a knowledge of the microwave irradiation effects on the properties of single metal oxides. In a study in this sense we have noted that under microwave irradiation many metal oxides behave as already established, however, in some cases different or not reported results were found, which are discussed in this contribution.