Microwave heating of materials: From polar liquid to metal oxides

Energy efficient and environment-friendly heating and processing of materials have been made possible with the use of microwaves. Some materials are heated by absorbing the electric field energy of microwaves, and others by their magnetic field energy [1]. In series of our studies under the MEXT Tokutei Ryoiki Project [2], we are investigating the heating mechanisms of water (polar liquid) [3] and metallic oxide powders (solid). We have shown theoretically using molecular dynamics simulations that the heating mechanism certainly depends on materials: water is heated by electric field and metallic oxides by magnetic field. For the study of the former process, an explicit water model (Fig.1) is used, which has proven that water heating is due to rotational excitation of water molecules and irreversible energy transfer to translational energy by molecular collisions (Fig.2); crystal ice is not heated because of a strong hydrogen-bonded network. The latter heating can be explained by interactions between the microwave magnetic field and electronic spins of metallic atoms. References: [1] Peelamedu,R.D., Fleming,M., Agrawal, D.K., and Roy,R., Preparation of titaniu