Enhancement of Diffusion, Densification and Solid-State Reactions in Dielectric Materials Due to Interfacial Interaction of Microwave Radiation: Theory and Experiment

A detailed theoretical model and experimental study are presented that formulate and prove the existence of a robust ponderomotive force (PMF) near the interfaces in a granular dielectric material under microwave radiation. The model calculations show that the net direction of the PMF is pore angle-dependent. For most of the pore angles, the net force is towards the interface creating a mass transport that fills the interfacial pores and facilitates densification. For small ranges of angles, near 180o and 360o, PMF drives the ions in the reverse direction and depletes the pores. However, the net force for such ranges of angles is small. The PMF also enhances the diffusion of the mobile ionic species and, consequently, accelerates the solid-state reaction by increasing the collision probability. The proof-of-concept experiments show that a mixture of elemental powders can diffuse, react, and form dense materials when radiated by the microwave in just a few minutes. Such characteristics, together with field-induced decrystallization, offer a novel and simple approach for the synthesis of nanostructured compounds, which can have practical implications in ceramic technologies and thermoelectric materials.