Microwave-Induced Attractive Force Between Dielectric Spheres-A Potential Non-Thermal Effect in Microwave Sintering

We present a detailed analysis of the polarization-charge buildup and electric-field intensification between two dielectric spheres under microwave radiation, with an emphasis on the resulting attractive force between the spheres. The study is motivated by an outstanding issue in microwave sintering of powder compacts. Microwave processing generally requires a substantially lower temperature than in a conventional furnace. This suggests some physical effects in the wave-powder interactions aside from the rapid volumetric heat deposition. The understanding of these effects is of importance to the full realization of this promising technology. Thermally activated particle bonding and inter-particle neck growth are key densification processes in both conventional and microwave sintering. The present study shows that the attractive force is intrinsic to the latter method. The force density and total force are derived in analytical forms and numerically evaluated. Results show that their strength is significant enough to play a constructive role in particle bonding and neck growth.

Keywords: Microwave; Dielectric material sintering; Induced polarization charges; Gap electric field intensification; Attractive electric force