Localized Dielectric Sintering With Magnetron for Microwave Material Processing

Abstract

The process of sintering occurs when enough heating energy is applied on the particles of precursor powders to coalesce together and form a solid material without melting. Solidification takes place through cross mass diffusion along common interfaces and this technique has been used extensively by the materials processing community for ceramic part manufacturing. However, in most cases, furnaces are being used to elevate the temperature of material powder precursors globally throughout the entire volume of the intended parts. Instead of this approach, the present work explores the feasibility of using localized heating induced by coherent microwave radiation. Microwave-based material processing involves coupling between thermal and electromagnetic physics where the microwave radiation heats the sample locally via volumetrically tailored heat fluxes. However, changes in temperature change the dielectric properties of the sample, which then in turn affect microwave propagation. The nonlinearity introduced by the temperature dependence of the material properties into the relevant partial differential equations of this coupled system is further complicated by poorly defined dielectric, thermal, and thermo-electric properties of the dielectric precursor powders at temperatures required for sintering. This work focuses on analyzing a TE106 2.45 GHz microwave cavity used for processing BaTiO3, or BTO, precursor powder. Both a physical and a virtual experiment were carried out in tandem to understand the microwave propagation and dielectric property evolution with respect to temperature. It was demonstrated that appropriate tuning of the material properties (i.e., density, specific heat, heat conductivity, dielectric permittivity and loss tangent) relative to temperature enabled localized heating predicted by our model to match that of the physical experiment.