| This thesis presents the results of modeling, characterization and application of microwave energy to ceramic processing. Microwave processing of materials provides several advantages that in many cases help improve product quality, uniformity of grain structure, and yield. The ability of the microwave energy to penetrate and, hence, heat from within the product, helps reduce processing time, costs, and in some cases reduce the sintering temperature. There is also some evidence that microwave processing of materials actually provides improved microstructure and other properties. Microwave processing of ceramics makes it possible to remove water, binders, and sintering without rupture or cracking, reduce internal stress, lower thermal gradients, and control the state of oxide. However, microwave heating of material and sintering of ceramics is a complex process that is not understood completely and there are many remaining problems that still need to be solved before this new technique can be transferred from the research laboratory to actual industrial use.;The basic equations describing the interactions of ceramics with electromagnetic fields are derived first. Modeling the green ceramic during microwave sintering as a deformable dielectric, a continuum mechanics model is used to describe the interaction of electromagnetic waves with the deformable thermoelastic body. Combined with the thermal and mass diffusion equations into the consideration, such a description is unique, efficient and complete in modeling microwave processing macroscopically. A further application of this theory would enable the prediction of the stress fields generated in the ceramic body if temperature gradients occur. Using those equations, microwave heating of ceramics is modeled. The Finite Difference Time Domain (FDTD) method is also used to simulate heating of ceramics in a single mode cavity and analyze the insulation scheme. To further understand microwave sintering and heating of ceramics, an experimental study using a single mode high power microwave heating device was conducted. This device makes it possible to simultaneously heat and sinter ceramics and characterize the process with the same source. In this experimental work, a ceramic rod in the microwave cavity is modeled by an equivalent T network. The reflection caused by the ceramic rod, coupling aperture and variable short is measured by a modified reflectometer attached to the transmission line. The dielectric property of the ceramic rod is the function of the measured reflection coefficient. An inversion technique would allow for retrieving corresponding dielectric properties of the ceramics during heating or sintering. The ceramic rod samples are either a densified product obtained commercially or a green coupon obtained through an extrusion process. The single mode high power microwave cavity was also used in the ceramic processing. |
