ABSTRACT. Microwave sintering is a complex process combining the propagation and absorption of electromagnetic waves in the ceramic material, heat transport within the geometric body, and densification. The heating behavior is a result of a dynamic balance between the rate of electromagnetic energy absorbed within the bulk of the material being processed and the radiated energy loss from its surface. Therefore, knowledge of the evolution of the dielectric and thermal properties is critical to the development of microwave processing of advanced structural and functional ceramics.

Although the sintering process is well understood qualitatively, the database concerning the evolution of properties during sintering is often inadequate. Both the intrinsic physical properties and the relationship between the microstructure and the physical properties are not well known for many ceramics and composites of practical interest. To properly address these issues there is a need to better understand how the microstructure of a compacted powder system evolves during sintering. In this presentation we shall show that the thermal and dielectric properties of ceramic materials can be calculated using the same method. In addition, the practical implications of those properties on microwave sintering at very high heating rates (> 1000^oC/min), processing of nano-powders, maintaining temperature and density uniformity in bodies of complex geometry, and processing of multi-component composites will be discussed.

This work was supported by the Office of Naval Research/Naval Research Laboratory, and in part by the Air Force Office of Scientific Research, Ceramics and Materials Program.

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