Microwave systems for the processing of advanced ceramics

Microwave processing systems are continually evolving to incorporate more unique capabilities and design features. These new developments are instrumental in expanding the scope of microwave systems for studying complex phenomena in materials synthesis and processing. On a more fundamental level, questions concerning the nature of interactions between microwaves and ceramic materials systems can be addressed to provide direct impact on processing strategies for advanced ceramic materials. A novel microwave processing system is being developed to study fundamental issues in the sintering of advanced ceramic materials with enhanced dielectric, thermal, optical, and mechanical properties for applications in microelectronics, biomaterials, and structural applications. The system consists of a single and dual frequency microwave furnace that operates at 2.45 and 28 GHz, an optical pyrometric temperature measuring system, and an optical, non-invasive, non-contact, extensometer for measuring sintering shrinkage and kinetics. The additional ability to process at 28 GHz provides opportunities to sinter a wider range of ceramic materials by direct coupling. An even more exciting benefit of the dual frequency system is the potential to process ceramics at two frequencies simultaneously. This capability can provide a unique way to tailor the microstructure of advanced ceramics by controlling the extent of both volumetric and surface heating. Experimental results for microwave sintering studies involving ZnO, hydroxyapatite, AlN-SiC composites, and alumina composites will be presented, with an emphasis on the processing of nanograin ceramics. In particular, the role of surface modification and microwave field intensification effects will be discussed.