Advanced ceramics for microwave tubes

The search for advanced, high performance ceramics for microwave tubes with improved thermal and electrical properties brought about an increased interest in novel processing and characterization techniques. AlN-SiC composites are being studied as possible replacement materials for BeO and BeO-SiC composites currently used in microwave tubes. Such a replacement is needed because beryllium based powders are toxic and long term carcinogenic. Although the dielectric properties of AlN-SiC can be made to closely match the dielectric properties of BeO-SiC, the AlN based system is not yet a suitable substitute when high thermal conductivity is required. Our work is focused on (a) microwave processing of AlN and AlN-SiC composites, and (b) material characterization in order to discover the relationships that link the microstructure, constitution and processing history with the resultant material properties. Microwave-processing techniques suitable for AlN and AlN-SiC composites, as well as ultra rapid (4800 /spl deg/C/min) microwave processing, will be discussed. Dielectric, thermal and microstructure characterization techniques will be also described.