Advanced high thermal conductivity ceramics for power microwave tubes

Summary form only given. Microwave sintering approaches have been used to develop a family of AlN based composites that exhibit superior thermal conductivities and tailored dielectric losses. These materials are needed to replace toxic BeO-based composites for power microwave tube applications. Our activities concentrated on the improvement of thermal conductivity, dielectric and mechanical properties (hardness and toughness) of various aluminum nitride composites. Single phase, polycrystalline AlN with thermal conductivity up to 224 W/mK and dielectric loss of tan /spl delta/=0.01 was achieved by controlled microwave processing. The addition of controlled amounts of TiB/sub 2/ and SiC increased the dielectric losses while maintaining relatively high thermal conductivity values. These advanced AlN based composites can be used in power microwave tubes for suppression of mode competition in cavities, support helices in TWTs, and for microwave windows.