The Improved Thermal Conductivity of a Potting Material for High-Power Fast Warm-Up Cathodes

With the increasing power, frequency, and operating life of microwave tubes, the performance and reliability of cathode heater assemblies become critical, largely influenced by thermal conductivity, electrical resistivity, and shrinkage of the materials used. This study presents the development of a potting material achieving a high thermal conductivity of 22.14 W/(m K) and a low linear shrinkage of 5.5%. The material was synthesized from two alumina powders differing in size and morphology, and aqueous slurries suitable for centrifugal casting were prepared with a solid loading of up to 70 vol.%. Centrifugal casting allowed for the production of green bodies with relative densities exceeding 70%. The sintered state achieved a maximum relative density of 86.75% without the addition of sintering aids. Comprehensive analysis of the rheological behavior of the slurries, microstructure of the potting material, thermal conductivity, and sintering shrinkage was performed. Furthermore, effective models were employed to rationalize the powder proportions in relation to thermal conductivity, showing that experimental data align with theoretical predictions under specific conditions. The findings underscore significant advancements in potting material properties for enhanced performance in high-power applications.