A modified method for producing carbon-loaded vacuum-compatible microwave absorbers from a porous ceramic

The well-established procedure for producing microwave absorbers by carbon loading a porous ceramic has been modified to enhance the cleanliness of the final product and to improve the controllability of the loss tangent. The changes include soaking the ceramics in an acid bath to leach out undesirable metal oxides and a multiple-step carbonization using both carbon dioxide and hydrogen firings. These modifications allow the use of an aluminum silicate material known as Aremcolox 502-1100 as a starting material for absorbers in critical applications, such as a system with an osmium-coated dispenser cathode. The processing steps are described in detail and their relevance to the development of a high-peak power X-band gyroklystron is discussed. Representative values of the complex dielectric constants at 9.9 GHz for various carbon contents are presented