Preparation of sintered alumina and boron nitride with low loss high temperature dielectric properties

Available data on inorganic dielectrics indicate that Al₂O₃ and BN have better electrical properties than most other materials at high temperatures, even though measurements were made on samples of ordinary purity. It is also significant that improvements made in the quality of single crystal sapphire in recent years have resulted in increasingly better electrical properties. These facts prompted the investigation of highly purified Al₂O₃ and BN. This project involved not only the synthesis of these materials in as high purity as possible, but also their fabrication into a form suitable for making electrical measurements. It is with the latter process and how it affects the electrical properties that much of this paper is concerned. Electrical measurements, tan γ (60-0⁵ cy/sec.), resistivity (500 V d-c), and dielectric constant were made at temperatures from 100° to 500°C. The specimens used for making these measurements were two-inch sintered discs, approximately .03 inch thick.