Synthetic Mica Investigations: I, A Hot‐Pressed Machinable Ceramic Dielectric

Abstract

A new ceramic composed entirely of synthetic fluorine mica manufactured by the hot‐pressing technique is described. Its chemical, physical, and electrical properties are given. As the extensive isomorphism possible in the mica structure permits the variation and control of properties over a wide range, the characteristics of several different synthetic mica compositions are included. Hot‐pressed mica is soft (2+ to 4+, Mohs' scale) and machinable, yet has a transverse strength of more than 8000 lb. per sq. in. As an electrical insulator, it compares with fused silica and ultra‐low‐loss steatite. With a rise in temperature, the dielectric constant remains essentially unchanged up to 300°C.; some synthetic mica compositions show an increase of less than 3% when they are heated to 400°C. The power factor of several synthetic mica compositions remains less than 2% at 400°C., being 0.05% at room temperature.