The evaluation of mica for use in electron tubes

An important aspect of electron tube fabrication is quality control over the component tube parts. An investigation of the electrical, physical and gas desorption-adsorption properties of mica has been conducted. The data show no general relations among these properties; the measurement of any one property is thus inadequate as a test procedure. Studies have been carried out on gas desorption by mica in order to determine which processing procedures degas the mica most thoroughly. Vacuum outgassing as a function of time and temperature and bakeout procedures were the main processing variables studied. It has been determined that micas used in electron tubes can be vacuum outgassed so as to reduce the gas potential to one-tenth that of micas treated in a more conventional manner. It has been found that well-outgassed micas show gettering characteristics. By gas adsorption techniques, a study of the gettering property of mica has been carried out using those gases usually present in electron tubes.