NICKEl - IRON ALLOY KOVAR Composition (Nominal): NI 29; Co17; Fe Balance;) ;(A low expansion alloy which has been widely used for making hermetic seals with the harder Pyrex glass and ceramic materials such as in power tubes, microwave tubes, transistors, and diodes, as well as integrated circuits. :) (Specifications: Kovar alloy is manufactured to meet the requirements of ASTM Specification F-15.