Kovar® Alloy Supply

Kovar ® is an iron-nickel-cobalt alloy, using 29% nickel. Kovar ® is a light gray, controlled expansion alloy with a dull or lustrous finish. Kovar ® has an extremely low coefficient of thermal expansion, that is very close to hard glass such as Pyrex and therefore perfect for the application of glass to metal hermetic seals. Chemically, it bonds to glass with oxides of nickel and cobalt. Cobalt makes the oxide layer easier to melt and dissolve in molten glass. Kovar ® is one of the most popular controlled expansion alloys as it is not porous.

Source: https://vulcanmetalgroup.com/kovar/