Kovar

    Kovar is an iron-nickel-cobalt alloy, which is the most commonly used alloy in the glass-to-metal hermetic sealing of vacuum connectors. Its expansion coefficient matches with several kinds of hard glass and ceramics. Kovar glass seals can be baked to 460°C. A typical Kovar alloy contains 53% Fe, 29% Ni, 17% Co, less than 0.5% Mn, 0.2% Si, and a total of less than 0.25% Al, Mg, Zr and Ti.

     The cobalt in Kovar can form fusible oxides when the alloy is heated, which is beneficial for coating glass or ceramics on metals. Kovar can be brazed and welded with soft solder or hard solder, and can also be molded or cut after annealing. The commonly used welding method in vacuum technology is copper brazing in the H₂ furnace.

     Although Kovar has good corrosion resistance, it is still inferior to stainless steel, so it should be stored in a dry place. Kovar does not react with mercury and mercury vapor. Kovar alloy has ferromagnetism below 453°C (its Curie point), and its magnetic susceptibility is a function of the magnetic field. When the magnetic field increases to 7000G, the magnetic susceptibility reaches the maximum value of 3700G^-1, and then drops again.

(Huiputech)