29Ni53Fe17Co (Kovar) is a nominal 29%Ni-17%Co-54%Fe alloy that is a well-known glass-sealing alloy suitable for sealing to hard glasses.

29Ni53Fe17Co has a nominal expansion coefficient of approximately 5 ppm/°C and inflection temperature of ~450 °C.

29Ni53Fe17Co is used for making hermetic seals with the harder Pyrex glasses and ceramic materials. This alloy has found wide application in power tubes, microwave tubes, transistors, and diodes. In integrated circuits, it is used for the flat pack and the dual-in-line package.

Chemical composition

IronFeBal. Nickel Ni28.5-29.5% CobaltumCo16.8-17.8%

Mechanical property

Alloy State Tensile Strength, N/mm²
strip 570.00
wire 585.00

Physical properties

Density (g/cm3) Melting To (oC)
8.17 1449.0

Coefficient of expansion

Alloy Linear Coefficient of Thermal Expansion ā,10-6/℃
20-200℃ 20-300℃ 20-400℃ 20-450℃ 20-500℃ 20-600℃ 20-700℃ 20-800℃
Kovar 5.9 5.3 5.1 5.3 6.2 7.8 9.2 10.2


  • optoelectronics components
  • electronic tubes (power, X-ray, …)
  • medical devices
  • satellite components