Kovar is a Nickel-Cobalt ferrous alloy invented to meet the need for a reliable glass-to-metal seal required in electronic devices. Its temperature coefficient and thermal expansion characteristics are similar to borosilicate glass, and allow a tight mechanical joint between the two materials over a range of temperatures.
It finds application in glass-to-metal seals in scientific apparatus, and conductors entering glass envelopes of electronics parts such as vacuum tubes (valves), X-ray and microwave tubes, and some light bulbs.
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Characteristics of Kovar:
Kovar is magnetic at any temperature under the Curie point (435°C or 815°F). Other characteristics include:
- Low thermal expansion
- Melting point of 1,450°C
- Thermal conductivity of 17.3 W/m • k
- Tensile strength of 75,000 psi
- Yield strength of 50,000 psi
Kovar Chemical Etching Applications:
Kovar is designed to have the same thermal expansion characteristics as boroscilicate glass to allow tight mechanical joint between the two materials over a wide temperature range. Common applications include:
- Metal parts bonded to hard glass envelopes
- Power tubes for electronics
- X-ray tubes for medical equipment
- Telecommunication components
- Has thermal expansion like glass and its nonlinear thermal expansion curve can often be made to match a glass, thus allowing the joint to tolerate a wide temperature range
- Chemical composition is controlled within narrow limits to assure precise uniform thermal expansion properties
- Kovar alloy is magnetic at all temperatures below the Curie point