KOVAR A/C & HEATING
the free encyclopedia Nickel–cobalt ferrous alloy For other uses · inc. · Delaware [ · 1 ] · ) is a nickel – cobalt ferrous alloy compositionally identical to Fernico 1 · ppm /K between 30 and 200  · to ≈ 10  · ppm/K at 800  · and conductors entering glass envelopes of electronic parts such as vacuum tubes (valves) · X-ray and microwave tubes and some lightbulbs . [ · citation needed ] · Kovar was invented to meet the need for a reliable glass-to-metal seal · which is required in electronic devices such as light bulbs · vacuum tubes · cathode-ray tubes · Kovar not only has thermal expansion similar to glass · but its nonlinear thermal expansion curve can often be made to match a glass · thus allowing the joint to tolerate a wide temperature range. Chemically · grey-blue or grey-brown color indicates a good seal. A metallic color indicates lack of oxide · while black color indicates overly oxidized metal
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1, designed to have substantially the same thermal expansion characteristics as borosilicate glass (≈ 5  ppm /K between 30 and 200 °C , to ≈ 10 ppm/K at 800 °C) to 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 electronic parts such as vacuum tubes (valves), X-ray and microwave tubes and some lightbulbs . [ citation neede
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