Fernico

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Fernico is a group of several slightly different alloys made of iron (Fe), nickel (Ni) and cobalt (Co), which have a similar low thermal expansion as the technically used borosilicate glass over a wide temperature range. Fernico is used, among other things, to make the electrical connections in the evacuated glass bulbs of electron tubes . If metals with a significantly different thermal expansion behavior are used, temperature changes in the boundary area between the metallic leadthrough and the glass body would otherwise lead to cracks and thus an undesired entry of air into the electron tube.

Electron tube base with electrical contacts. The bushings for the contact pins through the glass bottom of the tube are made of Fernico.

The name Fernico represents the chemical names of the alloy components except for the letter "R" and was originally a brand name of the General Electric Company .

Two forms of this alloy are used, the weight percentages of the alloys are as follows:

Type Fe Ni Co
FerNiCo I 53.8% 29% 17%
FerNiCo II 54% 28% 18%

Both alloys have a similar coefficient of thermal expansion of approx. 5  ppm and also have permanent magnetic properties. However, due to better alternatives, they are rarely used as permanent magnet material.

FerNiCo I is also known as Kovar . In addition, there are other special alloys with a similar range of application as Cunife , which are based on copper as the main component and nickel and iron .

history

In the USA, the researcher Albert W. Hull developed an alloy of iron (Fe), nickel (Ni) and cobalt (Co) with a very low thermal expansion in early 1930 . It was required to be able to lead the metal connections of tubes through glass without the risk of breakage when exposed to thermal stress. He named this alloy Fernico using the abbreviations of the alloy metals. Further research into the material at General Electric Company then discovered that Fernico possessed certain soft magnetic properties. It was then also used as a magnetic core for inductors .

literature

  • Karl Jousten (Hrsg.): Wutz manual vacuum technology . 11th edition. Vieweg + Teubner, 2012, ISBN 978-3-8348-1745-7 .

Individual evidence

  1. ^ S. Okamura: History of Electron Tubes . IOS Press, 1995, ISBN 978-90-5199-145-1 , pp. 114-115 .
  2. ↑ a b Sealing of Glass to Other Materials. Retrieved June 1, 2013 .
  3. ^ Albert Wallace Hull, 1880-1966, A Biographical Memoir by CG Suits and JM Laffert, Copyright 1970 National Academy of Sciences Washington DC PDF