Valve metal

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A valve metal is a metal that, through anodic oxidation, forms a layer of metal oxide that is electrically non-conductive .

For example, in aqueous electrolyte, when a positive direct voltage is applied, aluminum oxidizes to Al 2 O 3 , tantalum to Ta 2 O 5 , niobium to Nb 2 O 5 or zirconium to ZrO 2 . This effect, discovered by Eugène Ducretet in 1875 , is used in electrolytic capacitors and electrolytic rectifiers . The name goes back to the now outdated term "valve" for rectifier .

literature

  • Eugène Ducretet: Note sur un rhéotome liquide à direction constante, fondé sur une propriété nouvelle de l'aluminium. In: J. Phys. Theor. Appl., 1875 (4), 1, pp. 84-85.
  • Ekbert Hering, Klaus Bressler, Jürgen Gutekunst: Electronics for engineers and natural scientists . Springer, 2014, ISBN 978-3-642-05499-0 , pp. 124 ( Google Books ).
  • An example of the use of the term 'valve' in the electrotechnical context: Adolf Güntherschulze: Electrical rectifiers and valves . Springer-Verlag Berlin Heidelberg, 1924, ISBN 978-3-662-40917-6 , doi : 10.1007 / 978-3-662-41401-9 (English translation is online at [1] ).