Widmanstätten structure
As Widmanstatten structures predominantly in are meteoritic detectable material characteristic structures referred to, which are visible when iron meteorites the type octahedrite sanded, polished, and with methanolhaltiger nitric acid to be etched. The explanation for this appearance is the different chemical resistance of the nickel - iron - minerals Kamacite and taenite . While the Ni-poor kamacite is more strongly attacked and dissolved, the Ni-rich taenite crystals remain. Widmanstätten structures also appear in other areas of metallurgy , for example in steels, titanium and zirconium alloys.
The structure arises in the initially homogeneous iron-nickel alloy made of taenite with very slow cooling (1 to 100 Kelvin per million years) between 700 and 450 ° C in the solid state through crystallization of the kamacite along certain surfaces specified in the crystal structure of the taenite. This is how Kamacit panels are created that are arranged like the surfaces of an octahedron. In between, gusset and ribbon-shaped remains of taenite remain. The long cooling times make it understandable why these structures cannot be reproduced on earth and are therefore a distinguishing feature of meteoritic iron. Only on a much smaller scale, so that they can only be observed under a microscope, similar structures also arise in carbon steel when heated to near the melting point as a so-called Widmanstätten structure.
The structures were named by Karl Franz Anton von Schreibers after the Austrian natural scientist Alois von Beckh-Widmanstätten (1754–1849). Widmanstätten discovered the structure in Vienna in 1808 on an etched surface of the iron meteorite of Hraschina, but this was not published until 1820 by Schreibers. The English chemist William (or Guglielmo) Thomson (not to be confused with William Thomson , Lord Kelvin), who lives in Italy, described the structure as early as 1804. He treated a metallic piece of the Krasnoyarsk pallasite with acid to remove rust, thus developing the structure.
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Individual evidence
- ↑ Dominic Phelan, Rian Dippenaar: Widmanstätten Ferrite Plate Formation in Low-Carbon Steels, Metallurgical and Materials Transactions A, volume 35A, December 2004, p. 3701.
- ^ F. Heide, F. Wlotzka, Meteorites, Messengers from Space. Springer-Verlag 1995
- ^ Case on May 26, 1751 in Hrašćina near Zagreb ; see website of the Natural History Museum Vienna
- ^ Carl von Schreiber: Contributions to the history and knowledge of meteoric stone and metal masses. JGHeubner, Vienna 1820.
- ^ Guglielmo (William) Thomson (1804) Essai sur le fer malléable trouvé en Sibérie par le Prof. Pallas. Bibliothèque Britannique 27, 135.
- ^ FA Paneth: The discovery and earliest reproduction of the Widmanstätten structure. Geochimica et Comochimica Acta 18 (1960) 176