Widmanstätten pattern

As Widmanstatten structures only in meteoritic material detectable characteristic structures are called, which are visible when iron meteorites sanded the type octahedrite, polished and etched with nitric acid methanolhaltiger. The explanation lies in the different resistance of the nickel-iron minerals kamacite and taenite. While the Ni - poor kamacite is stronger attacked and dissolved, the Ni-rich Taenitkristalle stop.

The structure is formed in the first homogeneous iron-nickel alloy of Taenite at very slow cooling (1 to 100 degrees per million years) 700-450 ° C in the solid state crystallization of the Kamacits along particular in the crystal structure of the predetermined Taenits surfaces. This results in plates kamacite arranged as the surfaces of an octahedron. In between gore and ribbon-like leftovers from taenite remain. The long cooling times make it understandable why these structures on Earth can not be imitated and therefore are distinctive of meteoritic iron. Only on a much smaller scale, so that they can only be observed in the microscope, caused similar structure in carbon steel when heated to near the melting point of a so-called Widmanstatten structure.

Were named the structures of Karl Franz Anton von Schreiber after the Austrian scientist Alois of Beckh Widmanstätten - ( 1754-1849 ). Widmanstatten discovered the structure in 1808 in Vienna at an etched surface of the iron meteorites Hraschina became, it was published but it was only in 1820 by the writer. Regardless of living in Italy, English chemist William ( or Guglielmo ) Thomson (not to be confused with William Thomson, Lord Kelvin ) described the structure 1804. He treated a metallic piece of the pallasite Krasnoyarsk with acid to remove rust, and so developed the structure.