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Widmanstätten pattern
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Widmanstätten pattern
A Widmanstätten pattern /ˈvɪdmɑːnˌʃteɪtɪn/ (VID-man-shtay-tin), also known as a Thomson structure, is a figure of long phases of nickel–iron, found in the octahedrite shapes of iron meteorite crystals and some pallasites.
Iron meteorites are very often formed from a single crystal of iron-nickel alloy, or sometimes several large crystals that may be many meters in size, and often lack any discernible crystal boundary on the surface. Large crystals are scarce in metals, and in meteors they occur from extremely slow cooling from a molten state in the vacuum of space when the Solar System first formed. Once in the solid state, the slow cooling then allows the solid solution to precipitate a separate phase that grows within the crystal lattice, which forms at particular angles that are determined by the lattice. In meteors, these interstitial defects can grow large enough to fill the entire crystal with needle or ribbon-like structures easily visible to the naked eye, almost entirely consuming the original lattice. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellae. Commonly, in gaps between the lamellae, a fine-grained mixture of kamacite and taenite called plessite can be found.
Widmanstätten structures describe analogous features in modern steels, titanium, and zirconium alloys, but are usually microscopic.
In 1808, these figures were observed by Count Alois von Beckh Widmanstätten, the director of the Imperial Porcelain works in Vienna. While flame heating iron meteorites, Widmanstätten noticed color and luster zone differentiation as the various iron alloys oxidized at different rates. He did not publish his findings, claiming them only via oral communication with his colleagues. The discovery was acknowledged by Carl von Schreibers, director of the Vienna Mineral and Zoology Cabinet, who named the structure after Widmanstätten. However, it is now believed that the discovery of the metal crystal pattern should be assigned to the English mineralogist William (Guglielmo) Thomson, as he published the same findings four years earlier.
Working in Naples in 1804, Thomson treated a Krasnojarsk meteorite with nitric acid to remove the dull patina caused by oxidation. Shortly after the acid made contact with the metal, strange figures appeared on the surface, which he detailed as described above. Civil wars and political instability in southern Italy made it difficult for Thomson to maintain contact with his colleagues in England. This was demonstrated in his loss of important correspondence when its carrier was murdered. As a result, in 1804, his findings were only published in French in the Bibliothèque Britannique. At the beginning of 1806, Napoleon invaded the Kingdom of Naples and Thomson was forced to flee to Sicily and in November of that year, he died in Palermo at the age of 46. In 1808, Thomson's work was again published posthumously in Italian (translated from the original English manuscript) in Atti dell'Accademia Delle Scienze di Siena. The Napoleonic wars obstructed Thomson's contacts with the scientific community and his travels across Europe, in addition to his early death, obscured his contributions for many years.
The most common names for these figures are Widmanstätten pattern and Widmanstätten structure; however, there are some spelling variations:
Due to the discovery priority of G. Thomson, several authors suggested calling these figures Thomson structure or Thomson-Widmanstätten structure.
The formation of Ni-poor kamacite proceeds by diffusion of Ni in the solid alloy at temperatures between 450 and 700 °C, and can only take place during very slow cooling, about 100 to 10,000 °C/Myr, with total cooling times of 10 Myr or less. This explains why this structure cannot be reproduced in the laboratory.
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Widmanstätten pattern
A Widmanstätten pattern /ˈvɪdmɑːnˌʃteɪtɪn/ (VID-man-shtay-tin), also known as a Thomson structure, is a figure of long phases of nickel–iron, found in the octahedrite shapes of iron meteorite crystals and some pallasites.
Iron meteorites are very often formed from a single crystal of iron-nickel alloy, or sometimes several large crystals that may be many meters in size, and often lack any discernible crystal boundary on the surface. Large crystals are scarce in metals, and in meteors they occur from extremely slow cooling from a molten state in the vacuum of space when the Solar System first formed. Once in the solid state, the slow cooling then allows the solid solution to precipitate a separate phase that grows within the crystal lattice, which forms at particular angles that are determined by the lattice. In meteors, these interstitial defects can grow large enough to fill the entire crystal with needle or ribbon-like structures easily visible to the naked eye, almost entirely consuming the original lattice. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellae. Commonly, in gaps between the lamellae, a fine-grained mixture of kamacite and taenite called plessite can be found.
Widmanstätten structures describe analogous features in modern steels, titanium, and zirconium alloys, but are usually microscopic.
In 1808, these figures were observed by Count Alois von Beckh Widmanstätten, the director of the Imperial Porcelain works in Vienna. While flame heating iron meteorites, Widmanstätten noticed color and luster zone differentiation as the various iron alloys oxidized at different rates. He did not publish his findings, claiming them only via oral communication with his colleagues. The discovery was acknowledged by Carl von Schreibers, director of the Vienna Mineral and Zoology Cabinet, who named the structure after Widmanstätten. However, it is now believed that the discovery of the metal crystal pattern should be assigned to the English mineralogist William (Guglielmo) Thomson, as he published the same findings four years earlier.
Working in Naples in 1804, Thomson treated a Krasnojarsk meteorite with nitric acid to remove the dull patina caused by oxidation. Shortly after the acid made contact with the metal, strange figures appeared on the surface, which he detailed as described above. Civil wars and political instability in southern Italy made it difficult for Thomson to maintain contact with his colleagues in England. This was demonstrated in his loss of important correspondence when its carrier was murdered. As a result, in 1804, his findings were only published in French in the Bibliothèque Britannique. At the beginning of 1806, Napoleon invaded the Kingdom of Naples and Thomson was forced to flee to Sicily and in November of that year, he died in Palermo at the age of 46. In 1808, Thomson's work was again published posthumously in Italian (translated from the original English manuscript) in Atti dell'Accademia Delle Scienze di Siena. The Napoleonic wars obstructed Thomson's contacts with the scientific community and his travels across Europe, in addition to his early death, obscured his contributions for many years.
The most common names for these figures are Widmanstätten pattern and Widmanstätten structure; however, there are some spelling variations:
Due to the discovery priority of G. Thomson, several authors suggested calling these figures Thomson structure or Thomson-Widmanstätten structure.
The formation of Ni-poor kamacite proceeds by diffusion of Ni in the solid alloy at temperatures between 450 and 700 °C, and can only take place during very slow cooling, about 100 to 10,000 °C/Myr, with total cooling times of 10 Myr or less. This explains why this structure cannot be reproduced in the laboratory.
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