Ancient Metal Mirror Alloy Revisited: Quasicrystalline Nanoparticles Observed

Autor: S. Yamjala, Jainagesh A. Sekhar, R. Balamuralikrishnan, A. S. Mantri, Sabyasachi Saha, P. Rama Rao
Rok vydání: 2015
Předmět:
Zdroj: JOM. 67:2976-2983
ISSN: 1543-1851
1047-4838
DOI: 10.1007/s11837-015-1524-3
Popis: This article presents, for the first time, evidence of nanocrystalline structure, through direct transmission electron microscopy (TEM) observations, in a Cu-32 wt.% Sn alloy that has been made by an age-old, uniquely crafted casting process. This alloy has been used as a metal mirror for centuries. The TEM images also reveal five-sided projections of nano-particles. The convergent beam nano-diffraction patterns obtained from the nano-particles point to the nano-phase being quasicrystalline, a feature that has never before been reported for a copper alloy, although there have been reports of the presence of icosahedral ‘clusters’ within large unit cell intermetallic phases. This observation has been substantiated by x-ray diffraction, wherein the observed peaks could be indexed to an icosahedral quasi-crystalline phase. The mirror alloy casting has been valued for its high hardness and high reflectance properties, both of which result from its unique internal microstructure that include nano-grains as well as quasi-crystallinity. We further postulate that this microstructure is a consequence of the raw materials used and the manufacturing process, including the choice of mold material. While the alloy consists primarily of copper and tin, impurity elements such as zinc, iron, sulfur, aluminum and nickel are also present, in individual amounts not exceeding one wt.%. It is believed that these trace impurities could have influenced the microstructure and, consequently, the properties of the metal mirror alloy.
Databáze: OpenAIRE
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