高麗青銅貨(海東通寶(ヘドントンボ))の表面腐食層の微細構造

抄録

  The microstructure of the surface corrosion layer of the bronze coin Headongtongbo fabricated in the Koryo period (11^th-12^th centuries) in Korea has been investigated. The coin was first produced in 1097 and had been circulated in the first Koryo dynasty. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to determine the structure of the specimen. The matrix composition of the specimen is Cu-6.1 mass%Sn-1.4 mass%Pb-0.5 mass%S. Metallic phase αCu, Pb and Cu₂S are observed in the bronze matrix. The surface corrosion layer consists of brown, grayish brown and greenish corrosion matters. The closer to the surface, the Cu concentration decreases. Conversely, the closer to the surface, Pb and Sn concentrations increase. The brownish layer consists of CuO. A mixture of Cu₂O, CuO and SnO₂ is observed from the grayish brown layer on the αCu matrix. The greenish corrosion layer is malachite (Cu₂(CO₃)₂(OH)₂) containing Sn and Pb. Chlorine introduced from the environment is detected from a part of the corrosion layer.