奈良時代に製作された和同開珎の表面腐食層の微細構造

Abstract

The microstructures of a corrosion layer formed on the surface of two Japanese oldest coins, Wadoukaichin (surface color: dark brown and green) were studied. Compositions of these coins are that main element is Cu and Sn and traces are Pb, Fe and As. X-ray diffraction patterns show that copper di-hydroxide (Cu(OH)2 2H2O), Cu1.81S and Cu2O are detected on the surface corrosion layer of dark brown sample, and Cu2(CO3)(OH)2 (malachite), Cu3(CO3)2(OH)2 (azurite) and Cu2O are detected on the surface corrosion layer of green sample. Optical microscope images show that the surface corrosion layer of dark brown sample is porous, and blue and green grains on the brown layer are existed on that of green sample. From spectrographs of these grains, the peak wavelength of green grains is matched to that of malachite, but this of blue grains is shifted to long wavelength side of about 40 nm at azurite on an influence of trace contaminations. The corrosion layer has two layers, surface layer is plate-like texture, and under layer is aggregation microstructure from TEM observation. The crystal structure of these two layers is matched to azurite from the electron beam diffraction patterns.