Jung Eun Choi and Masahiro Kitada
Graduate School of Arts, Tokyo University of the Arts, Tokyo 110-8714
The microstructure of the bronze coin, Headongtongbo, circulated around 1097 and fabricated in the Korai period (10∼14th centuries) has been investigated. The coin is 23.4 mm in diameter and 1.7 mm in thickness with weight of 4.75 g. Transmission electron microscope, X-ray diffraction, scanning electron microscope, and electron dispersive X-ray analyses are used to determine the structure of the specimen. The composition of the specimen is Cu-6.1 mass%Sn-1.4 mass%Pb-0.5 mass%S. αCu, Pb and Cu2S grains are observed using an optical microscope. The Cu2S phase has been observed in a Korai bronze mirror, as reported in the previous paper. The αCu phase shows a recrystallized polygonal structure. In some part of the αCu grains, twins and fine twinlike lines are observed. Cu2S particles are dispersed in αCu grains and the grain boundary. In αCu grains near the surface, grain boundaries and the twin boundary are corroded preferentially. The Cu2S grains retain their original shape and remain in the corroded layer. αCu corrodes from Cu2O to CuO, and then to Cu2CO3(OH)2.
ancient bronze coin, Headongtongbo, copper, tin, lead, chalcopyrite, copper oxide, malachite, corrosion
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