Microstructure of Bronze Mirror Fabricated in the Korai Period

Abstract

  The microstructure of bronze mirror fabricated in the Korai period (10~14^th centuries) has been investigated. Transmission electron microscope, X-ray diffraction, scanning electron microscope, electron dispersive X-ray analyses are used to determine the structures of the specimen. The composition of the specimen is Cu-15.2 mass%Pb-9.3 mass%Sn-0.5 mass%S, and Fe and As are detected as trace elements. The optical microstructure of the mirror consists of αCu, Cu₄₁Sn₁₁ (δphase), Pb and a phase containing Cu and S. The phase containing S has never been observed in Japanese mirrors or Chinese mirrors. This phase agrees with Cu₂S listed in JCPDS No. 33-0490. Most of the Cu₂S grains exist around Pb grains. The PbS nano crystal containing Cu phase that does not correspond to any known compound is observed between the Pb and the Cu₂S grains. It is thought that Cu₂S is an intermediate product matter in the refinement of copper ore, chalcopyrite (CuFeS₂).