A Study on Manufacturing Technique and Corrosion Characteristics of Bronze Dirk, Bronze Sword, Bronze Mirror in Early Iron Age Excavated from the Osong Site in Cheongju

Metallography, SEM-EDS, and Raman Micro-Spectroscopy analysis were conducted on bronze dirk, bronze sword, and bronze mirror excavated from the pit tomb No. 1-1 at 12th Point of Osong Site in Cheongju to study the manufacturing techniques and corrosion properties. The bronze dirk, bronze sword and bronze mirror are judged to be binary alloys of Cu(79.16∼79.89 wt%)-Sn (19.12∼20.34 wt%). The microstructure is a cast structure composed of δ phase and (α+δ) eutectoid, and no heat treatment was performed. As a result of classifying the corrosion characteristics, it was confirmed that the bronze dirk, bronze sword, bronze mirror were Type I. As a result of EDS analysis in subsurface area, tin oxide is located as a selective corrosion of (α+δ) eutectoid, and as a result of Raman Micro-Spectroscopy analysis, corrosion products of Cassiterite and Malachite were identified for the bronze dirk and Cassiterite for bronze sword and bronze mirror. The secondary metallic copper was mainly present in the hole left by corrosion of Pb particles and on the (α+δ) eutectoid, and was found to be 100.00 wt% of Cu as a result of the analysis, confirming that all of them were high-purity copper.