Inspection about the Corrosion of Metallic Archaeological Artifacts in Ground (IV)

Honda, Takashi*; Yamaguchi, Shingo*

In general, it is difficult to evaluate non-destructively the corroded states of iron-based archaeological remains, as they are fully covered by thick rust formed under ground during a long period over a hundred years. The purpose of this study is to estimate the corrosion amounts of such remains with using X-ray CT and summarize the longevity of iron in soil. It has been clarified that rust and residual metallic iron can be quantitatively divided by this technique. Therefore, it is supposed that the amounts of corrosion can be figured out on the basis of thickness and density of rust. Eight remains dug out at seven relics were analyzed. The burial periods in soil were estimated to be from 1000 to 1500 years. Metallic iron remained in six remains, and the corrosion amounts were figured out to be from 0.5 to 3 mm in these periods. In addition, the soil environments of relics were analyzed, and the relation between corrosion behaviors and environmental factors was discussed. The rust was composed of outer goethite and inner magnetite layers in normally oxidizing conditions. On the other hand, a few samples were buried in slightly oxidizing environments, and these were covered by magnetite single layers. The corrosion amount of remains in such an environment was small compared to the others.