Investigation of Deterioration for Large Outdoor Iron Statues Relics: A Case Research of Chairman MAO Iron Statue in Qinghai, China

Abstract

In this study, the Chairman MAO iron statue in Qinghai, China was analyzed via multi-analytical methodology, including polarizing microscope, SEM-EDS, metallographic analysis, high-resolution X-ray diffractometer, ion chromatographic analysis, silver nitrate titration detection in rust samples. The iron cultural relics are affected by factors such as their chemical composition, metallographic structure and surface characteristics, casting process, and natural storage environment. Although the corrosion rate is different, the corrosion is inevitable. With the corroborative evidence derived from the above analyses, it could be determined that the long-term preservation of cast iron statues in outdoor natural environments is prone to oxidation and corrosion, which due to the poor air circulation inside the statue of Chairman Mao Zedong, the humidity is significantly higher than that of the outside. In addition, due to the large temperature difference between day and night in this area, the condensed water is easy to form, causing the inner cavity of the statue and the welding parts to be rusted particularly seriously by the electrochemical corrosion and chemical corrosion. Compared with single chemical corrosion, electrochemical reaction can greatly accelerate the corrosion of iron. This result provided important scientific basis onto the production crafts of the precious casting, and the correlation between environment and deterioration for large outdoor iron relics, contributing to the conservators to make informed decisions on restoration.