Abstract:
The bronze samples from Shandong Province were analyzed using a metallurgical microscopy and a scanning electron microscopy equipped with an energy-dispersive spectroscopy system (SEM-EDS). This analysis reveal that α-phase preferential corrosion was more prevalent in bronze mirror samples, whereas δ-phase preferential corrosion was more common in other types of bronze samples. Notably, both types of corrosion coexist in a few samples. The surface of antique bronze mirrors was typically smooth and susceptible to corrosion due to oxygen absorption in soil, seawater, and the atmosphere. In contrast, the surface of other types of bronze was typically rough, and occluded cell corrosion was prone to occurring at surface defects. The solution within the occluded cell was markedly acidic due to the hydrolysis of metal ions, which might potentially reverse the α and δ phases. The results of the simulated corrosion test proved that bronze corrosion started from the α-phase in an environment with low acidity and alkalinity and from the δ-phase in a strong acid condition. The δ-phase in the occluded cell acted as the anode and underwent oxidation to produce copper ions, while the α-phase served as the cathode and underwent reduction to form pure copper grains. Because of the slow diffusion of ions in the electrolyte solution, the current inside the corrosion cell was intermittent due to concentration polarization, and a twin-crystal structure sometimes appeared in the generated copper grains.