A Mechanism study of type-I Tin Rich Patina on the Surface of Ancient Bronzes

Abstract The formation mechanism of type-I patina and the existence state of Cu on the surface of ancient bronze are not clear. This study compared the surface patina of ancient bronze with pure SnO₂ nanoparticles prepared by hydrothermal method. The main crystalline component of the patina was ~ 5 nm SnO₂ nanoparticles, which are very similar to those of pure SnO₂, indicating their comparability. Cu element was found in patina, but it did not form crystals. The XRD diffraction peak of the patina shifted, indicating that Cu entered the SnO₂ lattice and caused crystallinity decreased. Compared to pure SnO₂, new peaks appeared in the XPS spectra of Cu and O in the patina, which are speculated to be Cu-O-Sn binding which is the key character of type-I patina. It indicates that type-I patina is mainly composed of crystalline SnO₂ nanoparticles with some Cu dissolves in its lattice structure. The concentration of Cu in SnO₂ crystal cells is limited, and mainly copper forms amorphous Cu₂O with Sn. Sn can increase the structural stability of Cu₂O, making it easy to enter it which hinders the crystallization of Cu₂O. When the Sn content is insufficient, sufficient Cu-O-Sn amorphous cannot be formed, and Cu₂O may crystallize.