Anti-tarnishing amorphous alumina films on silver coins

Amorphous alumina films were deposited on silver coin surfaces by reactive magnetron sputtering to improve the anti-tarnishing property of silver. Glance angle X-ray diffraction (GXRD), X-ray photoelectron spectoscopy (XPS) and atomic force microscopy (AFM) were used to analyze the chemical slate and surface morphology of alumina films. The corrosion potential of silver coins covered with amorphous alumina was increased, and corrosion current density was decreased in 0. 5 mol/L NaCl+10 mmol/L Na₂S mixing solution. The accelerated test in H₂S vapor showed that the alumina film had excellent anti-tarnishing properties.