Electrodeposited lanthanum film as chromate replacement for tinplate

The lanthanum film as chromate replacement was prepared on tinplate by the electrodeposition method. Sulfide-stain resistance of the La-passivated, unpassivated and Cr-passivated tinplates was evaluated using a cysteine tarnish test. Corrosion behavior of these tinplates in 0.1 M citric–citrate buffer solution was investigated using electrochemical impedance spectroscopy (EIS). The composition and thickness of the lanthanum film were studied using X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence spectrometry (XRF). According to the results, the lanthanum film significantly improves protection of tinplate against sulfide-stain and corrosion. In comparison to the Cr-passivated tinplate, the La-passivated tinplate exhibits better sulfide-stain resistance and similar corrosion resistance. The lanthanum film mainly consists of La2O3 and its hydrates such as La(OH)3 and La2O3·H2O. The total lanthanum amount of the film is 0.0233 g/m2.