Characterization of cathodic film formed during reduction of chromic acid: role of sulphuric acid concentration

Abstract

The surface composition of chromium, electrodeposited from a chromic acid solution with different amounts of sulphuric acid, has been investigated by means of Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). The quantity of sulphuric acid is a critical parameter in order to form metallic chromium instead of a non-reducible chromium (III) oxide layer. The intermediate cathodic film formed on the electrode before the metallic chromium deposition has been investigated and XPS measurements have shown that a chromium oxide film is formed whatever the sulphuric acid concentration. However, in the presence of sufficient amounts of sulphate, this oxide is dissolved or the layer is broken down, giving rise to a free steel surface where the reduction of chromate ions into metallic chromium can take place.