Chrome plating from sulfate-oxalate Cr(III) baths. Structure, composition, and corrosion behavior

The studies on chrome-plating from sulfate-oxalate Cr(III) baths are generalized. It is shown that the metal is deposited from the mentioned baths at a current efficiency over 40% and forms deposits of any thickness. Chrome-plating may be carried out in the cells with undivided cathodic and anodic compartments, which reduces the current efficiency to 25-30%. The reflectivity and color of the deposits do not differ from tho e of the deposits from standard chrome-plating baths based on Cr(VI). Special attention is paid to the studs C ies of the corrosion and electrochemical behavior of deposited layers. Steady-state polarization curves in a 0.5 M H2SO4 indicate that the studied chromium deposits exhibit no active-dissolution range. The free corrosion-potential is shifted in the positive direction compared with coatings deposited from standard chrome-plating baths and falls into the passivity range. According to XPS method, the passive film is about several nanometers thick and, along with oxide compounds of chromium, includes its carbides formed during the electroplating.