Activation effect of halides on chromium electrodeposition from chromic acid baths

The current efficiency of chromium electrodeposition and cathodic polarization curves were determined in halide-chromic acid-sulphuric acid systems. The composition of the cathodic films formed was determined by XPS and AES. The results show that sulphate is an effective catalyst for the deposition of bright chromium and that the current efficiency of the chromium deposition increases remarkably when F^– and Cl^– are added to the bath, and also that F^– and Cl^– participate in the formation of the films. The depth profile curves of the film show that halide is distributed in the inner layer of the film, and SO₄^2– in the surface layer. It is deduced that F^– and Cl^– form a bridged complex, [C^III-X^–-Cr^III], in which electron transition is easily carried out.