The effects of pH and polyethylene glycol on the Cr(III) solution chemistry and electrodeposition of chromium

The effects of pH and the organic additive, polyethylene glycol (PEG), on the trivalent chromium electroplating were investigated in view of the solution stability, electrochemical reactions and the properties of deposited layer. It was sought out that the concentration of chromic complexes in the chromic bath with formic acid was closely dependent on pH. The chromic complex formation in the bath, examined by theoretical calculation and UV–vis absorption measurement, was not affected by PEG addition. However, adsorbed PEG molecules on the cathode surface caused the hydrogen evolution rate to be retarded and the deposited coating morphology smooth, small cracks and nodular structure. The variations of solution acidity and organic additive concentration affected the complex formation, the cathodic reaction and the physical property of the deposit.

► Cr coating was deposited from Cr3+ solution with PEG additive.
► pH and PEG affected on the Cr3+ solution chemistry and electrodeposition.
► PEG molecules were chemically inert with Cr3+ electroplating solution.
► PEG can improve the microstructure and properties of Cr deposited.
► The optimum of plating was determined at pH 2.5 and 2.0 g/L PEG.