Statistical optimisation of trivalent chromium bath and characterisation of coating defects

Abstract

The influences of chemicals used in the Cr electrodeposition bath on the brightness and efficiency of Cr coating were studied using fractional factorial design of experimental method. Cr coating defects that emerged during the coating were investigated using a scanning electron microscope (SEM). Analysis of variance test was performed to check the accuracy of each effect in the statistical studies. The statistical results show that boric acid enhances the efficiency and thickness of Cr coating the most. The stability of Cr coating is dependent on two parameters: pH and Cr⁺³ ion concentration in the Cr III bath. SEM images and energy dispersive spectroscopy measurements showed that the blackness and dullness defects on Cr coating are due to the emergence of chromium (III) sulphide (Cr₂S₃) and fast hydrogen evolution on Cr coating.

Keywords:

• Trivalent chromium coating
• Saccharin
• Malonic acid
• Chromium coating defects
• Electroplating