Nanostructured Black Nickel Coating as Replacement for Black Cr(VI) Finish

• Main Authors: Marina M. Mennucci, Rodrigo Montes, Alexandre C. Bastos, Alcino Monteiro, Pedro Oliveira, João Tedim, Mário G. S. Ferreira
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Applied Sciences
• Subjects: black nickel coatings; electrochemical testing; electrodeposition; hull cell; nanostructured coatings
• Online Access: https://www.mdpi.com/2076-3417/11/9/3924

This work compares different electrodeposition procedures to produce nickel black coatings as greener and less toxic alternatives to Cr(VI)-based coatings used in different applications. Nickel and nickel-plated brass served as substrates in studies with a Hull cell and polarization curves. After a set of comparative experiments, the best electrodeposition procedure was further studied and optimized. Optimal conditions were found with a bath consisting of 75 g/L NiCl₂·6H₂O + 30 g/L NaCl and a current density of 0.143 A dm⁻² applied for 5 min at room temperature. Furthermore, a pre-treatment with 18.5 vol.% of hydrochloric acid in water was found to be necessary to warrant good coating adhesion to the substrate. The black color is attributed to the development of a nanostructured surface that absorbs the incident light. Corrosion testing was performed in 0.5 M NaCl aqueous solution using electrochemical impedance spectroscopy (EIS) and polarization tests.