Electrochemical deposition of copper nanowire coatings on anodized aluminum for antibacterial surfaces

Introduction: A process is developed to deposit a coating of copper on aluminum in the form of crystalline copper nanowires growing out of the pores of anodized aluminum to completely cover the oxide surface in a self-limiting process. The aim was to create stable, strongly adhering, and strongly antimicrobial copper surface coatings on aluminum.

Materials and methods: The anodization is as the latest development done in a one step process with alloys of aluminum and pure aluminum. Copper is deposited electrolytically, following the anodization and a short etching of the top surface to widen the pore openings after the anodization. No thinning of the bottom barrier oxide layer in the pores is necessary for the deposition of copper. The copper initially fills the pores unevenly, but if the deposition is continued, one arrives at a full coverage of the surface by nanowires growing out of the pores and forming spherical clusters.

Results: The resulting full surface coverage of these spherical clusters, appearing with a somewhat uneven morphology, can be leveled out mechanically to a relatively smooth and continuous top surface. The antibacterial properties of surfaces of items produced with these steps are certified by Danish authorities and a four-year test has proven a long-term effect and stability of the coating.

Conclusions: The aims to create a strong, well-adherent, and robust coating of aluminum with copper has been achieved in the simplest possible process by using the porous oxide created by anodization as a template substrate for a direct electrochemical copper deposition without application of further chemical ingredients. The antibacterial, frictional and hydrophobic properties of this coating have been demonstrated.