New cyanide-free ammonia bath for brass alloy coatings on steel substrate by electrodeposition

The electrodeposition of highly adherent brass alloy coating onto steel substrate was successfully achieved using a cyanide-free ammonia solution. Ammonia solution forms soluble complexes with both Zn²⁺ and Cu²⁺ ions with high stability constants. The bath composition necessary to obtain smooth and highly adherent red brass alloy contains: CuSO₄.5H₂O 30 g/L, ZnSO₄.7H₂O 30 g/L, NH₃ 88ml /L, (NH₄)₂SO₄ 50 g/L, KOH 20 g/L, pH 9.65, t = 15 min., i = 0.12 Adm^-2 and at 20°C. The investigations were carried out using voltammetric techniques such as; potentiodynamic cathodic polarization curves, anodic linear stripping voltammetry and cyclic voltammetry. The zinc content in the brass alloy deposits was ranged from 5-18.5 wt%. The cyclic voltammetric data indicating that the rate of growth is controlled by mass transfer of copper and zinc ions to the growing center. The first stage of nucleation and growth of brass alloy fit the model of three dimensional instantaneous nucleation. The brass deposit was characterized by XRD and SEM measurements.