Electrodeposition and characterization of Zn–Mn alloy coatings obtained from a chloride-based acidic bath containing ammonium thiocyanate as an additive

• Published in: Surface & coatings technology Vol. 203; no. 9; pp. 1167 - 1175
• Main Authors: Díaz-Arista, P., Ortiz, Z.I., Ruiz, H., Ortega, R., Meas, Y., Trejo, G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.01.2009
• Subjects: Ammonium thiocyanate; Electrodeposition; Zinc–manganese alloys; Ammonium thiocyanate; Zinc–manganese alloys; Electrodeposition
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2008.10.015

The electrodeposition of Zn–Mn alloys was performed using a chloride-based acidic bath containing ammonium thiocyanate (NH 4SCN) as an additive. An electrochemical study using cyclic voltammetry (CV), performed for each of the metal ions (Zn(II) and Mn(II)), showed that neither metal ion forms complexes with NH 3, and that Mn(II) but not Zn(II) forms complexes with SCN −. The influence of NH 4SCN on the morphology, composition and crystallographic structure of the electrodeposited Zn–Mn alloys was studied using scanning electron microscopy (SEM), glow discharge spectroscopy (GDS) and X-ray diffraction (XRD). The results show that the presence of NH 4SCN in the solution induces an increase in the Mn content of the alloy, from 3% in the Zn–Mn alloy obtained in the absence of additive to 6.2% in the alloy obtained in the presence of additive. In addition, the presence of NH 4SCN favors the formation of coatings comprised of a mixture of ε-phase Zn–Mn(002) + α-phase Zn–Mn(111) alloys. These coatings were compact and smooth and exhibited a lower corrosion rate compared to the coatings obtained in the absence of NH 4SCN, which where comprised of a mixture of Zn, ε-phase Zn–Mn and α-phase Zn–Mn alloys.