RETRACTED: Electrodeposition and characterization of manganese coatings obtained from an acidic chloride bath containing ammonium thiocyanate as an additive

Abstract

The influence of ammonium thiocyanate (NH 4 SCN) on the electrodeposition and morphology of manganese coatings obtained from a chloride-based acidic solution was investigated by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) measurements. The EQCM data are presented as plots of dΔm/dt versus E, known as massograms. Because massograms are not confounded by the hydrogen evolution reaction, they more clearly show the manganese reduction and oxidation processes. By comparing the voltammograms with their corresponding massograms, it was possible to differentiate mass changes due to Faradaic processes from those involving no net charge transfer. Morphology, elemental composition profiles, and the structure of the manganese coatings were analyzed by scanning electron microscopy (SEM), glow discharge spectrometry (GDS), and X-ray diffraction (XRD). The results showed that in the absence of NH 4 SCN, Mn(OH) 2(s) is formed in the potential range -0.9 to -1.1 V vs. SCE because of the hydrogen-evolution reaction in this region. At more cathodic potentials, Mn(OH) 2(s) was incorporated into a β-manganese deposit. Both of these species undergo dissolution by apparently non-Faradaic processes during the potential scan in the positive direction. In the presence of NH 4 SCN, the percentage of codeposited Mn(OH) 2(s) decreased, and sulfur was detected in the lower layers of the manganese coatings. Moreover, the formation of α- and γ-manganese was favored.