Electrodeposition and Characterization of Sacrificial Copper-Manganese Alloy Coatings

Abstract

Cu-Mn electrodeposition from simple sulfate electrolytes with the only addition of ammonium sulfate was studied under different current densities, at pH 2.6-2.8 and pH 6.4-6.6, and at different cupric ion concentrations. An electrochemical investigation of this Cu-Mn electrodeposition system was conducted by potentiodynamic methods and cyclic voltammetry. Electrodeposition was performed galvanostatically. Mn content in the alloy increased with increasing current density. Three types of coatings were obtained: spongy Cu-rich oxygen-containing films at low current density, crystalline Mn-rich coatings at intermediate current density ͑type I͒, and amorphous coatings at high current density ͑type II͒. At high pH ͑6.4-6.6͒, the composition of type I coatings could be controlled by adjusting the current density, while at low pH ͑2.6-2.8͒ composition becomes more controllable by varying the Cu 2ϩ concentration (͓Cu 2ϩ ͔). The optimal current density to obtain type I coatings is shifted upward with increasing ͓Cu 2ϩ ͔. A Cu-rich interlayer is formed between the Cu-Mn film and the stainless steel substrate. The bulk of type II coatings is mainly composed of metallic Cu and Mn. Metal complexation equilibria with NH 3 can explain the influence of Cu additions on coating morphology and composition.Electroplated cadmium ͑Cd͒ is widely utilized in surface finishing applications to improve corrosion resistance and tribological properties of a variety of components. In these instances, cadmium coatings provide sacrificial corrosion protection, low friction coefficient, ductility, good electrical conductivity, and solderability. However, both cadmium as a metal and cadmium processing, which utilizes cyanide-based solutions, are extremely toxic to the environment and to humans, and the release of the metal and of processing effluents is strictly controlled. Until now, no single coating has been proposed that possesses all the attributes needed to replace cadmium. 1-4 It is thus important to develop alternative, environmentally friendly processes and materials capable of substituting Cd as a sacrificial coating to steel.Electrodeposited coatings of manganese ͑Mn͒ and its alloys potentially combine high corrosion protection performance, good tribological behavior, and suitable mechanical properties. Therefore, they have been studied as a replacement for cadmium in the sacrificial protection of steel. 5 Pure manganese is not usually considered a suitable protective coating for steel because of its high chemical reactivity, which leads to fast dissolution of the coating, and its brittle nature. 5-8 The first problem, however, can be overcome by alloying Mn with other metals such as zinc, 6,9-13 nickel, 14,15 iron, 16,17 chromium, 18 cobalt, 19 or tin. 20 Among these, electrodeposited Zn-Mn alloys are claimed to approach ''real commercial exploitation.'' 21 Mn and Zn in these alloys show synergistic effects with a corrosion resistance superior to the individual metals and to other Zn alloys in laboratory chloride environments. 11 Thi...

Electrodeposition and characterization of sacrificial copper-manganese alloy coatings: Part II. Structural, mechanical, and corrosion-resistance properties

“…pct Cu) with a 10 m nominal thickness obtained at different current densities and at pH 6.4 to 6.6. When the current density is less than 100 mA/cm 2 , spongy and porous deposits are obtained, mainly comprised of (hydro)oxides, [21] and almost no signal can be detected by XRD. Crystalline ␥Ј Cu 14.5 Mn 85.5 coatings (type I, 150 mA/cm 2 ) do not show any fcc copper peaks, demonstrating that a Cu-Mn solid solution is formed by electrodeposition.…”

“…As the current density increases over 400 mA/cm 2 , the (111) peak becomes broader, indicating a decrease in grain size or a transition to an amorphous structure (type II), which is also confirmed by the observed variation of microstructure with current density. [21] At pH 2.6 to 2.8, the Cu content in type I Cu-Mn coatings can be effectively varied by changing the cupric ion concentration [Cu 2ϩ ] in the electrolyte. [21] The peak shift with varying copper content can, again, be identified in XRD patterns ( Figure 3(a)).…”

“…In Part I of this series of articles, [21] we performed an electrochemical and morphological study of Cu-Mn alloy electrodeposited from electrolytes containing metal sulfates and ammonia at pH 2.6 to 2.8 and 6.4 to 6.6. We found that Mnrich coatings of good quality could be obtained at a high current density and that the Cu content (2 to 14 at.…”

Maximizing Army's Return on Investment in Civilian Development

“…Therefore, manganese is difficult to deposit. As hydrogen evolution always occurs, the pH in the vicinity of the cathode increases, but probably not to such extent that the free NH 3 , and Mn(OH) 2 would be formed and incorporated into the films. Under these conditions, type II coatings would be obtained.…”

Study of the Influence of the Electrolysis Parameters on Mn-Zn, Mn-Cu and Mn-Cu-Zn Alloys Coatings from Electrolytes Containing Complexing Ligands

“…To decrease chemical activity and brittle form of manganese it is alloyed with metals of lower negative standard potential, e. g. with Cu, Zn, Co, Ni, Fe and others, which leads to stabilization of γ-Mn form. For example, introduction of up to 3% of copper into manganese contributes to preservation of γ-Mn modification for a long period [5][6][7]. In contrast with pure Zn electrodeposited coating manganese-containing electrodeposited alloys (e.g.…”