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DOI: 10.14738/aivp.86.9136
Publication Date: 1st November, 2020
URL: http://dx.doi.org/10.14738/aivp.86.9136
Replacement of Copper Cyanide by Copper Sulfate on
Electroless Brass Plating Process
Gladis P. Mendoza-Aragón, Roal Torres-Sánchez, Adan Borunda-Terrazas,
Carlos Domínguez-Ríos, and A. Aguilar-Elguézabal
Centro de Investigación en Materiales Avanzados, S.C.
Miguel de Cervantes No. 120, Complejo Industrial Chihuahua
Chihuahua, México C.P. 31136
carlos.dominguez@cimav.edu.mx
ABSTRACT
Environmentally friendly processes and health protection are industrial requirements nowadays.
Surface finishing industry demands the improvement of the composition of bath solutions, and
specifically, reduction or elimination of the use of toxic substances to simplify complexity on
wastewater treatment. This work presents results on the replacement of copper cyanide by copper
sulfate in the composition of an electroless brass plating bath used on zamak alloy coating. The effect
of the concentration of copper sulfate on the morphological and brass film color characteristics was
studied. Characterization of plated pieces was made by scanning electron microscopy, optical
microscopy, L*, a*, b* color parameters and by spectrophotometry and electrochemical techniques.
Results indicate that copper cyanide can be successfully substituted, being possible to control the
color of brass plating on this new process.
Keywords: Brass; Electroless; Cyanide; Sulfate; Electrochemical; Zamak;
Highlights
Electroless brass coating friendly to the environment.
The treatment of wastewater from electroless brass coating is easier and less expensive.
With this electroless brass coating several shades of yellow color can be produced depending on the
concentration of copper sulphate.
1 Introduction
Brass plating, which originated in the mid-1600s, is one of the processes most frequently used to coat
alloys. The ancient process consists on the dissolution of solid brass in nitric acid mixed with cyanide
to prepare the plating bath, which is a health risk bath due to the volatility of the substances used in
this process. It was not until 1920 that electrolytic process was developed as an alternative to the use
of solid brass, were cyanide precursor of copper and zinc were used [1].
The interest in brass coating focuses on two main areas: functional and decorative. For decorative
purposes, the brass coating is mainly applied to hardware. In this application, the color of the brass is
very important. Coatings are usually thin (0.005 mm) and the coating has little protection against
corrosion in harsh environments [2].
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European Journal of Applied Sciences, Volume 8 No. 6, December 2020
Services for Science and Education, United Kingdom 103
Examples of functional purposes of brass plating include increasing the adhesion between rubber and
steel, improving the corrosion resistance of marine vessels, use in the automotive industry as an
intermediate layer on bumpers, application as lubricating film for the drawing of steel, and so on.
Brass plating applied electrolytically may be a potential substitute for dyes and resins. Although the
latter technology is gaining some acceptance, commercial costs, difficult adaptability to high-volume
processes, and the fact that the finish cannot rust or age artificially reduce its fields of application, so
brass is an excellent alternative [3].
Baths for coating metal objects with brass by both electrolytic and electroless processes are based on
the use of copper cyanide, zinc cyanide, and sodium cyanide, these processes are considered highly
hazardous to health by the high toxicity of cyanide, thus there is a great interest in replacing cyanide
salts for the preparation of brass baths.
Attempts have been made to eliminate or reduce the use of cyanides in brass electrolytic baths and
other types of metal plating, such as silver coating [4], where a low cyanide content is used in the bath,
gold plating with thiosulfate instead of gold cyanides [5], the use of a non-cyanide bath for electroless
gold plating on Ni substrates [6], and cyanide-free zinc plating [7]. Developed a brass electroplating
bath free of cyanides, based on CuSO4, ZnSO4, and sodium glucoheptonate, with pH above 10.0 and
using current densities of 0–5 A/dm2
, obtaining brass film with thickness of 5–50 μm. According to
their results, the Cu70Zn30 brass characteristic color was obtained with current densities above 1
A/dm2 [8]. There is a patent for cyanide-free electroplating brass plating, based on pyrophosphate and
orthophosphate, for the application of a brass film with a thickness of 0.05 to 0.1 μm on a metallic foil
substrate [9]. In other research, studied the effect of polyalcohol sorbitol on an electrolytic bath of
Cu-Zn and reported the capability to obtain colors of Cu-Zn deposit from golden to grayish bright brass
[10].
Studies on cyanide-free electrolytic Sn-Zn bath plating using sulfate-tartrates at pH from 4 to 5 have
also been published [11]. Another research on the electroplating of Cu-Zn alloy in an alkaline solution
by adding D-mannitol was reported [12]. Also, studied electrolytic Cu-Zn plating based on
Ethylenediaminetetraacetic acid (EDTA) as Cu2+complexing, a cyanide-free process with the capability
to obtain yellow brass color [13]. Ballesteros et al., studied the electrochemical deposition of Cu-Zn
using chloride of Cu and Zn and glycine as complexing agent; this electrolytic bath was also free of
cyanides and worked at room temperature [14]. Recently, Minggang et al., studied the influence of
copper sulfate for electrolytic Cu-Zn plating in a cyanide-free bath using 1-hydroxyethylidene-1, 1-
diphosphonic acid (HEDP), potassium citrate, Cu and Zn sulfates, and potassium hydroxide to adjust
the pH to 13 [15].
The work of Ramirez et al., is among the most recent efforts to apply a cyanide-free Cu-Zn coating,
authors investigated several Cu and Zn bath compositions using sulfates, triethanolamine as a
chelating agent, sodium hydroxide, and an alkaline pH of approximately 14. By controlling the amount
of triethanolamine and the applied current density Cu/Zn ratio on film can be controlled and the
Cu70Zn30 coating could be obtained [16].
A comparative study of four N-based additives added to an electroplating bath of Cu-Zn-Sn with
different amounts of additives showed that it was possible to control the color of the alloy and obtain
a color that imitated gold color. The four additives were triethanolamine (TEA), ammonium fluoride
(AF), ammonia triacetic acid (NTA), and polyacrylamide (PAM). The color varied from a red to a color
that imitated gold, and Cu-Zn-Sn blackened coatings could be obtained by using a larger quantity of
the additives [17].
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Gladis P. Mendoza-Aragón, Roal Torres-Sánchez, Adan Borunda-Terrazas, Carlos Domínguez-Ríos, and A.
Aguilar-Elguézabal. Replacement of Copper Cyanide by Copper Sulfate on Electroless Brass Plating Process.
European Journal of Applied Sciences, Volume 8 No 6, Dec 2020; pp: 102-112
URL: http://dx.doi.org/10.14738/aivp.86.9136 104
Despite of the advances to develop a cyanide free electroplating process for brass film deposition,
there is scarce work made for the electroless process. In a previous work on electroless brass plating
for zamak alloy [18-21], we reported the possibility to produce acicular or nodular morphology on Cu- Zn film through the control of Rochelle salt concentration in the bath. That process of this study was
originally developed and patented by our group using cyanide precursor. In those works, the bath
composition contained ZnO, CuCN, NaCN, NaOH, Rochelle salt, and NH3OH-Na2CO3 to adjust the pH.
Attending the need of greener and less risky processes we started a research in order to replace CuCN
by the environmentally friendly CuSO4. The process reported in this work concerns an electroless
plating that besides to reduce cyanide content on bath, solves several problems that are present in
the electroplating of brass.
2 Experimental
Samples of zamak alloy with dimensions of 20 mm × 20 mm × 2 mm were used as a substrate. Pieces
were roughened with 220 and 600 grit sandpapers and then weighed in groups of three pieces to start
the process of electroless brass plating. Three samples were coated by electroless plating for each
experimental condition. In order to properly prepare the surface of the pieces of zamak alloy for the
electroless brass the following baths were prepared:
a) Alkaline degreasing bath, which was prepared with Na2CO3 and Na3PO4-12H2O as
recommended by ASTM B252-92 [22], bath temperature of 70–85 °C, current density of
30–55 A/dm2
, time of 180 s, and rinsing with distilled water.
b) A cathodic degreasing bath of sodium hydroxide (NaOH), which was used to complete the
removal of oils and fats and to ensure good adhesion of the electroless brass plating ASTM
B 252-92. The conditions of the bath were room temperature, a current density of 16
A/dm2
, a time of 40 s, and rinsing with distilled water.
After surface preparation, the next step was immersion in the electroless brass plating bath, for which
the content of CuSO4 was varied while keeping the concentration of the other reagent’s constant in
accordance with our previous work [18-21]. The composition and conditions of the baths used in the
experiments are shown in Table 1.
Table 1. Compositions and Conditions of Electroless Baths
Chemical Reactive Concentration of reactive in bath
(mol/L)
B1 B2 B3 B4 B5 B6 B7
NaOH 1.12 1.12 1.12 1.12 1.12 1.12 1.12
NaCN 1.50 1.50 1.50 1.50 1.50 1.50 1.50
ZnO 0.11 0.11 0.11 0.11 0.11 0.11 0.11
CuSO4 0.05 0.07 0.08 0.10 0.11 0.13 0.15
Na2CO3 0.20 0.20 0.20 0.20 0.20 0.20 0.20
NH4OH 0.16 0.16 0.16 0.16 0.16 0.16 0.16
NaK(C4H4O6)•4H2
O
0.12 0.12 0.12 0.12 0.12 0.12 0.12
Bath Conditions
Temperature (oC) 70 70 70 70 70 70 70
Time (min.) 15–30 15–30 15–30 15–30 15–30 15–30 15–30
Stirring Cst.* Cst.* Cst.* Cst.* Cst.* Cst.* Cst.*
pH 11 11 11 11 11 11 11
Cst.*= Constant