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Research Paper Replacement of Copper Cyanide by Copper Sulfate In Academia Journal of Environmetal Science 7(4): 037-048, April 2019 DOI: 10.15413/ajes.2019.0600 ISSN: ISSN 2315-778X ©2019 Academia Publishing Research Paper Replacement of copper cyanide by copper sulfate in brass electroless bath Accepted 20th April, 2019 ABSTRACT Environmental friendly processes and health protection are industrial requirements nowadays. In the surface finishing industry, there are greater opportunities for the improvement of the composition of bath solutions, reduction or elimination of the use of toxic substances, and the formation of residues with high complexity for your disposal. This study presents results on the replacement of copper cyanide by copper sulfate in the composition of an electroless brass plating bath; this electroless brass plating process can be applied directly to zamak alloys, low-carbon steels, or aluminum. The effect of the concentration of copper Gladis P. Mendoza-Aragón, Roal Torres- Sánchez, Adan Borunda-Terrazas, Alfredo sulfate on the morphological and brass film color characteristics was studied. For Aguilar-Elguézabal and Carlos Domínguez- this purpose, the characterization was done by scanning electron microscopy, Ríos* optical microscopy, and L*, a*, b*color parameters using spectrophotometry and electrochemical techniques. The composition of the bath consists of zinc oxide as a Centro de Investigación en Materiales +2 Avanzados, S.C., Miguel de Cervantes No. 120, source of Zn ions, a suitable complexing agent, and a stabilizer, under alkaline pH Complejo Industrial Chihuahua, Chihuahua, and temperature of 75±C. The results indicate that it is possible to control the México C.P. 31136. color of brass plating through this new process by selecting the Cu+2/Zn+2 ratio. *Corresponding author. E-mail: [email protected]. Tel: 52 614 Key words: Brass, electroless, cyanide, sulfate, electrochemical, zamak, 4391117. spectrophotometer, copper. INTRODUCTION Brass plating, which originated in the mid-1600s, is one of bumpers, application as lubricating film for the drawing of the processes most frequently used to coat alloys. The steel, and so on. Brass plating may be a potential substitute ancient process consists of the dissolution of solid brass in for dyes and resins applied electrolytically, a technology is nitric acid mixed with cyanide to prepare the plating bath, relatively new. Although the latter technology is gaining which is a health risk due to the obvious volatility of the some acceptance, commercial costs, difficult adaptability to substances used in this process. It was not until 1920 that high-volume processes, and the fact that the finish cannot the electrolytic process was developed as an alternative to rust or age artificially reduce its fields of application, so the use of solid brass (Kowalski, 1998). brass is an excellent substitute (Kowalski, 1998). The interest in brass coating focuses on two main areas: Baths for coating metal objects with brass by both functional and decorative. For decorative purposes, the electrolytic and electroless processes are based on the use brass coating is mainly applied to hardware. In this of copper cyanide, zinc cyanide, and sodium cyanide, these application, the colorof the brass is very important. processes are considered highly hazardous to health and Coatings are usually thin (0.005 mm) and the coating has highly toxic. Since cyanide-based precursor is still used, little protection against corrosion in harsh environments there is a great interest in replacing cyanide salts for the (Blum and Hogeboom, 1949; Strow, 2005). preparation of brass baths. Examples of functional purposes of brass plating include Attempts have been made to eliminate or reduce the use increasing the adhesion between rubber and steel, of cyanides in brass electrolytic baths and other types of improving the corrosion resistance of marine vessels, use in metal plating, such as silver coating (Sanchez et al., 1996), the automotive industry as an intermediate layer on where a low cyanide content is used in the bath, gold Academia Journal of Environmental Science; Mendoza-Aragón et al. 038 plating with thiosulfate instead of gold cyanides (Sullivan Hurtado-Macias et al., 2010; Domínguez-Ríos et al., 2005), it and Kohl, 1997), the use of a non-cyanide bath for was evaluated the effect of sodium-potassium tartrate on electroless gold plating on Ni substrates (Sato et al., 2002), the morphological characteristics and the Cu-Zn film and cyanide-free zinc plating (Nabil, 2002). Fujiwara and composition, obtaining an acicular morphology on deposits Enomoto (1988) developed a brass-plating bath free of with low levels of Rochelle salt and nodular morphology cyanides based on CuSO4, ZnSO4, and sodium with a high content of Rochelle salt in the bath. glucoheptonate dehydrate with pH above 10.0 using The process of this study was originally developed and current densities of 0–5 A/dm2. The thickness of the brass patented by our group using cyanide precursor film was 5–50 m. According to their results, the Cu7OZn3O (Domínguez-Ríos et al., 2008; Domínguez et al., 2001; brass characteristic color was obtained with current Hurtado-Macias et al., 2010; Domínguez-Ríos et al., 2005). densities above 1 A/dm2. There is a patent for cyanide-free In these studies, the bath composition contained ZnO, electroplating brass plating based on pyrophosphate and CuCN, NaCN, NaOH, Rochelle salt, and NH3OH-Na2CO3 to orthophosphate, with the application of a brass film with a adjust the pH. Due to environmental pressures and for thickness of 0.05 to 0.1 m on a metallic foil substrate toxicological reasons, we started a research in order to (Ameen and Orloff, 1998). Carlos and De Almeida (2004) replace CuCN by the environmentally friendly CuSO4. The studied the effect of polyalcohol sorbitol on an electrolytic process reported in this study concerns an electroless bath bath of Cu-Zn and reported the capability to obtain colors of that solves several problems that are present in the Cu-Zn deposit from golden to grayish bright brass. electroplating of brass. Studies on cyanide-free electrolytic Sn-Zn bath plating using sulfate-tartrates at pH from 4 to 5 have also been published (Guaus and Torrent-Burgués, 2005). Another EXPERIMENTAL research on the electroplating of Cu-Zn alloy in an alkaline solution by adding D-mannitol was reported (Juskenas et Samples of zamak alloy with dimensions of 20 mm × 20 mm al., 2007). De Almeida et al. (2011) studied electrolytic Cu- × 2 mm were used as a substrate. They were roughened Zn plating based on Ethylenediaminetetraacetic acid with 220 and 600 grit sandpapers and then weighed in (EDTA) as Cu2+complexing, a cyanide-free process with the groups of three pieces to start the process of electroless capability to obtain yellow brass color. Ballesteros et al. brass plating. Three samples were subjected to electroless (2014) studied the electrochemical deposition of Cu-Zn plating for each experimental condition. To properly using chloride of Cu and Znandglycine as complexing agent; prepare the surface of the pieces of zamakalloy for the this electrolytic bath was also free of cyanides and worked electroless brass, the following baths were prepared: at room temperature. Recently, Minggang et al. (2015) studied the influence of copper sulfate for electrolytic Cu-Zn a) Alkaline degreasing bath, which was prepared with plating in a cyanide-free bath using 1-hydroxyethylidene-1, Na2CO3 and Na3PO4-12H2O as recommended by ASTM 1-diphosphonic acid (HEDP), potassium citrate, Cu and Zn B252-92 (2009), a bath temperature of 70–85C, a current sulfates, and potassium hydroxide to adjust the pH to 13. density of 30–55 A/dm2, time of 180 s, and rinsing with Among the most recent efforts to apply a cyanide-free distilled water. Cu-Zn coating, we can review the study of Ramírez and b) A cathodic degreasing bath of sodium hydroxide (NaOH), Calderón (2016) who investigated several Cu and Zn bath which was used to complete the removal of oils and fats compositions using sulfates, triethanolamine as a chelating and to ensure good adhesion of the electroless brass plating agent, sodium hydroxide, and an alkaline pH of (ASTM B252-92, 2009). The conditions of the bath were approximately 14. It can have different compositions of the room temperature, a current density of 16 A/dm2, a time of Cu-Zn film and by controlling the amount of 40 s, and rinsing with distilled water. triethanolamine and the applied current density, a Cu7OZn3O coating could be obtained. After surface preparation, the next step was immersion in A comparative study of four N-based additives added to a the electroless brass plating bath, for which the content of plating bath of Cu-Zn-Sn with different amounts of CuSO4 was varied while keeping the concentration of the additives showed that it was possible to control the color of other reagents constant in accordance with our previous the alloy and obtain a color that imitated gold color. The studies (Domínguez-Ríos et al., 2008; Domínguez et al., four additives were triethanolamine (TEA), ammonium 2001; Hurtado-Macias et al., 2010; Domínguez-Ríos et al., fluoride (AF), ammonia triacetic acid (NTA), and 2005). The composition and conditions of the baths used in polyacrylamide (PAM). The color varied from a red to a the experiments are shown in Table 1. color that imitated gold, and Cu-Zn-Sn blackened coatings The surface characterization and measurement of the could be obtained by using a larger quantity of the additives thickness of the electroless brass coating was performed by (Ding et al., 2018). scanning electron microscopy (FSEM) using a Jeol JSM 7400 In previous studies on electroless brass plating on zamak instrument and the weight gain was calculated alloy (Domínguez-Ríos et al., 2008; Domínguez et al., 2001; gravimetrically. For measurement of the L*, a*, and b* color Academia Journal of Environmental Science; Mendoza-Aragón et al.
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