Electrochemical studies of zinc–nickel codeposition in sulphate bath Mortaga M. Abou-Krisha Faculty of Science, Chemistry Department, South Valley University, Qena, Egypt Received 23 June 2004; received in revised form 30 January 2005; accepted 30 January 2005 Available online 12 March 2005 Abstract The electrodeposition of Zn–Ni alloys from a sulphate bath was studied under different conditions. The bath had the composition 0.40 M sodium sulphate, 0.01 M sulphuric acid, 0.16 M boric acid, 0.20 M zinc sulphate and 0.20 M nickel sulphate. It is found that the plating bath temperature has a great effect on the cyclic voltammograms, galvanostatic measurements during electrodeposition, and consequently linear polarization resistance for corrosion study and the alloy composition. Under the examined conditions, the electrodeposition of the alloys was of anomalous type. X-ray diffraction measurements revealed that the alloys consisted of the d-phase (Ni 3 Zn 22 ) or a mixture of the two phases d and g (Ni 5 Zn 21 ). The comparison between Ni deposition and Zn–Ni codeposition revealed that the remarkable inhibition of Ni deposition takes place due to the presence of Zn 2+ in the plating bath. The Ni deposition starts at 0.85 V in the bath of Ni deposition only, but the deposition starts at more negative potentials in the codeposition bath although the concentration of Ni 2+ is the same in the both baths. # 2005 Elsevier B.V. All rights reserved. Keywords: Zn–Ni alloy; Electroplating; Anomalous codeposition; Plating bath temperature; Electrochemical studies; Sulphate bath 1. Introduction In recent years, great interest has been shown in the possibilities offered by the electrodeposition of alloys, mainly in the automotive industry. Usually the mechanical and chemical properties of metals are improved by alloying. In particular, it is known that the mechanical properties of zinc electrodeposits can be improved by alloying zinc with nickel [1,2]. Using Zn–Ni alloy deposits on iron also increases their corrosion resistance [3–8]. The electrodeposition of Zn–Ni alloys is classified by Brenner [9] as an anomalous codeposition, where zinc, which is the less noble metal, is preferentially deposited. Although this phenomenon [10] has been known since 1907, the codeposition mechanisms of zinc and nickel are not well understood [11,12]. Many studies have attempted to understand the characteristics of the deposition process [13–16]. There are some propositions to explain the anomalous codeposition of Zn–Ni alloys. The first attributes the anomalous www.elsevier.com/locate/apsusc Applied Surface Science 252 (2005) 1035–1048 E-mail address: mortaga_aboukrisha@yahoo.com. 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.01.161