Corrosion Study of Zinc, Nickel, and Zinc-Nickel Alloys in Alkaline Solutions by Tafel Plot and Impedance Techniques
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ZINC is one of the most used metals in electroplating. It is generally used as sacrificial anode in cathodic protection of steel against corrosion. Due to its practical uses, the corrosion mechanism of zinc was studied in field exposures as well as in laboratory under controlled environments. It is well known that in a NaOH electrolyte, pH > 12, a passive layer composed from a Zn(OH)2 or ZnO is formed on the zinc sample.[1–3] Zinc is a favorable anode in primary batteries because of its high capacity, high discharge efficiency, and high safety features associated with its manufacturing process and use.[4] Zinc was added with mercury to suppress the evolution of hydrogen gas brought on by the selfdischarge reactions of zinc and by the increase in internal cell impedance.[5–18] The use of mercury has become an environmental issue, and the attention has been focused on developing mercury-free batteries. In general, either zinc or its alloys are used as anodes in ABDEL-RAHMAN EL-SAYED, Professor of Electrochemistry, and HOSSNIA S. MOHRAN, Professor of Physical Chemistry, and HANY M. ABD EL-LATEEF, Postdoctoral Student, are with the Chemistry Department, Faculty of Science, Sohag University, 82524 Sohag, Egypt. Contact e-mail: [email protected] Manuscript submitted December 16, 2010. Article published online October 6, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
these batteries. The purity of the zinc is very high, i.e., of the order of 99.9 wt pct or more. Hence, the development of zinc or zinc-based alloys as anodes for alkaline power sources has become a necessity, and in this connection, development of mercury-free zinc assumes great importance. Similarly, Zn-air battery technology also requires mercury-free zinc anodes. As is known, Zn corrosion in alkaline solution is cathodic controlled, so the rate of the cathodic hydrogen evolution limits the Zn corrosion rate. Hence, the best way to slow the corrosion process is to reduce the hydrogen evolution rate, which can be achieved by the introduction of a small amount of other metals such as Bi, Pb, Al, and In into Zn.[19] Recently, the authors[20] added a small amount from Ni (0.5 pct) to zinc in order to improve the electrochemical behavior of the discharge cell and to suppress the anodic reaction of zinc. The electrochemical behavior of nickel in alkaline solutions has received considerable attention, primarily because of the application of Ni in rechargeable alkaline batteries.[21] Nickel and its alloys exhibited excellent corrosion resistance in aqueous aggressive environments, which are attributed to the ability of nickel to form a stable passive film on its surface.[22–31] In spite of the appearance of so many publications on the corrosion behavior of Zn-Ni alloy electrodeposition in aqueous solutions, there is no work on the electrochemical behavior of synthetic Zn-Ni alloy by fusion. VOLUME 43A, FEBRUARY 2012—619
The object of the present investigation as to study, via Tafel plot and electrochemical impedance spectroscopy (EIS), the effect of Ni con
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