Electrocodeposition of Nanocrystalline Single-Phase γ-Zn[sub 3]Ni Alloy on Composite Graphite

Abstract

The single-phase gamma zinc-nickel alloy ͑␥-Zn 3 Ni͒ nanocrystal was deposited on composite graphite electrode at a scan rate of 10,000 mV s −1 . The average particle size obtained was 11.8 Ϯ 3.1 nm. Transmission electron microscopy analysis indicated that codeposition applied potential, i.e., nucleation overpotential, scan rate, and codeposition time were critical on crystal sizing and Ni content in the matrix. Cyclic voltammetry and analysis of X-ray diffraction have also indicated that single-phase ͑␥-phase͒ alloy was, indeed, obtained at the scan rate used. The results also revealed that 19.0 wt % Ni nanoparticles were uniformly dispersed in the phase compositions of the alloy coating.Nanostructure materials with their unique and fascinating properties have prompted scientists to explore the possibilities of using them in industrial applications. For example, bimetallic thin films and nanoalloys, especially those with magnetic quality, could be used in storage systems, 1 superconductors, electrochromic materials, catalysts, and decorative and protective coatings. 2,3 Zinc is usually used as sacrificial anode, which provides cathodic protection to iron. However, this coating corrodes rapidly; hence, Zn-Ni alloy coating containing up to 12 wt % Ni 4 is used as the passivation agent to minimize this problem. Zn-Ni alloys exhibit a high protective function against corrosion, good mechanical properties, 5 and low hydrogen brittleness 6 as compared to pure zinc and galvanized steel. It has been widely applied as a highly corrosion-resistant coating, especially in steel mills and automotive and computer industries. 7-9 Zn-Ni alloy has a higher negative potential than cadmium and, hence, dissolves rapidly in corrosive environments. But, it is a good replacement for cadmium coating due to the latter's toxicity. 10 The electrodeposition of Zn-Ni alloy is classified as an anomalous type of codeposition. 11 In the electrodeposition, Zn, a thermodynamically less-noble metal than Ni, is preferentially deposited. The formal electrode potentials ͑E o ͒ for Zn 2+ /Zn and Ni 2+ /Ni pairs are −0.762 and −0.236 V, respectively. The alloy composition always has a greater abundance of zinc than of nickel. Higher Ni content leads to a more-positive open-circuit potential, which in turn reduces the motivation force for the galvanic corrosion. 10 The commonly employed Zn-Ni alloy in the aeronautical industry has 15-22 wt %. 12 Attempts to rationalize the anomalous electrodeposition of the Zn-Ni alloy are not quite successful. 13-15 One reason could be the favorable kinetic effect of Zn deposition as compared to Ni deposition. 13 The increase in pH near the cathode surface, followed by the formation of Zn hydroxide precipitate and the inhibition of Ni discharge, is also suggested. 14,15 In addition to this, the effects of organic additives on improved Ni content in the alloy composition are also investigated. 6,13 There are three intermetallic phases, i.e., ␥, , and ␦ based on Ni content, on the equilibrium-phase diagram for the Zn-Ni...

Graphene-Supported Nanoelectrocatalysts for Fuel Cells: Synthesis, Properties, and Applications

“…However, the poor electrical conductivity of nickel oxides, hydroxides, and its oxidized NiOOH form may restrict their catalytic performance to some extent. Therefore, much work has been focused on using different additives to improve the electrocatalytic property of nickel, among which ethanol electrooxidation by Pd–Ni, Cu–Ni,and Ni–Zn in alkaline solution has been reported.…”

Electrodeposition of nanocrystalline Zn–Ni coatings with single gamma phase from an alkaline bath

“…or adding additives. Alfantez et al [20] produced nanocrystalline Zn-Ni coatings from a chloridebased electrolyte and Tehrani et al [21] presented nanocrystalline single γ-Zn 3 Ni phase by cyclic voltammetry at a scan rate of 10 V/s. Their coatings were both obtained from acid bath.…”

Quantitative Analysis of Chemical and Phase Composition of Zn−Ni Alloy Coating by Potentiodynamic Stripping

“…In Zn−Ni coatings obtained by electrochemical method, the α ‐phase (solid solution of Zn in Ni), γ‐ phase (Ni 5 Zn 21 ), and η ‐phases (solid solution of Ni in Zn) are mainly found besides zinc‐phase and nickel‐phase [10]. Additionally, other phases may also be found: δ ‐phase (Ni 3 Zn 22 ) [2, 11, 12–21], γ 1 ‐phase (NiZn 3 ) [15, 19, 22–25] and β ‐phase (ZnNi) [20, 25–27]. The main drawback of XRD method is that it can be hardly used for the study of thin coating, losing the accuracy for <10 μm thicknesses [28].…”

“…Section 3 starts from stripping voltammetry in the electrolyte for the alloy deposition . For such qualitative analysis the anode response of CV is used in ammonia electrolytes [10, 18, 24, 33, 45], sulphate [12, 17, 26, 46, 47–49], and chloride [13, 15, 21, 23, 34,50,51] electrolytes, in electrolytes with sulfamic acid [52], acetates [27, 53, 54], as well as in complex electrolytes based on pyrophosphate [55–57], citrate [2], amines [58], glycine and ammonia [59]. After general characterization of the coating (subsection 3.2) and choosing optimal conditions for alloy dissolution (Subsection 3.3) we present the results of qualitative (Subsection 3.4) and quantitative (Subsection 3.5) analysis by stripping voltammetry in alkaline ammonia‐glycinate electrolyte, free from Ni 2+ i ions.…”