Electrodeposition Behavior of Zn–Ni Alloy from Alkaline Zincate Solutions Containing Various Brighteners and its Microstructure

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<p>The effect of brighteners on the deposition behavior of Zn–Ni alloys and their microstructure was investigated. Zn–Ni alloys were electrodeposited on Cu electrode at 10–5000 A·m−2, 105 C·m−2, and 308 K. Although the degree of suppression of hydrogen evolution differed depending on the kind of brightener, the transition current density at which the deposition behavior shifted from normal to anomalous was practically the same in all the solutions containing brighteners. The current efficiency of the alloy deposition significantly decreased with the addition of brighteners, which had a suppression effect on the Zn deposition. Considering that the brighteners suppressed the Ni deposition more than the Zn deposition, the Ni content in the deposited films decreased with the addition of brighteners. When the brightener of a straight-chain polymer comprising a quaternary ammonium cation (PQ) that can suppress the diffusion of ZnO22− and Ni ions in a solution was added, the Ni content in the deposited films increased with increasing current density in a high-current-density region. This was attributed to the fact that Zn, which was preferentially deposited over Ni earlier, reached the diffusion limitation of ZnO22−, and Ni deposition did not reach the diffusion-limited current density. When PQ and a quaternary ammonium salt with a benzene ring were added to the solution, the films obtained at the diffusion-limited current density of ZnO22− exhibited smooth surfaces comprising fine crystals. With the addition of brighteners to increase the overpotential for deposition, the γ-phase (the intermetallic compound of Ni2Zn11) of the deposited films easily formed.</p>

Journal

  • ISIJ International

    ISIJ International 63 (8), 1394-1404, 2023-08-15

    The Iron and Steel Institute of Japan

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