Zinc-Nickel Alloy Electrodeposition – Influence of Triethanolamine

V. Ravindran *and V.S. Muralidharan

 Central Electrochemical Research Institute, Karaikudi 630 006, Tamil Nadu, India

 

Received 16 January 2006; accepted 19 November 2006

 

 

Abstract

Compared to pure zinc plating, zinc alloys provide several advantages. A zinc alloy generally offers superior sacrificial protection to steel since it corrodes more slowly than pure zinc. A search for a non-cyanide zinc plating bath resulted on the development of a zinc nickel sulphamate bath. To obtain better quality zinc-nickel deposits, triethanolamine was added to the bath. In this paper the influence of triethanolamine in zinc-nickel plating from sulphamate bath has been investigated through current efficiency measurements, cyclic voltammetry, scanning electron microscope, and X-ray diffraction techniques. In the presence of triethanolamine in the zinc-nickel sulphamate bath the current efficiency of alloy deposition increased to a maximum of 99% at the current density of 1.5 Adm^-2 and thereafter decreased. TEA adsorbed on the electrode surface obeying Henry’s isotherm. On mild steel surfaces, uniform smooth slate gray deposit with smaller crystallites was produced, in presence of TEA in solution, and the electrodeposits exhibited additional Zn(OH)₂ and g-Ni₃Zn₂₂ phases. Hydrogen evolution was suppressed by TEA and thereby current efficiency is increased for alloy deposition.

 

Keywords: cyclic voltammetry, electrodeposition, triethanolamine, XRD, Zn-Ni.

 

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* Corresponding author. E-mail address:  visalakshi47@yahoo.com