Electrodeposition of Ni, Sn and Ni–Sn Alloy Coatings from Pyrophosphate-Glycine Bath

Abstract

In this work the electrodeposition of Ni, Sn and Ni–Sn alloy from the solution containing pyrophosphate and/or glycine has been investigated by cyclic voltammmetry (CV), potentiostatic pulse and polarization curve measurements on two substrates, Ni and GC. It has been shown that the process of Sn electrodeposition in pure pyrophosphate solution commences at the potential of about −0.90 V on both substrates being characterized by the formation of isolated 3D crystals and their further growth by the reduction of [Sn(Pyr)2]6− complex. On the GC surface Sn 3D crystals remain isolated, following 3D nucleation and growth mechanism which does not fit any of the theoretically predicted models. Ni–Sn alloy deposition in the solution containing both cations (Sn2+, Ni2+) and both anions (pyrophosphate and glycine) occurs by the same growth mechanism as pure Sn deposition by simultaneous reduction of [Sn(Pyr)2]6−, [Ni(Pyr)2]6−and/or [Ni(Pyr)3]− complexes at pH 8.0. Depending on the current density/potential of the Ni–Sn alloy coating deposition onto Ni electrode the composition of the flat and compact coatings varies in the range from 66 to 50 atom% Ni, i.e. 34 to 50 atom% Sn.