Study of nickel-cobalt alloy electrodeposition from a sulfamate electrolyte with different anion additives

The experimental results of the present study show that the composition of the electrodeposited nickel-cobalt alloy in sulfamate electrolytes containing anion additives is influenced in a complicated manner by the concentrations of cobalt(II) ion and citric acid, pH, and applied current density. The operating conditions were found under which the increase in the pH of the solution adjacent to the cathode is inhibited. Citrate anions form a wide variety of complexes with nicker and cobalt. Protonated citrate complexes of nickel(ll) and cobalt(II) are apt to be involved in the electrochemical alloying process. Acetate anions serve to buffer the sulfamate solutions. Nickel-cobalt electrochemical alloying leads to an increase in the reaction rate of cobalt at the expense of the nickel reaction rate. The data confirm that inhibition of the more noble metal by the less noble one does not depend on the anion composition of the electrolyte. (C) 2000 The Electrochemical Society. S0013-4651(00)02-107-8. Ail rights reserved.