Electrodeposition of nickel-cobalt alloys: The effect of process parameters on energy consumption

Nickel-cobalt alloys have many important applications in the electrical, electronic, mechanical and aeronautic industries. This binary alloy can be produced by electrowinning, the aim being to obtain a dense deposit under operative conditions that optimises current efficiency and specific energy consumption. In this work nickel-cobalt electrodeposition under galvanostatic conditions was studied in acid sulphate medium. This binary alloy was electrowon from a bath containing about 40 g/L Ni and a cobalt concentration ranging from 2 to 8 g/L. Current densities ranging from 180 to 400 A/m(2) and temperatures from 27 to 60 degreesC were tested. The effects of current density, temperature and electrolyte pH have been investigated. Since hydrogen evolution accompanies Ni-Co electrodeposition, maintaining the pH in the appropriate range is necessary; thus, the effects of the addition of two buffers, H3BO3 and (NH4)(2)SO4, have been investigated. The tests highlighted that the control of process parameters is critical. The best results, in terms of energy consumption and deposit quality, were obtained in the presence of boric acid, at high temperature and in a cell having two separated compartments. (C) 2001 Elsevier Science Ltd. All rights reserved.