Electrocrystallisation of nickel: Effect of certain metal ions

Abstract

The effects of alkali metal ions Li+, Na+, K+ and transition metal ions Cr3+ and Mo6+ on the cathodic current efficiency, deposit quality, crystallographic orientations, deposit morphology and polarisation behaviour of the cathode during nickel electrocrystallisation on stainless steel substrate from aqueous sulphate solutions containing boric acid were investigated. The alkali metal ions had virtually no effect on the cathodic current efficiency, deposit quality, crystallographic orientations, deposit morphology and cathodic polarisation. On the other hand, there were significant variations in the current efficiency and deposit characteristics when Cr3+ or Mo6+ were present in the electrolyte. Current efficiency decreased by more than 10% even at lower concentrations (greater than or equal to 100 mg/L). Similarly purity of the deposits was affected by the presence of either of the metal ions. In the presence of Cr3+ there was progressive shifting of the nucleation potential of nickel towards more negative values, whereas, in the case of Mo6+ the nucleation potential shifted initially towards positive values in the concentration range 2-40 mg/L, but then towards negative values when its concentration exceeded 40 mg/L.