The salt of formula [H2EDTA2+][HSO4-]2 (dihydrogen ethylenediaminetetraacetate di(hydrogen sulfate(VI)) was used to examine the physicochemical properties of the resulting Ni layer and evaluate the applicability of the salt as a new additive for Watts-type baths. The Ni coatings deposited from baths containing [H2EDTA2+][HSO4-]2 were compared with those obtained from other baths. The nucleation of nickel on the electrode was proven to occur the slowest in the bath that contained the mixture of [H2EDTA2+][HSO4-]2 and saccharin compared with other baths. The addition of [H2EDTA2+][HSO4-]2 alone (bath III) generated a coating with a morphology similar to that obtained from bath I (without additives). Despite the similar morphology and wettability of the Ni-coated surfaces plated from various baths (all Ni coatings were hydrophilic with contact angles in the range of 68 to 77°), some differences in electrochemical properties were noted. The corrosion resistance for the coatings plated from baths II and IV containing saccharin (Icorr = 1.1 and 1.5 µA/cm2, respectively) and the mixture of saccharin and [H2EDTA2+][HSO4-]2 (Icorr = 0.88 µA/cm2), respectively, was similar or even better than the coating obtained from baths without [H2EDTA2+][HSO4-]2 (Icorr = 9.02 µA/cm2).
Keywords: EDTA salt additive; corrosion resistance; nickel coatings; versenium cation.