Effects of nickel ion contents on electrodeposition, composition, structure and properties of palladium-nickel alloys

摘要

The effects of nickel ion contents on the electrodeposition, composition, structure and properties of palladium-nickel alloys were studied from a nearly neutral Pd(NH_3)_2Cl_2-NiSO_4·6H_2O bath by adjusting the Ni~(2+)/Pd~(2+) ion mole ratios. The results demonstrate that coatings with 17.1-44.0 wt-% Ni can be successfully electrodeposited by simply adjusting the Ni~(2+)/Pd~(2+) ion mole ratios from 0.5:1 to 2.5:1. The coatings are bright, pore-free and crack-free with fine and compact grains. The structure of the coatings is a solid solution in a face-centred cubic structure; its lattice constant gradually decreases with a corresponding increase in the Ni content. The coatings exhibit a comparable corrosion resistance in a 3.5%NaCl solution, where the corrosion potentials E_(corr) are between -0.010 and -0.064 V(saturated calomel electrode). Corrosion current densities j_(corr) slightly increased from 9.8 to 21.3 μA cm~(-2), with the Ni content increasing from 17.1 to 44.0 wt-%. The microhardness of the coatings increased with a corresponding increase in their Ni contents, and shows the highest value of 511 kg mm~(-2) with 44.0 wt-%Ni. The coatings exhibit comparable contact resistances of 0.2-0.4 mΩ.