Effect of Annealing on Surface Morphology and Structure of Nickel Coatings Deposited from Deep Eutectic Solvents

Nanocrystalline nickel coatings deposited on a copper base material from DES made of choline chloride and ethylene glycol in 1:2 molar ratio containing 1 mol dm(-3) NiCl2.6H(2)O were modified through post-deposition heat treatment at the temperatures from 100 to 400 & DEG;C. As-deposited coatings were composed of spheroidal agglomerates with the size of several hundred nanometers interspersed with lamellar crystals, but after annealing at 300 & DEG;C and 400 & DEG;C only single nano-sized plates embedded in a granular and porous layer remained. As the temperature of the heat treatment increased from 100 & DEG;C to 400 & DEG;C, the mean crystallite size increased from 13 to 35 nm. The change in crystallite size was accompanied by a change in microhardness, the maximum value of which was measured for the annealed coating at 200 & DEG;C. As a result of heat treatment, coatings were gradually covered by a layer of oxidized nickel species. XPS analyses showed that NiOOH and Ni(OH)(2) dominated among them. Above 200 & DEG;C the share of these compounds began to decline in the face of the increasing share of NiO. This, in turn, clearly translated into a deterioration of the corrosion resistance of Ni coatings annealed at 300 & DEG;C, and especially at 400 & DEG;C, during exposure in 0.05 mol dm(-3) NaCl solution.

Automated summary

The nanocrystalline nickel coatings on a copper base material were modified through post-deposition heat treatment at temperatures ranging from 100 to 400°C. The increase in heat treatment temperature led to an increase in mean crystallite size and a deterioration in corrosion resistance due to the increase in oxidized nickel species in the coatings.