Electrodeposition of Ni-zirconia or Ni-titania composite coatings from a methanesulfonic acid bath

Abstract

The study addresses the patterns of formation of Ni-ZrO2 and Ni-TiO2 composite coatings from methanesulfonate and sulfate electrolytes at pH 3. It has been shown that the aggregative stability of the dispersed phase particles is better in the methanesulfonate electrolyte than in the sulfate electrolyte. As a result, at the same volume concentration of the non-metallic phase in both electrolytes, the concentration of particles is larger in the methanesulfonate electrolyte. This ensures the formation of composite coatings from methanesulfonate electrolyte with a content of non-metallic particles increased by 20–30 vol% compared to sulfate electrolyte. A mechanism for forming a composite coating has been proposed, which takes into account the different rates of the metal phase electrodeposition on the electrode surfaces that are free from the dispersed phase or conditionally occupied. A mathematical model of composite coating formation has been developed, which adequately describes the obtained experimental data. Incorporation of the non-metallic phase into the nickel matrix leads to a change in the coating structure and decrease in the sizes of metal grains. It has been found that the physicochemical properties of Ni-ZrO2 and Ni-TiO2 composite coatings depend on the content of non-metallic phase particles in them. It has been revealed that the microhardness of Ni-ZrO2 coatings obtained from methanesulfonate electrolyte is 10 % higher than the microhardness of coatings deposited from sulfate electrolyte, which is due to a higher content of the non-metallic phase. The photocatalytic activity of Ni-TiO2 composite coatings correlates with the content of the dispersed phase in them, which is due to the participation of TiO2 particle surfaces, accessible to irradiation, in the photocatalytic reaction. It has been found that an increased content of the dispersed phase in Ni-ZrO2 and Ni-TiO2 composite coatings obtained from methanesulfonate electrolyte leads to increased values of their microhardness and photocatalytic activity.