PRODUCTION AND PROPERTIES OF COMPOSITE ELECTROCHEMICAL COATINGS WITH ELECTROCHEMICALLY DISPERSED GRAPHENE BASED ON NICKEL MATRIX

Abstract

In this work, the effect of addition of colloidal solutions of electrochemical exfoliated graphene (EEG) to the Watts bath on the process of obtaining composite coatings based on a nickel matrix was studied. It was found that the introduction of nanoparticle additives has a significant effect on the value of cathodic overvoltage during electro reduction of Ni2+. The strongest inhibition of the cathode process takes place with the introduction of 0.2 g/l of additives investigated. Further increase in the concentration of nanoparticles in the bath reduces the effect. The inhibition of the cathodic reduction of Ni2+ is associated with the adsorption of graphene nanoparticles on the active faces of growing nickel crystallites and the blocking of the accessible surface for Ni2+ reduction. Due to the increase in cathodic polarization during the deposition of the composite coating, the crystallites of the deposited nickel decrease in size and the texture of the crystal structure of the coating changes. According to energy dispersive spectroscopy data, carbon has been included in the composite coating. The carbon content in the coating increases with increasing concentration of nanoparticles in the working electrolyte. The inclusion of negatively charged nanoparticles of electrochemically dispersed graphene in the resulting precipitate becomes possible due to adsorption of Ni2+ and recharging of graphene nanoparticles. It was found that the optimal concentration of electrochemically dispersed graphene in the working electrolyte is 0.1-0.2 g/l. At a given nanoparticle content in the working bath, the porosity and roughness of the coatings decreases. The Tafel polarization curves for composite coating samples obtained in a 0.5M NaCl solution showed that the inclusion of graphene nanoparticles in the resulting coating leads to a shift of the corrosion potential to the negative area. With an increase in the carbon content in the coating, the shift in corrosion potentials increases, and the value of corrosion currents increases. For samples of composite coatings obtained at an EEG additive concentration of 0.1 g/l, a slight improvement in the protective properties is noted, which is associated with a decrease in the porosity of the coatings.