Influences of Saccharin on Electrochemical Behavior of Nickel Electrodeposition

Abstract

Electrodeposition of Ni was performed in acid Watt's solutions. Saccharin concentrations were varied in order to analyze its influence on the electrochemical behaviors of Ni deposition. Investigations were conducted using CHI660D, by methods of linear potential sweep, cyclic voltammetry and A. C. Impedance. Results indicate that with the increase of saccharin concentration, the cathodic polarization, apparent activation energy and the electrochemical reaction resistance of Ni electrodeposition increase. The exchange current density decreases with the increase of saccharin concentration. The electrodeposition of Ni is a mixing process controlled by electrochemical polarization and concentration polarization. The change of saccharin concentration does not affect the electrodeposition mechanism of Ni. But there is an obvious inhibition and blocking effect of saccharin on nickel electrodeposition. When the concentration of saccharin is 4g/L, its adsorption capacity in electrode is close to saturation. The saccharin concentration should be less than 4g/L. Introduction Ni coating has excellent tensile strength, wear resistance, corrosion resistance, ductility and toughness. As a protective and decorative coating, it is widely used in aerospace, automotive and material engineering. The physical properties of Ni deposit are closely related to the bright agent. Due to containing polar groups C-SO 2-with strong polarity, saccharin molecules can be adsorbed on the surface of the cathode. It accelerates the nucleation rate and increases the number of nuclei, so that the Ni deposit is compact, uniform, bright and smooth with fine grains, and its internal stress is small. Therefore, as a good primary brightener, saccharin is widely used in the Ni plating process. There have been many reports about the effects of saccharin on electrodeposition Ni [1-13]. Most of the literature focuses on the influence of saccharin on structure and surface morphology [4-6, 9, 12], hardness [8], roughness [1], grain size [3] of Ni deposits. These reports didn't investigate in detail the effect of saccharin on the nickel deposition process and the essential reason for saccharin improving the performance of nickel deposits. Literature on the effects of electrochemical behavior and characteristics of saccharin on nickel electrodeposition is also limited. In this paper, influence of saccharin on the electrochemical behavior of Ni electrodeposition is investigated by cathodic polarization, cyclic voltammetry and A.C. impedance methods. Variation of kinetic parameters of the exchange current density, activation energy and electrochemical reaction resistance of Ni electrodeposition with saccharin concentration is further investigated. The aim of this paper is to provide some theoretical basis for the industrial application of nickel electroplating. The innovation in the work is to study the law of the exchange current density, activation energy and other kinetic parameters during the electrodeposition of nickel.