Ni-sic Composite Electrode Deposition Process Kinetics And Coating Electrochemical Corrosion Behavior Research

The electrodeposited mechanism was studied, especially the influence of SiC particles. The SEM and X-ray were performed in order to study the morphology and microstructure of the SiC powder. And the adsorption action of SiC particles in the solution was characterized by precision pH apparatus. On this condition, cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) at cathodic potentials were performed in the pure nickel system (PN), Ni-SiC codeposition system (NS) and Ni-SiC codepositon system with accelerant (NSA), all these experiments were tested by the CHI660C instrument. Furthermore, we also have studied the corrosion behaviors of these three types of coatings immersing in the 3.5%NaCl and 3.5%NaCl+0.3%H₂O₂ solution by Tafel plots and electrochemical impedance spectroscopy.The results show that SiC particles make for the polygon morphology, and the mean diameter is 7μm . From the X-ray reflection, we find most of the SiC particles have the 6H crystal structure. When these powders were added into the deposition solution, they would be packed by lots of H⁺ and Ni²⁺ or other ions. As a result, they will present negative potential. Under the pH value of 3.70, ions adsorpotion is most obviously.In order to make clear the nucleation and growth process, we performed the potentiostatic I-t transients tests for the above three kind of solution systems. The results show that, the electrocrystallization of nickel prefer to two step. In the initial of the first process, the codeposition of compound systems follow a 3-D progressive nucleation/growth mechanism of Bewick-Fleshmann-Thrisk model, along with the increase of negative potential, this process passes through a transformation between BFT progressive mechanism and BFT instanstaneous mechanism. The second stage, along with the increase of negative potential, the nucleation/growth process follow the BFT instanstaneous mechanism and SH instanstaneous mechanism successively. However, either Ni-SiC codeposition coatings or pure nickel coationgs, the nucleation relaxation time t_m decreases regularly with the increasing of the negative potential, while the corresponding current I_m were almost in the same quantity. Obviously, because of the addition of the SiC powders, the nucleation potential of nickel turns to positive direction. And the nucleation relaxation time t_m decreases clearly.The results of electrochemical impedance spectroscopy show that, outside the farady potential zone, the adsorption character of SiC powders will change the surface charge arrangement. It destroys the shield effects of hydrate and large molecules adsorpped on the working electrode surface, and decreases the transfer resistance largely. When the voltages near or exceed the electrodeposited potential, the double lays capacitance microstructure was dropped, the advantages of SiC were destroyed too. The impedance will as same as the pure nickel solution.In the 3.5%NaCl and 3.5%NaCl+0.3%H₂O₂ solution, these three types lays shows the different corrosion behaviors. In 3.5%NaCl solution, pure nickel coatings display a greater corrosion resistance value than codeposition coatings. However, in the strong oxidable solution, codeposition coatings obtain more protection than pure nickel coationg. A great deal of complex three dimension net structures were imported to layers. It causes a great increase of charge transfer resistance, seperates the corrosion current efficiently, and protects the matrix from destroyed environment.