Synthesization And Electrochemical Corrosion Behavior Of Nano/Nanoscale-Twin Nickels

Nano materials have received more attention because of their good physical, chemical and mechanics performance and are widely used in metallurgy and corrosion areas. In our work, nano/nano-twin nickel coatings were synthesized using pulse electrodeposition by optimizing the plating parameters. X-Ray diffraction (XRD) and Transmission electron microscopy (TEM) were used to characterize the microstructure of the nano/nano-twin nickel samples. It indicated that the grain size of nano sample varied from 12 nm to 50 nm.The nano-twin sample consisted of irregular shaped grains (most of them were roughly equiaxed in three dimensions) with random orientations. Each grain contained a high density of growth twins of different orientation. Measurements of the lamella thickness showed a wide distribution ranging from 8 nm to about 62 nm. The length of twin lamellar geometry varied from about 100 nm to 400 nm.The second object of this work is focus on researching the electrochemical corrosion behavior of nano/nano-twin nickel and cast nickel in 0.1 M H₃BO₃, 0.025 M Na₂B₄O₇ 10H₂O and 0.1 M H₃BO₃,0.025 M Na₂B₄O₇ 10H₂O,NaCl. The corrosion behaviors of nano/nano-twin nickel coatings and cast nickel were compared by different electrochemical methods, such as polarization curves, electrochemical impedance spectrum (EIS) and Mott-Schottky analysis. The influences of electrodeposition parameters on grain sizes of coatings and nano/ nano-twin structure on the corrosion behavior were investigated. By employing Mott-Schottky analysis and Point Defect Mode (PDM Model), the semiconductor behavior of passive films formed on cast nickel and nano-twin nickel were investigated, results showed that both the passive films were P-type semiconductor, and the nano-twin structure has great effect on the point defect densities (N_A) and its diffusion coefficient (D_M) in the passive film.The main conclusions are as follows:(1) A watt's bath was used for synthesization of nano-twin nickel; the composition of plating bath is 240g/L-NiSO₄·6H₂O,30g/L NiCl₂·6H₂O,30g/L H₃BO₄.The corrosion and passive behavior of nano-twin nickel became better when pulse current densities increased.(2) A watt's bath was used for electroplating of nano nickel; the composition of plating bath is 240g/L NiSO₄·6H₂O,30g/L NiCl₂·6H₂O,30g/L H₃BO₄,1g/L saccharin. The grain size of nano nickel decreased when pulse average current densities increased, which lead to the apparent improvement of the corrosion and passive property of nano nickel.(3) Nano-twin nickel coating had lower i_corr,wider passive region, lower i_pand higher E_b compared with cast nickel. This showed that nano- twin nicke had better corrosion and passive behavior, kinetics parameters of passive films illustrated that diffusion coefficients of nano-twin nickel are two magnitudes less, thickness of passive films on nano-twin nickel are 1/3 of cast nickel.The results showed that nano-twin nickel had thinner, compacter and steadier passive films.(4) Nano-twin nickel possessed much higher resistance to pitting corrosion compared with the cast counterpart in the borate buffer solution contained various[CL'].