| Ionic liquid (IL) is defined as liquid which solely consist of cations and anions at room temperature. As a new developed solvent, IL owns a number of interesting and advantageous characteristics, such as wide electrochemical windows, wide working temperature range, high electrical conductivity, and good thermal and chemical stability. Zn-Co alloy and Zn-Sn alloy has a lot more excellent mechanical properties and chemical properties, such as corrosion resistance, ductility, wear resistance and weldability. Therefore, these alloys should be widely used in steel protective coatings, automotive parts, electronics parts and other industrial fields. However, the current system to get more of these alloys is necessary to add a complexing agent or additive aqueous systems, and these complexing agents or additives harmful to the environment. Therefore, it is necessary to find an environmentally friendly solvent.In this study, the electrochemical behavior of Zn(II) and Co(II) in ionic liquid [EMIm] [BF4] and in [EMIm][BF4]-H2O mixtures and the effects of bath temperature, and deposition potential on the surface morphology and composition of Zn-Co films were investigated, as well as the electrochemical behavior of Zn(II) and Co(II) in ChCl-EG eutectic ionic liquid and the influence of bath temperature, and deposition potential on the surface morphology and composition of Zn-Sn coatings were investigated. High resolution scanning electron microscope (SEM) was used to characterize the film surface morphology and an energy dispersive analysis (EDX) was used for chemical composition analysis of the elements in the deposited films. The X-ray diffraction (XRD) was employed to obtain XRD spectra of the deposited layer.Firstly, The deposition potential of Zn and Co were studied by cyclic voltammogram(CV), respectively. And Compared with the CVs of 0.10 M Zn(BF4)2/0.05 M Co(BF4)2 in [EMIm][BF4], it was found that the dissolution of Co in mixture system shifted from -0.52 V to-0.65 V and the dissolution of Zn in mixture system shifted from -1.09 V to -0.87 V. The results indicated that the codeposition alloy of Zn and Co was obtained. The reduction peak current in the Zn-Co codeposition process increased significantly, which was attributed to a mutual promotion process, deposition of Co preferentially had induced effect on Zn.Secondly, CVs of 0.10 M Zn(BF4)2/0.05 M Co(BF4)2 in [EMIm][BF4] solution with different water contents were investigated. Both the reduction current and the dissolution current increased significantly with the water content, indicating that the transfer rates of metal ions increased with an increase of the water content. When water content increased from 2.5% to 10%, the reduction current of Zn(II) increased from 1.82×10-4 A to 3.69×10-4 A, but the reduction peak potential of Zn(II) shifted from -1.51 V to -1.59 V.The effect of different water content, deposition time and deposition potential on surface morphology and composition of deposition coatings were studied in this paper. With the addition of water, the reduction potential shifted to negative direction, while the reduction current enhanced significantly, which led to a faster growth of Zn/Co nuclei than the formation of Zn/Co nuclei.The effects of the scan rate on the CVs of 0.10 M Zn(BF4)2/0.05 M Co(BF4)2 in [EMIm][BF4]-H2O 5%(v/v) solution and in [EMIm][BF4] were investigated. It was also found from CVs that reduction reaction of Zn(II) and Co(II) on a gold working electrode was an irreversible process. The diffusion coefficient Do for Zn(II) and Co(II) in [EMIm]BF4-H2O (5%) bath were 2.37×10-5 cm2/s and 2.55×10-5 cm2/s, respectively. With the same method, the diffusion coefficient Do of Zn(II) and Co(II) in [EMIm][BF4] were obtained, and were 3.92×10-6 cm2/s and 4.77×10-6 cm2/s, respectively. The calculation results indicated that the diffusion coefficients(Do) of Zn(II) and Co(II) in [EMIm][BF4]-H2O (5%) bath were much larger than those in [EMIm][BF4], which implied that the solution viscosity was decreased while the mass transfer rate and migration rate of the Zn(II) and Co(II) species were increased significantly with addition of water. The Chronoamperometric results indicated that the electrodeposition of Zn-Co alloys on gold electrode followed the mechanism of three-dimensional instantaneous nucleation and growth process.And then, electrodeposition of Zn-Sn alloy in the ChCl-EG deep eutectic ionic liquid was studied. Furthermore, the composition of bath, bath temperature, and deposition potential had effect on chemical composition, surface morphology and corrosion resistance were investigated. The ZnCl2-SnCl2-ChCl-EG system had the smallest potential difference between the reduction potential of Zn(II) and Sn(II), making it favorable for codeposition of Zn-Sn alloy. In addition, the deposition potential shifted negatively result in the particles on surface became larger and an increase of Zn content of Zn-Sn alloy. And with the increase of bath temperature, the Zn content of Zn-Sn alloy increased.The potentiodynamic polarization technique was used to investigate electrochemical behavior of materials. The potentiodynamic polarization studies indicated that the corrosion resistance of the films depended on the morphology and film composition (Sn content). The deposition potential shifted positively result in the particles on Zn-Sn alloy surface became smaller and more compact, and Sn content increased. Hence, the corrosion resistance increased. |
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