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Study of single pulse electro deposition of Zn-Ti alloy in ionic liquids

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Tutor: XuCunYing
School: Kunming University of Science and Technology
Course: Non-ferrous metallurgy
Keywords: Urea-ZnCl2ionic liquids,Zn-Ti alloys,Pulse electrodeposition,Corrosion resistanc
CLC: TG174.44
Type: Master's thesis
Year:  2013
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Abstract:
Zn-Ti alloys have shown an excellent corrosion resistance performance when the the content of titanium is less than1%. Therefore, Zn-Ti alloys can be used as a new material of steel protection. In this thesis, pulse electroplating technology was adopted to electrodeposit Zn-Ti alloys in the Urea-ZnCl2ionic liquid by adding TiCl4, the composition and morphology of the coatings were analysed by EDS,XRD,SEM et.al.The electrodeposition behavior of Zn-Ti alloys was systematiclly analysed by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy methods, etc. It has shown that the reduction potential of Zn(Ⅱ) moved negatively by adding TiCl4and the deposition of Ti was induced by the reduction of zinc. The reduction process of Ti(Ⅳ) were step by step: Ti(Ⅳ)→Ti(Ⅲ)→Ti(Ⅱ)→Ti(0). And it is easy to produce TiCl3passive film, which can be absorbed on the cathode surface, inhibiting Zn-Ti alloy deposition. The deposition of Zn-Ti alloys could be controlled by electrochemical reaction and diffusion simultaneously.The anodic dissolution behavior of zinc and titanium in Urea-ZnCl2and Urea-ZnCl2-TiCl4ionic liquids was investigated by linear sweep voltammetry. The titanium passivation phenomena is observed, and the limiting current density is small,while passivation phenomenon of zinc was not observed,current density increased with the overpotential increasing in the wide range of the overpotential.Moreover, with the increasing of titanium ion concentration in Urea-ZnCl2system, the dissolution rate (or current density) of zinc decreased; Increasing temperature and the stirring speed can increase the dissolution rate.The effect of depositing ways and pulse parameters on Zn-Ti alloys deposition has been investigated,which have a great influence on quality of coatings. At the same condition, the coatings obtained by pulse deposition were more smooth and dense, and the particles are uniformly and smaller, which had good corrosion resistance. Pulse deposition of Zn-Ti alloys,the deposition rate and titanium content in the alloys increased, the particles decreased, the coating was more smooth and dense as the increase of average current density. Pulse parameters, such as pulse average current density, duty cycle and pulse frequency, could play an essential role on the electrodeposition of Zn-Ti alloys. Compared with direct current deposition, the pulse electrodeposition of Zn-Ti alloys can show more excellent performances on deposition rate, microstructure, titanium content of the alloys and current efficiency. With the increase of current density ranging, coating particles became smaller. However, with the increase of duty ratio, particle sizes of coating increase and coatings became coarse. With the increase of pulse frequency, the phenomenology pulse damping can can observed, which leads to the decrease of current efficiency. The best electrodeposition condition can be listed as fellows:average current density pulse is7-9mA/cm2, pulse frequency is111HZ, pulse duty ratio is10%-15%.Alloy coatings corrosion resistance experiments have been made in3.5wt%NaCl solution.The results have shown that the corrosion resistance of Zn-Ti alloys are superior to pure zinc; the titanium content of Zn-Ti (<1wt%) alloys could affect the corrosion resistance significantly. Corrosion resistance of the Zn-Ti alloys obtained by pulse electrodeposition could be improved with the increase of titanium content, average current density and pulse frequency. However, the pulse duty ratio can play a negative role in the corrosion resistance.
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