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The Study of Corrosion Mechanism of Anode Materials in the Plating Process of Tin Free Steel(TFS)

Author: WangYuCheng
Tutor: LiJianZhong
School: Northeastern University
Course: Chemical processes
Keywords: tin free steel anode erosion electrochemistry
CLC: TG172
Type: Master's thesis
Year: 2012
Downloads: 3
Quote: 0
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Abstract


The use of tin free steel products is a variety of crow cap, twist off cap, easy peeled cap and drawn can,has increased in recent years. However, in the production of TFS, anode material is easy to be damaged by the corrosion of electroplate liquid. This is damage for shortes the durability cycle and brings great difficulty for the production of TFS. It is critical to study the theory of anode corrosion during the process of electroplating.In this paper, lead alloy anode at different concentration of chromium and fluorine of corrosion in electrolyte solution were researched by using weight method and atomic absorption method. And different conditions anticathode surface membrane structure transformation were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The anode in containing fluorine and chromium plating solution of electrochemical behavior were measurement with electrochemical method such as polarization curve, circulation voltammetric, EIS. And the anode semiconductor properties were discussed with Mott-Schottky equation. The results are as below we draw conclusions as the followings:(1) Lead alloy anode appeared corrosion in the fluorine solution, chromium solution and the mixed solution of Cr and F solution under the action of the electric field. The anode corrosion products mainly include PbO2and PbF2in the fluorine solution. The anode corrosion products were lead chromate and Pb2O in the chromium solution, and the anode corrosion products were lead oxide in the mixture of chromium fluorine solution.(2) With the increasing of oxidation time, the oxide film on lead anode increased firstly, and then decresased. When the oxidation times is up to1.5h, the thickness of the oxidation films reached to24μm. The effect of oxidation times was obviously to the surface morphology of oxidation film of the lead alloy anode, when the oxidation times were fixed at2h, it existed partly larger pores on the surface of lead anode. The surface structure of lead alloy anode was also changed, when the oxidation times came to0.5h, the diffraction peak of PbO was stronger, while the diffraction peak of PbCrO4and PbF2were weaker. With the extension of oxidation time, the diffraction peaks of PbCrO4and the PbF2was enhanced, respectively. When the oxidation time is2h, the diffraction peak of α-PbO2is significantly enhanced, but for PbF2, the diffraction peaks disappeared. As the oxidation time was further extended to2.5h, the alpha-PbO2by strength is significantly weakened, PbCrO4and the PbF2diffraction peaks are still strong.(3) Electrochemical studies showed that corrosion potential of surface of lead-based anode gradually increased with the oxidation time extending, when the oxidation time was more than two hours, corrosion potential reduced instead. CV curves showed that oxidation curve appeared a small oxidation peak near the voltage of-0.1V when the oxidation time was less than1.5hours; and appeared a clear oxidation peak from the potential of1.3V to1.5V; the potential of reduction curve was1.35V and appeared clear reduction peaks at-0.2V and-0.6V. The current of oxidation peak reduced apparently and reduction peaks at-0.6V disappeared when oxidation time was more than two hours. The images of EIS showed that the oxidation0.5h film have a single capacitive reactance arc. With increased with oxidation extended, not only had capacitive reactance arc, but also appeared warburg impedance. When the oxidation2.0h, lead alloy anode membrance impedence arc, and also includes obvious inductance arc with further extend the oxidized time, high frequency capacity arc radius reduced significantly.(4) it is discussed the cyclic voltammetry evaluation anode service life.When cycle process is conductd at80times, conduct ability of the anode is bad.(5) Cr-O ions group is the main factor to affect the electrode carrier density. Lead alloy anode is mainly embodied in the N type semiconductor in different components of the solution, but lead oxide anodes mainly P type semiconductor in chromium containing solution, semiconductor properties of graphite anode basically unchanged. Fluoride ions can improve the solution diffusion performance, improve anode carrier density. Cr-O ions group reuinon and diffusion performance take effect on anode semiconductor properties. The oxidation times take effect on carrier density.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Various types of metal corrosion
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