Dual Electrolytic Plasma Processing for Steel Surface Cleaning and Passivation
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JMEPEG DOI: 10.1007/s11665-017-2826-0
Dual Electrolytic Plasma Processing for Steel Surface Cleaning and Passivation L. Yang, P. Zhang, J. Shi, J. Liang, W.B. Tian, Y.M. Zhang, and Z.M. Sun (Submitted November 9, 2016; in revised form June 10, 2017) To remove the rust on rebars and passivate the fresh surfaces, electrodes reversing electrolytic plasma processing (EPP) was proposed and conducted in a 10 wt.% Na2CO3 aqueous solution. The morphology and the composition of the surface were investigated by SEM and XPS. Experimental results show that the rust on the surface was removed effectively by cathode EPP, and a passive film containing Cr2O3 was achieved by the succeeding anode EPP treatment, by a simple operation of reversing the bias. The corrosion resistance was evaluated in a 3.5 wt.% NaCl aqueous solution using an electrochemical workstation. In comparison, the corrosion resistance was improved by the succeeding anode EPP treatment, which is evidenced by a positive shift of the open-circuit potential, an increase in the electrochemical impedance representing the inner layer by 76.8% and the decrease in the corrosion current density by 49.6%. This is an effective and environment-friendly technique to clean and passivate rebars and similar steel materials. Keywords
electrolytic plasma processing, low alloy rebar, passive film, rust removal
1. Introduction Low alloy rebars are widely used for their high cost performance compared with the low-carbon steel and stainless steel ones. The oxide scale formed on the surface of low alloy rebars during the manufacturing process at high temperature is composed of plenty of rust such as wustite (FeO), hematite (Fe2O3), magnetite (Fe3O4) and a small amount of Cr2O3, which lead to local depletion of Cr near the surface, resulting in a decrease in the chloride threshold down to that of carbon steel (Ref 1, 2). Moreover, the localized and continuous cracks (or spallation) of the oxide scale are observed, and the local cracks create environment for pitting and crevice corrosion (Ref 1-3). Therefore, to prolong the service life of such alloy in harsh conditions, it is necessary to remove the oxide scales and then passivate the fresh surface by forming a dense Cr2O3 film to increase the corrosion resistance. The conventional process includes three steps, i.e., mechanical descaling to break up and disrupt the oxide scale, electrochemical pickling and the final chemical pickling to achieve the desirable surface such as a passive film. In the process of pickling, it is inevitable to use some hazardous acid solutions such as HF, HNO3 and HCl. (Ref 4-6). This study illustrates the feasibility of eliminating the usage of these hazardous chemicals in the low alloy rebar treatment process.
L. Yang, P. Zhang, W.B. Tian, and Z.M. Sun, Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189, China; J. Shi and Y.M. Zhang, Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineerin
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