Abstract
The effects of Clconcentration (0.5—2 mol/L) and temperature (25—80 )o n the corrosion behavior of alloy 690 in borate buffer solution were investigated using potentiodynamic po- larization (PD), electrochemical impedence spectroscopy (EIS) and semiconductor capacitance method (Mott-Scottky relation). Atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and potential-pH diagrams were employed to analyze the corrosion products. All of the polarization curves exhibited two passive regions and intergranular corrosion was observed on all samples. With the increase in both Clconcentration and temperature, the corrosion potential decreased and the cor- rosion current density became larger. Furthermore, increasing the temperature also resulted in lower pitting potentials and narrower passive regions. After anodic polarization for 45 min, the film formed in the first passive region with lower potential was composed of Cr2O3 ,F e2O3 and Ni(OH)2 ,a nd be- haved like a mixed-type semiconductor, while a thicker but less compact Ni2O3 film was formed in the second passive range with higher potential and behaved like a n-type semiconductor. The influences of Cland temperature on the corrosion behavior were discussed.
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