硼酸缓冲溶液中Cl^-浓度和温度对690合金腐蚀行为的影响

EFFECTS OF Cl^- CONCENTRATION AND TEMPERATURE ON THE CORROSION BEHAVIOR OF ALLOY 690 IN BORATE BUFFER SOLUTION

在硼酸缓冲溶液中,采用动电位极化、电化学阻抗谱(EIS)和半导体电容分析方法分别研究了Cl^-浓度(0.5-2 mol/L)和溶液温度(25-80℃)对690合金腐蚀行为的影响,并结合AFM,XPS及电位-pH图分析了钝化膜层的腐蚀产物.结果表明,不同Cl^-浓度和温度的溶液中,690合金均表现出沿晶腐蚀和二次钝化的特征.Cl^-浓度和溶液温度的提高均使690合金的自腐蚀电位下降,腐蚀电流密度增大,同时温度的升高还使690合金的点蚀电位降低,钝化区间变窄.恒电位极化相同时间,低电位的钝化区内的腐蚀产物主要为Cr,Fe的氧化物和Ni(OH)_2,钝化膜较薄且致密性好,体现n型与P型共存的特征.高电位的钝化区内的腐蚀产物主要为Ni_2O_3,钝化膜较厚但致密性差,体现n型半导体特征.

The effects of Cl- concentration （0.5--2 mol/L） and temperature （25--80℃） on the corrosion behavior of alloy 690 in borate buffer solution were investigated using potentiodynamic polarization （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 CI- concentration and temperature, the corrosion potential decreased and the corrosion 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, Fe2O3 and Ni（OH）2, and behayed 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 Cl- and temperature on the corrosion behavior were discussed.