苯甲酸钠浓度对乙二醇-水溶液中3A21铝合金电化学行为的影响

Effect of Sodium Benzoate Concentration on Electrochemical Behavior of 3A21 Aluminum Alloy in Ethylene Glycol Aqueous Solution

目的研究乙二醇-水溶液中苯甲酸钠(SB)含量对3A21铝合金腐蚀的影响,为预测长期服役且含苯甲酸钠的乙二醇-水溶液体系的腐蚀变化规律提供数据支撑。方法以乙二醇质量分数为36%的乙二醇-水溶液为基础体系,通过SEM表征3A21铝合金腐蚀前后的微观组织结构,利用开路电位(OCP)、交流阻抗谱(EIS)和动电位极化技术,研究3A21铝合金在苯甲酸钠质量分数为0~1.80%的溶液中的电化学腐蚀行为。结果当苯甲酸钠质量分数为0~1.80%时,随体系中苯甲酸钠含量的增加,3A21铝合金的自腐蚀电流密度逐渐减小,当苯甲酸钠质量分数大于1.40%后,自腐蚀电流密度不再显著降低。当苯甲酸钠质量分数为0~1.40%时,自腐蚀电流密度由0时的409.89 nA/cm^(2)减小至1.40%时的220.92 nA/cm^(2);电荷转移电阻逐渐增大,由0时的112.45 kΩ/cm^(2)增加至1.40%时的204.82 kΩ/cm^(2)。对3A21铝合金表面形貌SEM测试,苯甲酸钠的加入能有效抑制3A21铝合金的腐蚀,苯甲酸钠质量分数为1.40%时,对3A21铝合金的腐蚀抑制效果较好。结论苯甲酸钠的引入能够降低3A21铝合金在乙二醇-水溶液中的腐蚀速率,在0~1.40%范围内,随着乙二醇-水溶液中苯甲酸钠浓度的增大,其对3A21铝合金的腐蚀抑制效果呈现增强的趋势。

In order to study the effect of sodium benzoate content in ethylene glycol aqueous solution on the corrosion of 3A21 aluminum alloy,and provide data support for predicting the corrosion change law of ethylene glycol aqueous solution system with long-term service and sodium benzoate.The microstructure of 3A21 aluminum alloy before and after corrosion was characterized by SEM based onethylene glycol aqueous solution with ethylene glycol mass fraction of 36wt.%.The electrochemical corrosion behavior of 3A21 aluminum alloy with sodium benzoate mass fraction of 0~1.80wt.%was studied by open circuit potential(OCP),AC impedance spectroscopy(EIS)and potentiodynamic polarization technology.During 1 h of stabilization,the open circuit potential of 3A21 aluminum alloy shifted toward more positive values at the end of the immersion period.When the mass fraction of sodium benzoate is inthe range of 0-1.80wt.%,the change of sodium benzoate mass fraction in ethylene glycol aqueous solution did not change the reaction mechanism of anode and cathode,showing the same corrosion behavior.when the mass concentration of sodium benzoate was small,the adsorption film formed on the metal surface was not complete,with the increase of sodium benzoate mass fraction in the system,the adsorption film gradually became dense and complete,so the inhibition effect was enhanced and the self-corrosion current density was significantly reduced.The self corrosion potential showed positive and negative shifts,meanwhile,the self corrosion current density of 3A21 aluminum alloy decreased,From 409.89 nA/cm^(2)at 0 to 220.92 nA/cm^(2)at 1.40wt.%.The change of sodium benzoate concentration in the system did not lead to the change of impedance spectrum shape.There was only one time constant in the impedance spectrum,which showed a semicircular capacitive reactance arc reflecting the resistance capacitance relaxation process composed of charge transfer resistance and electric double-layer capacitance.Because sodium benzoate was adsorbed on the surface active point or the whole surface of the metal matrix,the transfer of charge or substance related to corrosion reaction was hindered.The charge transfer resistance increased with the increase of sodium benzoate mass fraction in the system,from 112.45 kΩ/cm^(2)at 0 to 204.82 kΩ/cm^(2)at 1.40wt.%.SEM test showed that the surface of 3A21 aluminum alloy was relatively flat,but some corrosion problems were also observed.There is only a small amount of local corrosion on the surface of 3A21 aluminum alloy sample.Therefore,the corrosion of 3A21 aluminum alloy in ethylene glycol aqueous solution is mainly uniform corrosion.In addition,the addition of sodium benzoate can reduce the corrosion rate of 3A21 aluminum alloy.Within the selected test concentration range,with the increase of sodium benzoate concentration in ethylene glycol aqueous solution,its corrosion inhibition effect on 3A21 aluminum alloy increased.For the long-term service ethylene glycol aqueous solution system containing sodium benzoate,the corrosion law can be predicted by tracking the attenuation change of sodium benzoate concentration.