环氧树脂涂覆LY12铝合金在NaCl溶液中的阻抗模型

Impedance Models of Epoxy Coated LY12 Aluminum Alloys in NaCl Solution

分别研究了裸LY12铝合金及涂覆环氧树脂涂层后合金在3.5%NaCl溶液中的电化学阻抗谱(EIS).结果表明,LY12铝合金在点蚀电位以下阻抗谱上出现两个容抗弧,高频段对应Cl-参与的成膜阻抗,低频段对应铝阳极溶解的电化学反应阻抗.合金发生点蚀后出现低频感抗弧.合金/电极在NaCl溶液中先发生涂层吸水,当水及O2抵达基体后建立起电化学反应界面,合金遭受腐蚀;受涂层阻挡的影响,腐蚀产物的扩散逐渐成为控制步骤;当扩散速度较慢的Cl-抵达涂层/金属界面后,与界面处聚集的腐蚀产物间发生化学反应,完成成膜过程,阻抗谱上出现盐膜的阻抗,而扩散阻抗消失.提出了不同浸泡失效阶段涂层电极体系的阻抗模型.

Electrochemical impedance spectroscopy (EIS) of bare LY12 Al alloy and LY12/epoxy electrodes in 3.5%(mass fraction) NaCl solution has been investigated,respectively.The results show that the impedance spectra for bare LY12 alloys below the pitting potential (Epp) consist of two capacitance loops,relatingto the formation of Cl-containing salt film at high frequencies and anodically electrochemical dissolution of Al at low frequencies.An inductive loop was detected at low frequencies with potentials above the Epp.Water tends to uptake inepoxy coating preferentially in the early time.After water and oxygen reach thealloy base the electrochemical reaction interface will form on the base,and thealloy is corroded.Then the diffusion of the corrosion products becomes the ratedetermining step in the case of coating barrier.When the slow diffusion particle Cl-accesses to coating/alloy interface,Cl-interacts with the stimulatingcorrosion products and a chemical reaction salt film is formed,resulting in thepresence of film impedance and the disappear of diffusion impedance in EIS.According to the above experimental phenomena different impedance models in various immersion stages are proposed to fit the EIS measurements.