铝合金表面环氧涂层中水传输行为的电化学阻抗谱研究

EIS STUDIES OF WATER TRANSPORT IN EPOXY COATINGS COATED ON LY12 ALUMINUM ALLOYS

研究了LY12铝合金/环氧涂层电极在不同浓度NaCl溶液中的电化学阻抗谱(EIS),提出了涂层电极在浸泡过程中的不同阻抗模型。通过涂层电容值的变化得出环氧涂层在NaCl溶液中浸泡初期主要发生Fick扩散,中后期发生非Fick扩散Cl^-离子的存在使水的扩散系数增大,但却抑制了水与涂层组元间的相互作用,从而抑制了水的非Fick扩散过程。阻抗参数解析表明,金属/溶液界面的电化学反应阻抗主要决定于涂层中的吸水过程,后者直接决定基体/溶液界面的电化学反应面积。

Electrochemical impedance spectroscopy (EIS) of LY12 aluminum alloy based epoxy coating electrodes immersed in water solution with different concentrations of NaCl was investigated. Impedance models related to different immersion stages were also proposed. According to the time dependence of coating capacitance, the water sorption in epoxy coatings is mainly controlled by Fick diffusion during the initial stage of immersion, while by non-Fick diffusion in the medium and late stages. The presence of Cl- ion leads to increase in diffusion coefficient of water, however inhibits the interaction between water molecules and coating components, that is, impedes the non-Fick diffusion process. The evaluation of impedance parameters shows electrochemical reaction impedance of metal/electrolyte interface is primarily determined by water uptake in coatings. The water sorption of coatings directly determines electrochemical reaction area of base metal/electrolyte interface.