不同液膜厚度下电偶腐蚀当量折算研究

Study on Equivalent Conversion of Galvanic Corrosion Under Different Liquid Film Thickness

搭建薄液膜厚度测量与控制装置,采用微距参比电极后置法组建三电极体系,测量了在3.5%(质量分数,下同)NaCl不同液膜厚度下2024铝合金和TA15钛合金极化曲线和电偶电流,得到了不同厚度液膜下两种材料的电化学动力学参数;建立了基于薄壳电流分布的Comsol腐蚀仿真模型,得出了不同液膜厚度下的电偶电流以及电偶腐蚀与无电偶腐蚀时的当量折算系数。结果表明,利用仿真模型得到的电偶电流值与试验值吻合较好,50μm液膜厚度下的电偶电流约是溶液状态的25倍,随着液膜厚度的增大,电偶电流的下降速度逐渐增大,当液膜厚度达到1 000μm时,电偶电流趋近于溶液状态;50μm和100μm液膜厚度下电偶腐蚀折算系数约为无电偶状态下的5倍,当液膜厚度超过100μm时,折算系数急剧下降,到1 000μm时无论有无电偶腐蚀其折算系数均基本趋于1。

The polarization curves and galvanic currents of 2024 aluminum alloy and TA15 titanium alloy under different thickness of 3.5 wt% NaCl liquid film were measured and the electrochemical kinetic parameters of two kinds of materials under different thickness liquid membranes were determined by applying a liquid membrane thickness measurement apparatus and a three-electrode system with backward inserted micro-distance reference eletrode.To obtain the galvanic current under different liquid film thickness and equivalent conversion factor of galvanic-non galvanic corrosion.The Comsol corrosion simulation model based on the shell current distribution was established.The result manifested that the galvanic current value obtained by the simulation model agreed well with the experimental data,under the thickness of 50μm liquid film,the galvanic current was about 25 times of that of the solution,with the increase of liquid film thickness,the decrease speed of galvanic current increased gradually.When the liquid film thickness reaches 1 000μm,the galvanic current approached the solution state,the conversion coefficient of galvanic corrosion at50μm and 100μm liquid film thickness was about 5 times of that without galvanic couple.When the liquid film thickness was more than 100μm,the conversion coefficient dropped sharply.When the liquid film thickness was 1 000μm,whether there was galvanic corrosion or not,the conversion coefficient basically tended to 1.