采用矩形缝隙装置,研究了阴极极化条件下本体Na_2SO_4溶液浓度、pH值以及本体溶液的含氧状况对模拟剥离涂层下溶液的化学和电化学环境的影响,分析了剥离区域内X70钢表面发生的电化学反应.结果表明,增加本体Na_2SO_4溶液的浓度虽然有利于阴极电流在剥离涂层内传输,但会导致钢板表面钝化膜的破坏而发生腐蚀.本体溶液pH值为酸性时缝内的化学环境变化迅速,缝口处发生腐蚀反应;而碱性条件下剥离区的pH值基本不变.本体溶液供氧量的减少降低了剥离区域内阴极保护的有效距离.外加电位的中断使缝内溶液酸化,X70钢处于自腐蚀状态.
A rectangle crevice assembly was used to study the crevice corrosion behaviors of X70 steels in Na_2SO_4 solutions under cathodic polarization condition.Effects of bulk solution concentration,pH,dissolved oxygen concentration on the electrochemical and chemical environments under the simulated disbanded coating were analyzed.It is shown that the higher bulk solution concentration was in favor of the cathodic current flowing into the crevice.However.the passivation film on the steel was attacked and corrosion occurred.The pH values of the solution under the disbonded coating with the alkaline bulk solution hardly changed while it changed rapidly with the acidic one and the steel at the opening was corroded.The available cathodic protection distance decreased with the dissolved oxygen being removed in bulk solution.The switching off of the applied potential led to the solution acidification and a free corrosion state of the X70 steel.
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