Electrochemical Evolution Law Of Pure Iron Corrosion In Dynamic Electrolyte Film Process

In the actual atmospheric environment,it is difficult to keep the liquid film on the metal surface stable,and it has been constantly evaporating and condensing as the climate and meteorological conditions change,showing the characteristics of dynamic liquid film,so the dynamic liquid film corrosion is closer to the atmospheric environment.The true state of the liquid film on the metal surface can better reflect the behavior and mechanism of atmospheric corrosion in the initial stage.Aiming at the dynamic liquid film corrosion system,this paper uses a concentric three-electrode array local electrochemical test method to study the effects of parameters such as dynamic liquid film change rate,initial liquid film thickness,and number of liquid film change cycles on the electrochemical behavior of pure iron corrosion.The electrochemical evolution law of pure iron corrosion during drying and evaporation was monitored,and the influence of the galvanic effect of Al on the electrochemical distribution characteristics of pure iron corrosion was discussed,and the following main conclusions were obtained:The electrochemical response of the dynamic liquid film change rate,the initial liquid film thickness,and the number of cycles to the pure iron interface is studied.The results show that with the gradual increase of the dynamic liquid film change rate,the corrosion process of the electrode varies with the external environment.As well as the unbalanced response speed between the electrodes inside the electrode,the local cathode and anode differentiation of the corroded electrode is serious,and the local corrosion tendency increases;when the initial liquid film thickness is thin,the corrosion potential and coupling current are unevenly distributed,and the cathode and anode differentiation is serious.The corrosion rate is large;with the increase of the number of dynamic liquid film cycles,the position of the cathode and anode is fixed,and the local corrosion tendency of the initial state,half cycle and final state first increases slightly,and then the volatility gradually decreases.Due to the accumulation of corrosion products,the anode charge transfer resistance increases and the solution resistance decreases.In the evaporation process of the thin NaCl liquid film on the surface of the pure iron electrode,as the liquid film continues to thin,its corrosion tendency first increases,then decreases,and then increases;the liquid film changes from a uniform liquid film to discontinuous and dispersed Liquid film: In the middle and late stages of liquid film thinning,due to the influence of corrosion products and crystalline salts,the diffusion path of oxygen changes,resulting in the edge position being controlled by oxygen diffusion resistance.When studying the coupling effect of metallic aluminum on pure iron during the evaporation of NaCl liquid film,it was found that metallic aluminum,iron and electrolyte formed galvanic corrosion.The smaller the distance between aluminum and iron,the stronger the effect of galvanic effect;In the initial stage of evaporation,as the liquid film thins,oxygen diffusion accelerates,and the corrosion rate increases to an extreme value.With the further thinning of the liquid film,the oxide film formed on the surface of the metal aluminum and the deposition of corrosion products will cause the metal surface to passivate and reduce the reaction corrosion rate.In the final stage of evaporation,due to the serious differentiation of anode and cathode,the corrosion rate increases to a certain extent;the coupling of metal aluminum to iron accelerates the corrosion of metal.