Kinetics Of Local Electrode Process At The Interface Between Dynamic Droplet And Pure Iron

At the initial stage of atmospheric corrosion,the droplets on the metal surface will evaporate,condense and other phenomena,thus presenting dynamic droplet characteristics.Therefore,the theoretical exploration of the electrode process of the dynamic droplet corrosion system will be a significant progress,and it will be able to reflect the macro and micro characteristics of the atmospheric corrosion evolution process.In this paper,concentric three-electrode array local electrochemical test method was used to study the electrochemical evolution law of local corrosion at the interface between dynamic droplets and pure iron in two modes of evaporation and deliquesce,as well as the dynamics of electrode process and the coupling mechanism.The research results help to reveal the general law of local corrosion of uniform materials caused by dynamic corrosion environment,and enrich the theory of local corrosion.Using concentric three-electrode array test technology,the electrochemical distribution of three types of 3.5% Na Cl droplets of 50、110 and 270μL was explored during the dynamic process of evaporation.The reaction of dynamic evaporating droplets with pure iron is different from that of static droplets.Small: The local corrosion tendency increases first and then decreases.The local corrosion tendency of medium and large droplets reached the maximum in the middle and late stages.During evaporation,the salt is concentrated on the edge of the droplet,and the edge is prone to anodic reaction,and local corrosion is aggravated.Later salt crystallization,corrosion products and liquid film dispersion affect electrolyte migration,and local corrosion tends to increase.In the later stage,salt crystallization,corrosion products,and dispersed liquid film affect electrolyte migration,and local corrosion tends to increase.The close-packed concentric two-electrode array test technology was used to explore the electrochemical distribution during the deliquescent dynamic process of0.01 g Na Cl,during which the local corrosion tendency increased continuously.In the initial stage of accumulation of salt particles,oxygen transmission is blocked,the oxygen content in the droplets is low,and the anode and cathode are dispersed on the electrode surface.After the salt particles are completely dissolved,the anode gradually converges in the center,and the edge of the main droplet basically shows a cathode distribution.After the middle period,as the droplets expand,most of the newly covered electrode serves as a cathode.Under the same conditions,the EIS of the evaporation process,the EIS of the deliquescent process and the polarization curve were tested.Evaporation: The local electrode processes at the same position of droplets of different volumes are different;most of the local electrode processes are mainly controlled by oxygen diffusion,and a few electrodes are controlled by the anode process;in the later stage,most electrodes are affected by the precipitation of salt particles and corrosion product films.The electrochemical reaction resistance increases.Deliquescence: The central and peripheral reaction mechanisms are different.The impedance value of the center electrode shows an increasing trend over time,The edge electrode does not show a significant increase trend.But the same is that cathode charge transfer resistance is small and is mainly controlled by oxygen diffusion.The kinetic model does not consider the influence of coupling on the dynamics of the local electrode process,which has certain limitations.So continue to explore the effect of coupling on the local electrode process..The mixed potential of the electrodes under the coupling of 31 electrodes under400μL droplet is 0.34 V,and the electrode polarization type and degree are different at different positions.Anodic polarization: anode charge transfer resistance is significantly reduced and cathode charge transfer resistance is increased.In the coupled state,the self-corrosion current density at this position is significantly increased,and the corrosion tendency is greater.Cathodic polarization: Self-corrosion potential is negatively shifted,anode charge transfer resistance increases significantly,cathode charge transfer resistance decreases,and oxygen diffusion resistance also increases.This may be due to the corrosion product film formed on the electrode surface under the coupling effect.Due to the low potential of the center electrode under the medium droplet,by calculating the effective influence distance of the center electrode,it is found that the current distribution of the medium droplet will show a typical Evans ring distribution due to the coupling effect.It further proves that in the case of coupling,mutual polarization will occur between the electrodes...