The Study On Electrochemical Corrosion Behaviors Of Three Kinds Of Solvent-free Coating In The Soil Solution

Solvent-free epoxy coating is a new kind of product on the basis of the solvent type epoxy coating’s development, which not only simplifies the coating process of the epoxy coal tar coating, but also dose not produce pinhole coating by the volatile solvent after the solidification.It protect the coating’s corrosion resistance. Through the test of the open circuit potential, AC impedance and other electrochemical method,the electrochemical behavior of three kinds of coatings with different moisture contents and different chloride ion contents in soil was studied.Q235 carbon steel with YS coating, MD coating, SYLQ coating has excellent corrosion resistance in different water content and different chloride ion content in soil. With the increase of the content of soil H2O and Cl-, the open circuit potential of 3 coatings gradually shifted to the negative,the capacitance arc radius decreases and the impedance value gradually decreases,which means with the increase of H2O and Cl-content, the soil erosion of the coating increased.When the 3 coating with 200μm thickness buried in 40%H2O+0.6%NaCl soil, the stable open circuit potential of YS coating, MD coating and SYLQ coating specimens were -0.38V,-0.32V and -0.26V, which is positive to Q235 bare steel’s stable open circuit potential -0.65V,.with the increase of the thickness of the coating, the capacitance arc radius of AC impedance increases, and low frequency impedance value gradually increased, indicating that as the thickness of the coating increases, the shield blocking ability of the coating on the soil erosion improves.The low frequency impedance value of three 200μm coatings buried in 40%H2O+0.6%NaCl and 29%H2O+1.8%NaCl soil for 360d reach 1×107 Ω·cm2,which still follows the initial rules of immersion. With the extension of buried time, the water absorption rate of coating was increased, the impedance modulus decreased,and the corrosion resistance of three kinds of coating decreased gradually.Three kinds of coating buried in 40%H2O+0.6%NaCl and 29%H2O+1.8%NaCl soil for 360d has a good adhesion to the substrate, no traces of corrosion are found. The energy spectrum analysis and X- ray diffraction analysis of three kinds of coating metal peeled after coating found no iron chlorides and oxides.The prediction formula of coating corrosion life is established based on Grey Neural Network .The life prediction formula of 200μm thick YS, MD and SYLQ coatings buried in 40%H2O+0.6%NaCl soil were 765d,688d and 673d; life prediction of coating in 29%H2O+1.8%NaCl soil were 1199d,1032d and 890d.