| In order to address the problems of high energy consumption,complicated process and serious pollution to the environment,the cold galvanizing coating was developed.It is one component zinc rich coating that has high zinc content in the dried film larger than 96wt%.It is considered as the most promising alternative to hot-dip galvanizing because of its good anticorrosion performance.However,the development of this coating in our country has fall behind and problems still existed such as the high electrochemical activity of zinc particles that leads to the decrease of anticorrosion performance of the coating,futher studies are needed in this field.In this work,in order to optimize the formula,different sizes of zinc particles were chosen to prepare the coating.The simulation of EIS result shows that Zn800 has lower zinc corrosion reaction resistance,which leads to the longer coating cathodic protection duration of 2100 h,anticorrosion performance of the coating is better.The electrochemical measurements were conducted to analyze the mechanism of the cold galvanizing coating and the results show that during the entire failure process,there are four stages which are activation stage,cathodic protection stage,barrier effect stage and failure.The cathodic protection is an important indicator for the anticorrosion performance of the coating.Besides that,the trial to improve the anticorrosion performance of the coating was also conducted from the following four aspects:modified zinc particles with phosphoric acid,modified zinc particles with organics,aluminization of zinc particles and hydrophobic treatment on the coating surface.The potentiodynamic polarization result and SVET results show that the anticorrosion ability of zinc was improved after modification with phosphoric acid.The EIS results showed that the coating resistance was significantly improved and Warburg impedance was observed during the immersion,the barrier effect of the coating was enhanced.This is because zinc particles were passivated by the modification and the barrier effect of the coating was increased generation of sheet Zn3(PO4)2·4H2O product.In terms of modification with organics,KH560 and AC-FAS can improve the corrosion resistance of zinc particles but the zinc corrosion resistance in the coating was also raised that the cathodic protection duration was decreased,and the anticorrosion performance of the coating was degraded.On contrary to that,modification with Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)(PEDOT:PSS)also improved the corrosion resistance of zinc particles and decreased the zinc corrosion resistance in the coating,which results in the improvement of cathodic protection duration by 13.4%,the anticorrosion performance of the coating was improved.In the study of aluminization of zinc particles,it has been found that Znl5Al coating has better anticorrosion performance that the NS ST has reached up to 3500h and cathodic pretection duration was improved to 2800h,which was 75%longer than Zn coating.SEM and XRD analysis showed that addition of Al in the coating has generated the formation of flake corrosion products Zn5(OH)5Cl2·H2O on the coating surface,which increased the barrier effect of the coating;and also the formation of layered double hydroxide(LDH)Zn6Al2(OH)16CO3·4H20 at the coating/substrate interface,which functioned as an anion exchange layer to prevent Cl-from contacting the substrate,and the synergistic effect increase the anticorrosion protection performance of the coating.After the hydrophobic treatment,less corrosion product was found on the coating surface after immersion test and EIS showed high impedance than non-treated samples,the anticorrosion performance of the coating was improved.The simulation reveals that the contact area of coating and corrosive electrolyte was largely reduced to 13.3%and hydrophobic treatment is an effective method to improve the anticorrosive performance of the coating. |
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