Effect Of Corrosion Inhibitors On The Corrosion Resistance And Microstructure Of Steel Passive Film In Reinforced Concrete Containing Chloride

The passivation film as a protective layer of steel bars can prevent the corrosion of steel bars.The causes of steel bar corrosion include not only the material composition and surface state of steel bars in concrete,but also environmental factors such as chloride ion corrosion,humidity,carbonization and temperature.The characteristics of the steel passivation film in concrete,that is,the film thickness,composition and passivation stability are affected by the polarization time,potential and ion concentration in the medium,and the destruction of the passivation film structure will lead to the corrosion of the steel substrate.Active dissolution occurs in the environment,which puts a test on the durability of reinforced concrete structures.Steel corrosion inhibitor is a chemical substance that can hinder or delay the corrosion of steel bars.It is generally believed that corrosion inhibitors can migrate around the steel bar in the form of gas or liquid through the pores inside the concrete,and chemical reactions occur at the steel bar/concrete interface.It causes the surface of the steel bar to be oxidized to form a passivation film,or the surface of the steel bar is adsorbed by the corrosion inhibitor to form an adsorption film,or it is the above composite effect.Therefore,clarifying the failure process of the passivation film of the reinforcing steel in the concrete under corrosion and the mechanism of the formation of the passivation film of the steel under the effect of the steel corrosion inhibitor is an important content that needs urgent solution,so that the dull environment of the surface of the steel in the concrete can be improved under the premise of simple construction and low cost.In this paper,starting from the factors that affect the structure of the rebar passivation film in concrete containing chloride salt,the half-cell potential method,linear polarization method,AC impedance spectroscopy method,XPS and XRD were used to study the corrosion resistance of steel in concrete when anode,cathode and composite corrosion inhibitors were added under the influence of chloride salt corrosion,and the relationship between the corrosion performance and the microstructure characteristics of the passivation film on the surface of the steel,which provides a theoretical basis for optimizing the composition of the passivation film on the surface of the steel bar and improves the durability of the concrete structure.The main research results are as follows:1.In the chloride-containing concrete mixed with different types of corrosion inhibitors,the corrosion of the steel bars has been greatly improved compared to the case without corrosion inhibitors.The higher the amount of corrosion inhibitor is,the better the corrosion resistance becomes.Among them,under the action of cathode corrosion inhibitor DMEA and composite corrosion inhibitor Na₂CrO₄+BTA,when the mass ratio of corrosion inhibitor and chloride ion is 3,the corrosion resistance achieves the best.The effect of anode corrosion inhibitor in the early curing stage is better than that in the later curing stage,and sodium molybdate is better than sodium chromate in the same dosage.When the cathode corrosion inhibitor is added,the corrosion resistance of the steel bar in the concrete in the later curing stage is better,and the corrosion resistance of BTA is better than that of DMEA at the same dosage.The effect of the composite corrosion inhibitor does not change much during the curing stage,but the corrosion current density of the steel bar is basically lower than that of the single-component corrosion inhibitor.Generally speaking,the effect of the composite corrosion inhibitor is better,and the compounding effect of sodium molybdate and BTA is the best in the composite corrosion inhibitor.2.In the chloride-containing concrete mixed with anode corrosion inhibitor,the passivation film of reinforcing steel under the action of sodium chromate is mainly composed of FeOOH,FeO and a small amount of Fe₃O₄.At the same time,oxides of Cr elements including CrO₃ and Cr₂O₃are also detected on the surface.The relative content of FeO,Fe₃O₄ and Cr₂O₃ increased with the increase of sodium chromate content;Under the action of sodium molybdate,the steel passivation film includes FeOOH,FeO,Fe₃O₄,Fe₂O₃ and FeMoO₄.As the amount of sodium molybdate increases,the relative content of Fe₂O₃ and FeMoO₄ increases,while the relative content of FeOOH decreases.3.In the chloride-containing concrete mixed with cathodic corrosion inhibitor,the Fe element compounds in the steel passivation film under the action of BTA mainly include FeOOH,FeO,and Fe₃O₄.At the same time,BTA itself adsorbs on the surface of the steel through the N-Fe bond,forming an adsorption-type passive chemical film.With the increase of BTA content,the relative content of FeO and Fe₃O₄ also increased accordingly;Under the action of DMEA,the steel passivation film mainly includes FeOOH and Fe₂O₃,of which some FeO and Fe₃O₄ are also generated.DMEA does not participate in the composition of the passivation film itself.When the mass ratio of DMEA to chloride ion is equal to 3,the relative content of Fe₂O₃ and FeO in the passivation film reaches the highest,indicating that the dense and stable stability of the passivation film of the steel bar is the best.4.In the chloride-containing concrete mixed with a composite corrosion inhibitor,in addition to the compound of the element Fe,the main components of the passivation film of the steel also include an adsorption film and an oxide film generated when the corrosion inhibitor is added.When the Na₂CrO₄+BTA group and the Na₂MoO₄+BTA group were added,the relative content of iron compounds changed little.However,the relative content of Cr₂O₃ and N-Fe bonds generated by the combined action of Na₂CrO₄ and BTA,and the FeMoO₄ and N-Fe bonds generated by the combined action of Na₂MoO₄ and BTA,are significantly higher than those of the single-component corrosion inhibitor,which indicates that its corrosion-proof effect is better than that of the single-component corrosion inhibitor.5.Among the anode corrosion inhibitors,the relative content of FeOOH is higher when sodium chromate is used,while the relative content of iron oxide is significantly lower than that of sodium molybdate,whose passivation film has a higher density.At the same time,the addition of sodium molybdate will produce a stable FeMoO₄ which can effectively inhibit the occurrence and spread of pitting corrosion.Its effect of corrosion inhibition is better than sodium chromate;Among the cathode corrosion inhibitors,the relative content of the oxides of Fe element formed by the interaction of BTA and DMEA is relatively low,but BTA also forms a dense adsorption film on the surface of the steel bar,so that the effect of corrosion inhibition is better;Among the composite corrosion inhibitors,in addition to the formation of insoluble FeMoO₄ when sodium molybdate is used,MoO₄^2-adsorbed on the reinforcing steel matrix will generate ion dipoles,which promotes the better adsorption of BTA on the surface of the reinforcing steel.Among them,sodium molybdate and BTA have a synergistic effect after compounding,and the effect of corrosion inhibition is the best.