Effect Of Pollution On The Initial Corrosion Of Weathering Steel In Simulated Coastal-Industrial Atmosphere

Atmospheric corrosion of steel is a complicated problem due to the diversity of atmospheric environment.According to the type and level of pollutions in the air,atmospheric corrosion can be divided into rural,marine,industrial atmospheres and so on.The study of atmospheric corrosion is essential because atmospheric corrosion widely exists indoor and outdoor,and causes a lot of economic loss.In these studies,one of the most important focuses is on the influence of different pollutions like sulfur dioxide and chloride on the atmospheric corrosion behavior of steel.In the past few decades,many researches on the influence of different pollutions were conducted all over the world.In this paper,the effect of HSO₃^-and Cl^-on the initial corrosion of Q355GNH weathering steel in simulated coastal-industrial atmosphere was studied by 30 h wet/dry cyclic corrosion test,which was conducted by exposing the sample to an alternate condition of 10 min immersion in NaCl+NaHSO₃ solution and 50 min of drying at room temperature.The solution was prepared from analytical grade chemical of NaCl and NaHSO₃ and distilled water.For weight loss measurements,the rust on the steel surfaces was removed mechanically and chemically in a solution of hydrochloric acid and hexamethylenetetramine?corrosion inhibitor?.Surface macro and micro morphologies of rusted steel were observed using an optical microscope and scanning electron microscope.The corrosion products formed on the surface of weathering steel after wet/dry cyclic corrosion test were characterized by XRD.The polarization curves and electrochemical impedance spectroscopy?EIS?measurements were carried out using a classical three electrodes cell with platinum as the counter electrode,Ag/AgCl electrode as the reference electrode,and steel samples with an exposed area of 1 cm² as the working electrode.We can reach some conclusions from the results.The increase of NaHSO₃ concentration promoted the formation of?-FeOOH in the rust layer,and inhibited the formation of?-FeOOH and Fe₃O₄/?-Fe₂O₃.And the rust layer became more compact and corrosion-resistant with the increase of HSO₃^-concentration.The formation of rust layer in weathering steel surface can suppress interaction of the aggressive species and the underlying steel,thereby inhibiting the corrosion process and decreasing the corrosion rate of weathering steel.It is the reason why rusted steels have a lower corrosion rate than original steels.As the concentration of NaHSO₃ increases,corrosion rate of weathering steel in solution gradually increases but the total atmospheric corrosion rate of weathering steel gradually decreases with increase of HSO₃^-concentration because of the formation of a protective rust layer.The increase of NaCl concentration inhibited the formation of?-FeOOH in the rust layer,and promoted the formation of?-FeOOH and Fe₃O₄/?-Fe₂O₃.And the rust layer became less compact and corrosion-resistant with the increase of Cl^-concentration.The formation of rust layer in weathering steel surface can suppress interaction of the aggressive species and the underlying steel,thereby inhibiting the corrosion process and decreasing the corrosion rate of weathering steel.It is the reason why rusted steels have a lower corrosion rate than original steels.As the concentration of NaCl increases,corrosion rate of weathering steel in solution gradually increases and the total atmospheric corrosion rate of weathering steel gradually increases with increase of Cl^-concentration because of the formation of a less protective rust layer.