Synergistic Corrosion Mechanism Of Corrosive Ions And Iron Bacteria On Carbon Steel

The reclaimed water as the recirculating cooling water makeup water effectively alleviates the urban water crisis,but the high salinity and microbial problems brought by the reclaimed water increase the risk of system corrosion.Therefore,it is of great significance to study the synergistic corrosion effect of the corrosive ion concentration increase caused by the concentration multiple and microorganisms on metal pipes.It is of great significance to deeply understand the corrosion mechanism of metal pipes in recirculating cooling water systems and to explore ways to prevent corrosion.This paper takes the recirculating cooling water system with reclaimed water as makeup as the research background,selects the common pipe carbon steel as the research object,through microelectrode technology,electrochemical method and X-ray photoelectron spectroscopy?XPS?and other means,explore the corrosive mechanism of corrosive ions Cl^-,NH₄⁺,SO₄^2-and iron bacteria.The main conclusions are as follows.With the increase of Cl^-concentration in 3 and 4 times Cl^-concentration conditions,Cl^-and iron bacteria synergistically accelerate the corrosion of carbon steel before 3d,and then the corrosion of carbon steel was gradually inhibited by the biofilm of iron bacteria.In the 4times Cl^-concentration condition,the dispersion index n_b=1 at 1d.At this time,the number of iron bacteria on the test piece is 2-12 times that of other conditions.The uniform corrosion of carbon steel by Cl^-causes the iron bacteria to quickly and evenly adhere to the film.At the same time,the anode slope was the lowest in all conditions before 3d.At 3d,11.69%of Fe₃O₄was produced,indicating that Cl^-and iron bacteria cooperated to accelerate the dissolution of iron.After 7 days,the corrosion potential increased,the current density decreased,and the anode slope increased significantly,indicating that as the biofilm thickened and the corrosion products accumulated,the anode reaction was suppressed.The film resistance is as high as1592.6?·cm² at 4 times Cl^-concentration working condition for 15 days,and the corrosion is suppressed to a large extent.With the increase of SO₄^2-concentration in the 3 times and 4 times SO₄^2-concentration conditions,the growth period of the attachment of iron bacteria is prolonged,which delays the corrosion process of carbon steel.In the later period,crevice corrosion occurs mainly with iron bacteria biofilm.The increase of SO₄^2-concentration aggravates the competition effect of adsorption,slows the dissolution of iron and also inhibits the attachment and growth of iron bacteria to the surface of carbon steel before 3 days.The electric double layer capacitance Q_dll continued to increase within 15 days,the dispersion index n_dll and the charge transfer resistance R_stt continued to decrease,indicating that the iron bacterial biofilm is relatively uneven,and the carbon steel has pitting corrosion characteristics.The corrosion rate at 4 times SO₄^2-concentration condition is higher than the other conditions at 15d.The FeOOH content is still higher than 38%.The corrosion product layer is not stable,which promotes further corrosion.In the conditions of 3 times and 4 times NH₄⁺concentration,as the NH₄⁺concentration increases,the adhesion growth and uniform and dense film formation of iron bacteria are promoted.The corrosion reaction has been dominated by iron bacteria.Before 7d,the main cause was uniform corrosion caused by iron bacteria.After 11d,the dense biofilm formed a barrier,which inhibited the corrosion of carbon steel.4 times ammonia nitrogen NH₄⁺concentration condition 7d attached iron bacteria number 7.20×10⁵ cfu/mL,second only to 4times Cl^-concentration condition,the average corrosion rate reaches 0.38mm/a,which is the fastest at this time,indicating the adhesion growth of iron bacteria accelerates the corrosion of carbon steel.After 7 days,the slope of the cathode and anode increased simultaneously,and the corrosion current density decreased.At 15 days,the sum of the proportions of Fe₂O₃ and Fe₃O₄ was close to 80%,and the dispersion index n_b was close to or equal to 1.The dense and uniform corrosion product-the biofilm layer inhibited the progress of corrosion.Carbon The steel enters an incomplete passivation state.