Corrosion Behavior And Mechanism Of Copper At Nansha Islands Marine Atmospheric Environment

To implement the maritime power strategy,China needs to speed up the construction of Nansha islands and reefs and the development of marine engineering equipment.However,the corrosion damage caused by the climate environment in Nansha Islands to the infrastructure materials and equipment is much higher than that in other marine areas,which seriously affects the reliability and safety of marine engineering facilities.As important materials widely used in the fields of electronics,electricity and national defense industry,the corrosion data of copper and its alloys in the atmospheric environment of Nansha has not been reported.In order to take effective corrosion measures or develop new anticorrosion technology in Nansha area,it is necessary to study the corrosion mechanism of copper exposed in Nansha atmospheric environment.Nansha is a harsh marine atmosphere environment with high temperature,high humidity,high salinity and high irradiation,and its climate characteristics are very representative.In the existing studies,there is no relevant laboratory simulation accelerated corrosion test,and there is no reference basis for the long-term safe application of copper in Nansha atmospheric environment.Some studies have shown that ultraviolet(UV)radiation can accelerate the corrosion rate of copper,but the effect of UV on atmospheric corrosion products on copper surface is still less studied.In addition,studies of atmospheric corrosion of metals generally focus on the average parameters over time,and there are few reports on the initial corrosion behavior of materials,especially the corrosion of copper under aerosols.In the marine atmosphere,the most common deposited aerosols range in size from 1 μm to 100 μm,while the large droplets concerned in some experiments are hundreds of microns to millimeters in diameter,which is one to three orders of magnitude larger than ordinary marine aerosols.Therefore,metals under marine aerosols may undergo different corrosion mechanisms.In this paper,the corrosion laws of copper T2 and brass H62 in Nansha marine atmosphere and simulated Nansha atmospheric environment were studied by means of weight loss,X-ray diffraction(XRD),scanning electron microscope(SEM),energy dispersive spectrometer(EDS),stereomicroscope,electrochemical measurement and other analytical methods,and the effect of UV irradiation and marine aerosol droplets on the atmospheric corrosion of pure copper were also studied.The conclusions are as follows:During the field exposure,the corrosion depth of copper T2 increases linearly within 21 months,while that of brass H62 follows the law of power function,and the corrosion is a deceleration mode.The corrosion products on the surface of pure copper are mainly Cu2O and Cu2Cl(OH)3.The corrosion process of brass H62 involves the dezincting mechanism of Zn preferring dissolution,and the corrosion products formed on the surface are mainly composed of zinc-containing compounds Zn5(OH)8Cl2·H2O and NaZn4(SO4)Cl(OH)6·6H2O.In addition,copper-containing compounds are also detected on the front side.The corrosion product layer on the surface of pure copper and brass has a double-layered structure.The outer layer of the corrosion product layer on the front side is extremely thin,while the outer product layer on the back side is thicker.The protection afforded by the corrosion product layer on the front side of pure copper is improved gradually,while that on the back side is deteriorated.The protection provided by the corrosion product layer on both sides of brass is improved gradually,but for the same exposure time,the corrosion product layer on the back side appeared to be more protective.According to ISO 9223,Nansha is an extremely harsh marine atmospheric environment,classified as a corrosion category of CX.In simulated Nansha marine atmosphere by dry-wet cycle,the corrosion rate of copper T2 first decreases,then increases,and finally decreases again within 32 days of exposure.Whereas that of brass H62 decreases sharply and then tends to be stable.The corrosion products on pure copper are mainly Cu2O and Cu2Cl(OH)3.Brass has obvious dezincification corrosion phenomenon,and the corrosion products are mainly zinc-containing compounds.After 32 days of exposure,the corrosion product layer on copper T2 has poor adhesion with the matrix and no obvious Cu2O layer is observed.The surface morphology after removing the corrosion product is in the form of rugged hills.In the case of brass H62,there were numerous copper-rich holes with the depth of 20 μm～50 μm under the corrosion product layer due to dezincification process.At 35℃ and 80%RH constant temperature and humidity conditions,obvious Cu2O layer is observed on the surface of copper T2.Compared to the dry-wet cycle experiment where no obvious Cu2O layer is observed in,it shows that the long time wetting on the copper surface is more conducive to the formation of Cu2O.UV irradiation can accelerate the corrosion of pure copper,especially the formation of Cu2O.UV irradiation has the greatest effect on the atmospheric corrosion process of pure copper at the early stage of exposure.With the increase of exposure time,the effect of UV irradiation on atmospheric corrosion of pure copper weakened.In conclusion,the corrosion behavior of copper T2 in Nansha marine atmosphere can be well simulated by the constant temperature and humidity atmospheric corrosion experiment with UV irradiation combined with NaCl deposition.The corrosion behavior of copper under outdoor marine aerosol and NaCl aerosol droplets is similar,and the secondary spreading phenomenon occurs in both cases.The corrosion morphology of aerosol droplets can be divided into three areas:the original droplets coverage area(area I),the extension area where corrosion occurs(area Ⅱ)and the extension area without obvious corrosion(area Ⅲ).The largest amount of corrosion products is deposited on area I,mainly composed of Cu2O and Cu2Cl(OH)3;The corrosion products on area Ⅱ is mainly Cu2O.The higher the ambient relative humidity,the more serious the corrosion of pure copper under NaCl aerosol droplets,and the farther the thin liquid film spreads outward.The larger the concentration of NaCl droplets,the more NaCl diffused into the secondary spreading region,and the more serious the corrosion is.