Corrosion Behavior And Mechanism Of Carbon Steel At Nansha Lslands Marine Atmospheric Environment

Along with the increasing pace of marine resources development and strategic deployment of our country,we have found that the infrastructure materials and deployed aircraft were facing severe salt fog corrosion during the construction process of the south sea.Materials damage in this environment is much more serious than other sea areas.However,there still lack of material corrosion data and relevant fundamental research until now.As for carbon steel is usually one of the most widely used infrastructure material and reference material,its corrosion data exposed to Nansha Islands marine atmosphere is much more important.These corrosion data can not only provide important basis for environmental corrosivity category,but also provide reference for indoor accelerated corrosion test.Owing to its location near the equator and the direct impact of solar radiation,the tropical marine atmosphere is a representative and typical climate with high temperature,high humidity,high salinity,and high radiation.As main corrosion impact factors,temperature,humidity and salt deposit have caused widely attention.In the last few years,some studies were focused on influence of different humidity or salt concentration on corrosion behavior of carbon steel and some were focused on effect of uv illumination on metal corrosion behavior.However,there is still less research on the following issues,the synergistic effect of ultraviolet radiation(uv)and temperature on corrosion behavior of carbon steel,and effect of different uv intensity on corrosion behavior of carbon steel.In addition,compared with other areas of seawater composition of metal cations,K+ and Mg2+ are also rich in the south China sea except Na+.As known,the composition of salts in the atmosphere is closely related with the composition of the seawater,therefore Nansha marine atmosphere contains plentiful Cl-and a variety of metal cations,such as Na+,K+and Mg2+.The effect of these metal cations on corrosion behavior of carbon steel and surface structure of carbon steel in chloride ion atmosphere should cause more concern.Thus,to investigate these issues,in this paper,carbon steel is employed as the experimental material,weightness loss analysis,macroscopic observation,scanning electron microscopy(SEM).energy dispersive spectrometer(EDS),X-ray diffraction(XRD),optical profiler,a laser scanning confocal microscope(LSCM),and electrochemical analysis measurement were conducted to study the corrosion behavior of carbon steel exposed to Nansha Islands marine atmosphere,the synergistic effect of ultraviolet raditation and temperature on corrosion behavior,effect of different uv intensity on corrosion behavior of carbon steel,and effect of metal cations on corrosion behavior and surface structure of carbon steel in chloride ion atmosphere.The conclusions were shown as follows.During the outdoor exposure,the corrosion rate of Q235 and Q450NQR1 first increased then decreased as time prolonged,and the corrosion resistance of Q450NQR1 was much better than that of Q235 after 5 months.As time prolonged,the color of rust layer formed on surface of Q235 and Q450NQR1 gradually deepened and the corrosion current density first increased,then decreased.The rust layer composition of both steels were the same,and the protective index ?*/?*of Q235 was the maximum after 21 months exposure and that of Q450NQR1 was the maximum after 12 months exposure.The strength and plastic of carbon steel changed a lot as exposure time prolonged,expecially both the strength and plastic decreased after 12 months.In terms of the corrosion rate,rcorr,for the first year of exposure to different corrosivity categories defined in ISO 9223,the corrosivity category of this marine atmosphere was CX.This high level of corrosivity category are closely related to the local environmental factors.The environmental temperature has a large impact on corrosion rate,morphology of rust,and the composition of corrosion products.A change of temperature from 30? to 60? results in an increase rate of the average weightness loss by approximately 222%.The weightness loss rate changed as temperature from 30?to 45? was larger than that from 45? to 60?.The rust layer was relatively flat at 30?,when the temperature increased to 45? and above,the thickness of the rust layer was not uniform and there were some salient points locally.Also,with temperature increasing,the relative composition of ?-FeOOH gradually decreased,the current density of cathode polarization and the pitting depth increased.In this condition,influence of uv on corrosion rate of carbon steel closely related to temperature,and the higher the temperature the greater effect of uv on corrosion behavior.Thus,influence of uv on the corrosion behavior of carbon steel was associated with environmental temperature.Usually uv intensity changed with season and exposure time.Effect of different uv intensity of corrosion behavior of carbon steel has been investigated and the results show that when uv intensity increased to some extent,the corrosion rate was accelerated significantly.With exposure time prolonged,the roughness became lager and the rust layer became thicker as uv intensity increased.The composition of corrosion products were the same,but the relative content of different kind FeOOH was changed as uv intensity increased.In the absence of salt deposition,effect of uv intensity on corrosion behavior of carbon steel was not obvious.Thus,influence of uv intensity on corrosion behavior of carbon steel was associated with the amount of salt deposition on the surface of the carbon steel.In addition,all the metal cation Na+,K+,and Mg2+containing in Nansha Islands marine atmosphere had a great influence on corrosion behavior of carbon steel.The thickness loss of carbon steel exposed in K+ and Mg2+ containing atmosphere was much larger than that in Na+ containing atmosphere,especially in Mg2+ containing atmosphere.This was owing to higher protective ability index in these two atmospheres And also more ?-FeOOH was generated in Mg2+ containing atmosphere,which can promote the dissolution of the steel to a certain extent,then accelerated the corrosion process.In a word,the high level of corrosivity category in Nansha Islands is caused by high temperature,high uv intensity and the metal cations Na+,K+ and Mg2+containing in atmosphere.