| The protective performance of polyurea coatings is outstanding, it can improvethe service life of metal substrate effectively. However, the study on corrosionprevention of polyurea in marine environment is less, so it is very necessary toconduct the research of corrosion resistant performance of polyurea coatings for steelstructure protection in marine atmospheric environment. This paper aimed at theQingdao marine environment conditions, the temperature affects on mechanicalproperties of two polyurea coatings which included Qtech-202-A（A for short） andQtech-202-B（B for short） and the influence factors on adhesion of two coatingswere studied at first. Then the coatings whose comprehensive performance is betterwas selected to do the outdoor exposure and ultraviolet（QUV） accelerated agingexperiment research. The changing rule of adhesion, gloss, water absorption andmechanical properties of coatings in the two kinds of experimental environment wereobtained. And the corrosion resistant performance and failure behavior of the coatingswere analyzed by scanning electron microscope（SEM）, infrared spectra（FTIR） andelectrochemical impedance spectroscopy （EIS）. The experimental conclusions are asfollows:（1）The influence of temperature on the mechanical properties of coatings shows:in-10℃low temperature curing environment, the mechanical properties of A and Bcoatings were growing rapidly within7days, and reached a stable value at45th day.At this point, the hardness, tensile strength, elongation at break and tear strength of Acoatings were39HD,24.51MPa,489.65%and72.35N/mm respectively; they were44HD,28.68MPa,428.29%and76.36N/mm for B coatings at the same time. But in25℃room temperature curing environment7days, the mechanical properties of twocoatings were stabled which was equaled to the stable value that maintained in lowtemperature environment. In addition, both in low temperature and room temperaturecuring environment, the stable value of mechanical properties of B coatings weregreater than A coatings. （2）The affecting factors of coating adhesion research shows: when the thicknessof coatings adds to2.0mm from0.3mm, the adhesion of A with epoxy primer coatingsystem dropped to3.67MPa from5.66MPa, other coating systems also have the samelaw, so the adhesion of coatings is inversely proportional to its thickness. Theadhesion which was formed by using epoxy primer is higher than polyurethane primer.The adhesion to steel plate of B coatings was better than A coatings overall.（3） The results of outdoor exposure aging experiment reasarch including: themechanical properties of coatings were remain unchanged basically within90days,the glossiness fell to59.4°quickly, the bibulous rate and adhesion changed little. Butafter360days, the hardness, tensile strength, elongation at break and tear strength ofcoatings dropped to33HD,21.36MPa,413.21%and66.54N/mm respectively; theglossiness fell to27.3°, the gloss lost of surface was severely; the bibulous rateincreased to1.66%; the adhesion of polyurea coatings with epoxy and polyurethaneprimer were dropped to3.81MPa and3.41MPa respectively, the comprehensiveperformance of coatings kept well. SEM observation found that the surface ofcoatings was aging after experiment, the interface between coatings and steel plateappeared tiny crack which led to the adhesion decreased, the section of coatings hadno obvious change, its internal structure was completely, the protection performanceof coatings was still great. EIS test found that the impedance modulus value ofcoatings under low frequency was still greater than1010Ω.cm2, the porosity was2.37*109, the corrosion resistant performance was still outstanding after outdoorexposure10days. However, the impedance modulus value of coatings fell to106Ω.cm2, the porosity was2.66*10-6, the corrosion of steel had occurred, theprotective performance of coatings was poor after40days.（4） QUV accelerated aging experiment shows: after2400hours, the coatings wasdulling mostly, the mechanical properties of coatings were remain unchangedbasically, the water absorption rate and adhesion of coatings changed small, itscomprehensive performance changed little. But after7200hours, the hardness, tensilestrength, elongation at break and tear strength of coatings fell to32HD,20.33MPa,413.89%and63.87N/mm respectively, the surface of coatings was black completely, bibulous rate has increased to2.33%, the adhesion of two kinds of coating systemswere dropped to3.06MPa and2.57MPa respectively, the comprehensive performancedropped obviously. It has found that the surface aging of coatings was serious, theinternal aging was mild, the protective performance of coatings became poorer afterexperiments by SEM and FTIR spectra. After the sample undergo QUV acceleratedaging24hours, the impedance modulus value of coatings under low frequency was1010Ω.cm2, the porosity was6.54*10-10, it could prevent the corrosion medium frominfiltrating effectively. But after720hours, the impedance modulus value fell to105Ω.cm2, the porosity was5.75*10-4, so the coatings has been damaged, it wasdisabled.Based on the above studies, the change rule and influence factors of corrosionresistant performance of polyurea coatings for steel structure protection in marineatmospheric environment have been obtained, which provide basic data andtheoretical support for the engineering application. |
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