Study On ?-Fe₂O₃/TiO₂ Composite Film For Photogenerated Cathodic Protection Of 20 Steel

Photocathode protection is widely used in metal for corrosion protection owing to its energy saving,environmental friendliness,convenience and high efficiency.TiO₂is a high-efficiency,stable,non-toxic,low-cost n-type semiconductor,and its excellent optoelectronic properties and applications in corrosion protection have been extensively used in photo-generated cathodic protection of carbon steel.However,due to the diffusion of iron ions in the matrix,the photocatalytic performance of TiO₂will be destroyed,resulting in little protection effect when it is directly coated on the surface of carbon steel.To solve this problem,a pre-oxidation layer is prepared on 20 steel before TiO₂to suppress iron diffusion,and at the same time form an?-Fe₂O₃/TiO₂heterojunction thin film,which is intended to inhibit iron diffusion while enhancing the photocatalytic performance.(1)Two types of?-Fe₂O₃transition layers were obtained by different pre-oxidation(thermal oxidation and anodization)on 20 steel.The effect of the microstructure of the?-Fe₂O₃transition layer on the photoelectrochemical properties and photogenerated cathodic protection properties of?-Fe₂O₃/TiO₂heterojunction films was investigated.The photoelectric conversion properties of?-Fe₂O₃/TiO₂heterojunction films were evaluated by UV-visible absorption spectra(UV-vis),surface photovoltage spectroscopy(SPV),photoluminescence spectra(PL)and photocurrent density-time curves(I-t).Electrochemical impedance spectroscopy(EIS)and potential polarization curve were used to measure the photocathode protection performance of?-Fe₂O₃/TiO₂film photoanodes.The results show that the anodized samples have better photoelectric conversion efficiency and photogenerated charge migration rate than the samples obtained by thermal oxidation.Under AM 1.5G irradiation,the anodized?-Fe₂O₃/TiO₂thin film samples were used as photoanodes,which reduced the corrosion current density and corrosion potential of 20 steel in 0.5M Na Cl solution by 0.149 m A?cm^-2and 297 m V,exhibited excellent photoelectrochemical cathodic protection performance compared to samples pretreated by thermal oxidation.(2)In order to further explore the photo-generated cathodic protection performance of?-Fe₂O₃/TiO₂film on 20 steel,the effect of anodizing time(6,9,12,15,18,and 21 min)on the microstructure of?-Fe₂O₃transition layer was investigated,and the effect of?-Fe₂O₃/TiO₂microstructure on the photogenerated cathodic protection performance of 20 steel was studied.Microstructure,photoelectrochemical properties,and photogenerated cathodic protection of?-Fe₂O₃/TiO₂heterojunction films were obtained through the tests of optical microscope(OM),scanning electron microscope(SEM),ultraviolet-visible absorption spectrum(UV-vis),surface photovoltage spectrum(SPV),electrochemical impedance spectrum(EIS)and potential polarization curve.The results show that with the extension of the oxidation time,the thickness of the pre-oxidation layer,the photoelectric conversion efficiency,the photogenerated charge migration rate,and the photogenerated cathode protection efficiency all increase and then decrease.Among them,when the anodizing time is 15 min,the?-Fe₂O₃/TiO₂film exhibits the best photoelectrochemical performance and photocathode protection performance for20 steel.and the corrosion current density and potential are reduced by 0.107m A?cm^-2and 265 m V.(3)Based on the optimization of anodizing time,the effect of anodizing voltage(30,40,50,60,and 70 V)on the microstructure of?-Fe₂O₃transition layer was studied,and the impact of the microstructure of?-Fe₂O₃/TiO₂on 20steel photogenerated cathodic protection performance was investigated.Microstructure,photoelectrochemical properties,and photogenerated cathodic protection of?-Fe₂O₃/TiO₂heterojunction films were obtained through the tests of optical microscope(OM),scanning electron microscope(SEM),ultraviolet-visible absorption spectrum(UV-vis),surface photovoltage spectrum(SPV),electrochemical impedance spectrum(EIS)and potential polarization curve.The test results are as follows:in the range of 30 V to 70 V,as the oxidation voltage increases,the thickness of the?-Fe₂O₃pre-oxidation layer,the photoelectric conversion efficiency,the photo-generated charge transfer rate,and the photo-cathode protection efficiency of the coupled 20 steel all decrease after increase first.Among them,when the anode voltage is 40 V,?-Fe₂O₃/TiO₂film shows the best photoelectrochemical performance and photocathode protection performance for 20 steel,and its corrosion current density and potential are reduced by 0.095 m A?cm^-2and 227 m V,respectively.