Fabrication Nanocomposites And Properties Of Photogenerated Cathodic Protection On Titanium Substrates

Marine environmental corrosion is ubiquitous and detrimental problems of metals and alloys,restricting their widely applications in bunder,vessels,production platform etc.Cathodic protection technology provides sufficient protection for metals and alloys under marine environmental.Traditional cathodic protection can be classified two types:impressed current cathodic protection and sacrificial anode protection.However,traditional cathodic protection has some shortcomings,such as electric energy washing,sacrificial anode wasting and environmental pollution.Photogenerated cathodic protection technology is a new,green,non-polluting metal cathodic protection method.Only use sunlight that can achieve cathodic protection.TiO₂ has been one of the most important semiconductors because of its good chemical stability and defects in the film do not influence its use.However,TiO₂ can only absorb ultravilolet light which limits its particle application.In addition,photogenerated cathodic protection is difficult in the dark because the fast recombination by photogenerated electron-hole pairs.,This thesis compound narrow band gap semiconductor and deposition noble-metal to overcome this several shortcomings.This thesis fabricate Ti O₂ nanowires?Ag/CoFe₂O₄/TiO₂?Ag/CuFe₂O₄/TiO₂?Ag/NiS/TiO₂?Ag/Ag₃PO₄/TiO₂ and CdSe/CdS/TiO₂ five difference nanocompositions.The surface morphology,optical properties and composition were characterized by scanning electron microscope,UV-vis diffuse reflectance and X-ray photoelectron spectroscopy,respectively.Thephotocathodicprotectionpropertiesof nanocomposites for 304 stainless steel?304 SS?or Q235 carbon steel were measured by open circuit potential and photogenerated current density.The main results are listed as following:?1?We developed one-step anodization method to fabricate TiO₂ nanowires.The particle size and structures are union and visible.NaOH reaction time and concentration were investigated.Results show that TiO₂ nanowires prepared in 2 M NaOH solution and 120 min reaction time exhibited the best photocathodic protection for 304 SS.?2?Ag/Co Fe₂O₄/TiO₂ nanocomposites were fabricated by hydrothermal and photoreduction methods.When CoFe₂O₄ reaction time of 9 h,and AgNO₃concentration of 0.1 M have the best cathodic protection for 304 SS.The photopotential of the 304 SS coupled the nanocomposites was about-920 mV versus saturated calomel electrode under illumination and the photocurrent density reached420?A/cm².The nanocomposites increase the light absorption range from ultraviolet to visible area and solve the problem of low light utilization.?3?Ag/Cu Fe₂O₄/TiO₂ nanocomposites were fabricated by hydrothermal and photoreduction methods.When CuFe₂O₄ reaction time of 6 h,and AgNO₃concentration of 0.1 M have the best cathodic protection for 304 SS.The photopotential of the 304 SS coupled the nanocomposites was about-930 mV versus saturated calomel electrode under illumination and the photocurrent density reached475?A/cm².The formation of heterojunction electric field in nanocomposite increases the separation efficiency of photogenerated electron and hole,and solve the problem of electron and hole easy to recombination.?4?Ag/NiS/TiO₂ nanocomposites were fabricated by impregnating-depositon and photoreduction methods.With NiS 6 reaction circles and AgNO₃ concentration of 0.1M have the best cathodic protection for 304 SS.The photopotential of the 304 SS coupled the nanocomposites was about-925 mV versus saturated calomel electrode under illumination and the photocurrent density reached 410?A/cm².With the narrow band gap NiS deposited,the nanocomposite increase the light absorption range from ultraviolet to visible area and solve the problem of low light utilization.After 4 cycles,the protective potential and the photocurrent density are maintained at the initial level.Ag/NiS/TiO₂ nanocomposite has the best optical stability.?5?Ag/Ag₃PO₄/TiO₂ nanocomposites were fabricated by impregnating-depositon and photoreduction methods.With Ag₃PO₄ 6 reaction circles and AgNO₃concentration of 0.1 M have the best cathodic protection for 304 SS.The photopotential of the 304 SS coupled the nanocomposites was about-900 mV versus saturated calomel electrode under illumination and the photocurrent density reached130?A/cm².The nanocomposites increase the light absorption range from ultraviolet to visible area.The deposition of silver nanoparticles solved the problem of the instability of silver phosphate.?6?CdSe/CdS/TiO₂ nanocomposites were fabricated by impregnating-depositon and cycle voltammetry methods.With CdS 6 impregnating-depositon circles and CdSe 15 cycle voltammetry circles have the best cathodic protection for Q235 carbon steel.The photopotential of the Q235 carbon steel coupled the nanocomposite was about-1100 mV versus saturated calomel electrode under illumination and the photocurrent density reached 750?A/cm².The nanocomposite increase the light absorption range from ultraviolet to visible area and provide 200 mV cathodic protection.X-ray photoelectron spectroscopy shows that the purity of CdSe/CdS/TiO₂nanocomposite was high,and no impurities were introduced.All experimental results in this thesis demonstrated that photogenerated cathodic protection technology can provide an efficient solution strategy for marine environmental corrosion,which is a promising protection technology because its green and non-poluting properties.The ternary system nanocomposites have guiding significance for preparation and photogenerated cathodic protection property.