Corrosion Protection Of Photoelectrochemical Cathodic Protection Method To Magnesium Alloy

Magnesium alloys have advantages such as high specific strength and low density,and are extensively used in aerospace and other industrial fields.Magnesium alloys have high chemical activity and poor corrosion resistance in marine environments.Photoelectrochemical cathodic protection(PECCP)technology can provide effective cathodic protection to metals or alloys in the marine environments.The PECCP takes advantage of the photo-generated electrons generated by n-type semiconductors under light illumination to negatively polarize the metal and achievement of cathodic protection.Since the self-corrosion potential of magnesium alloys is relatively negative,while the conduction band potentials of the present semiconductor materials are relatively positive,the photo-generated electrons cannot directly transfer to the magnesium alloy substrate to achieve cathodic protection.Here,a nickel layer with high self-corrosion potential is deposited on the magnesium alloy to realize the indirect cathodic protection to the magnesium alloy by the photoelectric conversion effect of the semiconductor.The major research contents are as follows:(1)Nickel player with physical barrier and relatively high self-corrosion potential(Mg/Ni electrode)was deposited on the magnesium alloy by electroless deposition followed by electrodeposition.Cu₂O semiconductor was electrodeposited on the surface of nickel-coated magnesium alloy or pure nickel foil to form Cu₂O coating and electrode(Ni/Cu₂O photoelectrode).The obtained Cu₂O film was characterized by X-ray diffractometer(XRD),scanning electron microscope(SEM),and transmission electron microscope(TEM)etc.The PECCP efficacy of the Cu₂O semiconductor to the Mg/Ni was investigated by testing the photoelectrochemical performance of the nickel-and Cu₂O-coated magnesium alloy,or the Mg/Ni electrode coupled with Ni/Cu₂O photoanode,including the variations of photoelectric potential,and photogenerated current density,and EIS and Tafel curves.By coupling of the Ni/Cu₂O photoanode with Mg/Ni electrode,negative open circuit potential(OCP)shift and positive photoinduced current density observed,suggesting the transfer of photo-generated electrons from photoanode to Mg/Ni electrode.The OCP change after coupling suggests the prolonged protection of nickel layer as a physical barrier to magnesium alloy,realizing the indirect protection of the magnesium alloy by PECCP technology.Lastly,a protection mechanism based on nickel layer with high-potential to realize indirect protection of magnesium alloys by PECCP is proposed.(2)Nano titanium dioxide(TiO₂)semiconductor with large specific surface area and stable chemical properties has excellent photocatalytic performance.In this paper,TiO₂NTAs were obtained by controlling the temperature,time,voltage and other conditions of anodization,and the photoelectrodes with the best photoelectric properties are obtained based on the changes of the light-induced OCP and current density.SEM,XRD,TEM,Ultraviolet visible diffuse reflection(UV-vis)etc.methods.The OCP change of Mg/Ni electrode after coupling with TiO₂NTAs show that the photoinduced potential drop can reach 230 m V,and the potential value maintains at about-0.7 V,indicating that the TiO₂NTAs photoanode has good PECCP effect on the Mg/Ni.(3)In order to further improve and verify the protection of PECCP on magnesium alloys,the covalent organic framework nanomaterials COF-TpBD and TiO₂/TpBD composite materials were prepared by hydrothermal method.The results of XRD,X-ray photoelectron spectroscopy(XPS),TEM,Fourier transform infrared spectroscopy(FT-IR)etc.that the prepared samples are mainly COF-TpBD-based organic polymers,which grew on both the inner and outer walls of the TiO₂ nanotubes.The photocurrent density generated by the TiO₂/TpBD composite material reaches about 420?A cm^-2,and the potential drop is 660 m V,showing excellent photoelectrochemical activity and PECCP effect.