| The corrosion of metal materials in the marine environment is very serious,the traditional protection methods are mainly organic coating protection and sacrificial anode protection.The method of sacrificial anode for cathodic protection is a simple and less investment electrochemical protection way which does not require additional current and is widely used in practical production.However,due to its shortcomings such as fast consumption,low efficiency,short life and so on,the materials need to be replaced frequently and consume a lot.In recent years,the research of the application of environmentally friendly photocatalytic materials in the electrochemical cathodic protection of metal has attracted wide attention.Traditional coarse crystalline TiO2 semiconductor material has the UV region response because of a wide band gap and higher carrier recombination rate inhibits the photoelectric conversion efficiency,which make the application very poor.Therefore,some surface modification methods such as noble metal deposition,semiconductor composite and transition metal ion adulteration are used to improve its photocatalytic activity.At the same time,many researches on new photocatalytic materials,such as ZnO,CdS,WO3,Ta3Ns’s work has also gotten good results.In this paper,the electrochemical properties of Co(OH)2 surface modified TiO2 and new Ta3Ns photocatalytic materials were studied.The electrochemical behavior and mechanism of two materials in 3.5wt%simulated marine environment were studied,and the characterization before and after corrosion was analyzed,which supply theoretical basis for the research and development of photocatalytic cathode materials.The main conclusions are following:1.For TiO2 photocatalytic materials:(1)When the anatase and rutile TiO2 are coupled to the 304 stainless steel,the open circuit potentials under light reduces to-0.30V and-0.16V,so anatase TiO2 can achieve electrochemical protection on stainless steel(self-corrosion potential-0.17V.(2)After surface modification by Co(OH)2,the electrode potential of two crystal type TiO2 coupling with stainless steel reduces respectively to-0.42V and-0.25V,both of which can realize the electrochemical protection on stainless steel.Meanwhile,the long period test results show that both materials are still maintained at-0.31V and-0.20V after 12h illumination,therefor long time protection for stainless steel can be achieved.The Co(OH)2 surface modification can promote the separation of h-e,providing more active sites for the electrochemical reaction and improving the photoelectric properties,and thus greatly enhances the electrochemical protection of metal.(3)After 40 days immersion,Co(OH)2 is detached from the film,TiO2 nanotubes had a slight blockage,resulting in the potential changing near to the self-corrosion potential of stainless steel,the protective properties fall down.(4)The nanotube structure is changed by heat treatment temperature,and then affect the transfer of TiO2 photoelectron.The best electrochemical protection performance of TiO2 is prepared at 500℃ heat treatment with Co(OH)2 modified.2.For the new Ta3Ns photocatalytic materials:(1)When Ta3Ns without modification and modified by CoPi/Co(OH)2 are coupled to 304 stainless steel,the open circuit potential drops respectively to-0.1 1V-0.45V under illumination.Ta3N5 after the surface modification with CoPi/Co(OH)2 can realize the electrochemical protection for stainless steel.(2)The potential of the modified Ta3Ns is decreased and then increased slowly under illumination,part of Co(OH)2 falls off,and Ta3Ns material is easy to be oxidized by hole.Therefore its electrochemical protection performance is not stable,which is still difficult for the long-term application. |
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