| 304 stainless steel has been widely used due to its excellent performance,but it is easy to be corroded in the seawater.The research of 304 stainless steel anti-corrosion has already become a hot topic.Among many anti-corrosion methods,as a new type of anti-corrosion method called photocathodic protection has been studied in recent years.A photocathodic protection system consists of a photoanode and the protected metal.The electrons in the valence band are excited into the conduction band under illumination,leaving photoinduced holes in the valence band.Afterwards,the photoelectrons will flow into the metal,and make the potential more negative than its corrosion potential in the environment.ZnO is a kind of hexagonal wurtzite structure semiconductor material with a band gap width of 3.2 e V at the room temperature.There are many ways to prepare ZnO films,such as CVD,PVD and electrochemical deposition.Among these methods,electrochemical deposition has received exten sive attention as a low-cost,effective method in recent years.In this paper,our research focuses on two different aspects:the deposition potential and solution temperature.The main contents of this paper are as follows:(1)ZnO thin films were prepared on the surface of 304 stainless steel by cathodic electrodeposition method.The electrolyte was 0.005 M Zn(NO3)2 solution,the deposition potentials were-0.7 V,-1.0 V,-1.3 V and-1.6 V,and the deposition temperature was 65°C.The time-current density curves were recorded during the deposition process,and the surface morphologies of the samples were observed by scanning electron microscope.(2)The electrochemical performances of the ZnO films were evaluated by the open circuit potential,electrochemical impedance spectroscopy,potentiodynamic polarization curve and photocurrent density tests in 3.5 wt.%Na Cl solution.It was found that when UV light was switched on,the OCP of different samples immediately droped to more negative values.The values of the 304 stainless steel substrate caused by different ZnO films were different.It was observed that the OCPs quickly got recovered when the UV lamp was switched off.The ZnO films prepared at-1.0 V made the potential shift to the greatest negative valu e under UV illumination;whereas the ZnO deposited at-1.6 V showed the smallest.Electrochemical impedance spectroscopy test showed that the charge transfer resistance of the samples illuminated by UV was smaller than that without UV illumiantion.In the Tafel curves,the corrosion potential has been shifted to the negative position under UV illumination,but the corrosion density was much larger than that without UV illumination.According to the obtained corrosion current density,the sample was corroded more seriously under UV illumination.It seems that the prepared ZnO films has no protective effect on SS304 under light.The following research showed that the UV illumination led to a significant increase of the anodic current density and the enhanced current density may come from the photo-generated holes.(3)ZnO films were electrodeposited on ITO surface under-1.0 V,at 40°C,50°C,60°C,70°C,80°C.The time current density curves were recorded during the deposition process,and the microstructures of the samples were observed by SEM.It should be noted that the morphology of the 40°C sample was cauliflower like structure and at higher temperatures were nanorod like structure.(4)The results showed that the the cauliflower like ZnO film produced the largest photocurrent density and had the best photocathode protection effect for 304 stainless steel.According to the fluorescence emission spectrum,the samples of ZnO/ITO obtained at higher temperatures showed strong peaks at the UV region.While no PL emission was detected from the 40°C sample.That is to say the electron-hole recombination rate is very low.In addition to the luminescence band in the UV region,there was also a luminescence band in the visible part.However,the ZnO film obtained at 40°C displayed the highest PL emission intensity in the visible region.The peaks at visible region is caused by defects such as oxygen interstitial,oxygen vacancy and so on.Both the oxygen vacancy and interstitial oxygen defects are beneficial for the efficient separation of electron-hole pairs.So the films prepared at40°C display the best photocathodic performance. |
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