| As a traditional passivation method, chromate passivating process is a goodmethod to improve the corrosion resistance,it can also improve the surface quality andextend the service life of metals. But Cr6+ has great toxicity to both human body andenvironment. To avoid the disadvantageous influence of Cr6+, we need to replace thispassivation method. In recent years, people find out rare-earth metals, particularlywhich contain cerium salt, are effective corrosion inhibitors for aluminum, zinc, iron,magnesium, their alloys, stainless steel and carbon steel in atrocious environment. Ithas been successfully used in surface modification of various aluminum and Zn-platingsteel, but rare in the study of the stainless steel. In this paper , the improved corrosionresistance of stainless steels by rare-earth cerium conversion film were studied.(1)Research of the polishing technics of stainless steel.Based on performances of various acids in the polishing of stainless steel,polishing technics were studied.At the same time , for the sake of clean and brightsurface ,we add some the additive into the solution.(2) Stainless steel surface was dealed in the solution of both Ce2(SO4)3and H2O2.The optimum composition of the deal solution was gained by L9(34) orthogonaltest. The best technics parameters were as follows: Ce2(SO4)3: 0.010mol/L ; H2O2:100ml/L ; deal temperature:75℃;deal time:60min.(3) Conversion film has been tested by electrochemical anodic polarization curves.The inhibit mechanism of conversion film for stainless steel anodic corrosion,analyses and compares various conversion films were discussed. The results show thatthe corrosion potential increased from 20 mV which were tested for stainless steelbefore dealing to 250～1000 mV which were tested for conversion film on the stainlesssteel surface after dealing.(4) Tested for conversion film by EIS (electrochemical impedance spectroscopy)analysis.The results show that the polarization resistance for the untreated samples was0.05MΩ·cm-2 , which it increased to values 4 MΩ·cm-2 for the samples treated forconversion film on the stainless steel surface. Therefore, the polarization resistance ofconversion film on the stainless steel surface was increased by 80 times than that onstainless steel surface. (5) SEM tested for the conversion film.The particles deposit states and surface morphology of the films were investigatedby SEM . The results show that the particles on conversion film were interveined byeach other , which covered stainless steels closely. Conversion film made corrosionvelocity slower, which was achieved by conversion film isolation between stainlesssteel and corrosion solution.(6) EDS tested for the conversion film.EDS tested in order to identify which element play the main role in theenhancement of the passivation behaviour. The results show that the cerium played animportant role in inhibition the stainless steels corrosion . How the conversion filmsperformed depended on the quantity of the cerium in them.(7) To discuss reaction mechanism of forming conversion films on stainless steel surface.Integrating the results from the experiments of SEM, EDS and XRD, it can beconcluded that conversion film was made up of iron, chromium, nickel and ceriumoxides and hydroxides.
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