Cr-Free Passivation In Tin-Plating Sheet

With Cr6+ having the toxicity, disadvantage in environmental protection, its application at domestic and international suffer the restriction already and gradually, according to present condition. Now, there is no non-chromium passivation craft which can substitute chromium passivation. So the need of looking for a kind of replacing the green craft is very urgent affair.The research compared the passivation result of molybdate in system, zirconium sulfate in system, tungstate in system, octadecylamine in system and cerium nitrate in systems. It is discovered that the zirconium sulfate in system combined with octadecylamine in system and the molybdate in system are the better. They are nearer to the result of chromate than other systems. The following study finds that the brightness of the tested tinplates can't be strengthened. And the surface of the tinplate also has little darkly yellow piebald skins.So to choose the molybdate in system to do further research.Detailed studies are done about the molybdate in system,and find that phosphoric acid and manganese are helpful to the corrosion resistance of the tinplate.Hence the influence of the temperature, phosphoric acid concentration, manganese concentration, molybdate concentration, the time of passivation factor with regard to the external appearance of passive film and corrosion resistance were further studied.In order to further increase the corrosion resistance ,stabilityand the quality of passive film and strength it,using hydrogen peroxide to clean the tinplate'surface. Finally, one system was chosed, and further study on corrosion resistance and corrosion mechanism was carried on. The molybdate contents of the system is 20g·L-1, H3PO4 of 80g·L-1, manganese of 30g·L-1.In the condition of the best passive liquid constitute and the craft term the external appearance of molybdate in system for the tinplate which had bright color, and it were being tested by resistant to sulfide tarnishing and by acidoresistance. The corrosion current tested by Tafel test and the polarization resistance by EIS method indicated the different corrosion mechanism to substrate and higher corrosion resistance; explained the influence of different system on the content of films, corrosion resistance, corrosion mechanism and...