Effect of hydrogen peroxide on corrosion resistance of praseodymium-based conversion film on zinc surface
[Introduction]Hydrogen peroxide as a strong oxidizer was added to the chemical conversion solution with praseodymium nitrate as the main film-forming agent to further enhance the corrosion resistance of praseodymium-based conversion film.[Method]The effect of the volume fraction of hydrogen peroxide on the corrosion resistance of praseodymium-based conversion film was studied by copper sulfate dropping corrosion test,hydrogen evolution test,potentiodynamic polarization curve measurement,and electrochemical impedance spectroscopy. The micro-morphology and composition of conversion film was analyzed by scanning electron microscopy (SEM),energy-dispersive spectroscopy (EDS),and X-ray photoelectron spectroscopy (XPS).[Result]The corrosion resistance of praseodymium-based conversion film got better initially and then worse with the increasing of volume fraction of hydrogen peroxide. The conversion film obtained with 35 mL/L of hydrogen peroxide was compact and mainly composed of praseodymium hydroxides and oxides,and featured the best corrosion resistance.[Conclusion]A conversion film with excellent corrosion resistance can be obtained on zinc surface by adding an appropriate amount of hydrogen peroxide to the praseodymium-based conversion solution.
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