Study On The Preparation And Corrosion Inhibition Properties Of Molybdate Conversion Film Modified By Cr³⁺,Ni³⁺ Ions On The Steel Surface

Corrosion of reinforcement in concrete is one of the most important cause for reinforced concrete rupture,which will lead to a great loss to national economy and safety of people's life.Therefore,it is of great significance to improve the corrosion resistance of steel.The preparation of conversion coating can improve the corrosion resistance of steel under the lower cost condition.In this paper,guided by the passivation film theory,the low-toxic Cr3+,Ni3+ ions were added to a base molybdate conversion solution and the Cr3+,Ni3+-ions modified molybdate conversion film was prepared,which could adapt to the concrete high alkaline environment.The three gradient addition amount of Cr3+ or Ni3+ ion was added into the base separately,to prepare different Cr3+ or Ni3+ ion modified molybdate conversion film.The electrochemical properties have been investigated by cyclic polarization curve,electrochemical impedance spectroscopy(EIS),potentiostatic polarization curve and Mott-Schottky curve.The morphology and microstructure of the film has been characterized by scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS).The corrosion resistance performance of molybdate conversion film is improved effectively by Cr3and Ni3+ ions.When Cr(NO3)3 reached to the concentration of 15 g/L in the base solution,the corrosion resistance of film was enhanced shapely.The film is smooth,the amount of cracks decreased significantly.The film possesses better self-repairing property.And when Ni(NO3)3 increased to the concentration of 16 g/L in the solution,the passive current density and density of donors decrease significantly.The corrosion resistance has a significant improvement,though it showed no self-healing properties.After the study of the influence of one single ion,different conversion films were prepared through orthogonal design.The optimal formulation of conversion solution has been screened through protection potential and passive current density.The components and contents of treatment solution,which self-repairing performance and pitting corrosion resistance of the film were the best,were as follows:85%H3PO4 14 g/L,Na2MoO4 28 g/L,Cr(NO3)3 15 g/L,Ni(NO3)3 18 g/L.It can be used to the environment containing corrosive ions(such as Cl-).The components and contents of treatment solution,which the shielding performance of the film was the best,were as follows:85%H3PO4 12 g/L,Na2Mo04 28 g/L,Ni(NO3)3 18 g/L.The corrosion rate is the lowest.This formula is applicable to the corrosiveenvironment of ion concentration is low.