Electrochemical Behavior and Compositions of Passive Films of Amorphous Ni-P Coating in Acidic Environment

Amorphous Ni-P coating without pores was prepared by electroless plating. The electrochemical behavior of the as-plated Ni-P coating was investigated by potentiodynamic testing in 5 wt. % sulfuric acid solution. Results indicated that the high-phosphorus Ni-P coating has a passivation region in the acid solution. The passive films possessed n-type semiconductor characteristic basing on the Mott-Schottky analysis. Different anodic potentials and polarization time affect the passive films properties. The passive film shows the best corrosion resistance when the potentiostatic potential was 0.1 V and the polarization time was 30 min. XPS results show that the passive film consisted by Ni(OH)2 and Ni3(PO4)2.