Research on Corrosion Resistance and Formation Mechanism of Molybdate Composite Film

In order to reduce phosphorus pollution, the low phosphorus passivation process on Q235 steel was studied. The electrochemical method was used to test the corrosion resistance of sodium molybdate low phosphorus passivation. The polarization curve shows that the corrosion current of the sample passivated by low phosphorus is only 1/4 of that of the blank sample. Under scanning electron microscopy, the passivation film obtained by low phosphorus passivation treatment had the lowest phosphorus content and was more uniform and compact. The XPS (X-ray photoelectron spectroscopy) and OCP (open circuit potential) were used to study the film formation regularity and mechanism of low molybdenum sodium passivation. The results show that sodium molybdate low phosphorus passivation film has good corrosion resistance. The formation process of a passivation film can be divided into four stages alternating phosphating and passivation. The surface of the passivation film is mainly composed of phosphate, molybdate, molybdenum oxide, and their crystalline hydrates. The low phosphorus passivation process of sodium molybdate can reduce the concentration of phosphorus ions and reduce its pollution to the environment, which has broad application prospects.