Passivation characteristics and corrosion behavior of S32202 duplex stainless steel in different temperatures polluted phosphoric acid

Abstract

The passivation characteristics of S32202 duplex stainless steel in different temperatures polluted phosphoric acid were studied by electrochemical technology and X-ray photoelectron spectroscopy, and its corrosion behavior was studied through immersion corrosion and electrochemical corrosion. The results indicate that as the temperature increases, the open-circuit potential of the sample in polluted phosphoric acid moves forward, and the surface exhibits a rapid passivation process. The main phases of the passivation film are Fe2O3, Fe3O4, Cr2O3, Cr(OH)3, and corresponding phosphates and polyphosphates. The passivation film of the sample in polluted phosphoric acid exhibits n-p-n composite semiconductor properties. As the temperature increases, the electron density and number of defects in the passivation film increase, and the vulnerability of the passivation film increases. The increase in temperature promotes the formation of a porous thick film. The corrosion types of the sample in polluted phosphoric acid are total corrosion, phase boundary corrosion, and intergranular corrosion, accompanied by pitting corrosion in local areas. The corrosion current density and passivation current density of the sample gradually increase with increasing temperature, while the counter-passivation potential and passivation index decrease, the density and protective properties of the passivation film decrease. The doping of phosphate can alleviate the dissolution process of metals, but the increase in temperature increases the solution ionic activity and accelerates the rate of charge transfer at the interface. At the same time, FePO4, CrPO4 and other phosphates are poorly protected, and their large presence is not conducive to the stability of the passivation film structure, resulting in a decrease in the corrosion resistance of the material.