Effects of F^- Content on Localized Corrosion Development of 430 Stainless Steel in Ammonia Desulphurization Slurry

The occluded cell model of localized corrosion of 430 stainless steel in ammonia desulfurization solution was designed and optimized. The main parameters of the model were optimized by orthogonal test. Based on this, the effects of F^- content on the corrosion current, corrosion amount, pH, dissolved oxygen and ion migration of 430 stainless steel in the development of localized corrosion in the coexistence system of high content of fluorine and chlorine were analyzed. Combined with X-ray photoelectron spectroscopy (XPS) analysis, the effect of F^- content on the development of localized corrosion of 430 stainless steel in F^- and Cl^- system was determined. The results show that the optimal parameters of occluded cell model for the development of localized corrosion of 430 stainless steel were the ratio of internal solution volume to anode area of 69 mL/cm², the ratio of cathode area to anode area of 10, and the thickness of simulated rust layer of 1 mm. Low content of F^- increased conductivity and promoted corrosion. High content of F^- competes with Cl^-, and the combination of F^- and H⁺ in the occluded zone slowed down the consumption of dissolved oxygen and weakened acidification. F^- could form insoluble fluoride with iron dissolved in 430 stainless steel and deposit on the surface of metal anode, thus inhibiting the development of localized corrosion of 430 stainless steel.