Stainless Steel Cathode Material Surface Passivation Of New Technology And Its Performance And Applied Research

Stainless steel had been performed very well in many corrosive environments, it also can as cathode material, so-called ISA and KIDD Process in copper electrolytic refining. But stainless steel will suffer pitting attack when chlorine ion or other kinds of corrosive cathode ions exist, and it will bring on other serious corrosion. In order to reinforce stainless steel's anti-corrosion, it is necessary to alter its surface state by passivation.The technique of passivation of stainless steel was paid most attention. The stainless steel samples were treated by electrochemical passivation in nitric acid solution and chemical passivation in citric acid solution. The anti-corrosion performance of passive film was studied by chemical immersion method and electrochemical methods. The surface state of passive film was studied by microscope and XPS.The pitting potential (E_b) was tested by means of anodic polarization curve measuring. The results indicated that the E_b of samples increased greatly, about 1100mV. The optimum parameters of electrochemical passivation in nitric acid solution were 10%HNO₃, 800mV, 25°C and 15min. The optimum parameters of chemical passivation in citric acid solution were 4%citric acid, 65°C, 15min, and the time of re-treat in 50%HNO₃ was 11min.The chemical immersion experiments indicated that the anti-corrosion of passive films were very good, nothing was observed when stainless steel samples were dipped in 5%NaCl solution after 5 days, the corrosion rates were big when steel samples were dipped in 6%FeCl₃ solution, while the corrosion rates of treated samples were smaller observably than untreated samples.EIS analysis results indicated that the electric charge transfer resistance of treated sample was bigger than untreated sample, this also indicated that the anti-corrosion performance of treated samples was better than untreated samples.XPS analysis results indicated that the surface state of samples was similar by two kinds of different passivation methods. The passive film was formed with many compounds of Fe, Cr, etc. with different valences. Thereinto, Fe was exist in FeO, Fe₃O₄, Fe₂O₃, FeOOH, etc. Cr was exist in CrO₃, CrO₂, CrOOH, Cr(OH)₃, etc.As cathode material, stainless steel samples were applied in the copper electrolytic refining. The tank voltage was 0.31V, the current efficiency was 97%～98%, and its adhension strength was also perfect.