Kinetics of Passive Film Growth on 304 Stainless Steel in H2SO4 Pickling Solution under Chemical Oxidation

Abstract

H2SO4-H2O2 mixtures are a promising and environmentally friendly passivation medium for the stainless-steel pickling process. The corrosion behavior of stainless steel is highly dependent on the kinetics of passive film growth. Long-term electrochemical measurements, including polarization resistance, open circuit potential (OCP), and electrochemical impedance spectroscopy (EIS) measurements were performed to investigate the evolution of the passive state of 304 stainless steel. According to the OCP results, an active-passive transition takes place in 10 ks in 0.5 M H2SO4 solution containing 0.005 M to 0.3 M H2O2. Polarization resistance results indicate that the passive film thickness keeps growing after OCP stabilization in the presence of H2O2. Electrochemical impedance spectroscopy (EIS) results confirmed that the growth of the passive film in H2SO4-H2O2 solutions takes about 9 h. Additionally, according to the Point Defect Model (PDM) and Mott–Schottky analysis, the semiconductor properties of the passive film on 304 stainless steel in H2SO4-H2O2 solution were studied. The results indicate that the passive film is an n-type semiconductor. The donor density is in the range of 1.6 × 10−21 cm−3 to 24 and decreases exponentially with increasing film formation potential (this potential coincides with the final OCP in the corresponding H2SO4-H2O2 solutions). By postulating that most donors are oxygen vacancies, the point defect properties including diffusivity and electrical field strength are obtained.

In Situ Electrochemical Study of the Growth Kinetics of Passive Film on TC11 Alloy in Sulfate Solution at 300 °C/10 MPa

“…The evolution of OCP over time is shown in Figure 1a, and the first ten thousand seconds are presented in Figure 1b. Similar evolution of open circuit potential with time was reported for commercial pure titanium [40], Ti-6Al-4V [41] and 304 stainless steel [42]. It shows in Figure 1a that the potential exhibits a rapid shift at the initial stage of the measurement.…”

“…In the process of the OCP experiment, LP tests were carried out to characterize the passivation state of the alloy [42]. The evolution of the polarization resistance over time is shown in Figure 3.…”

“…The OCP begins to stabilize at about 15 ks, while the R p starts to become stable at about 30 ks. They attributed this to the interface reactions that keep on influencing the structure of the passive film, even though the OCP has reached a steady state [42].…”

“…The fact that the C f values become smaller while the R f values become larger demonstrates that the passive film becomes more and more dense and protective [42].…”

Laboratory‐scale simulation of industrial neutral electrolytic pickling as a bipolar system—Parameters affecting indirect polarization pickling of annealed stainless steel

“…This research is part of a wider study of neutral electrochemical pickling as the majority of published research is almost two decades old or concerning other parts of the pickling process, such as the utilization of pickling sludge, 27,28 final (mixed) acid pickling and possible replacement methods, [29][30][31][32][33][34][35] or the effect of pickling on the corrosion of stainless steel. 7,36,37 As the Ruthner Neolyte Process is widely used, 3,6,28,38 even a small increase in efficiency leads to both a local and global reduction of steel industries' energy requirements.…”