Effect of sulfur on corrosion behavior of Q235 and 16Mn steel in sodium aluminate solutions

Abstract

This study investigates the effect of sulfur on Q235 steel and 16Mn steel corrosion in sodium aluminate solution. The corrosion rate of Q235 steel and 16Mn steel reaches the maximum respectively when S 2− and S 2 O 3 2− form synergistic corrosion and S 2− is contained alone. But, the size of corroded particles is smaller in the solution containing only S 2 O 3 2− for two kinds of steel. The corrosion rate of 16Mn steel is greater than Q235 steel. Surface corrosion of two kinds of steel is both composed of sulfides (FeS and FeS 2 ) and oxides (Fe 2 O 3 , Fe 3 O 4 , Al 2 O 3 and NaFeO 2 ). The crystal particles of steel surface are mainly iron oxides according to EDS analysis. Nyquist plots of Q235 steel with different forms of sulfur have two capacitance-resistance arcs and no diffusion impedance. Nyquist plots of 16Mn steel with S 2 O 3 2− alone is consistent with Q235 steel. But, Nyquist plots of 16Mn steel presents a typical Warburg diffusion phenomenon with containing S 2− alone and forming synergistic corrosion.

Effect of Corrosion Time on the Synergistic Corrosion of Q235 Steel in Sodium Aluminate Solutions

“…While R f decreases with the corrosion time, indicating that the charge transfer is the main control step of corrosion and R f is small due to surface cracking at 4-5 d. At the same time, it found that when corroded for 3 d, the diffusion resistance (W R ) and diffusion exponent (W p ) of the Warburg component (at LF) is 428.5 Ω•cm −2 and 0.39, respectively. These results indicate that the corrosion products are dense and have a great influence on the ions diffusion, and the surface of the electrode has a certain degree of roughness and there is an ion dispersion effect [24,42], which is consistent with the results of SEM and AFM. In fact, faster scale nucleation leads to the appearance of smaller crystals that produce a compact layer.…”

“…The X'pert HighScore software was used to analyze the phase composition of the corrosion products, which may be composed of FeS, FeS2, Fe2O3, Fe3O4, Al2O3, MnS2 and NaFeO2 combined with thermodynamic analysis, which is suggested from the previous research [14,24,25] and is basically consistent with the EDS analysis in Figure 3. Although the phase composition of the corrosion products is the same, the peak intensity is different, which indicates that the crystallinity is different.…”

“…Judging from the spectrum results, the positions of the diffraction peaks of the corrosion products are basically the same with different corrosion times, which implies that the corrosion products with different corrosion times are also the same. Figure 4b is E-pH graph of Fe-Al-S-H2O at 110 °C derived from the HSC Chemistry software [24]. The possible physical phase of the Fe-Al-S-H2O system is analyzed thermodynamically at specific conditions.…”

“…Previous to this work, the influence of S 2− and S 2 O 3 2− and the structure of surface corrosion products in sodium aluminate solution on the corrosion behavior of Q235 steel was studied [14,24,45]. In this work, SEM, EDS, XRD, AFM, potentiodynamic polarization curve and EIS were combined with the aim to reveal the effect of corrosion time on the synergistic corrosion of Q235 steel in sodium aluminate solution containing sulfur.…”

“…Figure4bis E-pH graph of Fe-Al-S-H 2 O at 110 • C derived from the HSC Chemistry software[24]. The possible physical phase of the Fe-Al-S-H 2 O system is analyzed thermodynamically at specific conditions.…”