Effect of Sulfur on synergistic corrosion behavior of Q235 and 16Mn steel in sodium aluminate solution

Effect of Sulfur on synergistic corrosion behavior of Q235 and 16Mn steel in sodium aluminate solution | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Effect of Sulfur on synergistic corrosion behavior of Q235 and 16Mn steel in sodium aluminate solution Dongyu Li, Bianli Quan, Junqi Li, Chaoyi Chen, Jun Xu, Hanli Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4119985/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Sep, 2024 Read the published version in Scientific Reports → Version 1 posted 13 You are reading this latest preprint version Abstract In this study, the corrosion electrochemistry and corrosion behavior of two steels were studied under the simulated alumina production conditions. The corrosion rate of 16Mn steel is greater than that of Q235 steel. The effect of S 2− concentration on corrosion rate was significantly higher than that of S 2 O 3 2− . The synergistic corrosion rates of Q235 and 16Mn steels increase at first and then decrease with the sulfur content, and the peak value appears when the concentration of S 2− and S 2 O 3 2− is 4 g/L and 3 g/L respectively. There are two main types of corrosion products: one is surface octahedral grain, which is composed of Fe 2 O 3 , Fe 3 O 4 and Al 2 O 3 .The other is the interlayer corrosion between the surface layer and the matrix, which is composed of FeS, FeS 2 and NaFeO 2 .The formation mechanism of the corrosion and corrosion mechanism were obtained by analyzing the phenomenon of ion competitive adsorption. Further validation and analysis of ion competition adsorption phenomenon were conducted using first-principles calculations based on density functional theory (DFT). The formation of corrosion products on the steel surface was investigated at an ion level, and the adsorption energies of OH − and S 2− at the top site of Fe(110) surface were calculated. It was found that S 2− is more likely to be adsorbed on the Fe(110) surface compared to OH − . The corrosion mechanism of steel is discussed preliminarily. Physical sciences/Chemistry Physical sciences/Materials science Q235 steel 16Mn steel Sulfide Dynamics Potentiodynamic polarization Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1 Introduction High-sulfur and high-grade bauxite is suitable for Bayer process. The sulfur element in the ore mainly enters the solution as S 2− form under high-pressure and high-alkali dissolution conditions, which accounts for more than 90% of the total sulfur content, and include a small amount of S 2 O 3 2− , SO 3 2− , SO 4 2− and S 2 2 − 1 . However, the presence of the higher sulfur content of sodium aluminate solution is more likely to destroy the dissolution and sintering process of alumina 2,3 , especially, sulfide and thiosulfate aggravate the corrosion of steel equipment 4 . With the rapid development of the alumina industry, in order to effectively develop and utilize high-sulfur bauxite, reduce the harm of sulfur in the alumina industrial production, and control the sulfur in the ore into the solution, many scientific researchers at home and abroad have carried out a large number of experimental studies on the occurrence of sulfur and the dissolution behavior of sulfur 5,6 . However, with the recycling of mother liquor, sulfur accumulates in sodium aluminate solution and affects alumina production to a certain extent. Aiming at the corrosion problem of equipment materials caused by sulfur in sodium aluminate solution,Researcher has carried out corresponding research work in the early stage 7,8 . QUAN Bianli research found that there is a certain synergistic effect between sulfide and thiosulfate in the simulated sodium aluminate solution 9 . This effect has also been found in the oil and gas industry 10,11 . The synergistic corrosion is a complex process, which is affected by many factors 12 , especially the concentration of corrosives. GOLDMAN M found that small concentrations of sulfide were found to promote anodic dissolution as Fe-II carbonate complexes and to destabilize Fe-III oxides leading to the loss of passivity 13 . Shiqi Wang et al. revealed that the corrosion potential became more negative, and the anodic corrosion rate decreased with increasing chloride concentration due to the competitive adsorption of HS − and Cl − 14 . Tangqing Wu et al. revealed that NaHSO 3 concentration affected both cathodic and anodic behaviors, and the compactness and mechanical properties of the corrosion products degraded 15 . Miao Wu and Jinjie Shi showed the chloride-induced corrosion could be inhibited for low-carbon steel with molybdate, which is more pronounced with increasing concentration of molybdate and prolonged immersion time 16 . Therefore, the literature found that the co-existing ions and their concentrations have a greater impact on the corrosion of steel. Quantum chemical simulations can be used to intuitively understand the geometric and electronic structures of molecules and the adsorption of ions on metal surfaces, which has numerous applications in metal corrosion and protection. Over the past few decades, significant academic efforts have been devoted to studying the adsorption and activation of ions on metal iron surfaces. The adsorption of H + and Cl − in acidic solutions also plays an important role in combating corrosion and maintaining surface stability.Jun Hu 17 reported the effects of H 2 O, H + , Cl − , and HO − on three different planes, Fe(110), Cr(110), and Cr-doped Fe(110). By verifying the adsorption mechanisms of the four aforementioned adsorbates, it was found that the Cr-doped Fe(110) surface is the most stable among the three adsorption surfaces, indicating that the presence of Cr-doped crystals makes them more susceptible to corrosion. Qiao Sun et al 18 established a crystal atomic stacking model of ferrous sulfide and calculated the adsorption energy of ions on the exposed surface. They found that iron sulfide (FeS) exhibits cation selectivity, inhibiting the diffusion of corrosive ions towards the substrate, resulting in lower corrosion rates and uniform corrosion. On the other hand, magnetic pyrite (Fe 7 S 8 ) exhibits anion selectivity, leading to the accumulation of Cl − between the corrosion scale and the substrate, resulting in higher corrosion rates and localized corrosion. Mohammad Asif 19 investigated three corrosive components on the iron surface, namely (i) sulfur, (ii) hydrogen gas, and (iii) sulfates, and confirmed that Fe(110) has higher corrosion resistance compared to Fe(100) and Fe(310). Therefore, quantum chemical simulation calculations can better substantiate experimental results and improve the scientific rigor and accuracy of research. The author mainly conducted related research on the corrosion behavior of active sulfide on steel.This article mainly studies the corrosion behavior of two types of steel in a simulated solution of sodium aluminate containing sulfur. The corrosion behavior of Q235 steel and 16Mn steel was evaluated using electrochemical measurements and surface characterization techniques. First principles calculations were conducted to calculate the adsorption energies of S 2− and HO − on the Fe(110) surface and to discuss the competitive adsorption relationship between ions. Furthermore, the corrosion inhibition mechanisms of sulfides on both types of steel were established. This provides a theoretical reference for the subsequent development and application of high-sulfur bauxite and equipment protection. 2 Experiment Procedures 2.1 Specimens and Experimental Solutions The chemical compositions of Q235 steel and 16Mn steel in this study were listed in Table 1 . The rectangular cubes with the size of 15×15×1 mm 3 and 20×10×1 mm 3 were cut from the Q235 steel and 16Mn steel, respectively. The exposed sample surface was gradually ground with SiC sandpaper from 600 grit to 1800 grit and then cleaned in acetone and distilled water. Table 1 Chemical Composition of Q235 steel and 16Mn steel (Wt. %) Sample C Si Mn Cr P S Fe Q235 steel 0.207 0.055 0.233 0.105 0.069 0.019 Bal 16Mn steel 0.178 0.290 1.645 0.041 0.056 0.017 Bal The corrosion medium is the sulfur-containing sodium aluminate solutions (pH>14) in the experiments, which simulates the conditions of the alumina production seed decomposition process. The preparation method of the sodium aluminate solution is the same as that of literature 8 . The chemical composition of the sulfur-containing sodium aluminate solutions is 255 g/L NaOH, 110 g/L Al 2 O 3 , 1 g/L, 2 g/L, 3 g/L, 4 g/L, 5 g/L S 2− and 3 g/L S 2 O 3 2− . Alumina (Al 2 O 3 ·3H 2 O) reacts with NaOH to form sodium aluminate (NaAlO 2 ) 20 . The freshly prepared solution is necessary before each experiment. 2.2 Weight Loss Experiments The corrosion experiments were carried out at 110℃ for 120 h in the autoclave which are respectively the simulated normal temperature, the temperature of seed crystal decomposition and the temperature of the evaporation process in the alumina production. Five Q235 steel coupons and 16Mn steel coupons were used in each experiment. Three steel coupons were used for the measurement of the weight change, while the other two were used to detect the morphology and the phase composition, respectively. Finally, the corrosion products were removed using 500mL distilled water, 500mL HCl, and 10g hexamethylenetetramine (GB/T 6074 − 1992). The corrosion rate (R) (mm·year − 1 or mm·a − 1 ) was calculated using weight loss measurement and the formula to calculate is as follows: $$\text{R}=\frac{W\times 365\times 1000}{A\times T\times D}$$ 1 Where R is the corrosion rate in mm/a; W is the weight loss in g; A is the exposed surface area in mm 2 ; T is the immersion time in day; and D is the steel density in g/m 3 . 2.3 Corrosion Products Analysis All of the corrosion experiments with different S 2− and S 2 O 3 2− concentration were carried out in the autoclave (Weihai Zhengwei Machinery Equipment Co., Ltd.) at 383K 8 . After the experiment is completed, the morphology and elemental composition of the corrosion products on the steel surface are analyzed by the scanning electron microscopy (SEM, ZEISS SUPRA 40, Germany) with 10KV acceleration voltage and the electron type is secondary electron, and energy dispersive spectroscopy (EDS, AZ tec., Oxford, UK). The crystalline structure of the corrosion products was investigated by X-ray diffraction (XRD, X’pert Pro MPD Panalytical, Netherlands) with monochromated Cu-Ka radiation at the 2θ range of 10°~80°. The software of HighScore Plus (Panalytical, Almelo, Netherlands) was selected to analyze the data. 2.4 Electrochemical Tests Electrochemical measurements were carried out on the electrochemical workstation (Boi-Logic SAS, France) with a conventional three-electrode cell. The counter electrode was a platinum electrode (20*10*0.1mm, Beijing, Jingke), the reference electrode was a saturated calomel electrode (SCE, Lei Magnetic, Shanghai), and the working electrode was 16Mn steel with the exposed areas of about 2.00 cm 2 . Because SCE cannot withstand temperatures above 343K. So, the cell was placed in a water bath to maintain the experiment temperature (338K). Before the electrochemical experiment, the working electrodes were soaked in the corrosion solution at 338K with different S 2− and S 2 O 3 2− concentration. Electrochemical impedance spectrum (EIS) was carried out at open circuit potential (OCP) over the frequency from 10 5 Hz to 10 − 2 Hz, and the amplitude of the AC signal was 5 mV. All potentials reported in this paper were measured with respect to the SCE. Zview software (3.0a) and the equivalent circuits (EC) are used to process electrochemical impedance spectroscopy data. Potentiodynamic polarization measurements with a potential scan rate of 1mV·s − 1 were performed vs. OCP and the potential ranged from − 1.50V vs. SCE to 1.50 V vs. SCE. In order to obtain the electrochemical kinetic parameters such as the corrosion potentials (E corr ) and corrosion current densities (I corr ), Tafel fitting was performed on the polarization curve. 2.5 Theoretical calculation methods Using Materials Studio (Inc.), a lattice structure model of the Fe(110) surface was constructed (Fe(110) plane being the most stable surface under actual conditions). Subsequently, the adsorption energies of S 2- and OH - on the Fe(110) surface were calculated using the DMol3 module within Materials Studio. A periodic slab was established in the calculation, with a selected plane composed of the Fe(110) surface to simulate the surface. Four atomic layers, including two fixed bottom layers, were included along the direction perpendicular to the exposed surface. A vacuum region with a thickness of 15 Å was maintained between adjacent crystal layers, periodically arranged along the Z direction to avoid interference. The ions were placed on the surface top sites as the adsorption layer. During the geometry optimization process, the energy and electronic structure of the system were calculated using the Generalized Gradient Approximation (GGA) 21 and the Perdew, Burke, and Ernzerhof (PBE) exchange-correlation functional 22 . The spin was set to be unrestricted, and the formal spin was initialized 23 . The energy convergence criterion was higher than 1.0×10 − 5 Ha, and the structure was relaxed using a geometry optimization method until the forces experienced by all atoms were smaller than 0.002 Ha/A, meeting the convergence criteria. Double numerical quality basis sets were used, along with Double Numerical Polarization (DNP) functions. Effective Core Potentials (ECPs) were employed to handle the core electrons of metal atoms. A thermal smearing was adopted at 0.005 hartree. A Monkhorst-Pack grid with a 4×4×1 k-point sampling was used in the surface Brillouin zone for volume and surface calculations 24 . The k-point separation was set to be 0.05 Å. 3 Results and Discussion 3.1 E-pH graph Figure 1 is the E-pH diagram of Fe-Al-S-H 2 O system and Fe-Mn-Al-S-H 2 O system at 95℃ respectively. It shows that the element Fe exists stably in the form of HFeO 2 − in both systems. Element Mn exists stably in the form of MnO·Fe 2 O 3 . The element Al exists stably in the form of the conjugate FeAl 2 O 4 . The existence of substances under thermodynamic conditions does provide a basis for judging the corrosion mechanism. 3.2 Corrosion Rate Variation Laws The variation of corrosion rates after 5 days of immersion in sodium thiosulfate solutions containing 3g/L S 2 O 3 2- for Q235 and 16Mn steels at different S 2- concentrations is shown in Fig. 2 . From Fig. 2 (a), it can be observed that the corrosion rates of Q235 and 16Mn steels in sodium thiosulfate solutions containing 3 g/L S 2 O 3 2- exhibit three different scenarios with varying S 2- concentrations. ( 1 ) Scenario 1: Corrosion rates increase with increasing S 2- concentration. With the increase in S 2- concentration in the sodium thiosulfate solution, the active ion S 2- significantly activates the corrosion process of the steels. The corrosion rate of Q235 steel increases with S 2- concentration up to 4 g/L, while the corrosion rate of 16Mn steel increases up to 3 g/L. ( 2 ) Scenario 2: Corrosion rates reach maximum values. When the S 2- concentration in the sodium thiosulfate solution reaches a certain level, the added S 2- continues to react with the unreacted matrix until a uniform layer of corrosion product covers the steel surface. At this point, the corrosion rate of the steel reaches its maximum. For Q235 steel, the corrosion rate is maximized at an S 2- concentration of 4 g/L, while for 16Mn steel, the maximum corrosion rate is achieved at an S 2- concentration of 3 g/L. ( 3 ) Scenario 3: Corrosion rates decrease after reaching maximum values. As the S 2- concentration in the sodium thiosulfate solution increases, the corrosive S 2- ions react with the steel matrix and also undergo electron transfer reactions with S 2 O 3 2- in the solution, hindering further corrosion. Simultaneously, the corrosion products on the steel surface undergo transformation, forming a stable and dense corrosion layer that impedes the diffusion of ions towards the metal substrate. The combined effects result in a decrease in the corrosion rate of the steel. In order to obtain the corrosion kinetics equations and determine the corrosion kinetics parameters (reaction rate constant k and reaction order n) for Q235 and 16Mn steels at lower S 2- concentrations, a linear fitting of the corrosion rate vs. S 2- concentration data in Figure (a) was performed, as shown in Fig. 2 (b). The obtained kinetic parameters are presented in Table 2 . It can be observed from Fig. 2 (b) that the linear fitting shows a relatively good fit, with R2 values all above 0.95. The corrosion rate constants (k) for Q235 and 16Mn steels in sodium thiosulfate solutions containing both S 2- and S 2 O 3 2- are relatively small, while the reaction orders (n) are both greater than 1. By comparing the reaction rate constants (k) and reaction orders (n), it is observed that when the S 2- concentration reaches a certain value, the corrosion rate curves of both steels intersect. This explains the inconsistent corrosion rate behavior of the two steels with changing concentration, as discussed in section 3.4.1. In summary, the change in corrosion rates of Q235 and 16Mn steels in sodium thiosulfate solutions containing both S 2- and S 2 O 3 2- can be characterized as follows: Firstly, when the solution contains a relatively low concentration of S 2- , the S 2- ions adsorb on the steel surface and react with it, forming iron sulfides, which accelerate the corrosion process. Therefore, S 2- mainly plays a role in activating the corrosion, promoting its progression. However, as the S 2- concentration in the solution increases, the excess S 2- ions react with S 2 O 3 2- through electron transfer reactions, consuming the electrons released at the anode and promoting continuous anodic dissolution, thereby accelerating the corrosion process until the corrosion rate reaches its maximum. Secondly, as the concentration of S 2- ions continues to increase, the corrosion products on the steel surface transform into dense and stable iron oxides, which impede further corrosion. As a result, the corrosion rate of the steel decreases. Table 2 Corrosion kinetic fitting parameters of Q235 and 16Mn steels Material Kinetic equation Reaction rate constant k eaction order n R 2 Q235 lnR=-3.856 + 1.78lnC 0.02 1.78 0.9653 16Mn lnR=-3.182 + 1.48lnC 0.04 1.48 0.9459 3.3 Characteristics of Corrosion Products 3.3.1 Morphology and Element Composition Analysis Figure 3 shows the microscopic morphology and element distribution of corrosion products on the surface of Q235 steel and 16Mn steel when immersed in the sodium aluminate solution containing 3 g/L S 2 O 3 2- with different S 2- concentration for 5 days. It can be seen from the topography of 20000 times high magnification that when the concentration of S 2- is 1 g/L (Fig. 3 a, 3 b), the surface of Q235 and 16Mn steel generates a layer of dense, regular octahedral grains with good crystal shape and uniform particle size, which has a great hindrment effect on corrosion. When the concentration of S 2- is 2 g/L (Fig. 3 c, 3 d), the surface crystal particles gradually grow up and accumulate to form cuboid corrosion products. When the concentration of S 2- is 3 g/L (Fig. 3 e, 3 f), the surface corrosion products have obvious changes, and octahedral crystal particles are formed at the same time, another flocculent corrosion products are formed. As the concentration of S 2- continues to increase to 4–5 g/L (Fig. 3 g- 3 j), the surface octahedral crystal particles continue to accumulate and grow, and eventually form a layer of dense and uneven cube particles, which further hinder ion migration and slow down the corrosion process. By comparing SEM morphologies of the two steels, it is found that the corrosion products on the surface of 16Mn steel are denser and smoother than that of Q235 steel when the concentration of S 2- reaches 4–5 g/L (Fig. 3 g- 3 j). It is consistent with the result that the corrosion rate of 16Mn steel is lower than that of Q235 steel. It is also found that the corrosion products on the surface of Q235 and 16Mn steel are mainly composed of two forms, one is the octahedral crystal particles and cube particles formed by the octahedral stacking (Cross marking), the other is the interlayer flocculent corrosion products between the matrix and crystal particles (Square marking). Combined with EDS analysis of surface corrosion in Fig. 3 , it can be seen that both the octahedral crystal and cube particle corrosion are composed of Fe, O and Al, while the interlayer flocculent corrosion products is mainly composed of Fe, O, Al, S and Na. Combined with EDS element distribution diagram of Q235 steel in containing 5 g/L S 2- and 3 g/L S 2 O 3 2- sodium aluminate solution (Fig. 3 K), it can be seen that non-metallic element carbon (C) and metallic element chromium (Cr) are enriched in surface corrosion products, indicating that the carbon causes the formation of internal chemical battery in the corrosion process, at the same time, the loss of chromium in steel increases the tendency of pitting. Therefore, the more active elements participate in the corrosion reaction to form a dense layer of corrosion products, which can inhibit the contact between anions and steel matrix and slow down the corrosion process. In order to further analyze the characteristics and composition of corrosion products on the surface of Q235 and 16Mn steel, the elemental composition of corrosion products on the surface of steel containing 3 g/L S 2- and 3 g/L S 2 O 3 2- sodium aluminate solution was analyzed, and the results are shown in Fig. 3 (k-q). The results show that the elemental composition of the corrosion products on the two steels surface is consistent, indicating that the alloying elements have no effect on the elemental composition of the corrosion products on the surface. By comparison, it is found that the composition of flocculent corrosion products formed on the surface (circle) is the same as that formed on the interlayer of the matrix (box), both of which contain sulfur element, indicating that S 2- is adsorbed to the steel matrix and reacts with it to form iron sulfide. I. Betova 25 ,Xie Qiaoling 4 et al. believed that HS - in Bayer solution was more easily adsorbed to the steel surface to generate iron sulfide intermediate than OH - . Therefore, the steel surface preferentially adsorbs HS - in sodium aluminate solution to produce iron sulfide, which is embedded in the surface oxide and reduces the corrosion resistance of the corrosion layer. The octahedral crystal particles (cross) contain little sulfur because, as corrosion progresses, the sulfide formed on the steel surface continues to react with anions (OH - , S 2- , or S 2 O 3 2- ) in solution to form structurally stable iron oxides that inhibit corrosion. 3.3.2 XRD Analysis In order to characterize the effect of S 2− concentration on the composition of corrosion products on Q235 steel and 16Mn steel surface, XRD detection of the corrosion products with different S 2− concentration was performed, and the results are shown in Fig. 3 . It can be seen from Fig. 4 that when S 2− concentration is different, the peak position in XRD pattern is the same, but the peak intensity has a certain change and the crystallinity of the corrosion particles is different. It shows that S 2− concentration only affects the crystallinity of the crystalline particles. Therefore, the composition of corrosion products on the steel surface with different S 2− concentrations may be the same. Using X-pert High Score analysis software to analyze XRD spectra, it was found that the surface corrosion products with different S 2− concentrations consist of sulfides (FeS, FeS 2 ), oxides (Fe 2 O 3 , Fe 3 O 4 , and Al 2 O 3 ) and NaFeO 2 26 . The elemental composition of the corrosion products is consistent with that of EDS in the corrosion products shown in Fig. 4 . By XRD, EDS and microstructure analysis, it is found that the main octahedral crystal particles are oxide Fe 3 O 4 , while the main corrosion particles in the interlayer are sulfide FeS and FeS 2 . 3.4 Potentiodynamic polarization curve Figure 5 shows the effect of S 2− concentration on the polarization curve of Q235 steel and 16Mn steel after corrosion for 5 days in the sodium aluminate solution containing 3 g/L S 2 O 3 2− . It can be seen that the cathodic characteristics of the polarization curves of Q235 steel and 16Mn steel are basically the same, indicating that sulfide has no effect on the cathodic process of the two steels. The anodic curve shows a different change with the increase of S 2− concentration, and the corrosion of steel is mainly controlled by the anodic process. The anodic polarization curves showed obvious passivation and several anodic limit peaks appeared. The potential value corresponding to the anode peak varies with the concentration of S 2− . According to Nernst equation, the electrode potential reaction is related to the concentration of ions involved in the reaction (such as S 2− ), and the potential value is also different with the concentration of ions. For Q235 steel, when S 2− concentration increases from 1 g/L to 5 g/L, the potential range of activation zone is E corr ~ -1.1V, the potential range of transition zone is -1.1V~ -0.85V, and the potential range of passivation zone is -0.85V~ -0.2V. For 16Mn steel, the potential range of activation zone is E corr ~ -1.1V, the transition zone is -1.1V~ -0.7V, the passivation zone is -0.7V~ -0.2V in anodic polarization curve. It can be seen that although S 2− concentration is different, the pitting potential E p of Q235 steel and 16Mn steel is basically the same, both of which are 0.2V, indicating that the corrosion resistance of the two steels in sodium aluminate solution containing S 2− and S 2 O 3 2− is basically the same, and the change of S 2− concentration (1 g/L ~ 5 g/L) has little effect. As can be seen from Table 3 and Fig. 5 , the corrosion current I corr of Q235 and 16Mn steel increases first and then decreases with the increase of S 2− concentration, and the polarization resistance R p is opposite. When S 2− concentration is 4 g/L, the polarization resistance (R p ) of Q235 steel and 16Mn steel reaches the minimum value and the corrosion rate reaches the maximum value. The of polarization curve of Q235 steel is consistent with the result of the weight loss method and that of 16Mn steel is different from that of weight loss method. Table 3 Polarization results of Q235 and 16Mn steels with different concentration of S 2− Steel S 2− concentration / g·L − 1 E corr / V I corr / uA·cm − 2 β a / mV β c / mV R p / W·cm − 2 Corrosion Rate / mm·a − 1 Q235 1 -1.28 224.52 122.98 89.21 83.46 2.64 2 -1.28 799.49 192.23 120.28 37.03 9.40 3 -1.22 866.94 102.62 137.13 29.26 10.20 4 -1.24 2122.6 114.63 141.85 12.30 24.97 5 -1.28 443.31 143.23 107.22 58.84 5.21 16Mn 1 -1.25 495.4 112.37 97.91 44.55 5.83 2 -1.23 833.19 100.63 123.72 31.39 9.8 3 -1.23 791.28 93.46 120.54 32.97 9.3 4 -1.21 2948 119.55 206.33 10.87 34.67 5 -1.25 1417 216.61 155.43 29.43 16.67 3.5 Electrochemical impedance spectrum Figure 6 is EIS diagram of Q235 steel and 16Mn steel with different S 2− concentration in the sodium aluminate solution containing 3 g/L S 2 O 3 2− for 5 days. According to Nyquist and Bode diagrams, the electrochemical kinetic characteristics of Q235 steel and 16Mn steel are different. When S 2− concentration is ≤ 2 g/L, the electrode process of Q235 steel is mainly controlled by the charge transfer resistance (R ct ), the surface film resistance (R f ) and the diffusion impedance (Z W ). The entire electrode process has two time constants (τ ct and τ f ) and a Warburg diffusion. When S 2− concentration ≧ 3 g/L, the electrode process of Q235 steel is mainly controlled by the charge transfer of electrode reaction and the surface film layer, namely two time constants. When S 2− concentration is ≦ 3 g/L, the electrode process of 16Mn steel is mainly controlled by electrochemical reaction and ion diffusion. When S 2− concentration ≧ 4 g/L, the electrode process of 16Mn steel is mainly controlled by the charge transfer in the high frequency region and the film resistance in the middle frequency region. There are two capacitive reactance responses in Nyquist diagram, and neither inductive reactance arc nor diffusion appears. The Nyquist diagram shows a flattened semicircular shape, indicating that the electrode process of 16Mn steel is mainly controlled by charge transfer. According to the equivalent circuit in Fig. 7 , Zview software was used to fit the electrochemical impedance spectrum data of Q235 steel and 16Mn steel with different S 2− concentrations. Relevant electrochemical parameters are shown in Table 4 . The meanings of each electrochemical parameter in the equivalent circuit are the same as those in literature 8 . As can be seen from Table 4 , R ct of charge transfer resistance of Q235 steel and 16Mn steels at 3 g∙L − 1 S 2− is 612 Ω·cm − 2 and 0.039 Ω·cm − 2 , respectively, which are both small, indicating that the resistance of electrochemical reaction of the two steels is less. When S 2− concentration is 1 g∙L − 1 , the impedance of the passivation film (R f ) on the surface of two steels is 80.34 Ω·cm − 2 and 5.933 Ω·cm − 2 , respectively, which are both large, indicating that a relatively dense corrosion layer has been formed, which has a certain protective effect on the matrix. The results are consistent with the microscopic morphology analysis in section 3.2 . The comparison of R s , R ct and R f of the two steels shows that R s and R f are significantly smaller than R ct , indicating that charge transfer process is the main control step of corrosion at the initial stage of corrosion (5 days), which is consistent with the result of Nquist diagram. When the S 2− concentration is low, the diffusion impedance occurs in the electrode process of the two steels, indicating that S 2− at low concentration has a small driving force, and S 2− ions in the solution have a large resistance through the surface dense layer. Therefore, the ion diffusion at the interface becomes a control step in the corrosion process. Since R ct and R f are difficult to distinguish, R ct +R f is used to represent polarization resistance R p to analyze the corrosion process during the analysis of electrochemical impedance spectrum data by Zview software. Figure 7 shows the change of R p with the concentration of S 2− in the corrosion process. It can be seen from the figure that the Rp of both Q235 steel and 16Mn steel decreases first and then increases slowly with the increase of S 2− concentration. The R p of Q235 steel reaches the minimum value when S 2− concentration is 4 g/L, while that of 16Mn steel reaches the minimum value when S 2− concentration is 3 g/L, which is consistent with the results of weight loss method and polarization curve. Table 4 Impedance parameters obtained on Q235 and 16Mn steels with different concentrations of S 2- 3.6 Adsorption structures of related particles We calculated the adsorption energies of S 2− and OH − on the Fe(110) surface using first-principles calculations. We positioned S 2− and OH − separately on the top sites (TFe) of the Fe(110) surface. The formula for calculating the adsorption energy (E ads ) between the Fe(110) surface and the adsorbates is as follows: E ads = E iron−ion − E iron − E ion ( 1 ) Where E iron−ion represents the total energy of the system, E iron represents the energy of iron, and E ion is the energy of the free ion.In theory, the more negative the value of E ads , the more stable the adsorption between the adsorbate and the surface. The adsorption energies of the two ions on the Fe(110) surface are shown in Fig. 8 . Based on the calculations, the adsorption energy of S 2− on the Fe(110) surface is -28.04 eV, while the adsorption energy of OH − on the Fe(110) surface is -9.21 eV. It can be observed that S 2− has a higher affinity for adsorption on the Fe(110) surface compared to OH − . This suggests that in this system, S 2− is likely to adsorb on the steel surface, resulting in the corrosion product mainly being FeS. Subsequently, OH − can further adsorb, leading to the transformation of the corrosion product into iron oxide. This theoretical basis can provide insights into the sequence of corrosion product formation on the steel surface. 3.7 Corrosion Mechanism By analyzing the linear polarization curve and electrochemical impedance spectrum characteristics, the electrochemical corrosion behavior of Q235 and 16Mn steel in the solution containing S 2- and S 2 O 3 2- sodium aluminate was discussed. Combined with relevant literature reports 26–30 . the electrochemical corrosion mechanism of sulfur on Q235 and 16Mn steel was analyzed as follows: ( 1 )Effect of S 2- and S 2 O 3 2- on corrosion behavior of steels When the concentration of S 2- and S 2 O 3 2- in sodium aluminate solution is low (< 3 g∙L -1 ), the electron loss reaction of S 2- and S 2 O 3 2- inhibits the corrosion of steel to some extent. Since equations ( 1 ), ( 2 ) and ( 3 ) play the role of supplying electrons in the electrochemical system, they hinder the anodic dissolution of steel to a certain extent, resulting in the decrease of the corrosion rate. $${{S}_{2}O}_{3}^{2-}+6{OH}^{-}\to {2SO}_{3}^{2-}+{3H}_{2}O+4{e}^{-} {{\epsilon }}^{\theta }=0.58V$$ 1 $${S}^{2-}+6{OH}^{-}\to {SO}_{3}^{2-}+{3H}_{2}O+6{e}^{-} {{\epsilon }}^{\theta }=0.61V$$ 2 $${S}^{2-}\to {S}_{2}^{2-}+2{e}^{-} {{\epsilon }}^{\theta }=0.51V$$ 3 When S 2 O 3 2- concentration is higher (≥ 3 g∙L -1 ), it plays an electron consuming role in the electrochemical system through Eq. ( 4 ). Therefore, the anodic dissolution of steel is promoted to some extent. $${{S}_{2}O}_{3}^{2-}+{3H}_{2}O+8{e}^{-}\to 2{\text{S}}^{2-}+6{OH}^{-}$$ 4 However, when the concentration of S 2- and S 2 O 3 2- is higher (≥ 3 g∙L -1 ), the anodic dissolution of steel is hindered by the release of electrons through the synergistic reaction ( 5 ). $$2{S}^{2-}+{S}_{2}{O}_{3}^{2-}+6{OH}^{-}\to {S}_{2}^{2-}+2{SO}_{3}^{2-}+3{H}_{2}O+6{e}^{-}$$ 5 ( 2 )Effect of AlO 2 - in sodium aluminate solution on corrosion behavior of steel When AlO 2 - is adsorbed to the electrode surface, the following reactions (Eq. 6 – 8 ) will occur. $$Fe+Al{O}_{2}^{-}\to {FeAl{O}_{2}^{-}}_{\text{a}\text{d}\text{s}}$$ 6 $${F\text{e}}_{3}{O}_{4}+2{H}_{2}O+2{e}^{-}\to 3HF\text{e}{O}_{2}^{-}+{H}^{+}$$ 7 $${\chi FeAl{O}_{2}^{-}}_{\text{a}\text{d}\text{s}}+\left(3-{\chi }\right)HF\text{e}{O}_{2}^{-}+\left(1+\chi \right){H}^{+}\to {Fe}_{3-\chi }{Al}_{\chi }{\text{O}}_{4}+2{H}_{2}O+\chi Fe+2{e}^{-}$$ 8 Combined with the E-pH diagram of Fe-Al-Mn-S-H 2 O system at 95℃ shown in Fig. 1 , when χ = 2, the chemical formula \({Fe}_{3-\chi }{Al}_{\chi }{\text{O}}_{4}\) can be written as FeAl 2 O 4 , and the generation of FeAl 2 O 4 will inhibit the current density in the passivation process. However, as the diffusion rate of AlO 2 - to the surface of steel is slower than OH - , \({FeAl{O}_{2}^{-}}_{\text{a}\text{d}\text{s}}\) is difficult to be formed. Therefore, AlO 2 - has a certain inhibiting effect on the corrosion of steel, but the inhibiting effect is relatively small. ( 3 )Anodic dissolution of steel and formation mechanism of corrosion product layer When the solution contains OH - and S 2- , it has been reported in literature 4,31 that that the steel surface will have competitive adsorption for the two ions. If S 2- is adsorped on the surface of steel, the corrosion products are mainly FeS 32 , and the adsorption, activation and dissolution reactions are shown in Eq. ( 9 ). When the S 2- concentration in the solution reaches a certain level, the ratio of S 2- to OH - becomes smaller, and the steel surface is controlled by OH - adsorption. The corrosion products are mainly oxidation film, and the adsorption and activation dissolution reactions are shown in Eq. ( 10 ). $$Fe+{\text{S}}^{2-}=\text{F}\text{e}\text{S}+2{e}^{-}$$ 9 $$\text{F}\text{e}+{OH}^{-}=Fe{\left(\text{O}\text{H}\right)}_{2}+2{e}^{-}$$ 10 There are three anode limit peaks on the polarization curve of the steel electrode, which mainly occur the anodic dissolution of steel and the transformation between iron sulfide and iron oxide. The main steps are as follows: The corresponding potential of peak (Ⅰ) is roughly − 1.1V (vs SCE), and iron dissolves into HFeO 2 - . The dissolution reaction is shown in Eq. ( 11 ). $$HFe{\text{O}}_{2}^{-}+{\text{H}}_{2}\text{O}+2{e}^{-}=\text{F}\text{e}\left(s\right)+3{\text{O}\text{H}}^{-}$$ $${\epsilon }_{HFe{\text{O}}_{2}^{-}/Fe}=0.2844-0.1006\text{p}\text{H}+0.0335\text{l}\text{g}\left[HFe{\text{O}}_{2}^{-}\right]$$ 11 According to the E-pH diagram of S-H 2 O system and Fe-S-H 2 O system, the ions stably existing in the self-corrosive potential range are S 2- and HFeO 2 - . With the progress of anodic dissolution reaction, the concentration of HFeO 2 - in the solution keeps increasing and will react with S 2- in the solution in Eq. ( 12 ). $$HFe{\text{O}}_{2}^{-}+{S}^{2-}+3{\text{H}}_{2}O=\text{F}\text{e}\text{S}\downarrow +3{\text{O}\text{H}}^{-}$$ 12 FeS is a dark brown substance with loose structure, which cannot protect the surface of steel. However, due to the generation of FeS, the passivation of steel will be delayed, and the oxidation reaction on the surface of steel will continue to generate yellow pyrite FeS 2 with good density. The corresponding potential of peak (Ⅱ) is approximately − 1.0V (vs SCE), and HFeO 2 - will undergo further oxidation to form FeOOH (Eq. 13 ) and Fe 2 O 3 (Eq. 14 ). $$HFe{\text{O}}_{2}^{-}\to \text{F}\text{e}\text{O}\text{O}\text{H}+{\text{e}}^{-}$$ 13 $$\text{o}\text{r} 2HFe{\text{O}}_{2}^{-}\to {\text{F}\text{e}}_{2}{\text{O}}_{3}+{\text{H}}_{2}\text{O}+2{\text{e}}^{-}$$ 14 The corresponding potential of peak (ⅲ) is roughly − 0.8V (vs SCE), and FeS continues to react to generate FeS2 with good stability, as shown in Eq. 15 . $$\text{F}\text{e}{\text{S}}_{2}\downarrow +2{e}^{-}\to \text{F}\text{e}\text{S}+{\text{S}}^{2-} {\epsilon }_{Fe{\text{S}}_{2}/\text{F}\text{e}\text{S}}=0.792-0.0335lg\left[{S}^{2-}\right]$$ 15 XRD analysis shows that the main corrosion products are FeOOH, Fe 2 O 3 and Fe 3 O 4 . Therefore, as the potential increases, the FeS generated by the Eq. ( 16 ) continue to react in the solution to form a layer of structurally-stable brown-yellow FeOOH, and the surface corrosion products are eventually transformed into stable FeOOH, Fe 2 O 3 and Fe 3 O 4 to passivate them. $$2Fe\text{O}\text{O}\text{H}+{S}_{2}{O}_{3}^{2-}+12{H}^{+}+10{e}^{-}\to 2\text{F}\text{e}\text{S}+7{\text{H}}_{2}O$$ $${\epsilon }_{Fe\text{O}\text{O}\text{H}/\text{F}\text{e}\text{S}}=0.408-0.0805pH+0.0067lg\left[{S}_{2}{O}_{3}^{2-}\right]$$ 16 $$3\text{F}\text{e}\text{O}\text{O}\text{H}+{\text{H}}^{+}+{\text{e}}^{-}\to {\text{F}\text{e}}_{3}{\text{O}}_{4}+2{H}_{2}O {\epsilon }_{Fe\text{O}\text{O}\text{H}/{\text{F}\text{e}}_{3}{\text{O}}_{4}}={\phi }^{\theta }-0.067pH$$ 17 $$3{Fe}_{2}{O}_{3}+{H}_{2}O+2{e}^{-}=2{Fe}_{3}{O}_{4}+{2OH}^{-}{ \epsilon }_{{Fe}_{2}{O}_{3}/{Fe}_{3}{O}_{4}}=0.32-0.067pH$$ 18 In the above formula, the concentration of [HFeO 2 - ] is estimated according to the electric quantity Q flowing through the electrode, and the concentration of HFeO 2 - can be calculated by Eq. 11 . The concentration of S 2- and S 2 O 3 2- is calculated according to the concentration assigned. If the concentration of S 2- and S 2 O 3 2- is 5 g/L and 3 g/L, respectively. The pH of sodium aluminate solution was measured directly by the laboratory to be 14. So, it's estimated that \({\epsilon }_{HFe{\text{O}}_{2}^{-}/Fe}\) =−1.124 V, \({\epsilon }_{Fe{\text{S}}_{2}/\text{F}\text{e}\text{S}}=0.853 V\) , \({\epsilon }_{{Fe}_{2}{O}_{3}/{Fe}_{3}{O}_{4}}=-0.618 \text{V}\) , \({\epsilon }_{Fe\text{O}\text{O}\text{H}/\text{F}\text{e}\text{S}}\) =−0.714 V. C [HFeO 2 − ] = Q/(nFV) ( 17 ) According to electrochemical measurements, morphology analysis and EDS analysis, the schematic diagram of the corrosion mechanism of Q235 steel and 16Mn steel in sulfur-containing sodium aluminate solution is shown in Fig. 9 . Figure 9 a shows that the steel is immersed in the corrosive medium. Figure 9 b shows that the corrosive ions S 2− and HS − in the solution are preferentially adsorbed on the surface of the steel, forming a layer of corrosion products on the surface to hinder the diffusion of corrosive ions to the substrate. Figure 9 c shows that the corrosion products on the steel surface continue to undergo transformation reactions, forming a layer of oxide attached to the steel surface. Figure 9 d shows that the octahedral crystal particles on the steel surface have accumulated and aggregated to form a layer of cubic crystal particles. 4 Conclusions This study investigates the effect of two types of sulfur on the synergistic corrosion behavior of Q235 and 16Mn steels, The following conclusions were drawn: ( 1 ) The corrosion products on the steel surface are converted from sulfides to oxides, and the crystal form of oxides also changes from octahedral crystal to cubic crystal with the progress of corrosion.The corrosion products at different concentrations of S 2− consist of sulfides (FeS, FeS 2 ), oxides (Fe 2 O 3 , Fe 3 O 4 , and Al 2 O 3 ) and NaFeO 2 . ( 2 ) The anode area on the polarization curve represents four different stages of corrosion and there is a significant activation-passivation phenomenon. It shows that the higher S 2− concentration has a higher corrosion rate of steel. ( 3 )Through the first calculation, the results show that S 2− has a higher affinity for adsorption on the Fe(110) surface compared to OH − , and in this system S 2− is adsorbed on the steel surface, and the corrosion products are mainly FeS, and then the corrosion products of OH − are further converted into iron oxides. ( 4 ) EIS results show that when S 2− concentration is low ( ≦ 2g/L), the corrosion process of steel is controlled by the charge transfer and surface film. However, when S 2− concentration is higher (> 2g/L), the corrosion of steel is controlled by the charge transfer, the surface film layer and ion diffusion. Declarations Institutional review board statement Not applicable. Conflict of interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contribution DL and BQ conceived the experiment, DL,JX,and HW collected the data, DL, JX, HW,analyzed the data, DL wrote the initial draft, DL,JX and HW prepared figures,BQ,CC and JL obtained the research fund, DL,BQ,CC,JL,JX,and HW reviewed and approved the following draft. All the authors approved the publication of this work. Acknowledgments This work was supported by National Natured Science Foundation of China (grant no. U1812402, 52074096 and 51774102), Guizhou Province Outstanding Young Scientific and Technological Talent Training Plan ([2017]5626), Guizhou University Talent Introduction Project ([2019]43) and Guizhou University Cultivation Project ([2020]43). Data Availability Data supporting the fndings of this manuscript are available from the corresponding author upon request. References Liu, Z. et al. Digestion behavior and removal of sulfur in high-sulfur bauxite during bayer process. Minerals Engineering 149 , 106237 (2020). Zhou, X. et al. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4119985","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":287883448,"identity":"7e259f6e-7a2d-47c5-9664-2673803f803e","order_by":0,"name":"Dongyu Li","email":"","orcid":"","institution":"Guizhou University","correspondingAuthor":false,"prefix":"","firstName":"Dongyu","middleName":"","lastName":"Li","suffix":""},{"id":287883449,"identity":"97bfcfeb-502f-4d74-a10f-42086aca24ed","order_by":1,"name":"Bianli 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04:56:52","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4119985/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4119985/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-72639-x","type":"published","date":"2024-09-27T15:57:17+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54267849,"identity":"b8fd4780-04a0-42a5-8b33-dd43bd8d791c","added_by":"auto","created_at":"2024-04-08 05:46:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":22447,"visible":true,"origin":"","legend":"\u003cp\u003eE-pH graph of Fe-Al-S-H\u003csub\u003e2\u003c/sub\u003eO (a) and Fe-Mn-Al-S-H\u003csub\u003e2\u003c/sub\u003eO (b）\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/142c8c3464675ff2cfaed1e7.png"},{"id":54267848,"identity":"6cfc0776-0b79-437d-baad-454f87c880ea","added_by":"auto","created_at":"2024-04-08 05:46:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":23587,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of S\u003csup\u003e2-\u003c/sup\u003e concentration on synergistic corrosion rate of Q235 steel and 16Mn steel\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/c824fd46ac44bbcf60eca93f.png"},{"id":54267853,"identity":"79c35a98-0e9a-4020-a6f8-6f0f56292602","added_by":"auto","created_at":"2024-04-08 05:46:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1002135,"visible":true,"origin":"","legend":"\u003cp\u003eSEM morphologies and EDS analysis of steels surface corrosion with different of S\u003csup\u003e2-\u003c/sup\u003e concentration\u003c/p\u003e\n\u003cp\u003e(a: 1g/L S\u003csup\u003e2-\u003c/sup\u003e), (c: 2g/L S\u003csup\u003e2-\u003c/sup\u003e), (e: 3g/L S\u003csup\u003e2-\u003c/sup\u003e), (g: 4g/L S\u003csup\u003e2-\u003c/sup\u003e), (i: 5g/L S\u003csup\u003e2-\u003c/sup\u003e) morphologies of Q235 steel\u003c/p\u003e\n\u003cp\u003e(b: 1g/L S\u003csup\u003e2-\u003c/sup\u003e), (d: 2g/L S\u003csup\u003e2-\u003c/sup\u003e), (f: 3g/L S\u003csup\u003e2-\u003c/sup\u003e), (h: 4g/L S\u003csup\u003e2-\u003c/sup\u003e), (g: 5g/L S\u003csup\u003e2-\u003c/sup\u003e) morphologies of 16Mn steel\u003c/p\u003e\n\u003cp\u003e(k) Element distribution of Q235 steel in 5g/L S\u003csup\u003e2-\u003c/sup\u003e solution\u003c/p\u003e\n\u003cp\u003eCross mark (l) and square mark (m) of element analysis of Q235 steel\u003c/p\u003e\n\u003cp\u003eCross mark (n) and square mark (o) of element analysis of 16Mn steel\u003c/p\u003e\n\u003cp\u003eComposition comparison of three morphologies of Q235steel (p) and 16Mn steel (q) in 3g/L S\u003csup\u003e2- \u003c/sup\u003esolution\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/2f743e812bbc78bfaccd3d0e.png"},{"id":54267854,"identity":"6293072c-c2ea-4dfd-a36f-4728027b833b","added_by":"auto","created_at":"2024-04-08 05:46:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":32538,"visible":true,"origin":"","legend":"\u003cp\u003eXRD analysis of Q235 steel (a) and 16Mn steel (b) corrosion with different of S\u003csup\u003e2-\u003c/sup\u003e concentration\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/e2521a52a3fa8e53da0336c8.png"},{"id":54267852,"identity":"770a7446-4999-4ab9-90ff-3be7026ac24d","added_by":"auto","created_at":"2024-04-08 05:46:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":75780,"visible":true,"origin":"","legend":"\u003cp\u003ePolarization curves of Q235 steel(a) and 16Mn steel(b) with different concentration of S\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/6c234e7cee620350b7433b78.png"},{"id":54267850,"identity":"97975c0c-acef-46b2-b261-19b7efe44c45","added_by":"auto","created_at":"2024-04-08 05:46:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":57217,"visible":true,"origin":"","legend":"\u003cp\u003eEIS of Q235 and 16Mn steels with different concentration of S\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003ea – Nyquist plot, b- Nyquist amplificatory plot, c –Bode plot (log|Z| vs. frequency), d –Bode plot (phase angle vs. frequency)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/c4ada0821a76f62c2e9d1e04.png"},{"id":54268683,"identity":"884da177-83a8-40ba-9599-23edcf5c465e","added_by":"auto","created_at":"2024-04-08 06:02:50","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":39568,"visible":true,"origin":"","legend":"\u003cp\u003eEquivalent circuit for EIS of Q235 and 16Mn steels with different concentration of S\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e(a) Q235 steel (3, 4, 5 g/L S\u003csup\u003e2-\u003c/sup\u003e) and 16Mn steel (4, 5 g/L S\u003csup\u003e2-\u003c/sup\u003e)\u003c/p\u003e\n\u003cp\u003e(b) Q235 steel (1, 2 g/L S\u003csup\u003e2-\u003c/sup\u003e) and 16Mn steel (1, 2, 3 g/L S\u003csup\u003e2-\u003c/sup\u003e)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/b9a44e64f623a4a792c1f7a6.png"},{"id":54267856,"identity":"39372d2c-7269-41ec-9acb-93505c912c0a","added_by":"auto","created_at":"2024-04-08 05:46:50","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":140770,"visible":true,"origin":"","legend":"\u003cp\u003eDisplays the stable adsorption geometries of OH\u003csup\u003e-\u003c/sup\u003e(a)and S\u003csup\u003e2-\u003c/sup\u003e(b)on the Fe(110) surface, respectively. In the diagram, purple spheres represent iron atoms, yellow represents S atoms, red represents O atoms, and white represents H atoms. The unit for Eads is eV.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/c9c46e1c0c7662a0e1bfd77b.png"},{"id":54268242,"identity":"eb6d803b-5977-46fe-bc29-774aaef1008b","added_by":"auto","created_at":"2024-04-08 05:54:50","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":343232,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of corrosion mechanism of 16Mn steel\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/65a1c354a5c0019d39ab7c49.png"},{"id":65628317,"identity":"1d397e40-6a1f-4b4f-83da-35d934c82fd6","added_by":"auto","created_at":"2024-09-30 16:18:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2815705,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4119985/v1/7b706a27-21fc-4a4d-b400-178b29876cad.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Sulfur on synergistic corrosion behavior of Q235 and 16Mn steel in sodium aluminate solution","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eHigh-sulfur and high-grade bauxite is suitable for Bayer process. The sulfur element in the ore mainly enters the solution as S\u003csup\u003e2\u0026minus;\u003c/sup\u003e form under high-pressure and high-alkali dissolution conditions, which accounts for more than 90% of the total sulfur content, and include a small amount of S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, SO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;1\u003c/sup\u003e. However, the presence of the higher sulfur content of sodium aluminate solution is more likely to destroy the dissolution and sintering process of alumina \u003csup\u003e2,3\u003c/sup\u003e, especially, sulfide and thiosulfate aggravate the corrosion of steel equipment\u003csup\u003e4\u003c/sup\u003e. With the rapid development of the alumina industry, in order to effectively develop and utilize high-sulfur bauxite, reduce the harm of sulfur in the alumina industrial production, and control the sulfur in the ore into the solution, many scientific researchers at home and abroad have carried out a large number of experimental studies on the occurrence of sulfur and the dissolution behavior of sulfur\u003csup\u003e5,6\u003c/sup\u003e. However, with the recycling of mother liquor, sulfur accumulates in sodium aluminate solution and affects alumina production to a certain extent. Aiming at the corrosion problem of equipment materials caused by sulfur in sodium aluminate solution,Researcher has carried out corresponding research work in the early stage \u003csup\u003e7,8\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eQUAN Bianli research found that there is a certain synergistic effect between sulfide and thiosulfate in the simulated sodium aluminate solution\u003csup\u003e9\u003c/sup\u003e. This effect has also been found in the oil and gas industry\u003csup\u003e10,11\u003c/sup\u003e. The synergistic corrosion is a complex process, which is affected by many factors\u003csup\u003e12\u003c/sup\u003e, especially the concentration of corrosives. GOLDMAN M found that small concentrations of sulfide were found to promote anodic dissolution as Fe-II carbonate complexes and to destabilize Fe-III oxides leading to the loss of passivity\u003csup\u003e13\u003c/sup\u003e. Shiqi Wang et al. revealed that the corrosion potential became more negative, and the anodic corrosion rate decreased with increasing chloride concentration due to the competitive adsorption of HS\u003csup\u003e\u0026minus;\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u0026thinsp;14\u003c/sup\u003e. Tangqing Wu et al. revealed that NaHSO\u003csub\u003e3\u003c/sub\u003e concentration affected both cathodic and anodic behaviors, and the compactness and mechanical properties of the corrosion products degraded\u003csup\u003e15\u003c/sup\u003e. Miao Wu and Jinjie Shi showed the chloride-induced corrosion could be inhibited for low-carbon steel with molybdate, which is more pronounced with increasing concentration of molybdate and prolonged immersion time\u003csup\u003e16\u003c/sup\u003e. Therefore, the literature found that the co-existing ions and their concentrations have a greater impact on the corrosion of steel.\u003c/p\u003e \u003cp\u003eQuantum chemical simulations can be used to intuitively understand the geometric and electronic structures of molecules and the adsorption of ions on metal surfaces, which has numerous applications in metal corrosion and protection. Over the past few decades, significant academic efforts have been devoted to studying the adsorption and activation of ions on metal iron surfaces. The adsorption of H\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e in acidic solutions also plays an important role in combating corrosion and maintaining surface stability.Jun Hu\u003csup\u003e17\u003c/sup\u003e reported the effects of H\u003csub\u003e2\u003c/sub\u003eO, H\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, and HO\u003csup\u003e\u0026minus;\u003c/sup\u003e on three different planes, Fe(110), Cr(110), and Cr-doped Fe(110). By verifying the adsorption mechanisms of the four aforementioned adsorbates, it was found that the Cr-doped Fe(110) surface is the most stable among the three adsorption surfaces, indicating that the presence of Cr-doped crystals makes them more susceptible to corrosion. Qiao Sun et al\u003csup\u003e18\u003c/sup\u003e established a crystal atomic stacking model of ferrous sulfide and calculated the adsorption energy of ions on the exposed surface. They found that iron sulfide (FeS) exhibits cation selectivity, inhibiting the diffusion of corrosive ions towards the substrate, resulting in lower corrosion rates and uniform corrosion. On the other hand, magnetic pyrite (Fe\u003csub\u003e7\u003c/sub\u003eS\u003csub\u003e8\u003c/sub\u003e) exhibits anion selectivity, leading to the accumulation of Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e between the corrosion scale and the substrate, resulting in higher corrosion rates and localized corrosion. Mohammad Asif\u003csup\u003e19\u003c/sup\u003e investigated three corrosive components on the iron surface, namely (i) sulfur, (ii) hydrogen gas, and (iii) sulfates, and confirmed that Fe(110) has higher corrosion resistance compared to Fe(100) and Fe(310). Therefore, quantum chemical simulation calculations can better substantiate experimental results and improve the scientific rigor and accuracy of research.\u003c/p\u003e \u003cp\u003eThe author mainly conducted related research on the corrosion behavior of active sulfide on steel.This article mainly studies the corrosion behavior of two types of steel in a simulated solution of sodium aluminate containing sulfur. The corrosion behavior of Q235 steel and 16Mn steel was evaluated using electrochemical measurements and surface characterization techniques. First principles calculations were conducted to calculate the adsorption energies of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and HO\u003csup\u003e\u0026minus;\u003c/sup\u003e on the Fe(110) surface and to discuss the competitive adsorption relationship between ions. Furthermore, the corrosion inhibition mechanisms of sulfides on both types of steel were established. This provides a theoretical reference for the subsequent development and application of high-sulfur bauxite and equipment protection.\u003c/p\u003e"},{"header":"2 Experiment Procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Specimens and Experimental Solutions\u003c/h2\u003e \u003cp\u003eThe chemical compositions of Q235 steel and 16Mn steel in this study were listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The rectangular cubes with the size of 15\u0026times;15\u0026times;1 mm\u003csup\u003e3\u003c/sup\u003e and 20\u0026times;10\u0026times;1 mm\u003csup\u003e3\u003c/sup\u003e were cut from the Q235 steel and 16Mn steel, respectively. The exposed sample surface was gradually ground with SiC sandpaper from 600 grit to 1800 grit and then cleaned in acetone and distilled water.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical Composition of Q235 steel and 16Mn steel (Wt. %)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ235 steel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.207\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.233\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.069\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.019\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eBal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16Mn steel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.178\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.290\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.645\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.041\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.056\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eBal\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe corrosion medium is the sulfur-containing sodium aluminate solutions (pH\u0026gt;14) in the experiments, which simulates the conditions of the alumina production seed decomposition process. The preparation method of the sodium aluminate solution is the same as that of literature\u003csup\u003e8\u003c/sup\u003e. The chemical composition of the sulfur-containing sodium aluminate solutions is 255 g/L NaOH, 110 g/L Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, 1 g/L, 2 g/L, 3 g/L, 4 g/L, 5 g/L S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and 3 g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e. Alumina (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO) reacts with NaOH to form sodium aluminate (NaAlO\u003csub\u003e2\u003c/sub\u003e)\u003csup\u003e20\u003c/sup\u003e. The freshly prepared solution is necessary before each experiment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Weight Loss Experiments\u003c/h2\u003e \u003cp\u003eThe corrosion experiments were carried out at 110℃ for 120 h in the autoclave which are respectively the simulated normal temperature, the temperature of seed crystal decomposition and the temperature of the evaporation process in the alumina production. Five Q235 steel coupons and 16Mn steel coupons were used in each experiment. Three steel coupons were used for the measurement of the weight change, while the other two were used to detect the morphology and the phase composition, respectively. Finally, the corrosion products were removed using 500mL distilled water, 500mL HCl, and 10g hexamethylenetetramine (GB/T 6074\u0026thinsp;\u0026minus;\u0026thinsp;1992). The corrosion rate (R) (mm\u0026middot;year\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e or mm\u0026middot;a\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was calculated using weight loss measurement and the formula to calculate is as follows:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\text{R}=\\frac{W\\times 365\\times 1000}{A\\times T\\times D}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere R is the corrosion rate in mm/a; W is the weight loss in g; A is the exposed surface area in mm\u003csup\u003e2\u003c/sup\u003e; T is the immersion time in day; and D is the steel density in g/m\u003csup\u003e3\u003c/sup\u003e .\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Corrosion Products Analysis\u003c/h2\u003e \u003cp\u003eAll of the corrosion experiments with different S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration were carried out in the autoclave (Weihai Zhengwei Machinery Equipment Co., Ltd.) at 383K\u003csup\u003e8\u003c/sup\u003e. After the experiment is completed, the morphology and elemental composition of the corrosion products on the steel surface are analyzed by the scanning electron microscopy (SEM, ZEISS SUPRA 40, Germany) with 10KV acceleration voltage and the electron type is secondary electron, and energy dispersive spectroscopy (EDS, AZ tec., Oxford, UK). The crystalline structure of the corrosion products was investigated by X-ray diffraction (XRD, X\u0026rsquo;pert Pro MPD Panalytical, Netherlands) with monochromated Cu-Ka radiation at the 2θ range of 10\u0026deg;~80\u0026deg;. The software of HighScore Plus (Panalytical, Almelo, Netherlands) was selected to analyze the data.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Electrochemical Tests\u003c/h2\u003e \u003cp\u003eElectrochemical measurements were carried out on the electrochemical workstation (Boi-Logic SAS, France) with a conventional three-electrode cell. The counter electrode was a platinum electrode (20*10*0.1mm, Beijing, Jingke), the reference electrode was a saturated calomel electrode (SCE, Lei Magnetic, Shanghai), and the working electrode was 16Mn steel with the exposed areas of about 2.00 cm\u003csup\u003e2\u003c/sup\u003e. Because SCE cannot withstand temperatures above 343K. So, the cell was placed in a water bath to maintain the experiment temperature (338K). Before the electrochemical experiment, the working electrodes were soaked in the corrosion solution at 338K with different S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration. Electrochemical impedance spectrum (EIS) was carried out at open circuit potential (OCP) over the frequency from 10\u003csup\u003e5\u003c/sup\u003e Hz to 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e Hz, and the amplitude of the AC signal was 5 mV. All potentials reported in this paper were measured with respect to the SCE. Zview software (3.0a) and the equivalent circuits (EC) are used to process electrochemical impedance spectroscopy data. Potentiodynamic polarization measurements with a potential scan rate of 1mV\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were performed vs. OCP and the potential ranged from \u0026minus;\u0026thinsp;1.50V vs. SCE to 1.50 V vs. SCE. In order to obtain the electrochemical kinetic parameters such as the corrosion potentials (E\u003csub\u003ecorr\u003c/sub\u003e) and corrosion current densities (I\u003csub\u003ecorr\u003c/sub\u003e), Tafel fitting was performed on the polarization curve.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Theoretical calculation methods\u003c/h2\u003e \u003cp\u003eUsing Materials Studio (Inc.), a lattice structure model of the Fe(110) surface was constructed (Fe(110) plane being the most stable surface under actual conditions). Subsequently, the adsorption energies of S\u003csup\u003e2-\u003c/sup\u003e and OH\u003csup\u003e-\u003c/sup\u003e on the Fe(110) surface were calculated using the DMol3 module within Materials Studio. A periodic slab was established in the calculation, with a selected plane composed of the Fe(110) surface to simulate the surface. Four atomic layers, including two fixed bottom layers, were included along the direction perpendicular to the exposed surface. A vacuum region with a thickness of 15 \u0026Aring; was maintained between adjacent crystal layers, periodically arranged along the Z direction to avoid interference. The ions were placed on the surface top sites as the adsorption layer. During the geometry optimization process, the energy and electronic structure of the system were calculated using the Generalized Gradient Approximation (GGA)\u003csup\u003e21\u003c/sup\u003e and the Perdew, Burke, and Ernzerhof (PBE) exchange-correlation functional\u003csup\u003e22\u003c/sup\u003e. The spin was set to be unrestricted, and the formal spin was initialized\u003csup\u003e23\u003c/sup\u003e. The energy convergence criterion was higher than 1.0\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e Ha, and the structure was relaxed using a geometry optimization method until the forces experienced by all atoms were smaller than 0.002 Ha/A, meeting the convergence criteria. Double numerical quality basis sets were used, along with Double Numerical Polarization (DNP) functions. Effective Core Potentials (ECPs) were employed to handle the core electrons of metal atoms. A thermal smearing was adopted at 0.005 hartree. A Monkhorst-Pack grid with a 4\u0026times;4\u0026times;1 k-point sampling was used in the surface Brillouin zone for volume and surface calculations\u003csup\u003e24\u003c/sup\u003e. The k-point separation was set to be 0.05 \u0026Aring;.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 E-pH graph\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e is the E-pH diagram of Fe-Al-S-H\u003csub\u003e2\u003c/sub\u003eO system and Fe-Mn-Al-S-H\u003csub\u003e2\u003c/sub\u003eO system at 95℃ respectively. It shows that the element Fe exists stably in the form of HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in both systems. Element Mn exists stably in the form of MnO\u0026middot;Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. The element Al exists stably in the form of the conjugate FeAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. The existence of substances under thermodynamic conditions does provide a basis for judging the corrosion mechanism.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Corrosion Rate Variation Laws\u003c/h2\u003e \u003cp\u003eThe variation of corrosion rates after 5 days of immersion in sodium thiosulfate solutions containing 3g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e for Q235 and 16Mn steels at different S\u003csup\u003e2-\u003c/sup\u003e concentrations is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a), it can be observed that the corrosion rates of Q235 and 16Mn steels in sodium thiosulfate solutions containing 3 g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e exhibit three different scenarios with varying S\u003csup\u003e2-\u003c/sup\u003e concentrations.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) Scenario 1: Corrosion rates increase with increasing S\u003csup\u003e2-\u003c/sup\u003e concentration. With the increase in S\u003csup\u003e2-\u003c/sup\u003e concentration in the sodium thiosulfate solution, the active ion S\u003csup\u003e2-\u003c/sup\u003e significantly activates the corrosion process of the steels. The corrosion rate of Q235 steel increases with S\u003csup\u003e2-\u003c/sup\u003e concentration up to 4 g/L, while the corrosion rate of 16Mn steel increases up to 3 g/L.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) Scenario 2: Corrosion rates reach maximum values. When the S\u003csup\u003e2-\u003c/sup\u003e concentration in the sodium thiosulfate solution reaches a certain level, the added S\u003csup\u003e2-\u003c/sup\u003e continues to react with the unreacted matrix until a uniform layer of corrosion product covers the steel surface. At this point, the corrosion rate of the steel reaches its maximum. For Q235 steel, the corrosion rate is maximized at an S\u003csup\u003e2-\u003c/sup\u003e concentration of 4 g/L, while for 16Mn steel, the maximum corrosion rate is achieved at an S\u003csup\u003e2-\u003c/sup\u003e concentration of 3 g/L.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) Scenario 3: Corrosion rates decrease after reaching maximum values. As the S\u003csup\u003e2-\u003c/sup\u003e concentration in the sodium thiosulfate solution increases, the corrosive S\u003csup\u003e2-\u003c/sup\u003e ions react with the steel matrix and also undergo electron transfer reactions with S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e in the solution, hindering further corrosion. Simultaneously, the corrosion products on the steel surface undergo transformation, forming a stable and dense corrosion layer that impedes the diffusion of ions towards the metal substrate. The combined effects result in a decrease in the corrosion rate of the steel.\u003c/p\u003e \u003cp\u003eIn order to obtain the corrosion kinetics equations and determine the corrosion kinetics parameters (reaction rate constant k and reaction order n) for Q235 and 16Mn steels at lower S\u003csup\u003e2-\u003c/sup\u003e concentrations, a linear fitting of the corrosion rate vs. S\u003csup\u003e2-\u003c/sup\u003e concentration data in Figure (a) was performed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). The obtained kinetic parameters are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. It can be observed from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) that the linear fitting shows a relatively good fit, with R2 values all above 0.95. The corrosion rate constants (k) for Q235 and 16Mn steels in sodium thiosulfate solutions containing both S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e are relatively small, while the reaction orders (n) are both greater than 1. By comparing the reaction rate constants (k) and reaction orders (n), it is observed that when the S\u003csup\u003e2-\u003c/sup\u003e concentration reaches a certain value, the corrosion rate curves of both steels intersect. This explains the inconsistent corrosion rate behavior of the two steels with changing concentration, as discussed in section 3.4.1.\u003c/p\u003e \u003cp\u003eIn summary, the change in corrosion rates of Q235 and 16Mn steels in sodium thiosulfate solutions containing both S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e can be characterized as follows:\u003c/p\u003e \u003cp\u003eFirstly, when the solution contains a relatively low concentration of S\u003csup\u003e2-\u003c/sup\u003e, the S\u003csup\u003e2-\u003c/sup\u003e ions adsorb on the steel surface and react with it, forming iron sulfides, which accelerate the corrosion process. Therefore, S\u003csup\u003e2-\u003c/sup\u003e mainly plays a role in activating the corrosion, promoting its progression. However, as the S\u003csup\u003e2-\u003c/sup\u003e concentration in the solution increases, the excess S\u003csup\u003e2-\u003c/sup\u003e ions react with S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e through electron transfer reactions, consuming the electrons released at the anode and promoting continuous anodic dissolution, thereby accelerating the corrosion process until the corrosion rate reaches its maximum.\u003c/p\u003e \u003cp\u003eSecondly, as the concentration of S\u003csup\u003e2-\u003c/sup\u003e ions continues to increase, the corrosion products on the steel surface transform into dense and stable iron oxides, which impede further corrosion. As a result, the corrosion rate of the steel decreases.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCorrosion kinetic fitting parameters of Q235 and 16Mn steels\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKinetic equation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReaction rate constant k\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eeaction order n\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ235\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003elnR=-3.856\u0026thinsp;+\u0026thinsp;1.78lnC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.9653\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16Mn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003elnR=-3.182\u0026thinsp;+\u0026thinsp;1.48lnC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.9459\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Characteristics of Corrosion Products\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Morphology and Element Composition Analysis\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the microscopic morphology and element distribution of corrosion products on the surface of Q235 steel and 16Mn steel when immersed in the sodium aluminate solution containing 3 g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e with different S\u003csup\u003e2-\u003c/sup\u003e concentration for 5 days. It can be seen from the topography of 20000 times high magnification that when the concentration of S\u003csup\u003e2-\u003c/sup\u003e is 1 g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), the surface of Q235 and 16Mn steel generates a layer of dense, regular octahedral grains with good crystal shape and uniform particle size, which has a great hindrment effect on corrosion. When the concentration of S\u003csup\u003e2-\u003c/sup\u003e is 2 g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ed), the surface crystal particles gradually grow up and accumulate to form cuboid corrosion products. When the concentration of S\u003csup\u003e2-\u003c/sup\u003e is 3 g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ef), the surface corrosion products have obvious changes, and octahedral crystal particles are formed at the same time, another flocculent corrosion products are formed. As the concentration of S\u003csup\u003e2-\u003c/sup\u003e continues to increase to 4\u0026ndash;5 g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eg-\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ej), the surface octahedral crystal particles continue to accumulate and grow, and eventually form a layer of dense and uneven cube particles, which further hinder ion migration and slow down the corrosion process. By comparing SEM morphologies of the two steels, it is found that the corrosion products on the surface of 16Mn steel are denser and smoother than that of Q235 steel when the concentration of S\u003csup\u003e2-\u003c/sup\u003e reaches 4\u0026ndash;5 g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eg-\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ej). It is consistent with the result that the corrosion rate of 16Mn steel is lower than that of Q235 steel.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt is also found that the corrosion products on the surface of Q235 and 16Mn steel are mainly composed of two forms, one is the octahedral crystal particles and cube particles formed by the octahedral stacking (Cross marking), the other is the interlayer flocculent corrosion products between the matrix and crystal particles (Square marking). Combined with EDS analysis of surface corrosion in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e, it can be seen that both the octahedral crystal and cube particle corrosion are composed of Fe, O and Al, while the interlayer flocculent corrosion products is mainly composed of Fe, O, Al, S and Na. Combined with EDS element distribution diagram of Q235 steel in containing 5 g/L S\u003csup\u003e2-\u003c/sup\u003e and 3 g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e sodium aluminate solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eK), it can be seen that non-metallic element carbon (C) and metallic element chromium (Cr) are enriched in surface corrosion products, indicating that the carbon causes the formation of internal chemical battery in the corrosion process, at the same time, the loss of chromium in steel increases the tendency of pitting. Therefore, the more active elements participate in the corrosion reaction to form a dense layer of corrosion products, which can inhibit the contact between anions and steel matrix and slow down the corrosion process.\u003c/p\u003e \u003cp\u003eIn order to further analyze the characteristics and composition of corrosion products on the surface of Q235 and 16Mn steel, the elemental composition of corrosion products on the surface of steel containing 3 g/L S\u003csup\u003e2-\u003c/sup\u003e and 3 g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e sodium aluminate solution was analyzed, and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e(k-q). The results show that the elemental composition of the corrosion products on the two steels surface is consistent, indicating that the alloying elements have no effect on the elemental composition of the corrosion products on the surface. By comparison, it is found that the composition of flocculent corrosion products formed on the surface (circle) is the same as that formed on the interlayer of the matrix (box), both of which contain sulfur element, indicating that S\u003csup\u003e2-\u003c/sup\u003e is adsorbed to the steel matrix and reacts with it to form iron sulfide. I. Betova\u003csup\u003e25\u003c/sup\u003e,Xie Qiaoling\u003csup\u003e4\u003c/sup\u003e et al. believed that HS\u003csup\u003e-\u003c/sup\u003e in Bayer solution was more easily adsorbed to the steel surface to generate iron sulfide intermediate than OH\u003csup\u003e-\u003c/sup\u003e. Therefore, the steel surface preferentially adsorbs HS\u003csup\u003e-\u003c/sup\u003e in sodium aluminate solution to produce iron sulfide, which is embedded in the surface oxide and reduces the corrosion resistance of the corrosion layer. The octahedral crystal particles (cross) contain little sulfur because, as corrosion progresses, the sulfide formed on the steel surface continues to react with anions (OH\u003csup\u003e-\u003c/sup\u003e, S\u003csup\u003e2-\u003c/sup\u003e, or S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e) in solution to form structurally stable iron oxides that inhibit corrosion.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 XRD Analysis\u003c/h2\u003e \u003cp\u003eIn order to characterize the effect of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration on the composition of corrosion products on Q235 steel and 16Mn steel surface, XRD detection of the corrosion products with different S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration was performed, and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e that when S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is different, the peak position in XRD pattern is the same, but the peak intensity has a certain change and the crystallinity of the corrosion particles is different. It shows that S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration only affects the crystallinity of the crystalline particles. Therefore, the composition of corrosion products on the steel surface with different S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentrations may be the same. Using X-pert High Score analysis software to analyze XRD spectra, it was found that the surface corrosion products with different S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentrations consist of sulfides (FeS, FeS\u003csub\u003e2\u003c/sub\u003e), oxides (Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) and NaFeO\u003csub\u003e2\u003c/sub\u003e \u003csup\u003e26\u003c/sup\u003e. The elemental composition of the corrosion products is consistent with that of EDS in the corrosion products shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e. By XRD, EDS and microstructure analysis, it is found that the main octahedral crystal particles are oxide Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, while the main corrosion particles in the interlayer are sulfide FeS and FeS\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Potentiodynamic polarization curve\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the effect of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration on the polarization curve of Q235 steel and 16Mn steel after corrosion for 5 days in the sodium aluminate solution containing 3 g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e. It can be seen that the cathodic characteristics of the polarization curves of Q235 steel and 16Mn steel are basically the same, indicating that sulfide has no effect on the cathodic process of the two steels. The anodic curve shows a different change with the increase of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration, and the corrosion of steel is mainly controlled by the anodic process. The anodic polarization curves showed obvious passivation and several anodic limit peaks appeared. The potential value corresponding to the anode peak varies with the concentration of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e. According to Nernst equation, the electrode potential reaction is related to the concentration of ions involved in the reaction (such as S\u003csup\u003e2\u0026minus;\u003c/sup\u003e), and the potential value is also different with the concentration of ions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor Q235 steel, when S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration increases from 1 g/L to 5 g/L, the potential range of activation zone is E\u003csub\u003ecorr\u003c/sub\u003e~ -1.1V, the potential range of transition zone is -1.1V~ -0.85V, and the potential range of passivation zone is -0.85V~ -0.2V. For 16Mn steel, the potential range of activation zone is E\u003csub\u003ecorr\u003c/sub\u003e~ -1.1V, the transition zone is -1.1V~ -0.7V, the passivation zone is -0.7V~ -0.2V in anodic polarization curve. It can be seen that although S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is different, the pitting potential E\u003csub\u003ep\u003c/sub\u003e of Q235 steel and 16Mn steel is basically the same, both of which are 0.2V, indicating that the corrosion resistance of the two steels in sodium aluminate solution containing S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e is basically the same, and the change of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration (1 g/L\u0026thinsp;~\u0026thinsp;5 g/L) has little effect.\u003c/p\u003e \u003cp\u003eAs can be seen from Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the corrosion current I\u003csub\u003ecorr\u003c/sub\u003e of Q235 and 16Mn steel increases first and then decreases with the increase of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration, and the polarization resistance R\u003csub\u003ep\u003c/sub\u003e is opposite. When S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is 4 g/L, the polarization resistance (R\u003csub\u003ep\u003c/sub\u003e) of Q235 steel and 16Mn steel reaches the minimum value and the corrosion rate reaches the maximum value. The of polarization curve of Q235 steel is consistent with the result of the weight loss method and that of 16Mn steel is different from that of weight loss method.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePolarization results of Q235 and 16Mn steels with different concentration of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSteel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eS\u003csup\u003e2\u0026minus;\u003c/sup\u003econcentration\u003c/p\u003e \u003cp\u003e/ g\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eE\u003csub\u003ecorr\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ V\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eI\u003csub\u003ecorr\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ uA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eβ\u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ mV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eβ\u003csub\u003ec\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ mV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eR\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ W\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCorrosion Rate\u003c/p\u003e \u003cp\u003e/ mm\u0026middot;a\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003eQ235\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e224.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e122.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e89.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e83.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e799.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e192.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e37.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e9.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e866.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e102.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e137.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e29.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e10.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2122.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e114.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e141.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e24.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e443.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e143.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e107.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e58.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e5.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e16Mn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e495.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e112.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e97.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e44.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e5.83\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e833.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e100.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e123.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e31.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e9.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e791.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e93.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e120.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e32.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e9.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2948\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e119.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e206.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e34.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1417\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e216.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e155.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e29.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e16.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Electrochemical impedance spectrum\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e6\u003c/span\u003e is EIS diagram of Q235 steel and 16Mn steel with different S\u003csup\u003e2\u0026minus;\u003c/sup\u003econcentration in the sodium aluminate solution containing 3 g/L S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e for 5 days. According to Nyquist and Bode diagrams, the electrochemical kinetic characteristics of Q235 steel and 16Mn steel are different. When S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is \u0026le;\u0026thinsp;2 g/L, the electrode process of Q235 steel is mainly controlled by the charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e), the surface film resistance (R\u003csub\u003ef\u003c/sub\u003e) and the diffusion impedance (Z\u003csub\u003eW\u003c/sub\u003e). The entire electrode process has two time constants (τ\u003csub\u003ect\u003c/sub\u003e and τ\u003csub\u003ef\u003c/sub\u003e) and a Warburg diffusion. When S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration\u0026thinsp;≧\u0026thinsp;3 g/L, the electrode process of Q235 steel is mainly controlled by the charge transfer of electrode reaction and the surface film layer, namely two time constants. When S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is ≦\u0026thinsp;3 g/L, the electrode process of 16Mn steel is mainly controlled by electrochemical reaction and ion diffusion. When S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration\u0026thinsp;≧\u0026thinsp;4 g/L, the electrode process of 16Mn steel is mainly controlled by the charge transfer in the high frequency region and the film resistance in the middle frequency region. There are two capacitive reactance responses in Nyquist diagram, and neither inductive reactance arc nor diffusion appears. The Nyquist diagram shows a flattened semicircular shape, indicating that the electrode process of 16Mn steel is mainly controlled by charge transfer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAccording to the equivalent circuit in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003e, Zview software was used to fit the electrochemical impedance spectrum data of Q235 steel and 16Mn steel with different S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentrations. Relevant electrochemical parameters are shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The meanings of each electrochemical parameter in the equivalent circuit are the same as those in literature\u003csup\u003e8\u003c/sup\u003e. As can be seen from Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, R\u003csub\u003ect\u003c/sub\u003e of charge transfer resistance of Q235 steel and 16Mn steels at 3 g∙L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e S\u003csup\u003e2\u0026minus;\u003c/sup\u003e is 612 Ω\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 0.039 Ω\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively, which are both small, indicating that the resistance of electrochemical reaction of the two steels is less. When S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is 1 g∙L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the impedance of the passivation film (R\u003csub\u003ef\u003c/sub\u003e) on the surface of two steels is 80.34 Ω\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 5.933 Ω\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively, which are both large, indicating that a relatively dense corrosion layer has been formed, which has a certain protective effect on the matrix. The results are consistent with the microscopic morphology analysis in section \u003cspan refid=\"Sec10\" class=\"InternalRef\"\u003e3.2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe comparison of R\u003csub\u003es\u003c/sub\u003e, R\u003csub\u003ect\u003c/sub\u003e and R\u003csub\u003ef\u003c/sub\u003e of the two steels shows that R\u003csub\u003es\u003c/sub\u003e and R\u003csub\u003ef\u003c/sub\u003e are significantly smaller than R\u003csub\u003ect\u003c/sub\u003e, indicating that charge transfer process is the main control step of corrosion at the initial stage of corrosion (5 days), which is consistent with the result of Nquist diagram. When the S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is low, the diffusion impedance occurs in the electrode process of the two steels, indicating that S\u003csup\u003e2\u0026minus;\u003c/sup\u003e at low concentration has a small driving force, and S\u003csup\u003e2\u0026minus;\u003c/sup\u003e ions in the solution have a large resistance through the surface dense layer. Therefore, the ion diffusion at the interface becomes a control step in the corrosion process.\u003c/p\u003e \u003cp\u003eSince R\u003csub\u003ect\u003c/sub\u003e and R\u003csub\u003ef\u003c/sub\u003e are difficult to distinguish, R\u003csub\u003ect\u003c/sub\u003e+R\u003csub\u003ef\u003c/sub\u003e is used to represent polarization resistance R\u003csub\u003ep\u003c/sub\u003e to analyze the corrosion process during the analysis of electrochemical impedance spectrum data by Zview software. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the change of R\u003csub\u003ep\u003c/sub\u003e with the concentration of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e in the corrosion process. It can be seen from the figure that the Rp of both Q235 steel and 16Mn steel decreases first and then increases slowly with the increase of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration. The R\u003csub\u003ep\u003c/sub\u003e of Q235 steel reaches the minimum value when S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is 4 g/L, while that of 16Mn steel reaches the minimum value when S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is 3 g/L, which is consistent with the results of weight loss method and polarization curve.\u003c/p\u003e \n\u003cp\u003e\u003cstrong\u003eTable 4\u003c/strong\u003e Impedance parameters obtained on Q235 and 16Mn steels with different concentrations of S\u003csup\u003e2-\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\" width=\"578\" height=\"471\"\u003e\u003c/p\u003e\u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Adsorption structures of related particles\u003c/h2\u003e \u003cp\u003eWe calculated the adsorption energies of S\u003csup\u003e2\u0026minus;\u003c/sup\u003eand OH\u003csup\u003e\u0026minus;\u003c/sup\u003e on the Fe(110) surface using first-principles calculations. We positioned S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and OH\u003csup\u003e\u0026minus;\u003c/sup\u003e separately on the top sites (TFe) of the Fe(110) surface. The formula for calculating the adsorption energy (E\u003csub\u003eads\u003c/sub\u003e) between the Fe(110) surface and the adsorbates is as follows:\u003c/p\u003e \u003cp\u003eE\u003csub\u003eads\u003c/sub\u003e = E\u003csub\u003eiron\u0026minus;ion\u003c/sub\u003e \u0026minus; E\u003csub\u003eiron\u003c/sub\u003e \u0026minus; E\u003csub\u003eion\u003c/sub\u003e (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eWhere E\u003csub\u003eiron\u0026minus;ion\u003c/sub\u003e represents the total energy of the system, E\u003csub\u003eiron\u003c/sub\u003e represents the energy of iron, and E\u003csub\u003eion\u003c/sub\u003e is the energy of the free ion.In theory, the more negative the value of E\u003csub\u003eads\u003c/sub\u003e, the more stable the adsorption between the adsorbate and the surface. The adsorption energies of the two ions on the Fe(110) surface are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the calculations, the adsorption energy of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e on the Fe(110) surface is -28.04 eV, while the adsorption energy of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e on the Fe(110) surface is -9.21 eV. It can be observed that S\u003csup\u003e2\u0026minus;\u003c/sup\u003e has a higher affinity for adsorption on the Fe(110) surface compared to OH\u003csup\u003e\u0026minus;\u003c/sup\u003e. This suggests that in this system, S\u003csup\u003e2\u0026minus;\u003c/sup\u003e is likely to adsorb on the steel surface, resulting in the corrosion product mainly being FeS. Subsequently, OH\u003csup\u003e\u0026minus;\u003c/sup\u003e can further adsorb, leading to the transformation of the corrosion product into iron oxide. This theoretical basis can provide insights into the sequence of corrosion product formation on the steel surface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.7 Corrosion Mechanism\u003c/h2\u003e \u003cp\u003eBy analyzing the linear polarization curve and electrochemical impedance spectrum characteristics, the electrochemical corrosion behavior of Q235 and 16Mn steel in the solution containing S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e sodium aluminate was discussed. Combined with relevant literature reports \u003csup\u003e26\u0026ndash;30\u003c/sup\u003e. the electrochemical corrosion mechanism of sulfur on Q235 and 16Mn steel was analyzed as follows:\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e)Effect of S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e on corrosion behavior of steels\u003c/p\u003e \u003cp\u003eWhen the concentration of S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e in sodium aluminate solution is low (\u0026lt;\u0026thinsp;3 g∙L\u003csup\u003e-1\u003c/sup\u003e), the electron loss reaction of S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e inhibits the corrosion of steel to some extent. Since equations (\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e1\u003c/span\u003e), (\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) play the role of supplying electrons in the electrochemical system, they hinder the anodic dissolution of steel to a certain extent, resulting in the decrease of the corrosion rate.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${{S}_{2}O}_{3}^{2-}+6{OH}^{-}\\to {2SO}_{3}^{2-}+{3H}_{2}O+4{e}^{-} {{\\epsilon }}^{\\theta }=0.58V$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${S}^{2-}+6{OH}^{-}\\to {SO}_{3}^{2-}+{3H}_{2}O+6{e}^{-} {{\\epsilon }}^{\\theta }=0.61V$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$${S}^{2-}\\to {S}_{2}^{2-}+2{e}^{-} {{\\epsilon }}^{\\theta }=0.51V$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhen S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e concentration is higher (\u0026ge;\u0026thinsp;3 g∙L\u003csup\u003e-1\u003c/sup\u003e), it plays an electron consuming role in the electrochemical system through Eq.\u0026nbsp;(\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Therefore, the anodic dissolution of steel is promoted to some extent.\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$${{S}_{2}O}_{3}^{2-}+{3H}_{2}O+8{e}^{-}\\to 2{\\text{S}}^{2-}+6{OH}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eHowever, when the concentration of S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e is higher (\u0026ge;\u0026thinsp;3 g∙L\u003csup\u003e-1\u003c/sup\u003e), the anodic dissolution of steel is hindered by the release of electrons through the synergistic reaction (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e).\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$2{S}^{2-}+{S}_{2}{O}_{3}^{2-}+6{OH}^{-}\\to {S}_{2}^{2-}+2{SO}_{3}^{2-}+3{H}_{2}O+6{e}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e)Effect of AlO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e in sodium aluminate solution on corrosion behavior of steel\u003c/p\u003e \u003cp\u003eWhen AlO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e is adsorbed to the electrode surface, the following reactions (Eq.\u0026nbsp;\u003cspan refid=\"Equ7\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Equ9\" class=\"InternalRef\"\u003e8\u003c/span\u003e) will occur.\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$Fe+Al{O}_{2}^{-}\\to {FeAl{O}_{2}^{-}}_{\\text{a}\\text{d}\\text{s}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e\n$${F\\text{e}}_{3}{O}_{4}+2{H}_{2}O+2{e}^{-}\\to 3HF\\text{e}{O}_{2}^{-}+{H}^{+}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ9\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ9\" name=\"EquationSource\"\u003e\n$${\\chi FeAl{O}_{2}^{-}}_{\\text{a}\\text{d}\\text{s}}+\\left(3-{\\chi }\\right)HF\\text{e}{O}_{2}^{-}+\\left(1+\\chi \\right){H}^{+}\\to {Fe}_{3-\\chi }{Al}_{\\chi }{\\text{O}}_{4}+2{H}_{2}O+\\chi Fe+2{e}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eCombined with the E-pH diagram of Fe-Al-Mn-S-H\u003csub\u003e2\u003c/sub\u003eO system at 95℃ shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, when χ\u0026thinsp;=\u0026thinsp;2, the chemical formula \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({Fe}_{3-\\chi }{Al}_{\\chi }{\\text{O}}_{4}\\)\u003c/span\u003e\u003c/span\u003e can be written as FeAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and the generation of FeAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e will inhibit the current density in the passivation process. However, as the diffusion rate of AlO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e to the surface of steel is slower than OH\u003csup\u003e-\u003c/sup\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({FeAl{O}_{2}^{-}}_{\\text{a}\\text{d}\\text{s}}\\)\u003c/span\u003e\u003c/span\u003e is difficult to be formed. Therefore, AlO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e has a certain inhibiting effect on the corrosion of steel, but the inhibiting effect is relatively small.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e)Anodic dissolution of steel and formation mechanism of corrosion product layer\u003c/p\u003e \u003cp\u003eWhen the solution contains OH\u003csup\u003e-\u003c/sup\u003e and S\u003csup\u003e2-\u003c/sup\u003e, it has been reported in literature \u003csup\u003e4,31\u003c/sup\u003e that that the steel surface will have competitive adsorption for the two ions. If S\u003csup\u003e2-\u003c/sup\u003e is adsorped on the surface of steel, the corrosion products are mainly FeS\u003csup\u003e32\u003c/sup\u003e, and the adsorption, activation and dissolution reactions are shown in Eq.\u0026nbsp;(\u003cspan refid=\"Equ10\" class=\"InternalRef\"\u003e9\u003c/span\u003e). When the S\u003csup\u003e2-\u003c/sup\u003e concentration in the solution reaches a certain level, the ratio of S\u003csup\u003e2-\u003c/sup\u003e to OH\u003csup\u003e-\u003c/sup\u003e becomes smaller, and the steel surface is controlled by OH\u003csup\u003e-\u003c/sup\u003e adsorption. The corrosion products are mainly oxidation film, and the adsorption and activation dissolution reactions are shown in Eq.\u0026nbsp;(\u003cspan refid=\"Equ11\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003cdiv id=\"Equ10\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ10\" name=\"EquationSource\"\u003e\n$$Fe+{\\text{S}}^{2-}=\\text{F}\\text{e}\\text{S}+2{e}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e9\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ11\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ11\" name=\"EquationSource\"\u003e\n$$\\text{F}\\text{e}+{OH}^{-}=Fe{\\left(\\text{O}\\text{H}\\right)}_{2}+2{e}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e10\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThere are three anode limit peaks on the polarization curve of the steel electrode, which mainly occur the anodic dissolution of steel and the transformation between iron sulfide and iron oxide. The main steps are as follows:\u003c/p\u003e \u003cp\u003eThe corresponding potential of peak (Ⅰ) is roughly \u0026minus;\u0026thinsp;1.1V (vs SCE), and iron dissolves into HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e. The dissolution reaction is shown in Eq.\u0026nbsp;(\u003cspan refid=\"Equ12\" class=\"InternalRef\"\u003e11\u003c/span\u003e).\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$HFe{\\text{O}}_{2}^{-}+{\\text{H}}_{2}\\text{O}+2{e}^{-}=\\text{F}\\text{e}\\left(s\\right)+3{\\text{O}\\text{H}}^{-}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ12\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ12\" name=\"EquationSource\"\u003e\n$${\\epsilon }_{HFe{\\text{O}}_{2}^{-}/Fe}=0.2844-0.1006\\text{p}\\text{H}+0.0335\\text{l}\\text{g}\\left[HFe{\\text{O}}_{2}^{-}\\right]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e11\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAccording to the E-pH diagram of S-H\u003csub\u003e2\u003c/sub\u003eO system and Fe-S-H\u003csub\u003e2\u003c/sub\u003eO system, the ions stably existing in the self-corrosive potential range are S\u003csup\u003e2-\u003c/sup\u003e and HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e. With the progress of anodic dissolution reaction, the concentration of HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e in the solution keeps increasing and will react with S\u003csup\u003e2-\u003c/sup\u003e in the solution in Eq.\u0026nbsp;(\u003cspan refid=\"Equ13\" class=\"InternalRef\"\u003e12\u003c/span\u003e).\u003cdiv id=\"Equ13\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ13\" name=\"EquationSource\"\u003e\n$$HFe{\\text{O}}_{2}^{-}+{S}^{2-}+3{\\text{H}}_{2}O=\\text{F}\\text{e}\\text{S}\\downarrow +3{\\text{O}\\text{H}}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e12\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eFeS is a dark brown substance with loose structure, which cannot protect the surface of steel. However, due to the generation of FeS, the passivation of steel will be delayed, and the oxidation reaction on the surface of steel will continue to generate yellow pyrite FeS\u003csub\u003e2\u003c/sub\u003e with good density.\u003c/p\u003e \u003cp\u003eThe corresponding potential of peak (Ⅱ) is approximately \u0026minus;\u0026thinsp;1.0V (vs SCE), and HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e will undergo further oxidation to form FeOOH (Eq.\u0026nbsp;\u003cspan refid=\"Equ14\" class=\"InternalRef\"\u003e13\u003c/span\u003e) and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Eq.\u0026nbsp;\u003cspan refid=\"Equ15\" class=\"InternalRef\"\u003e14\u003c/span\u003e).\u003cdiv id=\"Equ14\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ14\" name=\"EquationSource\"\u003e\n$$HFe{\\text{O}}_{2}^{-}\\to \\text{F}\\text{e}\\text{O}\\text{O}\\text{H}+{\\text{e}}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e13\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ15\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ15\" name=\"EquationSource\"\u003e\n$$\\text{o}\\text{r} 2HFe{\\text{O}}_{2}^{-}\\to {\\text{F}\\text{e}}_{2}{\\text{O}}_{3}+{\\text{H}}_{2}\\text{O}+2{\\text{e}}^{-}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e14\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe corresponding potential of peak (ⅲ) is roughly \u0026minus;\u0026thinsp;0.8V (vs SCE), and FeS continues to react to generate FeS2 with good stability, as shown in Eq.\u0026nbsp;\u003cspan refid=\"Equ16\" class=\"InternalRef\"\u003e15\u003c/span\u003e.\u003cdiv id=\"Equ16\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ16\" name=\"EquationSource\"\u003e\n$$\\text{F}\\text{e}{\\text{S}}_{2}\\downarrow +2{e}^{-}\\to \\text{F}\\text{e}\\text{S}+{\\text{S}}^{2-} {\\epsilon }_{Fe{\\text{S}}_{2}/\\text{F}\\text{e}\\text{S}}=0.792-0.0335lg\\left[{S}^{2-}\\right]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e15\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eXRD analysis shows that the main corrosion products are FeOOH, Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. Therefore, as the potential increases, the FeS generated by the Eq.\u0026nbsp;(\u003cspan refid=\"Equ17\" class=\"InternalRef\"\u003e16\u003c/span\u003e) continue to react in the solution to form a layer of structurally-stable brown-yellow FeOOH, and the surface corrosion products are eventually transformed into stable FeOOH, Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e to passivate them.\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$2Fe\\text{O}\\text{O}\\text{H}+{S}_{2}{O}_{3}^{2-}+12{H}^{+}+10{e}^{-}\\to 2\\text{F}\\text{e}\\text{S}+7{\\text{H}}_{2}O$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ17\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ17\" name=\"EquationSource\"\u003e\n$${\\epsilon }_{Fe\\text{O}\\text{O}\\text{H}/\\text{F}\\text{e}\\text{S}}=0.408-0.0805pH+0.0067lg\\left[{S}_{2}{O}_{3}^{2-}\\right]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e16\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ18\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ18\" name=\"EquationSource\"\u003e\n$$3\\text{F}\\text{e}\\text{O}\\text{O}\\text{H}+{\\text{H}}^{+}+{\\text{e}}^{-}\\to {\\text{F}\\text{e}}_{3}{\\text{O}}_{4}+2{H}_{2}O {\\epsilon }_{Fe\\text{O}\\text{O}\\text{H}/{\\text{F}\\text{e}}_{3}{\\text{O}}_{4}}={\\phi }^{\\theta }-0.067pH$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e17\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ19\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ19\" name=\"EquationSource\"\u003e\n$$3{Fe}_{2}{O}_{3}+{H}_{2}O+2{e}^{-}=2{Fe}_{3}{O}_{4}+{2OH}^{-}{ \\epsilon }_{{Fe}_{2}{O}_{3}/{Fe}_{3}{O}_{4}}=0.32-0.067pH$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e18\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn the above formula, the concentration of [HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e] is estimated according to the electric quantity Q flowing through the electrode, and the concentration of HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e can be calculated by Eq.\u0026nbsp;\u003cspan refid=\"Equ12\" class=\"InternalRef\"\u003e11\u003c/span\u003e. The concentration of S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e is calculated according to the concentration assigned. If the concentration of S\u003csup\u003e2-\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e is 5 g/L and 3 g/L, respectively. The pH of sodium aluminate solution was measured directly by the laboratory to be 14. So, it's estimated that \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{HFe{\\text{O}}_{2}^{-}/Fe}\\)\u003c/span\u003e\u003c/span\u003e=\u0026minus;1.124 V, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{Fe{\\text{S}}_{2}/\\text{F}\\text{e}\\text{S}}=0.853 V\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{{Fe}_{2}{O}_{3}/{Fe}_{3}{O}_{4}}=-0.618 \\text{V}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\epsilon }_{Fe\\text{O}\\text{O}\\text{H}/\\text{F}\\text{e}\\text{S}}\\)\u003c/span\u003e\u003c/span\u003e=\u0026minus;0.714 V.\u003c/p\u003e \u003cp\u003eC [HFeO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e]\u0026thinsp;=\u0026thinsp;Q/(nFV) (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eAccording to electrochemical measurements, morphology analysis and EDS analysis, the schematic diagram of the corrosion mechanism of Q235 steel and 16Mn steel in sulfur-containing sodium aluminate solution is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e9\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e9\u003c/span\u003ea shows that the steel is immersed in the corrosive medium. Figure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e9\u003c/span\u003eb shows that the corrosive ions S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and HS\u003csup\u003e\u0026minus;\u003c/sup\u003e in the solution are preferentially adsorbed on the surface of the steel, forming a layer of corrosion products on the surface to hinder the diffusion of corrosive ions to the substrate. Figure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e9\u003c/span\u003ec shows that the corrosion products on the steel surface continue to undergo transformation reactions, forming a layer of oxide attached to the steel surface. Figure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e9\u003c/span\u003ed shows that the octahedral crystal particles on the steel surface have accumulated and aggregated to form a layer of cubic crystal particles.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThis study investigates the effect of two types of sulfur on the synergistic corrosion behavior of Q235 and 16Mn steels, The following conclusions were drawn:\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) The corrosion products on the steel surface are converted from sulfides to oxides, and the crystal form of oxides also changes from octahedral crystal to cubic crystal with the progress of corrosion.The corrosion products at different concentrations of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e consist of sulfides (FeS, FeS\u003csub\u003e2\u003c/sub\u003e), oxides (Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) and NaFeO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) The anode area on the polarization curve represents four different stages of corrosion and there is a significant activation-passivation phenomenon. It shows that the higher S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration has a higher corrosion rate of steel.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e)Through the first calculation, the results show that S\u003csup\u003e2\u0026minus;\u003c/sup\u003e has a higher affinity for adsorption on the Fe(110) surface compared to OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, and in this system S\u003csup\u003e2\u0026minus;\u003c/sup\u003e is adsorbed on the steel surface, and the corrosion products are mainly FeS, and then the corrosion products of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e are further converted into iron oxides.\u003c/p\u003e \u003cp\u003e(\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e) EIS results show that when S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is low (\u0026thinsp;≦\u0026thinsp;2g/L), the corrosion process of steel is controlled by the charge transfer and surface film. However, when S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration is higher (\u0026gt;\u0026thinsp;2g/L), the corrosion of steel is controlled by the charge transfer, the surface film layer and ion diffusion.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eInstitutional review board statement\u003c/h2\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConflict of interest:\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eDL and BQ conceived the experiment, DL,JX,and HW collected the data, DL, JX, HW,analyzed the data, DL wrote the initial draft, DL,JX and HW prepared figures,BQ,CC and JL obtained the research fund, DL,BQ,CC,JL,JX,and HW reviewed and approved the following draft. All the authors approved the publication of this work.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis work was supported by National Natured Science Foundation of China (grant no. U1812402, 52074096 and 51774102), Guizhou Province Outstanding Young Scientific and Technological Talent Training Plan ([2017]5626), Guizhou University Talent Introduction Project ([2019]43) and Guizhou University Cultivation Project ([2020]43).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData supporting the fndings of this manuscript are available from the corresponding author upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLiu, Z. \u003cem\u003eet al.\u003c/em\u003e Digestion behavior and removal of sulfur in high-sulfur bauxite during bayer process. \u003cem\u003eMinerals Engineering\u003c/em\u003e \u003cstrong\u003e149\u003c/strong\u003e, 106237 (2020).\u003c/li\u003e\n\u003cli\u003eZhou, X. \u003cem\u003eet al.\u003c/em\u003e Simultaneous removal of sulfur and iron by the seed precipitation of digestion solution for high-sulfur bauxite. \u003cem\u003eHydrometallurgy\u003c/em\u003e \u003cstrong\u003e181\u003c/strong\u003e, 7\u0026ndash;15 (2018).\u003c/li\u003e\n\u003cli\u003eZhanwei, L. \u003cem\u003eet al.\u003c/em\u003e Sulfur Removal by Adding Iron During the Digestion Process of High-sulfur Bauxite. \u003cem\u003eMetall Mater Trans B\u003c/em\u003e \u003cstrong\u003e49\u003c/strong\u003e, 509\u0026ndash;513 (2018).\u003c/li\u003e\n\u003cli\u003eXie, Q. \u0026amp; Chen, W. 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The corrosion rate of 16Mn steel is greater than that of Q235 steel. The effect of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e concentration on corrosion rate was significantly higher than that of S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e. The synergistic corrosion rates of Q235 and 16Mn steels increase at first and then decrease with the sulfur content, and the peak value appears when the concentration of S\u003csup\u003e2\u0026minus;\u003c/sup\u003e and S\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e is 4 g/L and 3 g/L respectively. There are two main types of corrosion products: one is surface octahedral grain, which is composed of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.The other is the interlayer corrosion between the surface layer and the matrix, which is composed of FeS, FeS\u003csub\u003e2\u003c/sub\u003e and NaFeO\u003csub\u003e2\u003c/sub\u003e.The formation mechanism of the corrosion and corrosion mechanism were obtained by analyzing the phenomenon of ion competitive adsorption. Further validation and analysis of ion competition adsorption phenomenon were conducted using first-principles calculations based on density functional theory (DFT). The formation of corrosion products on the steel surface was investigated at an ion level, and the adsorption energies of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and S\u003csup\u003e2\u0026minus;\u003c/sup\u003e at the top site of Fe(110) surface were calculated. It was found that S\u003csup\u003e2\u0026minus;\u003c/sup\u003e is more likely to be adsorbed on the Fe(110) surface compared to OH\u003csup\u003e\u0026minus;\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe corrosion mechanism of steel is discussed preliminarily.\u003c/p\u003e","manuscriptTitle":"Effect of Sulfur on synergistic corrosion behavior of Q235 and 16Mn steel in sodium aluminate solution","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-08 05:46:45","doi":"10.21203/rs.3.rs-4119985/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-06T05:13:51+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-17T21:25:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"28730828574104036972728718591561838630","date":"2024-07-17T19:38:34+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-10T19:13:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"96772445910386368097451421944634634142","date":"2024-05-19T18:20:20+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-04-13T06:20:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"68c7a65f-adb8-4c5b-b903-e404c58ef6f1","date":"2024-04-05T10:41:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"63781d6d-4913-4756-8ba2-4169374913f8","date":"2024-04-05T10:36:10+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-03T07:55:53+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-03T07:54:23+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-04-03T07:32:23+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-03T04:21:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-03-18T04:54:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bea07167-0efb-4268-8b65-84760e961396","owner":[],"postedDate":"April 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":30309944,"name":"Physical sciences/Chemistry"},{"id":30309945,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2024-09-30T16:12:59+00:00","versionOfRecord":{"articleIdentity":"rs-4119985","link":"https://doi.org/10.1038/s41598-024-72639-x","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-09-27 15:57:17","publishedOnDateReadable":"September 27th, 2024"},"versionCreatedAt":"2024-04-08 05:46:45","video":"","vorDoi":"10.1038/s41598-024-72639-x","vorDoiUrl":"https://doi.org/10.1038/s41598-024-72639-x","workflowStages":[]},"version":"v1","identity":"rs-4119985","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4119985","identity":"rs-4119985","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}