Initial Corrosion Behavior of 12Cr1MoV Steel in Thiosulfate-Containing Sodium Aluminate Solution

Abstract

When alumina is produced by the Bayer process with high-sulfur bauxite, the sulfur would strongly corrode the 12Cr1MoV steel made heat exchanger. This study investigated the initial corrosion behavior of the 12Cr1MoV steel exposed to a thiosulfate-containing sodium aluminate (TCSA) solution under the evaporation conditions of alumina production. The obtained corrosion rate equation is V = 6.306·t·exp(−0.71). As corrosion progressed, with the corrosion product film growing, the corrosion current density declines slowly, and the corrosion resistance of the steel is increased. At 1–3 days, the corrosion product film consisted of FeO, Fe2O3, and FeOOH. S2O32− lead to corrosion in local areas of the steel and pits appeared. AlO2− is transformed into Al(OH)3 and filled in the corrosion pits. At 4 and 5 days, Fe3O4 is generated in the outermost layer, and Al(OH)3 is shed from the corrosion pits. The corrosion mechanism of 12Cr1MoV steel in a TCSA solution is proposed based on the experimental results.

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

“…In the middle and later stages of corrosion, the corrosion products continue to react with the ions. On the one hand, the formation of structurally stable iron oxide causes surface pseudo-passivation, as shown in Equations ( 7)-( 13) [14,26,28], and on the other hand, the ionization of FeS occurs, as shown in Equation ( 14) [14,48]. These electrode reactions correspond to the anode pseudo-passivation zone of the polarization curves (Figure 7).…”

“…A mathematical fitting was performed to determine the mathematical relationship between the corrosion rate and the corrosion time, and it was found that the corrosion rate satisfied the mathematical model of the power function at the initial stage of corrosion [28][29][30], which is shown in Table 2, and the fitting curve is shown in Figure 6a. The fitting correlation coefficients in Table 2 are basically above 0.9, indicating that the fitting equation of corrosion dynamics of the Q235 steel has a good correlation with the experimental results.…”

“…The corrosion rate decreased with the extension of corrosion time (3-5 d), which illustrated that the corrosion products were formed on the steel surface as the steel matrix and ions (S 2− , S 2 O 3 2− , OH − and AlO 2 − ) in the solution adsorbed and reacted, which hindered the diffusion of the corrosive ions to the matrix surface and slowed down the corrosion. At the middle and late stage (7-13 d), the corrosion products accumulated, which effectively prevented the transfer of corrosive ions to the interior of the matrix, so that the corrosion became slow and tended to become gentle [28].…”

“…At the initial stage of corrosion, the matrix iron is ionized first, as shown in Equation (3) [11,28]. In addition, the matrix iron will directly adsorb HS − to generate FeS, as shown in Equation ( 4) [47].…”

Effect of Corrosion Temperature on the Corrosion of Q235 Steel and 16Mn Steel in Sodium Aluminate Solutions

“…9,10 With the recycling of alumina production, it is found that the steel has serious selective corrosion, pitting corrosion, corrosion cracking, and uniform corrosion. 11,12 In the production process of Bayer alumina, the different alumina production processes need to be completed at different temperatures, for example, the seed crystal decomposition temperature is 65 °C, the evaporation temperature is 110 °C, and the dilution temperature is 95 °C, approximately. 13 Therefore, the study of the corrosion behavior of corrosion temperature on the tank material is of great significance to material protection and material selection.…”