Growth of corrosion product film on 12Cr1MoV steel in sulfur-containing sodium aluminate solution

Abstract

The growth mechanism of product film on steel surface in sulfur-containing sodium aluminate solution was studied with relevance to processing of high-sulfur bauxite ores in Bayer process. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were used to study the growth of corrosion product film on 12Cr1MoV steel in sodium aluminate solution containing 5 g/L S2– and 3 g/L S2O2– 3. Results indicated that the corrosion rate gradually decreased with increasing corrosion time (t). The fitted corrosion rate equation was V = 4.365t–0.809. The corrosion resistance was highest after 5 d. The growth evolution of the product film was divided into three stages: film formation, film conversion and film growth. The final corrosion product film comprised an inner film layer mainly composed of Fe3O4 and an outer film layer mainly composed of FeS, FeS2 and Fe2O3.

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

“…After 5 d, the corrosion products are mainly composed of Fe3O4. According to previous studies [5,14,16], the following reactions occur. The peak A at −1.1 VSCE is attributed to the Fe matrix actively dissolving to form Fe(OH)3 − through Equation (4).…”

“…Three specimens were used for each experiment. The corrosion products were washed by immersion in a solution (500 mL HCl + 5 g C 6 H 12 N 4 + 500 mL H 2 O) and the change in weight due to material lost over time was used to calculate the average corrosion rate by Equation (2) [5]:…”

“…As corrosion products formed on the entire surface, the active corrosion reaction is inhibited, and the corrosion rate decreased [17]. The corrosion rate equation is fitted as follows [5]:…”

“…The peak B at −0.8 V versus SCE may be associated with the formation of Fe 3 O 4 through Equation (5). However, as the corrosion time increases, peak B gradually disappears, implying that the corrosion product film has a significant effect on the passivation behavior.…”

“…The accumulation of sulfur in the solution causes a series of hazards, such as the loss of alkalinity and the reduction of the alumina dissolution rate [4]. During the evaporation of the sodium aluminate solution, the sulfur strongly corrodes the heat exchanger made from 12Cr1MoV steel [5]. Although some desulfurization methods, such as roasting desulfurization [6] and wet desulfurization [7], can remove most of the sulfur, the sulfur concentration would continue to increase as the number of sodium aluminate solution cycles increasing.…”