Electrochemical, surface analytical, and spectroscopic study of passive film and pits formation on food grade ferritic stainless steel AISI‐430 in aqueous acetic acid containing chloride ions

Abstract

Pitting corrosion of food grade ferritic stainless steel AISI‐430 was studied in 20% aqueous acetic acid solution containing 0.5 M NaCl. Potentiodynamic polarization measurements at a slow scan rate reveal formation of metastable pits and repassivation. Surface analysis reveals remnants of the passive oxide layer adhered along the circumference of the pits, evidences of loss of microcrystallites, no significant loss in crystallinity during corrosion process and formation of mixed oxides of iron and chromium. The pitting of ferritic steel is an autocatalytic process, and the proposed mechanism suggests that both chloride and acetate ions play important role.

Effect of HAc on the Metastable Pitting Corrosion of 304 SS in NaCl Solution

“…Hence, both acetate ions (Ac − ) and undissociated acetic acid (molecular HAc) are present in the solution. Based on the calculation in Equation (1) of the dissociation constant ( K Hac ) and the value of the acetic acid (1.753 × 10 −5 at 25 °C) [ 1 , 13 ], the concentration of the dissociated acetate ions (Ac − ), the undissociated acetic acid (Hac) and the hydrogen ions (H + ) were calculated in each solution; the results are shown in Table 3 . It can be seen that under these conditions, acetic acid mainly exists in the form of molecules; there are very few dissociated acetate ions (0.00243 mol/L–0.00703 mol/L), which can, basically, be ignored.…”

“…Acetic acid is one of the most common organic acids. Stainless steels in a mixed solution of acetic acid and sodium chloride will suffer localized corrosion damage, such as pitting corrosion [ 1 , 2 ].…”

“…It is known that acetic acid (HAc) is a weak acid that can partially dissociate into hydrogen and acetate ions (HAc → H + + Ac − ), thereby decreasing the pH of a solution [ 1 , 12 , 13 ]. Some investigators have reported that the presence of HAc increases the corrosivity of a solution [ 13 , 14 ], whereas others have reported that HAc works as a weak anodic inhibitor [ 15 ].…”

“…Acetic acid at a low concentration could damage the passive film. Mahato et al [ 1 ] studied the pitting behavior of food-grade ferritic AISI-430 SS in 20% acetic acid with 0.5 mol/L NaCl and demonstrated that the acetate ions in the solution promote the dissolution of Fe and Cr atoms. Their results also showed that potentiodynamic polarization measurements at a slow scanning rate revealed the formation of metastable pits and repassivation.…”

Growth of Anodic Layers on 304L Stainless Steel Using Fluoride Free Electrolytes and Their Electrochemical Behavior in Chloride Solution

“…This bond occurs in compounds such as magnetite (Fe 3 O 4 ), maghemite (γ-Fe 2 O 3 ), and goethite (α-FeOOH) [ 40 ]. The low intensity bands at 1357 and 1446 cm −1 corresponded only to the α-FeOOH and γ-Fe 2 O 3 species, respectively, indicating their presence in the anodic layer [ 41 ]. On the other hand, the presence of an intense band at 550 cm −1 could be assigned to Ni–O stretching modes of Ni(OH) 2 [ 42 ], which overlaps with iron oxides peaks.…”