The Comparative Investigation of Corrosion and Passivation for X65 Carbon Steel in pH 1 to 5 HNO3 Solutions without and with 0.01 mol L–1 NaNO2

Abstract

The influence of 0.01 mol L-1 NaNO 2 addition on the corrosion and passivation of X65 carbon steel in pH 1 to 5 HNO 3 solutions was investigated and compared by electrochemical methods and microstructural techniques. In the pH 1 to 5 solutions without NaNO 2 , the X65 steel presented the electrochemical characteristic of active dissolution, and the corrosion rate of X65 carbon steel decreased gradually with the raise of pH value. By contrast, with the addition of 0.01 mol L-1 NaNO 2 in pH 1 to 5 HNO 3 solutions, the electrochemical characteristic of X65 carbon steel transferred from the active dissolution in the pH 1 to 5 solutions without NaNO 2 to the anodic passivation in the corresponding pH solutions with NaNO 2. For the X65 steel in the pH 1 to 5 solutions with NaNO 2 , with the raise of pH value, the corrosion rate also decreased gradually but the passivation capability strengthened obviously. The corrosion and passivation of X65 carbon steel in pH 1 to 5 HNO 3 solutions without and with 0.01 mol L-1 NaNO 2 were related to the cathodic reactions of H + reduction, O 2 reduction and NO 2-/HNO 2 reduction.

An electrochemical study of pH influences on corrosion and passivation for a Q235 carbon steel in HNO3–NaNO2, HAc–NaNO2and HCl–NaNO2solutions

“…2, for the Q235 steel in the pH 4 solutions, the CV peaks corresponding to the oxidation from Fe 2+ to Fe oxidation possible. 13,15,18 It is noteworthy from Fig. 2 that the CV peaks corresponding to the reduction of NO 2 À were absent, and similar results were also obtained by Li et al 26 and Valcarce et al 11 Regarding the cathodic reduction of NO 2 À , Zhou et al 13 reported the following electrode reaction in a CO 2 -saturated solution:…”

“…At the same time, the main cathodic reactions depend on the pH value of the acidic electrolytes. The H + reduction and the O 2 reduction occur at relatively low and high pH values, 15 respectively, which are given as follows: 2H + + 2e → H 2 ( E st = 0 V SHE ) O 2 + 2H 2 O + 4e → 4OH − ( E st = 0.401 V SHE ) …”

“…[7][8][9][10][11][12] In contrast, there are relatively few related studies in acidic electrolytes containing NO 2 À . [13][14][15][16][17] Zhou et al 13 studied the corrosion and passivation behaviors of Q235 carbon steel in CO 2 saturated solutions containing NO 2…”

The role of WO42−on surface passivation for Q235 carbon steel in tungstate solution

“…The O 1 s spectrum also exhibits three peaks at 530.10, 531.50 and 532.30 eV, respectively, corresponding to O element in O 2− , OH − and H 2 O. The signals of O 2− and OH − result from the passive film (Deng et al , 2020), and the signal of H 2 O results from the physically and/or chemically adsorbed water (Luo et al , 2012). The W 4d spectrum exhibits a single peak at 247.50 eV, which may be attributed to the adsorbtion of WO 4 2− on the electrode surface (Chaudhary et al , 2018); at the same time, the W 4f spectrum exhibits a spin-orbit splitting double-peak at 35.40 and 37.50 eV, respectively corresponding to W element in W 4f 7/2 and W 4f 5/2 , which is due to the depositions of FeWO 4 and Fe 2 (WO 4 ) 3 (Londono-Menjura et al , 2018).…”

The electrochemical behavior of corrosion and passivation for Q235 carbon steel in acidic phosphate buffer solutions without and with NO2−

“…By contrast, in acidic environments, the related investigations involving the effectiveness and mechanism of NO 2 − on the surface passivation of carbon steels are only just starting. In the previous works (Li et al , 2019; Zhou et al , 2019; Deng et al , 2020; Zhou and Yan, 2016; Zhou et al , 2019), the influences of NO 2 − on the electrochemical behavior of carbon steels in pure acidic solutions, such as HAc (Li et al , 2019), HCl (Zhou et al , 2019a, 2019b, 2019c, 2019d), HNO 3 (Deng et al .,2020) and CO 2 /H 2 CO 3 (Zhou and Yan, 2016), have been reported. The main results are summarized as follows: The electrochemical behavior transfers from the activation (A) in acidic solutions without NO 2 − to the activation-passivation (A-P) transition in the corresponding solutions with NO 2 − . In pure acidic solutions containing NO 2 − , the acidity, oxidability and composition of the bulk acids show some degree of influence on the pH range for the occurrence of A-P transition. The presence of inhibitive species in pure acidic solutions is beneficial to the occurrence of A-P transition, but the presence of aggressive species shows the opposite effect. Unfortunately, for the surface passivation of carbon steels in acidic environments, the detailed mechanism of NO 2 − is still not clear; besides, the present investigations concerning the effectiveness of NO 2 − are mainly focused on simple acidic solutions.…”