Purpose

The purpose of this paper is to reveal the mechanism of nitrite (NO_2⁻) for the surface passivation of carbon steels in acidic environments through investigating the influences of 0.01 mol/L NaNO₂ addition on the corrosion and passivation behaviors of Q235 carbon steel in acidic phosphate buffer (APB) solutions (pH 2 to 6).

Design/methodology/approach

The electrochemical techniques including open circle potential evolution, potentiodynamic polarization, electrochemical impedance spectroscopy and cyclic voltammetry were applied.

Findings

In APB solutions without NO_2⁻, the Q235 steel presented the electrochemical behaviors of activation (A), activation-passivation-transpassivation and self-passivation-transpassivation at pH 2 to 4, pH 5 and pH 6, respectively; the corrosion rate decreased with the up of pH value, and the surface passivation occurred in the pH 5 and pH 6 solutions only: the anodic passivation at pH 5 and the spontaneous passivation at pH 6.

Originality/value

In APB solutions without NO_2⁻, the corrosion rate decreased with the up of pH value, and the surface passivation occurred in the pH 5 and pH 6 solutions only: the anodic passivation at pH 5 and the spontaneous passivation at pH 6. With the addition of 0.01 mol/L NaNO₂, into APB solutions, the variation of corrosion rate showed the same rule, but the surface passivation occurred over the whole acidic pH range, including the anodic passivation at pH 2 to 4 and the spontaneous passivation at pH 5 to 6.

中文翻译：

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Q235碳钢在无和有NO2-的酸性磷酸盐缓冲溶液中的腐蚀和钝化电化学行为

目的

本文的目的是揭示亚硝酸盐的机构（NO _{2 ^-} ）通过考察0.01摩尔/ L的NaNO的影响对在酸性环境中碳钢的表面钝化₂除了在Q235碳钢的腐蚀和钝化行为酸性磷酸盐缓冲液（APB）溶液（pH 2至6）。

设计/方法/方法

电化学技术包括开环电势演化，电势极化，电化学阻抗谱和循环伏安法。

发现

在没有NO APB解决方案_{2 ^-}时，Q235呈现钢活化（A）的电化学行为，激活钝化-transpassivation和自钝化-transpassivation在pH 2〜4，pH为5和分别pH为6; 腐蚀速率随pH值的升高而降低，仅在pH 5和pH 6的溶液中发生表面钝化：pH 5时的阳极钝化和pH 6时的自发钝化。

创意/价值

在没有NO APB解决方案_{2 ^-} ，腐蚀速率随pH值的向上减小，并且仅发生于pH值5和6的pH溶液中的表面钝化：在pH 5的阳极钝化并在pH 6的自发钝化随着在APB溶液中添加0.01 mol / L NaNO _2时，腐蚀速率的变化规律相同，但表面钝化发生在整个酸性pH范围内，包括pH 2至4的阳极钝化和pH自发的钝化。 5至6