A Novel Inhibitor for L921A alloy Steel in a 3.5 % NaCl Solution

Corrosion inhibitors, acting as an effective method at lower operating cost, are often used to protect metallic materials from corrosion. Although many kinds of corrosion inhibitors have been used in circulating cooling water systems, a few papers have been published for introducing the applications of corrosion inhibitors in chloride media. By comparison, it is difficult to develop a novel inhibitor for alloy steels in chloride solutions or sea water. In this paper, a novel corrosion inhibitor for L921A alloy steel in a 3.5% NaCl solution was formulated by weight loss in conjunction with orthogonal tests. The inhibitory efficiency of this novel inhibitor was over 95.0%. It was found by electrochemical polarization that this novel inhibitor was a mixed type of inhibitor which had an ability to improve the pitting corrosion resistance of L921A alloy steel in a 3.5% NaCl solution. EIS spectra showed that L921A alloy steel in a 3.5% NaCl solution was subjected to pitting corrosion, due to that EIS spectrum with two time constants of L921A alloy steel in a 3.5% NaCl solution was composed of a capacitive loop at high frequency region and an inductive loop at low frequency region. However, EIS spectrum with two time constants consisted of a capacitive loop at high frequency region and a Warburg line at low frequency region when the novel inhibitor was added into a 3.5% NaCl solution. The thickness of inhibitory film increased with increasing immersion time, resulting in the increment of the electrochemical impedance of corrosion process of L921A alloy steel in a 3.5% NaCl solution. Finally, the formation of the inhibitory film was further studied by EDX and XPS technology. Key words: alloy steel; chloride solution, inhibitor; EIS, XPS; inhibitory mechanism