Protection of low carbon steel by oxadiazole derivatives and biocide against corrosion in simulated cooling water system

• Oxadiazole derivatives were investigated for low carbon steel corrosion in simulated solution.
• The inhibition efficiency depended to methyl group position.
• A synergism effect between oxadiazole derivatives and biocide was obtained.
• Large passivity current plateau was observed in the presence of mixture.
• Electrochemical results were confirmed by SEM/EDX analysis.

Electrochemical behavior of low carbon steel in simulated cooling water system in the absence and presence of oxadiazole derivatives, namely 2,5-bis(n-methylphenyl)-1,3,4-oxadiazole with (n = 2,3,4), denoted n-MPOX, have been investigated using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The polarizations measurements revealed that the oxadiazole derivatives inhibited both cathodic and anodic reactions. Inhibition efficiency depended on the methyl group position and followed the sequence: 3-MPOX ≥ 4-MPOX > 2-MPOX. In addition, their inhibitions were enhanced by the addition of non-oxidizing biocide CTAB. So, a large plate of passivation was registered in the case of mixture 1 (3-MPOX + CTAB) which reinforced the low carbon steel resistance against pitting corrosion. Scanning electron microscopy (SEM) observations and energy dispersive X-ray (EDX) analysis of the low carbon steel surface illustrate that the surface homogeneity increases in the presence of mixtures and confirmed the inhibitor effect after 2 days of immersion.

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