Corrosion inhibition of nickel in H2SO4 solution by alanine

The effect of alanine, as a safe inhibitor, was studied by measuring the corrosion of Ni in aerated and stagnant 1 M H2SO4 solution (pH ∼0.2). Measurements were performed under various conditions using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and the new electrochemical frequency modulation (EFM) methods. The obtained results showed that the addition of alanine alone gives a moderate inhibition and acts as an anodic-type inhibitor. The inhibition is due to physical adsorption of alanine on the metal surface. The inhibition efficiency enhances with increasing alanine concentration and immersion time but decreases with rise in temperature. The apparent activation energy, Ea, is higher in the presence than in the absence of alanine. Addition of I− ions greatly improves the inhibition efficiency of alanine. The synergistic effect is due to enhanced adsorption of alanine cations by chemisorbed I− anions on the metal surface. The results obtained from polarization, EIS and EFM techniques are in good agreement indicating that EFM method can be used successfully for monitoring corrosion rate of Ni in H2SO4 solution with and without alanine.

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► Corrosion of Ni in 1 M H2SO4 in the absence and the presence of alanine.
► Alanine acts as a moderate mixed type inhibitor.
► Physical adsorption of alanine and formation of protective film are on Ni surface.
► Addition of KI improves the inhibition efficiency (synergistic effect).
► EFM technique is in reasonably good agreement with the different techniques used.