The corrosion inhibition by two synthesized Schiff -bases of bis-(2-hydroxy-3-methoxy)-1,6-diaminohexane salicyladimine and bis-(2-hydroxy)-1,6-diaminohexane salicyladimine was investigated by weight loss, Tafel polarization and AC impedance on low alloy steel in 1M HCl. The results show that these Schiff -bases act as anodic type inhibitors. The inhibition efficiency obtained from all method employed are in good agreement. Changes in impedance parameters (R t and C dl ) are indicative of adsorption of Schiff-bases on the metal surface leading to the formation of protective film. Two Schiff-bases are found to adsorb on low alloy steel surface according to the Langmuir adsorption isotherm and thermodynamics calculations revealed that bis-(2-hydroxy-3-methoxy)-1,6-diaminohexane salicyladimine had larger adsorption constant and more negative free energy of adsorption than bis-(2-hydroxy)-1,6-diaminohexane salicyladimine.

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PurposeThe purpose of this paper is to investigate how to improve the corrosion inhibition behavior of molybdate‐based inhibitors for mild steel, using organic compounds containing a phenyl ring together with nitrite agent. As picrate contains a phenyl ring together with three substituent nitrite anions, it is used as an organic compound. In this study a new molybdate‐based inhibitor was introduced with the composition of 60 ppm molybdate/40 ppm nitrite/20 ppm picrate. Inhibition efficiency of molybdate alone and with nitrite and picrate on the uniform corrosion of mild steel in stimulated cooling water was assessed.Design/methodology/approachThe inhibition efficiency of molybdate alone and with nitrite and picrate on the uniform corrosion of mild carbon steel in stimulated cooling water (SCW) was assessed by electrochemical techniques such as potentiodynamic polarization, electrochemical impedance (AC impedance) measurements and weight loss determinations at the room temperature. Studies of electron microscopy included scanning electron microscopy (SEM) photography and X‐Ray energy dispersive (EDS) microanalysis were used.FindingsThe results obtained from the polarization and AC impedance curves were in agreement with those from the corrosion weight loss results. The results indicated that the new inhibitor was as effective as molybdate alone, though at one quarter of the concentration range of molybdate, which is economically favorable.Originality/valueThe paper demonstrates improvement in corrosion inhibition of mild steel in SCW via a blend of molybdate, nitrite and picrate as a new anodic inhibitor.

The effect of thiourea on electrochemical corrosion behavior of mild steel was investigated in 0.5M HCl solution at room temperature by electrochemical impedance spectroscopy (AC Impedance) and Tafel polarization (DC Polarization) methods. The results show that thiourea act as mixed type inhibitor. The inhibition efficiency obtained from AC Impedance and DC polarization methods are in good agreement. The Nyquist plots show that the corrosion behavior of mild steel in 0.5M HCl solution in the absence and in the presence of thiourea, consist a simple capacitive loop. Changes in impedance parameters (R ct and C dl ) are indicative of adsorption of thiourea on the metal surface, leading to the formation of protective film. Thiourea is found to adsorb on mild steel surface steel in 0.5M HCl solution, according to the Langmuir adsorption isotherm.

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