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The effect of 1-{[benzyl-(2-cyano-ethyl)-amino]-methyl}-5-methyl-1H-pyrazole-3carboxylic acid methyl ester (P1) and 1-{[benzyl-(2-cyano-ethyl)-amino]-methyl}-5methyl-1H-pyrazole-3-carboxylic acid ethyl ester (P2) was evaluated as corrosion inhibitors of steel in molar hydrochloric using weight loss measurements and electrochemical polarisation. The results obtained reveal that those compounds reduce the corrosion rate. The inhibiting action increases with the concentration of pyrazole compounds to attain 98.5 % at the 10-3 M of (P2). The increase in temperature leads to a decrease in the inhibition efficiency of the compounds in the temperature range 308 − 353 K. The adsorption isotherm of inhibitors on the steel has been determined. The thermodynamic data of activation and adsorption are determined.

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Purpose -The purpose of this paper is to investigate the inhibitive effect of the phosphite NaCo(H 2 PO 3 ) 3 zH 2 O (PhCo) for the corrosion of mild steel in HCl solutions. The study is another trial to find a mineral inhibitor for mild steel corrosion. Design/methodology/approach -The inhibitory effect has been evaluated by gravimetric and polarisation techniques at various temperatures. The type of adsorption inhibition and adsorption and kinetic data are determined. Findings -Results show that PhCo inhibits the corrosion of steel in acidic solution. The inhibition efficiency at 308 K increases with the inhibitor concentration to reach 96 per cent for 10 2 4 M, and then decreases at higher temperatures. Kinetic parameters such as E a , DH + a and DS + a were calculated. The adsorption of inhibitor obeys the Langmuir isotherm model. Thermodynamic parameters of adsorption including DG ad , DH ad , DS ad , and K eq(ad) were calculated in the presence of inhibitor.Research limitations/implications -Electrochemical studies (polarization method) show the partial action of inhibitor on anodic and cathodic reactions of the corrosion inhibition. Practical implications -The efficiency of the tested phosphite increases with its concentration to reach 96 per cent. It can be used in chemical cleaning and pickling processes at moderate temperature. Originality/value -This paper reveals the possible application of phosphites as environmentally valid inhibitors for corrosion under the specified conditions.

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