The corrosion inhibition by a triazole derivative (PAMT) on mild steel in phosphoric acid (H3PO4) solution has been investigated by weight loss and polarization methods. The experimental results reveal that the compound has a significant inhibiting effect on the corrosion of steel in H3PO4 solution. It also shows good corrosion inhibition at higher concentration of H3PO4. Potentiodynamic polarization studies have shown that the compound acts as a mixed-type inhibitor retarding the anodic and cathodic corrosion reactions with predominant effect on the cathodic reaction. The values of inhibition efficiency obtained from weight loss and polarization measurements are in good agreement. The adsorption of this compound is found to obey the Langmuir adsorption isotherm. Some kinetic and thermodynamic parameters such as apparent activation energy, frequency factor, and adsorption free energy have been calculated and discussed. 1. Introduction The use of inhibitors is one of the most practical methods for protection of metal against corrosion, especially in acidic media [1]. Most of the well-known acid inhibitors are organic compounds containing nitrogen, sulphur, and oxygen atoms. Compounds with π-electrons and functional groups containing heteroatoms which can donate lone pair electrons are found to be particularly useful as inhibitors for corrosion of metals [2–5]. The exiting data reveal that most organic inhibitors act by adsorption on the metal surface. This adsorption is influenced by the nature and surface charge of metal, the type of aggressive electrolyte and the chemical structure of inhibitors [6]. The compounds containing both nitrogen and sulphur can give excellent inhibition in contrast to compounds containing only nitrogen or sulphur [7]. Triazole and triazole-type compounds containing nitrogen, sulphur, and heterocycle on the corrosion inhibition of metal in acidic media have attracted more attention because of their excellent corrosion inhibition performance [8–11]. The some new triazole derivatives have been still continuously synthesized and investigated as inhibitors for corrosion of metals in acidic solutions [12–14]. For example, Zhang et al. studied the corrosion inhibition of a newly synthesized oxadiazol-triazole derivative for mild steel in sulphuric solution, their results indicated that the compound was effective corrosion inhibitor for mild steel in acid solution and its efficiency attained more than 97.6% at 298？K [15]. The researches by Fouda and Ellithy showed that some 4-phenylthiazole derivatives could inhibit the corrosion of
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