Evaluation And Investigation On Mechanism Of Heterocyclic Compounds As Corrosion Inhibitors In Acid Soultion Of Mild Steel

Corrosion inhibitors hold the important status in the metal protection project, and they are playing the more and more vital role in the national economy construction. Numerous researches on corrosion inhibition using organic compounds have been reported due to its highly efficient and cost-effective. It has been accepted that most organic compounds employed as corrosion inhibitors can adsorb on the metal surface through heteroatoms such as nitrogen, sulfur, oxygen, phosphorus and multiple bonds etc preventing steel from corrosion. Based on the conclusions, different srurctures of the heterocyclic triazole-type compounds have different chemical activities, and developing novel structural heterocyclic triazole compounds is the research focus at present. The trend in the field of corrosion ingibitor science is to develop environmentally-friendly and economic corrosion inhibitors through a thorough study of the adsorption behaviors and a full understanding of the inhibition mechanism.The thesis deals with synthesis of a series of heterocyclic triazole compounds bearing muti-adsorption centers in the molecule and the adsorption behaviors and inhibiting properties. The inhibiting performance of these heterocyclic triazole compounds evaluated by weight loss, electrochemical test, scanning electronic microscope (SEM), and quantum chemical calculations. The corrosion inhibiting mechanism of these compounds and the relationship between the molecular structure and their inhibiting efficiency were discussed. Some results were drawn as follows:The heterocyclic triazole compounds shown excellent inhibition properties for the corrosion of mild steel in 1M HCl solutions, and the inhibition efficiency increases with increasing the concentration of the inhibitors; The inhibition ability of these compounds is follow in the order of MTTE< FTPP < PTOE < NTOE ads⁰), adsorption entropy (ΔS_ads⁰)and adsorption free energy (ΔG_ads⁰) indicate that the adsorption process is a reduction in entropy and exothermic process. The negative values ofΔS_ads⁰ might be explained in the following way: before the adsorption of inhibitors onto the steel surface, inhibitor molecules might freely move in the bulk solution (the inhibitor molecules were chaotic), but with the progress in the adsorption, inhibitor molecules were orderly adsorbed onto the steel surface, as a result, a decrease in entropy.The heterocyclic triazole compounds were investigated as corrosion inhibitors of mild steel in 0.5 M H₂SO₄. Potentiodynamic polarization measurements shows that the three heterocyclic triazole compounds are the mixed-type inhibitors, and addition of inhibitors causes a decrease in the corrosion current, EIS measurements also indicated that the presence of inhibitors raises the charge transfer resistances, it shows that inhibitive abilities of inhibitors depends on the adsorption of molecule on metal surface. The negative values ofΔG_ads⁰ indicated that the adsorption of these triazole molecules is a spontaneous process, and both chemisorption and physisorption might take place on the mild steel surface. The adsorption of the three compounds on mild steel surface followed Langmuir adsorption isotherm with single molecular layer. The surface morphology also shows that the surface corrosion of mild steel could decrease remarkably after these three inhibitors added in sulphuric acid.The inhibition efficiency obtained using different techniques shows a good agreement with each other.Quantum chemical calculation was theoretically provided the absorption sites of these heterocyclic triazole compounds. Based on the research of the Quantitative Structure-Activity Relationship (QSAR) of these inhibitors, the possible mechanism of inhibition was presumed. It is useful to provide some valuable information to synthetic new corrosion inhibitors.