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Abstract Corrosion is one of the most important problems that metals are exposed to, which negatively affects various industries caused by the electrochemical interaction with the corrosion environment. This thesis discusses the corrosion of C-steel in an acidic medium and works to protect it by reducing its risks - as it is not possible eliminate corrosion completely-Using some organic compounds . The thesis included three main chapters: The first chapter Deals with introduction which included a historical introduction to the phenomenon of corrosion, the basics of the science of corrosion of metals, their forms, types, and methods of protection from them. The published research papers on the corrosion of the C-steel metal in acid solutions and the ability of organic inhibitors were also included the target of the thesis. The second chapter Includes the chemical composition of the C-steel used in the study and also ways to prepare solutions of acid (hydrochloric acid) and review of the name, chemical composition, molecular weight and molecular formula of organic compounds and description the chemical and electrochemical methods that were used to measure the rate of corrosion of measurement, as well as the preparation of the electrodes, the cell and solutions and methods of calculations. The third chapter Deals with the results obtained and their discussion and is divided into three sections: Section І: Contains the practical results of the weight loss method which and their discussion . The results were presented in tables and curves. The organic compounds used in the study reduce the corrosion of C-steel The efficiency of inhibition has been studied in the range of different concentrations of the two organic compounds. This method was used to find out the effect of temperature on the C-steel in hydrochloric acid solution at four different temperatures (30-45°C), and it was found that the rate of corrosion increases with increasing temperature, and hence decreasing inhibition efficiency, which shows that inhibition occurs through physical adsorption of inhibitors and follows the Langmuir isotherm and Temkin isotherm. The negative values of (ΔG˚) indicate that the adsorption process on the surface of C-steel is carried out spontaneously and the activation parameters for the compounds have been studied. The thermodynamic functions related to the activation process were also calculated with a discussion of the implications of their values. Section ІІ: Potentiodynamic polarization measurements were carried out for C- steel in hydrochloric acid solution .It was found that there is a displacement of the cathodic and anodic polarization curves to more -ve and more +ve values, It was found that the corrosion rate decreases with the increasing in the concentration of the inhibitor, thus increasing the efficiency of the inhibition process. These inhibitors act as mixed type inhibitors. Section ІІІ: AC impedance spectroscopy measurements were carried out for C-steel in hydrochloric acid in the absence and presence of inhibitors and is controlled by the charge transfer resistance(Rct) and revealed that the values of the transfer resistance increase by increasing the concentration of inhibitor. On The other hand (Cdl) decreased by increasing concentration of inhibitors . The thesis is written on (73) pages and contains (17) tables in which the results are written and (25) figures showing the results. |