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Abstract The corrosion is a great problem, which faced the world, we cannot hide this problem from our live but we can reduce it by several methods as the environment need. This work discus the corrosion inhibition of carbon steel in 1M HCl solution in precence of expired pharmaceutical drugs . This thesis includes three chapters:- A- Introduction An introduction about inhibitors (definition and classification), an introduction about corrosion (definition, forms and inhibition), and a literature survey on the previous studies on corrosion inhibition of carbon steel in aqueous solution is given. B- Materials and experimental techniques The experimental part includes complete description of preparation of solution, carbon steel electrode pretreatment, and electrolytic cell working procedures, weight loss measurements, and electrochemical measurements e. g. potentiodynamic polarization and A.C. impedance techniques. C- Results and discussion This chapter illustrate the compounds were tested as corrosion inhibitors using some techniques. First: Weight loss measurements The data reveals that, the inhibition efficiencies for all used expired drugs compounds increases with increasing its concentration. The Summary ___________________________________________________________ _____________________________________________________________________ XV inhibition efficiencies decrease with increase the temperature rang (25- 55ºC) except compound II. Second: Open circuit potential measurements (OCP) The potential of the carbon steel electrodes immersed in the 1M HCl were measured (against a standard saturated calomel electrode, SCE, placed in the same compartment) as a function of immersion time in absence and presence of different concentrations from expired drugs. Third: Potentiodynamic polarization measurements The data reveals that, all used expired drugs slightly shifted Ecorr to more negative potential and also the values of Icorr decreases including both anodic and cathodic Tafel slopes βa, βc in the presence of the used expired drugs and this confirms that compounds act as mixed type inhibitor. The inhibition efficiency increased with increment of inhibitor concentrations. This fact suggests that the inhibitor molecules may first be adsorbed on the steel surface and cover some sites of the electrode surface. Fourth: Electrochemical impedance spectroscopy (EIS) The data reveals that the increase of polarization resistance and decrease of the pseudo capacity with increasing inhibitor concentration indicates that these compounds have the ability to inhibit the corrosion rate of carbon steel in according to adsorption mechanism (formation of a surface film). The percentage inhibition efficiency increases by increasing concentration of inhibitors (expired drugs). The values of inhibition efficiency obtained from the weight loss measurements are in good agreement with those obtained from potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS). Summary ___________________________________________________________ _____________________________________________________________________ XVI The values of activation energy (Ea) were calculated from Arrhenius equation. The data reveals that, the activation energy decrease in the presence of used expired drugs which indicates that physical adsorption except compound II is chemical adsorption (strong adsorption of compound molecules on the metal surface). The change in enthalpy and entropy of activation values (ΔH*, ΔS*) were calculated from the transition state theory. The adsorption of these compounds on the carbon steel surface obeys the Langmuir adsorption isotherm. Thermodynamic parameters for adsorption process such as free energy (ΔGads) enthalpy (ΔHads) and entropy (ΔSads) for the used expired drugs were determined. The calculated ΔGads negative in values which indicates that the adsorption mechanism of the expired drugs on carbon steel in 1 M HCl solution is a mixed from physical and chemical adsorption and the adsorption of inhibitors on the metal surface are spontaneous process. All used expired drugs have positive sign of ΔHads indicating that the adsorption of expired drugs on the carbon steel surface in 1M HCl solution is endothermic process. The positive sign of ΔSads attributed to the increase of disorder due to the adsorption of only one inhibitor molecule by desorption of more water molecules. Fifth: Scanning electron microscope (SEM) The data reveals that, the surface of carbon steel was strongly damaged in absence of used expired drugs, However in the presence of these compounds (I-V) the surface of steel is free from pits and it is smooth. Such surface indicate that a good protective film present on the steel surface and also confirms the highest efficiency of the used expired drugs at 500 ppm concentration. Summary ___________________________________________________________ _____________________________________________________________________ XVII Chapter 4: “References” This chapter includes the references which can used in the present work and we can arrange in very simple and include more than 150 refresh references. |