الفهرس 
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Abstract
Metal corrosion is a great problem, which faced the world from the last years until now. We can’t hide this problem from our live but we can reduce “inhibit” it by several methods as the environment need. -This work discusses the corrosion of mil steel in 1M HCl. -This work contains three basic chapters: Chapter one: “INTRODUCTION Experimental chapter discusses: Definition of corrosion, the corrosion theory, classification of corrosion, forms of corrosion, cost of corrosion, factors influencing corrosion, methods of protection, type of inhibitors, electrochemical methods, corrosion inhibitors and literature survey on corrosion inhibition of stainless steel. Chapter two: EXPERIMENTAL AND TECHNIQUES :It includes the chemical composition of the mild steel, the preparation of the test specimens for the different techniques of measurements and methods of preparation of materials of various solutions used, preparation of the used hydrochloric acid solution, preparation of the used Plant extracts, solutions and procedures used for the corrosion measurements such as a weight loss and electrochemical techniques (potentiodynamic, EIS, EFM, AFM) and surface analysis (FT-IR, XPS). Chapter three: ”RESULTS AND DISCUSSION” This chapter is divided into three sections: Section (A): The first one is the chemical Techniques which make the evaluation of the inhibitor efficiency by the weight loss method for investigated compounds (50-300 PPM) in 1M HCl at (25- 45°C) revealed that the inhibitor efficiency increases with the increasing of the concentration. Also, study the effect of temperature on the corrosion rate of mild steel in 1M HCl over a temperature range from 25 to 45oC revealed that: 1. In case of (CA, CC, TA) extracts the inhibitor efficiency increased as a whole with increase the temperature. 2. In case of EA extract the inhibition efficiency decreased by increasing the temperature from 25 to 45 Co. This study also confirmed that the corrosion inhibition occurred through physical adsorption of the additives on mild steel surface. Including the calculation and discussion of thermodynamic kinetic parameters (ΔH*, Ea*and ΔS*) of the investigated inhibitors on mild steel surface by plotting various Transition state and Arrhenius curves. Also these plant extracts obey Langmuir adsorption isotherm. The degree of surface coverage (θ) for the inhibitors on the metal surface increases with increasing the concentration in the investigated inhibitors. The action of the inhibitors in the aggressive acid was assumed to be due to their adsorption at the metal /solution interface. The results were treated to obtain the thermodynamic parameters for the adsorption of inhibitors from Langmuir isotherm model and kinetic-thermodynamic model (ΔGoads, ΔHoads and ∆S◦ads) and the adsorption constant kads. This results indicating that the inhibition occurs through physical adsorption of the additives on mild steel surface. The negative values of ΔGoads indicate the corrosion of mild steel in 1M HCl is spontaneous. These studies study approved that: (CA, EA, CC,TA) extracts are a good green inhibitors. Section (B): 1. Potentiodynamic polarization measurements were carried out for mild steel in M HCl in the absence and presence of different concentrations of (CA, EA, CC, TA) extracts. The polarization curves indicated that these plant extracts are a mixed type inhibitors which inhibit both the cathodic and anodic processes. Corrosion rate decreased with increasing the concentration of the plant extracts and together with increase in both cathodic and anodic polarization, but the corrosion inhibition has a great effect on the cathodic polarization. Variation of inhibition efficiency with the structure of (CA, EA,CC, EA) extracts was interpreted in terms of the number of adsorption sites in the molecule and their electron charge density, molecular size, mode of adsorption and the polar effect of the substituent groups. 2. AC impedance spectroscopy measurements were carried out for mild steel in 1M HCl in the absence and presence of different concentrations of the investigated inhibitors under charge transfer control. The % IE obtained from EIS measurements are close to those deduced from polarization. 3. The electrochemical frequency modulation (EFM) technique was used as a rapid and non-destructive technique for corrosion rate measurements. It was carried out for mild steel in 1M HCl in the absence and presence of different concentrations of the investigated plant extracts. Corrosion current densities (icorr) obtained with this technique was in good agreement with those obtained from weight-loss, polarization and EIS methods. In addition of the causality factors were good internal check for verifying the validity of data obtained by this technique. The corrosion rate decrease with increasing the concentration of inhibitors and the inhibition efficiency (% IE) is found to increase with increasing the inhibitors concentrations. Section (C): Surface examination of mild steel includes the following methods: 1. AFM spectroscopy used for investigation the roughness of mild steel surface in the nonexistence and existence of the plant extracts (300 ppm). The surface roughness decreased in the presence of the inhibitors. 2. The metal specimen was analyzed by ATR- FTIR technique. Chemical bonds and Functional groups in a molecule had been detected by generate an infrared spectrum. This also confirmed the presence of physical adsorption of the inhibitors on the mild steel surface. 3. Mild steel surface examined by using XPS technique. It can perform the surface characterization by using monochromatic X-ray Al K-alpha radiation of (10-1350 eV). It confirmed the adsorption of plant extracts on mild steel surface and detects the chemical nature of the inhibitors and mild steel interface. In conclusion: The weight loss, polarization, electrochemical impedance spectroscopy (EIS) and EFM measurements support the assumption that corrosion inhibition primarily takes place through adsorption of the inhibitors on the mild steel surface. Agreement among these different independent techniques indicates the validity of the obtained results.