الفهرس 
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Abstract
The corrosion problem 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 in the metals by several methods as the environment need. This work discusses the corrosion of SS in 1M HCl. This work contains three basic chapters Chapter one: “INTRODUCTION“ This chapter discusses corrosion theory, causes of corrosion, forms of corrosion, corrosion migration, types of inhibitors, Literature survey of SS corrosion and aim of this study Chapter two: ”EXPERIMENTAL AND TECHNIQUES” It includes the chemical composition of the investigated material, preparation of the used hydrochloric acid solution, the used quinazoline and oxa(thia)diazole derivatives, solutions and procedures used for the corrosion measurements such as a weight loss and electrochemical techniques. Chapter three: ”RESULTS AND DISCUSSION” It deals with the results obtained and their discussion and this chapter is divided into two sections: Section (1): Chemical technique (weight loss) Evaluation of the inhibitor efficiency by weight loss method in the presence and absence of four compounds (quinazoline and oxa(thia)diazole derivatives) in 1M HCl at 25 0C. This revealed that the inhibitor efficiency increases with the concentration. ‐157 - from these studies, the order of inhibition efficiency of investigated compounds in 1M HCl had found to be: C2 > C1 C4 > C3 These quinazoline and oxa(thia)diazole derivatives obey Langmuir adsorption isotherm showing that the inhibition is by adsorption. The degree of surface coverage (θ) for the inhibitors on the metal surface increases with increasing the concentration in the corrosive medium. The action of the inhibitors in the aggressive acid had assumed to be due to their adsorption at the metal /solution interface. The effect of temperature on the corrosion inhibition of SS in 1M HCl was determined over the temperature range 25-450 C using weight loss measurements. The rate of corrosion increases with increasing the temperature together with decrease in inhibition efficiency, indicating that the inhibition occurs through physical adsorption of the additives on SS surface. Thermodynamic functions of activation had calculated of compounds. Section (2): Electrochemical technique 1- The effect of compounds on the cathodic and anodic polarization of SS in 1M HCl was investigated. Corrosion rate decreased with increasing of concentration of the compounds 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 investigated compounds 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. The order of increased inhibition efficiency of SS ‐158 - corrosion in HCl at all concentrations in the range (1x10-6 - 21x10-6 M) by polarization technique is C2 > C1 C4 > C3 2- The results obtained from (EIS) showed that the corrosion reactions in the absence and presence of compounds proceed under charge transfer control. The increase in concentration of the inhibitors leads to an increase in the value of the charge transfer resistance (Rct) i.e. a decrease of the corrosion rate of Stainless steel. The double layer capacitance (Cdl) of the corroding Stainless steel interface decreases with increase in the inhibitor concentration, suggesting an increase of the surface coverage of the inhibitor due to the adsorption of the inhibitor species at the Stainless steel surface. 3- The new technique electrochemical frequency modulation (EFM) has used as a rapid and non-destructive technique for corrosion rate measurements. Corrosion current densities (icorr) obtained with this technique had in good agreement with those obtained from Tafel extrapolation technique. In addition, of the causality factors were good internal check for verifying the validity of data obtained by this technique. In conclusion: The weight loss, polarization, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements support the assumption that corrosion inhibition primarily takes place through adsorption of the inhibitors on the SS 304 surface. Agreement among these different independent techniques indicates the validity of the obtained results.